ALBERT

Beschreibung: Publication date: Available online 18 March 2017 Source: Theoretical and Applied Mechanics Letters Author(s): Pengfei Hou, Ke Yuan, Bingjie Chen Because most piezoelectric devices have interfaces with fluid in engineering, it is valuable to study the coupled field between fluid and piezoelectric media. As the fundamental problem, the 3D Green’s functions for point forces and point charge loaded in the fluid and piezoelectric bimaterials are studied in this paper. Based on the 3D general solutions expressed by harmonic functions, we constructed the suitable harmonic functions with undetermined constants at first. Then, the couple field in the fluid and piezoelectric bimaterials can be derived by substitution of harmonic functions into general solutions. These constants can be obtained by virtue of the compatibility, boundary and equilibrium conditions. At last, the characteristics of the electromechanical coupled fields are shown by numerical results.

Beschreibung: Publication date: Available online 30 August 2017 Source: Theoretical and Applied Mechanics Letters Author(s): Tezhuan Du, Yiwei Wang, Chenguang Huang, Lijuan Liao The cavitation cloud of different internal structures results in different collapse pressures owing to the interaction among bubbles. The internal structure of cloud cavitation is required to accurately predict collapse pressure. A cavitation model was developed through dimensional analysis and direct numerical simulation of collapse of bubble cluster. Bubble number density was included in proposed model to characterize the internal structure of bubble cloud. Implemented on flows over a projectile, the proposed model predicts a higher collapse pressure compared with Singhal model. Results indicate that the collapse pressure of detached cavitation cloud is affected by bubble number density.

Beschreibung: Publication date: Available online 14 September 2017 Source: Theoretical and Applied Mechanics Letters Author(s): Bassem Barhoumi, Safa Ben Hamouda, Jamel Bessrour To reduce computational costs, an improved form of the frequency domain boundary element method (BEM) is proposed for two-dimensional radiation and propagation acoustic problems in a subsonic uniform flow with arbitrary orientation. The boundary integral equation (BIE) representation solves the two-dimensional convected Helmholtz equation (CHE) and its fundamental solution, which must satisfy a new Sommerfeld radiation condition (SRC) in the physical space. In order to facilitate conventional formulations, the variables of the advanced form are expressed only in terms of the acoustic pressure as well as its normal and tangential derivatives, and their multiplication operators are based on the convected Green’s kernel and its modified derivative. The proposed approach significantly reduces the CPU times of classical computational codes for modeling acoustic domains with arbitrary mean flow. It is validated by a comparison with the analytical solutions for the sound radiation problems of monopole, dipole and quadrupole sources in the presence of a subsonic uniform flow with arbitrary orientation.

Beschreibung: Publication date: Available online 14 September 2017 Source: Theoretical and Applied Mechanics Letters Author(s): Arash MahboubiDoust, Abas Ramiar, Morteza Dardel In this work, numerical study of two dimensional laminar incompressible flow around an oscillating NACA0012 airfoil is proceeded using the open source code OpenFOAM. Oscillatory motion types including pitching and flapping are considered. Reynolds number for these motions is assumed to be 12000 and effects of these motions and also different unsteady parameters such as amplitude and reduced frequency on aerodynamic coefficients are studied. For flow control on airfoil, dielectric barrier discharge plasma actuator is used in two different positions on airfoil and its effect is compared for the two types of considered oscillating motions. It is observed that in pitching motion, imposing plasma leads to an improvement in aerodynamic coefficients, but it does not have any positive effect on flapping motion. Also, for the amplitudes and frequencies investigated in this paper, the trailing edge plasma had a more desirable effect than other positions.

Beschreibung: Publication date: Available online 14 September 2017 Source: Theoretical and Applied Mechanics Letters Author(s): Bin Hu, Zengsheng Ma, Weixin Lei, Youlan Zou, Chunsheng Lu Electrode is a key component to remain durability and safety of lithium-ion (Li-ion) batteries. Li-ion insertion/removal and thermal expansion mismatch may induce high stress in electrode during charging and discharging processes. In this paper, we present a continuum model based on COMSOL Multiphysics software, which involves thermal, chemical and mechanical behaviors of electrodes. The results show that, because of diffusion-induced stress and thermal mismatch, the electrode geometry plays an important role in diffusion kinetics of Li-ions. A higher local compressive stress results in a lower Li-ion concentration and thus a lower capacity when a particle is embedded another, which is in agreement with experimental observations.

Beschreibung: Publication date: Available online 21 September 2017 Source: Theoretical and Applied Mechanics Letters Author(s): Jobin Varghese, V.M. Akhil, P.K. Rajendrakumar, K.S. Sivanandan Rotary pneumatic actuators that are made out of linear one are always best suited for exoskeleton joint actuation due to its inherent power to weight ratio. This work is a modified version of knee actuation system that has already been developed and major modifications are made in order to make it more suitable for human wearing and also to reduce its bulkiness and complexity. The considered actuator system is a rotary actuator where a pulley converts the linear motion of the standard pneumatic piston into the rotary motion. To prove the capability of the actuator, its performance characteristics such as torque and power produced are compared to the required torque and power at the knee joint of the exoskeleton in swing phase and are found to be excellent. The two-way ANOVA analysis is performed to find the effect of the throat area valve on knee angle. As the ANOVA analysis shows the significant effect of the throat area variation on the knee angle flexion made by the proposed actuator. A relationship between the throat area of flow control valve, that is connected to the exit port of the direction control valve, and angular displacement of the knee joint is been formulated. This relationship can be used to design a control system to regulate the mass flow rate of air at the exit and hence the angular velocity of the knee joint can be controlled. Graphical abstract

Beschreibung: Publication date: Available online 21 June 2017 Source: Theoretical and Applied Mechanics Letters Author(s): Yahaya Shagaiya Daniel, Zainal Abdul Aziz, Zuhaila Ismail, Faisal Salah The unsteady mixed convection flow of electrical conducting nanofluid and heat transfer due to a permeable linear stretching sheet with the combined effects of an electric field, magnetic field, thermal radiation, viscous dissipation, and chemical reaction have been investigated. A similarity transformation is used to transform the constitutive equations into a system of nonlinear ordinary differential equations. The resultant system of equations is then solved numerically using implicit finite difference method. The velocity, temperature, concentration, entropy generation and Bejan number are obtained with the dependence of different emerging parameters examined. It is noticed that the velocity is more sensible with high values of electric field and diminished with a magnetic field. The radiative heat transfer and viscous dissipation enhance the heat conduction in the system. Moreover, the impact of mixed convection parameter and Buoyancy ratio parameter on Bejan number profile has reverse effects. A chemical reaction reduced the nanoparticle concentration for higher values.

Beschreibung: Publication date: Available online 19 September 2017 Source: Theoretical and Applied Mechanics Letters Author(s): Huajian Gao

Beschreibung: Publication date: May 2017 Source: Theoretical and Applied Mechanics Letters, Volume 7, Issue 3

Beschreibung: Publication date: Available online 20 February 2017 Source: Theoretical and Applied Mechanics Letters Author(s): Zengyao Lv, Honglong Zhang, Chao Zhang, Yongmao Pei The stress-induced magnetic domain switching in FeGa thin films is studied using phase-field method. In particular, the magnetic field is applied along the [110] direction and biaxial stresses are applied along [100] and [010]. A compressive pre-stress corresponded to a smaller coercive magnetic field while a tensile pre-stress corresponded to a larger coercive field. At the same time, it is also found that butterfly and square-like magnetostriction loops transition exists at the critical opposite biaxial stress state, where are corresponding the single domain swing across a fan area back and forth and rotate a clockwise circle, respectively. The results can be explained by the stress tuned anisotropy energy well.

Beschreibung: Publication date: Available online 7 June 2017 Source: Theoretical and Applied Mechanics Letters Author(s): Sergey V. Ershkov The main objective for this research was the analytical exploration of the dynamics of planar satellite rotation during the motion of an elliptical orbit around a planet. First, we revisit the results of J. Wisdom et al. (1984), in which, by the elegant change of variables (considering the true anomaly f as the independent variable), the governing equation of satellite rotation takes the form of an Abel ODE of the second kind, a sort of generalization of the Riccati ODE. We note that due to the special character of solutions of a Riccati -type ODE, there exists the possibility of sudden jumping in the magnitude of the solution at some moment of time. In the physical sense, this jumping of the Riccati -type solutions of the governing ODE could be associated with the effect of sudden acceleration/deceleration in the satellite rotation around the chosen principle axis at a definite moment of parametric time. This means that there exists not only a chaotic satellite rotation regime (as per the results of J. Wisdom et al. (1984)), but a kind of gradient catastrophe (Arnold 1992) could occur during the satellite rotation process. We especially note that if a gradient catastrophe could occur , this does not mean that it must occur: such a possibility depends on the initial conditions. In addition, we obtained asymptotical solutions that manifest a quasi-periodic character even with the strong simplifying assumptions e → 0 , p = 1 , which reduce the governing equation of J. Wisdom et al. (1984) to a kind of Beletskii’s equation.

Beschreibung: Publication date: Available online 12 June 2017 Source: Theoretical and Applied Mechanics Letters Author(s): M. Arefi, A.M. Zenkour Wave propagation analysis for a functionally graded nanobeam with rectangular cross-section resting on visco-Pasternak’s foundation is studied in this paper. Timoshenko’s beam model and nonlocal elasticity theory are employed for formulation of the problem. The equations of motion are derived using Hamilton’s principals by calculating kinetic energy, strain energy and work due to viscoelastic foundation. The effects of various parameters such as wavenumber, non-homogeneous index, nonlocal parameter and three parameters of foundation are performed on the phase velocity of the nanobeam. The obtained results indicate that some parameters such as non-homogeneous index, nonlocal parameter and wavenumber have significant effect on the response of the system.

Beschreibung: Publication date: Available online 10 October 2017 Source: Theoretical and Applied Mechanics Letters Author(s): Q.D. Ouyang, G.J. Weng, A.K. Soh, X. Guo Coarse-grained (CG) metals strengthened by nanotwinned (NT) regions possess high strength and good ductility. As such, they are very suitable for applications in bullet–proof targets. Here, a numerical model based on the conventional theory of strain gradient plasticity and the Johnson–Cook failure criterion is employed to study the influences of volume fraction of NT regions on their ballistic performance. The results show that in general a relatively small twin spacing (4–10 nm) and a moderate volume fraction (7%–20%) will lead to excellent limit velocity and that the influences of volume fraction on limit displacement changes with the category of impact processes.

Beschreibung: Publication date: Available online 27 September 2017 Source: Theoretical and Applied Mechanics Letters Author(s): Jian Huang, Chao Yu, Yiwei Wang, Chang Xu, Chenguang Huang Quasi-periodical evolutions such as shedding and collapsing of unsteady cloud cavitating flow, induce strong pressure fluctuations, what may deteriorate maneuvering stability and corrode surfaces of underwater vehicles. This paper analyzed effects on cavitation stability of a trip bar arranged on high-speed underwater projectile. Small scale water tank experiment and large eddy simulation using the open source software OpenFOAM were used, and the results agree well with each other. Results also indicate that trip bar can obstruct downstream re-entrant jet and pressure wave propagation caused by collapse, resulting in a relatively stable sheet cavity between trip bar and shoulder of projectiles.

Beschreibung: Publication date: Available online 7 October 2017 Source: Theoretical and Applied Mechanics Letters Author(s): Qi Zhu, Wei He, Lei Chen, Jianguo Zhu, Wenfeng Hao To determine the interfacial properties of thermal barrier coatings (TBCs) is imperative for their durability evaluation and further improvements. A ceramic coating (topcoat) and a NiCoCrALY bondcoat were atmospheric-plasma-sprayed (APS) on a stainless steel substrate. A modified three-point bending test was adopted to initiate and propagate the topcoat/bondcoat (TC/BC) interfacial crack. After a complete delamination, the fracture surfaces were examined by an optical microscope, which shows that the cracking plane was merely on the TC/BC interface. Based on the experimental results of load–displacement and crack length-displacement, the strain energy release rate G for crack propagation was calculated, and the averaged magnitude was 77.1 J/m 2 . Repeatable results have indicated that the method can be used for the evaluation of interfacial fracture toughness in thermal barrier coatings and other multi-layer structures.

Beschreibung: Publication date: Available online 3 October 2017 Source: Theoretical and Applied Mechanics Letters Author(s): Andrew Hess, Shengqiang Cai, Tong Gao We study instability of a Newtonian Couette flow past a gel-like film in the limit of vanishing Reynolds number. Three models are explored including one hyperelastic (neo-Hookean) solid, and two viscoelastic (Kelvin-Voigt and Zener) solids. Instead of using the conventional Lagrangian description in the solid phase for solving the displacement field, we construct equivalent “differential” models in a Eulerian reference frame, and solve for the velocity, pressure and stress in both fluid and solid phases simultaneously. We find the interfacial instability is driven by the first-normal stress difference in the base-state solution in both hyperelasic and viscoelastic models. For the neo-Hookean solid, when subjected to a shear flow, the interface exhibits a short-wave (finite-wavelength) instability when the film is thin (thick). In the Kelvin-Voigt and Zener solids where viscous effects are incorporated, instability growth is enhanced at small wavenumber but suppressed at large wavenumber, leading to a dominant finite-wavelength instability. In addition, adding surface tension effectively stabilizes the interface to sustain fluid shear.

Beschreibung: Publication date: Available online 9 October 2017 Source: Theoretical and Applied Mechanics Letters Author(s): J.H. Chen, W.F. Xu, R.Z. Xie, F.J. Zhang, W.J. Hu, X.C. Huang, G. Chen In order to investigate the effect of sample size on the dynamic torsional behavior of the 2A12 aluminum alloy. In this paper, torsional split Hopkinson bar tests are conducted on this alloy with different sample dimensions. It is found that with the decreasing gauge length and thickness, the tested yield strength increases. However, the sample inner/outer diameter has little effect on the dynamic torsional behavior. Based on the finite element method, the stress states in the alloy with different sample sizes are analysed. Due to the effect of stress concentration zone (SCZ), the shorter sample has a higher yield stress. Furthermore, the stress distributes more uniformly in the thinner sample, which leads to the higher tested yield stress. According to the experimental and simulation analysis, some suggestions on choosing the sample size are given as well.

Beschreibung: Publication date: Available online 13 October 2017 Source: Theoretical and Applied Mechanics Letters Author(s): Dong Wook Kim, Tae Ho Kim, Heuy Dong Kim Shock tubes are devices which are used in the investigation of high speed and high temperature flow of compressible gas. Inside a shock tube, the interaction between the reflected shock wave and boundary layer leads to a complex flow phenomenon. Initially a normal shock wave is formed in the shock tube which migrates towards the closed end of the tube and that in turn leads to the reflection of shock. Due to the boundary layer interaction with the reflected shock, the bifurcation of shock wave takes place. The bifurcated shock wave then approaches the contact surface and shock train is generated. Till date only a few studies have been conducted to investigate this shock train phenomenon inside the shock tube. For the present study a CFD analysis has been performed on a two dimensional axi-symmetric model of a shock tube using unsteady, compressible Navier–Stokes equations. In order to investigate the detailed characteristics of shock train, parametric studies have been performed by varying different parameters such as the shock tube length, diameter, pressure ratio used inside the shock tube.

Beschreibung: Publication date: Available online 10 October 2017 Source: Theoretical and Applied Mechanics Letters Author(s): T. Engels, D. Kolomenskiy, K. Schneider, J. Sesterhenn We present numerical simulations of simplified models for swimming organisms or robots, using chordwise flexible elastic plates. We focus on the tip vortices originating from three-dimensional effects due to the finite span of the plate. These effects play an important role when predicting the swimmer’s cruising velocity, since they contribute significantly to the drag force. First we simulate swimmers with rectangular plates of different aspect ratio and compare the results with a recent experimental study. Then we consider plates with expanding and contracting shapes. We find the cruising velocity of the contracting swimmer to be higher than the rectangular one, which in turn is higher than the expanding one. We provide some evidence that this result is due to the tip vortices interacting differently with the swimmer.

Beschreibung: Publication date: Available online 15 November 2017 Source: Theoretical and Applied Mechanics Letters Author(s): Robert Rubinstein, Timothy T. Clark We review the concept of “equilibrium” in turbulence. It generally means a property of the energy spectrum, it can also be understood in terms of a scalar property, the Taylor–Kolmogorov formula relating the dissipation rate to the total energy and integral length scale. The implications of equilibrium and strong departure from equilibrium for turbulence modeling are stressed.

Beschreibung: Publication date: Available online 22 November 2017 Source: Theoretical and Applied Mechanics Letters Author(s): J. Brennan, C. Clancy, J. Harrington, R. Cox, F. Dias The pressure load at a vertical barrier caused by extreme wave run-up is analysed numerically, using the conformal mapping method to solve the two-dimensional free surface Euler equations in a pseudo-spectral model. Previously this problem has been examined in the case of a flat-bottomed geometry. Here, the model is extended to consider a varying bathymetry. Numerical experiments show that an increasing step-like bottom profile may enhance the extreme run-up of long waves but result in a reduced pressure load.

Beschreibung: Publication date: Available online 22 November 2017 Source: Theoretical and Applied Mechanics Letters Author(s): Nikolai Gorbushin, Yuri Petrov, Ya-Pu Zhao, Yin Zhang In the present work, we analyse the delamination problem under the combined dynamic load. We show the effect of background harmonic vibrations on critical amplitudes of the principal force pulse. The effect is demonstrated on the simple model of a string on an elastic foundation and the fracture phenomenon is predicted by the incubation time criterion. The results state the possibility of considerable decrease in threshold amplitude by a proper choice of the frequency of a background excitation.

Beschreibung: Publication date: Available online 22 November 2017 Source: Theoretical and Applied Mechanics Letters Author(s): Shufan Zou, Ankang Gao, Yipeng Shi, Jiezhi Wu Why the stall of an airfoil can be significantly delayed by its pitching-up motion? Various attempts have been proposed to answer this question over the past half century, but none is satisfactory. In this Letter we prove that a chain of vorticity-dynamics processes at accelerating boundary is fully responsible for the causal mechanism underlying this peculiar phenomenon. The local flow behavior is well be explained by a simple potential-flow model.

Beschreibung: Publication date: Available online 21 November 2017 Source: Theoretical and Applied Mechanics Letters Author(s): Linlin Kang, Luoqin Liu, Weidong Su, Jiezhi Wu We extend the impulse theory for unsteady aerodynamics, from its classic global form to finite-domain formulation, then to a minimum-domain version for discrete wake. Each extension has been confirmed numerically. The minimum-domain theory indicates that the numerical finding of Li and Lu (2012) is of general significance: The entire force is completely determined by only the time rate of impulse of those vortical structures still connecting to the body, along with the Lamb-vector integral thereof that captures the contribution of all the rest disconnected vortical structures.

Beschreibung: Publication date: Available online 1 December 2017 Source: Theoretical and Applied Mechanics Letters Author(s): Ling Zhou, Dehua Chen, Yang Tao, Guangyuan Liu, Shuheng Song, Shidong Zhong At supercritical conditions a porous strip (or slot strip) placed beneath a shock wave can reduce the drag by a weaker lambda shock system, and increase the buffet boundary, even may increase the lift. Passive shock wave/boundary layer control (PSBC) for drag reduction were conducted by SC(2)-0714 supercritical wing, with emphases on parameter of porous/slot and bump, such as porous distribution, hole diameter, cavity depth, porous direction and so on. An SQP optimization methods coupled with adjoint method was adopted to achieve the optimized shape and position of the bumps. Computational fluid dynamics (CFD), force test and oil test with half model all indicate that PSBC with porous, slot and bump generally reduce the drag by weaker lambda shock at supercritical conditions. According to wind tunnel test results for angle of attack of 2°at 0.8 Mach number, the porous configuration with 6.21% porosity results in a drag reduction of 0.0002 and lift-drag ratio increase of 0.2, the small bump configuration results in a drag reduction of 0.0007 and lift-drag ratio increase of 0.3. Bump normally reduce drag at design point with shock wave position being accurately computed. If bump diverges from the position of shock wave, drag will not be easily reduced.

Beschreibung: Publication date: Available online 1 December 2017 Source: Theoretical and Applied Mechanics Letters Author(s): S.J. Luo, Z.Y. Ni, Y.F. Liu The paper focuses on the triple jets interaction with a hypersonic external flow on a revolution body. The experimental model is a ogive-cylinder body with three supersonic nozzles, which are aligned along the flow direction. The freestream Mach number are 5 and 6. The spatial and surface flow characteristics were illustrated by the schlieren photographs and the typical pressure distribution. The results show that there are multi-wave system, separation, reattachment, multi-peak pressure, high- pressure and low-pressure zone boundaries obvious distinction in tri-jets interference flowfield. The present paper also analyzes how do the pressure ratio, the angle of attack, and Mach number effect on tri-jets interaction characteristics.

Beschreibung: Publication date: Available online 2 December 2017 Source: Theoretical and Applied Mechanics Letters Author(s): Natthaporn Kaewchoothong, Kittinan Maliwan, Chayut Nuntadusit, Takeishi Kenichiro The main objective of this research is to study the effect of rib arrangement on the distributions of the local heat transfer coefficient in a stationary channel. In this study, the ribs with square cross section were used to place on two side walls for study. The rib height-to-hydraulic diameter ratio ( e/D h ) and the rib pitch-to-height ( p/e ) ratio were fixed at 0.133 and 10, respectively. Three different types of rib arrangement for inclined ribs, V-shaped ribs and inverted V-shaped ribs were investigated. The rib angle of attack ( α ) was varied from 30°to 90°for inclined ribs and 45°and 60°for both V-shaped and inverted V-shaped ribs, and compared at constant Reynolds number Re =30000. Thermal Liquid Crystal sheet was applied for evaluating the heat transfer distributions. The results showed that the average Nusselt number on surface with rib inclined angle at 60°, 45°, and 60°V-shaped ribs was improved up to about 20%, 25% and 30% higher than case of angle 90°and the rib inclined angle at 60°V-shaped ribs provided the highest Nusselt number covering largest area when compared to the other cases.

Beschreibung: Publication date: July 2017 Source: Theoretical and Applied Mechanics Letters, Volume 7, Issue 4

Beschreibung: Publication date: Available online 15 December 2017 Source: Theoretical and Applied Mechanics Letters Author(s): Batsaikhan Munkhbat, Ari Hamdani, Hiroshige Kikura In the present work, an experimental study of bubbly two-phase flow in a rectangular bubble column was performed using two ultrasonic array sensors, which can measure the instantaneous velocity of gas bubbles on multiple measurement lines. After the sound pressure distribution of sensors had been evaluated with a needle hydrophone technique, the array sensors were applied to two-phase bubble column. To assess the accuracy of the measurement system with array sensors for one and two- dimensional velocity, a simultaneous measurement was performed with an optical measurement technique called Particle Image Velocimetry (PIV). Experimental results showed that accuracy of the measurement system with array sensors is under 10% for one-dimensional velocity profile measurement compared with PIV technique. The accuracy of the system was estimated to be under 20% along the mean flow direction in the case of two-dimensional vector mapping.

Beschreibung: Publication date: Available online 18 December 2017 Source: Theoretical and Applied Mechanics Letters Author(s): Guang Zhang, Heuy Dong Kim, Ying Zi Jin Particle-gas two-phase flows show significantly different behaviors compared to single gas flow through a convergent-divergent nozzle. Non-equilibrium effects, thermal and velocity lag results to the inefficiency of nozzle performance. In the present studies, theoretical analysis and numerical simulations were carried out to investigate particle-gas flows in a C-D nozzle. Homogeneous equilibrium model that no lag in velocity and temperature occurs between particles and gas phase was used to derive mass flow rate and sound speed of multiphase flows. Two-phase flows are regarded as isentropic flows that isentropic relations can be used for homogeneous equilibrium model. Discrete phase model (DPM) where interaction with continuous phase and discrete random walk model were considered was used to calculate particle-gas flows. Particle mass loadings were varied to investigate their effects on choking phenomena of particle-gas flows. Mass flow rate and sound speed of mixture flows were theoretically calculated by homogeneous equilibrium model and compared with numerical results. Shock wave structure and particle number density were also obtained to be different at different particle mass loading and operating pressure conditions.

Beschreibung: Publication date: Available online 18 December 2017 Source: Theoretical and Applied Mechanics Letters Author(s): S. Juntron, S. Jugjai A high performance flexible porous medium burner that can burn gaseous and liquid fuel with different type of flames (premixed and non-premixed) is proposed. The merit of the combustion within porous medium is that heat is recirculated from the combustion gas to porous medium at upstream wherein vaporization is taken place (in case of liquid fuel) or preheated (in case of gaseous fuel) before mixing with the combustion air followed by combustion within another porous medium at downstream. In a former version of the high performance flexible porous medium burner, the upstream porous medium is incorporated with a cooling system using the combustion air as a coolants to prevent thermal decomposition of fuels and thus the burner clogging caused by carbon deposit within the porous medium can be avoided. However, the cooling effect cannot be properly controlled such that the boiling point of the liquid fuel is maintained at suitable value irrespective of the volume flow rate of the combustion air, which is linearly varied with the firing rate of the burner. In particular at the lean burn condition, where high air flow rate is required with high cooling effect with porous medium. This can result in the porous medium temperature lower than the corresponding boiling point of the liquid fuel and thus evaporation of the fuel is failed and the combustion is ceased. Therefore, method of controlling the cooling air flow rate in the porous medium is proposed and studied in order to appropriately control the porous medium temperature and maintain it at above the boiling point irrespective of the combustion conditions. In this research, experimental and computation analysis are used to design the FPMB, with adjustable cooling effect. The result shown that, the new design of FPMB which has temperature in the upstream porous medium is higher than boiling point and lower than thermal decomposition temperature of fuel (kerosene) at all conditions and can be operated at a wide range of equivalence ratio without fuel decomposition and fuel non- vaporization problem.

Beschreibung: Publication date: September 2017 Source: Theoretical and Applied Mechanics Letters, Volume 7, Issue 5

Beschreibung: Publication date: Available online 28 December 2017 Source: Theoretical and Applied Mechanics Letters Author(s): Lei Wang, Yan-kui Wang, Zhong-yang Qi The asymmetric vortices over blunt-nose slender body at high angles of attack result in random side force. In this paper, a nose micro-blowing technology is used to control the asymmetric flow. Pressure measurement and particle image velocimetry (PIV) experiments are conducted in a low-speed wind tunnel to research effects of jet flow rate on asymmetric vortices over blunt-nose slender body. The angle of attack of the model is fixed at 50°and the Reynolds number for the experiments is 1.6 × 10 5 based on diameter of aft-body. A blow hole (5 mm in diameter) on the nose is processed at circumferential angle θ b =  90°and meridian angle γ b =  20°with jet momentum ratio C μ ranging from 5.30 × 10 -7 ∼ 1.19 × 10 −4 . Tests are made under two kinds of perturbations. One is called single perturbation with only blow hole and the other is called combined perturbation consist of blow hole and additional granules set on nose. The results show that whether the model has the single perturbation or the combined one, the sectional side force of x / D   =  3 varies in the same direction with the increasement of C μ and remains stable when C μ is greater than 3.29 × 10 −6 . But the stable force values are different according to various perturbations. The fact proves that the size and direction of the side force of blunt- nose slender body can be controlled by the nose micro-blowing.

Beschreibung: Publication date: Available online 25 October 2017 Source: Theoretical and Applied Mechanics Letters Author(s): Ya Liu, Shijun Luo, Feng Liu Numerical solutions of the steady transonic small-disturbance (TSD) potential equation are computed using the conservative Murman − Cole scheme. Multiple solutions are discovered and mapped out for the Mach number range at zero angle of attack and the angle of attack range at Mach number 0.85 for the NACA 0012 airfoil. We present a linear stability analysis method by directly assembling and evaluating the Jacobian matrix of the nonlinear finite-difference equation of the TSD equation. The stability of all the discovered multiple solutions are then determined by the proposed eigen analysis. The relation of stability to convergence of the iterative method for solving the TSD equation is discussed. Computations and the stability analysis demonstrate the possibility of eliminating the multiple solutions and stabilizing the remaining unique solution by adding a sufficiently long splitter plate downstream the airfoil trailing edge. Finally, instability of the solution of the TSD equation is shown to be closely connected to the onset of transonic buffet by comparing with experimental data.

Beschreibung: Publication date: Available online 8 March 2017 Source: Theoretical and Applied Mechanics Letters Author(s): Ruiqi Jiang, Jianliang Xiao, Jizhou Song The buckling of thin gel film has attracted much attention due to its applications in the design of three-dimensional structure from two-dimensional template. We have established an analytical model to study the swelling-induced buckling of a thin gel strip with one edge clamped and the others free. The closed-form solutions for the amplitude and wavelength of the buckled shape are obtained by energy minimization of the total potential energy. The analytical results agree well with finite element analysis based on the inhomogeneous gel theory without any parameter fitting. The model provides a route to study complex postbuckling behaviors of thin gel films and guidelines to design the buckled configuration quantitatively by controlling the swelling ratio.

Beschreibung: Publication date: Available online 14 March 2017 Source: Theoretical and Applied Mechanics Letters Author(s): Lihong Yang, Tao Fan, Liping Yang, Xiao Han, Zongbing Chen The bending responses of functionally graded (FG) nanobeams with simply supported edges are investigated based on Timoshenko beam theory in this article. The Gurtin–Murdoch surface elasticity theory is adopted to analyze the influences of surface stress on bending response of FG nanobeam. The material properties are assumed to vary along the thickness of FG nanobeam in power law. The bending governing equations are derived by using the minimum total potential energy principle and explicit formulas are derived for rotation angle and deflection of nanobeams with surface effects. Illustrative examples are implemented to give the bending deformation of FG nanobeam. The influences of the aspect ratio, gradient index and surface stress on dimensionless deflection are discussed in detail.

Beschreibung: Publication date: Available online 15 March 2017 Source: Theoretical and Applied Mechanics Letters Author(s): D.J. Kong, C. Ruan-Wu, Y.X. Luo, C.L. Zhang, Ch. Zhang Two-dimensional (2D) equations for multiferroic (MF) laminated plates with imperfect interfaces are established in this paper. The interface between two adjacent sublayers, which are not perfectly bonded together, is modeled as a general spring-type layer. The mechanical displacements, and the electric and magnetic potentials of the two adjacent layers are assumed to be discontinuous at the interface. As an example, the influences of imperfect interfaces on the magnetoelectric (ME) coupling effects in an MF sandwich plate are investigated with the established 2D governing equations. Numerical results show that the imperfect interfaces have a significant impact on the ME coupling effects in MF laminated structures.

Beschreibung: Publication date: Available online 25 April 2017 Source: Theoretical and Applied Mechanics Letters Author(s): L. Pellet, P. Christodoulides, S. Donne, C.J. Bean, F. Dias We present second-order expressions for the free-surface elevation, velocity potential and pressure resulting from the interaction of surface waves in water of arbitrary depth. When the surface waves have nearly equal frequencies and nearly opposite directions, a second-order pressure can be felt all the way to the sea bottom. There are at least two areas of applications: reflective structures and microseisms. Microseisms generated by water waves in the ocean are small vibrations of the ground resulting from pressure oscillations associated with the coupling of ocean surface gravity waves and the sea floor. They are recorded on land-based seismic stations throughout the world and they are divided into primary and secondary types, as a function of spectral content. Secondary microseisms are generated by the interaction of surface waves with nearly equal frequencies and nearly opposite directions. The efficiency of microseism generation thus depends in part on ocean wave frequency and direction. Based on the second-order expressions for the dynamic pressure, a simple theoretical analysis that quantifies the degree of nearness in amplitude, frequency and incidence angle, which must be reached to observe the phenomenon, is presented.

Beschreibung: Publication date: Available online 2 May 2017 Source: Theoretical and Applied Mechanics Letters Author(s): Wenhu Wang, Peiqing Liu This paper numerically studies the influence of the downward spoiler deflection on the boundary layer flow of a high-lift two-element airfoil consisting of a droop nose, a main wing, a downward deflecting spoiler and a single slotted flap. Both of the boundary layer of the upper surface of the spoiler and the confluent boundary layer of the upper surface of the flap become thicker, as the downward spoiler deflection increases. Compared to the attached flow at the angle of attack of 10°, the flow of the upper surface of the spoiler becomes separated at the angle of attack of 16°when the spoiler deflection is large enough, which corresponds to the boundary layer flow reversal in velocity profiles.

Beschreibung: Publication date: March 2017 Source: Theoretical and Applied Mechanics Letters, Volume 7, Issue 2

Beschreibung: Publication date: Available online 24 January 2017 Source: Theoretical and Applied Mechanics Letters Author(s): T. Chourushi Viscoelastic fluids due to their non-linear nature plays an important role in process and polymer industries. These non-linear characteristics of fluid, influence final outcome of the product. Such processes though looks simple are numerically challenging to study, due to the loss of numerical stability. Over the years, various methodologies have been developed to overcome this numerical limitation. In spite of this, numerical solutions are considered distant from accuracy, as first-order upwind-differencing scheme (UDS) are often employed for improving the stability of algorithm. To elude this effect, some works been reported in the past, where high-resolution-schemes (HRS) were employed and deborah number was varied. However, these works are limited to creeping flows and do not detail any information on the numerical stability of HRS. Hence, this article presents the numerical study of high shearing contraction flows, where stability of HRS are addressed in reference to fluid elasticity. Results suggest that all HRS show some order of undue oscillations in flow variable profiles, measured along vertical lines placed near contraction region in the upstream section of domain, at E ≈ 5 . Furthermore, by varying the elasticity number ( E ) , a clear relationship between numerical stability of HRS and E was obtained, which states that the order of undue oscillations in flow variable profiles is directly proportional to E .