4 Replies Latest reply on Apr 23, 2013 10:20 AM by Jared Conway

    Modal frequency

    Keshav Samrat Modi
      i did static frequency analysis for the metal plate. 5 results were obtained. each result had its own MODAL FREQUENCY. what is this modal frequency. what is its significance?
        • Re: Modal frequency
          Mike Pogue

          The frequencies are those at which the plate resonates. The modes, or mode shapes, are the shape of the vibrating structure at those frequencies. The amplitudes in a frequency study are meaningless. This study is to help you design a structure that does not resonate in the frequency band it will be exposed to. Check the "more like this" frame at the right of this discussion for more information.

          • Re: Modal frequency
            Anthony Botting

            One way to look at it: For example a cantilever beam: if, at the cantilever restraint, instead you bolted-on an oscillating motor at that location which could vibrate the beam perpendicular to the beam axis - now operate the motor at the mode1 frequency, the structure would vibrate as shown for that mode shape. If you operated the motor at the mode2 frequency, the structure would vibrate as shown for that mode shape, and so on. Those frequencies would correspond to "resonance" of the structure so you would not want to operate the motor at those frequencies (or, design the structure to have a different modal frequency than the motor frequency).

            The amplitudes have meaning in the sense of relative amplitude only. So, if red-colored areas have a value of 2, and green-colored areas have a value of 1, that means red colored areas will vibrate at twice the amplitude of green-colored areas. If you want actual amplitudes, you will need to apply an actual load and run a linear dynamic analysis (I am certain the "SolidWorks Simulation Premium" product has the "linear dynamics" included). Hope that helps.

            • Re: Modal frequency
              Keshav Samrat Modi

              in my case i need that my plate should vibrate when i apply sound waves to it. but it shows response to only sound waves corresponding to the the 3rd MF shown by the solidworks study. so can i conclude from it that it is plates fundamental frequency?

                • Re: Modal frequency
                  Jared Conway

                  based on your query here: https://forum.solidworks.com/thread/67291?tstart=0

                   

                  i think you might be confused about the output of the frequency analysis. the frequency analysis tells you the natural frequencies of your structure (is this waht you mean by fundamental frequencies) and the mode shapes. the mode shapes are shown using displacement but the displacements aren't real. you need a dynamic analysis for this.

                   

                  the frequencies that are determined are the frequencies that the structure would respond to if you applied a frequency to it (sound waves for example). if there are frequencies that you were hoping for it to respond to that don't show up, you need to redesign your part. or run a dynamic analysis to see how strong the response would be to see if it is sufficient. IE, it still will respond, just not to resonance.