2 Replies Latest reply on Feb 23, 2009 7:21 PM by Steve Zeise

    Extracting Modal Strain Energy

    Steve Zeise
      Is there a way to extract the strain energy from a particular mode shape? I know it is relative but that's OK. I am calculating the damping effect of viscoelastic materials on the assembly. I have modeled a Solidworks assembly with the structure in question and the viscoelastic material as a component in the assembly. The Modal Strain Energy technique involves calculating the ratio of the strain energy in the viscoelastic material to the total strain energy in the structure for a particular mode shape. I am able to calculate the strain energy ratio for a static analysis but not for a modal/frequency analysis.

      I guess a work around would be: Can the displacements from a mode shape be used to constrain a static analysis?

      Thanks
        • Extracting Modal Strain Energy
          Anthony Botting
          That is interesting, Steve. I don't believe the Simulation module calculates a relative strain energy when extracting mode shapes. I have not seen the technique you described before now. I believe you have to use the latter, i.e., decide on a "normalized" displacement field such as one from Frequency and use that for a static analysis to get a "normalized" strain field. Perhaps the normalization can be done by setting the maximum displacement in a particular mode shape to one, then run a static with non-zero displacements and show the relative strain energy. The issue becomes, I am unsure if other mode shape displacements are scaled relative to each other so you may not know how to scale non-zero displacement values for each mode shape. To be sure it may be best to use the Linear Dynamic module and just use a baseline white noise (constant) amplitude excitation across a bunch of frequencies. Then, for sure, the mode shapes will all be relative to each other, but at that point you could just plot strain energy, anyway.
            • Extracting Modal Strain Energy
              Steve Zeise
              Thanks Anthony for the reply. One clarification: I don't need to normalize across different mode shapes - I just need to ratio the total strain energy of one component to the total strain energy of the assembly for a particular mode shape. The ratio is a measure of the relative "work" being done by one component vs. another. The problem with using a static or even linear dynamic analysis is the inability to recreate a mode shape using an applied force/displacement or set of forces/displacements.

              Is there a way to "copy" a displacement field for a set of nodes from the frequency analysis and apply it to a static analysis? I remember Ansys having that ability as a way to do a substructure analysis. You could define a boundary and extract the node displacements at that boundary for the big assembly solution. Then you could take the node displacements and apply them to a detailed analysis that only considered the components inside the boundary.