# solve equation

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 November 30, 2010, 12:09 solve equation #1 New Member   Diego Villa Join Date: Mar 2010 Location: Genova Italy Posts: 28 Rep Power: 7 Hi all, I have a stupid question but I don't find the solution. I must solve the following equation: U & grad(eta) - Uz=0 where eta is a scalar field and U is velocity vector and Uz is the z-component of U. How can I write the scalar matrix etaEqn and solve it? Thanks.

 November 30, 2010, 13:08 #2 Senior Member     Santiago Marquez Damian Join Date: Aug 2009 Location: Santa Fe, Santa Fe, Argentina Posts: 420 Rep Power: 15 Hi, Is your U field divergence free [div(U)==0]???, in this case you have U & grad(eta) - Uz=0 -> div(U eta)-Uz=0 so that in FOAM solve(fvm::div(phi,eta)-U.component(vector::Z)==0); where phi is previously defined as phi=U&Sf, like is scalarTransportFoam, icoFoam, etc. Regards. __________________ Santiago MÁRQUEZ DAMIÁN, Ph.D. Post-doctoral Fellow Research Center for Computational Mechanics (CIMEC) - CONICET/FICH-UNL T.E.: 54-342-4511594 Ext. 1005 Güemes 3450 - (3000) Santa Fe Santa Fe - Argentina http://www.cimec.org.ar

 November 30, 2010, 13:15 #3 Senior Member     Santiago Marquez Damian Join Date: Aug 2009 Location: Santa Fe, Santa Fe, Argentina Posts: 420 Rep Power: 15 One more thing, Is your equation dimensionally consistent? Best. __________________ Santiago MÁRQUEZ DAMIÁN, Ph.D. Post-doctoral Fellow Research Center for Computational Mechanics (CIMEC) - CONICET/FICH-UNL T.E.: 54-342-4511594 Ext. 1005 Güemes 3450 - (3000) Santa Fe Santa Fe - Argentina http://www.cimec.org.ar

 November 30, 2010, 14:45 #4 New Member   Diego Villa Join Date: Mar 2010 Location: Genova Italy Posts: 28 Rep Power: 7 Thank you Santiago Marquez Damian I solve like you suggest and it works. Info<<"Inizio calcolo Matrice Eta"<

 November 30, 2010, 14:59 #5 Senior Member     Santiago Marquez Damian Join Date: Aug 2009 Location: Santa Fe, Santa Fe, Argentina Posts: 420 Rep Power: 15 I don't know, may be you can post the console output at the exploding moment and some data about the physical problem. Regards. __________________ Santiago MÁRQUEZ DAMIÁN, Ph.D. Post-doctoral Fellow Research Center for Computational Mechanics (CIMEC) - CONICET/FICH-UNL T.E.: 54-342-4511594 Ext. 1005 Güemes 3450 - (3000) Santa Fe Santa Fe - Argentina http://www.cimec.org.ar

 November 30, 2010, 16:46 #6 New Member   Diego Villa Join Date: Mar 2010 Location: Genova Italy Posts: 28 Rep Power: 7 I find the problem is the div shemes, I use a Gauss Linear and all explode, than I change in a Upwind and all works fine!!! Thank for the help.

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