Optomechanics – Unified Approach to Thermal Structural Optical Analysis

Colleagues:

Optics is a crazy industry.  We’re so dedicated to the digital computer that we often overlook underlying realities.  That’s especially true in the mechanical engineering art of heat transfer.  Management structures have insisted on each discipline using its own software which has Balkanized the disciplines of structures and heat transfer: i.e., the temperatures must be analyzed in a finite difference (FD) code and the results imported to a finite element (FE) code.  The importation involves extensive extrapolation and interpolation of the FD data to the much larger (often by two or three orders of magnitude) of the FE data-set and it can lead to some peculiar results.

AEH has long preferred a more Unified approach:  Select a code that can do them both, usually an FE code, and use engineering judgement to adapt the other discipline (usually a few boundary temperatures).  It usually requires several runs of the problem to assure that the underlying assumptions of the adaptation were appropriate but they go much faster than the Balkanized approach (and, often, more accurately for the optics behavior).

It’s the thermal-structural-optical method I used on the LACE Ultra-Violet Plume Instrument, which made Aviation Week’s75th Anniversary Issue.  Check out the UV plume image from AW’s cover, above!

More recently, a colleague was directed to thermally analyze an optical system in CFD and I was to apply his temperatures and gradients to calculate the boresight errors among the optical instruments.  Well, what he was handing me made no sense at all.  So, I added heat transfer terms to my opto-structural FE model and ran the operational transient of concern to the project.  The thermo-structural-optical results were spot-on.

There are a lot of ways that an engineer needs to keep his tools sharp.  And they require maintaining confidence in the analytical methods as well.

More later.  Happy Holloween!!!!!

Al H.
10-23-17

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