One-Way FSI
For some fixed geometry FSI problems, you can consider the coupling as being unidirectional. One physics interface affects the other, but it is not reciprocal. Typical examples are when the fluid slightly deforms the structure, or when small structural vibrations modify the fluid flow. In this case, it is not necessary to compute the solution with both physics interface solved together. It is more efficient to first solve for the governing physics interface only, and then the other one with results from the first as input. To solve such a problem sequentially, you need to create a study configuration manually, with one study step for each physics interface. The governing physics depends on the coupling type. For the case of fluid loading on a structure, the governing physics is the fluid one. For the case of velocity transmission to a fluid, the governing physics is the solid one.
Deformed geometry FSI, or fixed geometry fully coupled FSI, should not be solved using a one-way approach.
Below are the steps to follow to compute a one-way FSI problem sequentially:
1
In the study step settings windows, under the Physics and Variables Selection section, clear the physics that is solved in the second step, so that only the governing physics is selected.
2
Add a second study step to the study and in the settings windows make sure you have the governing physics cleared.
If the selected study steps are of stationary type, you can generate the default solver configuration, edit it if necessary, and compute the solution. The mapping of the solution from the first to the second study step is done automatically.
In case of a transient problem, continue with the steps below:
3
In the second study step settings window, expand the section Physics and Variables Selection. Under Initial values of variables solved for make sure the settings are defined as in the table below:
Settings
User controlled
Method
Solution
Study
<previous study step>
Selection
First
4
Under Values of variables not solved for define the settings as in the table below:
Settings
User controlled
Method
Solution
Study
<previous study step>
Selection
All
In the case of a fluid loading to structure coupling type, the structural mechanics problem can be treated as quasistatic. This can be handled by running the structural analysis as a parametric sweep over a number of static load cases, where time is used as the parameter.
For an example of one-way FSI using a quasistatic structural analysis, see Fluid–Structure Interaction in a Network of Blood Vessels: Application Library path Structural_Mechanics_Module/Fluid-Structure_Interaction/blood_vessel.