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General Mechanical

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Hydrostatic fluid elements: iterative solution

    • Janne
      Subscriber

      Hello all,

      when modeling fluids or gases contained by solids using HSFLD241 or HSFLD242 elements, the volume and pressure of the contained space is calculated using varitional quantities (as show in 13.242.2. Element Matrices and Load Vectors). How I understand this is that the volumetric change of the contained space is solved iteratively. My questions is, that if I have a static structural analysis where NLGEOM,off, is the volume still solved iteratively? If yes, then this happens inside the ANSYS Solver and the user cannot see it: I can accept it as it is. If the answer is no, is linear analysis solution still valid (assuming the deformations are small) or should NLGEOM be always on when using HSFLD elements?

      Wbr, Janne

    • Erik Kostson
      Ansys Employee

      Hi

      See the help manual (apdl - structural analysis guide - chapter 15 - Modeling Hydrostatic Fluids). You can search for this in the help manual and it will come up with that section

      It says there what the supported analysis types are and gives links to the theory behind them if one wants to look into that more.

      Hope that helps

      Erik

    • Janne
      Subscriber

      Hello Erik,

      I appreciate your prompt response. The cavity volume/pressure is coupled to the deformation of the solid, which is inherently a nonlinear relationship. What I have been able to find is this--you can run the analysis using:

      1) Geometrically linear analysis

      2) Geometrically linear analysis with NROPT,full (newton-raphson iteration)

      3) Geometrically nonlinear analysis with NLGEOM,on (also uses newton-raphson iteration)

      Obviously 3) is the most accurate because it includes large deflections. If one has small deformations, 2) is suggested. But what I am interested is how is the cavity volume/pressure solved in case 1) because this is 99.9% accurate with analytical exact methods (they don't iterate). 1) and 2) almost equal in terms of cavity volume/pressure and structural deformations and stresses (at least in my case study). 

      In case 1) does ANSYS have some initial guess of the volume change and uses that or what? 

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