Incorporation of air bearings into FEA model

dendavis

What is the best way to incorporate the effect of air bearings between two surfaces? If the stiffness and damping of an individual air bearing is given, how can this information be used in establishing an interface between the two surfaces enclosing the air bearing?

Victor

Do you really need to model both surfaces or can one be ground? If you only need one then elastic support might be OK for the stiffness. It's springs normal to the surface. If you need both surfaces then you might have to put individual line2 spring elements between them.

For damping between two surfaces:

• Damper element (Material properties -> Mechanical -> Damper). You would need matching nodes on both surfaces and join them with these line2 elements.
  
• *CONTACT DAMPING with CCX is damping between surfaces in the normal direction. See the CCX manual for details and enter the cards in CCX -> custom model definition.
  

An outside possibility is using a solid material for the air and giving it orthotropic properties so it's very soft in shear and uses Rayleigh damping for the damping. Per-element Rayleigh damping only works with the internal solver.

The spring or damper element options would only work for linear analysis because with large rotations, they'll start to apply rotational forces instead of purely normal.