title: An immersogeometric variational framework for fluid-structure interaction: application to bioprosthetic heart valves.
abstract: In this paper, we develop a geometrically flexible technique for computational fluid-structure interaction (FSI). The motivating application is the simulation of tri-leaflet bioprosthetic heart valve function over the complete cardiac cycle. Due to the complex motion of the heart valve leaflets, the fluid domain undergoes large deformations, including changes of topology. The proposed method directly analyzes a spline-based surface representation of the structure by immersing it into a non-boundary-fitted discretization of the surrounding fluid domain. This places our method within an emerging class of computational techniques that aim to capturegeometryon non-boundary-fitted analysis meshes. We introduce the term "immersogeometric analysis" to identify this paradigm. The framework starts with an augmented Lagrangian formulation for FSI that enforces kinematic constraints with a combination of Lagrange multipliers and penalty forces. For immersed volumetric objects, we formally eliminate the multiplier field by substituting a fluid-structure interface traction, arriving at Nitsche's method for enforcing Dirichlet boundary conditions on object surfaces. For immersed thin shell structures modeled geometrically as surfaces, the tractions from opposite sides cancel due to the continuity of the background fluid solution space, leaving a penalty method. Application to a bioprosthetic heart valve, where there is a large pressure jump across the leaflets, reveals shortcomings of the penalty approach. To counteract steep pressure gradients through the structure without the conditioning problems that accompany strong penalty forces, we resurrect the Lagrange multiplier field. Further, since the fluid discretization is not tailored to the structure geometry, there is a significant error in the approximation of pressure discontinuities across the shell. This error becomes especially troublesome in residual-based stabilized methods for incompressible flow, leading to problematic compressibility at practical levels of refinement. We modify existing stabilized methods to improve performance. To evaluate the accuracy of the proposed methods, we test them on benchmark problems and compare the results with those of established boundary-fitted techniques. Finally, we simulate the coupling of the bioprosthetic heart valve and the surrounding blood flow under physiological conditions, demonstrating the effectiveness of the proposed techniques in practical computations.
authors.affiliation: Center for Cardiovascular Simulation, Institute for Computational Engineering and Sciences, The University of Texas at Austin, 201 East 24th St, Stop C0200, Austin, TX 78712, USA.
authors.forename: David
authors.initials: D
authors.lastname: Kamensky
authors.affiliation: Department of Mechanical Engineering, Iowa State University, 2025 Black Engineering, Ames, IA 50011, USA.
authors.forename: Ming-Chen
authors.initials: MC
authors.lastname: Hsu
authors.affiliation: Department of Civil Engineering, University of Minnesota, 500 Pillsbury Drive S.E., Minneapolis, MN 55455, USA.
authors.forename: Dominik
authors.initials: D
authors.lastname: Schillinger
authors.affiliation: Department of Aerospace Engineering Sciences, University of Colorado at Boulder, 429 UCB, Boulder, CO 80309, USA.
authors.forename: John A
authors.initials: JA
authors.lastname: Evans
authors.affiliation: Center for Cardiovascular Simulation, Institute for Computational Engineering and Sciences, The University of Texas at Austin, 201 East 24th St, Stop C0200, Austin, TX 78712, USA.
authors.forename: Ankush
authors.initials: A
authors.lastname: Aggarwal
authors.affiliation: Department of Structural Engineering, University of California, San Diego, 9500 Gilman Drive, Mail Code 0085, La Jolla, CA 92093, USA.
authors.forename: Yuri
authors.initials: Y
authors.lastname: Bazilevs
authors.affiliation: Center for Cardiovascular Simulation, Institute for Computational Engineering and Sciences, The University of Texas at Austin, 201 East 24th St, Stop C0200, Austin, TX 78712, USA.
authors.forename: Michael S
authors.initials: MS
authors.lastname: Sacks
authors.affiliation: Center for Cardiovascular Simulation, Institute for Computational Engineering and Sciences, The University of Texas at Austin, 201 East 24th St, Stop C0200, Austin, TX 78712, USA.
authors.forename: Thomas J R
authors.initials: TJ
authors.lastname: Hughes
keywords: B-splines and NURBS; Bioprosthetic heart valve; Fluid–structure interaction; Immersogeometric analysis; Isogeometric analysis; Nitsche’s method; Penalty-based contact; Weakly enforced boundary conditions