# Adding and resolve a differential equation

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 November 15, 2012, 08:19 Adding and resolve a differential equation #1 New Member   Luigi Gurreri Join Date: Jul 2012 Posts: 15 Rep Power: 5 I have a transport equation of a scalar C in which it appears another (vectorial) variable i. Also I have a differential equation of i: div(i)=0. Can I introduce and resolve this equation in Ansys CFX, or it supports only algebraic equations?

 November 15, 2012, 16:50 #2 Senior Member   Chris DeGroot Join Date: Nov 2011 Location: Canada Posts: 387 Rep Power: 6 Yes you can add additional transport equations in CFX.

 November 16, 2012, 05:52 #3 New Member   Luigi Gurreri Join Date: Jul 2012 Posts: 15 Rep Power: 5 The problem is that I haven't a transport equation, but an additional differential equation to be solved

 November 20, 2012, 17:50 #4 Senior Member   Bruno Join Date: Mar 2009 Location: Brazil Posts: 236 Rep Power: 12 Well, is also a transport equation. Do you mean you want to solve only this equation and not the others? If that is the case, you can add and the following Expert Parameters to your simulation: Code: ```FLOW: Flow Analysis 1 EXPERT PARAMETERS: solve energy = f solve fluids = f solve turbulence = f END END``` You can also go to 'Insert > Solver > Expert Parameters > Model Over-rides' and disable other equations you see fit. Cheers

 November 21, 2012, 06:51 #5 New Member   Luigi Gurreri Join Date: Jul 2012 Posts: 15 Rep Power: 5 I have a transport equation of the variable C, in which there is a term containing i; also, I have the equation div i = 0. So, I have a system of two equation. I don't know how I can solve the latter equation

 November 21, 2012, 07:29 #6 Senior Member   Bruno Join Date: Mar 2009 Location: Brazil Posts: 236 Rep Power: 12 You have four variables (C, ix, iy, iz) but only two equations. Aren't you missing two extra equations to close your problem?

 November 21, 2012, 08:05 #7 New Member   Luigi Gurreri Join Date: Jul 2012 Posts: 15 Rep Power: 5 I think you're right! Maybe I need others equations. I will study better my problem