2 Replies Latest reply on Nov 11, 2009 8:54 PM by Bill McEachern

    Impulse analysis

      I have an offshore pipe diameter 150mm with fluid flowing at high speed. A valve is closed in 0.1 seconds and abruptly stops the flow. Is it possible to simulate this situation and derive the "hammer forces" exerted on the valve and the pipe when this happens?



        • Re: Impulse analysis
          Anthony Botting
          Hi Maria:
          I have done this before with solids using the wave equation from physics. You should be able to do this with a liquid, since it will be "still" for all practical purposes. Just make sure you have at least 10 elements spanning a wavelength of the shock wave (preferably, 20) to capture the shock wave correctly. You can use the nonlinear module, dynamic, to do a direct integration in time (note that all material properties and displacements will be in the linear realm - you're just using the nonlinear solver to perform the direct integration in time). Model the liquid in the pipe as a solid part, and put an impluse load (uniform displacement might be best over your 0.1 seconds) at one end of the pipe, and select a time step short enough, too. You can generally use a time step that is 1/20th of the shortest shock wave period that you want to capture. It will typically be an extremely large amount of integration that has to be done. You can animate the shock wave and see it actually traverse the length of the pipe and reflect. (note: this procedure also works using the explicit integrator in the "Drop test" module - it's much faster integration method but has a few more limitations than just using the nonlinear, dynamic module). Hope this helps.Anthony