Custom Drag, floating point error: invalid number
 

Hi.. I want to fit a custom drag law in simple gas-liquid pipe flow. As an exercise I coded the standard Morsi-Alexander drag Law through a UDF and enabled the drag through UDF. Now, the solver runs for some time and then gives Floating Point Error: Invalid Number. If I lower the underrelaxation, then it runs for a relatively longer time but gives the same error finally.

how to correct this plz help thanx in advance

PS: should I post the UDF I wrote ??