FEA of hydraulic bearing 1

[GSC]

Hello,

I would like to build an FE model to investigate the dynamics of a long shaft which is making axial alternating movement, and bending mostly due to its own weight. The shaft is supported by hydraulic bearings with pressure control. How shall I take these bearings into consideration in the model? Anybody has experience on this?
Is a hydraulic bearing in this case behaves like a spring or more like a damper? I would appreciate your input.

Thanks in advance
GSC

 

[Drej]

In the past I know people that have modelled these bearings using springs, so that might be a good place to start. The springs will provide support for the shaft but I think the damping will come principally from the shaft itself (material damping) due to the connection at the bearing(s), so you may need to include this - Rayleigh (alpha/beta) for example - especially if it's transient dynamic loading. Consider the type of "connection" or interface at the bearing/shaft when you apply the damping, as different connections types will provide different levels of damping. Other than that you can apply symmetry BCs to the shaft where the bearings act, but this would over-stiffen the shaft and might be considered too conservative.

-- drej --

 

[GSC]

Drej> Thank you for your post, I see the point in modelling the bearings as springs and assuming that material damping is present.

Can you please explain to me what do you mean with considering the type of connection when applying the damping? Do you refer here to the bearing type in the real world or to the various numerical models available in the FE?

GSC

 

[Drej]

GSC

For example, in some structural codes (ASCE 4-98 for example), the damping levels for a structure are dependent on whether the connections are bolted, welded or correspond to some type of pinned or other condition &c. For each of these conditions the damping level applied may be different depending on the code used as well. Hence, your bearing may resemble either a "pinned" or other type of connection, which will lead you to an appropriate level of damping for your shaft. Ideally, of course, you would need to carry out modal testing to obtain a more exact value of damping for your system.

Cheers,

-- drej --