The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
Janko Logar - One of the best experts on this subject based on the ideXlab platform.
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Fully Coupled Solution for the consolidation of poroelastic soil around geosynthetic encased stone columns
Geotextiles and Geomembranes, 2017Co-Authors: Boštjan Pulko, Janko LogarAbstract:Abstract The paper presents an extension of a recently developed fully Coupled elastoplastic method (Pulko and Logar, 2016) for the analysis of a poroelastic thick-walled soil cylinder around an elastoplastic end-bearing stone column to account for the influence of an elastic geosynthetic encasement. The method was developed in the framework of Biot's consolidation theory (Biot, 1941) and is based on a unit cell concept, wherein the column encasement is modeled as a thin elastic membrane, which can only sustain tension and acts in the radial direction. Analytical closed-form expressions for excess pore pressures, stresses, strains, displacements and encasement forces were derived in the Laplace domain. The final elastoplastic Solution in time domain was obtained numerically by using efficient numerical scheme for the inverse Laplace transform. The validity of the Solution was checked against finite element analyses and compared with previously developed analytical methods. The results showing the influence of column encasement on transient state of settlements, strains, excess pore pressures and encasement forces under instantaneous or time dependent load are presented and discussed.
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Fully Coupled Solution for the consolidation of poroelastic soil around elastoplastic stone column
Acta Geotechnica, 2016Co-Authors: Boštjan Pulko, Janko LogarAbstract:The paper presents a new fully Coupled elastoplastic Solution for the response of a poroelastic thick-walled soil cylinder around an elastoplastic stone column using Biot’s (J Appl Phys 12:155–164, 1941) consolidation theory. A unit cell concept is adopted for the soil–stone column analysis, and the problem is formulated in cylindrical coordinates. Expressions for excess pore pressure, stresses and displacements in the Laplace domain are derived analytically taking into account elastic or plastic behavior of the column. The inverse of the Laplace transform is evaluated numerically using an efficient scheme to obtain the final elastoplastic Solution in time domain. The validity of the new Solution has been checked against finite element Solution and compared with some previously developed analytical methods for the stone column analysis. The results showing settlements, change in excess pore pressures and stresses with time are presented in terms of time factor. The proposed Solution can be used to calculate transient state of settlements, distribution of deformations, stresses and excess pore pressures in soil and column under instantaneous or time-dependent monotonically increasing rigid vertical load.
Matthias Heil - One of the best experts on this subject based on the ideXlab platform.
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an efficient solver for the fully Coupled Solution of large displacement fluid structure interaction problems
Computer Methods in Applied Mechanics and Engineering, 2004Co-Authors: Matthias HeilAbstract:This paper is concerned with the fully Coupled (‘monolithic’) Solution of large-displacement fluid–structure interaction problems by Newton’s method. We show that block-triangular approximations of the Jacobian matrix, obtained by neglecting selected fluid–structure interaction blocks, provide good preconditioners for the Solution of the linear systems with GMRES. We present an efficient approximate implementation of the preconditioners, based on a Schur complement approximation for the Navier–Stokes block and the use of multigrid approximations for the Solution of the computationally most expensive operations. The performance of the the preconditioners is examined in representative steady and unsteady simulations which show that the GMRES iteration counts only display a mild dependence on the Reynolds number and the mesh size. The final part of the paper demonstrates the importance of consistent stabilisation for the accurate simulation of fluid–structure interaction problems.
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An efficient solver for the fully Coupled Solution of large-displacement fluid–structure interaction problems
Computer Methods in Applied Mechanics and Engineering, 2004Co-Authors: Matthias HeilAbstract:This paper is concerned with the fully Coupled (‘monolithic’) Solution of large-displacement fluid–structure interaction problems by Newton’s method. We show that block-triangular approximations of the Jacobian matrix, obtained by neglecting selected fluid–structure interaction blocks, provide good preconditioners for the Solution of the linear systems with GMRES. We present an efficient approximate implementation of the preconditioners, based on a Schur complement approximation for the Navier–Stokes block and the use of multigrid approximations for the Solution of the computationally most expensive operations. The performance of the the preconditioners is examined in representative steady and unsteady simulations which show that the GMRES iteration counts only display a mild dependence on the Reynolds number and the mesh size. The final part of the paper demonstrates the importance of consistent stabilisation for the accurate simulation of fluid–structure interaction problems
Philippe Geuzaine - One of the best experts on this subject based on the ideXlab platform.
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provably second order time accurate loosely Coupled Solution algorithms for transient nonlinear computational aeroelasticity
Computer Methods in Applied Mechanics and Engineering, 2006Co-Authors: Charbel Farhat, Kristoffer G Van Der Zee, Philippe GeuzaineAbstract:Abstract A methodology for designing formally second-order time-accurate and yet loosely-Coupled partitioned procedures for the Solution of nonlinear fluid–structure interaction (FSI) problems on moving grids is presented. Its key components are a fluid time-integrator that is provably second-order time-accurate on moving grids, the midpoint rule for advancing in time the Solution of the structural dynamics equations of motion, a second-order structure predictor for bypassing the inner-iterations encountered in strongly-Coupled Solution procedures, and a carefully designed algorithm for time-integrating the motion of the fluid-mesh. Following this methodology, two different loosely-Coupled schemes are constructed for the Solution of transient nonlinear FSI problems and proved to be second-order time-accurate. Three-dimensional numerical results pertaining to the simulation of the aeroelastic response to a gravity excitation of a complete F-16 configuration are also presented. In addition to confirming the theoretical results discussed in this paper, these numerical results highlight a very stable behavior of the designed loosely-Coupled partitioned procedures.
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SECOND-ORDER TIME-ACCURATE LOOSELY-Coupled Solution ALGORITHMS FOR NONLINEAR FSI PROBLEMS
2004Co-Authors: Philippe Geuzaine, Charbel FarhatAbstract:A methodology for designing formally second-order time-accurate and yet loosely Coupled partitioned procedures for the Solution of nonlinear fluid-structure interac- tion (FSI) problems is presented. Its key components are a fluid time-integrator that is provably second-order time-accurate on moving grids, the midpoint rule for advancing in time the Solution of the structural dynamics equations of motion, a second-order structure predictor for bypassing the inner iterations encountered in strongly-Coupled Solution proce- dures, and a carefully designed algorithm for time-integrating the motion of the fluid-mesh. Following this methodology, several second-order time-accurate loosely-Coupled schemes are constructed for the Solution of transient nonlinear FSI problems. Three-dimensional numerical results pertaining to the simulation of the aeroelastic response of the AGARD Wing 445.6 are also presented.
Homer F. Walker - One of the best experts on this subject based on the ideXlab platform.
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Globalization Techniques for Newton-Krylov Methods and Applications to the Fully Coupled Solution of the Navier-Stokes Equations
SIAM Review, 2006Co-Authors: Roger P. Pawlowski, John N. Shadid, Joseph P. Simonis, Homer F. WalkerAbstract:A Newton-Krylov method is an implementation of Newton’s method in which a Krylov subspace method is used to solve approximately the linear subproblems that determine Newton steps. To enhance robustness when good initial approximate Solutions are not available, these methods are usually globalized, i.e., augmented with auxiliary procedures (globalizations) that improve the likelihood of convergence from a starting point that is not near a Solution. In recent years, globalized Newton-Krylov methods have been used increasingly for the fully Coupled Solution of large-scale problems. In this paper, we review several representative globalizations, discuss their properties, and report on a numerical study aimed at evaluating their relative merits on large-scale two- and three-dimensional problems involving the steady-state Navier-Stokes equations.
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an inexact newton method for fully Coupled Solution of the navier stokes equations with heat and mass transport
Journal of Computational Physics, 1997Co-Authors: John N. Shadid, Raymond S Tuminaro, Homer F. WalkerAbstract:The Solution of the governing steady transport equations for momentum, heat and mass transfer in flowing fluids can be very difficult. These difficulties arise from the nonlinear, Coupled, nonsymmetric nature of the system of algebraic equations that results from spatial discretization of the PDEs. In this manuscript we focus on evaluating a proposed nonlinear Solution method based on an inexact Newton method with backtracking. In this context we use a particular spatial discretization based on a pressure stabilized Petrov-Galerkin finite element formulation of the low Mach number Navier?Stokes equations with heat and mass transport. Our discussion considers computational efficiency, robustness and some implementation issues related to the proposed nonlinear Solution scheme. Computational results are presented for several challenging CFD benchmark problems as well as two large scale 3D flow simulations.
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an inexact newton method for fully Coupled Solution of the navier stokes equations with heat and mass transport
Other Information: PBD: Feb 1997, 1997Co-Authors: John N. Shadid, Raymond S Tuminaro, Homer F. WalkerAbstract:The Solution of the governing steady transport equations for momentum, heat and mass transfer in flowing fluids can be very difficult. These difficulties arise from the nonlinear, Coupled, nonsymmetric nature of the system of algebraic equations that results from spatial discretization of the PDEs. In this manuscript the authors focus on evaluating a proposed nonlinear Solution method based on an inexact Newton method with backtracking. In this context they use a particular spatial discretization based on a pressure stabilized Petrov-Galerkin finite element formulation of the low Mach number Navier-Stokes equations with heat and mass transport. The discussion considers computational efficiency, robustness and some implementation issues related to the proposed nonlinear Solution scheme. Computational results are presented for several challenging CFD benchmark problems as well as two large scale 3D flow simulations.
Rainer Helmig - One of the best experts on this subject based on the ideXlab platform.
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multi rate time stepping schemes for hydro geomechanical model for subsurface methane hydrate reservoirs
Advances in Water Resources, 2016Co-Authors: Shubhangi Gupta, Barbara Wohlmuth, Rainer HelmigAbstract:Abstract We present an extrapolation-based semi-implicit multi-rate time stepping (MRT) scheme and a compound-fast MRT scheme for a naturally partitioned, multi-time-scale hydro-geomechanical hydrate reservoir model. We evaluate the performance of the two MRT methods compared to an iteratively Coupled Solution scheme and discuss their advantages and disadvantages. The performance of the two MRT methods is evaluated in terms of speed-up and accuracy by comparison to an iteratively Coupled Solution scheme. We observe that the extrapolation-based semi-implicit method gives a higher speed-up but is strongly dependent on the relative time scales of the latent (slow) and active (fast) components. On the other hand, the compound-fast method is more robust and less sensitive to the relative time scales, but gives lower speed up as compared to the semi-implicit method, especially when the relative time scales of the active and latent components are comparable.
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efficient fully Coupled Solution techniques for two phase flow in porous media parallel multigrid Solution and large scale computations
Advances in Water Resources, 1999Co-Authors: Peter Bastian, Rainer HelmigAbstract:This paper is concerned with the fast reSolution of nonlinear and linear algebraic equations arising from a fully implicit finite volume discretization of two-phase flow in porous media. We employ a Newton-multigrid algorithm on unstructured meshes in two and three space dimensions. The discretized operator is used for the coarse grid systems in the multigrid method. Problems with discontinuous coefficients are avoided by using a newly truncated restriction operator and an outer Krylov-space method. We show an optimal order of convergence for a wide range of two-phase flow problems including heterogeneous media and vanishing capillary pressure in an experimental way. Furthermore, we present a data parallel implementation of the algorithm with speedup results.
