Thermal Fluid-Structure Interaction Analysis
OptiStruct and AcuSolve are fully-integrated to perform a coupled Fluid-Structure Interaction Analysis based on a partitioned staggered approach.
At each sub-iteration (exchange/stagger) of TFSI analysis, the fluid thermal energy in AcuSolve is converted into nodal fluxes which are then transferred to the structural interface mesh of OptiStruct. These fluxes are used to calculate the temperature of the structure using OptiStruct. In addition to the flux from the fluid flow, additional structural heat transfer loads can also be applied. The resulting temperature of the structure is passed back to AcuSolve as the new fluid thermal analysis boundary. This TFSI cycle is illustrated in Figure 1.
Input
The detailed interface-specific input information is available in the Fluid-Structure Interaction page.
You will look at solution-specific information required to run Thermal FSI. You will first look at the input data required from the OptiStruct side to set up the model. Subsequently, you will list and explain some information about the interface boundary conditions that are specific to Thermal FSI and learn how to set them in the AcuSolve input file.
OptiStruct
Thermal FSI is the coupled simulation of Linear Transient Heat Transfer Analysis on the structure in conjunction with transient fluid heat transfer analysis in the fluid domain.
- The initial time step (DT on TSTEP) should be set equal to the initial time step in the AcuSolve model. This time step will also be constant throughout the solution (adaptive time stepping is not supported).
- The FSI Bulk Data Entryshould be added to the model. You can adjust the convergence tolerance parameters relevant to Thermal FSI (TCNVTOL and FXCNVTOL), the wait time (WAITTIME), and other parameters on this entry.
- The FSI Subcase Information Entry should be added to the linear transient heat transfer subcase and this entry should reference the corresponding FSI Bulk Data Entry.
The above steps allow you to successfully prepare the Linear Transient Heat Transfer model for FSI analysis.
AcuSolve
Thermal FSI is a coupling between the structural solver and the fluid flow analysis capabilities of the fluid solver. Therefore, you can look at the AcuSolve Command Reference Manual for detailed information about how to setup a model for fluid flow solutions. Here a few parameters relevant to Thermal FSI in the AcuSolve input file are looked at.
Use the EXTERNAL_CODE_SURFACE
command to define the interaction between the
fluid interface and the corresponding parameters. The command specifies the surface
topology, as well as the interface proprieties.
EXTERNAL_CODE_SURFACE( "<structure_label>" ) {
surfaces = Read( "<filename>.ebc" )
shape = "<element type>"
element_set = "<element set ID>"
mesh_displacement_type = <tied/slip>
temperature_type = <tied>
gap_factor = <Real>
gap = <Real>
}
For Thermal FSI, the temperature_type
and mesh_displacement_type
define how the fluid and structural interfaces interact (boundary conditions). The mesh_displacement
parameter should always be set to tied for Thermal FSI solutions.
temperature_type
specifies how the nodal temperature behaves in relation to
the structural mesh temperature. Currently only
temperature_type=tied
to tie the temperature to the mesh
temperature is supported. For Thermal FSI, currently, only heat transfer is
supported, and therefore, the mesh
parameter in the
EQUATION block should be set to eulerian
since the mesh is fixed. For more information, refer to External Equation Field Settings of the Fluid Structure
Interaction page.
Fluid-Solid Interface Conditions | Mesh Displacement | |
---|---|---|
Tied | ||
Temperature | Tied | Temperature |
When the fluid is allowed to slide along the solid mesh, neighborhood searches between the fluid
and solid meshes are continuously performed. The gap_factor
parameter specifies a non-dimensional (with respect to the length of the element
face) maximum allowable gap and the gap parameter specifies a non-dimensional
maximum gap distance between each quadrature point of the AcuSolve surface to the closest surface given by OptiStruct to check for gaps. If the distance is greater than
the gap, the computation stops with an error message.
Output
The FSI results are output to the corresponding working directories. The structural (OptiStruct) results are output to the H3D file by default and can be post-processed in HyperView.
However, this file will not contain the fluid results. The fluid results are available in the AcuSolve .log file in the AcuSolve working directory. The AcuSolve .log file can also be loaded into HyperView. During Thermal FSI Analysis, for the Structural Transient Heat Transfer solution, monitoring results are available by default at runtime, in the <filename>_ht.h3d file. This H3D file can be viewed in HyperView during runtime to monitor results.