Defining the Coupled Boundaries and Exchanged Fields

Define the fluid boundaries that couple with Simcenter Nastran at the fluid-structure interface and specify the fields that are exchanged during the co-simulation.

To specify the fluid boundaries at the fluid-structure interface, you require a co-simulation zone:
  1. Expand the External Links > [Link 1] > Zones node.
    Simcenter STAR-CCM+ automatically creates a co-simulation zone, [Zone 1], when creating the co-simulation link node. In general, you can create zones using the Zones node right-click menu.
To assign the fluid boundaries to a co-simulation zone:
  1. Expand the relevant Regions > [Fluid Region] > Boundaries > [FSI Boundary] node.
  2. Select the Physics Conditions > External Code Coupling Specification node and set External Code Coupling Specification to the relevant zone.


To account for the solid displacement at the fluid-structure interface, define a morphing motion for the fluid region:
  1. Right-click the Tools > Motions node and select New > Morphing.
  2. Select the Regions > [Fluid Region] > Physics Values > Motion Specification node and set Motion to Morphing.
To export the fluid loads to Simcenter Nastran:
  1. Expand the External Links > [Link 1] > Zones > [Zone 1] > Conditions node.
  2. Right-click the Exported Fields node and select Add Mechanical Field > Pressure.
Optionally, you can also export wall shear stress:
  1. Right-click the Exported Fields node and select Add Mechanical Field > Wall Shear Stress.
    NoteTo enable import of wall shear stress in Simcenter Nastran, add the --wallshear on argument to the Simcenter Nastran launch command. For more information, see Launching Simcenter Nastran for Co-Simulation.
To import the solid displacements from Simcenter Nastran:
  1. Right-click the Imported Fields node and select Add Mechanical Field > Displacement.


To update the fluid mesh in response to the imported solid displacements:
  1. Select the Imported Fields > Displacement node and set Field Treatment to Managed.
    With this setting, Simcenter STAR-CCM+ automatically sets the morphing specification for the coupled boundary:

    Alternatively, you can leave the Field Treatment as Unmanaged and set the relevant boundary conditions manually.

To specify the time interval between data exchanges:
  1. Select the [Link 1] > Conditions > Coupling Negotiation Option node and set Option to either:
    • Time-Step: sets the time interval between data exchanges to the time-step of the Simcenter STAR-CCM+ simulation.
    • Matched Coupling Time: allows you to specify the coupling time interval manually. When using this option, specify the coupling time interval value under the [Link 1] > Values > Coupling Time Interval node. The time interval must be equal or greater than the simulation time-step.
    In both cases, the time interval between exchanges is the same in both Simcenter STAR-CCM+ and Simcenter Nastran.
In this type of co-simulation, Simcenter STAR-CCM+ is responsible for mapping both the incoming and outgoing fields:
  1. Select the [Link 1] > Conditions > Mapping Option node and set Option to Map Both Directions.
    This option is the only one compatible with Simcenter Nastran co-simulation.