Introduction - If you have any usage issues, please Google them yourself
UDF to compute the orientation of a rotating valve, based on a
specified rotational speed.
Christoph Hiemcke, Fluent Inc., 12 Feb 2004
butterlfy_flex_UDF = name shown in Fluent GUI
dt = thread
cg_vel = cg velocity (global)
cg_omega = angular velocity (global)
time = current time
dtime = time step