For an acoustic-structural coupled solution
(SF,Nlist,FSI), support is available
for a nonlinear static structural solution using a morphed mesh
(MORPH) under the linear perturbation scheme
(ANTYPE and PERTURB).
Following is the general process for solving an acoustic-structural interaction with nonlinear static structural prestress:
Table 11.1: Acoustic Linear Perturbation Analysis Process
| Step | Task | Comments |
|---|---|---|
| 1 | Build the model | The model contains either FSI interface or displacement constraints. |
| 2 | Solve a nonlinear static structural problem | Perform a standard nonlinear static structural solution with the morphing operation. |
| 3 | Start a linear perturbation process | Restart the solution with the linear perturbation process. |
| 4 | Solve a modal or harmonic problem | Perform a modal or harmonic acoustic analysis. |
The nonlinear static structural analysis can lead to deformation in the structure. The
mesh in the acoustic fluid is morphed based on the structural displacement solution.
Activate mesh morphing during the nonlinear static structural analysis
(MORPH). Setting StrOpt = YES on the
MORPH command allows morphing in the model with structural
elements.
Because significant morphing occurs near the structural deformation only, it is not necessary to morph all acoustic elements for the sake of efficiency. Deactivate the morphing process in the specified acoustic elements via KEYOPT(5) = 1.
For a large structural deformation, the morphing procedure may fail during the
nonlinear static solution with ramped loads. Activating the bisection algorithm
(AUTOTS,ON) may improve the quality of the morphed mesh. If the
structural deformation can be ignored in the nonlinear static solution and the
MORPH command is not activated, setting
PRELP = YES on the ANTYPE command
keeps the acoustic mesh unchanged for the sake of efficiency.
Contact elements cannot be used on the structure-acoustics FSI interfaces for the acoustic linear perturbation process. Except for the morphed mesh, the acoustic elements have no other association with the nonlinear static analysis, including degrees of freedom and loads.
The final results are stored in the Jobname.rstp file for post-processing (see FILE).
Specify acoustic linear perturbation via one of the following commands:
Example 11.6: Acoustic Linear Perturbation Process
et,1,220,,0 ! coupled acoustic element et,2,186,, ! structural element … esel,s,type,,1 ! select acoustic elements nsle,s ! nodes on acoustic elements nsel,s,loc,x,0 ! nodes on fsi interface sf,all,fsi ! flag fsi interface … nsel,s,loc,x,0 ! select nodes on structural elements f,all,fx,100 ! apply force alls fini /solu nlgeom,on ! large deformation on autots,off ! auto step off nsubst,1 ! one sub-step antype,static ! static solution morph,on,,,,,,,,,on ! morphing with structural elements solve finish /solu antype,static,restart,,,perturb ! restart for linear perturbation perturb,modal,,,allkeep ! modal solution for linear perturbation solve,elform ! form new element matrices modopt,unsym,4,1 ! options with unsymmetric modal solver mxpand,4 ! expand modes after modal solution solve ! solve coupled modal problem finish /post1 file,file,rstp ! read results file /show,png set,1,1 plnsol,pres ! plot pressure /show,close finish
The linear perturbation analysis procedure does not support the FLNS method of solving a viscous-thermal acoustic analysis.
For more information, see Linear Perturbation Analysis in the Structural Analysis Guide.