Hi Manmohan, This error occurs because the simulation diverges. There are many reasons, such as too large time step, insufficent resolution in some region. You can try to reduced the TimeStep and check if the NAN error is postponed. You can also output the checkpoint before this error occurs to see which region diverges first. In addition, <I PROPERTY="SpectralVanishingViscositySpectralHP" VALUE="DGKernel" /> can be used to stablize to simulation. Cheers Ankang ________________________________ From: gaoak@pku.edu.cn <gaoak@pku.edu.cn> on behalf of Manmohan Labh <labhmanmohan25@gmail.com> Sent: 28 March 2020 09:17 To: nektar-users <nektar-users@imperial.ac.uk> Subject: [Nektar-users] Help - Error in running base condition for a square cylinder This email from labhmanmohan25@gmail.com 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 Nektar++ users, My name is Manmohan Labh. I am a Mechanical Engineering Under graduate form Indian Institute of Technology ( Indian School of Mines ) Dhanbad. I am trying to learn Nektar++ for my research on VIV in fluids. I tried running a simulation of flow past a stationary square cylinder, but i am facing difficulty in it. Please help me. I have attached all the generated files in this mail. Error - Fatal level 0 assertion violation NAN found during tìme integration. Regards, Manmohan Labh