Stabilized Space Time Fluid–structure Interaction Research Articles

METHODS FOR FSI MODELING OF SPACECRAFT PARACHUTE DYNAMICS AND COVER SEPARATION

Fluid–structure interaction (FSI) modeling of spacecraft parachutes involves a number of computational challenges beyond those encountered in a typical FSI problem. The stabilized space–time FSI (SSTFSI) technique serves as a robust and accurate core FSI method, and a number of special FSI methods address the computational challenges specific to spacecraft parachutes. Some spacecraft FSI problems involve even more specific computational challenges and require additional special methods. An example of that is the impulse ejection and parachute extraction of a protective cover used in a spacecraft. The computational challenges specific to this problem are related to the sudden changes in the parachute loads and sudden separation of the cover with very little initial clearance from the spacecraft. We describe the core and special FSI methods, and present the methods we use in FSI analysis of the parachute dynamics and cover separation, including the temporal NURBS representation in modeling the separation motion.

Fluid–structure interaction modeling of ringsail parachutes with disreefing and modified geometric porosity

Fluid---structure interaction (FSI) modeling of parachutes poses a number of computational challenges. These include the lightness of the parachute canopy compared to the air masses involved in the parachute dynamics, in the case of ringsail parachutes the geometric porosity created by the construction of the canopy from "rings" and "sails" with hundreds of "ring gaps" and "sail slits," in the case of parachute clusters the contact between the parachutes, and "disreefing" from one stage to another when the parachute is used in multiple stages. The Team for Advanced Flow Simulation and Modeling (T?AFSM) has been successfully addressing these computational challenges with the Stabilized Space---Time FSI (SSTFSI) technique, which was developed and improved over the years by the T?AFSM and serves as the core numerical technology, and a number of special techniques developed in conjunction with the SSTFSI technique. The quasi-direct and direct coupling techniques developed by the T?AFSM, which are applicable to cases with nonmatching fluid and structure meshes at the interface, yield more robust algorithms for FSI computations where the structure is light. The special technique used in dealing with the geometric complexities of the rings and sails is the homogenized modeling of geometric porosity (HMGP), which was developed and improved in recent years by the T?AFSM. The surface-edge-node contact tracking (SENCT) technique was introduced by the T?AFSM as a contact algorithm where the objective is to prevent the structural surfaces from coming closer than a minimum distance in an FSI computation. The recently-introduced conservative version of the SENCT technique is more robust and is now an essential technology in the parachute cluster computations carried out by the T?AFSM. As an additional computational challenge, the parachute canopy might, by design, have some of its panels and sails removed. 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 HMGP and needs to be actually resolved during the FSI computation. In this paper we focus on parachute disreefing, including the disreefing of parachute clusters, and parachutes with modified geometric porosity, including the reefed stages of such parachutes. We describe the additional special techniques we have developed to address the challenges involved and report FSI computations for parachutes and parachute clusters with disreefing and modified geometric porosity.

Space–Time and ALE-VMS Techniques for Patient-Specific Cardiovascular Fluid–Structure Interaction Modeling

This is an extensive overview of the core and special space–time and Arbitrary Lagrangian–Eulerian (ALE) techniques developed by the authors’ research teams for patient-specific cardiovascular fluid–structure interaction (FSI) modeling. The core techniques are the ALE-based variational multiscale (ALE-VMS) method, the Deforming-Spatial-Domain/Stabilized Space–Time formulation, and the stabilized space–time FSI technique. The special techniques include methods for calculating an estimated zero-pressure arterial geometry, prestressing of the blood vessel wall, a special mapping technique for specifying the velocity profile at an inflow boundary with non-circular shape, techniques for using variable arterial wall thickness, mesh generation techniques for building layers of refined fluid mechanics mesh near the arterial walls, a recipe for pre-FSI computations that improve the convergence of the FSI computations, the Sequentially-Coupled Arterial FSI technique and its multiscale versions, techniques for the projection of fluid–structure interface stresses, calculation of the wall shear stress and oscillatory shear index, arterial-surface extraction and boundary condition techniques, and a scaling technique for specifying a more realistic volumetric flow rate. With results from earlier computations, we show how these core and special FSI techniques work in patient-specific cardiovascular simulations.

Computational Methods for Parachute Fluid–Structure Interactions

The computational challenges posed by fluid–structure interaction (FSI) modeling of parachutes include the lightness of the parachute canopy compared to the air masses involved in the parachute dynamics, in the case of “ringsail” parachutes the geometric complexities created by the construction of the canopy from “rings” and “sails” with hundreds of ring “gaps” and sail “slits”, and in the case of parachute clusters the contact between the parachutes. The Team for Advanced Flow Simulation and Modeling ( ) has successfully addressed these computational challenges with the Stabilized Space–Time FSI (SSTFSI) technique, which was developed and improved over the years by the and serves as the core numerical technology, and a number of special techniques developed in conjunction with the SSTFSI technique. The quasi-direct and direct coupling techniques developed by the , which are applicable to cases with incompatible fluid and structure meshes at the interface, yield more robust algorithms for FSI computations where the structure is light and therefore more sensitive to the variations in the fluid dynamics forces. The special technique used in dealing with the geometric complexities of the rings and sails is the Homogenized Modeling of Geometric Porosity, which was developed and improved in recent years by the . The Surface-Edge-Node Contact Tracking (SENCT) technique was introduced by the as a contact algorithm where the objective is to prevent the structural surfaces from coming closer than a minimum distance in an FSI computation. The recently-introduced conservative version of the SENCT technique is more robust and is now an essential technology in the parachute cluster computations carried out by the . We provide an overview of the core and special techniques developed by the , present single-parachute FSI computations carried out for design-parameter studies, and report FSI computation and dynamical analysis of two-parachute clusters.

Space–time fluid–structure interaction modeling of patient‐specific cerebral aneurysms

AbstractWe provide an extensive overview of the core and special techniques developed earlier by the Team for Advanced Flow Simulation and Modeling (T★AFSM) for space–time fluid–structure interaction (FSI) modeling of patient‐specific cerebral aneurysms. The core FSI techniques are the Deforming‐Spatial‐Domain/Stabilized Space–Time (DSD/SST) formulation and the stabilized space–time FSI (SSTFSI) technique. The special techniques include techniques for calculating an estimated zero‐pressure (EZP) arterial geometry, a special mapping technique for specifying the velocity profile at an inflow boundary with non‐circular shape, techniques for using variable arterial wall thickness, mesh generation techniques for building layers of refined fluid mechanics mesh near the arterial walls, a recipe for pre‐FSI computations that improve the convergence of the FSI computations, the Sequentially‐Coupled Arterial FSI (SCAFSI) technique and its multiscale versions, techniques for the projection of fluid–structure interface stresses, calculation of the wall shear stress (WSS) and calculation of the oscillatory shear index (OSI) and arterial‐surface extraction and boundary condition techniques. We show how these techniques work with results from earlier computations. We also describe the arterial FSI techniques developed and implemented recently by the T★AFSM and present a sample from a wide set of patient‐specific cerebral‐aneurysm models we computed recently. Copyright © 2011 John Wiley & Sons, Ltd.

Fluid–structure interaction modeling and performance analysis of the Orion spacecraft parachutes

AbstractWe focus on fluid–structure interaction (FSI) modeling and performance analysis of the ringsail parachutes to be used with the Orion spacecraft. We address the computational challenges with the latest techniques developed by the T★AFSM (Team for Advanced Flow Simulation and Modeling) in conjunction with the SSTFSI (Stabilized Space–Time Fluid–Structure Interaction) technique. The challenges involved in FSI modeling include the geometric porosity of the ringsail parachutes with ring gaps and sail slits. We investigate the performance of three possible design configurations of the parachute canopy. We also describe the techniques developed recently for building a consistent starting condition for the FSI computations, discuss rotational periodicity techniques for improving the geometric‐porosity modeling, and introduce a new version of the HMGP (Homogenized Modeling of Geometric Porosity). Copyright © 2010 John Wiley & Sons, Ltd.

Fluid–structure interaction modeling of parachute clusters

AbstractWe address some of the computational challenges involved in fluid–structure interaction (FSI) modeling of clusters of ringsail parachutes. The geometric complexity created by the construction of the parachute from ‘rings’ and ‘sails’ with hundreds of gaps and slits makes this class of FSI modeling inherently challenging. There is still much room for advancing the computational technology for FSI modeling of a single raingsail parachute, such as improving the Homogenized Modeling of Geometric Porosity (HMGP) and developing special techniques for computing the reefed stages of the parachute and its disreefing. While we continue working on that, we are also developing special techniques targeting cluster modeling, so that the computational technology goes beyond the single parachute and the challenges specific to parachute clusters are addressed. The rotational‐periodicity technique we describe here is one of such special techniques, and we use that for computing good starting conditions for FSI modeling of parachute clusters. In addition to reporting our preliminary FSI computations for parachute clusters, we present results from those starting‐condition computations. In the category of more fundamental computational technologies, we discuss how we are improving the HMGP by increasing the resolution of the fluid mechanics mesh used in the HMGP computation and also by increasing the number of gores used. Also in that category, we describe how we use the multiscale sequentially coupled FSI techniques to improve the accuracy in computing the structural stresses in parts of the structure where we want to report more accurate values. All these special techniques are used in conjunction with the Stabilized Space–Time Fluid–Structure Interaction (SSTFSI) technique. Therefore, we also present in this paper a brief stability and accuracy analysis for the Deforming‐Spatial‐Domain/Stabilized Space–Time (DSD/SST) formulation, which is the core numerical technology of the SSTFSI technique. Copyright © 2010 John Wiley & Sons, Ltd.

Space–time finite element computation of complex fluid–structure interactions

AbstractNew special fluid–structure interaction (FSI) techniques, supplementing the ones developed earlier, are employed with the Stabilized Space–Time FSI (SSTFSI) technique. The new special techniques include improved ways of calculating the equivalent fabric porosity in Homogenized Modeling of Geometric Porosity (HMGP), improved ways of building a starting point in FSI computations, ways of accounting for fluid forces acting on structural components that are not expected to influence the flow, adaptive HMGP, and multiscale sequentially coupled FSI techniques. While FSI modeling of complex parachutes was the motivation behind developing some of these techniques, they are also applicable to other classes of complex FSI problems. We also present new ideas to increase the scope of our FSI and CFD techniques. Copyright © 2009 John Wiley & Sons, Ltd.

Wall shear stress calculations in space–time finite element computation of arterial fluid–structure interactions

The stabilized space–time fluid–structure interaction (SSTFSI) technique was applied to arterial FSI problems soon after its development by the Team for Advanced Flow Simulation and Modeling. The SSTFSI technique is based on the Deforming-Spatial-Domain/Stabilized Space–Time (DSD/SST) formulation and is supplemented with a number of special techniques developed for arterial FSI. The special techniques developed in the recent past include a recipe for pre-FSI computations that improve the convergence of the FSI computations, using an estimated zero-pressure arterial geometry, Sequentially Coupled Arterial FSI technique, using layers of refined fluid mechanics mesh near the arterial walls, and a special mapping technique for specifying the velocity profile at inflow boundaries with non-circular shape. In this paper we introduce some additional special techniques, related to the projection of fluid–structure interface stresses, calculation of the wall shear stress (WSS), and calculation of the oscillatory shear index. In the test computations reported here, we focus on WSS calculations in FSI modeling of a patient-specific middle cerebral artery segment with aneurysm. Two different structural mechanics meshes and three different fluid mechanics meshes are tested to investigate the influence of mesh refinement on the WSS calculations.

Space–time finite element computation of arterial fluid–structure interactions with patient‐specific data

AbstractThe stabilized space–time fluid–structure interaction (SSTFSI) technique developed by the team for advanced flow simulation and modeling is applied to the computation of arterial fluid–structure interaction (FSI) with patient‐specific data. The SSTFSI technique is based on the deforming‐spatial‐domain/stabilized space–time formulation and is supplemented with a number of special techniques developed for arterial FSI. These include a recipe for pre‐FSI computations that improve the convergence of the FSI computations, using an estimated zero‐pressure arterial geometry, layers of refined fluid mechanics mesh near the arterial walls, and a special mapping technique for specifying the velocity profile at an inflow boundary with non‐circular shape. In the test computations reported here, we focus on a patient‐specific middle cerebral artery segment with aneurysm, where the arterial geometry is based on computed tomography images. Copyright © 2009 John Wiley & Sons, Ltd.

Fluid–structure interaction modeling of ringsail parachutes

In this paper, we focus on fluid–structure interaction (FSI) modeling of ringsail parachutes, where the geometric complexity created by the “rings” and “sails” used in the construction of the parachute canopy poses a significant computational challenge. It is expected that NASA will be using a cluster of three ringsail parachutes, referred to as the “mains”, during the terminal descent of the Orion space vehicle. Our FSI modeling of ringsail parachutes is based on the stabilized space–time FSI (SSTFSI) technique and the interface projection techniques that address the computational challenges posed by the geometric complexities of the fluid–structure interface. Two of these interface projection techniques are the FSI Geometric Smoothing Technique and the Homogenized Modeling of Geometric Porosity. We describe the details of how we use these two supplementary techniques in FSI modeling of ringsail parachutes. In the simulations we report here, we consider a single main parachute, carrying one third of the total weight of the space vehicle. We present results from FSI modeling of offloading, which includes as a special case dropping the heat shield, and drifting under the influence of side winds.

Interface projection techniques for fluid–structure interaction modeling with moving-mesh methods

The stabilized space–time fluid–structure interaction (SSTFSI) technique developed by the Team for Advanced Flow Simulation and Modeling (T★AFSM) was applied to a number of 3D examples, including arterial fluid mechanics and parachute aerodynamics. Here we focus on the interface projection techniques that were developed as supplementary methods targeting the computational challenges associated with the geometric complexities of the fluid–structure interface. Although these supplementary techniques were developed in conjunction with the SSTFSI method and in the context of air–fabric interactions, they can also be used in conjunction with other moving-mesh methods, such as the Arbitrary Lagrangian–Eulerian (ALE) method, and in the context of other classes of FSI applications. The supplementary techniques currently consist of using split nodal values for pressure at the edges of the fabric and incompatible meshes at the air–fabric interfaces, the FSI Geometric Smoothing Technique (FSI-GST), and the Homogenized Modeling of Geometric Porosity (HMGP). Using split nodal values for pressure at the edges and incompatible meshes at the interfaces stabilizes the structural response at the edges of the membrane used in modeling the fabric. With the FSI-GST, the fluid mechanics mesh is sheltered from the consequences of the geometric complexity of the structure. With the HMGP, we bypass the intractable complexities of the geometric porosity by approximating it with an “equivalent”, locally-varying fabric porosity. As test cases demonstrating how the interface projection techniques work, we compute the air–fabric interactions of windsocks, sails and ringsail parachutes.

Arterial fluid mechanics modeling with the stabilized space–time fluid–structure interaction technique

AbstractWe present an overview of how the arterial fluid mechanics problems can be modeled with the stabilized space–time fluid–structure interaction (SSTFSI) technique developed by the Team for Advanced Flow Simulation and Modeling (T★AFSM). The SSTFSI technique includes the enhancements introduced recently by the T★AFSM to increase the scope, accuracy, robustness and efficiency of this class of techniques. The SSTFSI technique is supplemented with a number of special techniques developed for arterial fluid mechanics modeling. These include a recipe for pre‐FSI computations that improve the convergence of the FSI computations, using an estimated zero‐pressure arterial geometry, and the sequentially coupled arterial FSI (SCAFSI) technique. The recipe for pre‐FSI computations is based on the assumption that the arterial deformation during a cardiac cycle is driven mostly by the blood pressure. The SCAFSI technique, which was introduced as an approximate FSI approach in arterial fluid mechanics, is also based on that assumption. The need for an estimated zero‐pressure arterial geometry is based on recognizing that the patient‐specific image‐based geometries correspond to time‐averaged blood pressure values. In our arterial fluid mechanics modeling the arterial walls can be represented with the membrane or continuum elements, both of which are geometrically nonlinear, and the continuum element is made of hyperelastic (Fung) material. Test computations are presented for cerebral and abdominal aortic aneurysms, where the arterial geometries used in the computations are close approximations to the patient‐specific image‐based data. Copyright © 2007 John Wiley & Sons, Ltd.

Preface

This special issue is a collection of the papers contributed by authors who were invited to speak at the minisymposium on Stabilized, Multiscale and Multiphysics Methods, World Congress on Computational Mechanics, Los Angeles, CA, 16–22 July 2006. The minisymposium was organized by Arif Masud (University of Illinois at Urbana-Champaign), Tayfun E. Tezduyar (Rice University) and Thomas J.R. Hughes (University of Texas, Austin). The topics covered in this collection of papers can be categorized into two main areas: (i) Fundamental and Enabling Technologies, and (ii) Moving Boundaries and Interfaces. The topics covered in Fundamental and Enabling Technologies include: methods for advection-dominated processes, discontinuity-capturing and shock-capturing techniques, arterial drug delivery, methods for compressible flows, turbulent flow computations with finite calculus–finite element formulations, mixed finite element methods for Darcy–Stokes flow, objectivity in Laplace formulations of the Navier–Stokes equations, Galilean invariance of the stabilized methods for compressible flows, vorticity–strain residual-based turbulence modelling of the Taylor–Green vortex, spatial and temporal multiscale methods for transient convection–diffusion–reaction equations, semidiscrete formulations for transient transport at small time steps, adjoint weighted equations for steady advection in compressible flows, and dynamic subscales in the finite element approximation of thermally coupled incompressible flows. The second main area, Moving Boundaries and Interfaces, includes fluid–structure interactions (FSI), free-surface flows and fluid–fluid interfaces. The topics covered in this area include: the Stabilized Space–Time Fluid–Structure Interaction technique, FSI modelling in arterial fluid mechanics including aneurysms, effect of hypertensive blood pressure on cerebral aneurysm, mesoscale analysis of lipid bilayers with the dissipative particle dynamics method, 3D adaptive mesh moving schemes, CIP method based on adaptive Soroban grids, ship hydrodynamics, adaptive control systems using the fuzzy theory for multi-physics simulations, FSI modelling of membrane–wind interactions, modelling of fluid–solid and fluid–fluid interfaces with the Mixed Interface–Tracking/Interface–Capturing Technique, and modelling of free-surface flows with edge-based finite element methods. We would like to thank the authors for the effort in preparing their contributions and for meeting the deadlines. We also would like to thank those whom we asked for their help in reviewing these papers.

Modelling of fluid–structure interactions with the space–time finite elements: Arterial fluid mechanics

AbstractThe stabilized space–time fluid–structure interaction (SSTFSI) techniques developed by the Team for Advanced Flow Simulation and Modeling (T★AFSM) are applied to FSI modelling in arterial fluid mechanics. Modelling of flow in arteries with aneurysm is emphasized. The SSTFSI techniques used are based on the deforming‐spatial‐domain/stabilized space–time (DSD/SST) formulation and include the enhancements introduced recently by the T★AFSM to increase the scope, accuracy, robustness and efficiency of these techniques. The arterial structures can be modelled with the membrane or continuum elements, both of which are geometrically nonlinear, and the continuum element can be made of linearly elastic or hyperelastic material. Test computations are presented for cerebral and abdominal aortic aneurysms and carotid‐artery bifurcation, where the arterial geometries used in the computations are close approximations to the patient‐specific image‐based data. Copyright © 2007 John Wiley & Sons, Ltd.

Modelling of fluid–structure interactions with the space–time finite elements: Solution techniques

AbstractThe space–time fluid–structure interaction (FSI) techniques developed by the Team for Advanced Flow Simulation and Modeling (T★AFSM) have been applied to a wide range of 3D computation of FSI problems, some as early as in 1994 and many with challenging complexities. In this paper, we review these space–time FSI techniques and describe the enhancements introduced recently by the T★AFSM to increase the scope, accuracy, robustness and efficiency of these techniques. The aspects of the FSI solution process enhanced include the deforming‐spatial‐domain/stabilized space–time (DSD/SST) formulation, the fluid–structure interface conditions, the preconditioning techniques used in iterative solution of the linear equation systems, and a contact algorithm protecting the quality of the fluid mechanics mesh between the structural surfaces coming into contact. We present a number of 3D numerical examples computed with these new stabilized space–time FSI (SSTFSI) techniques. Copyright © 2007 John Wiley & Sons, Ltd.