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Re: [ATM] WAS: RE: ATM Digest, Vol 30, Issue 21; IS: FEA models of test stand induced deflections
Scott,
I can give you several options.
If you can output the data as the a retangular array
with the mirrror just touching the sides I can import
it into OpenFringe and display it and compute Zernike
constants for it.
Exact format should be one number per line. The first
two numbers are the row and column counts. Numbers
should be in ascii.
For example
100
100
1.2
2.2
Would be the first two numbers of row 1 of a 100 x 100
array.
It would help if the numbers were in wavelengths but
the need not be. You can choose whatever metric you
want for them and I can accomodate.
If instead you can only ouput x,y,z version of the
data inside the mirror, I can work with that as well.
Dale Eason
--- Scott Milligan <starzkey@charter.net> wrote:
> Folks:
>
> I own a licensed copy of the ALGOR FEA program, and
> have learned just enough
> about using it to generate useful models of mirror
> self-weight deflection
> under various support schemes. I would be willing
> to run a few test cases
> to see if these models help corroborate what has
> been observed on the test
> stand.
>
> The ALGOR model will give the surface displacement
> values at the nodes of
> the mesh; to make these results truly useful,
> however, I suspect one wants
> to fit these data to a reasonable set of Zernike
> polynomials, and do the
> usual subtraction of piston, tilt, & defocus before
> reaching conclusions
> regarding the suitability of a given mounting
> scheme. I haven't myself
> gotten around to writing such a routine (I'm sure
> that MathCad, R, or
> similar package could do it), but that is also an
> area where others in this
> group are strong.
>
> If a routine that resamples the (typically)
> irregular spacing of the FEA
> nodes onto a regular grid were to become available,
> then the raw
> displacement data can be input to a Zemax model, and
> the usual suite of
> image quality analyses then become available. Zemax
> can also accept Zernike
> input, but resampling the raw data to a uniform grid
> should, I expect,
> improve the accuracy of the Zernike fit as well.
>
> If we go forward with this, what I would need to
> construct successful FEA
> models would be something like the following:
>
> 1. Mirror substrate material (Pyrex, Silica, etc.)
> 2. Diameter, ROC, and thickness.
> 3. Support scheme description (i.e. 2 pegs @ 90
> degrees, stud through a
> central perforation, Sling, etc).
> 4. An initial assumption describing how the support
> structure actually
> establishes contact (i.e. single point in COG plane,
> line contact, etc.)
> 5. Orientation of gravity vector wrt to surface
> normal at mirror vertex.
> 6. If gravity vector is oriented other than
> orthogonal to surface normal,
> then some description of the backside support is
> necessary as well (i.e. #
> of support points and their locations).
>
> Models with simple geometry (i.e. revolved solids)
> are considerably less
> time consuming to set up and debug than are models
> containing intricate
> features such as lightweighting ribs, socket
> inserts, etc. So I suggest we
> start with something simple. An early lesson
> learned about FEA is that
> simple, "known" cases provide a necessary sanity
> check on the assumptions
> used to create the model.
>
> I have successfully executed several models using
> peg mount and center
> support mounts, with what I feel is good qualitative
> agreement to my own
> interferometric results, but have not yet tried to
> model anything like a
> sling. So if rapid progress counts for anything, I
> suggest not starting
> with a sling mount.
>
> Cheers,
>
>
> Scott Milligan
>
>
>
> -----Original Message-----
> From: atm-bounces@atmlist.net
> [mailto:atm-bounces@atmlist.net] On Behalf Of
> Stephen Koehler
> Sent: Friday, June 16, 2006 5:17 PM
> To: Wolfgang Rohr
> Cc: atm@atmlist.net
> Subject: Re: [ATM] ATM Digest, Vol 30, Issue 21
>
> Wolfgang,
>
> > you can help me:
> > In Germany we had a mirror testing project. 16
> persons were testing
> > one astigmatic mirror and the main problem was the
> support of that
> > astigmatic mirror. The problem is, how we cause
> any kind of
> > astigmatism by the support. You can subtract the
> induced astigmatism
> > if you can calculate the amount of it. And
> therefore we need a program
> > similar like Plop but to calculate the lateral
> pressure on a mirror.
> > Is there anybody who can help?
>
> This seems to directly pertain to my recent post to
> the interferometry
> group, where I describe a new (to me) algorithm for
> separating mirror from
> test stand aberrations from Zernike coefficients
> from the mirror at various
> angles of rotation. My current algorithm works with
> an arbitrary amount of
> rotational data, but can use as few as two
> rotations. The rotation angles
> are arbitrary, although some combinations are not
> very useful (e.g.,
> rotation of 0 degrees or 180 degrees).
>
> I think it would difficult to calculate test stand
> aberrations from
> simulation in a reliable way. It's much better just
> to measure it.
> --
> Steve Koehler
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