With the release of ANSYS 14.0, ANSYS Fluent users can perform two-way fluid–structure interaction (FSI) simulations using the ANSYS next-generation coupling technology — system coupling.
The system coupling component in ANSYS Workbench offers a generic way to couple two or more participants in the Workbench environment. In release 14.0, you can link Fluent and ANSYS Mechanical via system coupling to facilitate FSI simulations.
This post provides a broad overview of the capabilities offered with system coupling and the types of cases you can solve. I’ll try to avoid just listing the features.In ANSYS 14.0, system coupling lets you perform cosimulation, one-way and two-way force/displacement coupling between ANSYS Fluent and ANSYS Mechanical. Let’s look at what some of these terms signify. Cosimulation means that both solvers run simultaneously, exchanging data when needed without writing out intermediate results files. This is in contrast to static data transfers, in which one solver has already produced and written out its results. Static data transfers aren’t available yet using system coupling; but various approaches are available in previous releases. With cosimulation, data can be passed in one direction (one-way) or in both directions (two-way). A one-way cosimulation may pass force data to ANSYS Mechanical, but no displacements pass back to Fluent. On the other hand, a two-way simulation passes data in both directions. Lastly, force and mesh displacement are the variables that pass between the solvers for the current release.
When executing two-way FSI runs, coupling iterations are performed within each time step to converge the data transfers, which results in an implicit solution at convergence. This is termed an iteratively implicit approach to coupling. Implicit coupling is important, since an explicit approach typically requires a much smaller time step. Even after taking into account the extra iterations you perform with an iteratively implicit approach, run times are typically much shorter than with an explicit approach. The iteratively implicit approach also makes the solution more stable.
Stability at the fluid–solid interface can be a big concern with FSI simulations that use separate fluid and structural solvers, particularly when the structure is very flexible and the working fluid is a liquid. Biomedical cases, membranes, diaphragms and thin-walled structures often exhibit instabilities at the FSI interface. With system coupling, you can solve these types of cases without resorting to excessive underrelaxation or small time steps. For more details on this, enter “2022119″ in the “Search the Knowledge Resources” box on the ANSYS Customer Portal, or just search for “FSI.”
For those of you familiar with the ANSYS CFX with ANSYS Mechanical two-way FSI method, the new system coupling approach using Fluent adds fluid remeshing capabilities to FSI simulations. This allows you to solve FSI cases that would otherwise cause the fluid mesh to collapse.
For more information on system coupling, look for the upcoming ANSYS Fluent with ANSYS Mechanical FSI training course. This will include one-way and two-way FSI between using system coupling. Watch for this in the ANSYS Training Center in the next few weeks.