PSN-L Email List Message

Subject: Re: fiber optic strainmeters
From: John Hernlund hernlund@............
Date: Thu, 28 Dec 2000 20:05:04 -0800

barry lotz wrote:

> John
>     I had a couple of questions.  I was wondering how the cable would be
> supported ( or not)  ? Would there be friction between the conduit and cable due
> to bends in the cable or gravity?

In a smaller version they are building (without slack loops) they are simply fixing

each end, which is probably the best way.  The small strains they are interested in

looking at will probably produce a very small force per unit length which may be
lower than the static friction force.

> I know in prestressed concrete there are
> pretty sizable losses in tension due to friction, though I realize the magnitude
> of forces are considerable different..

Yes, we used to have problems with hydraulics in our high pressure equipment
due to the friction on the rams.

> I'm not familiar with how the longer
> length cables are suspended or supported. It would seem that even short
> suspended cables would have a  catanary (spelling?) shape which would change
> with distance between supports and thus  the cable might not stretch the same
> amount as the ground moves.

I think it is not suspended at all, but lays in whatever conduit it travels

> I guess could be calibrated and the strains corrected. I am also very interested

> in your progress and findings.

I am not connected with this particular project, and I only know what I know
about this from a dinner conversation I had with this guy at AGU.  I am quite
interested in seeing the data that may potentially come out of these types of
experiments though.  Lately I am working on computer models...mantle
convection, fluid dynamics and elasticity type stuff.


John Hernlund
Department of Earth and Space Sciences
University of California, Los Angeles


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Larry Cochrane <cochrane@..............>