5 Replies Latest reply on May 7, 2015 11:06 AM by CLAYTON JACOBS

    FEA modeling a manifold block

    CLAYTON JACOBS

      Imagine I have a simple square block made into a pipe threaded elbow.  In the right face and the top face, I drill a hole to intersect one other and thread the ends.  If I want to analyze just the PART, I can "fix" the bottom face and apply pressure to the holes.  I will get a resultant net force trying to push the block to the left.  FBD would makes this obvious.  So in reality the part doesn't go flying off because the area is counter-balanced down stream by the connecting hydraulic hoses.  So how do you like to model this sort of thing correctly?  We toy'ed with modeling a fake plug in the ports but that un-realistically stiffens the port.  We tried adding a net axial force on the port to counter-act the pressure force but that was clunky and not super accurate.  I'm really hoping there is a special SW tool that I just haven't found yet for these sorts of areas.  Any ideas/ suggestions would be appreciated!  Thanks!

        • Re: FEA modeling a manifold block
          Jared Conway

          can you post a picture and a description of what you want to learn in this analysis? also what tool do you have? simulation or simxpress?

          • Re: FEA modeling a manifold block
            CLAYTON JACOBS

            I'm using Simulation. Say the material is 304ss and the green ports are 5,000-7,000 psi oil.  I'm trying to model something completely different but this illustrates the example.  Pretend for example I screw a plug into the right side ports and use a hose to pressurize the top port.  Notice the right side of the vessel is less stiff than the left.  I'd like to get that deflection accurate but balance the net pressure force imbalance (ie the part will want to deflect to the left A LOT).  Note the subtleties of if I simply draw a "plug" body in the holes I will get a pressure balanced vessel but the "hoop stresses" (I'm using that term loosely here) in the part with not be accurate as the PLUG will stiffen the part. 
            pressure block.png

              • Re: FEA modeling a manifold block
                Jared Conway

                are you concerned with the loading or the fixture?

                • Re: FEA modeling a manifold block
                  Mark Ankrom

                  Seems like your model needs to balance the pressures in the pressure vessel.  The model you have won't hold pressure without "plugs" and applying unbalance pressure results in unrealistic motion.

                   

                  Sounds like you tried the first method - add axial loads at ports (I would suggest line loads) to represent the loads from the piping. This will cause some local stress concentration as you found out.

                   

                  The next method would  be to add a more realistic representation of the lines.  Adding 2 or 3 inches of piping that is capped for each of the ports would allow the pressure to balance with the correct FBD (determinate support)  and not disturb the "hoop" stresses.

                   

                  I have used many of the FEM packages and I have not seen any feature that handles this case for you.

                   

                  My opinion is you will need to build the model to represent the condition you are trying to simulate.

                   

                  Mark