Natural frequency.

[jisb007]

Hi,

Is it possible to extract the natural frequency of a system with soft gel-like material contained in a rigid body container? The gel is in contact with the container. I can extract the natural frequency of the gel (not including the container in the model), but am having trouble to include the container. In addition, how can I specify that they are in contact? ABAQUS gave me error message saying that *contact is only available in Explicit. Thanks a bunch!

 

[gwolf]

Just model the gel and container as solids and equivalence the mesh between the two. Works on the assumption that any vibrations are of sufficiently low magnitude that the gel does not become detached from the walls. Delete all constraints then extract the first 12 or so natural frequencies - the first 6 will be rigid body modes and the rest true modes. Ignore any gas in the container, it has such a low mass and stiffness that it won't have any effect on the answer.

 

[PamCrash]

1) If the gel has no shear stiffness, then use acoustic elements (e.g. AC3D8). Otherwise your results are useless.

2) If u use acoustic elements make sure u use correct boundary conditions for the free surface of the gel (d.o.f. 8/pressure = 0.)

3) connect fluid and structure via tie constraint. fluid = slave !

4) run frequency analysis

Good luck, Pam