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  • Articles  (123)
  • Elsevier  (88)
  • Wiley  (20)
  • Institute of Physics (IOP)  (15)
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  • Articles  (123)
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  • 1
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    Prediction of solute transport in a heterogeneous aquifer utilizing hydraulic conductivity and specific storage tomograms (2015)
    Wiley
    Details
    Publication Date: 2015-06-18
    Description: A sequential procedure of hydraulic tomographical inversion is applied to characterize at high resolution the spatial heterogeneity of hydraulic conductivity and specific storage at the field test site Stegemühle, Germany. The shallow aquifer at this site is examined by five short- term multi-level pumping tests with 30 pumping-observation pairs between two wells. Utilizing travel time diagnostics of the recorded pressure response curves, fast eikonal based inversion is shown to deliver insight into the sedimentary structures. Thus, the structural information from the generated travel time tomogram is exploited to constrain full calibration of the pressure response curves. Based on lateral extrapolation from the measured inter-well profile, a three-dimensional reconstruction of the aquifer is obtained. It is demonstrated that calibration of spatially variable specific storage in addition to hydraulic conductivity can improve the fitting of the model while the structural features are only slightly changed. At the field site, two tracer tests with uranine and sodium-naphthionate were also performed and their concentrations were monitored for two months. The measured tracer breakthrough curves are employed for independent validation of the hydraulic tomographical reconstruction. It is demonstrated that major features of the observed solute transport can be reproduced, and structures relevant for macro-dispersive tracer spreading could be resolved. However, for the mildly heterogeneous aquifer, the tracer breakthrough curves can also be approximated by a simplified homogeneous model with higher dispersivity. Therefore improved validation results that capture specific characteristics of the breakthrough curves would require additional hydraulic measurements. This article is protected by copyright. All rights reserved.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Bragg gravity-gradiometer using the 1 S 0 – 3 P 1 intercombination transition of 88 Sr (2018)
    Institute of Physics (IOP)
    Details
    Publication Date: 2018-04-13
    Description: We present a gradiometer based on matter-wave interference of alkaline-earth-metal atoms, namely 88 Sr. The coherent manipulation of the atomic external degrees of freedom is obtained by large-momentum-transfer Bragg diffraction, driven by laser fields detuned away from the narrow 1 S 0 – 3 P 1 intercombination transition. We use a well-controlled artificial gradient, realized by changing the relative frequencies of the Bragg pulses during the interferometer sequence, in order to characterize the sensitivity of the gradiometer. The sensitivity reaches 1.5 × 10 −5 s −2 for an interferometer time of 20 ms, limited only by geometrical constraints. We observed extremely low sensitivity of the gradiometric phase to magnetic field gradients, approaching a value 10 4 times lower than the sensitivity of alkali-atom based gradiometers, limited by the interferometer sensitivity. An efficient double-launch techni...
    Electronic ISSN: 1367-2630
    Topics: Physics
    Published by Institute of Physics (IOP)
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  • 3
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    Observations and measurements in cloud cavitating flows (2015)
    Institute of Physics (IOP)
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    Publication Date: 2015-01-16
    Description: The main purpose of this study is to shed light on the cloud cavitating flow and associated characteristic of pressure fluctuation near wall. A simultaneous sampling technique is used to synchronize the observations of cavitation instantaneous behaviour and the measurements of pressure signals near wall in a convergent-divergent channel. The results show that, a typical quasi-periodical sheet/cloud cavitation can be categorized into three stages: (1) the growth of attached cavity; (2) the shedding of the attached cavity; (3) the development and collapse of the detached cavities. At the stage one, the magnitudes of pressure fluctuation under the attached cavity are limited. However, they become significant in the closure region of attached cavity, especially, when attached cavity reaches its maximum length. At the stage two, the attached cavity begins to shed small detached cavity, leading to the generation of small local pressure fluctuations with higher frequency. At the stage ...
    Print ISSN: 1757-8981
    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Institute of Physics (IOP)
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  • 4
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    Applications of a curvature correction turbulent model for computations of unsteady cavitating flows (2015)
    Institute of Physics (IOP)
    Details
    Publication Date: 2015-01-16
    Description: A Curvature Correction model (CCM) based on the original k- ##IMG## [http://ej.iop.org/icons/Entities/epsilon.gif] {epsilon} model is proposed to simulate unsteady cavitating flows. The objective of this study is to validate the CCM model and further investigate the unsteady vortex behaviors of cavitating flows around a Clark-Y hydrofoil. Compared with the original k- ##IMG## [http://ej.iop.org/icons/Entities/epsilon.gif] {epsilon} model, predicted results are improved in terms of the cavity detachment and hydrofoil fluctuations. Results show that streamline curvature correction of CCM model overcomes the over-predictions of turbulence kinetic energy and eddy viscosity in cavitating vertical region with the original k- ##IMG## [http://ej.iop.org/icons/Entities/epsilon.gif] {epsilon}
    Print ISSN: 1757-8981
    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Institute of Physics (IOP)
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  • 5
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    Numerical investigation on added mass and damping force coefficient of an underwater vehicle in cavitating flows (2015)
    Institute of Physics (IOP)
    Details
    Publication Date: 2015-01-16
    Description: The objective of this paper is mainly to study the influence of cavitation on the added mass and damping force coefficient. Based on Reynolds averaged Navier-Stokes equations, the dynamic mesh is used to calculate the added mass, and the rotating coordinate frame method is applied to research on the damping force coefficient. In order to obtain fluid damping force coefficients, the movement pattern is set as a uniform circular motion. Then the additional force coefficient and pitch damping moment coefficient could be obtained using the method of least squares. The result shows that the method to calculate added mass is reliable by comparing with the analytical solution. With the cavitation number decreasing, the absolute value of the added mass of λ 22 decreases and λ 26 increases. What's more, both the absolute value of damping force and moment coefficient decrease substantially with the development of cavity when the cavitation number is large...
    Print ISSN: 1757-8981
    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 6
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    Partially Averaged Navier-Stokes method based on k-ω model for simulating unsteady cavitating flows (2015)
    Institute of Physics (IOP)
    Details
    Publication Date: 2015-01-16
    Description: The turbulence closure is significant to unsteady cavitating flow computations as the flow is frequently time-dependent accompanied with multiple scales of vortex. A turbulence bridging model named as PANS (Partially-averaged Navier-Stokes) purported for any filter-width is developed recently. The model filter width is controlled through two parameters: the unresolved-to-total ratios of kinetic energy f k and dissipation rate f ω . In the present paper, the PANS method based on k-ω model is used to simulate unsteady cavitating flows over a Clark-y hydrofoil. The main objective of this work is to present the characteristics of PANS k-ω model and evaluate it depending on experimental data. The PANS k-ω model is implemented with various filter parameters ( f k =0.2~1, f ω =1/ f k ). The comparisons with the experimental data show that with the decrease of the filter parameter f k
    Print ISSN: 1757-8981
    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 7
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    Structural evolution of long-duration meteor trail irregularities driven by neutral wind (2014)
    Wiley
    Details
    Publication Date: 2014-11-18
    Description: An experiment on spatial domain interferometry observations of meteor trail irregularities at a low-latitude location in China was conducted during August 2013 using the Sanya VHF coherent radar (18.4°N, 109.6°E). More than 3 thousand range-spread meteor trail echoes (RSTEs) were observed. Among the trail echoes, the spatial structure of meteor trail irregularities responsible for a single long-duration RSTE event persisting for ~4 min was reconstructed. This RSTE was found to be initially generated at 90 − 115 km altitudes and aligned along the radar beam boresight. After about the first minute of the trail lifetime, the trail echo appeared only in a narrow altitude range of 94 − 98 km. An analysis on the spatial pattern of the long-duration RSTE showed that the trail irregularities at lower range gates moved away from the region perpendicular to the geomagnetic field. The eastward drifts of the RSTE irregularities were found to decrease with increasing altitude, e.g., from 80 ms -1 at ~94 km to 20 ms -1 at ~100 km. Simultaneous horizontal neutral wind measurements made with the Fuke all-sky meteor radar (located north of Sanya) recorded a similar velocity profile. We suggest that the neutral wind could drive the spatial structural evolution of the RSTE irregularities, and help to determine the altitudes where the longest portion of the RSTE was located.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
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    Application of D-InSAR technology in urban land subsidence measurement: A case study on Beihai city (2018)
    Institute of Physics (IOP)
    Details
    Publication Date: 2018-10-12
    Description: Land subsidence monitoring is of great significance for the city safety and development. D-InSAR technology is widely used in city ground subsidence monitoring as the development of synthetic aperture radar satellite applications, because of the surface deformation information in all-weather conditions with merits of large coverage, fast reaction and high accuracy. This paper studied and analyzed the land subsidence in Beihai by the track method of differential radar interferometry; the information of land subsidence was obtained. The distribution of land subsidence in Beihai city is widespread; the maximum land subsidence was 0.1567m in the studying area from 2001 to 2011, with the maximum annual average subsidence rate of 0.0157m/a, the most serious land subsidence point is located in E109°16′49.443″, N21°37′45.243″. Combined with the field investigation, ascertain the main influencing factors of land subsidence in Beihai city is the exploitation of groundwater resources. The ...
    Print ISSN: 1755-1307
    Electronic ISSN: 1755-1315
    Topics: Geography , Geosciences , Physics
    Published by Institute of Physics (IOP)
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  • 9
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    A new hybrid DC circuit breaker topology (2018)
    Institute of Physics (IOP)
    Details
    Publication Date: 2018-10-31
    Description: Being advantageous for long-distance power transmission and new energy connection, DC system has wide range of applications in many scenarios. As the capacity of DC power grids increases, the fault current is more difficult to interrupt. And the DC circuit breaker which is very important for protecting DC grid attracts more and more attention of researchers. In this paper, a new hybrid DC circuit breaker topology based on the technique of thyristor forced current zero is proposed. The breaker is able to interrupt the fault current in several milliseconds, and the mechanical switch can be cut off at zero current. In addition, no extra power supply and control devices are needed, the pre-charging capacitor can obtain energy from DC grid directly. Therefore, the control process is simpler and the reliability is greatly improved. The operating principle of the proposed circuit breaker is analyzed in detail, and then the simulation is carried out in PSCAD/EMTDC which verifies the cor...
    Print ISSN: 1755-1307
    Electronic ISSN: 1755-1315
    Topics: Geography , Geosciences , Physics
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  • 10
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    Ligands Exchange Process on Gold Nanoparticles in Acetone Solution (2018)
    Institute of Physics (IOP)
    Details
    Publication Date: 2018-05-17
    Description: The ligands exchange process on gold nanoparticles (GNPs) was proceeded by using hydrophobic group (PPh 3 ) and hydrophilic group (THPO) in acetone solution. The FTIR and XPS results demonstrated that part of THPO was replaced by PPh 3 which was dissolved in polar solution (acetone); the results were in accordance with the electrochemical analysis where the differential capacity decreased with increasing exchange time. After 12 h, the exchange process terminated and the final ratio of PPh 3 and THPO was about 1.4: 1. This ratio remained unchanged although the PPh 3 and THPO modified GNPs re-dispersed in the PPh 3 acetone solution demonstrating the stable adsorption of both ligands after exchanging for 12 h. The TEM images showed that the gold nanoparticles were self-assembled from scattered to arranged morphology due to the existence of hydrophilic and hydrophobic ligands and led to Janus gold nanoparticles.
    Print ISSN: 1757-8981
    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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