6 Replies Latest reply on Aug 9, 2010 1:16 AM by 1-FKI4X8

    Test specifications for dynamic analysis

      Hi all,

      I am pretty new to dynamic analysis, eventhough i have been using SWX simulation for quite some time now. Pls help me understand these specifications and the procedure that needs to be followed in SolidWorks simulation

       

      Vibration Resistance:

      The equipment should be capable of trouble free operations under the influence of propeller vibrations at the frequencies up to 5 Hz with an amplitude of 1.0 mm and the frequencies 20 to 30 Hz with an acceleration of 1 G.

      freqency 5-33 Hz, +/- 0.16 mm constant displacement Duration, 2 Hrs

       

      Vibration Proof (at 1.0 g):

      Frequency 5-10 Hz, +/- 1.0 mm

      Frequency 10-20 Hz, +/- 0.63 mm

      Frequency 20-25 Hz, +/- 0.40 mm

      Frequency 25-30 Hz, +/- 0.28 mm

      Frequency 30-33 Hz, +/- 0.23 mm

      Sweep rate 1 octave/minute tested for 3 axes. Duration 15 minutes/axis.

       

      pls let me know the procedure to be followed to carry out this analysis.thanks

        • Re: Test specifications for dynamic analysis
          Joe Grant

          This is a complex subject but I'll help where I can. From a SW perspective you should obviously have your parts modeled and then execute a Linear Dynamic Study. Constrain or "Fix" your model and then apply External Loads "Base Excitation". Select displacement and put in 1mm. Then select "variation with frequency" and the curve option. Input your curve data from the specification (ie) displacement versus frequency. Run your analysis. You will need to do this a total of three times to account for the x, y, and z axis. 

           

          All this is done after you have already run a modal analysis to determine the structures natural frequencies.

           

          Is there any chance your quoted specification is in error? It is somewhat confusing to me. The "Resistance" part of the specification states "up to 5 Hz". What is the lower limit? 2Hz? 3 Hz?  I'm also confused as to how a specification gives what I interpret as two amplitude values, displacement and "G". If you vibrate at 5-10 Hz at +/- 1mm displacement there should be a resulting G value that is not 1 G.

           

          Good luck.

            • Re: Test specifications for dynamic analysis


              Hi Joe, thanks for your input. Let me tell you what I have understood from words please correct me if I am wrong.
              I have my model that is ready with me in SWX, and i am constarining it at the required location,
              I will be following this methodology in SWX let me know wheather it is right
              1) I will run a 'modal time history analysis' with base excitation of displacement of 1 mm,
              2) I will run 'harmonic analysis' and apply base excitation of 1 mm, but this time with 'variation with frequency' option and I use the data available. Please refer the attachment "harmonic.jpg" and let me know if the values I have read is correct or not.
              3) please elaborate what do you mean by "You will need to do this a total of three times to account for the x, y, and z axis" is there any setting i need to change if any to achieve this?
              I have also attached the model this is taken from SWX manual if you could please setup the problem for me on this model, it would be of immnense help to me. thanks in advance
              Rgds,
              Shankar

                • Re: Test specifications for dynamic analysis
                  Joe Grant

                  Shankar -

                   

                  You mis-understand #1. For the first step you run a Study by selecting the "Frequency" option. This type of analysis determines frequencies and mode shapes. All structures have frequencies that they are most likely to vibrate at called "natural frequencies". When you set up the analysis, right click and select properties and select a range of frequencies. In your case maybe 5 - 50Hz. Once you have completed this analysis, proceed with step #2 which is a Linear Dynamic analysis.

                   

                  For #3, what I meant by three times is that vibration testing is normally done by vibrating a part on a shaker table. Most tables can only vibrate in one direction at a time. You need to simulate the movement in each of three directions as your structure may behave differently depending on which direction you are applying the forcing  function. There is no button  for this but it is not difficult. Simply set up the model to run by applying the loads you describe in your post. Solve that analysis. Next Copy that analysis tab and rename it. Then just change the direction of the applied load. Then run that analysis.

                   

                  Hope this helps.