In English

Coupling algorithms for fluid structure interaction at low density ratios- Accuracy and stability analysis of weak coupling algorithms in partioned codes

Martin Ottosson
Göteborg : Chalmers tekniska högskola, 2018. Examensarbete - Institutionen för mekanik och maritima vetenskaper; 2018:38, 2018.
[Examensarbete på avancerad nivå]

In recent years the interest of numerical predictions of fluid-structure interaction has grown in industrial applications as well as in the research of the phenomenon due to the increase in computational power. Numerical predictions of fluid-structure interaction typically suffers from instability when the solid-to-fluid density ratio becomes small. The instability issues are most severe when weak coupling, without coupling iterations within each time step, methods are used. Further, the weak coupling introduces the so-called artificial added mass effect, that introduces an error in the coupling. At Fraunhofer-Chalmers Centre a state-of-the-art multiphase solver, IBOFlow, and a structural solver, LaStFEM, are developed. IBOFlow handles moving boundaries using the mirroring immersed boundary method with adaptive grid refinements. The incompressible Navier-Stokes equations together with the boundary conditions at the structural interface are solved on a Eulerian grid using the finite volume method. LaStFEM solves the structural equations together with the forces acting on the structural interface on a Lagrangian grid using the finite element method. In previous work, a strong coupling, with coupling iterations within each time step, and a simple weak coupling procedure has been implemented and validated. In this thesis different weak coupling procedures are implemented, compared and analyzed in the existing frame work. The accuracy and stability of the weak coupling algorithms are investigated and compared to the existing strong coupling procedure. The investigation is done by the usage of three benchmarking cases: A rigid sphere attached to an undamped spring in Stokes flow, a rigid cylinder attached to a damped spring in a laminar flow and an elastic beam attached to a rigid cylinder in a laminar flow. The temporal and spatial accuracy are both found to be of second-order. The lowest solid-to-fluid density ratio where a stable solution was achived using a weak coupling algorithm is well below one and much smaller than what has been found in the literature.

Nyckelord: Fluid structure interaction, FSI Benchmark, Weak coupling method, Partitioned approach, Low density ratio, Immersed boundary method

Publikationen registrerades 2018-12-13. Den ändrades senast 2018-12-13

CPL ID: 256396

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