The Experts below are selected from a list of 291 Experts worldwide ranked by ideXlab platform
Kurt Maute - One of the best experts on this subject based on the ideXlab platform.
-
An immersed boundary approach for shape and topology optimization of Stationary Fluid-structure interaction problems
Structural and Multidisciplinary Optimization, 2016Co-Authors: Nicholas Jenkins, Kurt MauteAbstract:This paper presents an approach to shape and topology optimization of Fluid-structure interaction (FSI) problems at steady state. The overall approach builds on an immersed boundary method that couples a Lagrangian formulation of the structure to an Eulerian Fluid model, discretized on a deforming mesh. The geometry of the Fluid-structure boundary is manipulated by varying the nodal parameters of a discretized level set field. This approach allows for topological changes of the Fluid-structure inter-face, but free-floating volumes of solid material can emerge in the course of the optimization process. The free-floating volumes are tracked and modeled as Fluid in the FSI anal-ysis. To sense the isolated solid volumes, an indicator field described by linear, isotropic diffusion is computed prior to analyzing the FSI response of a design. The Fluid is modeled with the incompressible Navier-Stokes equations, and the structure is assumed linear elastic. The FSI model is discretized by an extended finite element method, and the Fluid-structure coupling conditions are enforced weakly. The resulting nonlinear system of equations is solved mono-lithically with Newton's method. The design sensitivities are computed by the adjoint method and the optimization problem is solved by a gradient-based algorithm. The char-acteristics of this optimization framework are studied with two-dimensional problems at steady state. Numerical results indicate that the proposed treatment of free-floating vol-umes introduces a discontinuity in the design evolution, yet the method is still successful in converging to meaningful designs.
-
level set topology optimization of Stationary Fluid structure interaction problems
Structural and Multidisciplinary Optimization, 2015Co-Authors: Nicholas Jenkins, Kurt MauteAbstract:This paper introduces a topology optimization approach that combines an explicit level set method (LSM) and the extended finite element method (XFEM) for designing the internal structural layout of Fluid-structure interaction (FSI) problems. The FSI response is predicted by a monolithic solver that couples an incompressible Navier-Stokes flow model with a small-deformation solid model. The Fluid mesh is modeled as an elastic continuum that deforms with the structure. The Fluid model is discretized with stabilized finite elements and the structural model by a generalized formulation of the XFEM. The nodal parameters of the discretized level set field are defined as explicit functions of the optimization variables. The optimization problem is solved by a nonlinear programming method. The LSM-XFEM approach is studied for two- and three-dimensional FSI problems at steady-state and compared against a density topology optimization approach. The numerical examples illustrate that the LSM-XFEM approach convergences to well-defined geometries even on coarse meshes, regardless of the choice of objective and constraints. In contrast, the density method requires refined grids and a mass penalization to yield smooth and crisp designs. The numerical studies show that the LSM-XFEM approach can suffer from a discontinuous evolution of the design in the optimization process as thin structural members disconnect. This issue is caused by the interpolation of the level set field and the inability to represent particular geometric configurations in the XFEM model. While this deficiency is generic to the LSM-XFEM approach used here, it is pronounced by the nonlinear response of FSI problems.
Hossein Rokni - One of the best experts on this subject based on the ideXlab platform.
-
natural frequencies of rectangular mindlin plates coupled with Stationary Fluid
Applied Mathematical Modelling, 2012Co-Authors: Shahrokh Hosseinihashemi, Mahmoud Karimi, Hossein RokniAbstract:The present study is concerned with the free vibration analysis of a horizontal rectangular plate, either immersed in Fluid or floating on its free surface. The governing equations for a moderately thick rectangular plate are analytically derived based on the Mindlin plate theory (MPT), whereas the velocity potential function and Bernoulli’s equation are employed to obtain the Fluid pressure applied on the free surface of the plate. The simplifying hypothesis that the wet and dry mode shapes are the same, is not assumed in this paper. In this work, an exact-closed form characteristics equation is used for the plate subjected to a combination of six different boundary conditions. Two opposite sides are simply supported and any of the other two edges can be free, simply supported or clamped. To demonstrate the accuracy of the present analytical solution, a comparison is made with the published experimental and numerical results in the literature, showing an excellent agreement. Then, natural frequencies of the plate are presented in tabular and graphical forms for different Fluid levels, Fluid densities, aspect ratios, thickness to length ratios and boundary conditions. Finally, some 3-D mode shapes of the rectangular Mindlin plates in contact with Fluid are illustrated.
Thomas Richter - One of the best experts on this subject based on the ideXlab platform.
-
Optimal Control and Parameter Estimation for Stationary Fluid-Structure Interaction Problems
SIAM Journal on Scientific Computing, 2013Co-Authors: Thomas Richter, Thomas WickAbstract:We investigate optimization problems in which the state is given in terms of Fluid-structure interactions. The coupled problem is formulated with the help of the ALE (arbitrary Lagrangian--Eulerian) mapping. The solution approach is based on derivative-based optimization algorithms in which the derivatives are obtained with the help of the Lagrange formalism, leading to the so-called optimality system. The optimality system is then solved with Newton's method. The focus is on the proper derivation of the adjoint equations guiding the optimization formalism. Moreover, special attention is given to the adjoint information transport between the Fluid and structure subproblems. Numerical tests are used to substantiate the theoretical framework.
-
Goal-oriented error estimation for Fluid–structure interaction problems
Preprint: Computer Methods in Applied Mechanics and Engineering, 2011Co-Authors: Thomas RichterAbstract:In this work, we present an adaptive finite element method for the numerical simulation of Stationary Fluid-structure interaction problems. The coupled system is given in a variational and monolithic Arbitrary Lagrangian Eulerian framework. We derive methods for goal-oriented error estimation and mesh adaptation with the dual weighted residual method. Key to applying this error estimator is the underlying canonic variational formulation of the Fluid-structure interaction problem by mapping the flow problem to ALE coordinates. The developed method is applied to two and three dimensional Stationary benchmark problems coupling the incompressible Navier-Stokes equations with a nonlinear hyper-elastic material law.
-
Finite elements for Fluid-structure interaction in ALE and fully Eulerian coordinates
Computer Methods in Applied Mechanics and Engineering, 2010Co-Authors: Thomas Richter, Thomas WickAbstract:In this work we describe and compare two monolithic models for Fluid-structure interaction problems: First, the well-established ALE model using natural Lagrangian coordinates for the structural model and using an artificial coordinate system for the flow problem. Then, a novel approach, the fully Eulerian coordinates, where both subproblems, structure and Fluid are given in Eulerian coordinates. The approaches have in common that a closed variational formulation exists. This allows the use of implicit solution schemes, goal oriented error estimation and gradient based optimization algorithms.Aim of this work is the introduction and verification of the novel fully Eulerian model for Stationary Fluid-structure interaction problems. © 2010 Elsevier B.V.
Nicholas Jenkins - One of the best experts on this subject based on the ideXlab platform.
-
An immersed boundary approach for shape and topology optimization of Stationary Fluid-structure interaction problems
Structural and Multidisciplinary Optimization, 2016Co-Authors: Nicholas Jenkins, Kurt MauteAbstract:This paper presents an approach to shape and topology optimization of Fluid-structure interaction (FSI) problems at steady state. The overall approach builds on an immersed boundary method that couples a Lagrangian formulation of the structure to an Eulerian Fluid model, discretized on a deforming mesh. The geometry of the Fluid-structure boundary is manipulated by varying the nodal parameters of a discretized level set field. This approach allows for topological changes of the Fluid-structure inter-face, but free-floating volumes of solid material can emerge in the course of the optimization process. The free-floating volumes are tracked and modeled as Fluid in the FSI anal-ysis. To sense the isolated solid volumes, an indicator field described by linear, isotropic diffusion is computed prior to analyzing the FSI response of a design. The Fluid is modeled with the incompressible Navier-Stokes equations, and the structure is assumed linear elastic. The FSI model is discretized by an extended finite element method, and the Fluid-structure coupling conditions are enforced weakly. The resulting nonlinear system of equations is solved mono-lithically with Newton's method. The design sensitivities are computed by the adjoint method and the optimization problem is solved by a gradient-based algorithm. The char-acteristics of this optimization framework are studied with two-dimensional problems at steady state. Numerical results indicate that the proposed treatment of free-floating vol-umes introduces a discontinuity in the design evolution, yet the method is still successful in converging to meaningful designs.
-
level set topology optimization of Stationary Fluid structure interaction problems
Structural and Multidisciplinary Optimization, 2015Co-Authors: Nicholas Jenkins, Kurt MauteAbstract:This paper introduces a topology optimization approach that combines an explicit level set method (LSM) and the extended finite element method (XFEM) for designing the internal structural layout of Fluid-structure interaction (FSI) problems. The FSI response is predicted by a monolithic solver that couples an incompressible Navier-Stokes flow model with a small-deformation solid model. The Fluid mesh is modeled as an elastic continuum that deforms with the structure. The Fluid model is discretized with stabilized finite elements and the structural model by a generalized formulation of the XFEM. The nodal parameters of the discretized level set field are defined as explicit functions of the optimization variables. The optimization problem is solved by a nonlinear programming method. The LSM-XFEM approach is studied for two- and three-dimensional FSI problems at steady-state and compared against a density topology optimization approach. The numerical examples illustrate that the LSM-XFEM approach convergences to well-defined geometries even on coarse meshes, regardless of the choice of objective and constraints. In contrast, the density method requires refined grids and a mass penalization to yield smooth and crisp designs. The numerical studies show that the LSM-XFEM approach can suffer from a discontinuous evolution of the design in the optimization process as thin structural members disconnect. This issue is caused by the interpolation of the level set field and the inability to represent particular geometric configurations in the XFEM model. While this deficiency is generic to the LSM-XFEM approach used here, it is pronounced by the nonlinear response of FSI problems.
Thomas Wick - One of the best experts on this subject based on the ideXlab platform.
-
On the Differentiability of Fluid–Structure Interaction Problems with Respect to the Problem Data
Journal of Mathematical Fluid Mechanics, 2019Co-Authors: Thomas Wick, Winnifried WollnerAbstract:A coupled system of Stationary Fluid–structure equations in an arbitrary Lagrangian–Eulerian framework is considered in this work. Existence results presented in the literature are extended to show differentiability of the solutions to a Stationary Fluid–structure interaction problem with respect to the given data, volume forces and boundary values, provided a small data assumption holds. Numerical experiments are used to substantiate the theoretical findings.
-
Optimal Control and Parameter Estimation for Stationary Fluid-Structure Interaction Problems
SIAM Journal on Scientific Computing, 2013Co-Authors: Thomas Richter, Thomas WickAbstract:We investigate optimization problems in which the state is given in terms of Fluid-structure interactions. The coupled problem is formulated with the help of the ALE (arbitrary Lagrangian--Eulerian) mapping. The solution approach is based on derivative-based optimization algorithms in which the derivatives are obtained with the help of the Lagrange formalism, leading to the so-called optimality system. The optimality system is then solved with Newton's method. The focus is on the proper derivation of the adjoint equations guiding the optimization formalism. Moreover, special attention is given to the adjoint information transport between the Fluid and structure subproblems. Numerical tests are used to substantiate the theoretical framework.
-
Finite elements for Fluid-structure interaction in ALE and fully Eulerian coordinates
Computer Methods in Applied Mechanics and Engineering, 2010Co-Authors: Thomas Richter, Thomas WickAbstract:In this work we describe and compare two monolithic models for Fluid-structure interaction problems: First, the well-established ALE model using natural Lagrangian coordinates for the structural model and using an artificial coordinate system for the flow problem. Then, a novel approach, the fully Eulerian coordinates, where both subproblems, structure and Fluid are given in Eulerian coordinates. The approaches have in common that a closed variational formulation exists. This allows the use of implicit solution schemes, goal oriented error estimation and gradient based optimization algorithms.Aim of this work is the introduction and verification of the novel fully Eulerian model for Stationary Fluid-structure interaction problems. © 2010 Elsevier B.V.