General Mechanical

General Mechanical

How to plot the strain energy in modal analysis?

    • Samir Kadam
      Ansys Employee
      How to plot the strain energy in modal analysis?n
    • peteroznewman
      Subscriber
      Why do you want to plot strain energy in a modal analysis? nIn my experience, only the modal frequency, mode shape (normalized by mass or displacement) and the participation factor summary are important. Maybe others will comment.n
    • Rahul Kumbhar
      Ansys Employee
      to plot the strain energy results in modal analysis, use following commands:n/sho,pngnset,1,1 ! reads in mode 1 datanplns,send,elasticnset,1,2 ! reads in mode 2 datanplns,send,elasticnnAlso, one may use:netab,sene,senenpletab,senen
    • shkiefer
      Subscriber
      You can create a User Defined Result and enter ENERGYPOTENTIAL for the expression to get a plot of continuum element strain energy. You need to have had energy and possibly stress as selected outputs in output control.nIn my experience the plots of element strain energy are less insightful than total relative contribution of individual regions / components. The magnitudes mean nothing in a modal analysis but the relative proportion can tell you what components / regions are contributing the most for each mode. nFor example if you had 3 components then for each mode you could sum all strain energy for each component and divide by the sum of the entire model. The mode will be most sensitive to the stiffness of the component with the highest percentage of strain energy. If they are all approx. the same then you will need to change all of them to move the frequency much. Frequency scales with the square root of stiffness so it take pretty significant changes to move the needle.nSee this Medium post for some other information:n
    • peteroznewman
      Subscriber
      Great article!nIn my experience the plots of element strain energy are less insightful than total relative contribution of individual regions / components. The magnitudes mean nothing in a modal analysis but the relative proportion can tell you what components / regions are contributing the most for each mode.nCoincidentally, later in November 2020, I was taught exactly what you said in the quote above and describe in detail in your article. Thanks for the post!n
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