Why this udf is not working????

dkb_bg · December 27, 2011, 00:38

Hi all,
Plz help me
I have written this udf for density a function of pressure.i am woking on narrow diameter pipe and woking fluid is r134a single phase. since pressure is changing across the pipe so i want to change density with press. but fluent is showing follwing error

I am taking press inlet and press outlet

*UDF for liquid density*/
#include"udf.h"

DEFINE_PROPERTY(fluid_density,cell,thread)
{
real density;
real pressure = C_P(cell,thread);
density =1e-10*pressure*pressure-0.000*pressure+1385;
return density;
}

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.

duri · December 27, 2011, 09:52

The is no error in you UDF I checked it with fluent 6.3 as interpreted UDF in 64bit machine. Something else is causing the trouble.
why are you using 0.0*pressure it makes nosense, it could add some machine error (values like 1e-45) and this could cause problem in 32bit machine.

ComputerGuy · December 29, 2011, 18:28

Deepak,

While you can define whatever density you want, C_P(cell,thread) won't return the absolute pressure, which I think you're looking for. Consequently, I think you're getting a density approaching zero, which is probably throwing the error. Additionally, the second term in your formula (0.000*pressure+1385) will *never* be anything but zero, given that you're multiplying by zero.

Verify that you're using the proper calculation for density (more specifically, for pressure), and then let us know.

Best,
ComputerGuy

December 27, 2011, 00:38	Why this udf is not working????	#1
dkb_bg New Member deepak Join Date: Sep 2011 Location: india Posts: 8 Rep Power: 14	Hi all, Plz help me I have written this udf for density a function of pressure.i am woking on narrow diameter pipe and woking fluid is r134a single phase. since pressure is changing across the pipe so i want to change density with press. but fluent is showing follwing error I am taking press inlet and press outlet UDF for liquid density/ #include"udf.h" DEFINE_PROPERTY(fluid_density,cell,thread) { real density; real pressure = C_P(cell,thread); density =1e-10pressurepressure-0.000*pressure+1385; return density; } 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.

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December 27, 2011, 09:52		#2
duri Senior Member duri Join Date: May 2010 Posts: 245 Rep Power: 16	The is no error in you UDF I checked it with fluent 6.3 as interpreted UDF in 64bit machine. Something else is causing the trouble. why are you using 0.0*pressure it makes nosense, it could add some machine error (values like 1e-45) and this could cause problem in 32bit machine.

December 29, 2011, 18:28		#3
ComputerGuy Senior Member Real Name :) Join Date: Jan 2010 Location: United States Posts: 192 Rep Power: 16	Deepak, While you can define whatever density you want, C_P(cell,thread) won't return the absolute pressure, which I think you're looking for. Consequently, I think you're getting a density approaching zero, which is probably throwing the error. Additionally, the second term in your formula (0.000pressure+1385) will never* be anything but zero, given that you're multiplying by zero. Verify that you're using the proper calculation for density (more specifically, for pressure), and then let us know. Best, ComputerGuy