Usr_drag UDF error (MFiX-on-UBUNTU) and no error on (MFiX-on-WINDOWS)

I am using a user-defined drag model by modifying the usr_drag.f

I compiled the solver as in the user manual.

The udf works on MFiX-on-WINDOWS, but it doesn’t work on MFiX-on-UBUNTU

I appreciate if somebody showed me what I did wrong

Here is the error from the MFiX output
Program received signal SIGFPE: Floating-point exception - erroneous arithmetic operation.

Backtrace for this error:
#0 0x7fa04851ed01 in ???
#1 0x7fa04851ded5 in ???
#2 0x7fa09626d20f in ???
#3 0x7fa048bdb57a in drag_usr_
at /home/a …"

My guess is you are dividing, zero or taking the square root of a negative number or a similar erroneous operation. Build the solver in debug mode, it will most of the time point to the line when the error occurs.

1 Like

Dear jeff.dietiker,

Thanks for your reply!

I tested the attached udf on Windows and it was working well. On Ubuntu I complied the custom solver using the coda code and using the GUI as well. The build is successful, but when I run the code the calculation stop and I got the error.

usr_drag.f (4.6 KB)

Did you build in debug mode? Compilers will behave differently on different systems. Most probably you divide by zero when Re=0 (zero relative velocity). Move the test on Re=0 before you actually divide by Re. Something like:

  IF(Mug > 0.0) THEN
     RE = EPg*DPM*VREL*ROg/Mug
     RE = 1.0E+30
 IF (RE == 0.0D0) THEN
    lDgA = 0.0D0 

	IF (RE < 1000.0) THEN	
        C_d  = (24.0D0/RE)*(1.0D0 + 0.15D0*(RE**0.687D0))	
        C_d  = 0.440D0
	IF (EPg <= 0.985 ) THEN      !       (u_g = 0.40 m/s)	
	     hD = 0.001820D0*EXP(EPg/0.156190D0) - 0.008660D0 
	     hD = 1.0D0

     IF (EPg <= 0.4 ) then
        lDgA = 150.*(1.0D0 - EPg)*(1.0D0 - EPg)*Mug/EPg/DPM**2.+ &
	       1.75*(1.0D0 - EPg)*ROg*VREL/DPM  
       lDgA = (3.0D0/4.0D0)*C_d*EPg*(1.0D0 - EPg)*ROg*VREL*  &

Thank you very much!