Bulk Data Entry Defines the settings for Fluid-Structure Interaction Analysis with AcuSolve.


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Field Contents SI Unit Example
FSID Fluid-Structure Interaction identification number.

No default (Integer > 0) 1 2 3

SURFID ID of the damp surface defined by the SURF Bulk Data Entry.

Alternatively, the surface can be defined by an element set (via ELSET field) if the surface contains only shell, bar, or beam elements.

No default (Integer > 0)

ELSET Element SET ID of the damp surface elements. These can be shell, bar or beam elements.

The SURFID field should be used if the damp surface is the surface of a solid mesh.

No default (Integer > 0)

PORT Socket Port number for communication with AcuSolve.

This should be the same as the socket_port setting in the EXTERNAL_CODE block of the AcuSolve input data

Default = 10000 (Integer > 0, or blank)

FCNVTOL Tolerance for exchange convergence of forces.

Default = 0.005 (Real > 0.0, or blank)

DCNVTOL Tolerance for exchange convergence of displacements.

Default = 0.0001 (Real > 0.0, or blank)

TCNVTOL Tolerance for exchange convergence of temperatures (for future use).

Default = 0.005 (Real > 0.0, or blank)

FXCNVTOL Tolerance for exchange convergence of heat-fluxes (for future use).

Default = 0.0001 (Real > 0.0, or blank)

MINEX Minimum number of exchanges between OptiStruct and AcuSolve per time step. 6

Default = 1 (Integer > 0, or blank)

MAXEX Maximum number of exchanges between OptiStruct and AcuSolve per time step. 6

Default = 10 (Integer > 0, or blank)

= 0 (Default)
All the damp surfaces will be in tagged as "0"
= 1
All the damp surfaces will be tagged with PSHELL, PBEAM, or PBAR ID.

Each property ID must match the TAG ID specified by the EXTERNAL_CODE_SURFACE external_code_tags data in the AcuSolve input data.


FSIDATA Determines the data to be exchanged between OptiStruct and AcuSolve.
= 1 (Default)
Exchange forces and displacements.
= 2
Exchange forces/moments and displacements/rotations.
= 3
Exchange temperatures and heat-fluxes.

(Integer) 4

WAITTIME The time in seconds, that OptiStruct waits (after pre-processing is complete) for AcuSolve to respond.

Default = 3600 (Integer > 0, or blank)


  1. The FSID of a FSI Bulk Data Entry is unique. Multiple FSI Bulk Data Entries with the same FSID cannot be specified in the model.
  2. FSI Bulk Data Entries can be referenced in a subcase via the FSI Subcase Information Entry. The FSI Bulk Data Entry can be referenced by only one subcase in the model. Only one FSI Subcase Information Entry can be specified in a model.
  3. FSI Bulk Data can only be referenced by FSI Subcase Information Entry from a Linear Transient Heat Transfer Analysis or Nonlinear Direct Transient Analysis subcase only. This is only supported for Large Displacement Nonlinear analysis, and an error is issued if it is referenced in a Small Displacement Nonlinear subcase.
  4. Currently, only one of Structural Nonlinear Transient Fluid-Structure Interaction (FSIDATA=1/2) or Linear Transient Heat Transfer Fluid-Structure Interaction (FSIDATA=3) is supported in a single model. They both cannot be activated in a single model.
  5. Data common to OptiStruct and AcuSolve on this entry should be set equal in the input for both solvers.
  6. The maximum or minimum number of exchanges (MAXEX/MINEX) is set in the OptiStruct model. There may be multiple locations within the AcuSolve model, where the maximum/minimum number of staggers are defined. The FSI run will use the lowest maximum number of exchanges/staggers and the highest minimum number of exchanges/staggers out of all available data specified. Therefore, depending on AcuSolve, each time increment may end within a subset space lesser than or equal to [MINEX,MAXEX].