An open-source computational framework for immersed fluid-structure interaction modeling using FEBio and MFEM

Fluid-structure interaction (FSI) simulation of biological systems presents significant computational challenges, particularly for applications involving large structural deformations and contact mechanics, such as heart valve dynamics. Traditional ALE methods encounter fundamental difficulties with such problems due to mesh distortion, motivating immersed techniques. This work presents a novel open-source immersed FSI framework that strategically couples two mature finite element libraries: MFEM, a GPU-ready and scalable library with state-of-the-art parallel performance developed at LLNL, and FEBio, a nonlinear finite element solver with sophisticated solid mechanics capabilities designed for biomechanics applications developed at the University of Utah and Columbia University. This coupling creates a unique synergy wherein the fluid solver leverages MFEM’s distributed-memory parallelization and pathway to GPU acceleration, while the immersed solid exploits FEBio’s comprehensive suite of hyperelastic and viscoelastic constitutive models and advanced solid mechanics modeling targeted for biomechanics applications. FSI coupling is achieved using a fictitious domain methodology with variational multiscale stabilization for enhanced accuracy on under-resolved grids expected with unfitted meshes used in immersed FSI. A fully implicit, monolithic scheme provides robust coupling for strongly coupled FSI characteristic of cardiovascular applications. The framework’s modular architecture facilitates straightforward extension to additional physics and element technologies. Several test problems are considered to demonstrate the capabilities of the proposed framework, including a 3D semilunar heart valve simulation. This platform addresses a critical need for open-source immersed FSI software combining advanced biomechanics modeling with high-performance computing infrastructure.

💡 Research Summary

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This paper introduces an open‑source immersed fluid‑structure interaction (FSI) framework that couples two mature finite‑element libraries: MFEM, a high‑performance, GPU‑ready, and massively parallel library developed at Lawrence Livermore National Laboratory, and FEBio, a nonlinear finite‑element solver specialized for biomechanics developed at the University of Utah and Columbia University. The motivation stems from the limitations of traditional arbitrary Lagrangian‑Eulerian (ALE) methods, which suffer from mesh distortion and costly remeshing when dealing with large structural deformations, contact, and topological changes typical of heart‑valve dynamics.

The authors adopt a fictitious‑domain (FD) approach in which the fluid equations are extended over the entire computational domain while the solid is immersed within this background fluid mesh. Continuity of traction across the fluid‑solid interface is naturally enforced by the variational formulation, and velocity continuity is imposed via a distributed Lagrange multiplier defined over the overlapping region. This eliminates the need for an explicit moving interface mesh, making the method well‑suited for problems with extreme deformations and contact.

To improve accuracy on the under‑resolved grids that are inevitable with unfitted meshes, the framework incorporates variational multiscale (VMS) stabilization. VMS mitigates spurious oscillations and enhances the capture of pressure jumps and shear layers near the interface. The coupling is realized through a fully implicit, monolithic scheme that solves the fluid and solid equations as a single nonlinear system, providing robust convergence for strongly coupled cardiovascular FSI problems and allowing relatively large time steps.

The synergy between MFEM and FEBio is the core technical contribution. MFEM supplies scalable fluid solvers, distributed‑memory parallelism, and a clear pathway to GPU acceleration, while FEBio contributes an extensive suite of hyperelastic, viscoelastic, and anisotropic constitutive models, sophisticated contact algorithms, and specialized boundary conditions for cardiovascular applications. By interfacing these libraries at the C++ level, the framework enables users to leverage FEBio’s advanced solid mechanics capabilities without sacrificing MFEM’s high‑performance fluid computations.

The software architecture is modular, facilitating the addition of new physics (e.g., electrophysiology, growth, chemical transport) and new element types. Parallel execution is achieved via MPI, and GPU support is provided through CUDA/OpenCL, yielding near‑linear scalability across compute nodes.

Four numerical examples validate the implementation: (1) benchmark problems that confirm convergence rates; (2) a fluid‑structure interaction test with large deformation; (3) a contact‑rich scenario demonstrating the robustness of FEBio’s contact handling within the immersed context; and (4) a three‑dimensional semilunar heart‑valve simulation. The valve case showcases realistic leaf­let coaptation, dynamic pressure gradients, and detailed tissue stress/strain fields, all computed on a fixed background mesh. Performance measurements reveal speed‑ups of 5–10× when using GPUs compared with CPU‑only runs, and almost ideal strong scaling up to dozens of nodes.

In discussion, the authors emphasize that most existing open‑source immersed FSI tools lack the sophisticated solid‑mechanics modeling required for cardiovascular applications. Their framework fills this gap by providing a freely available, extensible platform that combines state‑of‑the‑art biomechanics models with cutting‑edge high‑performance computing infrastructure. The paper concludes that this tool will enable patient‑specific simulations, device design optimization, and mechanobiological studies that were previously impractical due to computational constraints.