Fluid structure interaction and damping ratio

Hello,

My model is a vascular cantilever beam (the first mode is pictured below). I work simultaneously on COMSOL and on my experiments. The channel is to be filled with a silicone fluid which will increase the damping of the structure (confirmed by experiments).

Note that I can perfectly model the beam with an empty channel on COMSOL, the results for damping and natural frequencies are identical to the experiments (I use the frequency domain analysis while applying a force at the tip of the beam). However, I still try to make the fluid structure interaction working (ie: adding the silicone fluid in the channel):

- I tried different approaches to model the silicone in the Solid Mechanics module: bulk + shear modulus, added mass + shear force, Young's Modulus + Poisson's ratio... Without good results.

- The "Fluid structure interaction" module in COMSOL looks perfect for this model, the inputs are the viscosity and the density of the fluid, no need to estimate bulk, shear modulus, etc... But I cannot make the simulation running since 1) there is no obstacle in the fluid flow -> error message and 2) frequency study is not available in FSI.

Thanks,
Matthias