Issue with convective ouflow BC
******************* 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. ******************* Hello everyone, I tried running an Adjoint Stability Analysis including Dongs convective outflow BC enforced through a Robin type specification as detailed in the user guide. I use a 2.5D expansion with version 5.7.0 and obtain satisfactory results with a high-order pressure BC. However, as I switch to a Robin BC, the following error appears: double free or corruption (!prev) ...indicating segmentation violation. I've attached some files of a MRE, which is basically just a cylinder at Re = 42. Is there anything wrong with my setup? Any help would be much appreciated. Best, Alex Gesendet mit [Proton Mail](https://proton.me/mail/home): Ein sicherer E-Mail-Dienst.
Hi Alex, I have not had a chance to look closely at this but possibly the issue is that these advanced BCs are only currently set up for non-linear problems. They rely on the total velocity dictating if the flow is inward or outwards but it may be that the stability codes are taking the linearised quantity rather quickly and than the base flow to evaluate this. Best, Spencer Sent from my iPhone On 6 Oct 2025, at 19:38, Alexander Schukmann <alexander.schukmann@protonmail.com> wrote: This email from alexander.schukmann@protonmail.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. Hello everyone, I tried running an Adjoint Stability Analysis including Dongs convective outflow BC enforced through a Robin type specification as detailed in the user guide. I use a 2.5D expansion with version 5.7.0 and obtain satisfactory results with a high-order pressure BC. However, as I switch to a Robin BC, the following error appears: double free or corruption (!prev) ...indicating segmentation violation. I've attached some files of a MRE, which is basically just a cylinder at Re = 42. Is there anything wrong with my setup? Any help would be much appreciated. Best, Alex Gesendet mit Proton Mail<https://proton.me/mail/home>: Ein sicherer E-Mail-Dienst. <session.txt> <mesh.txt> <base.txt> _______________________________________________ Nektar-users mailing list Nektar-users@imperial.ac.uk https://mailman.ic.ac.uk/mailman/listinfo/nektar-users
Hello Spencer, thank you for your quick reply. I obtained good results for the direct stability analysis with the following high-order outflow BC: <N VAR="u" VALUE="0.0" USERDEFINEDTYPE="HOutflow" /> <N VAR="v" VALUE="0.0" USERDEFINEDTYPE="HOutflow" /> <N VAR="w" VALUE="0.0" USERDEFINEDTYPE="HOutflow" /> <D VAR="p" VALUE="0.0" USERDEFINEDTYPE="HOutflow" /> However, for the adjoint operator, weird artifacts emerge at the outlet, indicating onsetting instability. For this reason I tried the Robin-type BC and failed. As I wrote before, using the following pressure BC, the adjoint results look reasonable: <D VAR="u" VALUE="0" /> <D VAR="v" VALUE="0" /> <D VAR="w" VALUE="0" /> <N VAR="p" VALUE="0" USERDEFINEDTYPE="H" /> Best, Alex Gesendet mit [Proton Mail](https://proton.me/mail/home): Ein sicherer E-Mail-Dienst. Sherwin, Spencer J <s.sherwin@imperial.ac.uk> schrieb am Dienstag, 7. Oktober 2025 um 8:35 nachm.:
Hi Alex,
I have not had a chance to look closely at this but possibly the issue is that these advanced BCs are only currently set up for non-linear problems. They rely on the total velocity dictating if the flow is inward or outwards but it may be that the stability codes are taking the linearised quantity rather quickly and than the base flow to evaluate this.
Best, Spencer
Sent from my iPhone
On 6 Oct 2025, at 19:38, Alexander Schukmann <alexander.schukmann@protonmail.com> wrote:
This email from alexander.schukmann@protonmail.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.
Hello everyone,
I tried running an Adjoint Stability Analysis including Dongs convective outflow BC enforced through a Robin type specification as detailed in the user guide. I use a 2.5D expansion with version 5.7.0 and obtain satisfactory results with a high-order pressure BC. However, as I switch to a Robin BC, the following error appears:
double free or corruption (!prev)
...indicating segmentation violation.
I've attached some files of a MRE, which is basically just a cylinder at Re = 42. Is there anything wrong with my setup? Any help would be much appreciated.
Best, Alex
Gesendet mit [Proton Mail](https://proton.me/mail/home): Ein sicherer E-Mail-Dienst. <session.txt> <mesh.txt> <base.txt> _______________________________________________ Nektar-users mailing list Nektar-users@imperial.ac.uk https://mailman.ic.ac.uk/mailman/listinfo/nektar-users
Hi Alex, These boundary conditions <D VAR="u" VALUE="0" /> <D VAR="v" VALUE="0" /> <D VAR="w" VALUE="0" /> <N VAR="p" VALUE="0" USERDEFINEDTYPE="H" /> Do not use much additional information (only for the pressure) and so are valid for both non-linear and linear simulations. The other type of boundary conditions require an evaluation of U.n on the outflow to decide if the flow is going inwards or outwards. I believe in the linearised case it may be using u’.n in the code which is likely wrong. We need to have a look at the formulation of these outflow condition first the linearised problem and update the code. Probably we should have a warning in this code if the flow is linearised! If you want to have a look at the formulation I can help getting the code updated. All the best, Spencer Sent from my iPhone On 7 Oct 2025, at 18:49, Alexander Schukmann <alexander.schukmann@protonmail.com> wrote: Hello Spencer, thank you for your quick reply. I obtained good results for the direct stability analysis with the following high-order outflow BC: <N VAR="u" VALUE="0.0" USERDEFINEDTYPE="HOutflow" /> <N VAR="v" VALUE="0.0" USERDEFINEDTYPE="HOutflow" /> <N VAR="w" VALUE="0.0" USERDEFINEDTYPE="HOutflow" /> <D VAR="p" VALUE="0.0" USERDEFINEDTYPE="HOutflow" /> However, for the adjoint operator, weird artifacts emerge at the outlet, indicating onsetting instability. For this reason I tried the Robin-type BC and failed. As I wrote before, using the following pressure BC, the adjoint results look reasonable: <D VAR="u" VALUE="0" /> <D VAR="v" VALUE="0" /> <D VAR="w" VALUE="0" /> <N VAR="p" VALUE="0" USERDEFINEDTYPE="H" /> Best, Alex Gesendet mit Proton Mail<https://proton.me/mail/home>: Ein sicherer E-Mail-Dienst. Sherwin, Spencer J <s.sherwin@imperial.ac.uk> schrieb am Dienstag, 7. Oktober 2025 um 8:35 nachm.: Hi Alex, I have not had a chance to look closely at this but possibly the issue is that these advanced BCs are only currently set up for non-linear problems. They rely on the total velocity dictating if the flow is inward or outwards but it may be that the stability codes are taking the linearised quantity rather quickly and than the base flow to evaluate this. Best, Spencer Sent from my iPhone On 6 Oct 2025, at 19:38, Alexander Schukmann <alexander.schukmann@protonmail.com> wrote: This email from alexander.schukmann@protonmail.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. Hello everyone, I tried running an Adjoint Stability Analysis including Dongs convective outflow BC enforced through a Robin type specification as detailed in the user guide. I use a 2.5D expansion with version 5.7.0 and obtain satisfactory results with a high-order pressure BC. However, as I switch to a Robin BC, the following error appears: double free or corruption (!prev) ...indicating segmentation violation. I've attached some files of a MRE, which is basically just a cylinder at Re = 42. Is there anything wrong with my setup? Any help would be much appreciated. Best, Alex Gesendet mit Proton Mail<https://proton.me/mail/home>: Ein sicherer E-Mail-Dienst. <session.txt> <mesh.txt> <base.txt> _______________________________________________ Nektar-users mailing list Nektar-users@imperial.ac.uk https://mailman.ic.ac.uk/mailman/listinfo/nektar-users
participants (2)
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Alexander Schukmann
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Sherwin, Spencer J