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The PFEM in OpenSees
Original Post - 06 Nov 2023 - Michael H. Scott
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The Particle Finite Element Method (PFEM), developed by researchers at CIMNE in Barcelona, is an effective approach for simulating fluid-structure interaction (FSI). Because it is Lagrangian, as opposed to Eulerian, the PFEM is a natural choice for coupling with the structural finite elements in OpenSees. And the coupling is monolithic, i.e., in one system of equations, as opposed to staggered schemes that switch between solid and fluid solvers.
Implementing the PFEM in OpenSees for FSI applications in natural hazards engineering was the subject of my CAREER award. And through that award, Minjie developed the OpenSees PFEM implementation as part of his Ph.D. dissertation.
Although several variations of the PFEM have been developed with wide ranging applications beyond FSI, the OpenSees implementation has two options: moving mesh and background mesh, both implemented and maintained by Minjie.
Moving Mesh
The moving mesh approach tracks the positions of particles and re-meshes the fluid domain at every time step. A standard example of dam break on an elastic obstacle is shown in the following video.
Due to continuous re-meshing and element distortions, the results of moving mesh PFEM analyses can be highly oscillatory and computationally expensive.
Background Mesh
The second incarnation of PFEM in OpenSees uses a background mesh approach, where the fluid mesh is fixed and re-meshing is only required along the fluid-structure interface. The same dam break example with the background mesh approach is shown below.
Without continuous re-meshing of the fluid domain, which is typically much larger than the solid domain, the background mesh approach is more efficient and stable than the moving mesh approach.
Development of the PFEM in OpenSees continues with applications to debris impact on structures and implementations for high performance computing. You can find PFEM examples for both the moving mesh and background mesh approaches on the OpenSeesPy website.