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fluid-structure coupling: ^^^ USER INFORMATION MESSAGE 9055 (PHASE0)

fluid-structure coupling: ^^^ USER INFORMATION MESSAGE 9055 (PHASE0)

fluid-structure coupling: ^^^ USER INFORMATION MESSAGE 9055 (PHASE0)

(OP)
Hello,

I would ask a question about Coupled Acoustic-Structure modeling.
I have modeled a simple cube of air with solid CTETRA elements, and around it I have built a mesh of shells with elastic properties. In order to do so, I have defined the grids of the outer surface of the cube twice, once for the definition of the shells, and another time for the definition of the grids of the volumic acoustic mesh. The 2 set of grids coincide, as it appears in the .f06 file, after running the modal analysis of the coupled model (using the ACMODL,IDENT,1 command).
The problem is that the natural frequencies extracted do not seem to be coupled frequencies, but the output frequencies look like the structural and acoustic frequencies of the uncoupled model.

The only message in the .f06 which might indicate something wrong in the coupling process, is the following:

^^^ USER INFORMATION MESSAGE 9055 (PHASE0)
^^^ THE FL./STR. INTERFACE CHECK IS FORCES AND MOMENTS RESULTING FROM A UNIT INCREASE IN PRESSURE, OR CHANGES
IN THE FLUID PRESSURE RESULTING FROM RIGID BODY MOTIONS OF THE STRUCTURE. THESE VALUES ARE DIRECTLY PROPORTIONAL
TO THE OPEN SURFACE OF THE FLUID.

In the Nastran Reference Manual, it is said that this kind of message appear in case of not-matching boundaries. Though I have checked the coincidence of the 2 meshes, and I am quite sure it is not the problem. Indeed, before this message, there is the list of "Matching Grid Table", where all the structural grids of the shells surrounding the volume are reported together with all the correspondent fluid nodes.

Thank you very much in advance. Any hint or comment would be very appreciated!
Emanuele

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