Now showing 1 - 6 of 6
  • Publication
    Metadata only
    Systematic evaluation of the interface description for fluid–structure interaction simulations using the isogeometric mortar-based mapping
    (Elsevier, 2019-04)
    Apostolatos, Andreas
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    Bletzinger, Kai Uwe
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    Wüchner, Roland
    © 2019 The Authors Within this study the influence of the interface description for partitioned Fluid–Structure Interaction (FSI) simulations is systematically evaluated. In particular, a Non-Uniform Rational B-Spline (NURBS)-based isogeometric mortar method is elaborated which enables the transfer of fields defined on low-order and isogeometric representations of the interface along which the FSI constraints are defined. Moreover, the concept of the Exact Coupling Layer (ECL) using the proposed isogeometric mortar-based mapping method is presented. It allows for smoothing fields that are transferred between two standard low-order surface discretizations applying the exact interface description in terms of NURBS. This is especially important for highly turbulent flows, where the artificial roughness of the low-order faceted FSI interfaces results in spurious flow fields leading to inaccurate FSI solutions. The approach proposed is subsequently compared to the standard mortar-based mapping method for transferring fields between two low-order surface representations (finite volume method for the fluid and finite element method for the structure) and validated on a simple lid-driven cavity FSI benchmark. Then, the physically motivated 3D example of the turbulent flow around a membranous hemisphere (Wood et al., 2016) is considered. Its behavior is predicted by combining the large-eddy simulation technique with the isogeometric analysis to demonstrate the usefulness of the isogeometric mortar-based mapping method for real-world FSI applications. Additionally, the test case of a bluff body significantly deformed in an eigenmode shape of the aforementioned hemisphere is used. For this purpose, both “standard” low-order finite element discretizations and a smooth IGA-based description of the structural surface are considered. This deformation is transferred to the fluid FSI interface and the influence of the interface description on the fluid flow is analyzed. Finally, the computational costs related to the presented methodology are evaluated. The results suggest that the proposed methodology can effectively improve the overall FSI behavior with minimal effort by considering the exact geometry description based on the Computer-Aided Design (CAD) model of the FSI interface.
  • Publication
    Metadata only
    Numerical studies on the instantaneous fluid–structure interaction of an air-inflated flexible membrane in turbulent flow
    (2018) ;
    Apostolatos, Andreas
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    Bletzinger, Kai Uwe
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    Wüchner, Roland
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    The present paper is the numerical counterpart of a recently published experimental investigation by Wood et al. (2018). Both studies aim at the investigation of instantaneous fluid–structure interaction (FSI) phenomena observed for an air-inflated flexible membrane exposed to a turbulent boundary layer, but looking at the coupled system based on different methodologies. The objective of the numerical studies is to supplement the experimental investigations by additional insights, which were impossible to achieve in the experiments. Relying on the large-eddy simulation technique for the predictions of the turbulent flow, non-linear membrane elements for the structure and a partitioned algorithm for the FSI coupling, three cases with different Reynolds numbers (Re=50,000, 75,000 and 100,000) are simulated. The time-averaged first and second-order moments of the flow are presented as well as the time-averaged deformations and standard deviations. The predictions are compared with the experimental references data solely available for 2D planes. In order to better comprehend the three-dimensionality of the problem, the data analysis of the predictions is extended to 3D time-averaged flow and structure data. Despite minor discrepancies an overall satisfying agreement concerning the time-averaged data is reached between experimental data in the symmetry plane and the simulations. Thus for an in-depth analysis, the numerical results are used to characterize the transient FSI phenomena of the present cases either related to the flow or to the structure. Particular attention is paid to depict the different vortex shedding types occurring at the top, on the side and in the wake of the flexible hemispherical membrane. Since the fluid flow plays a significant role in the FSI phenomena, but at the same the flexible membrane with its eigenmodes also impacts the deformations, the analysis is based on the frequencies and Strouhal numbers found allowing to categorize the different observations accordingly.
  • Publication
    Metadata only
    Coupled simulations involving light-weight structures within turbulent flows: FSI strategy and non-matching interface treatment for isogeometric b-rep analysis
    (WILEY-VCH, 2018)
    Wüchner, Roland
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    Apostolatos, Andreas
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    Bletzinger, Kai-Uwe
    Lightweight shell structures have gained significant popularity in the engineering design as they offer high load carrying capacity for low cost. While classical Finite Element models of such structures have been extensively used in practice, the shell formulations for Isogeometric Analysis (IGA), particularly for Kirchhoff-Love shell structures [1], have demonstrated benefits arising from the smooth geometry description and the highly accurate solutions that are enabled. Moreover, the direct use of CAD-models for the structural simulations is possible based e.g. on the Isogeometric B-Rep Analysis (IBRA) [2]. Herein the application of IBRA to Fluid-Structure Interaction (FSI) simulations of wind turbines is demonstrated, thus naturally extending IBRA to coupled multiphysics problems.
  • Publication
    Metadata only
    Flow past a cylinder with a flexible splitter plate: A complementary experimental-numerical investigation and a new FSI test case (FSI-PfS-1a)
    (Elsevier, 2014) ;
    Kalmbach, Andreas
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    Sicklinger, Stefan
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    Wüchner, Roland
    Objectives: The objective of the present paper is to provide a challenging and well-defined validation test case for fluid-structure interaction (FSI) in turbulent flow to close a gap in the literature. The following list of requirements are taken into account during the definition and setup phase. First, the test case should be geometrically simple which is realized by a classical cylinder flow configuration extended by a flexible structure attached to the backside of the cylinder. Second, clearly defined operating and boundary conditions are a must and put into practice by a constant inflow velocity and channel walls. The latter are also evaluated against a periodic setup relying on a subset of the computational domain. Third, the material model should be widely used. Although a rubber plate is chosen as the flexible structure, it is demonstrated by additional structural tests that a classical St. Venant-Kirchhoff material model is sufficient to describe the material behavior appropriately. Fourth, the flow should be in the turbulent regime. Choosing water as the working fluid and a medium-size water channel, the resulting Reynolds number of Re = 30, 470 guarantees a sub-critical cylinder flow with transition taking place in the separated shear layers. Fifth, the test case results should be underpinned by a detailed validation process.Methods: For this purpose complementary numerical and experimental investigations were carried out. Based on optical contactless measuring techniques (particle-image velocimetry and laser distance sensor) the phase-averaged flow field and the structural deformations were determined. These data were compared with corresponding numerical predictions relying on large-eddy simulations and a recently developed semi-implicit predictor-corrector FSI coupling scheme.Outcome: Both results were found to be in close agreement showing a quasi-periodic oscillating flexible structure in the first swiveling FSI mode with a corresponding Strouhal number of about StFSI = 0.11. © 2014 Elsevier Ltd.
  • Publication
    Metadata only
    Fluid-structure interaction using a partitioned semi-implicit predictor-corrector coupling scheme for the application of large-eddy simulation
    (Elsevier, 2012-02) ; ;
    Münsch, Manuel
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    Gallinger, Thomas Gottfried
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    Wüchner, Roland
    The paper is concerned with an efficient partitioned coupling scheme developed for dynamic fluid-structure interaction problems in turbulent flows predicted by eddy-resolving schemes such as large-eddy simulation (LES). To account for the added-mass effect for high density ratios of the fluid to the structure, the semi-implicit scheme guarantees strong coupling among flow and structure, but also maintains the advantageous properties of explicit time-marching schemes often used for turbulence simulations. Thus by coupling an advanced LES code for the turbulent fluid flow with a code especially suited for the prediction of shells and membranes, an appropriate tool for the time-resolved prediction of instantaneous turbulent flows around light, thin-walled structures results. Based on an established benchmark case in laminar flow, i.e., the flow around a cylinder with an attached flexible structure at the backside, the entire methodology is analyzed thoroughly including a grid independence study. After this validation, the benchmark case is finally extended to the turbulent flow regime and predicted as a coupled FSI problem applying the newly developed scheme based on a predictor-corrector method. The entire methodology is found to be stable and robust. The turbulent flow field around the flexible structure and the deflection of the structure itself are analyzed in detail. © 2012 Elsevier Ltd.