User defined field functions
 

I'm relatively new to star ccm+,
I need your help in converting Ansys expression into star ccm+ user defined field functions;
Expressions are :

Spurious drag wake :refPressure/ Rair *areaInt(deltas)@Plane3 -refPressure/Rair*areaInt(deltas)@Plane2

Trefftz Plane drag:
0.5* refDensity* areaInt (( VelocityV^2+VelocityW^2))@plane3

Thanks in advance

Please provide an explanation of each term, I don't know what the terms mean.