# UDF function diverging

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 June 22, 2009, 08:23 UDF function diverging #1 Member   Akour Join Date: May 2009 Posts: 79 Rep Power: 17 hello all, I am trying to implement a source term on the x and y momentum equations that equals Q (space charge) x E_i (electric field) so I have defined two User defined scalars, one for the space charge which is composed of a unsteady function, a diffusivity function and a scalar flux function. All of which I effectively took out of the udf manual so i know there are no mistakes there. The electric field UDS only has a diffusion term (diffusion of the voltage), and a source term which equals Q/epsilon...and I have tested it on its own and it works so no mistakes there. However, Every time I run these two UDSs with the momentum field on (which I need to calculate the scalar flux term in the UDS) the mass conservation residuals diverge, and so I then get a floating point error. I think the problem is with the gradient of the scalar term, i.e. the source term for x-momentum = -C_R(c,t)*C_UDSI_G(c,t,0)[0]*C_UDSI_G(c,t,1). There is no C_UDSI_RG macro as far as I am aware... please note that the field=-(gradient of the voltage). which is why I need to calculate a gradient of a user defined scalar... If anyone knows if there is a better way I can implement the user defined gradient macros I would really appreciate it... Im attaching the momentum source UDFs which I believe are the problem. 3. MOMENTUM SOURCES #include "udf.h" DEFINE_SOURCE(xmom_source,c,t,dS,eqn) { real source; source = -C_R(c,t)*C_UDSI(c,t,1)*C_UDSI_G(c,t,0)[0]; dS[eqn] = 0; return source; } DEFINE_SOURCE(ymom_source,c,t,dS,eqn) { real source; source = -C_R(c,t)*C_UDSI(c,t,1)*C_UDSI_G(c,t,0)[1]; dS[eqn] = 0; return source; } Thanks in advance AK

 December 23, 2013, 05:05 #2 Member   xingangzheng Join Date: Jul 2009 Posts: 39 Rep Power: 17 Dear ak, Do you have solved this question. I have meet the same problem as you have meet. The gradient of the scalar term! How good method you have to treat it? thank you very much!

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