ALBERT

Description: 〈p〉Publication date: 13 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration, Volume 458〈/p〉 〈p〉Author(s): Xiao-Dong Yang, Zhen-Kun Guo, Wei Zhang, Yuan Ren, Melnik V.N. Roderick〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Although the substitution idea has been used occasionally in some engineering structures to study vibration characteristics, it is still short of systematic study in the vibrational engineering field. We summarize the techniques of the substitution method in this paper and apply such skill further to continuous and nonlinear systems, by which the dimension of the system can be reduced. By illustrated examples of frequency analysis on Timoshenko beam and composite sandwich structure, the substitution method has verified to be valid and efficient. The gyroscopic systems, represented by both rotating structures and orbits around libration points have also been presented to show the power of substitution method. Illustrated by the current examples, it is concluded that the substitution method has wide potential applications via studying the functional relations among all the degree-of-freedoms (DOFs) of non-gyroscopic or gyroscopic systems.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 27 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration, Volume 459〈/p〉 〈p〉Author(s): Trond F. Bergh〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We propose a novel procedure for solving the Deconvolution Approach to the Mapping of Acoustic Sources (DAMAS) inverse problem. The proposed procedure is a two-stage, hybrid greedy/non-greedy algorithm based on orthogonal matching pursuit (OMP, step 1) and non-negative matrix factorization (NMF, step 2). The purpose of the second step is to compensate for the suboptimal nature of matching pursuit. The method has been evaluated using Monte Carlo simulations and validated on experimental data. Both simulated and experimental results were compared to a few standard methods of deconvolution. These evaluations show that the proposed method has comparable, and in some cases, higher overall accuracy than the reference methods, particularly when the actual point spread function deviates from the modeled one. Simultaneously, the calculation time is low enough for near real-time use.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 3 July 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Jingxi Liu, Bo Xu, Lei Zhang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Gravity assist is widely applied in the deep space exploration because of its reliability and practicability. There are lots of research in the literature about the nearly coplanar situations. In this work, a three-dimensional model of gravity assist model is developed in a semi-analytical manner on the basis of the geometry relationship between the parameters of spacecraft before gravity assist and the orbital elements after gravity assist. The parameters include 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si278.svg"〉〈mrow〉〈msubsup〉〈mrow〉〈mi mathvariant="bold-italic"〉V〈/mi〉〈/mrow〉〈mrow〉〈mi〉∞〈/mi〉〈/mrow〉〈mrow〉〈mtext〉in〈/mtext〉〈/mrow〉〈/msubsup〉〈/mrow〉〈/math〉 (the hyperbolic excess velocity vector of the spacecraft before fly-by), 〈em〉H〈/em〉 (the height of fly-by) and 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si279.svg"〉〈mrow〉〈mi〉θ〈/mi〉〈/mrow〉〈/math〉 (the dihedral angle between approach plane and fly-by plane). These equations can be used for analyzing the change of orbital elements in the process of gravity assist, discussing the influence of different parameters on them and deriving the condition that remains the semi-major axis unchanged. Curve fitting of the feasible region boundary of 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si280.svg"〉〈mrow〉〈mi mathvariant="normal"〉Δ〈/mi〉〈mi〉i〈/mi〉〈/mrow〉〈/math〉 and contour plot of 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si281.svg"〉〈mrow〉〈mi mathvariant="normal"〉Δ〈/mi〉〈mi〉i〈/mi〉〈/mrow〉〈/math〉 are utilized to analyze the pattern of 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si282.svg"〉〈mrow〉〈mi mathvariant="normal"〉Δ〈/mi〉〈mi〉i〈/mi〉〈/mrow〉〈/math〉 changing with different parameters. This method is a valuable reference for designing gravity assist trajectories to high inclination targets in the Solar system.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 13 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration, Volume 458〈/p〉 〈p〉Author(s): Li Ma, Li Cheng〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Damping material is one of the essential components to achieve effective Acoustic Black Hole (ABH) phenomena. Alongside the expected energy absorption by the viscoelastic coating, recent research revealed its adverse effect in increasing the sound radiation efficiency of ABH structures. The conflicting role that damping layers play calls for a balanced and meticulous design of their deployment to draw the best possible vibration or acoustic benefit. This paper proposes a general methodology for optimizing the layout of damping layers coated on the surface of an ABH plate through topological optimization. By combining a semi-analytical wavelet plate model with an optimizer, the sound radiation into a free space by the ABH plate is minimized at either a given frequency or within a frequency band. Results show that through optimization, a reduced sound power can be achieved, as compared with the intuitive coating at the central area of the ABH indentation. While the low frequency sound power reduction is due to the impaired structural vibration, the optimization-induced reduction in the radiation efficiency is shown to be the dominant factor that contributes to the minimization of the sound power at high frequencies. Changes in the topology of the coating, in relation to the optimization objective, are observed and interpreted. It is shown that the optimized coating area for acoustic optimization tends to be further away from the center of the indentation, in contrast to the case for structural vibration optimization. The optimized configuration warrants a systematic reduction of the sound radiation efficiency, as evidenced by a weakened vibration level of the supersonic components of the plate.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 27 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration, Volume 459〈/p〉 〈p〉Author(s): Debasish Jana, Suparno Mukhopadhyay, Samit Ray-Chaudhuri〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A method is proposed to determine optimal locations of input forces for experimental modal analysis. The input locations are optimal in a sense that the measured vibration responses, under inputs thus located, contain maximum information about unknown modal parameters of interest. These optimal input locations are obtained by maximizing the trace of the associated Fisher Information Matrix (FIM). Analytical expressions are obtained for the different derivatives involved, by expressing acceleration responses in terms of pseudo-modal responses. A dimensionless scaling is introduced to normalize the effect of different types of modal parameters. An explicit relation is also derived between the FIM and the mode shape components at input locations. It is shown that, in certain experimental scenarios, this relation may be used to directly obtain the optimal input locations from only the mode shapes. An extensive series of numerical simulations, including situations of single/multiple inputs and single/multiple modes of interest, is used to illustrate the proposed approach. It is observed that the modal parameters, identified using any suitable modal identification technique, have the lowest estimation uncertainty when the inputs are optimally located. As an application in damage detection, it is shown that modal parameters estimated from experiments with non-optimally located inputs may lead to incorrect damage localization. The proposed method is also applied to data from experiments performed on a laboratory scale truss model.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 1 July 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): N.Y. Zaalov, E.V. Moskaleva〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper describes a study of the daily and yearly variability of one of the main characteristics of sporadic E layers (Es), the critical frequency (foEs). Our analysis is based on ionograms recorded by GIRO network ionosondes. The study estimates the spatial and temporal variability of the Es layer parameters and generates their statistics at different seasons and phases of the solar cycle. In turn, the statistics of the Es layer parameters can provide an assessment of the capability of the HF propagation forecasting. Further, maps of the distribution of Es layer critical frequency are produced. This paper implements the “cloud” model of Es layer in HF propagation model (Northern Ionosphere Model & Ray Tracing, NIM-RT) that can accurately reproduce many features observed in experimental measurements. Within this framework, a number of vertical sounding ionograms with the presence of Es layer are simulated based on the NIM-RT software.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 21 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration〈/p〉 〈p〉Author(s): Iqbal Alshalal, Faten Al Zubaidi, Alaa Elsisi, Z.C. Feng〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Damage detection at the early stages of structural design is crucial to prevent the occurrence of unpredictable failures. The residual error method can be used to detect damage by monitoring the changes it induces in the equation of motion. The residual error method was originally applied to beam structures, but in this study, it is adapted to detect and locate damage in two-dimensional structures such as plates. To demonstrate this method, the damage is modeled as a reduction in stiffness while the mass is maintained at a constant value. The effect of damage on the equation of motion of the intact structure is then quantified by substituting the eigenmodes and eigenvalues of the damaged structure; the residual error then pinpoints the location of the damage and its relative severity. Thorough finite element method simulations are performed to assess the robustness and limitations of the method in several scenarios with single and multiple damages. Furthermore, the sensitivity of the method to various noise levels is tested. Finally, a comparison is drawn between the residual error method and the absolute difference mode shape curvature method. The obtained results show that the residual error method is able to detect and locate damage in one- and two-dimensional structures.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 24 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration, Volume 461〈/p〉 〈p〉Author(s): Vikas Sharma, C.O. Arun, I.R. Praveen Krishna〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The present paper proposes a new and simple mechanical model for predicting the maximum sloshing wave height (MSWH) in a partially filled, laterally excited cylindrical tank. The proposed model is a linear, two degree of freedom spring-mass-damper system which consists of two masses representing the sloshing and non-sloshing mass of the partially filled cylindrical tank. The model is validated through a series of experiments conducted on a cylindrical tank filled with water which is mounted in a slosh test rig. The proposed model successfully captures the beating phenomenon observed in sloshing wave height, when the tank is laterally excited near the resonant frequency of the liquid. The present study leads to a simpler, accurate and faster mechanical model which can predict the MSWH, frequency of sloshing liquid and the lateral sloshing force. The model can be readily used by the design engineers, instead of time consuming numerical models like computational fluid dynamics and smoothed particle hydrodynamics, in the preliminary design phase of any structure involving lateral sloshing and provide quick results which will substantially lead to shorter design cycle time.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 21 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): S.S. Rao, Monti Chakraborty, R. Pandey, A.K. Singh〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In this research work, we have analyzed the data of critical frequency of the F〈sub〉2〈/sub〉 region ionosphere over southern low latitude station COCO (Keeling) Island (Geog. Lat. 12.20⁰S; Geomag. Lat. 22.83⁰S; Geog. Long. 96.80⁰E) for the period 2009-2013 and result thereof have compared with the IRI-2016 model. Our analysis shows a good correlation between variations in 〈em〉fo〈/em〉F〈sub〉2〈/sub〉 and solar flux at F10.7 cm wavelength. With concern to geomagnetic activity during the period 2009-2013, it has found that the variability in the monthly mean Ap index remained below 20 nT throughout the period 2009-2013. Concerning quiet time F〈sub〉2〈/sub〉 region variability, our results explicated the solar cycle, semiannual, and seasonal/annual variation in 〈em〉fo〈/em〉F〈sub〉2〈/sub〉. Similar oscillations in 〈em〉fo〈/em〉F〈sub〉2〈/sub〉 have been explored using the Lomb-Scargle Periodogram technique. We have also observed the fundamental mode (27 days) and its overtones (9 and 13-day) in the geomagnetic activity parameter (Ap). Analysis of 〈em〉fo〈/em〉F〈sub〉2〈/sub〉 showed the consistent presence of the semiannual anomaly and absence of the winter anomaly during the ascending phase of solar cycle-24. A presence of an annual component in normalized 〈em〉fo〈/em〉F〈sub〉2〈/sub〉 has been examined using regression analysis. A comparative study of ionosonde observed 〈em〉fo〈/em〉F〈sub〉2〈/sub〉 with IRI-2016 modeled 〈em〉fo〈/em〉F〈sub〉2〈/sub〉 showed that the general ionospheric trends in IRI predictions are consonant with the observations for the diurnal, seasonal, and solar cycle variation. However, a deviation in the amplitude of 〈em〉fo〈/em〉F〈sub〉2〈/sub〉 up to the order of 5 MHz depending upon local time, seasons, and phases of the solar cycle has observed.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 20 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Mohammad Javad Kalaee, Yuto Katoh〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We consider the equatorial region of the magnetosphere, where the magnetic field is perpendicular (or near to perpendicular) to the density gradient and mode conversion process from UH to LO-mode waves or reverse process are expected. We review and study the mode conversion from UH (upper hybrid) to LO (left hand polarized ordinary) mode waves by a spatially two dimensional plasma fluid code. Several simulations with different initial wave vectors under the same background plasma condition have been performed. We focus on the conversion efficiency from the UH-mode waves with purely perpendicular wave normal angle to the LO-mode waves, since one of the source of generation UH wave can be Bernstein mode as the purely perpendicular electrostatic waves. For this special case, the UH wave normal is kept in perpendicular direction with respect to the magnetic field, and difficult to be in matching direction for conversion to LO mode〈em〉.〈/em〉 Simulation results show that the mode conversion efficiency in this particular case is very weak, since two branches of Z-mode wave and LO mode wave in the dispersion relation are disconnected. We present a discussion to show that for this case (purely perpendicular propagation) a special angle (except 90 degrees), between the magnetic field and the density gradient is necessary for occurrence of efficient mode conversion. For the case (purely perpendicular propagation and the magnetic field perpendicular to the density gradient), the mode conversion just occurred via the tunneling effect, where a steepness of the inhomogeneity plays an essential role.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 10 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration, Volume 460〈/p〉 〈p〉Author(s): Jonathan Martino, Kristof Harri〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This article discusses the modeling and simulation of the coupling problem in virtual shaker testing applications. An innovative model of the electrodynamic exciter is developed based on a transmission line approach and a two-port network over Z-modeling is presented. The exciter is modeled by a two degrees of freedom mechanical structure coupled to an electrodynamic transducer. While classical lumped modeling depends on the structure under test, this enhanced model is totally independent and only relies on the physical parameters of the shaker which can be identified by non-linear curve fitting. The presented model is also shown to be partially decoupled, allowing an improved identification of the system. The validity and limitations are verified by comparison with experimental results and the developed model efficiently predicts the output reaction of the shaker as well as the prevailing coupling in the interface.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0022460X19303815-fx1.jpg" width="477" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Description: 〈p〉Publication date: Available online 1 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Yanguang Fu, Xinghua Zhou, Dongxu Zhou, Jie Li, Wanjun Zhang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Sea level variability in the South China Sea (SCS) was investigated by means of satellite altimetry and tide gauge data over a 24 years period 1993–2016. The sea level anomalies (SLAs) retrieved from satellite and tide gauge data were compared. The differences between the two datasets showed a normal distribution with 87% within ±10 cm. Considering the individual time series, the results revealed that satellite and tide gauge SLAs are in good agreement, with root mean square deviations in the range 0.9–9.9 cm (average value is 2.7 cm), and correlation coefficients exceeding 0.7 for 85% of stations. Positive linear trends of sea level were estimated for both datasets, with good agreement in most cases. The averaged linear trend of SLAs in the SCS showed a rise of 4.4±0.3 mm year〈sup〉–1〈/sup〉 during 1993–2016, consistent with the nonlinear trend of satellite and tide gauge (4.3±0.3 and 3.9±0.1 mm year〈sup〉–1〈/sup〉, respectively) extracted through empirical mode decomposition.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 31 July 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration〈/p〉 〈p〉Author(s): J.L. Huang, W.J. Zhou, W.D. Zhu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Bifurcations and quasi-periodic motions of high-dimensional nonlinear models of a translating beam with a stationary load subsystem under harmonic boundary excitation, where there are combined parametric and forcing excitations, are investigated. It is demonstrated that by adjusting the frequency of the boundary excitation beyond bifurcation points, the nonlinear system exhibits quasi-periodic motion rather than the periodic response reported in an earlier publication. Particular attention is paid to the nonlinear dynamics of models with five and six included trial functions, where quantitative and qualitative results of frequency responses and quasi-periodic motions are significantly different from each other. The nonlinear governing equations of motion of the translating beam are established by using the Newton's second law. The Galerkin method is used to truncate the governing partial differential equation into a set of nonlinear ordinary differential equations. The incremental harmonic balance (IHB) method is used to solve for periodic responses of the high-dimensional models of the translating beam. The Floquet theory along with the precise Hsu's method is used to investigate stability of the periodic responses. The IHB method with two time scales developed earlier is extended to analyze quasi-periodic motion of the nonlinear system with combined parametric and forcing excitations whose spectrum contains uniformly spaced sideband frequencies. Quasi-periodic motion obtained from the IHB method with two time scales is in excellent agreement with that from numerical integration using the fourth-order Runge-Kutta method.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 13 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Pascal Willis〈/p〉

Description: 〈p〉Publication date: Available online 12 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration〈/p〉 〈p〉Author(s): Anil Kumar, Sandip Kumar Saha, Vasant A. Matsagar〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Response analysis of structural systems under impulse loading is extremely important for appropriate design against accidental loads such as blast. Herein, the response of elastic and inelastic single degree of freedom (SDOF) systems with uncertain parameters under random impulse loadings is investigated. Four different types of impulse loading profiles (rectangular-, half-sine wave-, and two triangular-shaped), having same duration and impulse, are applied to the SDOF systems with varying fundamental periods of vibration. Non-sampling stochastic simulation procedure based on the generalized polynomial chaos (gPC) expansion technique is used to model the dynamic response of the SDOF systems duly considering the uncertainties. Effects of uncertainty levels in the input parameters on the peak response and sensitivity of the peak response to the uncertain input parameters are investigated in detail. It is concluded that the propagation of uncertainties from the inputs to the response quantities is more prominent in stiffer systems. Amongst the impulse profiles considered, those pulses with sudden rise in force lead to higher deviations in response of the systems for a given uncertainty scenario. Further, it is observed that the shock response spectra of all the impulse loads are more sensitive to the uncertainties when time periods are less than or close to the loading duration. Furthermore, the gPC expansion-based simulation technique is observed to be an efficient alternative to computationally demanding conventional Monte Carlo (MC) simulation for quantifying the uncertainties.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 15 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 64, Issue 6〈/p〉 〈p〉Author(s): 〈/p〉

Description: 〈p〉Publication date: 15 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 64, Issue 6〈/p〉 〈p〉Author(s): 〈/p〉

Description: 〈p〉Publication date: Available online 7 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Kaishi Zhang, Wenhai Jiao, Liang Wang, Zishen Li, Jianwen Li, Kai Zhou〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Global Navigation Satellite System (GNSS), once dedicated to military and geodetic applications, is entering civilian life with the development of low-cost internal multi-GNSS chips in mass-market smart devices. The recently enabled Application Programming Interface (API) to GNSS raw measurement in Android Nougat operating system, make it possible to implement precise positioning technology on Android smart devices, such as Real-Time Kinematic Positioning (RTK) and Precise Point Positioning (PPP). An optimized kinematic positioning approach on Android smart devices with Doppler-Smoothed-Code (DSC) filter and Constant Acceleration (CA) model is assessed in this paper. In this optimized approach, DSC filter is used to reduce the code measurement noise, which is extremely high on smart devices and CA model is used to accurately predict the kinematic state of smart devices. The optimized approach is named Smart-RTK for its applicability to smart devices, respectively. The performance of the Smart-RTK approach is validated by two Google/HTC Nexus 9 tablets separately under stationary, walking, and vehicular condition. The numerical experiments show the significant improvement on positioning accuracy and continuity. The positioning Root Mean Square Error (RMSE) in horizontal component reaches about 0.3–0.6 m in stationary condition and 0.4–0.7 m in walking condition, improved by about 85% compared with that of chipset original solutions. In the subsequent vehicular experiment, the horizontal positioning RMSE is about 0.85 m, 50% better than that of chipset solutions.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 10 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration, Volume 460〈/p〉 〈p〉Author(s): Yang Liu, Yulai Zhao, Zi-Qiang Lang, Jintao Li, Xinxin Yan, Siyao Zhao〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Rotor cracking is a common fault in rotating machinery, that can often be detected based on the vibrations of such machinery. Therefore, many vibration signal based techniques have been developed for rotor fault detection. However, signal based fault diagnosis is often affected by noise and cannot be used to fully quantify the operating conditions of rotors, which are often more relevant to rotor structural characteristics compared to vibration behaviours. Nonlinear output frequency response functions (NOFRFs) represent a nonlinear system frequency analysis approach that was proposed to address challenges associated with applying signal based fault detection. NOFRFs have a wide range of applications in industry, including rotor fault diagnosis. In this study, a novel NOFRFs based criterion called the weighted contribution rate of NOFRFs is proposed to enhance the capability of the NOFRFs based rotor crack detection and quantification. The proposed criterion can amplify the impact of rotor characteristics that are sensitive to rotor cracks, which considerably improves the crack diagnosis performance. The effectiveness and advantages of the proposed rotor damage detection method are verified both experimentally and through simulations, demonstrating its potential applications in the early stages of rotor crack diagnosis.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉Only the vibration signal of the cracked rotor at two speeds are need to be measured. The index 〈em〉K〈/em〉 proposed based on the weighted contribution rate of nonlinear output frequency response functions method can be got with the vibration signal. The values of 〈em〉K〈/em〉 of the faulty rotor and the normal rotor are compared with each other to realize fault diagnosis.〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0022460X19304444-fx1.jpg" width="130" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Description: 〈p〉Publication date: 10 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration, Volume 460〈/p〉 〈p〉Author(s): D. Faux, O. Thomas, S. Grondel, É. Cattan〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper addresses the design of the elastic structure of artificial wings to optimize their dynamical behaviour to reproduce insect wings kinematics. Our bioinspired kinematics is based on the original concept of using the resonant properties of the wing structure in order to combine the motion of two vibration modes, a flapping and a twisting mode, in a quadrature phase shift. One way of achieving this particular combination is to optimize the geometry and elastic characteristics of the flexible structure such that the two modes are successive in the eigenspectrum and close in frequency. This paper first proposes a semi-analytical model, based on assembled Euler-Bernoulli beams, to understand, compute and optimize the artificial wing dynamic vibrations. Then, using this model, it is shown that it is possible to obtain several artificial wing structures with a flapping and a twisting mode close in frequency. Finally, experimental validations are performed on micromachined insect-sized prototypes to validate the model and the concept.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 10 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration, Volume 460〈/p〉 〈p〉Author(s): Kevin Yi-Wei Lin, Joel Mobley, Wayne E. Prather, Zhiqu Lu, Gautam Priyadarshan, Joseph R. Gladden〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The assessment of the internal structural integrity of dry storage casks with high burnup nuclear fuel assemblies is of critical importance for their transport to permanent repositories and during their extended storage service lives. The large size, structural complexity, and inability to access the interiors of the casks make this task challenging. The aim of this work is to evaluate the ability of vibrational characterization to assess the state of the internal cargo (i.e., fuel assemblies) in a cask strictly using measurements on the outer surface. In this study, we report on the identification of five modes of an unloaded full-scale Transnuclear-32 (TN-32) cask and examine the potential of using these modes to assess the internal configuration in a loaded condition. Vibrational spectra were acquired using impulse and continuous-wave techniques on both storage and transportation configurations from which the modal frequencies and the associated quality factors were determined. A finite element model of the TN-32 was constructed and used to identify the observed modes. The model was extended to include loaded configurations to assess how the presence of assemblies impacts the modal structure of the cask and its surface vibrations.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 6 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Prabhakar Tiwari, Navin Parihar, Adarsh Dube, Rajesh Singh, S. Sripathi〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In this study we present the behaviour of sporadic E-layer during a total solar eclipse (TSE) which occurred during the dawn/sunrise hours over a site located in the path of totality. A Canadian Advanced Digital Ionosonde (CADI) was operated at Allahabad (25.4° N, 81.9° E), a low latitude station located near the crest of equatorial ionization anomaly (EIA) in the Indian subcontinent to study the ionospheric effects of 22 July 2009 TSE. Corresponding to the eclipse period, a gradual increase of ftEs (top frequency of Es layer) in the 4–5 MHz range was seen on the control days. On 22 July (the TSE day), correlated changes in ftEs coinciding with the TSE progression was noted – (i) sharp decrease near first and second contact of TSE, (ii) an increase after first and second contact, and (iii) wavelike fluctuations in ftEs variation during eclipse hours and beyond. Much higher ftEs values were noted during the TSE hours in comparison to that seen on usual days. Strong blanketing Es layer developed during the TSE hours and persisted for slightly longer duration than its usual occurrence time. Near the TSE totality, slight lowering of the base height of Es layer was also noted.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 10 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration, Volume 460〈/p〉 〈p〉Author(s): Aditya Suryadi Tan, Jimmy Aramendiz, Kanu Hughan Ross, Thomas Sattel, Alexander Fidlin〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Tuned Vibration Absorbers are a widely used tool for suppressing the amplitude of a systems vibrations, one of the advantages being offered is that the absorber can be an add-on solution which is able to be adjusted offline. Many improvements have been made to the base system including the use of dry friction elements, and magneto- or electrorheological fluid (M-/ERF) elements. In this work the ability of both a dry friction based system and an electrorheological fluid (ERF) damper based system to reduce the amplitude response of a system over a wide range of frequencies through the use of the stick-slip effect is investigated through simulation. The unique advantage of using an ERF damper over a dry friction element are then investigated. Those are the ability of an ERF damper based system to adjust the breakaway force online and the ability of the damper to switch between the slip- and stick-states to further reduce the amplitudes over certain frequencies given that the excitation force is kept to a single frequency at a time. These investigations were first carried out through simulations and then through an experimental setup for both systems to prove the concepts in practice. The results of the experiment conclusively proved the ability of both systems to behave as predicted, especially the ability of the ERF damper to switch between stick- and slip-states to reduce vibration amplitudes in some frequencies.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 10 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration, Volume 460〈/p〉 〈p〉Author(s): M. Grialou, N. Totaro, J.-L. Guyader, A. Bocquillet〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In substructuring approaches in the field of acoustics, subdomains are mostly characterized by impedance or mobility at their interfaces with other subdomains. This allows handling large systems broken down into smaller, easier to solve subdomains and reaching higher frequency ranges. When a subdomain is characterized by experiments, the impedances are often measured on a dedicated setup aimed at uncoupling the subdomain from the other subdomains. This is often hardly feasible and the setup is insufficiently versatile. In the present article, an inverse method is proposed to experimentally identify the surface impedance of a passive acoustic (or vibro-acoustic) subdomain by means of measurements performed on the whole coupled system. An analytical study illustrates the ability of the approach to identify the impedance matrix of a passive subdomain with accuracy. Nevertheless, as many inverse methods, the system of equations to solve is ill-conditioned. To address this issue, an original approach for tackling the ill-posedness of the problem is proposed. It is based on a statistical analysis of different versions of the matrix to identify. Finally, an experimental validation of the proposed approach is detailed and shows a good agreement when comparing to an available analytical solution.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 10 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration, Volume 460〈/p〉 〈p〉Author(s): Pierre-Yvon Bryk, Renaud Côte, Sergio Bellizzi〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We present the first real size evidence of targeted energy transfer in a concrete building, with an efficient action on low frequency noise reduction. It is achieved by the means of a hybrid Electro-Acoustic Nonlinear Energy Sink (EA-NES). The EA-NES action is based on targeted energy transfer. As in previous works the EA-NES is made of two elements: a membrane with a nonlinear dynamics, and an active system based on a loudspeaker which controls the pressure applied to the rear face of the membrane. We study here a proportional feedback control law driving the loudspeaker in current mode, and compare it with the voltage mode command law. The experiment is fully modeled. A singular perturbation method around a 1:1 resonance is used to find the slow critical manifold of the system and its dependence on the control loop gain for the two driving modes, in view of finding conditions allowing Strongly Modulated Regime (SMR). A good quantitative agreement is found between the model and the experiments. In the experimental study we observe a range in the excitation level corresponding to SMR where the sound level in the room is limited. We study the influence of its parameters on the thresholds of the working range of the EA-NES. We measure up to 8 dB of attenuation around 43 Hz.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 19 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Jianfeng Duan, Zhaokui Wang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The 〈strong〉Magpie Bridge〈/strong〉 mission is a part of the Chang’E-4 mission, it is the first Chinese spacecraft carries out Earth-Moon communication mission at Earth-Moon libration points. The 〈strong〉Magpie Bridge〈/strong〉 operations team utilizes the Beijing Aerospace Control Center (BACC) Orbit Determination and Analysis Software (BODAS) to obtain the orbit, the measurements include range, Doppler and relay, relay-rate from China Deep Space Network (CDSN) and Very Long Baseline Interferometry (VLBI) system respectively. In order to effectively improve the accuracy of the orbit, we provided the solar radiation model with multiple characteristic surfaces. The new model is based on the structure and the real-time attitude of the satellite to solve the real-time solar pressure equivalent area. Compared with the cannon-ball model, it can calculate the solar pressure equivalent area of the satellite more accurately in orbit determination. By the analysis of the tracking measurement data, we found that the new solar radiation pressure model reduces the error of position and velocity compared to the cannon-ball model.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 19 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Mohammadreza Saghamanesh, Ehsan Taheri, Hexi Baoyin〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉One of the fundamental tasks in space mission design is to choose a set of inter-disciplinary mission-critical parameters that are used for both sizing spacecraft sub-systems and designing optimal trajectories. Trajectory design and sub-system sizing are tightly coupled tasks and mission designers are interested in algorithms that not only improve fidelity of the underlying models, but also facilitate comprehensive trade-off studies using dependable algorithms. This paper presents a systematic-design/computationally-efficient framework that makes use of a recently developed hybrid optimization method, which is a fusion between homotopic approach and particle swarm optimization to perform a robust homotopic approach. A salient feature of this framework is the flexibility in altering the fidelity of the dynamical models to beyond the conventional two-body model by including perturbations due to: 1) other planets of the Solar System, 2) solar radiation pressure, and 3) the oblateness effects of the Earth. Moreover, a comprehensive study on the impact of using different types of thrusters, different hyperbolic excess velocity values, and different launch opportunities is conducted. Extensive numerical simulations are performed for a heliocentric rendezvous mission from Earth to Mars and the results are compared against those in the literature.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 24 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration, Volume 461〈/p〉 〈p〉Author(s): M.J. Brennan, Y. Gao, P.C. Ayala, F.C.L. Almeida, P.F. Joseph, A.T. Paschoalini〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A common way to detect and locate leaks in buried water pipes is to use leak noise correlators. Vibration or acoustic signals are measured on or in the pipe using sensors placed either side of the leak, and the difference in the leak noise arrival times (time delay) at the sensors is estimated from the peak in the cross-correlation function of these signals. Over many years, much effort has been spent on improving the quality of the leak noise signals with the aim of improving the time delay estimate. In this paper it is shown that even if the signals suffer from severe amplitude distortion through either clipping or quantization, then an accurate time delay estimate can be obtained provided that the zero crossings in the noise data are preserved. This is demonstrated by using polarity co-incidence correlation on simulated and measured data. The use of random telegraph theory is also used as an approximation to allow the derivation of approximate analytical solutions for the cross-correlation function and cross spectral density of clipped noise to facilitate further insight into the effects of severe clipping.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 16 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Vegard Ophaug, Kristian Breili, Ole Baltazar Andersen〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉The coastal mean sea surface (MSS) has applications within oceanography as well as geodesy. Together with a geoid model, it forms an important component for geodetic mapping of ocean surface currents that are in geostrophic balance. Furthermore, it forms a bridge between open ocean MSS and in situ measurements of mean sea level at or close to land, it contributes to the mapping of the geoid and the marine gravity field, and it is essential for connecting tidal nautical chart datums to physical height systems or global geodetic reference frames.〈/p〉 〈p〉In this study, we determine a coastal MSS with an associated error field for Norway. The MSS is solely based on new-generation altimetry data, i.e., SAR(In) data from Sentinel-3A and CryoSat-2, as well as Ka-band data from SARAL/AltiKa. The data sets partly overlap in time and cover the time period from 2010 to 2017 inclusive. We have chosen these altimeters because they represent evolutions of conventional altimetry, with reduced footprint sizes as a main benefit. This is especially advantageous in the coastal zone, as a smaller footprint reduces the probability of radar pulses being contaminated by energy backscattered from land areas.〈/p〉 〈p〉The satellite missions were harmonized by applying inter-mission biases determined in a regional crossover analysis. Furthermore, in a zone closer to land than 25 km, we have replaced the global ocean tide model with a regional ocean tide model provided by the Norwegian Mapping Authority (NMA). We use an optimal interpolation technique to determine a coastal MSS grid and discuss it in context of the estimated error field.〈/p〉 〈p〉We assess our coastal MSS by comparison to state-of-the-art MSS products along three sections perpendicular to the coast, as well as ellipsoidal mean sea level as observed by an array of permanent tide gauges within the study area. In addition, we assess a higher-resolution version of our MSS in the NMA testbed for vertical datums, by comparison with temporary tide gauges. We find that the coastal MSS outperforms the global MSS models directly at the coast, with standard deviations of differences of 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si19.svg"〉〈mrow〉〈mo〉~〈/mo〉〈/mrow〉〈/math〉8 cm to the tide gauges, compared to 14–22 cm, obtained with the global MSS models. All MSS models largely agree along three sections perpendicular to the coast, with standard deviations of differences of 2–4 cm. The higher-resolution version of the coastal MSS performs similarly to the coastal MSS in comparison with the temporary tide gauges (standard deviation of differences of 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si20.svg"〉〈mrow〉〈mo〉~〈/mo〉〈/mrow〉〈/math〉8 cm), but its formal error field also quantifies large uncertainties at the coast and in the fjords, mainly due to the lack of altimetry observations. A trustworthy error field is decisive for the combination of altimetry with other sea-level observations.〈/p〉 〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 16 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Da-wei Qi, Le-ping Yang, Yuan-wen Zhang, Wei-wei Cai〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉As a novel approach to control the relative motion of a satellite formation, electromagnetic formation flight (EMFF) has some prominent advantages, such as no propellant consumption and no plume contamination, and has a broad prospect of application in such fields as on-orbit detection and optical interferometry. The current paper investigates the optimal control for the reconfiguration of a two-satellite electromagnetic formation using the nonlinear quadratic optimal control technique. Specifically, the effects of the Earth’s magnetic field on the EMFF satellites are analyzed, and then the nonlinear translational dynamic model of a two-satellite electromagnetic formation is derived by utilizing the analytical mechanics theory. Considering the high nonlinearity and coupling in the dynamic model and the actuator saturation, a closed-loop robust suboptimal control strategy based on the indirect robust control scheme and the 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si34.svg"〉〈mrow〉〈mi〉θ〈/mi〉〈mo linebreak="badbreak" linebreakstyle="after"〉-〈/mo〉〈mrow〉〈mi mathvariant="bold-italic"〉D〈/mi〉〈/mrow〉〈/mrow〉〈/math〉 technique is proposed with robust stability and optimality. To ensure a further reduction of control input, the designed suboptimal controller is modified by applying the Tracking-Differentiator. The feasibility of the derived translational dynamics and proposed control strategy for the robust reconfiguration mission is validated through theoretical analysis and numerical simulations.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 16 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Patrick Mungufeni, Babatunde A. Rabiu, Daniel Okoh, Edward Jurua〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This study characterised the Total Electron Content (TEC) over the African region during the years 2008 - 2015. The TEC data used were the integrated electron density observed during Radio Occultation (RO) event associated with Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) satellites. These TEC data were referred to as COSMIC TEC. The results indicate that the COSMIC TEC captures the well known features of the ionosphere such as: (i) occurrence of minimum and maximum TEC during 0:00 - 08:00 LT and 12:00 - 16:00 LT respectively, (ii) occurrence of secondary TEC enhancement (maximum) during 16:00 - 20:00 LT, (iii) lowest TEC values being observed in June solstice and highest TEC values observed in March equinox, (iv) TEC values increase as solar activity changes from low to high, (v) mid latitude TEC values are lower than those of low latitude regions, and (vi) occurrence of equatorial ionisation anomaly. In addition, we validated RO TEC observations of COSMIC satellites using Ground-based Global Navigation Satellite System (GNSS) receiver TEC observations (Ground TEC). To achieve this, we quantified the difference between Ground TEC and COSMIC TEC that were simultaneously observed within the vicinity of the ground receiver. The Upper Quartiles, UQ, of the magnitudes of the differences of coincident COSMIC and Ground TEC over southern mid-latitude regions were 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si19.svg"〉〈mrow〉〈mo〉〈〈/mo〉〈/mrow〉〈/math〉 4 TECU, while over low-latitude and northern mid-latitude regions, the values ranged from 6.17 - 11.20 TECU. The high TEC differences over low latitude regions compared to those over southern mid latitudes could have resulted from errors due to the spherical symmetry assumption during the RO retrievals. The question that remains is, why there are large TEC differences over the northern mid-latitude regions. Since COSMIC TEC captures the well known features of the ionosphere, it might in future be used for empirical modeling over African region, thus, making this study crucial.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 16 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Arunava Banerjee, Syed Muhammad Amrr, M. Nabi〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper proposes an optimal integral sliding mode control (ISMC) scheme for attitude regulation of the rigid spacecraft. This control technique is capable of handling inertial matrix uncertainties as well as external disturbances. To incorporate optimality into the robust control law, the ISMC is integrated with Legendre pseudospectral method (LPSM). The minimization of the cost function and constraint handling of the spacecraft is obtained by LPSM, while the ISMC provides disturbance rejection. LPSM is chosen for its relatively high rate of convergence and its capability of solving a wide range of challenging optimal control problems. Theoretical stability analysis of closed loop system using Lyapunov theorem guarantees the convergence of attitude states. A comparative analysis between the proposed LPSM-ISMC and Chebyshev Pseudospectral Method (CPSM) based ISMC, is also presented in this paper. The effectiveness of the proposed robust-optimal control strategy is established through simulation results.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 10 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration, Volume 460〈/p〉 〈p〉Author(s): Yi Yang, Ching-Tai Ng, Andrei Kotousov〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper investigates the second-order harmonics generation associated with propagation of Lamb wave in pre-stressed plates. The second-order harmonic phenomena appear in a weakly non-linear medium due to material and geometry nonlinearities. This study proposes finite element (FE) models to incorporate stress constitutive equations formulated by Murgnahan's strain energy function. The model is used to take into account the stress effect on second-order harmonic generation of Lamb wave propagation in weakly nonlinear media. The developed FE model is first validated against two-dimensional (2D) analytical solutions. A three-dimensional (3D) FE model is then developed and utilised to study more realistic problems, such as the rate of accumulation of the non-linear parameter 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"〉〈mrow〉〈mi〉β〈/mi〉〈mo〉'〈/mo〉〈/mrow〉〈/math〉 at different wave propagation angles when the plate is subjected to a bi-axial stress and the effect of the applied stresses on second-order harmonic generation in a plate with a fatigue crack. The results demonstrate that the applied stresses can notably change the value of 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"〉〈mrow〉〈mi〉β〈/mi〉〈mo〉'〈/mo〉〈/mrow〉〈/math〉 in different directions. The finding of this study can gain physical insight into the physical phenomenon of stress effect on second-order harmonic generation of Lamb wave. Thus, the current study opens an opportunity for the development of a new non-destructive stress evaluation technique for plate- and shell-like structural components. Moreover, the new technique can be easily incorporated with existing guided wave based-SHM systems and provide information regarding the change of the stress conditions. Such additional information can significantly improve the structural life prognosis and reduce risk of failures.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 27 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration, Volume 459〈/p〉 〈p〉Author(s): 〈/p〉

Description: 〈p〉Publication date: Available online 12 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration〈/p〉 〈p〉Author(s): Chenxi Wei, Xinchun Shang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The nonlinear behaviors of breathing cracked beam vibration are investigated. A continuous model based on Timoshenko beam theory is established, whose breathing effect is described by signal function in mathematics to simulate bilinear stiffness. A semi-analytical approach to solve the problem is developed by spatial difference discretization and transfer matrix method, in which local linearization and the Padé approximation are employed. The numerical results of validated examples have good agreement with experiments and FEM. As a typical indicator to breathing crack, the super-resonance responses under harmonic and fast frequency-sweep excitation are analyzed, such as waveforms, phase portraits and FFT results.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 5 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): D.V. Blagoveshchensky, M.A. Sergeeva〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Variations of ionospheric parameters Total Electron Content (TEC) by GNSS, critical frequency (foF2) by vertical sounding and electron density (Ne) by low-altitude satellite were studied at high, mid and low latitudes of the European sector during the magnetic storm of August 25-26, 2018. During the main phase of the storm the ionospheric F2-layer was under the positive disturbance at mid and low latitudes. Then the transition from the positive to negative ΔfoF2 values occurred at all latitudes. The recovery phase was characterized by negative ionospheric disturbance at all latitudes. This is due to the decrease of thermospheric O/N2 ratio during the recovery phase of the storm. The intense Es layers screened the reflections from the F2-layer on August 26〈sup〉th〈/sup〉 at high and at low latitudes but at different times. Some blackouts occurred due to the high absorption level at high latitudes. In general, foF2 and TEC data were highly correlated. The major Ne changes were at the low latitudes. In general, Ne data confirmed the ionospheric dynamics revealed with foF2 and TEC.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 5 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Jiawei Li, Pengqi Gao, Ming Shen, You Zhao〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The bistatic radar system has been one of the effective methods to detect the space debris in low earth orbit (LEO). Tianlai radio array with cylindrical-parabolic antennas is designed for dark energy detection, which has large field of view and high sensitivity, offering a fan-beam during the observation. We propose a bistatic radar system, which consists of Tianlai radio array and an incoherent scattering radar (ISR) assumed as a transmitter in the Qujing city of China, to detect space debris. In this paper, we calculate and analyze the detection capabilities of this system. The results show the bistatic radar system has the potential to detect small space debris of less than 10 cm in LEO. We provide a space debris detection method to obtain the position of the cross-beam satisfying the observation requirement with the TLE data of the space debris. The method can solve the problem of space synchronization between the radio array and ISR. We used the long-short baseline method of the radio array to locate the space target. The relationship among positioning error, the azimuth and the elevation angle are also discussed.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 5 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Jian-zhao Wang, Ying Wang, Shu-wu Dai, Chen Wang, Ji-nan Ma, Xiao-yu Jia, Yan-cun Li, Dai Tian, Jia-wen Qiu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A new solar electron event model is developed based on Virtual Timeline Method (VTM). We study events individually by analyzing the 17-year data of 3DP instrument on WIND spacecraft. This model is established in different solar cycle phases and is based on statistics of duration, fluence, and waiting time of solar electron events. The fluences follow a log-normal distribution and logarithmic durations fit well with logarithmic fluences linearly. We prove that waiting times of events significantly deviates from the Poisson process by investigating the stationary and event independence property of Poisson distribution. After a comparison study on waiting times, we choose the Lévy distribution in solar minimum and maximum years. During solar minimum, the event frequency is much lower than that of solar maximum, but the event magnitude is independent of solar cycle period. Large events also happen in solar minimum years. In different solar cycle phases, this model can output a spectrum with confidence level and mission duration by generating many series of virtual timelines composed of many pseudo-events based on Monte Carlo method. On the other hand, spectra in solar minimum years are softer than that in solar maximum years. The fluences in solar maximum years are about one order of magnitude higher than that in solar minimum years in a given mission period. We also compare this model with Interplanetary Electron Model (IEM) quantitatively and prove that this model is advanced.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 5 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Junmi Gogoi, Kalyan Bhuyan〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The geomagnetic storm is an important weather issue in the earth’s ionosphere-magnetosphere system. Many linear and nonlinear systems are involved in this earth-space environment. In order to understand the nonlinearly evolving dynamical system of magnetosphere and ionosphere, Time series analysis of foF2 data, Disturbance Storm Index Dst, Geomagnetic activity Index Ap and some other parameters during various solar cycles has been carried out in this work. The hourly data of critical frequency of F2 layer (foF2) for three ionosonde stations [Townsville (TV51R) 19.7°S, 146.9°E; Canberra (CB53N) 35.3°S, 149.1°E; Juliusruh (JR055) 54.6°N, 13.4°E] have been noted for 4 solar cycles viz., Solar Cycle 20, 21, 22 and 23. Hourly time series analysis has been performed to achieve some functional approaches such as statistical, analytical and spectral approach etc. to examine for the presence of periodicities in the data. Time Series is a sequential set of data which can be measured over time, and since the data being used for this work had been recorded as a function of time under various conditions, the appearance of missing observations in time series data is a very common issue. Different series may require different approaches to estimate these missing values. As such, to vanquish the problem of missing data we have attempted to estimate the missing value of foF2 data for various stations using the technique of Singular Value Decomposition (SVD). Another important method, Lomb Scargle Periodogram (LSP) has been performed on the Empirical Orthogonal Functions (EOFs) u1 and u2 (that has been obtained by SVD) along with the solar parameters such as solar flux f10.7, sun spot number (SSN) etc. and geomagnetic indices such as Dst index, Kp index & Ap index etc. for the four solar cycles to find the correlation, if any. For all the plots after performing LSP the power has been found out at 99% confidence level to see how much significant the generated data with respect to the parameters is. The periodicity obtained after performing LSP are divided into three terms namely:– (a) short-term periodicity, in which 27 days periodicity is found to be prominent, (b) mid-term periodicity, in which 1.3 year periodicity is found to be very common and (c) long-term periodicity, in which 11 years periodicity is very regular in almost among all the parameters and in the EOFs.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 2 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Robyn M. Millan, Rudolf von Steiger, Meir Ariel, Sergey Bartalev, Maurice Borgeaud, Stefano Campagnola, Julie C. Castillo-Rogez, René Fléron, Volker Gass, Anna Gregorio, David M. Klumpar, Bhavya Lal, Malcolm Macdonald, Jong Uk Park, V. Sambasiva Rao, Klaus Schilling, Graeme Stephens, Alan M. Title, Ji Wu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This is a COSPAR roadmap to advance the frontiers of science through innovation and international collaboration using small satellites. The world of small satellites is evolving quickly and an opportunity exists to leverage these developments to make scientific progress. In particular, the increasing availability of low-cost launch and commercially available hardware provides an opportunity to reduce the overall cost of science missions. This in turn should increase flight rates and encourage scientists to propose more innovative concepts, leading to scientific breakthroughs. Moreover, new computer technologies and methods are changing the way data are acquired, managed, and processed. The large data sets enabled by small satellites will require a new paradigm for scientific data analysis. In this roadmap we provide several examples of long-term scientific visions that could be enabled by the small satellite revolution. For the purpose of this report, the term “small satellite” is somewhat arbitrarily defined as a spacecraft with an upper mass limit in the range of a few hundred kilograms. The mass limit is less important than the processes used to build and launch these satellites. The goal of this roadmap is to encourage the space science community to leverage developments in the small satellite industry in order to increase flight rates, and change the way small science satellites are built and managed. Five recommendations are made; one each to the science community, to space industry, to space agencies, to policy makers, and finally, to COSPAR.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 2 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration〈/p〉 〈p〉Author(s): Shuiguang Tong, Yuanyuan Huang, Yongqing Jiang, Yanxiang Weng, Zheming Tong, Ning Tang, Feiyun Cong〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Gearboxes are at the heart of most rotating machines and they are considered as one of the main sources of vibration. As a key element in rotating machines, it is important to extract the gearbox vibration part from the mechanical system signal to assess the health state of the gearbox. In general, the gear meshing frequency part contains rich information which reflects its health state. In this paper, the authors find that in some cases when gearboxes work under heavy load, the meshing frequency part cannot be detected easily from the frequency spectrum. We think that the meshing frequency part may be modulated to the higher frequency band as the meshing impacts. To prove this point, a Multi-Input Single-Output (MISO) model is proposed to identify the local resonance excited by gear meshing impacts. In our method, a Meshing Impact Energy Distribution (MIED) graph is obtained through iteration to determine the demodulated frequency band. Experimental vibration data acquired form a healthy gearbox are illustrated to validate the performance of the proposed method. The forklift is taken as an example in the paper. Forklifts usually work in heavy load condition, and the gearbox vibration of a forklift is generally mixed with the ignition impacts of the diesel engine. The experiment result shows that for forklift machine system working in heavy load condition, its meshing frequency part of gearbox vibration signal is modulated into high frequency band. Further, the result shows that the proposed method is good at extracting the meshing frequency component when it is modulated into high frequency band especially when it is in heavy load condition.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 14 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Angelica Tarpanelli, Stefania Camici, Karina Nielsen, Luca Brocca, Tommaso Moramarco, Jérôme Benveniste〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The monitoring of rivers is not the primary objective of the Sentinel-3 mission. The first satellite of the constellation was launched in February 2016 and so far no study has investigated the joint use of altimeter, near-infrared and thermal sensors for discharge estimation. Nevertheless, similar sensors onboard other platforms have showed their ability to estimate river discharge also in scarcely gauged areas. The advantage of altimetry lies in the observation of water surface elevation, which can be proficiently used in approaches based on rating curve, empirical formulae or hydraulic modeling. Even though their use is limited, near-infrared sensors are successfully used to detect the variability of river discharge thanks to their high capacity to discriminate water from land. Thermal sensors are nearly completely unused, but the unique study that uses the difference in temperature of the river water between day and night for the estimation of water level, encourages its use for river discharge assessment as well. To improve the estimation of river discharge and foster studies that are aimed at monitoring ungauged rivers, the combination of the sensors is considered a viable path. The aim of this manuscript is to review these studies to show the limitations and the potentials of each sensor onboard the Sentinel-3 satellite and to investigate the added value of using these three sensors co-located on the same platform for river discharge monitoring.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 10 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration, Volume 460〈/p〉 〈p〉Author(s): Elias Arcondoulis, Con J. Doolan, Anthony C. Zander, Laura A. Brooks, Yu Liu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉An experimental investigation was performed in an anechoic wind tunnel involving acoustic measurements, hot-wire anemometry and surface flow visualisation techniques to investigate airfoil tonal noise generating mechanisms. Tests were conducted using a NACA 0012 airfoil at corrected angles of attack of 0° and 1.58° and Reynolds numbers of 50,000 to 150,000. A dual acoustic feedback model is presented, where feedback processes act independently on the airfoil pressure and suction surfaces between the point of boundary layer separation and the trailing edge. It is proposed that the tones generated on both airfoil surfaces, with the same or similar frequencies on each surface, interfere constructively. The primary tone possesses near exact frequencies on both surfaces, whereas the secondary tones have larger differences in frequencies between both surfaces, thus explaining their relative magnitudes based on acoustic superposition. This model provides a better comparison with the experimentally obtained tonal frequencies than the existing feedback models. Despite this agreement, the feedback model cannot perfectly predict the acoustic tones as the tones are not perfectly equispaced. An empirical feedback length is calculated by reverse engineering an acoustic feedback length scale by using the recorded primary tone as an input that also minimises the secondary tone prediction errors. This empirical length closely matches the dual acoustic feedback model presented in this paper.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 10 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration, Volume 460〈/p〉 〈p〉Author(s): Yan Wei-ming, Wang Bao-shun, He Hao-xiang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Particle damping (PD) technology has a remarkable effect in reducing vibration and noise for high frequency vibration such as mechanical analysis and aviation, and has been widely applied in some engineering practices. However, in the field of low frequency and low amplitude vibration control for building structures, the research and application of particle damper technology is still in the preliminary stage. The deficiencies and problems mainly include the mechanical model of PD is not perfect enough and the mechanism of vibration reduction is not clear enough. In the light of the shortcomings of the existing theoretical model of the PD, a mechanical model of the PD with friction effect between the particle and the structure is proposed, and the analytical solution of the displacement response for the mechanical model subjected to harmonic excitation is obtained. The model can fully represent the collision and non-collision process of PD, and the phase trajectories can embody the complex nonlinear characteristics of PD. The theoretical and motion characteristics of the PD are verified by the electromagnetic shaking table test of a single-story steel frame with PD, which proves the rationality of the theoretical model and the correctness of the analytical results, as well as the necessity of considering the friction effect. The parameters of mass ratio, excitation amplitude, excitation frequency and motion gap are further analyzed, so the mechanism of vibration reduction is clearer. Finally, compared with the traditional model of impact damper, it is obvious that the mechanical model of PD with friction effect can more reasonably evaluate the damping performance in practical engineering.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 14 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration〈/p〉 〈p〉Author(s): M. Liu, W.D. Zhu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉An efficient formulation of a circular Timoshenko beam is developed for static, vibration, and wave propagation problems. The B-spline wavelet on the interval (BSWI) interpolation functions are used to construct wavelet-based elements, which have analytical expressions at all levels and sufficient continuity. This paper derives static equilibrium, vibration, and wave propagation wavelet-based finite element models of in-plane and out-of-plane motions of circular beams according to the Hamilton's principle. Wave propagation characteristics of in-plane and out-of-plane waves in a phononic-crystal (PC) circular beam are analyzed using the wavelet-based finite element method (WFEM) based on the Bloch theorem. Effects of geometric parameters and material properties on in-plane and out-of-plane wave propagation characteristics of the PC circular beam are discussed. Numerical simulations show that the WFEM is more effective for static, vibration, and wave propagation problems than the traditional finite element method (TFEM). The WFEM can achieve the same accuracy as the TFEM with much fewer elements and degrees of freedom. It is shown that both in-plane and out-of-plane elastic wave band gaps exist in the PC circular beam, which exhibits some interesting phenomena due to coupling effects. This study can provide good support for wave filtering and vibration control of PC circular beam structures.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 27 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration, Volume 459〈/p〉 〈p〉Author(s): 〈/p〉

Description: 〈p〉Publication date: Available online 10 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Yekoye Asmare Tariku〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper mainly focuses on the evaluation of efficiency of the Sunspot Number (SSN) and the 10.7 cm Solar Radio Flux (F10.7) indices as a cause for the variation of the performance of the latest versions of the International Reference Ionosphere model (IRI 2016 with NeQuick, IRI01-corr and IRI2001 options for the topside electron density) and the IRI Extended to the Plasmasphere (IRI-Plas 2017) for the modeling of the Total Electron Content (TEC) over the West Pacific regions during the recent solar maximum (2012-2014) years. The Global Positioning System (GPS)-derived TEC data obtained from the dual frequency GPS receivers located at Observation Rock〈strong〉,〈/strong〉 OBSR (geog 46.90°N, 238.18°W, Geom. 52.46°N) and Husband, HUSB (44.12°N, 238.15°W, Geom. 49.73°N) have been considered for the validation of the performance of the models. The results show that both the GPS-derived TEC (GPS VTEC) and modelled (IRI 2016 and IRI-Plas 2017 VTEC) seasonal diurnal values tend to peak at 00:00 UT (16:00 LT) and 20:00 (12:00 LT) with the highest being observed mostly at 20:00 (12:00 LT); while, their minima are mostly observed at about 13:00 UT (05:00 LT). In addition, in utilizing the SSN, the best performance is generally observed in the June solstice months, especially by the IRI-Plas 2017 model. However, for the equinoctial and December solstice months, the best performance is generally observed by the IRI 2016 model with NeQuick and IRI01 options. It has also been shown that the root-mean-square deviations between the GPS-derived and modelled VTEC diurnal variation in using the F10.7 index are generally less than those of the SSN option in all months, revealing that both the IRI 2016 and IRI-Plas 2017 models generally show better performance using F10.7 index than the SSN. Hence, the F10.7 option is recommended for better TEC modeling employing the IRI 2016 and IRI-Plas 2017 models during the recent solar maximum years over the West Pacific region. In addition, both models cannot effectively estimate the geomagnetic storm time TEC variation.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 10 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration, Volume 460〈/p〉 〈p〉Author(s): Enrique G. Segovia-Eulogio, Jennifer Torres, Jesús Carbajo, Jaime Ramis, Jorge P. Arenas〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Viscoelastic layers under floating floors are often used to reduce impact sound. A standardized dynamic stiffness test is routinely used to estimate the performance of a layer as an impact sound isolator. During the test, a material sample is placed between a load plate and a motionless rigid foundation. In this work, equations that provide a useful analytical description of the standardized test are derived. The new analytical approach is linked with the analysis of multilayer elastomeric bearings. The new approach leads to simpler analytical solutions as compared with those of previous studies, which makes them easy to translate into computer codes. The obtained expressions are almost independent of the shape of the boundary and are only dependent on static values such as the area and moments of inertia of the contour. Taking advantage of the new closed-form solutions, it is shown that, under certain restrictions, the analytical approach may be used to experimentally estimate the elastic parameters of a flexible material using a harmonic (frequency-dependent) analysis. It is reported that results obtained using the proposed approach are in good agreement with those obtained using a commercial finite element software.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 10 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration, Volume 460〈/p〉 〈p〉Author(s): Quentin Agrapart, Florence Nyssen, Déborah Lavazec, Philippe Dufrénoy, Alain Batailly〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper provides new insight on the simulation of blade-tip/casing rubbing events within aircraft engines accounting for thermomechanical effects within the casing. A multi-physics numerical strategy is presented in order to simulate an interaction experimentally witnessed on a full-scale low-pressure compressor. Experimental data are used for an accurate representation of the blade's incursion depth within the abradable coating. This numerical strategy combines Safran's in-house tool for rotor/stator interaction simulations with a finite element based thermomechanical analysis carried out with Ansys. This work underlines the distinct contributions of both dynamical and thermomechanical phenomena in the simulated interaction. Competition between wear and thermal expansions is investigated as well as their consequences on blade dynamics. The proposed numerical strategy yields an accurate description of the interaction phenomenon as wear patterns, critical speed, amplitude growth rate of the blade vibration and temperature levels may be predicted.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 7 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Tao Chen, Zhen Zhao, Stephen R. Schwartz, Caishan Liu, Qi Wang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In this paper, we study the conveying dynamics in the helical groove of an auger drilling into lunar simulant. We demonstrate that the stress-coupling effect of the conveyed granules by the groove of a drill auger plays a significant role on the dynamics of conveyance. For this, a discrete element method (DEM) is adopted first to uncover the motion and the stress characteristics of conveyed granules in a working auger. Then, a simplified dynamic model following the stress characteristics of DEM is established. The simplified model can not only reflect the results by the discrete element method, but can also explain well the proportional relationship between the maximum conveying rate and the rotating speed of the auger in the experiment (Zhao et al., 2019).〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 5 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Haoye Lin, Bo Xu, Jingxi Liu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The accuracy in pulsar-based navigation system can be improved with a well-designed observation scheme. In this paper, based on the idea that minimises the size of position probability ellipsoid at each updating time, four strategies are put forward for determining observation order. As the calculation of posterior probability ellipsoid only requires a priori orbit information, the observation scheme can be designed during preliminary mission analysis. These strategies can be employed in both situations with single detector and multiple detectors. Numerical simulations show that the proposed observation strategies achieve good performance.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 5 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Adam Łyszkowicz, Anna Bernatowicz〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Sea level is a unique indicator in climate impact studies on any changes on the surface of the Earth. Traditionally, tide gauges allow observation of relative (relative to land) sea level changes at specific locations with a high resolution in time. Common method of sea level determination in XXI century is the combination of tide gauge observations with satellite observation data. So determined sea level changes are absolute changes and they are referred to the beginning of the ITRF system.〈/p〉 〈p〉Geocentric changes in the Baltic Sea level are monitored, inter alia, by the SONEL network. This network system does not include the southern coast of the Baltic Sea. The aim of this work is to fill this gap and to compute geocentric changes in the Baltic Sea at the stations: Hel, Władysławowo, Łeba, Ustka, Kołobrzeg, Świnoujście.〈/p〉 〈p〉The tide gauge data needed for the analysis were made available by the Institute of Meteorology and Water Management and the GNSS data was taken from web page Nevada Geodetic Laboratory. The analysis of the time series of tide gauge and GNSS observations was carried out using the TSAnalyzer software. We assumed that GNSS and tide gauge series have a seasonal signal (annual plus semi-annual) and a trend. First the outliers were removed from observation, then the jumps were viewing. The trend, annual and semi-annual terms were calculated for GNSS and tide gauge series.〈/p〉 〈p〉The results of the work are calculated geocentric changes in the Baltic Sea level along southern coast and they are at a level of 0.3 mm/year except Ustka where it reach value 4.68 mm/year.〈/p〉 〈/div〉 〈/div〉

Description: 〈p〉Publication date: 10 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration, Volume 460〈/p〉 〈p〉Author(s): Elsa Piollet, Florence Nyssen, Alain Batailly〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In order to improve the efficiency of aircraft engines, the reduction of clearances between blade tips and their surrounding casing is one avenue manufacturers consider to lower aerodynamic losses. This reduction increases the risk of blade tip/casing contact interactions under nominal operating conditions. Designers need tools to accurately predict subsequent nonlinear vibrations. Engineers and researchers have developed a variety of sophisticated numerical models to predict blades' responses. These models are related to distinct frameworks (time/frequency domain) and various solution algorithms (explicit/implicit time integration schemes, penalty/Lagrange multiplier contact treatment…) which calls for comparative analyses. However, published results are often limited for the sake of confidentiality thus preventing any detailed confrontation. While qualitative understanding can be gained from simplified academic models, full scale models are needed to predict complex interactions in a realistic manner. In this context, this paper proposes a benchmark featuring detailed simulations and analyses of a full 3D finite element model based on the open NASA rotor 37 compressor blade to facilitate reproducibility and collaboration across the research community. NASA rotor 37, a compressor stage widely used as a test case in aerodynamic simulations and validations, has the advantage of presenting a realistic blade geometry. The geometry of the blade is built from publicly available reports. The paper provides details on the geometry, the numerical model and the results to allow an easy use of this model across the fields of structural dynamics. Two contact scenarios are investigated: one with direct contact against the casing, and one with abradable material deposited on the casing to mitigate contact severity through wear. The nonlinear vibration response of the blade is simulated in the time domain. It is evidenced that the addition of the abradable material decreases the amplitude of vibration for most of the angular speeds investigated. However, new interactions appear for some angular speeds. The obtained results are consistent with previous simulations on industrial geometries. Based on works showing improved aerodynamic performances when the blade is tilted, a total of seven geometries are investigated: the reference blade, with a straight vertical stacking line similar to the original rotor 37, two forward-leaned blades, two backward-swept blades and two full forward chordwise swept blades. The sweep and lean variations are shown to have a dramatic impact on the vibration response: the backward sweep results in an increased blade's robustness to contact events and the full forward chordwise sweep in a reduced robustness, while the forward lean leads to a robustness similar to the reference blade.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 10 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration, Volume 460〈/p〉 〈p〉Author(s): B. Uspensky, K. Avramov, B. Liubarskyi, Yu Andrieiev, O. Nikonov〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉New approach for analysis and detuning of nonlinear torsional vibrations of diesel electric generator gear system is suggested. Nonlinear magnetic field of the generator is calculated by finite element method to obtain the disturbing moments, which act on the gear system. Moreover, others disturbing moments, which arise due to operation in diesel engine cylinders, are accounted. Essential nonlinear model of torsional vibrations with sixteen degrees-of- freedom is derived. This model accounts the nonlinear moments of two elastic clutches and the backlashes of gear pairs. The comparison of the numerical simulations data with experimental results is performed to verify the obtained model. The approach for essential nonlinear free torsional vibrations calculations is suggested. The harmonic balanced method is the basis of this approach. Sensitivity theory is used to detune the nonlinear forced torsional vibrations from resonances. The results of nonlinear torsional vibrations analysis are discussed.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 1 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Lionel Métrailler, Guillaume Bélanger, Peter Kretschmar, Erik Kuulkers, Ricardo Pérez Martínez, Jan-Uwe Ness, Pedro Rodriguez, Mauro Casale, Jorge Fauste, Timothy Finn, Celia Sanchez, Thomas Godard, Richard Southworth〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The magnetosphere sustained by the rotation of the Earth’s liquid iron core traps charged particles, mostly electrons and protons, into structures referred to as the Van Allen Belts. These radiation belts, in which the density of charged energetic particles can be very destructive for sensitive instrumentation, have to be crossed on every orbit of satellites traveling in elliptical orbits around the Earth, as is the case for ESA’s 〈em〉INTEGRAL〈/em〉 and 〈em〉XMM-Newton〈/em〉 missions. This paper presents the first working version of the 5DRBM-e model, a global, data-driven model of the radiation belts for trapped electrons. The model is based on in situ measurements of electrons by the radiation monitors on board the 〈em〉INTEGRAL〈/em〉 and 〈em〉XMM-Newton〈/em〉 satellites along their long elliptical orbits for respectively 16 and 19 years of operations. This model, in its present form, features the integral flux for trapped electrons within energies ranging from 0.7 to 1.75 MeV. Cross-validation of the 5DRBM-e with the well-known AE8min/max and AE9mean models for a low eccentricity GPS orbit shows excellent agreement, and demonstrates that the new model can be used to provide reliable predictions along widely different orbits around Earth for the purpose of designing, planning, and operating satellites with more accurate instrument safety margins. Future work will include extending the model based on electrons of different energies and proton radiation measurement data.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 10 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration, Volume 460〈/p〉 〈p〉Author(s): Stewart G. Haslinger, Michael J.S. Lowe, Peter Huthwaite, Richard V. Craster, Fan Shi〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Rapid and accurate methods, based on the Kirchhoff approximation (KA), are developed to evaluate the scattering of shear waves by rough defects and quantify the accuracy of this approximation. Defect roughness has a strong effect on the reflection of ultrasound, and every rough defect has a different surface, so standard methods of assessing the sensitivity of inspection based on smooth defects are necessarily limited. Accurately resolving rough cracks in non-destructive evaluation (NDE) inspections often requires shear waves since they have higher sensitivity to surface roughness than longitudinal waves. KA models are attractive, since they are rapid to deploy, however they are an approximation and it is important to determine the range of validity for the scattering of ultrasonic shear waves; this range is found here. Good agreement between KA and high fidelity finite element simulations is obtained for a range of incident/scattering angles, and the limits of validity for KA are found to be much stricter than for longitudinal wave incidence; as the correlation length of rough surfaces is reduced to the order of the incident shear wavelength, a combination of multiple scattering and surface wave mode conversion leads to KA predictions diverging from those of the true diffuse scattered fields.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 3〈/p〉 〈p〉Author(s): Christian Siemes, Moritz Rexer, Roger Haagmans〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We analyse the inter-boresight angles (IBA) measured by the star trackers on board the GOCE satellite and find that they exhibit small offsets of 7–9″ with respect to the ones calculated from the rotation of the star tracker reference frames to the satellite reference frame. Further, we find small variations in the offsets with a peak-to-peak amplitude of up to 8″, which correlate with variations of the star trackers’ temperatures. Motivated by these findings, we present a method for combining the attitude quaternions measured by two or more star trackers that includes an estimation of relative attitude offsets between star trackers as a linear function of temperature. The method was used to correct and combine the star tracker attitude quaternions within the reprocessing of GOCE data performed in 2018. We demonstrate that the IBA calculated from the corrected star tracker attitude quaternions show no significant offsets with respect to the reference frame information. Finally, we show that neglecting the star tracker attitude offsets in the processing would result in perturbations in the gravity gradients that are visible at frequencies below 2 mHz and have a magnitude of up to 90 mE. The presented method avoids such perturbations to a large extent.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 3〈/p〉 〈p〉Author(s): Qiang Zhang, Qile Zhao〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Spherical harmonic (SH) expansion is widely used to model the global ionosphere map (GIM) of vertical total electron content (VTEC). According to the impact of different data processing methods of the SH expansion model on the VTEC maps, we specifically performed comprehensive analysis in terms of the data sampling rate, the time resolution, the spherical harmonic degree, and the relative constraint. One month of GPS data (January in 2016) from the International GNSS (Global Navigation Satellite System) Service (IGS) network in a moderate ionospheric activity period at the descending phase of Solar Cycle 24 was processed. To improve the computational efficiency of the daily GIM generation, the data sampling rate of 5 min was recommended allowing the GIM precision loss within 0.10 TECU (total electron content unit). The global VTEC map could be better represented in temporal and spatial domains with higher time resolution and higher spherical harmonic degree, especially at low latitude bands and in the southern hemisphere. The GIM precision improvement was about 10.91% for 1-h and about 15.15% for 0.5-h compared with the commonly used 2-h time resolution. The use of spherical harmonic degree 17 or 20 instead of 15 could improve the precision by 3.19% or 6.06%. We also found that an optimal relative constraint had to be found experimentally considering both the GIM precision and the GIM root mean square (RMS) map.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 3〈/p〉 〈p〉Author(s): Xin Liu, Shubi Zhang, Qiuzhao Zhang, Nan Ding, Wei Yang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉With the Global Navigation Satellite System (GNSS) developing, the single-frequency single-epoch multiple GNSSs (multi-GNSS) relative positioning has become feasible. Since a larger number of the observed satellites make the instantaneous (single-epoch) positioning time-consuming, a proper satellite selection is necessary. Among the present methods, the satellite selection with a fixed high cut-off elevation angle (CEA) is least time-consuming. However, there is no criterion how large a fixed high CEA should be to achieve a high success rate and less time consumption. Besides, a fixed high CEA makes the number of visible satellites largely variable, which affects the success rate. Hence, a satellite selection strategy based on ambiguity dilution of precision (ADOP) is proposed. Firstly, the theoretical proof that the ADOP increases the least when removing satellites are all low-elevation-angle satellites is given, which is important to achieve the fast positioning with a high success rate. Then, the threshold 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈mi〉β〈/mi〉〈/mrow〉〈/math〉 is calculated for a different number of satellites and a given ADOP. The satellites are selected based on their elevation angles from high to low until 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈mi〉β〈/mi〉〈/mrow〉〈/math〉 of the selected satellites becomes smaller than the corresponding threshold; this method is called the extended floating CEA multi-GNSS (EF-multi-GNSS). The comparison of the single-frequency single-epoch positioning performance of the EF-multi-GNSS with the satellite selections based on a fixed low CEA (L-multi-GNSS) and a fixed high CEA (H-multi-GNSS) via the relative positioning experiments shows that: (1) the EF-multi-GNSS with a minimal number of satellites can achieve the fast positioning and a high success rate close to 100%. It can greatly reduce the time consumption of the L-multi-GNSS, by about 64.0%, by selecting 12.6 satellites of 23.4 satellites; (2) the floating CEA of EF-multi-GNSS eliminates the consideration how large a fixed high CEA should be, and a CEA larger than the fixed high CEA of the H-multi-GNSS makes it more suitable for different conditions.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 3〈/p〉 〈p〉Author(s): Tirthankar Basu, Swades Pal〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Darjeeling Himalaya is one of the several mountainous areas of India which is often suffered from landslide hazards. In this paper, a multi criteria evaluation is applied using 16 morphometric indicators, geology and lineaments to identify the areas vulnerable in respect to drainage and relief conditions. As both drainage and relief parameters exert strong influences on landslide intensity, both the diversity maps are integrated for final landslide susceptibility mapping. The obtained results show that 20.17 sq. km (7.61%) area within the basin is highly susceptible for landslides, where average drainage density is 3.78 km/sq. km, relative relief is greater than 408 m and slope is greater than 12°. The validation result shows that very high landslide susceptible zone is associated with very high frequency of landslide occurrence. Beside this, ROC curve also suggests good predicted rate (86.60%) for the model. So, the proposed method can be applied for predicting landslide susceptible zone.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 28 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): A. Mahmoudian, A. Senior, M. Kosch, W.A. Scales, M.T. Rietveld, B. Isham, X. Shi, M. Ruohoniemi〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Electromagnetic (EM) and electrostatic (ES) emissions can be generated in the ionosphere by high-power high-frequency (HF) radio waves transmitted from the ground. The signatures of the EM emissions observed on the ground are known as Stimulated Electromagnetic Emissions (SEE) and can be employed for remote measurement of ionospheric parameters. The experimental data from recent HF heating experiments near the fourth electron gyro-frequency (〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si41.gif" overflow="scroll"〉〈mrow〉〈mn〉4〈/mn〉〈msub〉〈mrow〉〈mtext〉f〈/mtext〉〈/mrow〉〈mrow〉〈mi mathvariant="italic"〉ce〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉) at EISCAT are presented. This paper compares the temporal behavior of SEE within a few Hertz up to 50 kHz of the transmission frequency to the time evolution of enhanced ion line (EHIL) in the incoherent scatter radar (ISR) spectrum. The correlation of Wideband SEE (WSEE) spectral lines within 1 kHz to 100 kHz such as the downshifted maximum (DM), downshifted peak (DP), and broad upshifted maximum (BUM), with HF enhanced ion lines (EHIL) is shown. It is shown that WSEE spectral lines can be used to reproduce the EHIL characteristics including altitude range, rise and decay time, maximum and minimum amplitude. A data reduction technique is developed to derive ionospheric parameters such as the electron density profile near the interaction altitude, magnetic field strength 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si42.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mrow〉〈mi〉B〈/mi〉〈/mrow〉〈mrow〉〈mn〉0〈/mn〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉 as well as the altitude profile of the EHIL using the temporal evolution of WSEE spectral lines near n〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si4.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mrow〉〈mi〉f〈/mi〉〈/mrow〉〈mrow〉〈mi mathvariant="italic"〉ce〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 28 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): S. Veretenenko, M. Ogurtsov〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In this work we continue studying possible reasons for temporal variability observed in correlation links between characteristics of the lower atmosphere and solar activity phenomena at the multi-decadal time scale. Temporal variations of correlation coefficients between troposphere pressure at extratropical latitudes and sunspot numbers are compared with the evolution of the large-scale circulation forms according to the Vangengeim-Girs classification, as well as the characteristics of the stratospheric polar vortex and global temperature anomalies. The results obtained show that temporal variability of solar activity/galactic cosmic ray (SA/GCR) effects on troposphere pressure (the development of extratropical baric systems) is characterized by a roughly 60-year periodicity and closely related to changes in the regime of large-scale circulation which accompany transitions between the different states of the polar vortex. It was suggested that the character of SA/GCR effects depends on the polar vortex strength influencing the troposphere-stratosphere coupling. It was shown that the evolution of the polar vortex may be associated with global temperature variations, with a possible reason for these variations being long-term changes of total solar irradiance.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 25 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Pouria Razzaghi, Ehab Al Khatib, Shide Bakhtiari〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Since space debris is a problem that has been continuously increasing, removal missions should be considered. Tethered space system (TSS) has wide application prospects in the future on-orbit missions such as debris removal. However, it is rather complex and difficult for TSS to realize stabilization of tumbling combinations after connecting to the debris. In this paper, the stabilization problem of this combination is studied.〈/p〉 〈p〉An adaptive sliding mode and State-Dependent Riccati Equation control methods are applied on a TSS to stabilize the system and de-orbit the space debris. The tether tension and stability of the in-plane and out-of-plane libration angles of the system are taken into account. The tether can only resist axial stretching. The thrusters, which are the sources of the system inputs are equipped on the satellite. The controllers regulate the tether to remain fully stretched and to decrease the altitude of the orbit continuously. The numerical simulation validates the proposed control schemes for de-orbiting the debris and put it in lower altitude orbit. This makes the debris retrieve to the atmosphere in less time than the actual orbit lifetime. The comparison between two control schemes is discussed.〈/p〉 〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 30 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Tao An, Xiaoyu Hong, Weimin Zheng, Shuhua Ye, Zhihan Qian, Li Fu, Quan Guo, Sumit Jaiswal, Dali Kong, Baoqiang Lao, Lei Liu, Qinghui Liu, Weijia Lü, Prashanth Mohan, Zhiqiang Shen, Guangli Wang, Fang Wu, Xiaocong Wu, Juan Zhang, Zhongli Zhang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Space Very Long Baseline Interferometry (VLBI) has unique applications in high-resolution imaging of fine structure of astronomical objects and high-precision astrometry, owing to the key long space-Earth or space-space baselines beyond the Earth’s diameter. China has been actively involved in the development of space VLBI in recent years. This paper briefly summarizes China’s research progress in space VLBI and the development plan in future.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 30 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): R Gardiner-Garden, M Cervera, R Debnam, T Harris, A Heitmann, D Holdsworth, D Netherway, B Northey, L Pederick, J Praschifka, A Quinn, M Turley, A Unewisse, B Ward, G Warne〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉The Elevation sensitive Oblique Incidence Sounder Experiment (ELOISE) was an extensive experiment undertaken by the Defence Science and Technology (DST) Group that focused on collecting ionospheric sensor data from multiple overlapping ionospheric paths in the Australian region in order to improve understanding of the characteristics of ionospheric variability and its effect on HF radio propagation. The experiment ran from July to October 2015 and included a period of three weeks of increased sample density and three days of dedicated over-the-horizon (OTH) radar operations. It was anticipated that ELOISE would sample a wide range of environmental conditions and present an opportunity to characterise periods of “normal variability” and periods of “exceptional variability” in the ionosphere.〈/p〉 〈p〉This report is a general description of the aims of this experiment and the types of data collected. Particular interest focused on observing and measuring variability in ionospheric electron density gradients and their effect on oblique HF propagation. To this end, ELOISE established a pair of two dimensional HF receiver arrays to directly measure the oblique angle of arrival (AoA) on many overlapping oblique paths. ELOISE also established a dense sub-network of spatially separated quasi-vertical incidence soundings in the vicinity of Alice Springs in central Australia. This enabled a comparison of gradients observed in a dense network of vertical sounders with gradient effects observed in oblique propagation passing overhead. Several additional ionospheric observing systems were also used to give complementary pictures of the fine scale characteristics of ionospheric variability in the region.〈/p〉 〈/div〉 〈div〉 〈h6〉Plain Language Summary〈/h6〉 〈p〉This paper is an overview of the 2015 Elevation sensitive Oblique Incidence Sounder Experiment (ELOISE), an experiment designed to observe and characterise mid-latitude ionospheric disturbances in the Australian region and understand their impact on high frequency (HF) signal propagation.〈/p〉 〈p〉ELOISE involved the simultaneous operation of a large collection of ionospheric sounders enabling ionospheric variability to be characterised on a finely sampled large scale.〈/p〉 〈p〉Particular efforts were made to provide direct high fidelity measurements of the angle of arrival (AoA) on many oblique HF propagation paths. These direct AoA measurements imply horizontal electron density gradients that can be compared to ionospheric gradients estimated from conventional models of the ionosphere derived from the spatial network of sounder sites.〈/p〉 〈p〉The size and scope of the experiment are detailed in this paper and some preliminary results are presented.〈/p〉 〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 27 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Stefan Frey, Camilla Colombo, Stijn Lemmens〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Numerical integration of orbit trajectories for a large number of initial conditions and for long time spans is computationally expensive. Semi-analytical methods were developed to reduce the computational burden. An elegant and widely used method of semi-analytically integrating trajectories of objects subject to atmospheric drag was proposed by King-Hele (KH). However, the analytical KH contraction method relies on the assumption that the atmosphere density decays strictly exponentially with altitude. If the actual density profile does not satisfy the assumption of a fixed scale height, as is the case for Earth’s atmosphere, the KH method introduces potentially large errors for non-circular orbit configurations.〈/p〉 〈p〉In this work, the KH method is extended to account for such errors by using a newly introduced atmosphere model derivative. By superimposing exponentially decaying partial atmospheres, the superimposed KH method can be applied accurately while considering more complex density profiles. The KH method is further refined by deriving higher order terms during the series expansion. A variable boundary condition to choose the appropriate eccentricity regime, based on the series truncation errors, is introduced. The accuracy of the extended analytical contraction method is shown to be comparable to numerical Gauss-Legendre quadrature. Propagation using the proposed method compares well against non-averaged integration of the dynamics, while the computational load remains very low.〈/p〉 〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 27 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Hassan Aboelkhair, Mostafa Morsy, Gamal El Afandi〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The climatic reanalysis datasets are one of the most important data types that could help to overcome scarce of observations. Therefore, the main objective of this study is to evaluate NASA POWER reanalysis data for surface monthly average temperatures at 2 m (maximum (T〈sub〉max〈/sub〉), minimum (T〈sub〉min〈/sub〉), mean (T〈sub〉mean〈/sub〉) and dew point (T〈sub〉d〈/sub〉), all in °C) and relative humidity (RH) in percentage compared to the observed data at 20 Egyptian weather stations. The results showed that there are a significant correlation and goodness of fit between NASA POWER reanalysis and observed data for all parameters except RH. For temperature variables, the coefficient of determination (R〈sup〉2〈/sup〉) and Willmott Index of agreement (WI) attain around 0.75 and 0.90 respectively, while the root mean square error (RMSE) reaches to less than 5 °C; and the mean bias error (MBE) ranges from −3 to +3 °C for 85% of stations. In addition, NASA POWER accuracy of temperature parameters increases gradually northward with the highest ratio at the northern coast of Egypt. Where, it is slightly overestimated (under 3 °C) T〈sub〉max〈/sub〉, T〈sub〉min〈/sub〉, and T〈sub〉mean〈/sub〉 at 80, 75 and 65% of the stations respectively. While it is slightly underestimated T〈sub〉d〈/sub〉 with 3 °C at 90% of the stations. Contrarily, NASA POWER data accuracy of RH increases southward, particularly in Aswan. Additionally, NASA POWER reanalysis has a considerable underestimation for RH data at most stations, where the dominant MBE percentage ranges from −12 to −5% for about 75% of the stations. As well as, the maximum RMSE and MBE for all elements were recorded in the Malwi station at Middle Egypt. Consequently, R〈sup〉2〈/sup〉, WI, RMSE, and MBE for temperature parameters are almost within an acceptable range for most selected Egyptian stations which are located in the area that dominated by the influence of the Mediterranean Sea (northern of 30°N) and western of 30°E with a distance between 2.5 and 14.5 km from the Sea. While, the good RH estimation is recorded at stations that are located south of the area that dominated by the influence of the Mediterranean Sea (south of 26°N). Finally, NASA POWER reanalysis datasets can be used in case of missing or scarce of observations in Egypt. Nevertheless, it still needs improvements by taking into consideration the influence of the Mediterranean Sea and the locality of (especially middle) Egypt on temperature and in particular on relative humidity estimations.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 30 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): D.V. Blagoveshchensky, M.A. Sergeeva, P. Corona-Romero〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The main feature of the geomagnetic disturbance which occurred on September 7-8, 2017, was that it consisted of two consecutive magnetic storms separated in time by ∼13 hours. It was of interest to reveal its particular features, characteristics and geomagnetic field variations during both storms and the influence they had on the ionosphere. The results are as follows. The character of the development of the first storm and its impact on the Earth’s magnetosphere and ionosphere are significantly different from the character of the development and impact of the second storm. There are prominent differences in the geomagnetic field variations at different longitudes along the same latitude sector. The asymmetry of the dayside and nightside effects was revealed. The variations of the riometer absorption level, critical frequencies of the ionosphere and Total Electron Content in each considered observation point corresponded to the variations of the magnetic field at this point.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 29 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration〈/p〉 〈p〉Author(s): Xiaoqing Yang, Kang Ding, Guolin He〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Long-time service and intricate work situation of gearbox make it liable to fault. The vibration signal of fault gear generally includes amplitude-modulation (AM) and phase-modulation (PM) components, which are the manifestation of fault and have strong connection with fault diagnosis. The corresponding relationships of AM and PM with gear fault type still lack of clarity. This paper proposes an accurate separation method of AM and PM signal, which contains squared amplitude demodulation and phase demodulation based on Bessel function of the first kind. Discrete spectrum correction technique is employed to correct modulation frequency and amplitudes in amplitude spectrum, which are utilized to establish system of nonlinear equations of AM and PM parameters. Trust-region reflective least square algorithm is then applied to solve these parameters and extract AM and PM components in sequence. The accuracy of this method is proved by various simulation signal. Additionally, simulation signals with different 〈em〉SRN〈/em〉s are employed to verify the anti-noise performance of the proposed method, which is further compared to Hilbert demodulation and energy-operator-based demodulation. Comparison results manifest the superiority of the proposed method in anti-noise performance. Experimental analyses confirm the effectiveness of this method and show the visible differences of separated PM components under different gear fault conditions, which can be used as an accordance of broken-tooth fault diagnosis. The relationship of the size of broken-tooth and modulation intensity is researched by the proposed method, which indicates that more serious broken-tooth degree behaves stronger modulation. A novel diagnosis method for gear broken-tooth fault is finally generated.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 28 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Bijay Kumar Sharma〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Matija Cuk et.al (2016) have proposed a new model for the birth and tidal evolution of our natural satellite Moon, born from impact generated terrestrial debris in the equatorial plane of high obliquity, high angular momentum Earth. This paper examines their findings critically in the light of advanced kinematic model (AKM) which includes Earth’s obliquity(ɸ), Moon’s orbital plane inclination (α) , Moon’s obliquity (β) and lunar’s orbit eccentricity (e). For the real Earth-Moon (E-M) system, the history of evolution of ɸ, α, β, e and (length of month)/(length of day) or LOM/LOD is traced from 45R〈sub〉E〈/sub〉 to 60.33R〈sub〉E〈/sub〉 where R〈sub〉E〈/sub〉 is Earth Radius. It is shown that AKM’s valid range of application is from 45R〈sub〉E〈/sub〉 to 60.33R〈sub〉E〈/sub〉 . The evolution of α, β, e is in correspondence with the simulation results of Matija Cuk et.al (2016) but evolution of Earth’s obliquity has a break at 45R〈sub〉E〈/sub〉 . According to AKM , earlier than 45R〈sub〉E〈/sub〉 Earth should achieve 0° obliquity in order to achieve the modern value of 23.44° obliquity. Cuk et al (2016) donot explain how this can be achieved. AKM stands vindicated because Science Advances_aax0684, AKM has successfully given near-precise theoretical formalism of LOD curve for the last 1.2Gy time span opening the way for early warning and forecasting methods for Earth-quake and sudden volcanic eruptions..〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 28 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Susan W. Samwel, Esraa A. El-Aziz, Henry B. Garrett, Ahmed A. Hady, Makram Ibrahim, Magdy Y. Amin〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉The trend towards the development of small satellites, or smallsats, has been increasing over the last few years. However, the harsh space radiation environment in which these smallsats operate provides a challenge to their survivability as their desired mission lengths increase from a few months to several years also. Smallsats typically use commercial off the shelf components (COTS) that are built for ground operations, not space use. Therefore, they may be more susceptible to the hazards of space radiation than traditional spacecraft which are typically designed to withstand the high radiation levels of space. The present paper provides a targeted assessment of representative COTS components using up to date models of the space radiation environment and its effects on smallsats in a polar Low Earth Orbit (LEO). This orbit will be assumed to be sunsynchronous (98.5° inclination) and at an altitude of 800km. We employed the new Solar Accumulated and Peak Proton and Heavy Ion Radiation Environment (SAPPHIRE) model which has been released recently in 2018, ISO-15390 GCR model, and AP8/AE8 models to estimate the space radiation environment for solar particles, galactic cosmic rays (GCRs), and trapped protons and electrons respectively. The basic damage effects that can be produced in materials and electronics in this orbit due to their exposure to the space radiation are evaluated. These effects are the Total Ionizing Dose (TID), Displacement Damage Dose (DDD), and Single Event Effects (SEE) as represented by Single Event Upsets (SEUs). SEU is evaluated for different COTS components which are believed to be representative of an optimum blend of capability and cost-effectiveness for the next generation of smallsats, including 20 nm Xilinx Kintex Ultra Scale FPGA Configuration RAM (XCKU040), 90-nm SRAM, and MLC NAND flash memory (MT29F128G08CBECBH6). For comparative purposes, the analyses are performed for both maximum and minimum solar activity.〈/p〉 〈p〉Based on these comparisons, we find as expected that the space radiation environment parameters vary with solar activity. The fluence of trapped electrons and solar protons at solar maximum are higher than those at solar minimum in contrast to the trapped protons and galactic cosmic rays at low altitudes. On the other hand, TID, DDD, and SEE all show higher values during maximum solar activity than during minimum solar activity.〈/p〉 〈p〉The use of shielding material for small satellites is mandatory for this orbit as observed TID, DDD, and SEES levels that can be reached are potentially of concern to designers. However, using Al shielding thickness of at least 1.5 mm can reduce the radiation effects to acceptable levels, for both maximum and minimum solar activity for missions of moderate (∼3 years) duration.〈/p〉 〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 28 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Weiwei Xu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The precise AMS data reveals distinctive properties of cosmic-ray positron and electron fluxes. The positron spectrum hardens starting from 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈mo〉∼〈/mo〉〈/mrow〉〈/math〉20 GeV. Most importantly, the positron spectrum exhibits a sharp drop-off at 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.gif" overflow="scroll"〉〈mrow〉〈mo〉∼〈/mo〉〈mn〉300〈/mn〉〈/mrow〉〈/math〉 GeV, showing the existence of an energy cutoff at highest energy. The electron spectrum is distinctly different from the positron spectrum in both the magnitude and energy dependence. The electron spectrum hardens from 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈mo〉∼〈/mo〉〈/mrow〉〈/math〉30 GeV. Remarkably, the electron spectrum is well described by a single power law from 55 GeV to 1 TeV and does not have an energy cutoff. These experimental data show that, at high energies, the cosmic-ray positrons predominately originate either from dark matter annihilation or from a new astrophysical source, whereas the cosmic-ray electrons originate from different sources.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 27 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Russell P. Patera〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The recently developed Vector Inertia Tensor Attitude Estimation, VITAE, method is enhanced by the addition of two different preprocessing algorithms that modify the observation vectors prior to attitude estimation. The first preprocessing algorithm is for use in cases that have one observation vector that is much more accurate than the other observation vectors. Such cases suffer numerical error caused by the large relative weight of the very accurate observation vector. Use of the preprocessing algorithm eliminates large variation in vector weights and resulting numerical error. The second preprocessing algorithm enables VITAE to generate results equivalent to a very accurate suboptimal attitude determination algorithm that produces results extremely close to the optimum solution. Preprocessing algorithms eliminate the need to select observation vector weights to remove eigenvalue degeneracy and allows the weights to be based solely on optimality, thereby improving estimation accuracy. When optimum weights are used, the inertia matrix is recognized as the information matrix, which links VITAE to other attitude estimation algorithms. The preprocessing algorithms used with VITAE were able to uncover erroneous results in a few published test cases. The VITAE solutions were validated analytically, through the inertia matrix’s inverse relationship to the error covariance matrix. A loss function comparison is also included to further validate the preprocessing algorithms and related VITAE solution.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 3〈/p〉 〈p〉Author(s): Shahida Parveen, Shahzad Mahmood, Anisa Qamar, Muhammad Adnan〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The interaction between two, four and six magnetoacoustic solitons in electron-positron plasmas are investigated. The extended Poincaré–Lighthill–Kuo (PLK) perturbation method is employed to derived two KdV equations for magnetoacoustic solitons moving towards each other and studied the head-on collision between them and their phase shifts. The Hirota bilinear method is used to have multi-soliton solutions of already derived two KdV equations for right and left moving solitons. The four and six magnetoacoustic solitons solutions of the two KdV equations are obtained to discuss their interaction and phase shifts. It is found that only compressive magnetoacoustic solitons structures are formed in electron-positron plasma. The present study may be useful to understand the collective phenomena related to head-on and overtaking magnetoacoustic solitons interaction in electron-positron plasmas that may occur in a pulsar magnetosphere.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 5〈/p〉 〈p〉Author(s): Qi Li, Jianping Yuan, Chong Sun〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In this paper, the motion control problem of autonomous spacecraft rendezvous and docking with a tumbling target in the presence of unknown model parameters, external disturbances, actuator saturation and faults is investigated. Firstly, a nonlinear six degree-of-freedom dynamics model is established to describe the relative motion of the chaser spacecraft with respect to the tumbling target. Subsequently, a robust fault-tolerant saturated control strategy with no precise knowledge of model parameters and external disturbances is proposed by combining the sliding mode control technique with an adaptive methodology. Then, within the Lyapunov framework, it is proved that the designed robust fault-tolerant controller can guarantee the relative position and attitude errors converge into small regions containing the origin. Finally, numerical simulations are performed to demonstrate the effectiveness and robustness of the proposed control strategy.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 5〈/p〉 〈p〉Author(s): Salih Alcay, Sermet Ogutcu, Ibrahim Kalayci, Cemal Ozer Yigit〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Besides the classical geodetic methods, GPS (Global Positioning System) based positioning methods are widely used for monitoring crustal, structural, ground etc., deformations in recent years. Currently, two main GPS positioning methods are used: Relative and Precise Point Positioning (PPP) methods. It is crucial to know which amount of displacement can be detected with these two methods in order to inform their usability according to the types of deformation. Therefore, this study conducted to investigate horizontal and vertical displacement monitoring performance and capability of determining the direction of displacements of both methods using a developed displacement simulator apparatus. For this purpose, 20 simulated displacement tests were handled. Besides the 24 h data sets, 12 h, 8 h, 4 h and 2 h subsets were considered to examine the influence of short time spans. Each data sets were processed using GAMIT/GLOBK and GIPSY/OASIS scientific software for relative and PPP applications respectively and derived displacements were compared to the simulated (true) displacements. Then statistical significance test was applied. Results of the experiment show that using 24 h data sets, relative method can determine up to 6.0 mm horizontal displacement and 12.3 mm vertical displacement, while PPP method can detect 8.1 mm and 19.2 mm displacements in horizontal and vertical directions respectively. Minimum detected displacements are found to grow larger as time spans are shortened.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 5〈/p〉 〈p〉Author(s): Rajesh Vaishnav, Som Sharma, K.K. Shukla, Prashant Kumar, S. Lal〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A comprehensive statistical analysis of the cloud base height (CBH) measured by ground-based Vaisala ceilometer (CL31) has been performed to study different layers of the cloud in the lower troposphere up to 7.5 km height over Ahmedabad, western India during 2014 and 2015. The total observations (∼69%) of cloud by using ceilometer show annual cloud occurrence frequency of around 64%. Seasonal variation of CBH and cloud occurrence frequency reveal that the maximum/minimum cloud cover is found during southwest (SW) Indian summer monsoon/pre-monsoon season. Three CBHs (CBH1, CBH2, and CBH3) are presented in monsoon period due to high cloud occurrence, and two CBHs (CBH1 and CBH2) are observed in other seasons due to low cloud occurrence by ceilometer over the observational site. The CBH1 (∼100–2000 m) and CBH2 (500–3000 m) are observed during SW monsoon and summer season, respectively. The CBH3 is occurred usually in SW monsoon season. Moreover, the cloud cover during the day and night time shows that the occurrence of cloud is more frequent in daytime than nighttime during pre-monsoon and post-monsoon season. The statistical analysis of cloud with ground-based observations is also performed in this study that may be useful for the development/improvement of regional weather and climate models to reduce the uncertainty in the prediction.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 3〈/p〉 〈p〉Author(s): B. Paul, B.K. De, A. Guha〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Following Tanna et al. (2013), we computed the percentage of occurrence of S〈sub〉4〈/sub〉 index for the period of 2012–2015 using the data of the dual frequency GPS receiver at the Tripura University, Agartala station (23.76°N, 91.26°E) situated at the northern crest of the equatorial ionization anomaly (EIA) region of the Indian Subcontinent. We have observed discrepancy in the results contradicting the actual scintillation occurrence. The distinctly noticeable discrepancy is that the maximum occurrence month is shifted to April 2013 instead of March 2014. The problem arises due to the denominator term used in the percentage of occurrence ratio i.e. the total number of days of observed scintillation activity during the complete period under consideration. But the conventional percentage of occurrence methodology uses the number of days of observation (the total number of days for which data is available) during each month in the denominator. It correctly assigns the maximum occurrence to March 2014 instead of April 2013 and the obtained monthly statistics follow the solar activity during this period.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 5〈/p〉 〈p〉Author(s): Yipeng Li, Yunpeng Wang, Yongchun Xie〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper proposes a consecutive point clouds-based estimation scheme to resolve the state estimation problem for tumbling non-cooperative space target during the rendezvous phase without a prior knowledge about its structure. First, a consistent pose estimation algorithm is realized by maintaining a global structure of the target that is reconstructed upon the pose graph optimization. Then an extend Kalman filter on Lie group is adopted to estimate the motion and inertia parameters of the target using the pose measurements of the point clouds. Finally, a semi-physical experimental study is carried out to evaluate the performance of the proposed estimation scheme. The result shows that the structure, motion and the inertia parameters can be estimated, and the total computation time is approximately linear with the number of point clouds.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 2 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Xing Meng, Hanxian Fang, Libin Weng, Zhendi Liu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Through concurrently measurements by Communication/Navigation Outage Forecasting System (C/NOFS), Sanya VHF radar and GPS ionospheric scintillation receiver on 12 March 2010, five plasma bubbles were found and three of them were observed by all those instruments. Two well-developed plumes with strong backscatter echoes were measured by Sanya radar and their corresponding depletions were observed by C/NOFS in Orbit 10317, 10318 and 10319. Broad plasma depletions resulting from merging process were found in orbit of 10318. The occurrence time and geophysical positions of scintillations correlate well with observations implemented by Sanya VHF radar and C/NOFS. Observations from three types of instrument indicate that the spread F irregularities have distinct scale. There were longitudinal differences between Sanya VHF radar and C/NOFS as irregularities measured, and the eastward drift of developed bubbles are responsible for these differences.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 3 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Dmitriy Korotyshkin, Evgeny Merzlyakov, Oleg Sherstyukov, Farhat Valiullin〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉New meteor radar (MR) horizontal wind data obtained during 2015–2018 at Kazan (56°N, 49°E) are presented. The measurements were carried out with a state-of-the-art SKiYMET meteor radar. Monthly mean vertical profiles of zonal and meridional components of the prevailing wind speeds, also amplitudes and phases of the components of diurnal (DT) and semidiurnal tide (SDT) winds are displayed as contour plots for a mean calendar year over the four recent years and compared with distributions of these parameters provided by the previous multiyear (1986–2002) meteor radar (MR) measurements at Kazan and by the recent HWM07 empirical model. The analysis shows that the SKiYMET zonal and meridional prevailing wind speeds are generally in good agreement, sharing the same seasonal features, with the earlier MR seasonal winds. Comparisons with the HWM07 model are not favourable: eastward solstitial cells as modelled are significantly larger, 〉30 m/s compared to 15–20 m/s. Also, reversal lines are too variable with height, and the positions of modelled cells (positive and negative) are unlike those of either MRs at Kazan or other MLT radars. Both MR systems provide the large SDT amplitudes, approximately 30 m/s and vertical wavelengths, approximately 55 km, for both components at middle latitudes in winter. They also show the well known strong SDT September feature (heights 85–100 km, the vertical wavelength ∼55–60 km), and the weak summer SDT for 80–91 km. HWM07 shows unrealistic amplitudes and phases above 90 km by height and month: minimal amplitudes in equinoxes and no September feature.〈/p〉 〈p〉The weak DT of middle to high latitudes provide similar amplitude and phase structures from both MRs, 1986–2002 and 2015–2017: largest amplitudes (10–12 or 8–10 m/s) for the evanescent meridional tide in summer, peaking in late July; weakest (0–2, 2–4 m/s) at 80 to 92–96 km, when the tide is vertically propagating (January, February, November, December) with a vertical wavelength near 40 km. Again, HWM07 differs in amplitude and phase structures: showing peak amplitudes in equinoxes: April, 15 m/s at 88 km; October, 21 m/s at 89 km.〈/p〉 〈p〉Coupling of the MR wind parameters with the ERA5 wind parameters is studied for a case in 2016. It is shown that the prevailing winds and DT amplitudes and phases of both datasets can be simply linked together, but that the ERA5 SDT amplitudes are significantly underestimated at the top model levels of the ERA5 reanalysis project.〈/p〉 〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 3 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): H.P. Gaikwad, A.K. Sharma, O.B. Gurav, G.A. Chavan, D.P. Nade, P.T. Patil, S.S. Nikte, G.P. Naniwadekar〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This study presents the quasi-two-day wave (Q2DW) characteristics of the mesosphere and lower thermosphere (MLT) region obtained by taking hourly mean values of horizontal wind velocities for 4  years (August 2013–July 2017) through continuous measurements using a medium-frequency (MF) radar (operating frequency – 1.98 MHz) located at the low-latitude Indian station Kolhapur (16.8°N; 74.2°E). The MF radar located at Kolhapur was upgraded in 2013, and these results of Q2DW have been reported for the first time after upgrading. The present study investigated variability in seasonal, annual, interannual, and solar indices of Q2DWs traveling in zonal (EW) and meridional (NS) components in the MLT region. The Q2DW activity is observed to be stronger during austral summer (January–February) (EW = ∼5 m/s and NS = ∼8–10 m/s) than during boreal summer (June–July) (EW = ∼5 m/s and NS = ∼6–8 m/s). The Q2DW amplitudes are larger in the meridional component than in the zonal one. A strong semiannual oscillation (SAO) has been observed in Q2DWs, with peak during January–February and June–July. In addition, small enhancement is seen in meridional Q2DW in October (∼5–6 m/s). It is observed that the entire spectrum (40–60 h) measured between 86 and 94 km contributes to the SAO amplitudes during January–February and June–July, whereas the waves measured between 42 h and 52 h contribute to enhancement in October similar to that reported elsewhere. In general, the Q2DW amplitude shows large interannual variability. The easterlies developed in the global circulation model in Northern hemisphere during May intensify up to around summer solstice. Q2DW activity peaks during westerly shear zone and intensifies with time at a lower thermospheric altitude (above 90 km). Small positive correlations (r = 0.2 for sunspot number and r = 0.1 for 10.7 cm solar flux) have been observed between Q2DW amplitudes and solar activity.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 31 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration, Volume 444〈/p〉 〈p〉Author(s): Van-Vuong Lai, Olivier Chiello, Jean-François Brunel, Philippe Dufrénoy〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The aim of this paper is to develop a full Finite Element (FE) computational method for the dynamics of unstable frictional rolling contact systems in order to calculate reference solutions in many applications, especially curve squeal for railway transportation but also roller bearing or metal cutting. The proposed method is characterized by the use of a fine FE discretization of the contact surface in a Eulerian frame, nonlinear frictional contact laws and model reduction techniques. An application to the frictional rolling contact between two annular cylinders is presented in both quasi-static and dynamic cases with mode coupling instabilities. The validation of the approach in quasi-static conditions is carried out by comparison with CONTACT software. Stability and transient results show that the technique is able to simulate friction-induced vibrations at high frequencies. Reduced models are tested and show a good agreement with the full model.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 24 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Abdelrazek M.K. Shaltout, Eid A. Amin, M.M. Beheary, R.H. Hamid〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We investigate on the relationship between flares and coronal mass ejections (CMEs) in which a flare started before and after the CME events which differ in their physical properties, indicating potentially different initiation mechanisms. The physical properties of two types flare-correlated CME remain an interesting and important question in space weather. We study the relationship between flares and CMEs using a different approach requiring both temporal and spatial constraints during the period from December 1, 2008 to April 30, 2017 in which the CMEs data were acquired by SOHO/LASCO (Solar and Heliospheric Observatory/Large Angle Spectrometric Coronagraph) over the solar cycle 24. The soft X-ray flare flux data, such as flare class, location, onset time and integrated flux, are collected from Geostationary Environmental satellite (GOES) and XRT Flare catalogs. We selected 307 CMEs-flares pairs applying simultaneously temporal and spatial constraints in all events for the distinguish between two associated CME-flare types. We study the correlated properties of coincident flares and CMEs during this period, specifically separating the sample into two types: flares that precede a CME and flares that follow a CME. We found an opposite correlation relationship between the acceleration and velocity of CMEs in the After- and Before-CMEs events. We found a log-log relation between the width and mass of CMEs in the two associated types. The CMEs and flares properties show that there were significant differences in all physical parameters such as (mass, angular width, kinetic energy, speed and acceleration) between two flare-associated CME types.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 31 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration, Volume 444〈/p〉 〈p〉Author(s): Penglin Gao, Alfonso Climente, José Sánchez-Dehesa, Linzhi Wu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉By studying platonic crystals based on lattices of cavities containing 〈em〉N〈/em〉-beam resonators, we conclude that crystals made of 1-beam resonators easily produce low-frequency omnidirectional bandgaps. Based on this favorable property, hardly obtained for resonant cavities containing a higher number of beams 〈em〉N〈/em〉 ≥ 2, we have designed single-phase metamaterial plates for the suppression of low frequency flexural waves in a broad range of frequencies. These metamaterials are obtained by using resonant cavities containing a multiple number 〈em〉M〈/em〉 of identical 1-beam resonators uniformly distributed in the cavity. Square lattices of this type of resonators have been studied by using the impedance matrix approach and the multiple scattering method. This semi-analytical method has been employed to show the existence of complete bandgaps whose width can be optimized by increasing 〈em〉M〈/em〉. For the case 〈em〉M〈/em〉 = 4, the largest number of resonators studied here, three complete bandgaps separated by two narrow passbands appear in the band structure. The formation of these complete bandgaps originates from the dynamic interaction between different local resonators as well as their interaction with the propagating waves in the host plate. By using composite structures consisting of platonic crystal slabs with complementary bandgaps, these separated bandgaps easily merge into a broadband wave attenuation region. The normalized width, defined as the percentage of the bandwidth to its central frequency, reaches 95.3%, representing an enhancement of about one order of magnitude compared with the absolute bandwidth obtained for the case of a single 1-beam resonator in the cavity. It is shown that the gaps can be easily tuned to lower frequencies by changing the geometrical parameters, such as the length of the beam, the radius and thickness of the smaller circular plate. Since the metamaterial is made of a single-phase material without attaching heavy masses, the work reported here provides a simple approach to construct low-cost structures with potential applications in aeronautic and astronautic industries for broadband vibration suppression at low frequencies.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 31 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration, Volume 444〈/p〉 〈p〉Author(s): Dong Yang, Francesca M. Sogaro, Aimee S. Morgans, Peter J. Schmid〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Helmholtz resonators (HRs) are widely used to damp acoustic oscillations, including in the combustors of aero-engines and power gas turbines where they damp thermoacoustic oscillations. The geometries of such combustors are often annular in shape, which means that low frequency acoustic modes exhibit both longitudinal and circumferential modeshapes, the latter across different circumferential wave numbers. For linear acoustic disturbances downstream of the flame, the presence of HRs leads to modal coupling and mode shape shifts, which makes design and placement of multiple HRs very complicated. A procedure which ensures that the design and placement of the HRs can be optimised for good acoustic damping performance would be very valuable, and such a procedure is presented in this work. A simplified linear, low-dimensional model for the acoustic behaviour in a hot annular duct sustaining a mean flow is extended to account for the attachment of multiple HRs. The HRs are assumed to sustain a cooling mean bias flow through them, towards the combustor, such that they can be modelled using linear, lumped element Rayleigh conductivity models. An optimisation method based on the gradient derived from adjoint sensitivity analysis is then applied to the low order network acoustic modelling framework for hot annular ducts incorporating HR models, for the first time. It is used to optimise over multiple HR geometry and placement parameters, to obtain optimum acoustic damping over all acoustic modes in a given frequency range. These optimisation procedures are validated via multi-dimensional parameter sweep results. Thus a novel and efficient tool for HR optimisation for thin annular ducts is presented.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 31 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration, Volume 444〈/p〉 〈p〉Author(s): Nicholas A. Capell, Daniel W. Carlson, Yahya Modarres-Sadeghi〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper reports findings from an experimental study on vortex-induced vibration of a horizontal, flexibly-mounted cylinder positioned near the free surface of fluid flow. The cylinder is allowed to oscillate in the vertical direction only. Oscillation amplitude and frequency data are presented as a function of reduced velocity and dimensionless depth from the free surface. Data are presented for cases of decreasing depth from where the resting cylinder is fully-submerged until its centerline is even with the free surface of the water. For a fully-submerged cylinder, VIV behavior is consistent with published findings of similar systems, producing a well-documented lock-in region with initial, upper, and lower branches. Broadly, as the cylinder is raised from the fully-submerged case, the amplitudes diminish and the lock-in region decreases in range and shifts toward higher reduced velocities. When the cylinder is very near the surface, a second region of oscillations occurs at higher reduced velocities. This region emerges in cases where the cylinder’s top edge is half a diameter below the free surface. For a short range of depths, the lock-in region and the non-zero amplitude region at higher reduced velocities coexist. But after a critical depth, the lock-in region disappears and oscillations are observed only at the higher reduced velocity region. Multi-frequency oscillations and regions of hysteresis are observed for some cases of low depth and high reduced velocity.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 31 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration, Volume 444〈/p〉 〈p〉Author(s): Shuo Li, Brian R. Mace, Jaspreet S. Dhupia〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper presents an approach to calculate the natural frequency and frequency response function (FRF) statistics of structures connected to attachments at uncertain locations. The main structure is divided into two regions to which the attachment can, or cannot, be connected. The approach is based on component mode synthesis analysis of finite element models of these regions. Multi-point constraints are used to connect the attachment to the main structure to avoid the need to re-mesh the structure. The use of characteristic constraint modes is used to reduce the number of interface degrees of freedom (DOFs) and hence reduce the computational cost further. One or more baseline systems, for which the attachment is connected at a given position, are analysed and the eigensolution found. A perturbation is then applied to the baseline solution to estimate the solution for other attachment locations. The method can be applied to any problem requiring multiple re-analysis. Here, emphasis is placed on probabilistic approaches using Monte Carlo Simulation (MCS), and the natural frequency and FRF statistics are then estimated through MCS. To illustrate the approach, numerical results are presented for a beam and a plate with a randomly attached mass and a plate with an attachment with a number of internal and attachment DOFs. Numerical results are compared with experimental measurements for the cases of a beam and a plate with an attached mass. The results indicate that the method provides accurate predictions at a significantly reduced computation cost when compared to multiple direct solutions.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 14 April 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration, Volume 445〈/p〉 〈p〉Author(s): Chia-Chin Wu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A 〈em〉modified〈/em〉 mode-superposition method (MMSM) was presented in this paper to solve the free vibration problem of the “unconstrained” beams that the 〈em〉conventional〈/em〉 mode-superposition method (CMSM) cannot easily tackle. For convenience, a beam without any attachments is called the “bare” beam, and the beam carrying any concentrated elements (CEs) is called the “loaded” beam, in this paper. Furthermore, the mode-superposition method (MSM) with only the “elastic” modes of the bare beam considered is called the CMSM, and the MSM with both the “elastic” and the “rigid-body” modes considered is called the MMSM. From the existing literature, one finds that the CMSM is one of the effective approaches for the free vibration analysis of a “constrained” bare beam (such as the C-C, P-P, or C-F beam) carrying various CEs, where “C, P and F” denote the abbreviations of “clamped, pinned and free”, respectively. However, the CMSM is not available for that of an “unconstrained” bare beam (such as the F-F beam) carrying various CEs. For this reason, this paper presented a MMSM to solve the title problem so that one can easily obtain the natural frequencies and mode shapes for both the “rigid-body” motions and the “elastic” vibrations of the F-F loaded Timoshenko beam. The main difference between a “constrained” bare beam and an “unconstrained” one is that the free vibration responses of latter consist of the “rigid-body” motions and those of the former do not, so that the coupling effect between the “rigid-body” motions and the “elastic” vibrations” of the F-F loaded beam are not considered by using the CMSM. To confirm the correctness of the presented theory and the developed computer program for this paper, all numerical results obtained from the MMSM are compared with those obtained from the finite element method (FEM) and good agreement is achieved. Numerical examples reveal that the CMSM can provide neither any information regarding the “rigid-body” motions nor the accurate natural frequencies and mode shapes for the “elastic” vibrations of a F-F loaded beam, and all the above-mentioned drawbacks of the CMSM have been improved by the presented MMSM.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 14 April 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration, Volume 445〈/p〉 〈p〉Author(s): D.J. Fourie, P.J. Gräbe, P.S. Heyns, R.D. Fröhling〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Railway wheel squeal is an unresolved noise pandemic facing the railway industry. Wheel squeal results from frictional self-excited vibration occurring in the wheel-rail contact. Solving the problem of squeal requires researchers to work towards a squeal model that can predict squeal wholly and in every situation. This will allow for squeal to be resolved during the design stages. The current research presents a frequency domain model for the excitation of squeal due to longitudinal creepage with rising, constant and falling friction. In this model the time varying part of the longitudinal creep force is modelled as a feedback loop and tested for stability with the Nyquist criterion. Crucial to the instability is modelling the dynamics of a wheel taking into consideration the moving load nature of the rotating wheel. If wheel rotation is accounted for in the model, modes in a doublet can become unstable through mode-coupling in the presence of large longitudinal creepage. The results of the model provide good agreement with that of squeal occurring on-track. Positive flow of energy for the modelled case of squeal results from the dynamic friction and normal forces being in phase with one another as well as the friction force causing normal displacement at the wheel-rail contact that is in phase with the normal displacement that caused the normal force in the first place. This closed phase loop causes positive interference of the normal vibration in the wheel-rail contact and allows the vibration amplitude to grow. Extending the model to include lateral creepage shows that the vibration of the wheel-rail contact can be unstable due to unsteady longitudinal creepage for more directions of the resulting creep force compared to unsteady lateral creepage in a case with constant friction.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 14 April 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration, Volume 445〈/p〉 〈p〉Author(s): C. Bourquard, N. Noiray〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Acoustic dampers are efficient and cost-effective means for suppressing thermoacoustic instabilities in combustion chambers. However, their design and the choice of their purging air mass flow is a challenging task, when one aims at ensuring thermoacoustic stability after their implementation. In the present experimental and theoretical study, Helmholtz (HH) and Quarter-Wave (QW) dampers are considered. A model for their acoustic impedance is derived and experimentally validated. In a second part, a thermoacoustic instability is mimicked by an electro-acoustic feedback loop in a rectangular cavity, to which the dampers are added. The length of the dampers can be adjusted, so that the system can be studied for tuned and detuned conditions. The stability of the coupled system is investigated experimentally and then analytically, which shows that for tuned dampers, the best stabilization is achieved at the exceptional point. The stabilization capabilities of HH and QW dampers are compared for given damper volume and purge mass flow.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 31 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration, Volume 444〈/p〉 〈p〉Author(s): Ulf Jakob F. Aarsnes, Nathan van de Wouw〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We consider a distributed axial-torsional drill-string model with a rate-independent bit-rock interaction law to study the occurrence and non-local characteristics of axial and torsional self-excited vibrations as caused by the regenerative effect. A first contribution of the paper is the derivation of a non-dimensional version of the full non-linear distributed drill-string–bit-rock interaction model and showing how it relates to the minimal set of characteristic quantities. Using this model the study shows how multiple axial modes of the drill-string are excited, or attenuated, depending on the bit rotation rate. This indicates that a lumped drill-string model approximation is insufficient for the general case. Then, a comprehensive simulation study is performed to create a stability map for the occurrence of stick-slip oscillations. In particular, the significance of the axial topside boundary condition, i.e., constant velocity vs. constant hook-load, is evaluated. A central finding is that increasing the axial loop gain (determined by the bit-rock parameters) tends to both increase the area of stable torsional dynamics and increase the rate of penetration for a constant imposed weight on bit. This also corresponds to a more severe axial instability.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 26 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration〈/p〉 〈p〉Author(s): Jan Awrejcewicz, Claude-Henri Lamarque〈/p〉

Description: 〈p〉Publication date: 31 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration, Volume 444〈/p〉 〈p〉Author(s): Yimin Wei, Shixi Yang, Wenhua Chen, Jianmin Li〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The propagation mechanism of vibration in a media such as a non-uniform rotating shaft is an important topic since it can help to control the vibration of the media, or to reduce the noise. Vibration propagates in a non-uniform rotating shaft in the form of elastic waves and the propagation characteristics of the waves are affected by the non-uniform factors, the transverse cracks and the rotating speed, etc. This study deals with the propagation characteristics of the elastic waves in a non-uniform shaft with transverse cracks by adopting the Transfer Matrix method. First, the transfer matrix for a single non-uniform shaft is derived by constructing the motion equations derived with Equilibrium Equations. Second, the transfer matrix for a transverse crack is studied. Crack Mode III is adopted, and the transverse crack is modeled as a local spring, the local flexibility coefficient of which is deduced. The transfer matrix for the non-uniform shaft with transverse cracks is then derived by combining the individual matrixes. Finally, several numerical examples are used to illustrate the influence of different crack depths and alternative rotating speeds on the propagation characteristics of the elastic waves, which are compared with the results from the experimental analyses. It's shown that a new stop band will come out at lower frequency region when a transverse crack occurs and the bandwidth of which will be wider and wider as the increase of the depth of the crack, and the rotating speed mainly affects the first stop band, the central frequency of which will decrease as the increase of the rotating speed.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 31 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Sound and Vibration, Volume 444〈/p〉 〈p〉Author(s): Haibin Yang, Yong Xiao, Honggang Zhao, Jie Zhong, Jihong Wen〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The underwater acoustic screens made of periodically perforated rubber layers with metal plates are often used to enhance reflections and reduce transmissions of sound in water, under high hydrostatic pressure. Previous studies have tended to focus on the acoustic response of finite-thickness structures of the screens, rather than on the wave propagation properties of the corresponding infinite crystal structures. In this work, a numerical method, which combines finite element method and the layer-iteration technique, is developed to study the complex band structure of the infinite crystals and the acoustic response of the finite-thickness structures for the screens. Numerical results for the screens with elastic and viscoelastic rubber materials are presented for analyzing the features of propagation modes, band gaps, and attenuation of the waves in the screens. Reflection, transmission and absorption spectra of the screens are compared with the corresponding complex band structure of the infinite crystals in detail for providing a comprehensive understanding of the wave propagation and attenuation properties of the screens.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 24 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Jesus A. Dominguez, Jonathan Whitlow〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉As part of our research on the feasibility of producing commodities from lunar regolith by thermal-driven processes with minimal terrestrial precursors we need to characterize, reproduce, and understand thermophysical properties of the molten regolith still unforeseen under the lunar vacuum conditions at a scalable sample size. Two unanticipated phenomena, apparently caused by lunar melt’s surface tension under vacuum, have been revealed in our research work, vacuum void formation and upwards migration. In this paper we present our findings and thinkable explanation on the upwards migration phenomenon experimentally observed and consistently replicated as JSC-1A lunar regolith simulant melted at high vacuum. Upwards migration of molten lunar regolith will make future lunar ISRU’s melting processes both challenging as molten bulk material would migrate upwards along the container’s walls, and also promising on new opportunities for alternative ISRU’s sustainable processes as regolith’s upwards migration takes place in uniformed thin-film pattern. Among the potential ISRU’s processes that might use controlled thermal thin-film-based migration without the necessity of terrestrial precursors are production of feedstock for 3D printing, fractional separation of regolith’s component’s (O〈sub〉2〈/sub〉, metals, and alloys) via pyrolysis, film coating, purification of valuables solid crystals including silicon, and fabrication of key elements for microfluidic, and MEMS devices. Thermal upwards migration phenomenon on JSC-1A’s melt is formulated and explained by the authors as due to thermal Marangoni effect (also known as thermo-capillarity) in which temperature gradients within the melt’s bulk and along the crucible’s wall yield the surface tension large enough to supersede the gravitational force and yield the experimentally observed upwards thin-film migration. As far as the authors know, upwards thermal migration of molten JSC-1A (or other lunar simulant regolith) under vacuum has not been reported in the literature. A thermal mathematical model accounting for thermal Marangoni effect on molten JSC-1A agrees with what experimentally was observed, the formation of the meniscus on the melt-wall surface interface along with an incipient upwards migration in thin-film pattern along the crucible wall that, according to the model, experiences large temperature gradient, an important factor to trigger the thermal Marangoni effect along with the fact that surface tension of the molten lunar regolith material is temperature dependent.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 15 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 6〈/p〉 〈p〉Author(s): B.R. Kalita, P.K. Bhuyan, P. Nath, A. Hazarika, K. Wang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The deviation of the IRI estimates of the monthly mean foF2 in the low mid latitude of 95°E–130°E longitude sector is investigated using simultaneous ground measurements at four stations during 2010–2014. The stations form two conjugate pairs of the same geo-magnetic latitude at two fixed longitudes enabling direct longitudinal and hemispheric comparison. The temporal, spatial, seasonal and solar activity variations of the deviations are discussed with reference to the longitudinal density variation in the transition region between low and midlatitudes. Cases of underestimation/overestimation as well as good estimate are noted. Underestimation (overestimation) in the daytime and overestimation (underestimation) in the nighttime of 95°E (130°E) are common. The longitudinal difference in the measurements suggests negative (positive) foF2 gradient from west to east in daytime (nighttime). In contrast, the IRI predicts flatter or increasing longitudinal profiles from 95°E to 130°E. The local time and longitudinal variation of the IRI deviations can be attributed to the combined role of the longitudinal EIA structure as well as midlatitude zonal wind-magnetic declination effect. The station/season independent deviations relate the role of solar activity representation in the IRI. These deviations may be attributed to the weak IRI response to rapid solar flux fluctuations.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 15 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 6〈/p〉 〈p〉Author(s): William A. Hartman, William D. Schmidl, Ronald Mikatarian, Ivan Galkin〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A “Real-Time” plasma hazard assessment process was developed to support International Space Station (ISS) Program real-time decision-making providing solar array constraint relief information for Extravehicular Activities (EVAs) planning and operations. This process incorporates real-time ionospheric conditions, ISS solar arrays’ orientation, ISS flight attitude, and where the EVA will be performed on the ISS. This assessment requires real-time data that is presently provided by the Floating Potential Measurement Unit (FPMU) which measures the ISS floating potential (FP), along with ionospheric electron number density (Ne) and electron temperature (Te), in order to determine the present ISS environment. Once the present environment conditions are correlated with International Reference Ionosphere (IRI) values, IRI is used to forecast what the environment could become in the event of a severe geomagnetic storm. If the FPMU should fail, the Space Environments team needs another source of data which is utilized to support a short-term forecast for EVAs. The IRI Real-Time Assimilative Mapping (IRTAM) model is an ionospheric model that uses real-time measurements from a large network of digisondes to produce foF2 and hmF2 global maps in 15 min cadence. The Boeing Space Environments team has used the IRI coefficients produced in IRTAM to calculate the Ne along the ISS orbital track. The results of the IRTAM model have been compared to FPMU measurements and show excellent agreement. IRTAM has been identified as the FPMU back-up system that will be used to support the ISS Program if the FPMU should fail.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 3 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Guanglin Ma, Lixin Guo, Jutao Yang, Libin Lv, Jing Chen, Tong Xu, Shuji Hao, Jian Wu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Beat wave (BW) high frequency (HF) ionospheric heating experiments were conducted to generate very low frequency (VLF) waves. The VLF waves were registered with a VLF receiver located ∼15 km east of the European Incoherent Scatter (EISCAT) heating facility in Tromsø, Norway. A fluxgate magnetometer was used to monitor auroral electrojet current, and ionospheric conditions were measured using a Dynasonde. Correlation coefficients between VLF amplitudes and the deviation of geomagnetic north–south components were calculated. Experimental results show that strong and positive correlation exists the majority of the time, but sometimes no correlation or even a negative correlation occurred. This is consistent with similar past experiments that took place with exclusively AM generation. These results therefore support the conclusion that BW generation of VLF waves is no different than with AM, likely occurring in the D or lower E ionospheric region.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 3 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Xin Wei, Desheng Wen, Zongxi Song, Jiangbo Xi, Weikang Zhang, Gang Liu, Zhixin Li〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A full-sky star identification algorithm based on radial and dynamic cyclic patterns is presented with the aim of solving the “lost-in-space” problem. The dynamic cyclic pattern match is applied with a maximum cumulate comparison method to identify sensor-catalog pairings in initial match, which substantially eliminates the effects of the star position noise, magnitude noise, and false stars. After initial match pairings of stars are obtained, a chain part extension technique is employed to quickly search for the longest match chain as the final result. Experimental results indicate that the proposed algorithm is highly robust to star position noise, magnitude noise and false stars. In a series of simulations, the identification rate of the algorithm is 97.50% with 2.0 pixels star position noise, 96.90% with 0.4 Mv star magnitude noise and 95.30% with four false stars respectively. Moreover, the algorithm achieves an identification rate of 58.08% when only six stars are in the field of view.〈/p〉〈/div〉 〈/div〉