Re: The Tuned-Mass Damper

["Paul Camp" <pjcamp@coastal.edu>]

Seems to me this is the same as the "antiroll tank" problem in 
Walker's Flying Circus book. The oscillation of the building would be 
90 degrees out of phase with the external oscillations and the 
oscillation of the mass damper would be 90 degrees out of phase with 
that, giving a damper 180 degrees out of phase with the external 
oscillations.

> At 16:11 11/17/97 -0500, Gene Mosca wrote:
> > Hi All,
> >
> > The tuned-mass damper is used to dampen oscillations in tall building.  A
> > large concrete block (400 tons) slides "floating" on a layer of oil. 
> ...
> > What I don't understand is the 180 degree phase angle.  It seems to me
> > that at resonance the driving force and the displacement of the
> > oscillating mass are 90 degrees out of phase, and if the driving force is
> > provided by a helical steel spring (not a pneumatic spring--whatever that
> > is) the displacements of the opposite ends of the spring are 90 degrees
> > out of phase.  Am I correct?  If so, do pneumatic springs operate
> > differently so that at resonance the opposite ends are 180 degrees out of
> > phase?
> >
> > Gene

Paul J. Camp                   "The Beauty of the Universe
Assistant Professor of Physics  consists not only of unity
Coastal Carolina University     in variety but also of 
Conway, SC   29528              variety in unity.
pjcamp@coastal.edu                    --Umberto Eco
pjcamp@postoffice.worldnet.att.net    The Name of the Rose
(803)349-2227                         
fax: (803)349-2926