Why am I getting a warning message in ANSYS 8.1 about negative Beta damping
from the fluid136 (squeeze film) element?

You can safely ignore that message. The ABEXTRACT command used with the
fluid136 element calculates alpha and beta damping values that will give the
percent of critical damping calculated for the two input modes
(see section 5.10.3 of the Structural Analysis Guide.) This calculation frequently
produces a negative beta damping value, which means the damping is decreasing
very rapidly from the first frequency to the second which is typical of squeeze
film damping.

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