×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Modal analysis of acoustic cavity with flexible boundary

Modal analysis of acoustic cavity with flexible boundary

Modal analysis of acoustic cavity with flexible boundary

(OP)
Hi,
I want to know is it possible to perform a modal analysis of acoustic cavity with “flexible boundary” in MSC NASTRAN? for example for finding the acoustic modes of passenger compartment of a vehicle...

RE: Modal analysis of acoustic cavity with flexible boundary

Short answer is yes. This is exactly what most automotive OEMs are doing with MSC Nastran acoustics.

If you have a cavity only mesh, the free faces of the fluid mesh are considered rigid. The physical interpretation is a perfectly reflective boundary condition, like a reverberation chamber (which is almost perfectly reflective).

To have a flexible boundary, you need to define the flexibility, and this is typically done by enclosing the fluid cavity in a structural mesh. Where the structure touches the fluid, a coupling matrix is generated automatically and couples the fluid free faces to the structural "wetted" surface. Be careful, the fluid cavity mesh is usually coarser than the structural mesh, and this can lead to regions where either the free faces of the fluid are not sufficiently close to the structure (so no coupling is generated for these regions), or if the coupling search tolerances are too large, you can end up coupling to structure which is physically too far away from the free faces. This may happen where the structure has a double panel, one behind the other, and coupling occurs to the second panel when it should not. You can output the coupling surface as a list of GRID points and elements that have been detected as "coupled" and look at them in a graphics system. Then you can either "tune" the tolerances of the search algorithm or even add to or remove from the GRID point/element list to "manually" define the regions where coupling is to be generated.

DG

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login



News


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close