R-3 Repository :: Browsing by Author "Tezduyar, Tayfun E."

Browsing by Author "Tezduyar, Tayfun E."

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A Comparative Study Based on Patient-Specific Fluid-Structure Interaction Modeling of Cerebral Aneurysms
(2011) Brummer, Tyler Matthew; Tezduyar, Tayfun E.
The Team for Advanced Flow Simulation and Modeling (T*AFSM) at Rice University has been developing techniques to address the computational challenges involved in fluid-structure interaction (FSI) modeling. The Stabilized Space-Time FSI (SSTFSI) core technologies, in conjunction with an array of special techniques, is used in a comparative study of patient-specific cerebral aneurysms. Ten cases, from three different locations, are studied, half of which were ruptured. The study compares the wall shear stress, oscillatory shear index, and the arterial-wall stress and stretch, with the original motivation of finding significant differences between ruptured and unruptured aneurysms. Simpler approaches to computer modeling of cerebral aneurysms are also compared to FSI modeling.
A Computational Analysis of Novel Non-circular Nozzles
(2014-04-24) Baskici, Gokhan; Akin, John Edward.; Tezduyar, Tayfun E.; Meade, Andrew J., Jr.
This thesis presents a computational analysis for determining the flow properties of novel non-circular nozzles. In last few decades, non-circular nozzles have been investigated intensively due to their remarkably superior capabilities in enhancing mass entrainment over circular nozzles. In this thesis, to increase the amount of ambient fluid entrained in the jet flow, three different geometrical modifications are applied to non-circular nozzles. These modifications include changing contraction profiles, the twist angles of transition, and nozzle lengths. The flow properties of air emanating from geometrically modified non-circular nozzles are studied by using computational fluid dynamics (CFD) in the Star CCM+ fluid solver. This computational analysis shows that suitably modified non-circular nozzles are very effective passive flow conditioning devices and can modify the flow field. Particularly, nozzle with a sharp exit and large twist angle entrains the ambient fluid at a higher rate than the circular and other modified non-circular nozzles.
A general-purpose IGA mesh generation method: NURBS Surface-to-Volume Guided Mesh Generation
(Springer Nature, 2024) Kuraishi, Takashi; Takizawa, Kenji; Tezduyar, Tayfun E.
The NURBS Surface-to-Volume Guided Mesh Generation (NSVGMG) is a general-purpose mesh generation method, introduced to increase the scope of isogeometric analysis in computing complex-geometry problems. In the NSVGMG, NURBS patch surface meshes serve as guides in generating the patch volume meshes. The interior control points are determined independent of each other, with only a small subset of the surface control points playing a role in determining each interior point. In the updated version of the NSVGMG we are introducing in this article, in the process of determining the location of an interior point in a parametric direction, more weight is given to the closer guides, with the closeness measured along the guides in the other parametric directions. Tests with 2D and 3D shapes show the effectiveness of the NSVGMG in generating good quality meshes, and the robustness of the updated NSVGMG even in mesh generation for complex shapes with distorted boundaries.
A hyperelastic extended Kirchhoff–Love shell model with out-of-plane normal stress: I. Out-of-plane deformation
(Springer Nature, 2022) Taniguchi, Yasutoshi; Takizawa, Kenji; Otoguro, Yuto; Tezduyar, Tayfun E.
This is the first part of a two-part article on a hyperelastic extended Kirchhoff–Love shell model with out-of-plane normal stress. We present the derivation of the new model, with focus on the mechanics of the out-of-plane deformation. Accounting for the out-of-plane normal stress distribution in the out-of-plane direction affects the accuracy in calculating the deformed-configuration out-of-plane position, and consequently the nonlinear response of the shell. The improvement is beyond what we get from accounting for the out-of-plane deformation mapping. By accounting for the out-of-plane normal stress, the traction acting on the shell can be specified on the upper and lower surfaces separately. With that, the new model is free from the “midsurface” location in terms of specifying the traction. We also present derivations related to the variation of the kinetic energy and the form of specifying the traction and moment acting on the upper and lower surfaces and along the edges. We present test computations for unidirectional plate bending, plate saddle deformation, and pressurized cylindrical and spherical shells. We use the neo-Hookean and Fung’s material models, for the compressible- and incompressible-material cases, and with the out-of-plane normal stress and without, which is the plane-stress case.
A linear-elasticity-based mesh moving method with no cycle-to-cycle accumulated distortion
(Springer Nature, 2021) Tonon, Patrícia; Sanches, Rodolfo André Kuche; Takizawa, Kenji; Tezduyar, Tayfun E.
Good mesh moving methods are always part of what makes moving-mesh methods good in computation of flow problems with moving boundaries and interfaces, including fluid–structure interaction. Moving-mesh methods, such as the space–time (ST) and arbitrary Lagrangian–Eulerian (ALE) methods, enable mesh-resolution control near solid surfaces and thus high-resolution representation of the boundary layers. Mesh moving based on linear elasticity and mesh-Jacobian-based stiffening (MJBS) has been in use with the ST and ALE methods since 1992. In the MJBS, the objective is to stiffen the smaller elements, which are typically placed near solid surfaces, more than the larger ones, and this is accomplished by altering the way we account for the Jacobian of the transformation from the element domain to the physical domain. In computing the mesh motion between time levels tn and tn+1 with the linear-elasticity equations, the most common option is to compute the displacement from the configuration at tn. While this option works well for most problems, because the method is path-dependent, it involves cycle-to-cycle accumulated mesh distortion. The back-cycle-based mesh moving (BCBMM) method, introduced recently with two versions, can remedy that. In the BCBMM, there is no cycle-to-cycle accumulated distortion. In this article, for the first time, we present mesh moving test computations with the BCBMM. We also introduce a version we call “half-cycle-based mesh moving” (HCBMM) method, and that is for computations where the boundary or interface motion in the second half of the cycle consists of just reversing the steps in the first half and we want the mesh to behave the same way. We present detailed 2D and 3D test computations with finite element meshes, using as the test case the mesh motion associated with wing pitching. The computations show that all versions of the BCBMM perform well, with no cycle-to-cycle accumulated distortion, and with the HCBMM, as the wing in the second half of the cycle just reverses its motion steps in the first half, the mesh behaves the same way.
A node-numbering-invariant directional length scale for simplex elements
(World Scientific, 2019) Takizawa, Kenji; Ueda, Yuki; Tezduyar, Tayfun E.
Variational multiscale methods, and their precursors, stabilized methods, have been very popular in flow computations in the past several decades. Stabilization parameters embedded in most of these methods play a significant role. The parameters almost always involve element length scales, most of the time in specific directions, such as the direction of the flow or solution gradient. We require the length scales, including the directional length scales, to have node-numbering invariance for all element types, including simplex elements. We propose a length scale expression meeting that requirement. We analytically evaluate the expression in the context of simplex elements and compared to one of the most widely used length scale expressions and show the levels of noninvariance avoided.
A Penalty Method Approach to Experimental Data Coupling in the Sequentially Optimized Meshfree Approximation
(2014-04-23) Wood, Jeffre; Meade, Andrew J., Jr.; Akin, John Edward.; Tezduyar, Tayfun E.
This thesis presents an overview of recent changes that have been made to the Sequentially Optimized Meshfree Approximation (SOMA) and provides a proof of concept for a penalty method algorithm for coupling experimental data with a computational fluid dynamics (CFD) solver. The penalty method provides a means to apply experimental data to improve SOMA's convergence rate and time to convergence. Using the driven cavity problem as validation, approximations produced using this adaptation are shown. The results successfully reproduces the flow from which the data was taken creating a means of using limited experimental data to generate a complete picture of a simulation domain. Flexibility in data type, location, and quantity are demonstrated as well as the effects of experimental error on the results and a means of negating it.
Advanced fluid-structure interaction techniques for modeling ringsail parachutes
(2010) Wright, Samuel E., III; Tezduyar, Tayfun E.
The Team for Advanced Flow Simulation and Modeling (T☆FSM) at Rice University specializes in developing fluid-structure interaction (FSI) modeling techniques for several classes of challenging problems including geometrically complex parachutes. Current modeling technologies are expanded upon with emphasis placed on more realistic FSI modeling of the Orion spacecraft ringsail parachutes. A method for generating a starting condition that matches NASA drop test data and allows for a fair comparison of design variations is introduced. The effect of the geometric porosity distribution on parachute performance and stability is analyzed for three parachute configurations. Rotationally periodic computations that model flow past the complex canopy geometry are presented. Fabric and geometric porosity coefficients are calculated for an improved FSI porosity model. A spatially multiscale technique is used to compare fabric stresses with and without a vent hoop.
Aorta zero-stress state modeling with T-spline discretization
(Springer, 2018) Sasaki, Takafumi; Takizawa, Kenji; Tezduyar, Tayfun E.
The image-based arterial geometries used in patient-specific arterial fluid–structure interaction (FSI) computations, such as aorta FSI computations, do not come from the zero-stress state (ZSS) of the artery. We propose a method for estimating the ZSS required in the computations. Our estimate is based on T-spline discretization of the arterial wall and is in the form of integration-point-based ZSS (IPBZSS). The method has two main components. (1) An iterative method, which starts with a calculated initial guess, is used for computing the IPBZSS such that when a given pressure load is applied, the image-based target shape is matched. (2) A method, which is based on the shell model of the artery, is used for calculating the initial guess. The T-spline discretization enables dealing with complex arterial geometries, such as an aorta model with branches, while retaining the desirable features of isogeometric discretization. With higher-order basis functions of the isogeometric discretization, we may be able to achieve a similar level of accuracy as with the linear basis functions, but using larger-size and much fewer elements. In addition, the higher-order basis functions allow representation of more complex shapes within an element. The IPBZSS is a convenient representation of the ZSS because with isogeometric discretization, especially with T-spline discretization, specifying conditions at integration points is more straightforward than imposing conditions on control points. Calculating the initial guess based on the shell model of the artery results in a more realistic initial guess. To show how the new ZSS estimation method performs, we first present 3D test computations with a Y-shaped tube. Then we show a 3D computation where the target geometry is coming from medical image of a human aorta, and we include the branches in our model.
Arterial fluid mechanics computations with the stabilized space-time fluid-structure interaction techniques
(2007) Nanna, W. L. Bryan; Tezduyar, Tayfun E.
The stabilized space-time fluid-structure interaction (SSTFSI) techniques developed by the Team for Advanced Flow Simulation and Modeling (T☆AFSM) are applied to the field of arterial fluid mechanics through the FSI modeling of a cerebral artery with a small, saccular aneurysm. All arterial structures are modeled with membrane elements, which are geometrically nonlinear. FSI computations of cardio-vascular systems presently interest the scientific community as such types of analysis provide a non-invasive means of analyzing a patient's condition and risk for aneurysm rupture, a potentially life-threatening condition. Test computations for varying arterial wall thickness and blood pressure are presented for this cerebral aneurysm, with the arterial geometries of the computations closely approximating patient-specific image-based data. Results show the T☆AFSM's ability to handle complex and realistic FSI simulations while demonstrating the capability and utility of FSI simulations in the field of cardiovascular fluid mechanics.
Carrier-Domain Method for high-resolution computation of time-periodic long-wake flows
(Springer Nature, 2023) Liu, Yang; Takizawa, Kenji; Tezduyar, Tayfun E.; Kuraishi, Takashi; Zhang, Yufei
We are introducing the Carrier-Domain Method (CDM) for high-resolution computation of time-periodic long-wake flows, with cost-effectives that makes the computations practical. The CDM is closely related to the Multidomain Method, which was introduced 24 years ago, originally intended also for cost-effective computation of long-wake flows and later extended in scope to cover additional classes of flow problems. In the CDM, the computational domain moves in the free-stream direction, with a velocity that preserves the outflow nature of the downstream computational boundary. As the computational domain is moving, the velocity at the inflow plane is extracted from the velocity computed earlier when the plane’s current position was covered by the moving domain. The inflow data needed at an instant is extracted from one or more instants going back in time as many periods. Computing the long-wake flow with a high-resolution moving mesh that has a reasonable length would certainly be far more cost-effective than computing it with a fixed mesh that covers the entire length of the wake. We are also introducing a CDM version where the computational domain moves in a discrete fashion rather than a continuous fashion. To demonstrate how the CDM works, we compute, with the version where the computational domain moves in a continuous fashion, the 2D flow past a circular cylinder at Reynolds number 100. At this Reynolds number, the flow has an easily discernible vortex shedding frequency and widely published lift and drag coefficients and Strouhal number. The wake flow is computed up to 350 diameters downstream of the cylinder, far enough to see the secondary vortex street. The computations are performed with the Space–Time Variational Multiscale method and isogeometric discretization; the basis functions are quadratic NURBS in space and linear in time. The results show the power of the CDM in high-resolution computation of time-periodic long-wake flows.
Compressible-flow geometric-porosity modeling and spacecraft parachute computation with isogeometric discretization
(Springer, 2018) Kanai, Taro; Takizawa, Kenji; Tezduyar, Tayfun E.; Tanaka, Tatsuya; Hartmann, Aaron
One of the challenges in computational fluid–structure interaction (FSI) analysis of spacecraft parachutes is the “geometric porosity,” a design feature created by the hundreds of gaps and slits that the flow goes through. Because FSI analysis with resolved geometric porosity would be exceedingly time-consuming, accurate geometric-porosity modeling becomes essential. The geometric-porosity model introduced earlier in conjunction with the space–time FSI method enabled successful computational analysis and design studies of the Orion spacecraft parachutes in the incompressible-flow regime. Recently, porosity models and ST computational methods were introduced, in the context of finite element discretization, for compressible-flow aerodynamics of parachutes with geometric porosity. The key new component of the ST computational framework was the compressible-flow ST slip interface method, introduced in conjunction with the compressible-flow ST SUPG method. Here, we integrate these porosity models and ST computational methods with isogeometric discretization. We use quadratic NURBS basis functions in the computations reported. This gives us a parachute shape that is smoother than what we get from a typical finite element discretization. In the flow analysis, the combination of the ST framework, NURBS basis functions, and the SUPG stabilization assures superior computational accuracy. The computations we present for a drogue parachute show the effectiveness of the porosity models, ST computational methods, and the integration with isogeometric discretization.
Computation of Flapping-Wing Fluid–Structure Interaction
(2016-04-25) Zhang, Ruochun; Tezduyar, Tayfun E.
This thesis is on computational fluid–structure interaction (FSI) analysis of bioinspired wing flapping, based on an actual locust in wind tunnel. The wing motion is partially prescribed from high-speed video recordings of the locust. The computational analysis is performed with the Sequentially Coupled FSI (SCFSI) method as well as (full) FSI modeling. The thesis features using the Space–Time Slip Interface (ST-SI) technique to address the computational challenge created by near topology changes. Furthermore, we explore the possibility of using in the analysis the ST Isogeometric Analysis (ST-IGA) with NURBS basis functions in space. We start that exploration by conducting a developed-flow computation for the starting positions of the wings. The work provides a valuable way in studying insects of different species with flapping wings, and in understanding the aerodynamic performance of different bioinspired aerial vehicles. The core computational technology is the ST Variational Multiscale (ST-VMS) method, which is a moving-mesh method that allows us maintain mesh quality and resolution near fluid–structure interfaces and offers accurate solutions in both space and time. In addition, techniques including ST-SI method, ST-IGA method and mesh-moving based on elasticity equations (JBS), are employed in the computation.
Computational Aerodynamics Modeling of Flapping Wings With Video-Tracked Locust-Wing Motion
(2013-07-24) Puntel, Anthony; Tezduyar, Tayfun E.; Akin, John Edward.; Meade, Andrew J., Jr.; Takizawa, Kenji
The thesis focuses on special space--time computational techniquesintroduced recently for computational aerodynamics modeling of flapping wings of an actual locust. These techniques complement the Deforming-Spatial-Domain/Stabilized Space--Time (DSD/SST) formulation, which is the core computational technique. The DSD/SST formulation was developed for flows with moving interfaces, and the version used in the computations is "DST/SST-VMST," which is the space--time version of the residual-based variational multiscale (VMS) method. The special space--time techniques are based on using NURBS basis functions for the temporal representation of the motion of the locust wings. The motion data is extracted from the high-speed video recordings of a locust in a wind tunnel. In addition, temporal NURBS basis functions are used in representation of the motion of the volume meshes computed and also in remeshing. These ingredients provide an accurate and e fficient way of dealing with the wind tunnel data and the mesh. The thesis includes a detailed study on how the spatial and temporal resolutions influence the quality of the numerical solution.
Computational aerodynamics modeling of the reefed stages of ringsail parachutes
(2009) Christopher, Jason Daniel; Tezduyar, Tayfun E.
The Team for Advanced Flow Simulation and Modeling (T*AFSM) at Rice University has been using the Stabilized Space-Time Fluid-Structure Interaction (SSTFSI) they developed to model parachute aerodynamics. The complexity of ringsail parachutes requires additional techniques for successful modeling of the reefed stages. Methods developed for this purpose include sequential shape determination, which is an iterative method for determining a shape and corresponding flow field, and coupled FSI using a circumferentially symmetrized traction applied to the parachute. In addition to modeling the reefed stages, these methods provide a suitable starting point for full FSI computations. A multiscale sequentially-coupled FSI computation, together with cable symmetrization, can be used to obtain a refined structural mechanics solution where needed. Furthermore, pressure distribution generation can be used to match structural shapes to drop test observations.
Computational Analysis of a Diesel Engine Exhaust Manifold and Turbocharger Turbine
(2018-04-20) Fu, Mingyuan; Tezduyar, Tayfun E.
The unsteady nature of the flow in turbocharges makes computational flow analysis challenging. The unsteadiness comes from the engine cycle and the flow in the exhaust manifold and turbocharger turbine. An additional challenge is that the time scale of the engine cycle is much larger than that of the turbine because of high turbine rotation speeds. This requires long-duration computations in the turbine time scale. We provide computational analysis of the turbine with different inflow and turbine rotation rates and the combined system of the manifold, turbine and the gas purifier device with steady and unsteady inflow. The core computational method is the space--time (ST) variational multiscale (ST-VMS) method. The other key methods are the ST Slip Interface (ST-SI) method, ST/NURBS mesh update method (STNMUM), and the ST Isogeometric Analysis (ST-IGA). The ST framework provides higher-order accuracy. The VMS feature of the ST-VMS addresses the computational challenges associated with turbulent flows. With the ST-SI, the mesh covering the rotor spins with it, retaining the high-resolution representation of the boundary layers. The SI between the spinning mesh and the rest of the mesh accurately connects the two sides of the flow field. An SI also provides mesh generation flexibility in a general context by accurately connecting the two sides of the solution computed over nonmatching meshes, which is helpful in isogeometric discretization. The STNMUM enables accurate representation of the mesh rotation. The ST-IGA provides more accurate representation of the geometry and increased accuracy in the flow solution. Because the ST-IGA provides higher spatial accuracy with less number of control points, and consequently with larger effective element sizes, it also enables using larger time-step sizes while keeping the Courant number at a desirable level for good accuracy. The computations show that the ST methods we use here are very effective in turbocharger flow analysis.
Computational Analysis of Flow in a Turbocharger Turbine with Pulsating Inflow
(2016-08-30) Mei, Sen; Tezduyar, Tayfun E.
The turbine of an automobile turbocharger commonly operates under pulsating inflow, which leads to an undesired “hysteresis” performance. This study is to investigate this phenomenon by presenting a computational flow analysis that can capture the pulsating flow physics in a turbocharger turbine. We use a method of higher-order accuracy, and the key techniques include: (i) the Space–Time Variational Multiscale (ST-VMS) method, which is a stabilized formulation and a turbulence model, (ii) the ST Slip Interface (ST-SI) method, which maintains the solution quality near rotor surface, (iii) the Isogeometric Analysis (IGA), where we use NURBS basis functions in space and time, and (iv) weakly-imposed Dirichlet boundary conditions, which can give accurate mean flow solutions on a coarse mesh with unresolved boundary layers. The geometric model is from a realistic turbocharger turbine. The pulsating inflow conditions are taken from a 1D engine-cycle simulation. The computations are carried out with an incompressible-flow solver. The results show that the turbine is likely to operate far from nominal conditions under pulsating inflow, and geometric features such as exhaust manifold and vanes play a significant role in improving the performance. The techniques show a good potential for solving difficult turbomachinery problems.
Coronary arterial dynamics computation with medical-image-based time-dependent anatomical models and element-based zero-stress state estimates
(Springer, 2014) Takizawa, Kenji; Torii, Ryo; Takagi, Hirokazu; Tezduyar, Tayfun E.; Xu, Xiao Y.
We propose a method for coronary arterial dynamics computation with medical-image-based time-dependent anatomical models. The objective is to improve the computational analysis of coronary arteries for better understanding of the links between the atherosclerosis development and mechanical stimuli such as endothelial wall shear stress and structural stress in the arterial wall. The method has two components. The first one is element-based zero-stress (ZS) state estimation, which is an alternative to prestress calculation. The second one is a “mixed ZS state” approach, where the ZS states for different elements in the structural mechanics mesh are estimated with reference configurations based on medical images coming from different instants within the cardiac cycle. We demonstrate the robustness of the method in a patient-specific coronary arterial dynamics computation where the motion of a thin strip along the arterial surface and two cut surfaces at the arterial ends is specified to match the motion extracted from the medical images.
Enhanced-discretization and solution techniques in flow simulations and parachute fluid-structure interactions
(2004) Sathe, Sunil Vijay; Tezduyar, Tayfun E.
We present three innovative approaches for simulations of parachute fluid-structure interactions (FSI), which otherwise tend to be unstable because of extreme sensitivity of thin membrane structure to massive fluid dynamic forces. In the first approach, we use an iterative scheme in conjunction with augmented structural mass matrix to achieve convergence in coupling the fluid and the structure motion. In the second approach, we use a coupled formulation that includes the inter-dependence of fluid and structure motion. The dependence of flow on domain deformation is addressed iteratively in this approach. Finally in the third approach, we use a directly coupled formulation that fully incorporates the inter-dependence of fluid, structure and mesh motion. All the three approaches accurately predict parachute FSI and successful FSI simulations of soft landing of T-10, G-12 and G-11 parachutes are presented to provide corroborating evidence. To further improve the quality of FSI simulations, carried out using any of the three coupling approaches, we present more enhanced-discretization and solution techniques. We present definitions of the stabilization parameters used in SUPG and PSPG formulations based on local length scales that are shown to be accurate and less dissipative. We also present an Enhanced-Discretization Space-Time Technique (EDSTT) that has tremendous potential in saving significant amount of computational time as it allows us to use different time-step sizes in different regions of a computational domain. Complementary to EDSTT, we propose an Enhanced-Discretization Successive Update Method (EDSUM) which resolves small scale information in flow simulations. We have also described a variation of EDSUM that gives dramatic rates of convergence in solving linear equation systems. Another effort toward accurately solving linear equation systems is the Enhanced-Approximation Linear Solution Technique (EALST) that we propose for improving the convergence in selected regions of the flow. All these techniques are successfully tested on a variety of problems and the results obtained are unequivocally satisfactory.
Fluid--Structure Interaction Modeling of Modified-Porosity Parachutes and Parachute Clusters
(2013-09-16) Boben, Joseph; Tezduyar, Tayfun E.; Akin, John Edward.; Meade, Andrew J., Jr.; Takizawa, Kenji
To increase aerodynamic performance, the geometric porosity of a ringsail spacecraft parachute canopy is sometimes increased, beyond the "rings" and "sails" with hundreds of "ring gaps" and "sail slits." This creates extra computational challenges for fluid--structure interaction (FSI) modeling of clusters of such parachutes, beyond those created by the lightness of the canopy structure, geometric complexities of hundreds of gaps and slits, and the contact between the parachutes of the cluster. In FSI computation of parachutes with such "modified geometric porosity," the flow through the "windows" created by the removal of the panels and the wider gaps created by the removal of the sails cannot be accurately modeled with the Homogenized Modeling of Geometric Porosity (HMGP), which was introduced to deal with the hundreds of gaps and slits. The flow needs to be actually resolved. All these computational challenges need to be addressed simultaneously in FSI modeling of clusters of spacecraft parachutes with modified geometric porosity. The core numerical technology is the Stabilized Space--Time FSI (SSTFSI) technique, and the contact between the parachutes is handled with the Surface-Edge-Node Contact Tracking (SENCT) technique. In the computations reported here, in addition to the SSTFSI and SENCT techniques and HMGP, we use the special techniques we have developed for removing the numerical spinning component of the parachute motion and for restoring the mesh integrity without a remesh. We present results for 2- and 3-parachute clusters with two different payload models. We also present the FSI computations we carried out for a single, subscale modified-porosity parachute.

Browsing by Author "Tezduyar, Tayfun E."

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