Rob
Ansys Employee

It's not so much the main DEFINE sections that determine whether you need to parallelise the UDF but the loops and calls from within the code  https://ansyshelp.ansys.com/account/Secured?returnurl=/Views/Secured/corp/v221/en/flu_udf/flu_udf_sec_using_udfs_parallel.html    It's generally a good idea to test UDFs on a simple system, and you can try running 1, 2 and 4 cores to see whether anything behaves differently when writing your code.