Fluid-structure interaction (FSI) can be simulated for systems that are cyclically symmetric (see the Cyclic Symmetry Analysis Guide). The main actions required to run a cyclic FSI problem are:
Create a model appropriately defined as cyclically symmetric using the CYCLIC command.
Ensure that the model contains supported acoustic and structural elements.
Acoustic elements: FLUID30, FLUID220, FLUID221, FLUID243, FLUID244 Structural elements: PLANE182, PLANE183, SOLID185, SOLID186, SOLID187, SOLSH190 You can explicitly define the FSI boundary by issuing the SF,,FSI (or SFA,,FSI) command for the coupled acoustic elements. If SF,,FSI is not specified, the FSI boundary is automatically detected.
Choose one of the supported solutions:
Static analysis. If the static analysis will be used for a downstream linear perturbation analysis, include the MORPH command to activate morphing and the CYCOPT,MSUP,0 command to include duplicate sector results.
Undamped modal solution using the unsymmetric eigensolver (MODOPT,UNSYM). The CYCOPT,MSUP,0 command is required in a cyclic FSI modal solution to include duplicate sector results.
Harmonic response analysis (HROPT,FULL).
Postprocess the cyclic solution (/CYCEXPAND,,ON).
The acoustic boundary conditions and loads listed below are supported in a cyclic symmetry FSI analysis. Acoustic boundary conditions that introduce damping are not supported for cyclic FSI modal analyses.
Acoustic boundary conditions:
Free surface flag (for sloshing effect): SF,,FREE; SFE,,FREE; SFA,,FREE
Gravitational acceleration (for sloshing effect): ACEL
Pressure boundary: D,,PRES
Impedance boundary: SF,,IMPD; SFE,,IMPD (not supported in a modal analysis)
Exterior Robin radiation boundary condition: SF,,INF (not supported in a modal analysis)
Absorption coefficient: SF,,ATTN (not supported in a modal analysis)
Viscous-thermal boundary layer: SF,,BLI
Acoustic loads:
Example 11.9: Cyclic FSI; Linear Perturbation Modal Solution
et,1,186,, ! Structural element et,2,220,, ! Acoustic element keyopt,2,2,1 ! Uncoupled acoustic element et,3,220 ! Acoustic element keyopt,3,2,0 ! Coupled acoustic element (FSI) … esel,s,type,,1 ! Select structural elements nsle,s ! Nodes on interface in structural element esel,s,type,,2 ! Select acoustic elements esln,r,0 ! Select nodes on FSI interface sf,all,fsi ! Flag FSI coupling interface alls … d,all,all,0 ! Apply structural BCs to selected nodes … sf,all,pres,p0 ! Apply acoustic BCs to selected elements … cyclic ! Define cyclic symmetry … fini /solu antype,static ! Static solution morph,on,,,,,,,,,on ! Morphing with structural elements nlgeom,on ! Large deformation on cycopt,msup,0 ! Keep duplicate sector solve ! Solve structural problem 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,10 ! Choose unsymmetric modal eigensolver solve ! Solve acoustic problem finish /post1 file,,rstp ! Postprocess from perturbed results set,1,1 ! Get the first step and substep /cycexpand,,on ! Expand the cyclic solution … plnsol,u,x !Plot structural results … plnsol,pres !Plot fluid results fini