Computational engineering for wind-exposed thin-walled structures

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Computational engineering for wind-exposed thin-walled structures 5 250 CFD 18 nodes, 10 elements CSD 15 nodes, 8 elements Fig. 5. Discretization of the interface displacement upper boundary [mm] 200 150 100 50 0 −50 −100 −150 t 1 = 0:025 s t 2 = 0:0125 s t 3 = 0:00625 s −200 0 0.5 1 1.5 2 2.5 3 3.5 time [s] Fig. 6. Displacement for dierent t uniform renement was performed in two levels which leads to 13,200 and 105,600 hexaeder elements and 40 or 160 quadrilaterals for the interface, respectively. The coarsest grid for the CSD simulation consisting of only 2 elements is also shown in Fig. 7. Uniform renement yields surface meshes of 8 or 32 quadrilateral elements for the structure simulation, respectively. CFD 18 nodes, 10 elements CSD 6nodes, 2 elements Fig. 7. Initial interface discretization displacement upper boundary [mm] 300 250 200 150 100 50 0 −50 −100 −150 CFD10=CSD 2 CFD40=CSD 8 CFD160=CSD 32 −200 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 time [s] Fig. 8. Displacement for dierent interface discretizations Fig.8points out the insucient accuracy of the results corresponding to the initial interface discretizations and the good agreement of the transient displacements achieved with the rened meshes. In particular the CSD mesh consisting only of 2 elements for the y-direction is too coarse to obtain useful results. 4.2 Vertical plate under a sudden wind gust The geometry and material properties of the second test case are the same as before. Fig. 9 shows a cutting plane through the uid domain which is open with an inlet (left boundary), an outlet (right boundary), and symmetric boundary conditions at the top as well as in z-direction. At the beginning of the coupled simulation the uid suddenly accelerates and adopts
6 Ansgar Halfmann et al. immediately a constant inowvelocity ofU1 = 10 m/s being equivalent to a Reynolds number of Re L =50. As a consequence the structural oscillations are induced by the saltus of the uid velocity and reach a stationary deformation state after a certain time. Fig. 10 shows again the displacement of the upper boundary of the plate for various timestep sizes. The interface discretizations comply to the grids pictured in Fig. 5. Only minor distinctions could be identied for the dierent time discretizations. Furthermore, the in- uence of the spatial interface discretization was investigated using the grids shown in Fig.11 and performing an uniform renement of two levels for the CSD grid whereas the mesh for the uid domain remains unchanged. It is again obvious displacement upper boundary [mm] U 8 70 60 50 40 30 20 10 y 1111111111111111111111111111111111111111111111111111111111111 0000000000000000000000000000000000000000000000000000000000000 1111111111111111111111111111111111111111111111111111111111111 0000000000000000000000000000000000000000000000000000000000000 A Fig. 9. System conguration 0 0 0.5 1 1.5 2 2.5 3 3.5 time [s] B L t 1 = 0:025 s t 2 = 0:0125 s t 3 = 0:00625 s t 4 = 0:003125 s t 5 = 0:0015625 s Fig. 10. Displacement for dierent t that the bending oscillations of the plate cannot be represented suciently accurate by a CSD mesh with only two elements in y-direction, see Fig. 12. x CFD 18 nodes, 10 elements CSD 9nodes, 4 elements Fig. 11. Initial interface discretization displacement upper boundary [mm] 60 50 40 30 20 10 CFD10=CSD 4 CFD10=CSD 6 CFD10=CSD 8 0 0 0.5 1 1.5 2 2.5 3 3.5 time [s] Fig. 12. Displacement for dierent CSD interface discretizations 4.3 Tent roof Fig. 13 shows a screenshot of the CAD-environment representing the geometric model of a real-life structure as a starting point for the simulation.
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Computational engineering for wind-exposed thin-walled structures

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