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Re: [ATM] PLOP and triangles
The underlying problem with plop's thin plate model and point supports is that plop incorporates shear. At a point load the shear stress is infinite, so a sharp peak appears over the support. However, this peak covers a small area, so RMS optimization does not weigh it heavily.
Perhaps there is a way to replace those point supports with small pads of non-zero area and finite pressure, and thereby get rid of the singularity.
At one time I was doing this in MSC Nastran, but that product does not support optimization the plop does. I think that for all but the most elite bozillionaires of us, plop is, for now, the best we have.
Looing forward, if anybody wants to do it, it would be nice to have...
(1) Pads instead of points
(2) A spherical shell model instead of a thin flat plate
(3) Full three dimensional force modeling (to calculate distortion from sling and potatoe chip deformation).
I don't think this will happen in my lifetime.
Those who do not like plop are free to use CELL.EXE and clamp their mirror clips real tight.
. . . Richard
-----Original Message-----
From: Michael Lindner <mikell@optonline.net>
Sent: Sep 9, 2004 4:08 PM
To: Jay Kirkland <jaykirk2@compusmart.ab.ca>, atm@atmlist.net
Subject: Re: [ATM] PLOP and triangles
On Thursday 09 September 2004 10:16 am, Jay Kirkland wrote:
> I've read from various posts that for PLOP designed mirror cells to work,
> even a millimeter or two of inaccuracy during construction will have a
> major impact on cell performance.
Don't believe everything you read.
> (This despite the fact...
Case in point...
> So is there a way of running PLOP using real-world
> points/pads/acorn-washer diameters instead of mathematical points?
No, but if you want to, feel free to write such a program - it will be a lot
of work, but will no doubt be well received. I believe one list member did an
exhausting [sic] analysis of several Plop designed cells with non-zero
diameter pads, and concluded that the performance difference was minimal. If
that person is out there, please speak up.
Clear skies.
--
Michael Lindner
http://www.starastronomy.org *** http://home.att.net/~mikel
http://www.atmsite.org *** http://www.atmlist.net
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