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Basic equations for density current

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Chinese Science Bulletin 1996年第16期41卷 1402-1408页

作者：王光谦方红卫 Department of Hydraulic Engineering Tsinghua University Beijing 100084 China

Initiated by practical demands the research on density current was carried out in early time in such areas as hydraulic engineering, geology, navigation and environmental conservation. As a result, great achievements have been made during the past years. Previous study on density current was mainly of practical background; that is to say,

关键词： basic equation density current theoretical analysis

Construction of Crack Perturbation Model and Forward Semi-analytical Model of Attached Eddy current Sensor

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Transactions of Nanjing University of Aeronautics and Astronautics 2015年第3期32卷 279-288页

作者：焦胜博程礼李晓微李培源高君宇 Aeronautics and Astronautics Engineering College Air Force Engineering University School of Software XiDian University

Fatigue damage monitoring is critical metallic structure health monitoring of aircraft.The sensor should be high sensitive,easy to be integrated into structure and well adaptable for poor working conditions.Therefore,an attached eddy current sensor with flexible plane is put forward and its characteristics are analyzed.By extracting material′s conductivity as the crack features,forward semi-analytical model is established and parameter optimizations are carried out.Crack perturbation model of attached eddy current sensor is constructed,and perturbation voltages of sensing channels under three-dimension structural crack are obtained.To verify the sensor′s performance,monitoring experiment on crack extension is conducted under condition of 3 MHz frequency.The validation experimental results show that perturbation model of 2A12-T4 aluminum alloy agrees well with experiment results,and perturbation model errors of four sensing channels are within 25%.The attached eddy current sensor is capable of testing the crack nondestructively and measuring the crack extension quantitatively with the accuracy of 1mm.

关键词： attached eddy current sensor semi-analytical model

Particle Trajectories in Nonlinear Water Wave on Uniform current

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China Ocean Engineering 2008年第4期22卷 611-621页

作者： Hung-Chu HSU Yang-Yih CHEN Chia-Yan CHENG Wen-Jer TSENG Tainan Hydraulics Laboratory National Cheng Kung University Department of Marine Environment and Engineering National Sun Yat-Sen University Coastal and Offshore Resources Research Center Fisheries Research Institute Department of Civil Engineering Cheng Shiu University

The study in this paper is focusing on trajectories of particles in the irrotational progressive water waves coexisting with uniform current. The parametric equations of particle trajectories over a range of levels in a Lagrangian type of description are developed analytically via the Euler-Lagrange transformation. The Lagrangian wave period of particle motion differing from the Eulerian wave period and the mass transport can also be obtained directly. The third-order solution of particle trajectory exhibits that they do not move in closed orbital motion but represent a net movement that decreases exponentially with the water depth. Uniform current is found to have significant effect on the trajectories and drift velocity of gravity waves. Overall, the influence of increased uniform current is to increase the relative horizontal distance traveled by a particle, as well as the magnitude of the time-averaged drift velocity on the free surface. For adverse current cases, a reverse behavior is found. The obtained third-order solutions satisfy the irrotational condition contrasted to the Gerstner waves and are verified by reducing to those of two-dimensional gravity waves in Lagrangian coordinates.

关键词： wave current Lagrangian Euler- Lagrange transformation particle trajectory

Effect of induced shielding current transmission in longitudinal direction on levitation force of melt grown single-domain YBa_2Cu_3O_(7-x) cylindrical superconductor

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Science China(Physics,Mechanics & Astronomy) 2004年第2期47卷 146-153页

作者： R. Nicolsky R. de Andrade Jr LASUP-DEE UFRJ Ilha do Fundao Cx.P.68515 21945-970 Rio de Janeiro RJ Brasil Correspondence should be addressed to Yang Wanmin LASUP-DEE UFRJ Ilha do Fundao Cx.P.68515 21945-970 Rio de Janeiro RJ Brasil Correspondence should be addressed to Yang Wanmin

A novel layer deletion method is used to experimentally investigate the effect of induced shielding current transmission (ISCT) in the longitudinal direction on the levitation force of a single-domain YBa2Cu3O7-x (YBCO) cylindrical superconductor (f30? mm). In the experiment the sample was gradually sliced into two equal sheets, at the middle height along a diameter with 5 mm every step. The experimental results show that the levitation force is closely related with the ISCT in the longitudinal direction. Any layer deletion, even a small piece of layer deletion can reduce the levitation force of the sample. After the whole layer was deleted the levitation force can diminish about 50%. It is also found that the levitation force is directly proportional to the effective factor of surface area, which is equal to the top surface area divided by the total surface area parallel to the top surface of the sample.

关键词： melt growth, single domain YBCO, levitation force, induced current distribution.

Evaluation of overhead line current unbalance in meshed grids and its reduction

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Journal of Modern Power Systems and Clean Energy 2018年第6期6卷 1204-1212页

作者： Jakub EHRENBERGER Jan ?VEC Department of Electrical Power Engineering Czech Technical University in Prague

This paper describes new methodology in the current unbalance calculations in meshed grids. The meshed grids, mainly the transmission ones, consist of more parts connected together which are formed using different conductor types, phase sequence arrangements,tower constructions, and various number of lines on the same tower. Therefore several computational challenges arise in comparison with the widely discussed point-topoint configuration. The methodology divides the grid into a number of impedance matrices respecting all the self and mutual impedances among all conductors and all parallel lines. Another challenging issue for the line impedancedescription is changing the number of shield wires along the line if the line is composed of several sections with different tower configurations. For the current unbalance calculation, shield wires must also be included in the algorithms, and matrices of various dimensions can be obtained. For the overall matrix description to be used,dimensions of all matrices in final equations must be equal,and therefore the virtual shield wires are created. To compare more conductor transposition cases with each other, the line loadings caused by voltage sources should be equal. This is necessary mainly in case of meshed grids where the supplying sources on different lines can have strong mutual couplings. This can be achieved by an appropriately designed optimization of the connected voltage sources.

关键词： current unbalance Phase sequence arrangement Shield wire Unbalance factor Zero-sequence set

Effect of nonlinear wave-current interaction on flow fields and hydrodynamic forces

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Science China Mathematics 1997年第6期40卷 622-632页

作者：王涛李家春 Institute of Mechanics Chinese Academy of Sciences Beijing 100080 China

A fifth-order theory for solving the problem of interaction between Stokes waves and exponential profile currents is proposed. The calculated flow fields are compared with measurements. Then the errors caused by the linear superposition method and approximate theory are discussed. It is found that the total wave-current field consists of pure wave, pure current and interaction components. The shear current not only directly changes the flow field, but also indirectly does so by changing the wave parameters due to wave-current interaction. The present theory can predict the wave kinematics on shear currents satisfactorily. The linear superposition method may give rise to more than 40% loading error in extreme conditions. When the apparent wave period is used and the Wheeler stretching method is adopted to extrapolate the current, application of the approximate theory is the best.

关键词： Stokes wave exponential current nonlinear interaction.

Interactions of nonlinear gravity waves and uniform current in Lagrangian system

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Acta Oceanologica Sinica 2009年第1期28卷 89-98页

作者： HSU Hung-Chu CHEN Yang-Yih LI Meng-Syue TSENG Wen-Jer Tainan Hydraulics Laboratory National Cheng Kung University Department of Marine Environment and Engineering National Sun Yat-Sen University Department of Civil Engineering Cheng Shiu University

The particle trajectory on a weakly nonlinear progressive surface wave obliquely interacting with a uniform current is studied by using an Euler-Lagrange transformation.The third-order asymptotic solution is a periodic bounded function of Lagrangian labels and time,which imply that the entire solution is uniformly-valid.The explicit parametric solution highlights the trajectory of a water particle and mass transport associated with a particle displacement can now be obtained directly in Lagrangian form.The angular frequency and Lagrangian mean level of the particle motion in Lagrangian form differ from those of the Eulerian.The variations in the water particle orbits resulting from the oblique interaction with a steady uniform current of different magnitudes are also investigated.

关键词： Lagrangian particle trajectory nonlinear water wave current drift velocity

Limitations of absolute current densities derived from the Semel & Skumanich method

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Science China(Physics,Mechanics & Astronomy) 2009年第11期52卷 1678-1685页

作者： LI Jing1 & FAN YuHong2 1 Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA 2 High Altitude Observatory, Earth and Sun Systems Laboratory, National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307, USA Institute for Astronomy University of Hawaii Honolulu USA High Altitude Observatory Earth and Sun Systems Laboratory National Center for Atmospheric Research Boulder USA

Semel and Skumanich proposed a method to obtain the absolute electric current density, |Jz|, without disambiguation of 180° in the transverse field directions. The advantage of the method is that the uncertainty in the determination of the ambiguity in the magnetic azimuth is removed. Here, we investigate the limits of the calculation when applied to a numerical MHD model. We have found that the combination of changes in the magnetic azimuth with vanishing horizontal field component leads to errors, where electric current densities are often strong. Where errors occur, the calculation gives |Jz| too small by factors typically 1.2 - 2.0.

关键词： numerical MHD model magnetic field electric current density

Eddy current Analyses by Domain Decomposition Method Using Double-Double Precision

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Computer Modeling in Engineering & Sciences 2018年第9期116卷 349-363页

作者： Mizuma Takehito Takei Amane University of Miyazaki 1-1Gakuen Kibanadai-nishiMiyazaki-shiMiyazakiJapan

A matrix equation solved in an eddy current analysis,??-??method based on a domain decomposition method becomes a complex symmetric system.In general,iterative method is used as the solver.Convergence of iterative method in an interface problem is improved by increasing an accuracy of a solution of an iterative method of a subdomain problem.However,it is difficult to improve the convergence by using a small convergence criterion in the subdomain problem.Therefore,authors propose a method to introduce double-double precision into the interface problem and the subdomain problem.This proposed method improves the convergence of the interface problem.In this paper,first,we describe proposed method.Second,we confirm validity of the method by using Team Workshop Problem 7,standard model for eddy current analysis.Finally,we show effectiveness of the method from two numerical results.

关键词： Double-double precision domain decomposition method eddy current analysis parallel finite element method