Setting the FSI Coupling

You define two-way coupled FSI between the solid diaphragm and the fluid overset region.

In this simulation, displacement from the structure acts on the fluid. Coupling options are activated when you create and apply appropriate motion models to the fluid and the structure.
To apply motion models and activate coupling:
  1. Right-click the Tools > Motions node and select New > Solid Displacement.
  2. Repeat the previous step and select New > Morphing.
  3. Select the Regions > FluidOverset > Physics Values > Motion Specification node and set Motion to Morphing.
  4. Select the Regions > FluidOverset > Boundaries > ZeroGapWall > Physics Conditions > Morpher Specification node, and set Specification to Floating.
  5. Select the Regions > Structure > Physics Values > Motion Specification node, and set Motion to Solid Displacement.
    These steps complete the set up for the coupling in the direction structure to fluid. You can verify the coupling by looking at the FSI Coupling Specification on the FSI interface boundary in the fluid overset region. The fluid overset region FSI Coupling Specification is set to Solid Displacement as shown in the image below.
    From the fluid to the structure, the coupling is set by default to be the fluid traction. You can verify this coupling by looking at the FSI Coupling Specification on the FSI interface boundary in the solid region. As shown in the image below, the solid region FSI Coupling Specification is set to Fluid Load - Pressure & Wall Shear Stress.

You define the motion of the plunger using a Translation motion. You can define the translational velocity as the derivative of the position of the plunger with respect to time. This simulation contains a predefined expression report that defines the plunger position as:

${Time} <= <4.0 s> ? <-2.2 mm> * ${Time} / <4.0s> : <-2.2 mm>

This expression reads that if the solution time is less than 4.0 seconds then the position output is -2.2 mm divided by 4.0 seconds, multiplied by the current solution time. If the solution time is greater than 4.0 seconds then the position output is -2.2 mm. The output of the PlungerPosition is the displacement of the Plunger in the following time-step.

  1. To create a report that defines the velocity of the Plunger as the time derivative of the PlungerPosition report:
    1. Right-click the Reports node and select New > User > Expression.
    2. Rename Expression 1 to PlungerVelocity and set the following properties:
      Property Setting
      Dimensions Velocity
      Units m/s
      Definition ${Time} <= <4.0 s> ? <-2.2 mm> / <4.0 s> : <0.0 m/s>
  2. To define the translation motion:
    1. Right-click the Tools > Motions node and select New > Translation.
    2. Select the Tools > Motions > Translation node and set Translation Velocity to:
      [0.0,0.0,${PlungerVelocityReport}]m/s
  3. Save the simulation.