1 Reply Latest reply on Jan 27, 2015 1:38 AM by Jared Conway

    Force calculation does not agree with plotted variables

    Amit Katz

      I have a simulation of a solid object resting on a perforated drum, with a vacuum pressure behind, as pictured:




      Please focus only on the highlighted face and ignore the rest.


      As you can see there are only a few places where there is solid-fluid contact, namely at the holes (which are 5mm in diameter.) The pressure is approximately uniform, a -25 inches of water. Only 12 of the holes have vacuum pressure. Neglecting friction, one would expect the force on this solid to be = 12 x (25 inches H2O) x pi() x (2.5mm)^2. This equation is equal to approximately 150 gram-force (http://www.wolframalpha.com/input/?i=3*4*25+in+wc*pi*%282.5mm%29%5E2+to+gram-force).


      When I do a surface parameter on this face I get this result from Flow Sim:

      Integral ParameterValueX-componentY-componentZ-componentSurface Area [in^2]
      Normal Force [grf]1745.461-1202.013-1265.621-3.873e-0040.3972
      Force [grf]1745.461-1202.013-1265.621-3.872e-0040.3972


      As you can see the force and normal force are identical, there is no shear force. The error here is not small, it is a factor of 10 off from what I would expect. Does anybody know why this would be? Did I miss something?