General Mechanical

General Mechanical

Problem in choosing the surface for fixed support.

    • bharathgl
      Subscriber

      Hello everyone,

      I am trying to perform a simulation on a flange system with a metal gasket. When I apply a load of 30 KN on the bolts on each side (See attached image 1). Then, the tension chain will move down. When the tension chain moves down, the flank surface of the tension chain meets the flank of the flange and pushes both the flanges in an inward direction which compresses the gasket (See Fig 2). Hence, there is a force (60 KN acting on the flank of the flange from the chain). Now, I want to do a simulation only with the tension chain to check whether it can withstand the applied force without any deformation. While doing so I get different results when I fix (Fixed support) different surfaces of the tension chain. I am not sure about on which face I should use fixed support so that it represents the actual problem. Can someone tell me which face should I fix? e.g. The flank of the tension chain, drill hole.

      Looking forward to your response.

      Thanks in advance.

      Bharath

    • peteroznewman
      Subscriber
      bharathgl @bharathgnn
    • bharathgl
      Subscriber
      . I was expecting a reply from you. n
    • peteroznewman
      Subscriber
      sorry, website got a little bit broken on my first reply.nYour geometry and loading are symmetric about two planes, and it is appropriate to make it three orthogonal planes.nGo back to CAD and cut your model on three planes about the center so you are left with 1/8 of the geometry. That would be the top, front, right half of the model. Keep the front flange in the model and a half thickness of gasket. nIn Mechanical, on each cutting plane, create a Displacement support that sets the displacement to 0 on the coordinate normal to the cutting plane, leaving the other directions Free. For example, the XY plane has a normal in the Z direction. On the XY cutting plane, put a Z=0 Displacement, leaving X and Y Free, on every cut face. Repeat on the other two planes. nUse Bonded Contact on the flat faces of the gasket and flange. Use Frictional Contact on the flank faces of the flange to the tension cable. nThere are flat faces on the flange at a larger diameter than the gasket, do those end up seating on each other? If so, you will need to add a rigid surface at the center plane and another Frictional contact to stop that face from crossing the center plane. If not, then the gasket will support the flange in the axial direction.nApply 15 kN to the half face of the tension cable.nThis is a nonlinear problem, so you will want to turn on Automatic Time Stepping and set the initial substeps to 100. Under the Connections folder, insert a Connection Tool and check that the Frictional Contact is Closed. If it is Near Open with a tiny gap, edit the contact and use Adjust to Touch.n
    • bharathgl
      Subscriber
      nThank you so much for your response and time Mr. Peter. Initially, I want to see the structural stability of the complete tension chain (without cutting the geometry) (see fig). i.e. also in the absence of flange and gasket. Consider only the tension chain as shown in fig below and I am applying a load of 30 KN on each side. In this case, what will be the boundary condition. Which surface of the tension chain I should fix i.e where should I apply fixed support. When I fix the flank of the chain the results are different. When I fix the drill hole again the results are different. Can you help me in this? Thanks a lot, in advance.nFurthermore, I should not cut the geometry to 1/8th (maybe I can cut about xy and xz plane see fig 2) because I wanted to see the force distribution on the knife edge of the flange. e.g. At the place of bolt i.e. where the load is applied the gasket compression will be more but at the middle of the flange (on the top) there will be very less penetration of knife edge. Which I want to see. Instead of applying displacement support can I use frictionless support ( Symmetry boundary condition) ? In this case, can I able to check how much is the force transferring from the knife edge of the flange to gasket? Only the knife edge seats on the gasket. nnThanks in advance.nBharathn
    • peteroznewman
      Subscriber
       nIs the knife edge on both flanges? If so, this is a symmetric model. If only one flange has a knife edge and the other is flat, then you can't use symmetry to cut the gasket in half.nThe answer to the question of what supports the tension chain is contact with the flank face of the flange and potentially contact of the two flat faces of the flange with each other outside the gasket diameter. You didn't answer my question on whether these faces clamp together.nFirst build the 1/8 model as I described above, then we can talk about the results.n
    • bharathgl
      Subscriber
      nThanks again for your help. It means a lot. Yes, The knife edge is available on both the flanges. The above marked faces (red) will touch each other when the load is more than 30 KN (which means tension chain will be pulled further down in radial direction that makes both the flanges to move towards gasket) at the same time the knife edge penetrates into the gasket to the maximum (0.4 mm on each side). But practically that is not required. A knife edge penetration of 0.2 mm per side is enough for air tight seal. So, these faces will not be in contact when a load of 30 KN is applied. nThe support to the tension chain is the contact between the flank of the tension chain and the flank of the flange and also the contact between only the knife edge (tip) and gasket. These flanges are like a long pipe with one flange being fixed. I have cut this for simplification. So practically there will be a contact only between the knife edge and gasket. The other one is between the flank of the flange and chain. I built the model into 1/8. nThanks in advance. nn
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