Fluids

Fluids

Difference of pressure values with each run repeatations

    • Vaishnavi
      Subscriber

      Hello Team!


      I have completed few successful runs of wave-structure interactions. I can generate wave and get converged solution. I set a solution monitor for pressure on the surface where fluid ends - I called this as FSI (suppressed solid starts from this edge). My problem is that I repeated the same run with increasing and decreasing the number of time steps. The x-y plot of the value of pressure over the FSI interface shows a series of values which do not match at all if the time step is changed. Whats more surprising is that, when I tried getting the max. vertex values over the FSI surface over a period of time, it doesnt match either! I want to know if my simulation is completely wrong? how can changing time step alter the values completely! In one trial it is +3000 and another it is -2000 something. Pls help!!



       



       


      This is my geometry, but the results that I have shown are from the 2D analysis. 


      I intend to find the location of max pressure on the structure. any leads on this?


       

    • DrAmine
      Ansys Employee
      Forget about the FSI part: did you change the number of time steps or time step size?
    • Vaishnavi
      Subscriber

      Hi!


      I added the number of time steps yes.


      I havent altered the time step size.


      I am writing the files of xy plot of total pressure. Should I also be looking at solution monitor of vertex/maximum of total pressure?


      Whoch file should we be referring for observing the solution? My aim is to know the position and value of maximum pressure on a surface.

    • Rob
      Ansys Employee

      Check for convergence too. Also, how did you start the model?  Run without the structural part to see how it's behaving.  Taking facet maximum can be misleading with poor mesh/convergence as you can pick up rogue spikes that give weird results. 

    • Vaishnavi
      Subscriber

      hello rwoolhou,


       


      The issue seems resolved. I require to see solution monitor for a longer duration of time and ignore the initial data as it is the flow development time.


      I wish to get the value of force on the structure. So should I be selecting the vertex maximum of integral of pressure values? If I see solution monitor I get to see pressure wrt time on the surface. but when I see x-y plot, does this give average of pressure values when I click "Vertex or facet maximum" What should i select for obtaining correct results?


       

    • DrAmine
      Ansys Employee

      To get the force of the structure it is better to monitor/quantify the force. 

    • Vaishnavi
      Subscriber
      Okay. But then what do with get when we click on x-y plot under results under solution window? If I write or plot value of pressure against direction vector (x-0, y-1, z-0), does it mean I get the value of pressure (on selected surface) with Reference to y coordinate?
    • DrAmine
      Ansys Employee
      You get the value if pressure along that coordinate on the selected boundary. You can export the values of pressure and shear stress on the surface via generic ASCII export.
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