Thanks a lot for your suggestion Mr. YassernYes, Mr Rob, it is wall & shadow (coupled wall) bound fluid region.nIssue is resolved. Having another issue on loading UDF on wall & its shadow surface, solution isn't converging. What will be the reason as you can see in the screenshot line are parallel. But before loading UDF, its converging after few iterations. Now it has been past 3000.nRegards,nAbbas Razannn