Question on Jellyfish Self-Propulsion Simulation

[LIMING CHAO]

Dear all, 

I hope you are doing well.

I am currently working on a two-dimensional jellyfish self-propulsion simulation using the IBFE-based swimming framework in IBAMR. 

However, I have encountered an issue in my simulations: vortices appear to enter the interior region of the jellyfish body even the gravity has been added (as shown in the attached figure), and the jellyfish does not generate forward propulsion or net swimming motion. 

In addition, I have noticed that in some cases the jellyfish body becomes slightly asymmetric during the motion, even though the imposed kinematics are fully symmetric. I suspect that this asymmetry may be caused by the internal vortices and the resulting unbalanced fluid forces.  

I am wondering whether this behavior could be related to:

• the immersed boundary configuration or mesh setup,

• the treatment of gravity or buoyancy forces,

• or boundary conditions that may allow vortex penetration into the body interior.

I would greatly appreciate any suggestions or insights from the community on how to prevent vortices from entering the body and achieve stable forward swimming.

I have attached my simulation code and input files for reference.

Thank you very much for your time and help.

Best,

Li-Ming