Discussion Forum

Dear all,

I am working on a bearing with a flexible inner surface.

I have chosen the hydrodynamic bearing module to help me with my research.

However, I don't know how to define the clearance of the bearing.

Since the inner surface of the bearing is flexible, I have to couple the bearing clearance with the deformation of the inner surface.

I used a shell module and a spring foundation to model the flexible inner surface of the bearing.

Therefore, it is only necessary to couple the deformation of the shell to the bearing clearance.

However, according to the COMSOL help file, the clearance is a function of polar coordinates.

Where a is the coordinate of a point on the bearing surface along the bearing axis. phi is the azimuth angle of a point on the bearing surface with respect to the local y direction of the bearing.

I need to find out the relationship between clearance, a and phi as shown in Figure 1. But the result of the deformation of the shell lies in Cartesian coordinates as shown in Figure 2. The figures are in the attachment.

I tried to use the expression

where C is a constant and shell.u is the displacement of the shell. But the variable shell.u is the absolute value of the displacement, and it can't distinguish between inward depression and outward projection.

My question is, how can I make the displacement shell.u distinguish between positive and negative based on the normal direction of the surface? My question seems to be similar to the following case

https://www.comsol.com/forum/thread/320572/Using-a-color-scheme-to-indicate-phase-direction-of-surface-displacement-revisited

However, the case is a flat surface, so it is easy to use the component of displacement instead of displacement, but this does not seem to be easy for cylindrical surfaces.

Or how do I convert the displacement calculations into polar coordinates?

Or can I get the coordinates after deformation? I tried using the material coordinate (X,Y,Z), but it seems to agree with the results of the spatial coordinate (x,y,z).

Thanks very much for your help.