6 Replies Latest reply on Jul 3, 2007 10:29 AM by Rogier Van Rossen

    applying a uniform load on a group of faces

    Rogier Van Rossen
    Rogier Van Rossen Jun 28, 2007 2:01 PM
      I'd like to set a uniform load on a model with some separate faces (read: a load on faces with a gap between, so I'm not able to knit them)

      I attached a part to clear things out.
      When I set a force on separate faces, the resultant will be the force x number of faces. so when I apply a force of 100N and select 3 faces....the resultant will be 300N

      one option is to measure the projected area of the faces and calculate a pressure normal to a reference plane. Apart from this method to be very time consuming, I cannot find a simple way to measure the projected area.

      There must be an easier way to do this..... anyone?
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        • applying a uniform load on a group of faces
          genexxer genexxer
          genexxer genexxer Jun 30, 2007 3:15 PM (in response to Rogier Van Rossen)
          After I thought about this I mostly agree that it should be easier to get the bc's for separate faces to add up to a value in pre-processing. In post-processing, I suggest comparing the reaction force (Rx,Ry, Rz) result to the desired resultant and modify the force setting accordingly. I made an avi recording of this and its 11MB. If you want it send me an email. corrdude@gmail.com
          • applying a uniform load on a group of faces
            Rogier Van Rossen
            Rogier Van Rossen Jul 2, 2007 11:17 AM (in response to Rogier Van Rossen)
            Hi Genexxer,

            Thanks for your reply!

            I couldn't read the values in the youtube avi, but I think I get what you mean.
            - You set a force on the faces and run the study
            - Measure the resultant force
            - Measure the factor that it's off
            - Adjust the load
            - Run again

            This has some disadvantages:
            - Only possible with 1 load case or a model that is easy to find out the reaction force
            - the forces will not be equally divided along the surface (just scale up your result and you will see a big dent with the small surface)
            - A study can take a looooong time to render, so it would be wasting time.
              • applying a uniform load on a group of faces
                Vince Adams
                Vince Adams Jul 2, 2007 1:57 PM (in response to Rogier Van Rossen)
                If you are looking for a uniformly distributed load of a given value, I'd use a pressure, not a force. Otherwise, the steps Genexxer suggested are probably the "best". Applying a total load across a set of faces (vs. per entity) and checking total applied load in the pre-processor are both enhancements we are looking into.

                PLEASE fill out enhancement requests for these if you'd like to see them implemented! While we know about the need and they recur on the list of enhancements, the more requests we get, the higher a priority they get.

                Thanks!

                Vince
                • applying a uniform load on a group of faces
                  genexxer genexxer
                  genexxer genexxer Jul 3, 2007 4:15 AM (in response to Rogier Van Rossen)
                  Disadvantage one is a toughie. gotta get some enhancement requests going.

                  Disadvantage 2 ... I agree with Vince...use pressure and iterate to converge the setting for the pressure. But this leads to Disadvantage 3.


                  Disadvantage 3...I had it solve in about 10 or 15 seconds each time. Your mileage may vary. I did it on my vintage 2004 cpu with 1GB RAM and 2.8Ghz. That has to be modest by most forum readers' standards. If scaling this up to a large number of nodes redlines the solver time, iterate with draft elements. Draft usually produces a wrong resultant but can be calibrated to high quality elements resultant on a smaller model.

                  Thanks,
                  G
                • applying a uniform load on a group of faces
                  Rogier Van Rossen
                  Rogier Van Rossen Jul 3, 2007 10:29 AM (in response to Rogier Van Rossen)
                  I'll fill in an enhancement request.

                  About the method Vince uses, It is kind of the way I use now.
                  - make a sketch on the reference plane.
                  - Create an outline around all faces
                  - calculate projected area (sadly there is no easier way to measure a projected area)
                  - Divide the force by the area to calculate the pressure
                  - apply the calculated pressure

                  But still I hoped I was missing the easy way.
                  So an enhancement request it will be, tnx for your help!