共查询到20条相似文献,搜索用时 31 毫秒
1.
A Normal Mode Stability Analysis of Numerical Interface Conditions for Fluid/Structure Interaction
下载免费PDF全文
![点击此处可从《Communications In Computational Physics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
In multi-physics computations where a compressible fluid is coupled with
a linearly elastic solid, it is standard to enforce continuity of the normal velocities and
of the normal stresses at the interface between the fluid and the solid. In a numerical
scheme, there are many ways that velocity- and stress-continuity can be enforced in
the discrete approximation. This paper performs a normal mode stability analysis of
the linearized problem to investigate the stability of different numerical interface conditions
for a model problem approximated by upwind type finite difference schemes.
The analysis shows that depending on the ratio of densities between the solid and
the fluid, some numerical interface conditions are stable up to the maximal CFL-limit,
while other numerical interface conditions suffer from a severe reduction of the stable
CFL-limit. The paper also presents a new interface condition, obtained as a simplified
characteristic boundary condition, that is proved to not suffer from any reduction of
the stable CFL-limit. Numerical experiments in one space dimension show that the
new interface condition is stable also for computations with the non-linear Euler equations
of compressible fluid flow coupled with a linearly elastic solid. 相似文献
2.
An Edge-Based Smoothed Finite Element Method with TBC for the Elastic Wave Scattering by an Obstacle
下载免费PDF全文
![点击此处可从《Communications In Computational Physics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Ze Wu Junhong Yue Ming Li Ruiping Niu & Yufei Zhang 《Communications In Computational Physics》2021,30(3):709-748
Elastic wave scattering has received ever-increasing attention in military and medical fields due to its high-precision solution. In this paper, an edge-based smoothed finite element method (ES-FEM) combined with the transparent boundary condition (TBC) is proposed to solve the elastic wave scattering problem by a rigid obstacle with smooth surface, which is embedded in an isotropic and homogeneous elastic medium in two dimensions. The elastic wave scattering problem satisfies Helmholtz equations with coupled boundary conditions obtained by Helmholtz decomposition. Firstly, the TBC of the elastic wave scattering is constructed by using the analytical solution to Helmholtz equations, which can truncate the boundary value problem (BVP) in an unbounded domain into the BVP in a bounded domain. Then the formulations of ES-FEM with the TBC are derived for Helmholtz equations with coupled boundary conditions. Finally, several numerical examples illustrate that the proposed ES-FEM with the TBC (ES-FEM-TBC) can work effectively and obtain more stable and accurate solution than the standard FEM with the TBC (FEM-TBC) for the elastic wave scattering problem. 相似文献
3.
N. Anders Petersson & Bj& ouml rn Sj& ouml green 《Communications In Computational Physics》2014,16(4):913-955
We develop a super-grid modeling technique for solving the elastic wave
equation in semi-bounded two- and three-dimensional spatial domains. In this method,
waves are slowed down and dissipated in sponge layers near the far-field boundaries.
Mathematically, this is equivalent to a coordinate mapping that transforms a very large
physical domain to a significantly smaller computational domain, where the elastic
wave equation is solved numerically on a regular grid. To damp out waves that become poorly resolved because of the coordinate mapping, a high order artificial dissipation operator is added in layers near the boundaries of the computational domain.
We prove by energy estimates that the super-grid modeling leads to a stable numerical
method with decreasing energy, which is valid for heterogeneous material properties
and a free surface boundary condition on one side of the domain. Our spatial discretization is based on a fourth order accurate finite difference method, which satisfies
the principle of summation by parts. We show that the discrete energy estimate holds
also when a centered finite difference stencil is combined with homogeneous Dirichlet conditions at several ghost points outside of the far-field boundaries. Therefore,
the coefficients in the finite difference stencils need only be boundary modified near
the free surface. This allows for improved computational efficiency and significant
simplifications of the implementation of the proposed method in multi-dimensional
domains. Numerical experiments in three space dimensions show that the modeling
error from truncating the domain can be made very small by choosing a sufficiently
wide super-grid damping layer. The numerical accuracy is first evaluated against analytical solutions of Lamb's problem, where fourth order accuracy is observed with
a sixth order artificial dissipation. We then use successive grid refinements to study
the numerical accuracy in the more complicated motion due to a point moment tensor
source in a regularized layered material. 相似文献
4.
Operator Factorization for Multiple-Scattering Problems and an Application to Periodic Media
下载免费PDF全文
![点击此处可从《Communications In Computational Physics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
This work concerns multiple-scattering problems for time-harmonic equations in a reference generic media. We consider scatterers that can be sources, obstacles
or compact perturbations of the reference media. Our aim is to restrict the computational domain to small compact domains containing the scatterers. We use Robin-to-Robin (RtR) operators (in the most general case) to express boundary conditions for
the interior problem. We show that one can always factorize the RtR map using only
operators defined using single-scatterer problems. This factorization is based on a decomposition of the diffracted field, on the whole domain where it is defined. Assuming
that there exists a good method for solving single-scatterer problems, it then gives a
convenient way to compute RtR maps for a random number of scatterers. 相似文献
5.
Jiwei Zhang Zhizhong Sun Xiaonan Wu & Desheng Wang 《Communications In Computational Physics》2011,10(3):742-766
The paper is concerned with the numerical solution of Schrödinger equations
on an unbounded spatial domain. High-order absorbing boundary conditions
for one-dimensional domain are derived, and the stability of the reduced initial boundary
value problem in the computational interval is proved by energy estimate. Then a
second order finite difference scheme is proposed, and the convergence of the scheme
is established as well. Finally, numerical examples are reported to confirm our error
estimates of the numerical methods. 相似文献
6.
Application of the LS-STAG Immersed Boundary/ Cut-Cell Method to Viscoelastic Flow Computations
下载免费PDF全文
![点击此处可从《Communications In Computational Physics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Olivier Botella Yoann Cheny Farhad Nikfarjam & Marcela Stoica 《Communications In Computational Physics》2016,20(4):870-901
This paper presents the extension of a well-established Immersed Boundary
(IB)/cut-cell method, the LS-STAG method (Y. Cheny & O. Botella, J. Comput. Phys.
Vol. 229, 1043-1076, 2010), to viscoelastic flow computations in complex geometries.
We recall that for Newtonian flows, the LS-STAG method is based on the finite-volume
method on staggered grids, where the IB boundary is represented by its level-set function.
The discretization in the cut-cells is achieved by requiring that global conservation
properties equations be satisfied at the discrete level, resulting in a stable and
accurate method and, thanks to the level-set representation of the IB boundary, at low
computational costs.In the present work, we consider a general viscoelastic tensorial equation whose particular
cases recover well-known constitutive laws such as the Oldroyd-B, White-Metzner
and Giesekus models. Based on the LS-STAG discretization of the Newtonian stresses
in the cut-cells, we have achieved a compatible velocity-pressure-stress discretization
that prevents spurious oscillations of the stress tensor. Applications to popular benchmarks
for viscoelastic fluids are presented: the four-to-one abrupt planar contraction
flows with sharp and rounded re-entrant corners, for which experimental and numerical
results are available. The results show that the LS-STAG method demonstrates an
accuracy and robustness comparable to body-fitted methods. 相似文献
7.
This work proposes a generalized boundary integral method for variable coefficients
elliptic partial differential equations (PDEs), including both boundary value
and interface problems. The method is kernel-free in the sense that there is no need
to know analytical expressions for kernels of the boundary and volume integrals in
the solution of boundary integral equations. Evaluation of a boundary or volume integral
is replaced with interpolation of a Cartesian grid based solution, which satisfies
an equivalent discrete interface problem, while the interface problem is solved by a
fast solver in the Cartesian grid. The computational work involved with the generalized
boundary integral method is essentially linearly proportional to the number
of grid nodes in the domain. This paper gives implementation details for a second-order
version of the kernel-free boundary integral method in two space dimensions
and presents numerical experiments to demonstrate the efficiency and accuracy of
the method for both boundary value and interface problems. The interface problems
demonstrated include those with piecewise constant and large-ratio coefficients and
the heterogeneous interface problem, where the elliptic PDEs on two sides of the interface
are of different types. 相似文献
8.
Leopold Grinberg & George Em Karniadakis 《Communications In Computational Physics》2008,4(5):1151-1169
Ultra-parallel flow simulations on hundreds of thousands of processors require new multi-level domain decomposition methods. Here we present such a new
two-level method that has features both of discontinuous and continuous Galerkin
formulations. Specifically, at the coarse level the domain is subdivided into several
big patches and within each patch a spectral element discretization (fine level) is employed. New interface conditions for the Navier-Stokes equations are developed to
connect the patches, relaxing the C0continuity and minimizing data transfer at the
patch interface. We perform several 3D flow simulations of a benchmark problem and
of arterial flows to evaluate the performance of the new method and investigate its
accuracy. 相似文献
9.
Igor Kliakhandler & Alexander Kurganov 《Communications In Computational Physics》2009,6(4):743-757
We present a simple and efficient strategy for the acceleration of explicit Eulerian
methods for multidimensional hyperbolic systems of conservation laws. The
strategy is based on the Galilean invariance of dynamic equations and optimization of
the reference frame, in which the equations are numerically solved. The optimal reference
frame moves (locally in time) with the average characteristic speed of the system,
and, in this sense, the resulting method is quasi-Lagrangian. This leads to the acceleration
of the numerical computations thanks to the optimal CFL condition and automatic
adjustment of the computational domain to the evolving part of the solution. We show
that our quasi-Lagrangian acceleration procedure may also reduce the numerical dissipation
of the underlying Eulerian method. This leads to a significantly enhanced
resolution, especially in the supersonic case. We demonstrate a great potential of the
proposed method on a number of numerical examples. 相似文献
10.
Numerical Simulation of Compressible Vortical Flows Using a Conservative Unstructured-Grid Adaptive Scheme
下载免费PDF全文
![点击此处可从《Communications In Computational Physics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Giuseppe Forestieri Alberto Guardone Dario Isola Filippo Marulli & Giuseppe Quaranta 《Communications In Computational Physics》2012,12(3):866-884
A two-dimensional numerical scheme for the compressible Euler equations
is presented and applied here to the simulation of exemplary compressible vortical
flows. The proposed approach allows to perform computations on unstructured moving grids with adaptation, which is required to capture complex features of the flow-field. Grid adaptation is driven by suitable error indicators based on the Mach number
and by element-quality constraints as well. At the new time level, the computational
grid is obtained by a suitable combination of grid smoothing, edge-swapping, grid
refinement and de-refinement. The grid modifications—including topology modification due to edge-swapping or the insertion/deletion of a new grid node—are interpreted at the flow solver level as continuous (in time) deformations of suitably-defined
node-centered finite volumes. The solution over the new grid is obtained without explicitly resorting to interpolation techniques, since the definition of suitable interface
velocities allows one to determine the new solution by simple integration of the Arbitrary Lagrangian-Eulerian formulation of the flow equations. Numerical simulations
of the steady oblique-shock problem, of the steady transonic flow and of the start-up
unsteady flow around the NACA 0012 airfoil are presented to assess the scheme capabilities to describe these flows accurately. 相似文献
11.
Benchmark Computations of the Phase Field Crystal and Functionalized Cahn-Hilliard Equations via Fully Implicit,Nesterov Accelerated Schemes
下载免费PDF全文
![点击此处可从《Communications In Computational Physics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Jea-Hyun Park Abner J. Salgado & Steven M. Wise 《Communications In Computational Physics》2023,33(2):367-398
We introduce a fast solver for the phase field crystal (PFC) and functionalized Cahn-Hilliard (FCH) equations with periodic boundary conditions on a rectangular domain that features the preconditioned Nesterov’s accelerated gradient descent
(PAGD) method. We discretize these problems with a Fourier collocation method
in space, and employ various second-order schemes in time. We observe a significant speedup with this solver when compared to the preconditioned gradient descent
(PGD) method. With the PAGD solver, fully implicit, second-order-in-time schemes
are not only feasible to solve the PFC and FCH equations, but also do so more efficiently than some semi-implicit schemes in some cases where accuracy issues are
taken into account. Benchmark computations of four different schemes for the PFC
and FCH equations are conducted and the results indicate that, for the FCH experiments, the fully implicit schemes (midpoint rule and BDF2 equipped with the PAGD
as a nonlinear time marching solver) perform better than their IMEX versions in terms
of computational cost needed to achieve a certain precision. For the PFC, the results
are not as conclusive as in the FCH experiments, which, we believe, is due to the fact
that the nonlinearity in the PFC is milder nature compared to the FCH equation. We
also discuss some practical matters in applying the PAGD. We introduce an averaged
Newton preconditioner and a sweeping-friction strategy as heuristic ways to choose good
preconditioner parameters. The sweeping-friction strategy exhibits almost as good
a performance as the case of the best manually tuned parameters. 相似文献
12.
José A. Carrillo Alina Chertock & Yanghong Huang 《Communications In Computational Physics》2015,17(1):233-258
We propose a positivity preserving entropy decreasing finite volume scheme
for nonlinear nonlocal equations with a gradient flow structure. These properties allow
for accurate computations of stationary states and long-time asymptotics demonstrated
by suitably chosen test cases in which these features of the scheme are essential.
The proposed scheme is able to cope with non-smooth stationary states, different time
scales including metastability, as well as concentrations and self-similar behavior induced
by singular nonlocal kernels. We use the scheme to explore properties of these
equations beyond their present theoretical knowledge. 相似文献
13.
Source-Independent Amplitude-Semblance Full-Waveform Inversion Using a Hybrid Time- and Frequency-Domain Approach
下载免费PDF全文
![点击此处可从《Communications In Computational Physics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Benxin Chi & Lianjie Huang 《Communications In Computational Physics》2020,28(1):328-341
Full-waveform inversion is a promising tool to produce accurate and high-resolution subsurface models. Conventional full-waveform inversion requires an accurate estimation of the source wavelet, and its computational cost is high. We develop a
novel source-independent full-waveform inversion method using a hybrid time- and
frequency-domain scheme to avoid the requirement of source wavelet estimation and
to reduce the computational cost. We employ an amplitude-semblance objective function to not only effectively remove the source wavelet effect on full-waveform inversion, but also to eliminate the impact of the inconsistency of source wavelets among
different shots gathers on full-waveform inversion. To reduce the high computational
cost of full-waveform inversion in the time domain, we implement our new algorithm
using a hybrid time- and frequency-domain approach. The forward and backward
wave propagation operations are conducted in the time domain, while the frequency-domain wavefields are obtained during modeling using the discrete-time Fourier transform. The inversion process is conducted in the frequency domain for selected frequencies. We verify our method using synthetic seismic data for the Marmousi model. The
results demonstrate that our novel source-independent full-waveform inversion produces accurate velocity models even if the source signature is incorrect. In addition,
our method can significantly reduce the computational time using the hybrid time- and frequency-domain approach compared to the conventional full-waveform inversion in the time domain. 相似文献
14.
Three-Dimensional Lattice Boltzmann Flux Solver and Its Applications to Incompressible Isothermal and Thermal Flows
下载免费PDF全文
![点击此处可从《Communications In Computational Physics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Yan Wang Chang Shu Chiang Juay Teo Jie Wu & Liming Yang 《Communications In Computational Physics》2015,18(3):593-620
A three-dimensional (3D) lattice Boltzmann flux solver (LBFS) is presented
in this paper for the simulation of both isothermal and thermal flows. The present
solver combines the advantages of conventional Navier-Stokes (N-S) solvers and lattice
Boltzmann equation (LBE) solvers. It applies the finite volume method (FVM) to
solve the N-S equations. Different from the conventional N-S solvers, its viscous and
inviscid fluxes at the cell interface are evaluated simultaneously by local reconstruction
of LBE solution. As compared to the conventional LBE solvers, which apply the
lattice Boltzmann method (LBM) globally in the whole computational domain, it only
applies LBM locally at each cell interface, and flow variables at cell centers are given
from the solution of N-S equations. Since LBM is only applied locally in the 3D LBFS,
the drawbacks of the conventional LBM, such as limitation to uniform mesh, tie-up
of mesh spacing and time step, tedious implementation of boundary conditions, are
completely removed. The accuracy, efficiency and stability of the proposed solver are
examined in detail by simulating plane Poiseuille flow, lid-driven cavity flow and natural
convection. Numerical results show that the LBFS has a second order of accuracy
in space. The efficiency of the LBFS is lower than LBM on the same grids. However,
the LBFS needs very less non-uniform grids to get grid-independence results and its
efficiency can be greatly improved and even much higher than LBM. In addition, the
LBFS is more stable and robust. 相似文献
15.
Masashi Endo Martin Čuma & Michael S. Zhdanov 《Communications In Computational Physics》2009,6(2):269-289
We develop a new formulation of the integral equation (IE) method for
three-dimensional (3D) electromagnetic (EM) field computation in large-scale models
with multiple inhomogeneous domains. This problem arises in many practical applications
including modeling the EM fields within the complex geoelectrical structures
in geophysical exploration. In geophysical applications, it is difficult to describe an
earth structure using the horizontally layered background conductivity model, which
is required for the efficient implementation of the conventional IE approach. As a result,
a large domain of interest with anomalous conductivity distribution needs to be
discretized, which complicates the computations. The new method allows us to consider
multiple inhomogeneous domains, where the conductivity distribution is different
from that of the background, and to use independent discretizations for different
domains. This reduces dramatically the computational resources required for large-scale
modeling. In addition, using this method, we can analyze the response of each
domain separately without an inappropriate use of the superposition principle for the
EM field calculations. The method was carefully tested for the modeling the marine
controlled-source electromagnetic (MCSEM) fields for complex geoelectric structures
with multiple inhomogeneous domains, such as a seafloor with the rough bathymetry,
salt domes, and reservoirs. We have also used this technique to investigate the return
induction effects from regional geoelectrical structures, e.g., seafloor bathymetry and
salt domes, which can distort the EM response from the geophysical exploration target. 相似文献
16.
An Efficient Neural-Network and Finite-Difference Hybrid Method for Elliptic Interface Problems with Applications
下载免费PDF全文
![点击此处可从《Communications In Computational Physics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Wei-Fan Hu Te-Sheng Lin Yu-Hau Tseng & Ming-Chih Lai 《Communications In Computational Physics》2023,33(4):1090-1105
A new and efficient neural-network and finite-difference hybrid method is
developed for solving Poisson equation in a regular domain with jump discontinuities
on embedded irregular interfaces. Since the solution has low regularity across the interface, when applying finite difference discretization to this problem, an additional
treatment accounting for the jump discontinuities must be employed. Here, we aim to
elevate such an extra effort to ease our implementation by machine learning methodology. The key idea is to decompose the solution into singular and regular parts. The
neural network learning machinery incorporating the given jump conditions finds the
singular solution, while the standard five-point Laplacian discretization is used to obtain the regular solution with associated boundary conditions. Regardless of the interface geometry, these two tasks only require supervised learning for function approximation and a fast direct solver for Poisson equation, making the hybrid method easy
to implement and efficient. The two- and three-dimensional numerical results show
that the present hybrid method preserves second-order accuracy for the solution and
its derivatives, and it is comparable with the traditional immersed interface method in
the literature. As an application, we solve the Stokes equations with singular forces to
demonstrate the robustness of the present method. 相似文献
17.
A Computational Model for Simulation of Shallow Water Waves by Elastic Deformations in the Topography
下载免费PDF全文
![点击此处可从《Communications In Computational Physics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Alia Al-Ghosoun Ashraf S. Osman & Mohammed Seaid 《Communications In Computational Physics》2021,29(4):1095-1124
We propose a coupled model to simulate shallow water waves induced by
elastic deformations in the bed topography. The governing equations consist of the
depth-averaged shallow water equations including friction terms for the water free-surface and the well-known second-order elastostatics formulation for the bed deformation. The perturbation on the free-surface is assumed to be caused by a sudden
change in the bottom beds. At the interface between the water flow and the bed topography, transfer conditions are implemented. Here, the hydrostatic pressure and
friction forces are considered for the elastostatic equations whereas bathymetric forces
are accounted for in the shallow water equations. The focus in the present study is on
the development of a simple and accurate representation of the interaction between
water waves and bed deformations in order to simulate practical shallow water flows
without relying on complex partial differential equations with free boundary conditions. The effects of location and magnitude of the deformation on the flow fields and
free-surface waves are investigated in details. Numerical simulations are carried out
for several test examples on shallow water waves induced by sudden changes in the
bed. The proposed computational model has been found to be feasible and satisfactory. 相似文献
18.
Numerical Simulation of Unidirectional Stratified Flow by Moving Particle Semi-Implicit Method
下载免费PDF全文
![点击此处可从《Communications In Computational Physics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Shaoshan Rong Haiwang Li Martin Skote Teck Neng Wong & Fei Duan 《Communications In Computational Physics》2014,15(3):756-775
Numerical simulation of stratified flow of two fluids between two infinite
parallel plates using the Moving Particle Semi-implicit (MPS) method is presented.
The developing process from entrance to fully development flow is captured. In the
simulation, the computational domain is represented by various types of particles.
Governing equations are described based on particles and their interactions. Grids are
not necessary in any calculation steps of the simulation. The particle number density
is implicitly required to be constant to satisfy incompressibility. The weight function
is used to describe the interaction between different particles. The particle is considered to constitute the free interface if the particle number density is below a set point.
Results for various combinations of density, viscosity, mass flow rates, and distance
between the two parallel plates are presented. The proposed procedure is validated
using the derived exact solution and the earlier numerical results from the Level-Set
method. Furthermore, the evolution of the interface in the developing region is captured and compares well with the derived exact solutions in the developed region. 相似文献
19.
Joe Imae 《Optimal control applications & methods.》1998,19(5):299-313
In this paper we consider continuous-time unconstrained optimal control problems. We propose a computational method which is essentially based on the closed-loop solutions of the linear quadratic optimal control problems. In the proposed algorithm, Riccati differential equations play an important role. We prove that accumulation points generated by the present algorithm, if they exist, satisfy the weak necessary conditions for optimality, under some assumptions including Kalman's sufficient conditions for the bounded Riccati solutions. In addition, we also propose the simple but effective technique to guarantee the boundedness of the solutions of Riccati equations. Lastly, we illustrate the usefulness of the present algorithm through simulation experiences. Copyright © 1998 John Wiley & Sons, Ltd. 相似文献
20.
Claus Danielson 《Optimal control applications & methods.》2021,42(1):236-260
This article presents an alternating direction method of multipliers (ADMM) algorithm for solving large‐scale model predictive control (MPC) problems that are invariant under the symmetric‐group. Symmetry was used to find transformations of the inputs, states, and constraints of the MPC problem that decompose the dynamics and cost. We prove an important property of the symmetric decomposition for the symmetric‐group that allows us to efficiently transform between the original and decomposed symmetric domains. This allows us to solve different subproblems of a baseline ADMM algorithm in different domains where the computations are less expensive. This reduces the computational cost of each iteration from quadratic to linear in the number of repetitions in the system. In addition, we show that the memory complexity for our ADMM algorithm is also linear in number of repetitions in the system, rather than the typical quadratic complexity. We demonstrate our algorithm for two case studies; battery balancing and heating, ventilation, and air conditioning. In both case studies, the symmetric algorithm reduced the computation‐time from minutes to seconds and memory usage from tens of megabytes to tens or hundreds of kilobytes, allowing the previously nonviable MPCs to be implemented in real time on embedded computers with limited computational and memory resources. 相似文献