5 Replies Latest reply on Sep 17, 2011 1:17 PM by Anthony Botting

    SRS damping

    David Kramer

      The damping assumptions are not clear in this module.  I assume the input spectrum is created with the assumption of a Q=10 or 5% of critical as is standard in the industry.  Twenty modes are included in this assembly model under test and unlike random, modal damping is not an option in the analysis set-up.  What is the default for the model response? 

      Thanks for your assistance. 

        • Re: SRS damping
          Kirby Meyer

          Hello Dave

           

          On our bench we have found that 5% damping is reasonable for rather stiff systems at frequencies below 1000 Hz.   Above 1000 Hz, 2.5% was reasonable.   You may assume 10% for the modes where lubricant or liquids in system may assist in dampening, but don't quote me.   (Some test data here suggest 10%.)

           

          Kirby

            • Re: SRS damping
              Dave Kramer

              Thanks for the reply.  The question is not whether the damping numbers are correct but however what value does the software give them?  If you create a new Response Spectrum Analysis, damping input is not asked for as in the random vibration.  Is there a built in default from which the response can be ratio'ed to the particular model under test?

            • Re: SRS damping
              Dave Kramer

              For the Response Spectrum Analysis, both the input spectrum and the structural response assume 5% damping or a Q=10.  Not stated explicitly so I ran an SDOF model through the solver.  If your structure responds with more or less damping, then the response would be scaled linearly. 

              • Re: SRS damping
                Anthony Botting

                HI David: It was explained to me from a VAR (GoEngineer), the damping is accounted for in the input spectrum, so it would be the responsibility of whomever created the input spectrum to tell you the damping value used to generate that particular response spectrum. I have seen in the literature that it is traditional to assume 5%, as Dave mentioned.