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Windsock
The windsock has a length of 1.5 m and a diameter ranging from 0.25 m upstream to 0.15 m downstream. Initially the windsock is in a horizontal position, and the starting condition for the flow field is the developed flow field corresponding to a rigid windsock held in that horizontal position. Then the gravity is turned on for the windsock, the FSI starts, and the windsock starts falling down. The wind velocity is constant at 10 m/s. The thickness, density and stiffness of the windsock are 2.0 mm, 100 kg/m3 and 1.0x10^6 N/m2, respectively. The upstream edge of the structure is held fixed while the remaining structure is free and flaps in cycles.
The numerical methods used in this computation were introduced and implemented on parallel computing platforms by the T*AFSM. The set of numerical methods introduced by the T*AFSM over the years and used in this computation includes the DSD/SST formulation [14], the quasidirect FSI method [5, 6], the stabilized spacetime FSI (SSTFSI) technique [7], and a number of special FSI techniques [7]. Among the special FSI techniques used in the computation is the FSI Geometric Smoothing Technique (FSIGST) [7], specifically its directional version, FSI Directional GST (FSIDGST) [7]. The computation was carried out on the ADA system at Rice University. For more details on this computation, see [7].









Fig. 1. The windsock and the flow field (illustrated with "smoke" particles) at various instants. For details of the FSI computation, see [7]. The visualization, including the computation of the "smoke" particles, was performed by Kenji Takizawa. 









Fig. 2. The windsock and the flow field (illustrated with "smoke" particles) at various instants. For details of the FSI computation, see [7]. The visualization, including the computation of the "smoke" particles, was performed by Kenji Takizawa. 

Fig. 3. The windsock visualization won the "Best Computer Visualization Award for Animation Section" at APCOM'07 Conference in Kyoto, Japan, 2007. 


Fig. 4. The windsock and velocity vectors at two instants. For details of the FSI computation, see [7]. 
References
1. T.E. Tezduyar, "Stabilized Finite Element Formulations for Incompressible Flow Computations", Advances in Applied Mechanics, 28 (1992) 144.
2. T.E. Tezduyar, M. Behr and J. Liou, "A New Strategy for Finite Element Computations Involving Moving Boundaries and Interfaces  The DeformingSpatialDomain/SpaceTime Procedure: I. The Concept and the Preliminary Numerical Tests", Computer Methods in Applied Mechanics and Engineering, 94 (1992) 339351.
3. T.E. Tezduyar, M. Behr, S. Mittal and J. Liou, "A New Strategy for Finite Element Computations Involving Moving Boundaries and Interfaces  The DeformingSpatialDomain/SpaceTime Procedure: II. Computation of Freesurface Flows, Twoliquid Flows, and Flows with Drifting Cylinders", Computer Methods in Applied Mechanics and Engineering, 94 (1992) 353371.
4. T.E. Tezduyar, "Computation of Moving Boundaries and Interfaces and Stabilization Parameters", International Journal for Numerical Methods in Fluids, 43 (2003) 555575.
5. T.E. Tezduyar, S. Sathe, R. Keedy and K. Stein, "SpaceTime Techniques for Finite Element Computation of Flows with Moving Boundaries and Interfaces", Proceedings of the III International Congress on Numerical Methods in Engineering and Applied Sciences, Monterrey, Mexico, CDROM (2004).
6. T.E. Tezduyar, S. Sathe, R. Keedy and K. Stein, "SpaceTime Finite Element Techniques for Computation of FluidStructure Interactions", Computer Methods in Applied Mechanics and Engineering, 195 (2006) 20022027.
7. T.E. Tezduyar and S. Sathe, "Modeling of FluidStructure Interactions with the SpaceTime Finite Elements: Solution Techniques", International Journal for Numerical Methods in Fluids, 54 (2007) 855900.
