40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  40m Log  Not logged in ELOG logo
Message ID: 3186     Entry time: Fri Jul 9 11:41:58 2010
Author: Gopal 
Type: Summary 
Category: Optic Stacks 
Subject: Top Optic Layer Complete; Mechanical Tests Giving Problems 

For the last week, I have been attempting to determine the mirror stack transfer function which relates mechanical mirror response to a given ground-motion drive. The idea is to model the stacks in COMSOL and ultimately apply mechanical tests for manual calculation.

 

Procuring the correct drawings to base my 3D models off of was no simple task. There are two binders full of a random assortment of drawings, and some of them are associated with the smaller chambers, while others are appropriate for the main chamber, which is what we're interested in right now. For future workers, I suggest checking that your drawings are appropriate for the task at hand with other people before wasting time beginning the painstaking process of CAD design in COMSOL.

 

The drawings that I ultimately decided to use are attached below. They detail four layers of stacks, each which arrange 15, 12, 8, and 5 (going from bottom to top) Viton damping springs in an orderly fashion. The numbers have been chosen to keep the load per spring as constant as possible, in order for all springs to oscillate with as close a resonant frequency to each other as possible.

 

Stack_1_Drawing.JPG   Stack_2_Drawing.JPG

 

 Stack_3_Drawing.JPG    Stack_4_Drawing.JPG

 

 Isolation_Stack.JPG

 

After making some minor simplifications, I have finished modeling the top stack:

 

Stack_4_1.png

 

After triangular meshing, before my many failed attempts at mechanical testing:

 

Stack_4_2.png

 

Both the Viton and steel portions have been given their material properties, and so I should be (theoretically ) ready to perform some eigenfrequency calculations on this simplified system. If my predictions are correct, these eigenfrequencies shouldn’t be too far of the eigenfrequencies of the 4-layer stacked system, because of the layout of the springs. I’ve tried doing mechanical tests on the top stack alone, but there hasn’t been much progress yet on this end, mostly because of some boundary value exceptions that COMSOL keeps throwing at me.

 

In the next couple weeks or so, I plan to extend this model to combine all four layers into one completed stack, along with a simple steel base and mirror platform. I also plan to figure out how to make eigenfrequency and transfer function measurements.

 

Lastly, to anyone who is experienced with COMSOL, I am facing two major roadblocks and could really use your help:

 

1) How to import one model into another, merge models together, or copy and paste the same model over and over.

2) Understanding and debugging run-time errors during mechanical testing.

 

If you have any idea how to attack either of these issues, please talk to me! Thanks!

 

ELOG V3.1.3-