Computational engineering for wind-exposed thin-walled structures

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Computational engineering for wind-exposed thin-walled structures Ansgar Halfmann 1 , Ernst Rank 1 , Markus Gluck 2 ,Michael Breuer 2 ,Franz Durst 2 ,Jurgen Bellmann 3 , and Casimir Katz 3 1 Lehrstuhl fur Bauinformatik, Technische Universitat Munchen, 80290 Munchen, Germany 2 Lehrstuhl fur Stromungsmechanik, Universitat Erlangen-Nurnberg, 91058 Erlangen, Germany 3 SOFiSTiK AG, 81541 Munchen, Germany Abstract. In this paper a computer-aided simulation approach for uid-structure interaction of wind-exposed structures is presented. In the center of our software architecture is the geometric model of the structure, from which a nite element mesh for the structure and a nite volume mesh for the uid are derived. The attention is concentrated to thin-walled structures like membranes and thin shells composed of light and exible materials. The interaction of uid and structure is eected by wind-induced vibrations and causes large elastic deformations of the structure. A powerful simulation tool is provided by couplingtwo codesdeveloped for ow simulation and structural dynamics by a fully implicit coupling algorithm. Results of three-dimensional simulations of uid-structure interaction for several test cases as well as for a real-life example will be presented. 1 Introduction During the last few years much progress has been achieved to integrate analysis and design in civil engineering [9]. The computer-aided design process starts by setting up a geometric model being used for the denition of all structural properties as well as for the loads on the construction. From this geometric model a computational model is derived as the basis for the following dimensioning of the construction. This computer-aided engineering process has to support eciently the primary goals of any civil engineering design, i.e. the development of constructions satisfying the requirements of safety during their whole lifetime, resisting all expected inuences they might be exposed to. Considering for example light textile constructions like the convertible shade roof for a large court of the Prophet's Mosque in Madinah consisting of several Fig. 1. Convertible shade roof [10]
2 Ansgar Halfmann et al. large umbrellas (Fig. 1 [10]), the most demanding engineering task is to dimension the construction so that it will resist wind loads. Following the Davenport-Wind-Load-Chain an assumed local wind prole for a given terrain can be established according to the European Design Code EC 1 [5]. This wind distribution causes a pressure eld on the structure. If simplied, conventional load assumptions for this pressure distribution are made, the structures may be strongly over-designed. Yet, also an under-design with the danger of a collapse may result from this simplied procedure, as the mutual inuence of neighbouring constructions could change the wind pressure eld dramatically. Therefore, todays standard of practice are time-consuming and costly experiments in wind tunnels. A model of the construction is considered and wind pressure elds on its surface are measured to be used for later numerical structural analysis. One of the major drawbacks of this mixed computational and experimental approach is the diculty toquickly change the geometry of the model construction for the wind tunnel experiment. Therefore, it would be highly desirable to have a'numerical wind tunnel' available, being directly integrated in the civil engineering design and analysis process, and enabling to investigate a structure also under the inuence of neighbouring constructions. Several steps in this direction have been performed by the authors in a joint research project during the past two years and will be presented in this contribution. 2 Software architecture The software architecture shown in Fig. 2 is inuenced by the idea of a loose coupling strategy based on highly specialized and well evaluated simulation codes, each developed for the special eld of the interacting system. In a rst step, the structural model is dened, using a classical CAD environment onaPCoraworkstation. Toconsider dierent stress distributions in a membrane, it is possible to compute the geometric shape of pure membrane structures in a formnding process [2]. Thereby the deformed shape of the structure under dead load is computed by a nite element analysis starting from an inital geometry. Using special membrane elements and assuming an initial stiness caused by isotropic prestressing PC / workstation supercomputer STL-file ICEM-CFD fluid-simulation FASTEST-3D Geometrical Model +boundary conditions AutoCAD / SOFiPLUS formfinding process MpCCI SOFiMESH DO_MESH structure-simulation ASE creates PC / workstation TECPLOT / Explorer Wingraf / Animator CDBASE Fig. 2. Software structure and neglecting any bending stiness, the deformed shape will lead to the soap lm form with its constant isotropic stress distribution. All geometric information is stored in a database describing a b-rep (boundary repre-
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Computational engineering for wind-exposed thin-walled structures

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