Browsing by Author "Tezduyar, Tayfun E"

Now showing 1 - 6 of 6
  • Thumbnail Image
    Item
    A Study on Weakly-Imposed Dirichlet Boundary Conditions in Internal Flows
    (2016-04-25) Pan, Linqi; Tezduyar, Tayfun E
    This thesis is on weakly-imposed Dirichlet boundary conditions in incompressible and compressible flow. Our target is internal flows. The weakly-imposed conditions are compared with strongly-imposed conditions for mean flow solutions from the incompressible-flow space–time variational multiscale (ST-VMS) method. The numerical tests include ST finite element analysis with linear basis functions in space and time, and ST Isogeometiric Analysis (IGA) with NURBS basis functions in space and linear basis functions in time. The thesis contains three test computations: 1) Incompressible-flow 2D ST finite element computation of laminar flow between parallel plates. 2) Incompressible-flow 3D ST finite element computation of laminar flow in a pipe. 3) Incompressible-flow 3D ST-IGA computation of high-Reynolds number turbulent flow in a pipe. The NURBS mesh generation strategy for the compressible flow in a pipe is also included in the thesis. The weakly-imposed Dirichlet boundary conditions are tested at different spatial and temporal resolutions and penalty parameter values.
  • Thumbnail Image
    Item
    Computational Flow Analysis of a Cyclone Vacuum Cleaner
    (2019-04-17) Zhang, Yutong; Tezduyar, Tayfun E
    Computational flow analysis of a cyclone vacuum cleaner can provide valuable fluid mechanics information for efficient design and operation. The vacuum cleaner is made of multiple cones, each with a rotational flow field that facilitates the dust collection. Reliable computational analysis requires both accurate representation of the complex geometry and high-resolution representation of the boundary layers near the internal surfaces of the cones. We address these computational challenges with the Space–Time Variational Multiscale (ST-VMS) method and isogeometric discretization, using NURBS basis functions. The ST framework has higher-order accuracy in general, and the VMS feature of the ST-VMS addresses the challenge created by the turbulent nature of the flow. The isogeometric discretization provides a more accurate representation of the geometry and increased accuracy in the flow solution. We conduct our studies for both single-cone and multi-cone configurations, and the comparison of the results from the two helps us discern the reasonableness of using single-cone flow analysis in place of full-machine flow analysis.
  • Thumbnail Image
    Item
    Coronary Artery Computational Flow Analysis with Isogeometric Discretization
    (2017-07-26) Yu, Yuxuan; Tezduyar, Tayfun E
    Patient-specific computational flow analysis of the coronary artery can provide valuable information that the doctor can use in making treatment decisions. Reliable analysis requires addressing a number of computational challenges. The challenges include the dynamic nature of the analysis due to the arterial motion, accurately representing the flow near the arterial wall, and nonlinearity of the arterial-wall material. Our core technology in addressing these challenges is the Space-Time Variational Multiscale method, which, because of its moving-mesh nature, maintains the high-resolution representation of the boundary layers near the wall as the artery moves. The isogeometric discretization increases the fluid mechanics accuracy even more by providing smoother representation of the wall geometry and more accuracy in the flow solution. The image-based geometries do not come from a zero-stress state (ZSS) of the arterial wall, which we need in nonlinear structural mechanics, and we handle that with a special method for computing the element-based ZSS. In our comparative studies, we compute the unsteady flow field i) for a given, fixed shape of the artery, ii) for wall deformation driven by the physiological blood pressure, iii) for wall motion fully prescribed based on the time-dependent medical images, and iv) for wall deformation driven by the physiological blood pressure in combination with the motion of a thin strip along the arterial surface coming from the medical images.
  • Thumbnail Image
    Item
    Flow Analysis of Vibration Modes in Turbocharger Turbines
    (2024-04-19) Pritchard, Noah; Tezduyar, Tayfun E
    The purpose of this research is to help understand the influence of time-dependent fluid dynamics forces on the fatigue failure of turbomachinery blades. To that end, we conduct computational flow analysis of a turbocharger turbine with 13 rotor blades and 14 stator blades for precomputed time-dependent blade deformation patterns. The flow analysis is carried out for the rotor vibration modes corresponding to a set of natural frequencies lower than but close to the frequency associated with the upper end of the turbine operation range. The core computational method is the Space–Time Variational Multiscale (ST-VMS) method. The ST-VMS serves as a moving mesh method. That enables mesh-resolution control near the rotor surfaces and high-resolution boundary-layer representation. The core method is complemented with the “ST-SI-IGA,” which is the synthesis of the ST Slip Interface (ST-SI) method and ST Isogeometric Analysis (ST-IGA). The ST-SI enables the use of ST-VMS as a moving-mesh method even with the inner mesh rotating with the rotor. The ST-IGA with IGA basis functions in space brings superior accuracy to the geometry representation and flow solution. The ST-IGA with IGA basis functions in time enables higher-accuracy representation of the rotor motion and blade deformations.
  • 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 Interface-Tracking Computations with Contact Between Solid Surfaces
    (2014-04-25) Buscher, Austin J; Tezduyar, Tayfun E; Takizawa, Kenji; Akin, John E; Meade, Andrew J
    To address the computational challenges associated with contact between moving solid surfaces, such as those in cardiovascular fluid–structure interaction (FSI), parachute FSI, and flapping-wing aerodynamics, we introduce a space–time (ST) interface-tracking method that can deal with topology change (TC). In cardiovascular FSI, our primary target is heart valves. The method is a new version of the Deforming-Spatial-Domain/Stabilized ST (DSD/SST) method, and we call it ST-TC. It includes a master–slave system that maintains the connectivity of the "parent" mesh when there is contact between the moving interfaces. It is an efficient, practical alternative to using unstructured ST meshes, but without giving up on the accurate representation of the interface or consistent representation of the interface motion. We explain the method with conceptual examples and present 2D and 3D test computations with models representative of the classes of problems we are targeting.