
[Sponsors] 
August 24, 2005, 21:56 
hi Hrvoje Jasak,
I have a que

#1 
Member
Leosding
Join Date: Mar 2009
Posts: 51
Rep Power: 10 
hi Hrvoje Jasak,
I have a question in your phd thesis. In page 123, about Nonorthogonality error, it reads "For the complete diffusion term, the nonorthogonality error has the following form: E_d = \ Sigma _f S \ cdot [ ( \ rho U)_f K \ cdot (\ Nambla \ phi)_f] =\ Nambla \ cdot (\ Gamma_D \ cdot \ Nambla \ phi), where \ Gamma _D =(\ rho U)_f k. " I think in expresion $ E_d $ shoud get rid of "(\ rho U)_f" item, maybe "(\ rho \Gamma _\ phi)_f" which refers to Equation (3.24) in Page 83. Am I right? 

August 25, 2005, 08:37 
You are right  thank you very

#2 
Senior Member
Hrvoje Jasak
Join Date: Mar 2009
Location: London, England
Posts: 1,806
Rep Power: 25 
You are right  thank you very much.
I will try to rebuild the Thesis and put an updated version on my web site, but this might be quite painful. Thanks for the effort, I really appreciate it. Hrv
__________________
Hrvoje Jasak Providing commercial FOAM/OpenFOAM and CFD Consulting: http://wikki.co.uk 

August 25, 2005, 10:25 
Hi Hrv,
I have another questi

#3 
Member
Leosding
Join Date: Mar 2009
Posts: 51
Rep Power: 10 
Hi Hrv,
I have another question. In your PHD thesis page 145,equation(3.136) is $a_P U_P = H(U) \ Nambla p $, it is a semidiscretised form, it reads "It has been consequently divided through by the volume in order to enable face interpolation of the coefficients." So the expression of equation (3.136) is right. It means the item $\ Nambla p$ is derived from \ frac{\ int _V \ Nambla p dV}{V_P}=\ frac{(\ Nambla p)_P V_P}{V_P}. then refer equation(3.10) in page 79 and equation(3.26)in page 84, " $(\ Namble \ phi)_P = \ frac {1}{V_P} \ Sigma _f S \ phi_f$" but in page 146, equation(3.142) final form of discretised incompressible NS system for momentum equation is $a_P U_P = H(U)  \ Sigma_f S (p)_f $, it means the item $\ Nambla p$ in equation 145 is equal with $\ Sigma_f S (p)_f$, and this conflicts with equation(3.26), right? Maybe my understanding is wrong! Leosding 

August 27, 2005, 18:22 
I don't see what your problem

#4 
Senior Member
Hrvoje Jasak
Join Date: Mar 2009
Location: London, England
Posts: 1,806
Rep Power: 25 
I don't see what your problem is:
grad P discretises as: \grad \phi = \ frac {1}{V_P} \ Sigma _f S \ phi_f In order to discretise the momentum equation, I have to integrate over the CV, which brings in the volumes. So, if I want to interpolate the coefficients, I have to make them intensive and I divide the equation by the volume. Nothing tricky there... Hrv
__________________
Hrvoje Jasak Providing commercial FOAM/OpenFOAM and CFD Consulting: http://wikki.co.uk 

August 28, 2005, 08:12 
I know your mean.
My qustion

#5 
Member
Leosding
Join Date: Mar 2009
Posts: 51
Rep Power: 10 
I know your mean.
My qustion is(again): In order to discretise the momentum eqution, with integrate over the CV, you will gain the equation: A<sub>P</sub> U<sub>P</sub> = H<sup>'</sup>(U)+Ñp V<sub>P</sub> Equ(A); then wanting to interpolate the coefficients, you divide the equation Equ(A) by the volume V<sub>P</sub>, and get (3.136) in your thesis: a<sub>P</sub>U<sub>P</sub> = H(U)+Ñp; but the equation (3.142) is a<sub>P</sub>U<sub>P</sub> = H(U)+SS(p)<sub>f</sub>; Does it imply the Ñp = SS(p)<sub>f</sub>?( I think it's wrong, as of (3.26) in page 84,Ñf<sub>P</sub>=1/V<sub>P</sub>SSf<sub>f</sub>.) Of course, if equation (3.142) is from directly integrating (2.24) over the CV, it is right, then it imply the a<sub>P</sub> in (3.136) and (3.142) are different. If (3.142) is from (3.136), the item "SS(p)<sub>f</sub>" should be divided by "V<sub>P</sub>", right? Thank for your kindness to my stupid question. Leo 

August 28, 2005, 08:20 
Before you divide by the volum

#6 
Senior Member
Hrvoje Jasak
Join Date: Mar 2009
Location: London, England
Posts: 1,806
Rep Power: 25 
Before you divide by the volume you've got the volume integral of grad p which is equal to the sum_f S_f p_f.
After the division you have: aP UP = H(U)+ grad p; So: grad p = 1/V sum_f S_f p_f Hrv
__________________
Hrvoje Jasak Providing commercial FOAM/OpenFOAM and CFD Consulting: http://wikki.co.uk 

August 28, 2005, 09:44 
yes, the equation:
Ñp=1/V SS<

#7 
Member
Leosding
Join Date: Mar 2009
Posts: 51
Rep Power: 10 
yes, the equation:
Ñp=1/V SS<sub>f</sub> p<sub>f</sub> is RIGHT! but how did you derive to (3.142) from (3.136) directly? They are smae "a<sub>P</sub>" token in two equations. It's selfcontradicting from your thesis. 

Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
PhD thesis of  rt  Main CFD Forum  0  May 18, 2006 12:02 
question regarding thesis topic  cfdstudent  Main CFD Forum  2  November 22, 2005 12:39 
Thesis question  Newton  Main CFD Forum  1  October 3, 2005 15:16 
PhD thesis  RK  Main CFD Forum  1  June 29, 2005 12:05 
ask for a PHD thesis  yangchen  Main CFD Forum  1  June 5, 2005 17:03 