Mike Lowinske

Modal Frequency varying significantly with type of mesh

Discussion created by Mike Lowinske on Mar 2, 2009
Latest reply on Jul 21, 2009 by Michael Buckley
Hi all,

I have been playing around with the frequency simulation, doing a study on a part using different approaches and meshes. What I am doing a study on is a hollow core metal door with a uniform wall thickness of .125". I have approached it in the following ways:

1. As a solid body with a very fine, standard mesh.
2. As a solid body with a very fine curvature based mesh.
3. As a 3D surface feature, with an assigned shell thickness of .125" and specified as "thin" with a very fine standard shell mesh.
4. As a 3D surface feature, with an assigned shell thickness of .125" and specified as "thin" with a very fine curvature based shell mesh.
5. As a 3D surface feature, with an assigned shell thickness of .125" and specified as "thick" with a very fine standard shell mesh.
6. As a 3D surface feature, with an assigned shell thickness of .125" and specified as "thick" with a very fine curvature based shell mesh.

Simulating these ways gives significantly different results. The frequencies at a certain mode are varying by almost 900 hertz between the highest and lowest frequency from the six results. Both of the solid body simulations with either mesh give results that are similar to each other but on the higher end and the shell mesh results are similar to each other but on the lower end.

So I have some questions. When doing a frequency analysis, why do the frequencies vary so much between shell and solid meshes? What is the real difference between specifying the surface body as either thin or thick and when would one be used over the other? Which of the methods I did would be the most accurate method of finding the frequencies (I honestly have no idea what they would be for this door)?

*edit* forgot to mention that I am applying no forces or restraints to the body

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