Re: The Tuned-Mass Damper

[brian whatcott <inet@intellisys.net>]

At 00:46 11/19/97 -0500, you wrote:
> brian whatcott wrote:
> > . . .  
> > I was hoping for an illuminating answer to this interesting physical
> >  question of considerable practical importance.
> > . . .
>
> OK, I'll give it a shot.  If one hangs a mass from a spring and then
> drives the UPPER end of the spring into oscillation with a sinusoidal
> driving force (this is Leigh's example system in an MET post, but with a
> sinusoidal driver), this same force is transmitted to the mass  by the
> (massless, frictionless) spring.  Now the mass' acceleration will also
> be in phase with this force and the mass' displacement is always 180
> degrees away from its acceleration, resonance or no!
>
> Hope this is useful,
> -Bob
> -- 
>
>
> Bob Sciamanda	

We now have the clear cut scientific prediction
on our modest scale.
 The experiment which can test this prediction
can be set up with 9 light-duty elastic bands of 
unstretched length 8cm each, and two masses of 150gm and 40 gm.

We model the building dynamics with 2 elestic bands supporting
the 140 gm weight.
 This in turn supports the modeled damper, consisting of
 7 elestic bands hooked together, and holding a 40 gm weight.

If we provide a displacement/release of the building mass (140gm)
we see it is not in tune with the damper.
 We expediently reduce the effective length of the top bands
to increase the 'building' resonant frequency until it matches the damper's
frequency.

We see that the phase of the relative distance between the two masses
appears to vary as we tune the arrangement.
 We note that the maximal displacement of the 'building' mass decays
in different ways with varied tuning.

This might possibly be worth a videotape analysis.

Sincerely,

brian whatcott <inet@intellisys.net>
Altus OK