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August 28, 2012, 22:33 
FEM VS FVM in CFD

#1 
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hello, may I ask what the advantadges and disadvantadges of FEM and FVM in CFD? And why the mainstream commercial CFD codes are based on FVM? Thanks a lot!


August 29, 2012, 02:11 

#2 
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I read these in a book, might be helpful for you.
The Finite Volume method can accommodate any type of grid, so it is suitable for complex geometries. The grid defines only the control volume boundaries and need not be related to a coordinate system. The method is conservative by construction, so long as surface integrals (which represent convective and diffusive fluxes) are the same for the control volume's sharing the boundary. An important advantage of finite element methods is the ability to deal with arbitrary geometries; there is an extensive literature devoted to the construction of grids for finite element methods. The grids are easily refined; each element is simply subdivided. Finite element methods are relatively easy to analyze mathematically and can be shown to have optimality properties for certain types of equations. The principal drawback, which is shared by any method that uses unstructured grids, is that the matrices of the linearized equations are not as well structured as those for regular grids making it more difficult to find efficient solution methods. 

August 29, 2012, 05:40 

#3 
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Daniel Barcarolo
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If I may add...
From my experience they provide the same quality of results. The software COMSOL is based on FEM and solves both fluid and structure (and other stuff). By the way, here you have another advantage of FEM: if you want to solve multiphysics FEM is well suited for it. 

August 30, 2012, 10:45 

#4  
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Rami BenZvi
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Quote:
FVM is easier to formulate, and there is a large and long volume of research using it. Another reason for its larger spread is conformism of the CFD community. There is another point. the FVM is conservative by constuction, while the FEM is not necessarily so. There is a debate how important this property is for better accuracy. To the best of my knowledge, FEM is usually more accurate for a given grid. 

August 30, 2012, 14:18 

#5 
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plus you can't do real good shock capturing with a globally continuous method! I guess that's the main reason why FV is the standard.


August 30, 2012, 14:53 

#6 
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Filippo Maria Denaro
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As already stated, FV can be seen as a particula type of FEM for a specific choice of the shape function.
I would add that often the term FV is used for the discretization of the integral form of the equation as well as for the differential form in divergence form. In my opinion this abitude is not correct, FV should be uniquely addressed for the discretization of the integral form, that has a physical background expressed by the transport (Reynolds) theorem. The integral form is the only physically admissable for any case and FV are the congruent translation in the discrete sense. 

September 2, 2012, 04:23 

#7  
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Rami BenZvi
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Quote:
R. BenZvi, M. Perl, A. Libai, A Curved Axisymmetric Shell Element for Nonlinear Dynamic Elastoplastic Problems, Part II  Implementation and Results, Computers and Structures, Vol. 42, No. 4, pp. 641648, 1992.A newer concept in FEM is the discontinuous Galerkin metod. A nice review, showing very nice examples for shocks and other discontinuities is B. Cockburn and C.W. Shu, RungeKutta Galerkin Methods for ConvectionDominated Problems, J of Scientific Computing, Vol 16 No. 3, pp. 173261, 2001. 

September 2, 2012, 04:50 

#8  
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Quote:
Maybe I put it wrongly, I should have said: High order shock capturing is the problem! Oh and in my opinion: What makes DG better for compressible flows is the fact that it is discontinuous  a property borrowed from FV, not FEM. Thanks for posting you references up there. Is the paper available freely`? 

September 2, 2012, 05:15 

#9 
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Rami BenZvi
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I don't think the papers are free. I can email you a copy of mine (if you are not afraid of shell theory...).


September 2, 2012, 07:09 

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September 2, 2012, 09:42 

#11 
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