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May 3, 2012, 13:55 

#21  
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Filippo Maria Denaro
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Quote:
First of all, I suggest starting with an initial condition of uniform flow everiwhere (U= constant, V=0) and a linear pressur law along x 

May 5, 2012, 09:23 

#22  
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Dr. Madhukar M Rao
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Quote:
Also, are you using split A or split B formulation for timestepping (see Zienkiewicz's book) ? 

May 6, 2012, 14:55 

#23  
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Hector Redal
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Quote:
I am using the split A formulation for the timestepping. According to the reference (Zienkiewicz's book), this split allows the use of equal interpolation for the shape functions in quad elements. I am using shape functions for the velocity and for the pressure with equal degrees for both. 

May 7, 2012, 02:32 

#24  
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Dr. Madhukar M Rao
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Quote:
[1] use a velocity/pressure element combination that satisfies BB. [2] ensure global mass conservation by adjusting the outlet velocity field such that the outlet mass flow matches the inlet mass flow. Best regards, Madhukar 

May 7, 2012, 12:51 

#25  
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Quote:
It seems that I did the same simulation work. I just set the all pressure conditions as zerogradient except the outlet one is fivedvalue 0. And the velocity is uniform: U=1 and V=0 at inlet, fixed wall is zero and outlet is zerogradient. the solution as shown in pic,the left down one is the velocity at inlet and right one is the velocity at x=4. I find the velocity at the inlet is not zero but half of the inlet. I am not sure if the solution is right or not. Thank you, Wei Last edited by hewei; May 7, 2012 at 15:11. 

May 7, 2012, 15:48 

#26  
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Hector Redal
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Quote:
Firtst of all, I would like to thank you for your help and support. After this, I would like to mention that accorting to the reference (Zienkiewicz, chapter 3.4: Circunventing the Babuska  Brezzi restricction ), split A avoids any restriction on the nature of the two shape functions used for velocity and for pressue. As I have mentioned in an previous answer, I am using equal degree in both velocity shape functions and pressure shape functions. According to this reference: A finite element formulation for the Stokes problem allowing equal velocitypressure interpolation. Ramon Codina  Jordi Blasco. Comput. Methods Appl. Mech. Engrg 143 (1997) 373  391, the use of equal velocity interpolation can be used in the CBS scheme algorithm. Consequently, a doubt arises to me at this point. If according to Zienkiewicz and Codina/Blasco this type of interpolation functions are feasible, why are they failing in my case? Kind regards. 

May 7, 2012, 15:50 

#27  
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Hector Redal
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Quote:
I would like bring up the following question. Are you using the same algorithm than me for carrying this simulation? What I would like to know if you are using the CBS algorithm for the finite element method. Best regards, 

May 7, 2012, 17:11 

#28  
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Quote:
I used the OpenFoam to simulate the flow, as we know ,the OpenFoam is basically on FV method,I adopted the icoFoam to do that, so I am not sure this information may help you on FEM. yours, Wei 

May 8, 2012, 00:05 

#29  
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Dr. Madhukar M Rao
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Quote:
Assuming that you wrote your own code, you can check the results against one of the freely available open source codes. Best regards, Madhukar 

June 2, 2012, 07:04 

#30  
Senior Member
Hector Redal
Join Date: Aug 2010
Location: Madrid, Spain
Posts: 151
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Quote:
After struggling with the code, I discovered a bug in my code when assembling the force terms in the CBS Algorithm. The force term were correctly calculated, but the assembly utility failed to assemble the forces from each element. Once I have fixed this bug, I have rerun the test case. I am enclosing the results I have obtained. It appears to me that this are miles better than the ones I had previously got. What's your impression about these new results? I have also updated the results for the lid driven cavity flow. You can take a look at them in the following link: https://sites.google.com/site/hector.../cfdexample1 I would like to thank all of you for your kind help and support. Thank you very much!!! Best regards, Hector Redal 

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