Dear Dr. Amine Sir,nSir, the fluid in my project is drilling fluid which follows the Herschel-Bulkley viscosity model. So for a proper analysis I need the UDF. I need to compare my results with another model to validate my results. The other model used Herschel-Bulkley viscosity model UDF. nYes Sir. But I need a whole tutorial on how to write the UDF in C++ or C language, since I also have to specify the critical stress, flow behavior index, consistency index and yield stress and I don't know how it's done. Is there any?nI saw in Ansys 2020R2 there is a new window Strain Rate in Herschel-Bulkley viscosity model. Looked for it in the user manual but there is nothing there on Strain rate and how it works.nnThank You Sir for answering. n