******************* 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 nektar++ community, I have been using version 5.0.0 of nektar++ to run unsteady incompressible flow simulations of the 3DH1D type, i.e. 2d spectral elements combined with Fourier expansion along one homogeneous direction. The problem I am encountering is interpolation of the resulting field data. I used the nektar++ example file for incompressible Navier Stokes solver ChanFlow_3DH1D_Flowrate_MVM.xml and ran the field interpolation as follows: FieldConvert -m interpfield:fromxml=ChanFlow_3DH1D_Flowrate_MVM.xml:fromfld=ChanFlow_3DH1D_Flowrate_MVM_1.chk \ rect2d.xml interp.chk where rect2d is the file containing the mesh information (Geometry and Expansion) only, the same information copy-pasted from the session .xml file used as input.( When I used the entire session file, same as input file, the module would immediately crash due to segmentation fault.) I received the following error message after the execution of the above: Fatal : Level 0 assertion violation Failed to type cast m_exp[0] terminate called after throwing an instance of 'Nektar::ErrorUtil::NekError' what(): Level 0 assertion violation Failed to type cast m_exp[0] Aborted (core dumped) I have checked the resulting field data specified in ChanFlow_3DH1D_Flowrate_MVM_1.chk , after converting it to .vtu, and it looks to be without obvious faults. I have also had no problems so far interpolating from 2D or 3D cases to the same geometry. Could this be a specific issue about interpolation for the 3DH1D case, or was there an error in the session file or my command execution? I would really appreciate if you could elucidate this matter for me. Best regards, Cheng-Nian Xiao