Learning Forum

[Sampetai_Koen]

Hi,
I am trying to conduct a modal analysis to a plate in the shape of a wing, which is placed on a foam, thus I have used elastic support with a very low stiffness coefficient). However, since the plate weights 281gr and each one of the 12 sensors weights approximately 5gr, I have decided to include them into the analysis. I have tried to do so by using Remote Points, applied to a specific node designated by location in respect to the coordinate system located in the bottom left corner. I have also set up the Behavior to rigid and have manually set Inactive to all DOFs, as the sensors are glued to the plate. X-coordinate is set to 1.5mm as the plate's thickness is 3mm and I have designed its midsurface. Then, I promoted the Remote points to Named Selections. Finally, I have used point masses and I assigned the corresponding remote point (as a named selection) to each point mass. Even though the simulation runs and gives some results, I don't think they are very trust-worthy, as I compared the experimental results to simulation. I know that the stiffness coefficient of the elastic support might have to do with that, but I believe that I might have done something wrong in the process of assigning the masses. Can someone tell me if I have made the correct actions or if I have to follow a different route?

PS: I have tried just selecting the surface of the plate as the geometry for the remote points but I get errors, saying that the areas of the mass points coincide which causes problems.

Thanks in advance,

SK

[Erik Kostson]

 

 

Hi

So do not use a soft foam and elastic support in fea.

When you do a free experimental modal analysis suspend the structure on thin slings/ropes. 

For FEA , then run a free modal analysis in ansys ( free so no BC).

For point masses assign them straight to nodes (needs to mesh before doing this, and select node select/scoping ), and don’t use remote attachments of rigid type as it adds stiffness just use a direct attachment on node.

 

If thin plate/ structure use shell elements for surface geometry.

 

Finally for such a light structure a laser vibrometer is the best choice as it is non-contact and does not add mass.

All the best

 

Erik