Keyur Kanade
Ansys Employee
Duplicate of n

Hi all,For my PhD project, I'm working on fluid-structure interaction (FSI) models of abdominal aortic aneurysms (AAA) using Ansys Mechanical APDL, Fluent and System Coupling (version 2020R1). I've been able to simulate quite a few FSI models, but I'm facing problems with a subset of models. The flow and pressure at the inlet and outlet of the model are written to a text file. If I plot the flow for a successful model, I get something that looks like this:Flow - successful modelhttps://us.v-cdn.net/6032193/uploads/QXRUW6SACZ96/flow.jpgAnd the pressure (outlet pressure calculated using a 3-element Windkessel model) looks like this:Pressure - successful modelhttps://us.v-cdn.net/6032193/uploads/25QAAGJM5HEZ/pressure.jpgHowever, If I plot the flow and pressure for a unsuccessful model, I get:Flow - unsuccessful modelhttps://us.v-cdn.net/6032193/uploads/ISO966OCOI1T/flow.jpgAt time = 1.735 s, a high increase in outlet flow can be seen.Pressure - unsuccessful modelhttps://us.v-cdn.net/6032193/uploads/IVSSF2ZML9T5/pressure.jpghttps://us.v-cdn.net/6032193/uploads/25R2UTF4XXKL/image.pngZooming in at the pressure around t = 1.735 s, a sharp increase in inlet pressure can be seen. The outlet pressure (prescribed using the Windkessel model) doesn't show any abnormalities in this step. Therefore, I think the prescribed pressure at the outlet at t = 1.735 s is correct. However, I don't understand why the outlet flow is suddenly increased in this timestep. Due to this sudden flow increase, the pressure is altered as well, causing a weird pressure profile. In this model, the simulation still finished, but in two other models, a similar sudden jump in flow is observed and the simulation crashes later on (after 0.5 or even 1.5 cycles). If I look at the velocity vectors, streamlines, pressure, WSS and displacements of the last cardiac cycle (starting at 1.6 s), I don't see any abnormalities until the sudden jump in flow. I've included the videos of the velocity vectors and streamlines.https://us.v-cdn.net/6032193/uploads/6ETBX8R4OBX8/velocity.mp4https://us.v-cdn.net/6032193/uploads/28QNYVF7GJIL/streamlines.mp4I know it's a long shot, but I was hoping one of you could help me find the problem (and hopefully, I can find a solution). Is there anyone who can point me towards the correct direction?Thanks in advance!Best regards,Judithhttps://forum.ansys.com/discussion/25217/fluid-structure-interaction-problem-sudden-jump-in-pressure-flow