Now showing 1 - 5 of 5
  • Publication
    Metadata only
  • 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
    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
    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.