Focuses on a study on the fully implicit Crank Nicholson (CN) schemes and three projection methods for approximate preservation of component-consistency under projection. Transformation from incompressible Navier-Stok...Focuses on a study on the fully implicit Crank Nicholson (CN) schemes and three projection methods for approximate preservation of component-consistency under projection. Transformation from incompressible Navier-Stokes equations to differential algebraic equations CN schemes; Local errors of CN projection methods; Numerical boundary conditions.展开更多
Numerical simulation based on computational fluid dynamics （CFD） is a useful approach for quantitatively investigating the underlying thermal-mechanical conditions during FSW, such as temperature field and material ...Numerical simulation based on computational fluid dynamics （CFD） is a useful approach for quantitatively investigating the underlying thermal-mechanical conditions during FSW, such as temperature field and material deformation field. One of the critical issues in CFD simulation of FSW is the use of the frictional boundary condition, which represents the friction between the welding tool and the workpiece in the numerical models. In this study, three-dimensional numerical simulation is conducted to analyze the heat transfer and plastic deformation behaviors during the FSW of AA2024. For comparison purposes, both the boundary velocity （BV） models and the boundary shear stress （BSS） models are employed in order to assess their performances in predicting the temperature and material deformation in FSW. It is interesting to note that different boundary conditions yield similar predictions on temperature, but quite different predictions on material deformation. The numerical predictions are compared with the experimental results. The predicted deformation zone geometry by the BSS model is consistent with the experimental results while there is large difference between the predictions by the BV models and the experimental measurements. The fact that the BSS model yields more reasonable predictions on the deformation zone geometry is attributed to its capacity to automatically adjust the contact state at the tool/workpiece interface. Based on the favorable predictions on both the temperature field and the material deformation field, the BSS model is suggested to have a better performance in numerical simulation of FSW than the BV model.展开更多
The evolution of two spanwise-aligned low-speed streaks in a wall turbulent flow, triggered by the instability of the subharmonic varicose （SV） mode, is studied by a direct numerical simulation （DNS） method in a s...The evolution of two spanwise-aligned low-speed streaks in a wall turbulent flow, triggered by the instability of the subharmonic varicose （SV） mode, is studied by a direct numerical simulation （DNS） method in a small spatial-periodic channel. The results show that the SV low-speed streaks are self-sustained at the early stage, and then transform into subharmonic sinuous （SS） low-speed streaks. Initially, the streamwise vortex sheets are formed by shearing, and then evolve into zigzag vortex sheets due to the mutual induction. As the intensification of the SV low-speed streaks becomes prominent, the tilted streamwise vortex tubes and the V-like streamwise vortex tubes can be formed simultaneously by increasing ＋~. When the SV low-speed streaks break down, new zigzag streamwise vortices will be generated, thus giving birth to the next sustaining cycle of the SV low-speed streaks. When the second breakdown happens, new secondary V-like streamwise vortices instead of zigzag streamwise vortices will be generated. Because of the sweep motion of the fluid induced by the secondary V-like streamwise vortices, each decayed low-speed streak can be divided into two parts, and each part combines with the part of another streak, finally leading to the formation of SS low-speed streaks.展开更多
The aim of the present paper is to study the numerical solutions of the steady MHD two dimensional stagnation point flow of an incompressible nano fluid towards a stretching cylinder.The effects of radiation and conve...The aim of the present paper is to study the numerical solutions of the steady MHD two dimensional stagnation point flow of an incompressible nano fluid towards a stretching cylinder.The effects of radiation and convective boundary condition are also taken into account.The model used for the nanofluid incorporates the effects of Brownian motion and thermophoresis.The resulting nonlinear momentum,energy and nano particle equations are simplifed using similarity transformations.Numerical solutions have been obtained for the velocity,temperature and nanoparticle fraction profles.The influence of physical parameters on the velocity,temperature,nanoparticle fraction,rates of heat transfer and nanoparticle fraction are shown graphically.展开更多
Based on water inrush accident of 1841 working face of Desheng Coal Mine in Wu'an, Hebei province, China, an evaluation model of hydrodynamic characteristics of the project is set up and simulated using Matlab. It...Based on water inrush accident of 1841 working face of Desheng Coal Mine in Wu'an, Hebei province, China, an evaluation model of hydrodynamic characteristics of the project is set up and simulated using Matlab. It is assumed that the pipe flow would transform into seepage flow when the aggregates are plugged into the water inrush channel and the seepage flow would disappear along with grouting process. The simulation results show that the flow velocity will increase with an increase in height of aggregates accumulation body during the aggregates filling process; the maximum seepage velocity occurs on the top of plugging zone; and the water flow decreases with increasing plugging height of water inrush channel. Finally, the field construction results show that the water inrush channel can be plugged effectively by the compacted body prepared with aggregate and cement slurry.展开更多
Earth medium is not completely elastic, with its viscosity resulting in attenuation and dispersion of seismic waves. Most viscoelastic numerical simulations are based on the finite-difference and finite-element method...Earth medium is not completely elastic, with its viscosity resulting in attenuation and dispersion of seismic waves. Most viscoelastic numerical simulations are based on the finite-difference and finite-element methods. Targeted at viscoelastic numerical modeling for multilayered media, the constant-Q acoustic wave equation is transformed into the corresponding wave integral representation with its Green＇s function accounting for viscoelastic coefficients. An efficient alternative for full-waveform solution to the integral equation is proposed in this article by extending conventional frequency-domain boundary element methods to viscoelastic media. The viscoelastic boundary element method enjoys a distinct characteristic of the explicit use of boundary continuity conditions of displacement and traction, leading to a semi-analytical solution with sufficient accuracy for simulating the viscoelastic effect across irregular interfaces. Numerical experiments to study the viscoelastic absorption of different Q values demonstrate the accuracy and applicability of the method.展开更多
In this note, some properties of the interior of numerical ranges of operators are established, and an alternative proof of Embry's theorem associated with the interior of a numerical ranges of an operator is give...In this note, some properties of the interior of numerical ranges of operators are established, and an alternative proof of Embry's theorem associated with the interior of a numerical ranges of an operator is given(see [3]).展开更多
This study deals with the stagnation point flow of ferrofluid over a flat plate with non-linear slip boundary condition in the presence of homogeneous-heterogeneous reactions.Three kinds of ferroparticles,namely,magne...This study deals with the stagnation point flow of ferrofluid over a flat plate with non-linear slip boundary condition in the presence of homogeneous-heterogeneous reactions.Three kinds of ferroparticles,namely,magnetite(Fe_3O_4),cobalt ferrite(CoFe_2O_4) and manganese zinc ferrite(Mn-ZnFe_2O_4) are taken into account with water and kerosene as conventional base fluids.The developed model of homogeneous-heterogeneous reactions in boundary layer flow with equal and unequal diffusivities for reactant and autocatalysis is considered.The governing partial differential equations are converted into system of non-linear ordinary differential equations by mean of similarity transformations.These ordinary differential equations are integrated numerically using shooting method.The effects of pertinent parameters on velocity and concentration profiles are presented graphically and discussed.We found that in the presence of Fe_3O_4-kerosene and CoFe_2O_4-kerosene,velocity profiles increase for large values of α and β whereas there is a decrement in concentration profiles with increasing values of if and K_s.Furthermore,the comparison between non-magnetic(A1_2O_3) and magnetic Fe_3O_4 nanoparticles is given in tabular form.展开更多
In this paper,we concentrate on high-order boundary treatments for finite volume methods solving hyperbolic conservation laws.The complex geometric physical domain is covered by a Cartesian mesh,resulting in the bound...In this paper,we concentrate on high-order boundary treatments for finite volume methods solving hyperbolic conservation laws.The complex geometric physical domain is covered by a Cartesian mesh,resulting in the boundary intersecting the grids in various fashions.We propose two approaches to evaluate the cell averages on the ghost cells near the boundary.Both of them start from the inverse Lax-Wendroff(ILW)procedure,in which the normal spatial derivatives at inflow boundaries can be obtained by repeatedly using the governing equations and boundary conditions.After that,we can get an accurate evaluation of the ghost cell average by a Taylor expansion joined with high-order extrapolation,or by a Hermite extrapolation coupling with the cell averages on some“artificial”inner cells.The stability analysis is provided for both schemes,indicating that they can avoid the so-called“small-cell”problem.Moreover,the second method is more efficient under the premise of accuracy and stability.We perform numerical experiments on a collection of examples with the physical boundary not aligned with the grids and with various boundary conditions,indicating the high-order accuracy and efficiency of the proposed schemes.展开更多
In this paper,we propose a new class of discontinuous Galerkin(DG)methods for solving 1D conservation laws on unfitted meshes.The standard DG method is used in the interior cells.For the small cut elements around the ...In this paper,we propose a new class of discontinuous Galerkin(DG)methods for solving 1D conservation laws on unfitted meshes.The standard DG method is used in the interior cells.For the small cut elements around the boundaries,we directly design approximation polynomials based on inverse Lax-Wendroff(ILW)principles for the inflow boundary conditions and introduce the post-processing to preserve the local conservation properties of the DG method.The theoretical analysis shows that our proposed methods have the same stability and numerical accuracy as the standard DG method in the inner region.An additional nonlinear limiter is designed to prevent spurious oscillations if a shock is near the boundary.Numerical results indicate that our methods achieve optimal numerical accuracy for smooth problems and do not introduce additional oscillations in discontinuous problems.展开更多
A Constrained Interpolation Profile （CIP）-based model is developed to predict the mooring force of a two-dimensional floating oil storage tank under wave conditions, which is validated against to a newly performed e...A Constrained Interpolation Profile （CIP）-based model is developed to predict the mooring force of a two-dimensional floating oil storage tank under wave conditions, which is validated against to a newly performed experiment. In the experiment, a box-shaped floating oil storage apparatus is used. Computations are performed by an improved CIP-based Cartesian grid model, in which the THINC/SW scheme （THINC： tangent of hyperbola for interface capturing; SW： Slope Weighting）, is used for interface capturing. A multiphase flow solver is adopted to treat the water-air-body interactions. The Immersed Boundary Method （IBM） is implemented to treat the body surface. Main attention is paid to the sum force of mooring line and velocity field around the body. It is found that the sum force of the mooring line increases with increasing wave amplitude. The body suffers from water wave impact and large body motions occur near the free surface. The vortex occurs near the sharp edge, i.e., the sharp bottom comers of the float- ing oil storage tank and the vortex shedding can be captured by the present numerical model. The present model could be further improved by including turbulence model which is currently under development. Comparison between the computational mooring forces and the measured mooring forces is presented with a reasonable agreement. The developed numerical model can predict the mooring line forces very well.展开更多
The numerical quadrature methods for dealing with the problems of singular and near-singular integrals caused by Burton-Miller method are proposed, by which the conventional and fast multipole BEMs （boundary element ...The numerical quadrature methods for dealing with the problems of singular and near-singular integrals caused by Burton-Miller method are proposed, by which the conventional and fast multipole BEMs （boundary element methods） for 3D acoustic problems based on constant elements are improved. To solve the problem of singular integrals, a Hadamard finite-part integral method is presented, which is a simplified combination of the methods proposed by Kirkup and Wolf. The problem of near-singular integrals is overcome by the simple method of polar transformation and the more complex method of PART （Projection and Angular ＆ Radial Transformation）. The effectiveness of these methods for solving the singular and near-singular problems is validated through comparing with the results computed by the analytical method and/or the commercial software LMS Virtual.Lab. In addition, the influence of the near-singular integral problem on the computational precisions is analyzed by computing the errors relative to the exact solution. The computational complexities of the conventional and fast multipole BEM are analyzed and compared through numerical computations. A large-scale acoustic scattering problem, whose degree of freedoms is about 340,000, is implemented successfully. The results show that, the near singularity is primarily introduced by the hyper-singular kernel, and has great influences on the precision of the solution. The precision of fast multipole BEM is the same as conventional BEM, but the computational complexities are much lower.展开更多
This work deals with the numerical localization of small electromagnetic inhomogeneities. The underlying inverse problem considers, in a three-dimensional bounded domain, the time-harmonic Maxwell equations formulated...This work deals with the numerical localization of small electromagnetic inhomogeneities. The underlying inverse problem considers, in a three-dimensional bounded domain, the time-harmonic Maxwell equations formulated in electric field. Typically, the domain contains a finite number of unknown inhomogeneities of small volume and the inverse problem attempts to localize these inhomogeneities from a finite number of boundary measurements. Our localization approach is based on a recent framework that uses an asymptotic expansion for the perturbations in the tangential boundary trace of the curl of the electric field. We present three numerical localization procedures resulting from the combination of this asymptotic expansion with each of the following inversion algorithms： the Current Projection method, the MUltiple Signal Classification （MUSIC） algorithm, and an Inverse Fourier method. We perform a numerical study of the asymptotic expansion and compare the numerical results obtained from the three localization procedures in different settings.展开更多
Imposing appropriate numerical boundary conditions at the symmetrical center r=0 is vital when computing compressible fluids with radial symmetry.Extrapolation and other traditional techniques are often employed,but s...Imposing appropriate numerical boundary conditions at the symmetrical center r=0 is vital when computing compressible fluids with radial symmetry.Extrapolation and other traditional techniques are often employed,but spurious numerical oscillations or wall-heating phenomena can occur.In this paper,we emphasize that because of the conservation property,the updating formula of the boundary cell average can coincide with the one for interior cell averages.To achieve second-order accuracy both in time and space,we associate obtaining the inner boundary value at r=0 with the resolution of the corresponding one-sided generalized Riemann problem(GRP).Acoustic approximation is applied in this process.It creates conditions to avoid the singularity of type 1/r and aids in obtaining the value of the singular quantity using L’Hospital’s rule.Several challenging scenarios are tested to demonstrate the effectiveness and robustness of our approach.展开更多
A coupled numerical method for the direct numerical simulation of particle-fluid systems is formulated and implemented, resolving an order of magnitude smaller than particle size. The particle motion is described by t...A coupled numerical method for the direct numerical simulation of particle-fluid systems is formulated and implemented, resolving an order of magnitude smaller than particle size. The particle motion is described by the time-driven hard-sphere model, while the hydrodynamic equations governing fluid flow are solved by the lattice Boltzmann method （LBM）, Particle-fluid coupling is realized by an immersed boundary method （IBM）, which considers the effect of boundary on surrounding fluid as a restoring force added to the governing equations of the fluid. The proposed scheme is validated in the classical flow-around-cylinder simulations, and preliminary application of this scheme to fluidization is reported, demonstrating it to be a promising computational strategy for better understanding complex behavior in particle-fluid systems.展开更多
In this paper the velocity field and water level height of two- dimensional unsteady flow in open channel with double-line bridge are modelled with finite difference method of alternate direction.The ADI method is mod...In this paper the velocity field and water level height of two- dimensional unsteady flow in open channel with double-line bridge are modelled with finite difference method of alternate direction.The ADI method is modified according to the rapidly changed speed of the flow.Since empirical formulas are reasonably chosen at the inner-boundary,the calculating steadiness is increased and the calculating results improved. These are closer to real data.展开更多
The lattice Boltzmann method （LBM） has gained increasing popularity in the last two decades as an alternative numerical approach for solving fluid flow problems. One of the most active research areas in the LBM is i...The lattice Boltzmann method （LBM） has gained increasing popularity in the last two decades as an alternative numerical approach for solving fluid flow problems. One of the most active research areas in the LBM is its application in particle-fluid systems, where the advantage of the LBM in efficiency and parallel scalability has made it superior to many other direct numerical simulation （DNS） techniques. This article intends to provide a brief review of the application of the LBM in particle-fluid systems. The numerical techniques in the LBM pertaining to simulations of particles are discussed, with emphasis on the advanced treatment for boundary conditions on the particle-fluid interface. Other numerical issues, such as the effect of the internal fluid, are also briefly described. Additionally, recent efforts in using the LBM to obtain closures for particle-fluid drag force are also reviewed.展开更多
基金the National Natural Science Foundation of China and the Laboratory of Scientific and Engineering Computing of the Institute of
文摘Focuses on a study on the fully implicit Crank Nicholson (CN) schemes and three projection methods for approximate preservation of component-consistency under projection. Transformation from incompressible Navier-Stokes equations to differential algebraic equations CN schemes; Local errors of CN projection methods; Numerical boundary conditions.
基金supported by the National Natural Science Foundation of China(Grant No.51375259 and Grant No.51705280)the Ministry of Science and Technology of China(Grant No.2012ZX04012-011)+1 种基金Special Program for Applied Research on Super Computation of the NSFC-Guangdong Joint Fund(the second phase,Grant No.U1501501)the Tsinghua National Laboratory for Information Science and Technology
文摘Numerical simulation based on computational fluid dynamics （CFD） is a useful approach for quantitatively investigating the underlying thermal-mechanical conditions during FSW, such as temperature field and material deformation field. One of the critical issues in CFD simulation of FSW is the use of the frictional boundary condition, which represents the friction between the welding tool and the workpiece in the numerical models. In this study, three-dimensional numerical simulation is conducted to analyze the heat transfer and plastic deformation behaviors during the FSW of AA2024. For comparison purposes, both the boundary velocity （BV） models and the boundary shear stress （BSS） models are employed in order to assess their performances in predicting the temperature and material deformation in FSW. It is interesting to note that different boundary conditions yield similar predictions on temperature, but quite different predictions on material deformation. The numerical predictions are compared with the experimental results. The predicted deformation zone geometry by the BSS model is consistent with the experimental results while there is large difference between the predictions by the BV models and the experimental measurements. The fact that the BSS model yields more reasonable predictions on the deformation zone geometry is attributed to its capacity to automatically adjust the contact state at the tool/workpiece interface. Based on the favorable predictions on both the temperature field and the material deformation field, the BSS model is suggested to have a better performance in numerical simulation of FSW than the BV model.
基金supported by the National Natural Science Foundation of China(Nos.11372140 and11202102)the Innovation Project for College Graduates of Jiangsu Province(No.CXZZ13-0189)
文摘The evolution of two spanwise-aligned low-speed streaks in a wall turbulent flow, triggered by the instability of the subharmonic varicose （SV） mode, is studied by a direct numerical simulation （DNS） method in a small spatial-periodic channel. The results show that the SV low-speed streaks are self-sustained at the early stage, and then transform into subharmonic sinuous （SS） low-speed streaks. Initially, the streamwise vortex sheets are formed by shearing, and then evolve into zigzag vortex sheets due to the mutual induction. As the intensification of the SV low-speed streaks becomes prominent, the tilted streamwise vortex tubes and the V-like streamwise vortex tubes can be formed simultaneously by increasing ＋~. When the SV low-speed streaks break down, new zigzag streamwise vortices will be generated, thus giving birth to the next sustaining cycle of the SV low-speed streaks. When the second breakdown happens, new secondary V-like streamwise vortices instead of zigzag streamwise vortices will be generated. Because of the sweep motion of the fluid induced by the secondary V-like streamwise vortices, each decayed low-speed streak can be divided into two parts, and each part combines with the part of another streak, finally leading to the formation of SS low-speed streaks.
文摘The aim of the present paper is to study the numerical solutions of the steady MHD two dimensional stagnation point flow of an incompressible nano fluid towards a stretching cylinder.The effects of radiation and convective boundary condition are also taken into account.The model used for the nanofluid incorporates the effects of Brownian motion and thermophoresis.The resulting nonlinear momentum,energy and nano particle equations are simplifed using similarity transformations.Numerical solutions have been obtained for the velocity,temperature and nanoparticle fraction profles.The influence of physical parameters on the velocity,temperature,nanoparticle fraction,rates of heat transfer and nanoparticle fraction are shown graphically.
基金Financial support for this work, provided by the National Natural Science Foundation of China (Nos. 41072031, 40172119)the Natural Science Foundation of Hebei Province of China(No. D2012402008)
文摘Based on water inrush accident of 1841 working face of Desheng Coal Mine in Wu'an, Hebei province, China, an evaluation model of hydrodynamic characteristics of the project is set up and simulated using Matlab. It is assumed that the pipe flow would transform into seepage flow when the aggregates are plugged into the water inrush channel and the seepage flow would disappear along with grouting process. The simulation results show that the flow velocity will increase with an increase in height of aggregates accumulation body during the aggregates filling process; the maximum seepage velocity occurs on the top of plugging zone; and the water flow decreases with increasing plugging height of water inrush channel. Finally, the field construction results show that the water inrush channel can be plugged effectively by the compacted body prepared with aggregate and cement slurry.
基金supported by the National Natural Science Foundation of China (No. 41130418)the Strategic Leading Science and Technology Programme (Class B) of the Chinese Academy of Sciences (No. XDB10010400)
文摘Earth medium is not completely elastic, with its viscosity resulting in attenuation and dispersion of seismic waves. Most viscoelastic numerical simulations are based on the finite-difference and finite-element methods. Targeted at viscoelastic numerical modeling for multilayered media, the constant-Q acoustic wave equation is transformed into the corresponding wave integral representation with its Green＇s function accounting for viscoelastic coefficients. An efficient alternative for full-waveform solution to the integral equation is proposed in this article by extending conventional frequency-domain boundary element methods to viscoelastic media. The viscoelastic boundary element method enjoys a distinct characteristic of the explicit use of boundary continuity conditions of displacement and traction, leading to a semi-analytical solution with sufficient accuracy for simulating the viscoelastic effect across irregular interfaces. Numerical experiments to study the viscoelastic absorption of different Q values demonstrate the accuracy and applicability of the method.
基金Supported by the National Natural Science Foundation of China(11571211,11301318,11171197,11471200)Supported by the Fundamental Research Funds for the Central Universities(GK201301007)
文摘In this note, some properties of the interior of numerical ranges of operators are established, and an alternative proof of Embry's theorem associated with the interior of a numerical ranges of an operator is given(see [3]).
文摘This study deals with the stagnation point flow of ferrofluid over a flat plate with non-linear slip boundary condition in the presence of homogeneous-heterogeneous reactions.Three kinds of ferroparticles,namely,magnetite(Fe_3O_4),cobalt ferrite(CoFe_2O_4) and manganese zinc ferrite(Mn-ZnFe_2O_4) are taken into account with water and kerosene as conventional base fluids.The developed model of homogeneous-heterogeneous reactions in boundary layer flow with equal and unequal diffusivities for reactant and autocatalysis is considered.The governing partial differential equations are converted into system of non-linear ordinary differential equations by mean of similarity transformations.These ordinary differential equations are integrated numerically using shooting method.The effects of pertinent parameters on velocity and concentration profiles are presented graphically and discussed.We found that in the presence of Fe_3O_4-kerosene and CoFe_2O_4-kerosene,velocity profiles increase for large values of α and β whereas there is a decrement in concentration profiles with increasing values of if and K_s.Furthermore,the comparison between non-magnetic(A1_2O_3) and magnetic Fe_3O_4 nanoparticles is given in tabular form.
基金supported in part by the NSFC Grant 12271499supported in part by the R&D project of Pazhou Lab(Huangpu)under Grant 2023K0609 and the NSFC Grant 12126604.
文摘In this paper,we concentrate on high-order boundary treatments for finite volume methods solving hyperbolic conservation laws.The complex geometric physical domain is covered by a Cartesian mesh,resulting in the boundary intersecting the grids in various fashions.We propose two approaches to evaluate the cell averages on the ghost cells near the boundary.Both of them start from the inverse Lax-Wendroff(ILW)procedure,in which the normal spatial derivatives at inflow boundaries can be obtained by repeatedly using the governing equations and boundary conditions.After that,we can get an accurate evaluation of the ghost cell average by a Taylor expansion joined with high-order extrapolation,or by a Hermite extrapolation coupling with the cell averages on some“artificial”inner cells.The stability analysis is provided for both schemes,indicating that they can avoid the so-called“small-cell”problem.Moreover,the second method is more efficient under the premise of accuracy and stability.We perform numerical experiments on a collection of examples with the physical boundary not aligned with the grids and with various boundary conditions,indicating the high-order accuracy and efficiency of the proposed schemes.
基金supported in part by the NSFC Grant 12271499the Cyrus Tang Foundation.Research is supported in part by the NSF Grant DMS-2309249supported in part by the NSFC Grant 12126604.
文摘In this paper,we propose a new class of discontinuous Galerkin(DG)methods for solving 1D conservation laws on unfitted meshes.The standard DG method is used in the interior cells.For the small cut elements around the boundaries,we directly design approximation polynomials based on inverse Lax-Wendroff(ILW)principles for the inflow boundary conditions and introduce the post-processing to preserve the local conservation properties of the DG method.The theoretical analysis shows that our proposed methods have the same stability and numerical accuracy as the standard DG method in the inner region.An additional nonlinear limiter is designed to prevent spurious oscillations if a shock is near the boundary.Numerical results indicate that our methods achieve optimal numerical accuracy for smooth problems and do not introduce additional oscillations in discontinuous problems.
基金supported by the National Natural Science Foundation of China (51209184,51279186,51479175)
文摘A Constrained Interpolation Profile （CIP）-based model is developed to predict the mooring force of a two-dimensional floating oil storage tank under wave conditions, which is validated against to a newly performed experiment. In the experiment, a box-shaped floating oil storage apparatus is used. Computations are performed by an improved CIP-based Cartesian grid model, in which the THINC/SW scheme （THINC： tangent of hyperbola for interface capturing; SW： Slope Weighting）, is used for interface capturing. A multiphase flow solver is adopted to treat the water-air-body interactions. The Immersed Boundary Method （IBM） is implemented to treat the body surface. Main attention is paid to the sum force of mooring line and velocity field around the body. It is found that the sum force of the mooring line increases with increasing wave amplitude. The body suffers from water wave impact and large body motions occur near the free surface. The vortex occurs near the sharp edge, i.e., the sharp bottom comers of the float- ing oil storage tank and the vortex shedding can be captured by the present numerical model. The present model could be further improved by including turbulence model which is currently under development. Comparison between the computational mooring forces and the measured mooring forces is presented with a reasonable agreement. The developed numerical model can predict the mooring line forces very well.
基金supported by the National Natural Science Foundation of China(11304344,11404364)the Project of Hubei Provincial Department of Education(D20141803)+1 种基金the Natural Science Foundation of Hubei Province(2014CFB378)the Doctoral Scientific Research Foundation of Hubei University of Automotive Technology(BK201604)
文摘The numerical quadrature methods for dealing with the problems of singular and near-singular integrals caused by Burton-Miller method are proposed, by which the conventional and fast multipole BEMs （boundary element methods） for 3D acoustic problems based on constant elements are improved. To solve the problem of singular integrals, a Hadamard finite-part integral method is presented, which is a simplified combination of the methods proposed by Kirkup and Wolf. The problem of near-singular integrals is overcome by the simple method of polar transformation and the more complex method of PART （Projection and Angular ＆ Radial Transformation）. The effectiveness of these methods for solving the singular and near-singular problems is validated through comparing with the results computed by the analytical method and/or the commercial software LMS Virtual.Lab. In addition, the influence of the near-singular integral problem on the computational precisions is analyzed by computing the errors relative to the exact solution. The computational complexities of the conventional and fast multipole BEM are analyzed and compared through numerical computations. A large-scale acoustic scattering problem, whose degree of freedoms is about 340,000, is implemented successfully. The results show that, the near singularity is primarily introduced by the hyper-singular kernel, and has great influences on the precision of the solution. The precision of fast multipole BEM is the same as conventional BEM, but the computational complexities are much lower.
基金supported by ACI NIM (171) from the French Ministry of Education and Scientific Research
文摘This work deals with the numerical localization of small electromagnetic inhomogeneities. The underlying inverse problem considers, in a three-dimensional bounded domain, the time-harmonic Maxwell equations formulated in electric field. Typically, the domain contains a finite number of unknown inhomogeneities of small volume and the inverse problem attempts to localize these inhomogeneities from a finite number of boundary measurements. Our localization approach is based on a recent framework that uses an asymptotic expansion for the perturbations in the tangential boundary trace of the curl of the electric field. We present three numerical localization procedures resulting from the combination of this asymptotic expansion with each of the following inversion algorithms： the Current Projection method, the MUltiple Signal Classification （MUSIC） algorithm, and an Inverse Fourier method. We perform a numerical study of the asymptotic expansion and compare the numerical results obtained from the three localization procedures in different settings.
基金This work was partially supported by Science Challenge project TZ2016002NSFC with Nos.11771055,11671050,11871113,11871114,12026607,121710493D numerical simulation platform TB14-1 of the China Academy of Engineering Physics.
文摘Imposing appropriate numerical boundary conditions at the symmetrical center r=0 is vital when computing compressible fluids with radial symmetry.Extrapolation and other traditional techniques are often employed,but spurious numerical oscillations or wall-heating phenomena can occur.In this paper,we emphasize that because of the conservation property,the updating formula of the boundary cell average can coincide with the one for interior cell averages.To achieve second-order accuracy both in time and space,we associate obtaining the inner boundary value at r=0 with the resolution of the corresponding one-sided generalized Riemann problem(GRP).Acoustic approximation is applied in this process.It creates conditions to avoid the singularity of type 1/r and aids in obtaining the value of the singular quantity using L’Hospital’s rule.Several challenging scenarios are tested to demonstrate the effectiveness and robustness of our approach.
基金sponsored by Ministry of Finance under the grant ZDYZ2008-2National Key Science and Technology Project under the grant 2008ZX05014-003-006HZthe Chinese Academy of Sciences under the grant KGCX2-YW-124
文摘A coupled numerical method for the direct numerical simulation of particle-fluid systems is formulated and implemented, resolving an order of magnitude smaller than particle size. The particle motion is described by the time-driven hard-sphere model, while the hydrodynamic equations governing fluid flow are solved by the lattice Boltzmann method （LBM）, Particle-fluid coupling is realized by an immersed boundary method （IBM）, which considers the effect of boundary on surrounding fluid as a restoring force added to the governing equations of the fluid. The proposed scheme is validated in the classical flow-around-cylinder simulations, and preliminary application of this scheme to fluidization is reported, demonstrating it to be a promising computational strategy for better understanding complex behavior in particle-fluid systems.
文摘In this paper the velocity field and water level height of two- dimensional unsteady flow in open channel with double-line bridge are modelled with finite difference method of alternate direction.The ADI method is modified according to the rapidly changed speed of the flow.Since empirical formulas are reasonably chosen at the inner-boundary,the calculating steadiness is increased and the calculating results improved. These are closer to real data.
文摘The lattice Boltzmann method （LBM） has gained increasing popularity in the last two decades as an alternative numerical approach for solving fluid flow problems. One of the most active research areas in the LBM is its application in particle-fluid systems, where the advantage of the LBM in efficiency and parallel scalability has made it superior to many other direct numerical simulation （DNS） techniques. This article intends to provide a brief review of the application of the LBM in particle-fluid systems. The numerical techniques in the LBM pertaining to simulations of particles are discussed, with emphasis on the advanced treatment for boundary conditions on the particle-fluid interface. Other numerical issues, such as the effect of the internal fluid, are also briefly described. Additionally, recent efforts in using the LBM to obtain closures for particle-fluid drag force are also reviewed.
