## PSN-L Email List Message

Subject: Re: Dampng anharmonicity and Seismometry
From: ChrisAtUpw@.......
Date: Sat, 9 Feb 2008 22:21:57 EST

In a message dated 09/02/2008, Brett3mr@............. writes:

I  will also assume that the pothole forces are very small compared with the
spring force and just represent small variations from  linearity.

Hi Brett,

This is the trouble. They are NOT small compared to  the restoring force.
To get a really long period, the gradient of the  spring force with
position is nearly flat, but you are still offsetting the full  mass Mg.
Consequently the deflection produced by a small  step change in the
spring properties can produce a large mass  movement.
Note that noise is assumed to have a mean level of  zero. The effects we
have to cope with are discreet steps in the zero  level.

Regards,

Chris Chapman

In a message dated 09/02/2008, Brett3mr@............. writes:
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>  I=20 will also assume that the pothole forces are very small compared with the=20 spring force and just represent small variations from=20 linearity.
Hi Brett,

This is the trouble. They are NOT small compare= d to=20 the restoring force.
To get a really long period, the gradient of th= e=20 spring force with position is nearly flat, but you are still offsetting the=20= full=20 mass Mg.
Consequently the deflection produced by a small= =20 step change in the spring properties can produce a large mass=20 movement.
Note that noise is assumed to have a mean level= of=20 zero. The effects we have to cope with are discreet steps in the zero=20 level.

Regards,

Chris Chapman