 Wed Nov 13 23:55:44 2013, Chris Couste, Optics, Analysis, Optical Mount Vibrational Analysis
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Project: Vibrational Analysis of Optical Mounts
Goal: Use COMSOL to run finite element analysis on simplified models of different types of optical mounts available to us, in order to find which
shape/style/material reacts the least to external sound pollution. Once the few best candidates have been identified, develop test to experimentally determine |
Mon Nov 18 15:56:59 2013, Chris Couste, Optics, Analysis, Representative Models 
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The simpler models of the optical mounts are finished, they will be run through the comsol analysis software soon.
see pictures below: |
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Fri Nov 22 21:04:53 2013, Chris Couste, Optics, Analysis, analysis
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| The analysis is making nice eigenmode and stress mode models, but the displacement experiment needs work. Should be fixed by monday. |
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Fri Jan 24 17:26:38 2014, Chris Cousté, Optics, Analysis, Mount Analysis Functional!
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The comsol eigenmode analysis is complete, and the only thing left to do on this part of the project is to run the analysis on a range of different
configurations of optical mounts as well as a range of materials. This compilation will be posted on this elog in the next few weeks, due to the fairly
long runtime of the analysis software. |
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Sun Feb 16 21:10:56 2014, Chris Cousté, Optics, Analysis, Optical Mount data compilation 1: Aluminum
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The time is finally here! this is the highest displacement of each mount in its lowest few eigenfrequencies, using 6061 Aluminum as a material.
pictures will be added in a future log, because I'm going to make them into one file. Other materials will also be tested to see if there is variance in
these findings, but only relevant data will be posted. |
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Thu Apr 17 16:52:09 2014, Evan, General, Characterization, Interpreting logfiles and picking a solver
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Here are two entries by Walter Frei on the Comsol blog that I've found useful.
Solving Linear Static Finite Element Models: Tells you
how to interpret all those numbers that Comsol dumps into its logfiles. |
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Sun Jun 22 23:44:56 2014, Sam Moore, Optics, , Going through Heinert's 'TR noise of cylindrical test masses' paper
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At this point, my are goals are to 1) convert the time-dependent heat equation into stationary, complex form, 2) use the Levin approach to calculate
the TR noise given this stationary PDE, and 3) verify the results in COMSOL
I have looked at the Heinert paper and converted the time-dependent partial differential Heat equation to a stationary, complex one. I |
 Mon Jun 23 11:40:17 2014, Sam Moore, Optics, , Going through Heinert's 'TR noise of cylindrical test masses' paper
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Quote:
At this point, my are goals are to 1) convert the time-dependent heat equation into stationary, complex form, 2) use the Levin approach to |
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Mon Jun 23 16:10:17 2014, Matt A., Optics, , Going through Heinert's 'TR noise of cylindrical test masses' paper
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Quote:
At this point, my are goals are to 1) convert the time-dependent heat equation into stationary, complex form, 2) use the Levin approach |
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Tue Jun 24 14:35:42 2014, Sam Moore, Optics, General, Trying to Verify the Heinert Model
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Tue Jun 24 17:05:24 2014, Sam Moore, Optics, General, Trying to Verify the Heinert Model
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It does appear that the simplified model is only relevant for the simulations. To quote Heinert: "An efficient computation is only possible
for the simple model, as the advanced model would require an element of size more than 106 ." I have run Koji's code that replicates
Heinert's figure 3. I have attached the resulting temperature distribution and noise amplitude curve. In the noise amplitude curve, the red |
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Sat Jun 28 21:59:11 2014, Sam Moore, Optics, General, Difficulty with the COMSOL stationary module; Test Cases
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Here, I describe some test cases to see if COMSOL's solutions are agreeing with some simple analytical solutions. Right now, I have two plots
showing COMSOL's solution and my analytical solution on separate plots. I will be plotting there difference to see if they really match up.
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Sun Jun 29 15:37:18 2014, Sam Moore, Optics, General, Difficulty with the COMSOL stationary module; Test Cases
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Quote:
Here, I describe some test cases to see if COMSOL's solutions are agreeing with some simple analytical solutions. Right now, |
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Sun Jun 29 20:25:44 2014, Koji, Optics, General, Difficulty with the COMSOL stationary module; Test Cases
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What about this example? The result is easier to understand intuitively.
Consider a bar with the length of L.
Let's say there is no body heat applied, but the temperature of the bar at x=L is kept at T=0 |
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Sat Jul 5 13:04:32 2014, Sam Moore, Optics, , Heinert Model TR Noise Verification
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Agreement with Heinert's paper for cylindrical TR noise has now been achieved. Using the stationary state assumption to calculate the temperature
profile, the computation time was reduced compared to the previous time-dependent approach. Here are the plots showing the agreement. I have shown
the plots for a 1D axisymmetric model, in addition to a full 3D model in COMSOL. Both give the same result. |
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Mon Jul 7 19:47:00 2014, Koji, Optics, , Heinert Model TR Noise Verification
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How close are these FEA calculations with the analytical values?
Can you plot residual too? (Put analytical values, 1D, abs(1D - analytical), 3D, and abs(3D - analytical) all together.) |
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Fri Jul 11 10:58:18 2014, not Koji, Optics, , Heinert Model TR Noise Verification
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Quote:
How close are these FEA calculations with the analytical values? |
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Mon Jul 14 19:09:14 2014, Sam Moore, Optics, General, Using Heinert's Solution for Duan's Parameters
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I have plotted Heinert's analytical solution for TR noise using Duan's parameters. Since TO and TE noise can be found by simply rescaling
TR noise, these have been included in the plot as well. The solid curve represents the analytical solution, while the tick marks represent COMSOL's
solution. I have used COMSOL for both a 1D axisymmetric and a 3D model. Since Duan's cylinder has a radius of 125 microns, but a length of |
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Thu Jul 10 16:51:14 2014, Sam Moore, Optics, General, Duan and Heinert Comparison
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(See Plots in attached document)
My plan has been to replicate Duan's numerical thermoconductive (TE + TR) phase noise plot presented in his paper (section V). I am trying |
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Mon Jul 14 19:14:31 2014, Sam Moore, Optics, General, Duan and Heinert Comparison
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Quote:
(See Plots in attached document) |
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Thu Jul 31 20:55:38 2014, Sam Moore, Optics, General, Finding the Right Meshing for the TIR cavity
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In this document, I try to identify I good mesh by comparing the numerical solution from that mesh with my analytical model. Since there
are problems with carrying out the analytical calculation, it is still not entirely clear which mesh should be used.
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Sat Aug 2 00:22:34 2014, Sam Moore, Optics, General, Finding the Right Meshing for the TIR cavity
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Quote:
In this document, I try to identify I good mesh by comparing the numerical solution from that mesh with my analytical model. Since |
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Tue Sep 30 11:30:27 2014, Nic, Dmass, Evan, General, Configuration, Gravity in Comsol
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Here is
a set of slides by Yoichi Aso on how to handle gravity in Comsol. |
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Sat Sep 5 15:04:43 2015, Dennis Coyne, Mechanics, Configuration, summary of FEA modal model to State Space model
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At the 2014 commissioning workshop, I presented
a summary of my efforts in converting finite element modal models into state space models:
https://dcc.ligo.org/LIGO-G1400099 |
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Sat Sep 5 15:17:41 2015, rana, General, Configuration, FEA logs merged
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I moved the only entry from the 'ENG_FEA' log into the COMSOL log and then renamed that logbook as 'FEA' since we don't need
two FEA logs.
Also renamed 'AdhikariLab' log as ATF. |
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Tue Jun 28 15:50:45 2016, Joy Westland, Mechanics, Analysis, A Simple Model of the Modal Analysis of a Cantilever Circular/Cylinder Cross Section in ANSYS tutorial
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Here is a tutorial to implement a simple Modal Analysis of a Cantilever Cylinder
1. Open the ANSYS workbench
2. Drop and drag the "Modal" analysis system into the project schematic |
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Tue Jun 28 16:54:23 2016, Nikhil Mathur, Mechanics, Analysis, Ansys 14.5 Indroductory Tutorial: Modal Frequency Convergence
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| This tutorial will go through how to show frequency convergence for a cylindrical cantilever using Ansys 14.5 and Mathematica. |
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Wed Jun 29 14:14:44 2016, Joy Westland, Mechanics, Analysis, ANSYS Tutorials with Basic Meshing
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Here are a series of tutorials for basic meshing principles from ANSYS Meshing Basics:
ANSYS Meshing Fine Mesh Basic Tutorial 1: https://www.youtube.com/watch?v=sZIX3CJkWBE
ANSYS Meshing Method Basic Tutorial
2: |
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Fri Jul 29 14:33:41 2016, Joy Westland, Mechanics, General, A Tutorial in Importing SolidWorks Files and Applying a Gaussian Force in ANSYS for a LIGO Test Mass
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Here is a tutorial in importing SolidWorks into ANSYS and the steps needed to apply a Gaussian Force to the LIGO test mass that’s imported.
Using SolidWorks:
Download the SolidWorks Zip Folders from the DCC
https://dcc.ligo.org/login/index.shtml?entityID=https%3A%2F%2Fdcc.ligo.org%2Fshibboleth-sp&return=https%3A%2F%2Fdcc.ligo.org%2FShibboleth.sso%2FLogin%3FSAMLDS%3D1%26target%3Dss%253Amem%253A15b6c314d87e3fa8b3768d89cb6b9836fe39c754 |
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Mon Jul 24 15:35:34 2017, Mariia, General, Configuration, Running Comsol to Matlab
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WIth Gautam's help, I have created a user directory in 40 meter Lab and copied Rana's documents (MATLAB coating files) from flash card
into it. After that, from this elog by Rana : COMSOL: remote server w/ matlab
from Fri Dec 4 18:32:02 2015, ran the matlab document BarrelCoating which |
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Mon Jul 24 15:54:26 2017, Koji, General, Configuration, Running Comsol to Matlab
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The number of licenses already used by whom / still remains can be confirmed by running the following command on a comsol-installed linux machine
$ cd /usr/local/comsol51/multiphysics/license/glnxa64
$ ./lmstat -c ../license.dat -a |
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Wed Jul 26 20:14:46 2017, rana, General, Configuration, Running Comsol to Matlab
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| I've just tried this out on my desktop machine using COMSOL 5.1 and its still working. Which COMSOL is installed on optimus at the 40m ? |
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Fri Jul 28 15:48:58 2017, Mariia, General, Configuration, Comsol batch for windows
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Using the written path from elog by ericq: Computer Scripts/Programs, Comsol can
be run from the directory on the distant computer: /cvs/cds/caltech/apps/linux64/comsol51/bin/glnxa64/comsol batch -inputfile Model1.mph -outputfile
Model_solv.mph. To transfer files from Linux to Windows : the command pscp. |
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Mon Jul 31 22:18:57 2017, rana, General, General, using more than 12 cores in matlab
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Since 2014, the limit of 12 workers using the matlab parallel computing toolbox has been lifted. Today, I was
able to get this to work. There's a trick.
Usually, when you start up matlab and run a parallel thing like 'parfor', it just uses a default |
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Thu Nov 2 17:23:56 2017, Aaron, Mechanics, PonderSqueeze, Modelling suspension noise
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aLIGO Suspensions Toy Model
On Wednesday I started making my own model of the aLIGO suspensions, with the top of the silica fibers attached
to ears that are fixed rather attached to an additional suspension stage (so this will be a one stage suspension).
I grabbed the aLIGO ear design from the DCC: |
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Fri Nov 3 15:03:10 2017, Aaron, Mechanics, PonderSqueeze, Modelling suspension noise
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Model Geometry
Test Mass
I found the dimension of the test mass flat in the drawings of the
mock test mass design here: LIGO-D080687. |
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Wed Nov 15 14:05:12 2017, Aaron, Mechanics, PonderSqueeze, Modelling suspension noise
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Model Geometry
I pared down the number of parameters in the model to only the necessary ones. These are the ones that
remain:
TM_radius: Radius of the test mass
TM_width: Width of the test mass
TM_flats: length
of TM flats
ear_length: length of the ear
horn_spacing: length of the ear
horn_gap: gap between |
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Mon Dec 4 16:27:13 2017, aaron, Mechanics, PonderSqueeze,
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Meshing Surface Layers
Defining New Selections
I don't know why I wasn't seeing this problem with previous models (perhaps
because I wasn't importing any CAD or STEP files), but my latest attempts at meshing and selecting specific domains of my model were being thwarted
by inconsistent domain definitions. I was previously always manually selecting domains, which is confusing because all domains just get assigned a number |
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Mon Dec 4 17:42:53 2017, gautam, Mechanics, PonderSqueeze, FEA on optimus
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We could run the simulations on the 32 core machine in the 40m lab (optimus)? I think Mariia was running some of her studies on optimus, and even though
we had some problems with the licensing initially, I think she resolved these and has detailed the procedure in her elogs...
Quote:
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Mon Dec 4 19:49:32 2017, gautam, Mechanics, PonderSqueeze, FEA on optimus
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It's a good idea, I'll check out her elogs and get it started tonight.
I found that I had the relative tolerance set too low (0.001, while the iterations were not converging further than 0.02 or so); I changed
it to 0.1, which let me run over a few modes relatively quickly once I reduced the number of sections on the main part of the fiber to 10. This is not |
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Tue Dec 5 10:50:54 2017, aaron, Mechanics, PonderSqueeze, FEA on optimus
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I had some trouble running this on optimus.
Optimus has COMSOL 5.1 installed, but I made these files in 5.3. I downloaded the comsol 5.3 dvd.iso file last night, but on install I'm
now getting the error "No locks available." I wasn't sure if this is a file permissions issue (sometimes the file has been 'locked' |
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Tue Dec 5 19:50:47 2017, aaron, Mechanics, PonderSqueeze, FEA on optimus
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Gautam advised me against trying to install version 5.3, lest it break version 5.1--I had already gone through the install, but looking at the install
manual it says it shouldn't affect previous installs except that the default behavior when double clicking .mph files will always choose the latest
version of COMSOL. Since we mostly run on the command line we should be fine. That said I haven't tested files with COMSOL 5.1. |
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Tue Dec 12 11:50:12 2017, aaron, Mechanics, PonderSqueeze, FEA on optimus
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Simulation results
First run
Gautam ran the COMSOL model on sandbox1 since we were trying
to run it before I had a home directory there to run from my login. Since that first run, Larry set me up on sandbox1 so I was able to run a few more times
with some tweaked model parameters.
Here are the results from the first run, which uses the nominal aLIGO test mass |
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Thu Jan 18 21:13:59 2018, aaron, Optics, PonderSqueeze, modifications to Gautam's 40m finesse model
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I made a copy of Gautam's 40m model to add the unstable filter cavity for the ponderomotive squeezing project. I wanted to make a more explanatory
record of the changes I've made because I think some of them might be necessary for other scripts using gautam's original model, but I have
not implemented them in that file (also just for my own paper trail). |
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Mon Jan 22 21:13:25 2018, aaron, Mechanics, PonderSqueeze, tips from Shoaib
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I talked with Shoaib about some changes I could make to the FEA model to improve convergence and reduce memory usage. Summary:
use a hex mesh rather than tetrahedral
Use more structured meshes. In particular, I can make an angled swept the mesh
in the tapered portions rather than using a free mesh in these regions, defining the mesh only on one boundary
Use a nonconformal mesh, so adjacent |
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Mon Jan 29 23:02:13 2018, aaron, Mechanics, PonderSqueeze, tips from Shoaib
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I started implemented some of these changes:
Started the mesh with a boundary free quad mesh on the interface between the upper tapers and the main part of the fiber. I used the
following size setting
Maximum element size is fiber_taper_length, which I felt was a good characteristic maximum because it wouldn't |
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Sat Mar 17 15:27:48 2018, rana, General, General, file size >> small
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When saving your COMSOL files do these two things to make the files much smaller (good for saving in version control and sharing):
File -> Compact History
Preferences -> Files -> Optimize for File Size (not speed)
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Mon Aug 20 15:44:56 2018, rana, General, General, file size >> small
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Also,
click 'Clear Mesh' under the mesh menu
'Clear Solutions' under the Study menu
In this way
the file sizes will be ~100 kB instead of 10's of MB. |
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Sun Aug 26 16:42:54 2018, rana, Mechanics, Analysis, Test Mass Thermal Noise: Consistency Checks
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For the Voyager test masses, we have been considering a barrel coating to increase the IR emissivity to increase the radiative cooling power. We also
seek to estimate the added Brownian thermal noise that arises from this.
Dmitry Kopstov (from MSU) made a baseline model for this which we have been modifying. The latest is in the CryogenicLIGO git repo in the FEA |
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Sun May 7 18:22:35 2017, rana, General, Voyager, Voyager ITM: Radiative cooling with cold shield and cold CP
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I took Aidan's COMSOL model for the ITM from
a couple years ago and updated it with some more details:
Through radiative cooling only, the ITM is cooled to 103 K. Taking it to 123 K will be accomplished by adding a ring heater to the ITM.
Assume |
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Sun Aug 26 19:21:27 2018, rana, General, Voyager, Voyager ITM: Radiative cooling with cold shield and cold CP
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this is a time dependent model of the previous steady-state one
Cold Shield and CP held at a constant 60 K
3 W heat input to the ITM from the main laser beam
radiative cooling
to the shield
ITM barrel emissivity = 0.9
ITM HR/AR emissivity = 0.5/0.5
So the cooldown time w/o a heat switch |
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Thu Feb 14 12:38:51 2019, Ching Pin, Mechanics, , comsol modelling
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So I did a simple comsol model of laser heating of a silicon disk, with only radiation, to see the temperature variation at steady state, which could
be the limiting factor for high Q at 123 K, due to the thermalelastic effect.
The model just uses a simple 2 inch disc, at 0.028 cm thick, with the flats not incorporated in yet. |
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Fri Feb 15 21:05:31 2019, Ching Pin, Mechanics, , comsol modelling
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So I got the time dependence to work, but I'm not sure what went wrong in the first time anyways. I'll trying to get a sense of how long
it takes for the temerature to semi-equlibrate, and coming to grips with comsol as a whole. There seems to be some inaccuracies when the timing increases, |
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Tue Feb 19 19:52:53 2019, Ching Pin, Mechanics, , comsol modelling
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The time step response to heating via laser (22.5 mW) is given in the attached picture, for 2 starting temperatures, 122.5 K and 122.8 K. We see that
it takes fairly long to equlibrate, with a time constant of about 500 s, and is consistent across both temps. The y axis is average temperature across
the surface of the disc, and the x axis is time. I believe that the heat distribution profile would be very similar with time, simply because of how much |
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Fri Mar 1 19:33:40 2019, Ching Pin, Mechanics, , comsol modelling
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I've changed the heating to be from two heat sources, to better model the situation with a heater and a laser. The heater deposits 22 mW, with the
laser deposting .5 mW. The overall temperature distribution is smaller then before, as expected, but doesn't really change much. The heater is simulated
with a deposited beam with a gassian beam profile with a standard deviation (s.d.) of 8 mm. The laser to the size has a .3 mm s.d. for contrast. I |
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Mon Mar 4 17:22:07 2019, Ching Pin, Mechanics, , comsol modelling
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I've updated the material properties to vary with temperature, mainly in the range of 90-140 K. Using the parametric sweep function to vary the
input power of the heater, we get the eigenfreqencies' dependence on temperature to show up. The fractional dependence of 1.3e-5 /K around 123 K matches
with what Aaron calculated in this elog entry, which is always a good sign that nothing |
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Wed Mar 6 09:51:18 2019, Ching Pin, Mechanics, , comsol modelling
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So I tried adding the sapphire lens to the comsol model, and I am having teething issues. I can't seem to get the solver to converge, but I'm
working on it. |
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Thu Mar 7 10:10:37 2019, Ching Pin, Mechanics, , comsol modelling
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There are no issues with the thermal side of the modeling, the issue seems to be with the structural mechanics side. I'm not sure what I'm doing
wrong though, but it just isn't converging. In any case, seeing that this is my last day here, I'll just point out that the version without the
lens is saved in cvs/cds/caltech/users/cp/current working model.mph, while the model with the lens is saved in the same folder under the file name testing |
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Tue May 12 14:16:28 2020, Koji, General, General, FEA tutorial resources
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cf. Forwarded email from Stephen
1) Tuesday Demo - Basics of FEA Meshing G2000696
2) CIT SYS User Guides, How to Use the FEA User Group T2000295 |
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Fri Dec 4 18:32:02 2015, rana, General, Configuration, COMSOL: remote server w/ matlab
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This summarizes how to get the remote comsol server to run. COMSOL 5.1.0.234 is now on tegmeni thanks to Larry.
On the server:
rana@tegmeni|~> /usr/local/comsol51/multiphysics/bin/comsol server -login force |
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Tue Aug 11 11:16:29 2020, aaron, General, Configuration, COMSOL with Matlab without display
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When running comsol with matlab interface on sandbox1, it is usually most convenient to ssh with screen forwarding (eg '-CY') and launch COMSOL
with matlab by following the instructions in the livelink
manual. |
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Tue Aug 11 16:35:07 2020, aaron, General, Configuration, COMSOL: remote server w/ matlab
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To run COMSOL on sandbox1 with no graphical Interface, here are the steps that worked for me (Tue Aug 11 16:35:51 2020) from a
mac on the Caltech VPN.
1. ssh onto sandbox1 with screen forwarding (-Y). Make sure you have a compatible version of XQuartz or a substitute. -C specifies data |
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Thu Jun 22 14:12:04 2023, Raj, General, aLIGO, Finesse Modelling for aLIGO
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The aLIGO model available on IFOSim uses the first surface of the mirror as Port 1 and the other surface as Port 2. This requires us to use negative
radii of curvatures among others to get the correct modeling. However, this makes adding surface maps more difficult and was causing issues with
getting the simulations to follow what is expected. The surface_map attribute for mirrors doesn't allow us to specify the mirror port in Finesse. |
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Thu Jul 6 11:35:55 2023, Rajashik, General, General, Basic Demonstration of Cavity Scan
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| Attached are plots of how HOMs are introduced by defects in the mirror. This is just an example for a basic FP Cavity. |
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Fri Jul 21 16:42:57 2023, Rajashik, Optics, Analysis,
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Initially, ideal conditions were considered, without any deformations or thermal heating effects in the mirrors. This offered a baseline model from which
subsequent tests could draw comparisons.
Following this, more complex scenarios were introduced into the model: mirror-shape defects caused by suspension and thermal lensing due to heat |
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Sat Jul 29 00:19:02 2023, Rajashik, Optics, General,
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I have coded a rudimentary triangular model using parameters provided by Aaron. In this model, I have kept a simple PDH signal which is the REFL power
demodulated with the EO frequency. The PDH signal is then fed to the laser to modulate the frequency.
There are some points of confusion I have in this model such as the high loop gain required to achieve locking. I think this may be |