3 Replies Latest reply on Mar 6, 2014 10:34 AM by Jared Conway

    Non-uniform force/pressure - units messed up?

    A. Telet

      Hi all,

       

      I happily admit that the UI for applying non-uniform force/pressure is not working well along with my brains, and this together with lack of possibility(?) to verify total loads applied to a face, make me uncertain about the whole aspect of applying loads by this feature. Now I also have this nagging feeling that the units are playing me a trick as well - so now I consider baking bread instead of calculating stress levels and deflections....

       

      I have a 24000mm long structure that shall have linearely varying load beginning with -125N/mm at one end, through zero at midspan, and +125N/mm at the oposite end

      (This shall create a moment about the centre of 1,2e10 Nmm = 12000kNm)

      I create a coordinate system in the centre of the structure to have the +/- values of the load, but how should the formula/equation for applying correct force look like? And how can i check/verify that the applied (sum of) loads are correct for e.g. each face?

      I have tried all variations for "equations" for non-uniform force/pressure I can think of, but the results are so ridicilously far from expected that I suspect there is some flaw in the input load unit / model unit handling.

       

      Anyone exprienced something similar?

      I do hope Solidworks come up with a better interface for applying non-uniform loads, and possibility to verify applied load to each face.... Unless someone can enlighten me beyond all my problems here

       

      -a-

        • Re: Non-uniform force/pressure - units messed up?
          Jared Conway

          "and this together with lack of possibility(?) to verify total loads applied to a face"

           

          calculate the total force of your nonuniform pressure, make a simple part, apply your non uniform pressure, measure reaction force, compare forces to validate. we call this a "smoke test" in our one-on-one mentoring. good habit regardless of what you're doing.

           

          what i find easiest for developing the equation is to start in excel, once you have the coefficients of the equation, its just a matter of plugging them in.

           

          something that might help is start with something that has examples like rho G h for hydrostatic pressure. then you can expand from there.

           

          what would you want to see for a better input method? you can always submit an enhancement request through the customerportal.

            • Re: Non-uniform force/pressure - units messed up?
              A. Telet

              Jared,

              I agree on Your "smoke test" approach. However, it would have been a NICE feature to click a face/vertex/whatever PRIOR to running the solver in my "real" model, to get listed the sum of loads applied to the selected item.

               

              Your proposed Excel approach for the equation is also agreed upon, and for the most is a more-or-less straightforward task. However, in my business (and I suppose most other fields) 95-99% of non-uniform loads are LINEAR, where you know min/max values, and/or rate of growth. I therefore think SW should include an option for application of linear variable loads (in addition to the existing equation option, of course) Such application of linear variable loads are common in i.a. all beam-analysis software I have used for the last 25 years, and should be possible to include in SW as well.

               

              My original point was that load application to any model should be the "easiest" task during the simulation process - but the way SW have laid out the non-uniform loading regime, it have become the most time consuming after part modeling and contact sets.

              But, again You are right. I should submit ER instead of complaining here...