Hi Junda, Not sure if anyone has responded to your email. What you describe sounds reasonably correct. When extracting the xml file using NekMesh be aware that the extract module refers to the composite of a surface where as in the FieldConvert module you need to provide the boundary regions. I am not sure if this might be the reason you are not getting the answer you expect. To report issues you can add them on our gitlab page under: https://gitlab.nektar.info/nektar/nektar/-/issues Many thanks, Spencer. On 5 Apr 2022, at 09:00, 张俊达 <jundazhang@sjtu.edu.cn<mailto:jundazhang@sjtu.edu.cn>> wrote: ******************* 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. ******************* Hi all: I am new to Nektar++, I have used Nektar++ to simulate a simple steady state 2-D thermal conduction problem, where I define the boundary conditions as one for temperature determination (Dirichlet conditions) and one for heat flow density determination (Neumann conditions). When I want to use the scalargrad module in fieldconvert to calculate the gradient of a boundary to get the heat flow density in where the temperature is determined. It said I need a xml file to process the fld file. I reference the “5.5.11 Extract a boundary region: extract module” in user-guide, use extract module in nekmesh to get the xml file of the boundary and get the .dat file. But the data seems wrong for the u_scalar_gradient data is same in each point and the value is the temperature value that I defined in this boundary. So could you tell me if I choose the right xml file or which operation I miss out? How can I get the gradient on the boundary or nearby? By the way, I meet the segmentation fault when I use some fieldconvert module. if there any way can help me make it report which step that occur this fault? Many thanks for your help! Best! Junda Zhang _______________________________________________ Nektar-users mailing list Nektar-users@imperial.ac.uk<mailto:Nektar-users@imperial.ac.uk> https://mailman.ic.ac.uk/mailman/listinfo/nektar-users