Modal Analysis of Small Plate

- July 30, 2018 at 8:11 pm
  
  zchini
  Subscriber
  
  I am trying to recreate a modal analysis test I did on a simple plate. the issue I am having is that I am not sure how to define the supports for the plate in ANSYS. The plate was placed on soft foam, so that it would not be in contact with any hard surface, but I do not know how to represent this in the ANSYS Modal simulation. I have included an image of the plate on the foam so it is clear what the testing setup was. Any help would be greatly appreciated..
- July 30, 2018 at 9:39 pm
  
  Sandeep Medikonda
  Ansys Employee
  
  Hi, My initial guess would be to model it with springs beneath to replicate the behavior of the foam?
  
  You can start with the elastic foundation (Right click on Modal>Insert>Elastic Support) and provide a stiffness for the foundation (similar to what the foam would offer).
  
  ~Sandeep
- July 30, 2018 at 9:53 pm
  
  peteroznewman
  Subscriber
  
  You could have a plate with no support, effectively floating in space. There will be six zero frequency modes for the rigid body motions, but the seventh mode shape and above will be the free vibrations of the plate floating in space.
- July 31, 2018 at 12:41 am
  
  sk_cheah
  Subscriber
  
  I prefer bungee cords at only two corners of the plate so that it is less stiff in the direction of thickness. You could also excite it from the other side of the accelerometer to reduce spatial error. Please see this really good paper on boundary conditions setup. In short, the first flexible mode should be at least 15x of the highest rigid body mode to be really close to free-free (floating in space).
  
  Kind regards,
  Jason