Hi Shuaifeng, Sorry for a slow response to your question. As I recall the ordinate is arbitrary and is converted from your input mesh internally to an x-aligned coordinate (1D coordinate) of similar length. So this can help with post-processing a more realistic geometry. Blood flow can become negative at different points in the pulsatile cycle as is observed by Womersley flow and likely this is due to reflection in your model. I would not expect the mean flow to necessarily become negative however so it could also be due to your mesh setup. Best, Spencer. From: nektar-users-bounces@imperial.ac.uk <nektar-users-bounces@imperial.ac.uk> on behalf of 有人即有江湖 <shuaifengshi20@gmail.com> Date: Wednesday, 10 January 2024 at 00:42 To: nektar-users <nektar-users@imperial.ac.uk> Subject: [Nektar-users] PulseWaveSolver This email from shuaifengshi20@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. Dear all， Happy new year！I'm sorry to bother you. I am a new user of nektar++, I'm currently implementing 1D blood flow simulation based on nektar++. I have two questions now. I have some questions about the setting of the ordinate in the geometric parameters of blood vessels in the xml file. The abscissa in the geometric parameters of blood vessels is obviously related to the length of blood vessels. But is the ordinate in the geometric parameters of blood vessels related to some parameters of blood vessels? Or is the ordinate arbitrary? The second question is that there is always negative blood flow velocity in the running result of the xml file I wrote or the xml sample provided by the official. Is this normal? I can only assume at this point that it's due to wave reflections in the blood flow. Kind regards, Shuaifeng