Hi Yaguang, If you generate the mesh in GMSH you need to tell it that two boundaries are periodic, peralign is able to detect the periodicity but not to redistribute the nodes to ensure it. Take a look at section 5.3.3 Other Mesh Commands in the GMSH manual and that should tell you how to set a periodic BC. Thanks, Guglielmo ________________________________ From: nektar-users-bounces@imperial.ac.uk <nektar-users-bounces@imperial.ac.uk> on behalf of 谢亚广 <xieyaguang@iet.cn> Sent: 14 April 2024 12:57 To: nektar-users <nektar-users@imperial.ac.uk> Subject: [Nektar-users] Questions about the plane of rotational periodic symmetry This email from xieyaguang@iet.cn 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. Hello Kaloyan Kirilov, I'm not sure how to reply to your messages via email, so I have to start a new discussion each time. I want to start by using GMSH to NEKTAR, and then use the peralign module in Nekmesh to align p1 and p2 for rotational periodicity. To pinpoint the problem, I have simplified the mesh to its most basic test state. However, no matter what I try, I am unable to achieve the aforementioned requirements using NekMesh -m peralign; it always results in errors. Assuming thi .geo file corresponds to a 2D mesh named test.msh, my operations are as follows: NekMesh test.msh test.xml:xml:uncompress NekMesh -m peralign:surf1=5:surf2=6:dir=z:rot=PI/6 test.xml test_p.xml Subsequently, an error occurs: [ProcessPerAlign] WARNING: Could not find matching edge for surface element 3. Skipping periodic alignment. I hope I have made myself clear. Thank you for your assistance. Best regards, Yaguang.