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

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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 

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On 6 Oct 2025, at 19:38, Alexander Schukmann <alexander.schukmann@protonmail.com> wrote:



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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


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<session.txt>
<mesh.txt>
<base.txt>
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