[jjddllxx]

Hi guys!

We are trying to simulate the synovial fluid inside the synovial cavity of the human knee. Attached you can find all files from constant, system, and geometry file.

Geometry and mesh seem to work fine, the problem comes when doing the simulation. We are simulating the passage of a person (walking) and how the fluid moves inside the cavity, so we have added velocities to the outer patches of the cavity: left, movingWall, farFieldWall, and right. fixedWall cells should be fixed.

We would expect to have high pressure when the cavity is compressed, that means the foot is in contact with the ground, and low P when food not in contact with the floor. We are not seeing this results after the simulation.
We have observed that even if the fixedWall (bottom part of cavity) is set as uniformFixedValue constant 0 (no movement), in paraView I see the cavity is moving down. Ideal would be to consider it as a closed cavity, where the fluid remains inside and therefore, when there is compression of the cavity due to the bone pressure, the pressure inside the cavity should considerably rise. We are not observing this high pressure, and probably it is because the cavity is moving down and expanding, which is not the real case.

Do you know why this may happen? Why is the cavity moving down if we set fixedWall as 0 velocity. I have also tried to set a little positive velocity in these patches (to move up) but still moving down. Is our system not sufficiently defined?
This is an incompressible fluid simulation, and we are using PIMPLE algorithm.

We are simulating 1/4 of the knee joint (doing an approximation), simulating the right upper side of the frontal (coronal) plane or femoral condyle section, that is why we are setting symmetry in left and fixedWall patches as boundary condition.

Any hints will be super appreciate it, and if you need more info, just ask for it!

Thanks a lot in advance!

Judit
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(juditllop2699@gmail.com)