Browsing by Author "Avsar, Reha"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Spacecraft Parachute Fluid Mechanics Computation Based on Space--Time Isogeometric Analysis With T-splines
    (2021-12-03) Avsar, Reha; Tezduyar, Tayfun E
    This thesis is on fluid and structural mechanics computation of spacecraft parachutes based on isogeometric discretization with T-splines. Contrary to the non-uniform rational B-splines (NURBS), T-spline representation does not require a regular control grid, allowing a set of control points to end without traversing the whole domain. We generate a T-spline mesh directly from a block-structured NURBS mesh. In T-spline representation, we use knot removal at the unnecessarily refined regions of the NURBS mesh and reduce the number of control points. We use knot insertion at interfaces between nonmatching meshes. Then, having the matching pairs of control points on each side of the interface, we use knot removal to remove the other knots on the interface sides and enhance the continuity in the whole domain. This gives continuity, or increased continuity, to the volume mesh, improving the solution accuracy and reducing the total number of unknowns compared to NURBS computations. We first present, for a 2D parachute model, fluid--structure interaction computation based on the Space--Time Isogeometric Analysis (ST-IGA) with NURBS and T-splines. Then, we present spacecraft parachute incompressible- and compressible-flow computations based on the ST-IGA with T-splines.
  • Thumbnail Image
    Item
    Space–time VMS flow analysis of a turbocharger turbine with isogeometric discretization: computations with time-dependent and steady-inflow representations of the intake/exhaust cycle
    (Springer, 2019) Otoguro, Yuto; Takizawa, Kenji; Tezduyar, Tayfun E.; Nagaoka, Kenichiro; Avsar, Reha; Zhang, Yutong
    Many of the computational challenges encountered in turbocharger-turbine flow analysis have been addressed by an integrated set of space–time (ST) computational methods. The core computational method is the ST variational multiscale (ST-VMS) method. The ST framework provides higher-order accuracy in general, and the VMS feature of the ST-VMS addresses the computational challenges associated with the multiscale nature of the unsteady flow. The moving-mesh feature of the ST framework enables high-resolution computation near the rotor surface. The ST slip interface (ST-SI) method enables moving-mesh computation of the spinning rotor. The mesh covering the rotor spins with it, and the SI between the spinning mesh and the rest of the mesh accurately connects the two sides of the solution. The ST Isogeometric Analysis enables more accurate representation of the turbine geometry and increased accuracy in the flow solution. The ST/NURBS Mesh Update Method enables exact representation of the mesh rotation. A general-purpose NURBS mesh generation method makes it easier to deal with the complex geometries involved. An SI also provides mesh generation flexibility in a general context by accurately connecting the two sides of the solution computed over nonmatching meshes, and that is enabling the use of nonmatching NURBS meshes in the computations. The computational analysis needs to cover a full intake/exhaust cycle, which is much longer than the turbine rotation cycle because of high rotation speeds, and the long duration required is an additional computational challenge. As one way of addressing that challenge, we propose here to calculate the turbine efficiency for the intake/exhaust cycle by interpolation from the efficiencies associated with a set of steady-inflow computations at different flow rates. The efficiencies obtained from the computations with time-dependent and steady-inflow representations of the intake/exhaust cycle compare well. This demonstrates that predicting the turbine performance from a set of steady-inflow computations is a good way of addressing the challenge associated with the multiple time scales.
  • Thumbnail Image
    Item
    T-splines computational membrane–cable structural mechanics with continuity and smoothness: II. Spacecraft parachutes
    (Springer Nature, 2023) Terahara, Takuya; Takizawa, Kenji; Avsar, Reha; Tezduyar, Tayfun E.
    In this second part of a two-part article, we present spacecraft parachute structural mechanics computations with the T-splines computational method introduced in the first part. The method and its implementation, which was also given in the first part, are for computations where structures with different parametric dimensions are connected with continuity and smoothness. The basis functions of the method were derived in the context of connecting structures with 2D and 1D parametric dimensions. In the first part, the 2D structure was referred to as “membrane” and the 1D structure as “cable.” The method and its implementation, however, are certainly applicable also to other 2D–1D cases, and the test computations presented in the first part included shell–cable structures. Similarly, the spacecraft parachute computations presented here are with both the membrane and shell models of the parachute canopy fabric. The computer model used in the computations is for a subscale, wind-tunnel version of the Disk–Gap–Band parachute. The computations demonstrate the effectiveness of the method in 2D–1D structural mechanics computation of spacecraft parachutes.