# Finite Element vs. Finite Volume Codes

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 December 22, 2005, 12:53 Finite Element vs. Finite Volume Codes #1 Salman Guest   Posts: n/a Can anybody explain to me the difference between finite element and finite volume CFD codes? Which one is preferable for what type of problems? Thanks.

 December 22, 2005, 12:56 Re: Finite Element vs. Finite Volume Codes #2 tiger Guest   Posts: n/a Most CFD people use the finite volume because of it's stability over the finite element.

 December 22, 2005, 20:19 Re: Finite Element vs. Finite Volume Codes #3 diaw Guest   Posts: n/a I have found that the FEM showcases the underlying physics in a superior way to FVM, which tends to, by its cell-averaging design, damp certain physical phenomena. The nodal interconnectivity of FEM gives useful inter-node information. I understand that there is information in the Wiki on the FVM - FEM comparison. diaw...

 December 26, 2005, 20:07 Re: Finite Element vs. Finite Volume Codes #4 zxaar Guest   Posts: n/a on Wiki on the FVM - FEM comparison is still not written, i wished to add but i do not understant much of FEM, so left it for people who excel in FEM.

 December 29, 2005, 01:45 Re: Finite Element vs. Finite Volume Codes #5 Hubert Janocha Guest   Posts: n/a FEM is normaly apllied to structurall analysis, because the code calculates a length expansion, and out of this it calculates the stress as the first derivation of the length. To be able to do this the FEM-Cell must have at least a linear weight function, which means there are two points discribing a line (e.g. in 3D 8 nodes per hexaeder-cell). The fist derivation of it is a constant function. When you have for e.g. a 1D problem, you would get a piecewise (per dx-interval) constant stairways shape of the stress, which is not really accurate. So you better choose a quadratic weight function (means in 1D there are 3 points defining a quadratic funtion), to get a linear stress in the dx-intervall. For a first shot many peaple using the linear cells in combination with a higher mesh resolution. In CFD there is no need to calculate a first derivation of a value. Because of this a constant weight function is sufficient (FV-Methode, only 1 node per cell). You can increase the result accuracy by using FE-Methods, but is has a great overhead, which let dramatically decrease the speed of the solution progress. To manage at least 8 nodes per cell (linear wight function) instead of only 1 node per cell leads to a extrem memory requirement. Conclusion: In Structural analysis you don't have a choice, you have to use at least a linear cell, because of the first derivation of the length. But in CFD, (especially for large meshes and in transient calculations) FEM-Methods are not really practicable, in these days (!). By the way; when using more and smaller cells in general, the needed geometrical accuracy given by the modell-walls (especially in CFD) is much higher. Hope this helps Hubert Janocha

 January 2, 2006, 19:14 Re: Finite Element vs. Finite Volume Codes #6 Salman Guest   Posts: n/a Thanks for all your replies. Some CFD packages that use FEM approach, present it as part of the natural evolution of things. Now I have a better idea.

 January 3, 2006, 09:26 Re: Finite Element vs. Finite Volume Codes #7 diaw Guest   Posts: n/a For fluids, FEM will provide intricate flow details that FVM would be hard-pressed to do. The interconnectivity between nodes is precisely why FEM does such a good job. I think of FVM as a glorified form of FDM - a net of point samplings taken over the flow domain. diaw...

 January 3, 2006, 13:58 Finite elemnent and finite volume #8 S. Dhinakaran Guest   Posts: n/a Finite volume codes are easy to write. Writing a finite element code is laborious and it takes much time.

 January 6, 2006, 04:19 Re: Finite elemnent and finite volume #9 Alex Muthaiah Guest   Posts: n/a 1)Finite Element basically works on Weighted residual method and Finite Volume works bascially on Conservation priniciples. 2)In FEM nodal connectivity is important to get solution if u r not able to make so it will take as freeedge in solution domain. But in FVM nodal connectivity is not mandatory but face connectivity is must since flux b/t cell face has to conserve. ciyo Alex Fresh and HappyS5 like this.

 January 6, 2006, 22:59 Re: Finite elemnent and finite volume #10 diaw Guest   Posts: n/a >>>1)Finite Element basically works on Weighted residual method and Finite Volume works bascially on Conservation priniciples. -------- FVM is also a Weighted Residual method... with constant weighting (ref Patankar - p30) diaw...