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In this work a Lattice Boltzmann (LB) fluid flow solver based on unstructured quadtree/octree type Eulerian grids is coupled with a spectral Finite Element (p-FEM) structural mechanics solver based on a Lagrangian description to predict bidirectional fluid-structure interaction (FSI). The methods and algorithms are described in detail. Benchmark computations of a coupled transient problem of a 2D beam-like structure in a channel as defined by the DFG-Research Unit 493 are presented.

In this contribution the use of hexahedral elements for the structural simulation in a fluid structure interaction framework is presented, resulting in a consistent kinematic and geometric description of the solid. In order to compensate the additional numerical effort of the three-dimensional approach, an anisotropic -adaptive method for linear elastodynamic problems is proposed, resulting in a clearly higher efficiency and higher convergence rates than uniform -extensions. Special emphasis is placed on the accurate transfer of loads considering the fluid discretization for computation of the surface load integrals. For a coupling with a cartesian grid based Lattice Boltzmann code it was found that oscillations in the interface tractions may excite higher structural modes possibly leading to a nonstable coupling behavior. A first remedy to this problem was a linear modal analysis of the structure, thus allowing to control the number of modes to be considered without disregarding bidirectional fluid structure interactions. Preliminary results are presented for the FSI benchmark configuration proposed in this book.

The aim of this contribution is to propose a methodology for the analysis and improvement of light, thin-walled structures with reference to aeroelastic effects. Those kind of problems demand for the appropriate combination of different physical and numerical disciplines to account for the relevant factors inherent to the simulation of light, thin-walled structures undergoing large displacements as well as highly turbulent air flows. To fulfill these requirements the occurring wind-structure interaction is accessed by a surface-coupled fluid-structure interaction (FSI) method. This is realized in a modular and flexible software environment with the use of a partitioned coupling approach: the structural field is solved by the in-house finite element program CARAT using several finite element types and advanced solution techniques for form finding, nonlinear and dynamical problems. The flow field is solved by the CFD software package CFX-5 of ANSYS Inc. A prerequisite to allow for the assessment of aeroelastic problems, beyond the mere exchange of data between the two physical fields, is the utilization of stable as well as efficient coupling strategies. In particular, it is shown that in the case of lightweight structures interacting with incompressible fluid flows the coupling strategy plays an important role regarding the feasibility of the simulations. This contribution will present theory and realization of a corresponding implementation enhanced by illustrative examples. Moreover, the comprehensiveness of this approach opens the possibility for multiphysics optimization.

Experimental studies on reference test cases are of capital importance to support the development of models and coupling strategies for numerical simulations on fluid-structure interaction problems. From the experimental view point, the study of the coupled unsteady fluid flow and structure motion requires specially adapted test rigs and measurement techniques to obtain accurate time-resolved results. This demand has triggered the present contribution to design and to study a two-dimensional reference test case on laminar fluid-structure interaction. A new experimental facility to be operated with high viscous fluids was build exclusively for the present study and a Particle Image Velocimetry system was adapted to measure both the periodical flow velocity field and the structure deflection modes. Finally the reference experiment was defined and performed. An extended investigation was conducted on the two-dimensional reference structure model at a Reynolds number of 170 and lead to very reproducible and accurate results compiled in a data base.

We describe new benchmark settings for the rigorous evaluation of different methods for fluid-structure interaction problems. The configurations consist of laminar incompressible channel flow around an elastic object which results in self-induced oscillations of the structure. Moreover, characteristic flow quantities and corresponding plots are provided for a quantitative comparison.