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August 1, 2015, 09:58
resolved
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Gylles
Join Date: Aug 2015
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You should go: Solve --> Solution Methods --> Transient Formulation -->Second Order Implicit (on).

Good luck!!

Quote:
 Originally Posted by Sandilya Garimella ;149133 Hello All I am trying to solve for time varying electric potential for the potential equation ?(i.e) poisson's equation the unsteady from is helmholtz equation [d^2 /(dt)^2] (phi) + grad^2 (phi) = source I discretized the unsteady term (which is double derivative in time) using backward differencing and separated the terms into two terms as given in manual Following this I wrote a simple UDF as given below DEFINE_UDS_UNSTEADY(unsteady_function,c,t,i,apu,su ) { real vol; real delt; real time; real phi1; real phi2; vol = C_VOLUME(c,t); delt = CURRENT_TIMESTEP; time = CURRENT_TIME; if(i==0) { phi1 = C_STORAGE_R(c,t,SV_UDSI_M1(i)); /* value of phi at (n-1) time step */ if(time<5.0e-6) { phi2 = 0; } else { phi2 = C_STORAGE_R(c,t,SV_UDSI_M2(i)); /* value of phi at (n-2) time step */ } /* C_UDSI_M2(c,t,i);*/ *apu = (mu * epsilon * vol) / (delt * delt); *su = (-2 * phi1 + phi2 )*mu * epsilon * vol / (delt * delt); } } But when I run after hooking the UDF, till 5.0e-6 seconds the transient solutions converges. But when it has to access the (n-2) time step term then the there is an error "ACCESS VIOLATION" Can anyone help me to figure out if there is an error Error: FLUENT received fatal signal (ACCESS_VIOLATION) 1. Note exact events leading to error. 2. Save case/data under new name. 3. Exit program and restart to continue. 4. Report error to your distributor. Error Object: () Can anyone help me to figure out if there is an error

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