******************* This email originates from outside Imperial. Do not click on links and attachments unless you recognise the sender. If you trust the sender, add them to your safe senders list https://spam.ic.ac.uk/SpamConsole/Senders.aspx to disable email stamping for this address. ******************* Dear all,I am relatively new to CFD and Nektar++. Although there are much studies perfomed by Nektar++ on flows over rough surface/bed, I could not find detailed information on how to define a rough surface.I intended to define a rough surface/boundary (not a single roughness element or hump), and then, to investigate the boundary layer developed over this surface. For this purpose, do I need an external program like GMSH or is there any parameters (such as Nikuradse equivalent sand roughness or roughness height) or modules implemented in Nektar++? Any help would be greatly appreciated!Many thanks,Selman BaysalR. A. in HydraulicsDept. of Civil Eng'gÇanakkale Onsekiz Mart University--ITU Civil Eng., BSc.ITU Coastal Sci. & Eng., MSc.