******************* 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 hope this email finds you all well. I am trying to simulate flow around a sphere. I get an error of segmentation fault. I am generating a mesh from gmsh, converting it into Nektar format, then using the IncNavierStokesSolver. I am wondering whether it may be a problem with the association of composite IDs in boundary conditions. However I do not seem to find the problem. I attach the files I am using. If anyone could have a look and help me understand what I am doing wrong I would be very grateful. Anyways, I also have another question that may be related with the issue above. What is the way to know which composite ID corresponds to the related physical surface of your geometry? In other words, is there a way to associate a composite ID to a specific surface in order to assign boundary conditions? For example, in my case, in file s_session.xml, I say C[1] (ID="0") is the inlet surface because in file s.xml it is the first composite, which, I am assuming, corresponds to the first physical surface I have defined in file s.geo (Physical Surface("inlet")={2};). Is this correct? I hope my questions make sense. Thank you in advance for your help, and Happy Easter! Kind regards, Silvia