Also to All:
Nonlinearity (better called mechanical complexity) is what ultimatel=
y limits, at low frequencies, the performance of every seismograph; but it =
is not the kind of nonlinearity that feedback overcomes in remarkable fashi=
on, as is commonly well known. The kind that is not accommodated is relat=
ed to the very reason materials creep-because of defect structures. At the=
mesoscopic level, these defect structures cause the potential energy well =
to be other than smooth. In other words, the force required to accomplish =
feedback (standard electrical engineering) is not able, at very low levels,=
to operate on an error signal that is consistent with simple-minded theore=
tical expectations. As one of my astute students years ago said, "physics=
is easy if you don't dig too deep".
If the force feedback approach were as perfect as some want to belie=
ve, then there would have been no reason to hold the IRIS sponsored "broadb=
and conference" several years ago, which I attended. A poster session tha=
t I presented at that conference is online at http://www.iris.edu/stations/=
seisWorkshop04/PDF/tahoeI1.pdf
Anyone with practical experience in materials science (well versed in =
the foundations of the discipline) will recognize that internal friction of=
the spring in a seismometer has got to have consequences. One of the firs=
t occasions for the reality of this fact to be noted was when Gunar Strecke=
isen measured the damping as a function of period of a vertical instrument =
operating with a LaCoste zero-length spring. What he found as a grad stude=
nt doing this experiment (as I was told by Erhard Wielandt, the world's bes=
t known expert concerning force feedback instruments) - was that the qualit=
y factor was not proportional to the frequency as required by a viscous dam=
ped simple harmonic oscillator theory. Rather it was measured to be quadra=
tic in the frequency, which is described by the nonlinear damping theory th=
at I developed years ago. If you want to Google 'nonlinear damping' and al=
so 'linear damping' (without the tick marks of a literal search) you will s=
ee that I have devoted many years of intense research to this subject. It =
is indeed complex, to the point of bewildering. But it is high time that s=
ome capable people begin to look at whether my claims have merit or not. S=
ome reputable individuals have slowly come around to thinking I'm not quite=
as crazy as they once thought.
If you Google "optical seismograph ucsd", you will find a paper conce=
rned with a latest generation (bonafide) instrument that is not of force fe=
edback type. The author list includes Prof. Wielandt. Much of the work pr=
esented in that paper was performed by PhD student Otero. I encourage folk=
s to take a look at this article, since it describes an instrument that cou=
ld once and for all settle the debate that has come now to Larry Cochrane's=
list-serve.
By the way, five years ago Dr. Wielandt wrote a paper that you might al=
so want to look at; it is online at
http://www.docstoc.com/docs/48159410/Hysteresis-Creep-Internal-Friction-and=
-Damping-of-mechanical--dislocation
and is titled "Are hysteresis, creep, and damping of mechanical oscillators=
consequences of the same mechanism of internal friction"
If you have trouble with the link I pasted here, just Google 'damping c=
reep Wielandt'. He quotes me in this article, and it has been in place for=
the last five years. His thinking at the time was not 'settled', but my g=
uess is that this 'preliminary' manuscript would have by now vanished from =
the web if he had changed his mind about it.
Randall
Also to All:
Nonlinearity=
(better called mechanical complexity) is what ultimately limits, at =
low frequencies, the performance of every seismograph; but it is not the ki=
nd of nonlinearity that feedback overcomes in remarkable fashion, as is com=
monly well known. The kind that is not accommodated is related =
to the very reason materials creep—because of defect structures. =
; At the mesoscopic level, these defect structures cause the potential ener=
gy well to be other than smooth. In other words, the force required t=
o accomplish feedback (standard electrical engineering) is not able, at ver=
y low levels, to operate on an error signal that is consistent with simple-=
minded theoretical expectations. As one of my astute students y=
ears ago said, “physics is easy if you don’t dig too deep”=
;.
=
If the force feedback approach were as perfect as some wa=
nt to believe, then there would have been no reason to hold the IRIS sponso=
red “broadband conference” several years ago, which I attended.=
A poster session that I presented at that conference is online=
at http://www.iris.edu/stations/seisWorkshop04/PDF/tahoeI1.pdf
Anyone with practical exp=
erience in materials science (well versed in the foundations of the discipl=
ine) will recognize that internal friction of the spring in a seismometer h=
as got to have consequences. One of the first occasions for the reali=
ty of this fact to be noted was when Gunar Streckeisen measured the damping=
as a function of period of a vertical instrument operating with a LaCoste =
zero-length spring. What he found as a grad student doing this experi=
ment (as I was told by Erhard Wielandt, the world’s best known expert=
concerning force feedback instruments) – was that the quality factor=
was not proportional to the frequency as required by a viscous damped simp=
le harmonic oscillator theory. Rather it was measured to be quadratic=
in the frequency, which is described by the nonlinear damping theory that =
I developed years ago. If you want to Google ‘nonlinear damping=
’ and also ‘linear damping’ (without the tick marks of a =
literal search) you will see that I have devoted many years of intense rese=
arch to this subject. It is indeed complex, to the point of bewilderi=
ng. But it is high time that some capable people begin to look at whe=
ther my claims have merit or not. Some reputable individuals have slo=
wly come around to thinking I’m not quite as crazy as they once thoug=
ht.
=
; If you Google “optical seismograph ucsd”, you will find =
a paper concerned with a latest generation (bonafide) instrument that is no=
t of force feedback type. The author list includes Prof. Wielandt.&nb=
sp; Much of the work presented in that paper was performed by PhD student O=
tero. I encourage folks to take a look at this article, since it desc=
ribes an instrument that could once and for all settle the debate that has =
come now to Larry Cochrane’s list-serve.
<=
p class=3DMsoNormal> By the way, five years ago Dr. =
Wielandt wrote a paper that you might also want to look at; it is online at=
and is titled “Are hysteresis, creep, and damping of mechani=
cal oscillators consequences of the same mechanism of internal frictionR=
21;
If you have troub=
le with the link I pasted here, just Google ‘damping creep Wielandt&#=
8217;. He quotes me in this article, and it has been in place for the=
last five years. His thinking at the time was not ‘settledR=
17;, but my guess is that this ‘preliminary’ manuscript would h=
ave by now vanished from the web if he had changed his mind about it.<=
/o:p>
Randall
=