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Re: [ATM] WAS: RE: ATM Digest, Vol 30, Issue 21; IS: FEA models of test stand induced deflections
Dale:
Ok, great. I will probably need to massage the raw output from ALGOR a bit
to fit one of your desired formats, but I expect that Either Excel or
MathCad can help me with that task. If you have a candidate for a first
experiment that you would like to investigate, just send me the relevant
information describing the situation and I will proceed from there.
Scott Milligan
-----Original Message-----
From: Dale Eason [mailto:atmpob@yahoo.com]
Sent: Saturday, June 17, 2006 11:11 PM
To: Scott Milligan; 'Stephen Koehler'; 'Wolfgang Rohr'
Cc: atm@atmlist.net
Subject: 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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