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Entry  Tue Jul 27 18:42:57 2010, Gopal, Update, Optic Stacks, Bode Magnitude Plot and Concerns Bode_Mag_MC1_MC3.png
    Reply  Wed Jul 28 01:05:44 2010, rana, Update, SEI, Bode Magnitude Plot and Concerns 
       Reply  Wed Jul 28 12:16:03 2010, Gopal, Update, SEI, Bode Magnitude Plot and Concerns Bode_Disp_MC1_MC3_y.png
Message ID: 3301     Entry time: Tue Jul 27 18:42:57 2010     Reply to this: 3304
Author: Gopal 
Type: Update 
Category: Optic Stacks 
Subject: Bode Magnitude Plot and Concerns 

I completed the frequency domain analysis mentioned previously in the x-direction. Although I ran it from 1-10 Hz, with 0.1-Hz increments, COMSOL was unable to complete the task past 7 Hz because the relative error was beyond the relative tolerance. To solve this issue, I'd have to rerun the simulation with a finer mesh, an unfavorable option because of the already-extensive run times. The Bode magnitude plot from this simulation is attached:



This simulation raises some questions about the feasibility of this method:


1) Do we have the computing power necessary?


I already moved my work from my personal Mac Pro to Kallo (4 GB --> 12 GB RAM difference). Now, instead of crashing the program constantly, I typically wait a half hour for a standard run of the model. Preferably, I could move my work to Megatron or some other workhorse-computer... but I also know that many of the big boys are already being strained as is.


2) Is it possible to take measurements through Matlab?


This way, I could write a script to instruct COMSOL and just run a few tests at a time overnight. Also, I wouldn't have to sit and record measurements manually as I've done here. The benefits of such an improvement warrant further attention. I'll work on this option next.


3) Up until what frequency do we need to model?


As I've shown, normal meshing yields data up to 7 Hz. Is this enough? Do we need more data? Certainly not less, I'm quite sure. We need to keep in mind that as frequency range increases, run times increase exponentially.


4) How do we incorporate gravity into the equation?


Gravity will produce a bit of extra force in the non-restoring direction for off-axis deviations, slightly decreasing the expected frequency. Whether or not this is an important effect is questionable, since the deviations are typically on the order of a micron, which is orders of magnitude smaller than the initial displacement I'm using on the base. I've decided to ignore this complication for now.



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