Rigid or Flexible Foundation???? Basic knowlege.

[Monrooy]

Some one , can define the diference between a rigid or flexible foundation acording to table ISO 10816-3 for evaluate severity of vibration.

This selection have relationship with natural frecuency of the rotor?

Thanks,

A.Monroy

 

[Tmoose]

I believe there will be background ISO documents that would have definitions similar to the descriptions in the NEMA MG standards. One of the several, very practical (born of many field "experiences") definitions in NEMA section 7.6 is the MINIMUM static deflection of resilient mounts. Although the attached chart says "springs," not all springs can be counted on to look like coils of wire or rubber sheet

a "rigid" foundation has 3D stiffness sufficient that all rigid-body modes have resonant frequencies well above rotating frequency.

a "flexible" foundation would have RBMRFs well below rotating frequency.

Discussions about the proper meaning of "well below/well above" RF are likely to include numbers ranging from 10%, thru 40% and beyond. I would not participate in those discussions.