 Thu Jul 25 15:54:58 2013, Deep Chatterjee, Optics, General, TR results for different dimensions 
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Quote:
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 Mon Jul 29 22:42:57 2013, Deep Chatterjee, Optics, General, Avoiding transient solutions in the Computation of TE/TR noise
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An error was being encountered in the computation of the TR noise lately. It was observed that while running the simulations in the case of the materials
which have a lower value of the thermal diffusivity (silicon / sapphire at room temperature), the simulated result were slightly off from the analytic
result. On the other hand, if the simulation was run with a material of higher diffusivity(same materials at lower temperature), the match would be better. |
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Wed Jul 31 15:39:11 2013, Deep Chatterjee, Optics, General, First try with paramter optimization for TE and TR noise profiles
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After the simulations have been found to match to a fair extent with the analytic results by Heinert and Liu and Thorne, the attempt is check out the
parameters for which the TE and TR noise are
close to each other. This was done with the analytic results. The frequency range 10 - 1000 Hz was looked into. In between this range, the quantity |
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Thu Aug 8 17:17:19 2013, Deep Chatterjee, Optics, General, Something like cancellation
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For the material parameters of Sapphire at 300K, the TE and TR Noise profiles, though not very close, lie close to within an order of magnitude. Sapphire
has a positive coefficient of linear expansion. We just inverted the sign of this quantity
and the ran the codes that puts heat and pressure simultaneously to the test mass. The total noise looks to be lower than the TR noise which is |
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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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Tue Feb 5 13:15:13 2013, Dmass, General, General, COMSOL: who's using up all the licenses?
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Quote:
When you want to find out who's using up all the licenses, you can run lmstat -a do find out. |
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Tue Apr 2 19:24:07 2013, Emory Brown, Optics, , First steps producing a Finite Element Model to find the internal Brownian noise of a LIGO test mass
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Motivation:
Reduction of Brownian thermal noise in future gravitational wave detectors is of significant interest. It has been |
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Mon Jun 3 21:01:46 2013, Emory Brown, Optics, General, Analytic Calculation of Thermal Noise due to Brownian Motion using Levin and Thorne's Methods
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Motivation:
Reduction of Brownian thermal noise in future gravitational wave detectors is of significant interest. It has been suggested that changing the
shape of the mirrors used may reduce the Brownian thermal noise. Before we can study how alterations in mirror shape effect Brownian thermal noise, we |
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Tue Jun 4 17:25:11 2013, Emory Brown, Optics, General, Comparison of First Results from COMSOL Model to the Analytic Solution
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Motivation: Before we can attempt to modify the mirror designs to reduce the thermal noise due to Brownian motion in them, we must verify that
our model works and that its results match with the analytically calculated ones.
Methods: I had previously constructed a model of a cylindrical mirror in COMSOL: http://nodus.ligo.caltech.edu:8080/COMSOL/3. |
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Mon Jun 17 11:06:17 2013, Emory Brown, General, General, Plans for the week of 6-17-13 through 6-22-13
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This week I will update my previous eLog entry with a nicely labeled plot showing both lines on the same plot, then I intend to implement improved meshing
on the mirror in the COMSOL model I have constructed, increasing the number of elements on the mirror's face and the central axis of the mirror such that
there are more elements in the regions where the applied force is greatest. This should result in more accurate and faster to compute simulations, |
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Mon Jun 17 14:59:20 2013, Emory Brown, Optics, General, Improved Meshing in a COMSOL Model
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In order to make computations more efficient and possibly allow the set of boundary conditions based on Liu and Thorne's suggestion of a gravitational
force preventing bulk motion of the mirror (described in http://nodus.ligo.caltech.edu:8080/COMSOL/3)
we want to be able to more optimally mesh our structures. In particular, we would like to have a finer mesh on the face of the mirror and especially |
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Tue Jun 18 15:26:50 2013, Emory Brown, Optics, General, Attempting to Implement Liu and Thorne's Boundary Conditions
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Liu and Thorne demonstrated in their paper that the optimal set of boundary conditions for a problem like the one I am working on is the balance the
force applied to one of the mirror faces by an opposing force of equal magnitude distributed throughout the body of the mirror. When we first attempted
to implement this boundary condition, we obtained an error from COMSOL indicating that a solution could not be generated as " |
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Wed Jun 19 14:59:13 2013, Emory Brown, General, General, The Relative Residual Convergence Error
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We have been encountering an error in COMSOL for a while of the form "Failed to find a solution.; The relative residual (###) is greater than
the relative tolerance.; Returned solution is not converged.; -Feature: Stationary Solver 1 (sol1/s1); -Error: Failed to find a solution." The
error has occurred when attempting to find a stationary solution in models with boundary loads and no fixed constraints (preventing an edge from moving). |
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Thu Jun 20 12:51:44 2013, Emory Brown, General, General, The Relative Residual Convergence Error
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I used the same integrator that we had setup for use with the stationary solver. I had expected it to either fail or return a very different result,
but assumed that the fact that it was returning the same result as when it was used after the previous solvers indicated that it was able to use that solver
to find the value. After seeing this comment I went back and checked and the solver was setup to use the last stationary solution regardless which |
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Sun Jun 23 14:00:05 2013, Emory Brown, General, General, Manipulating the Relative Tolerance
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We have been seeing an error when attempting to use a stationary solver in conjunction with a set of boundary conditions which does not fix the
face of the mirror opposite the applied force. I have tried a number of settings changes and tweaks in order to attempt to get the stationary solver
to converge on our model. I have found that by switching to the PARDISO solver and increasing the relative tolerance to 500, the solution will converge |
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Mon Jun 24 16:02:43 2013, Emory Brown, Optics, General, Rebuilding a minimal version of our COMSOL model
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I rebuilt our COMSOL model in order to see if I could find any errors in it and to clean out unnessesary features and parameters. The model
returned the same results as before, and I did not find anything wrong with it while rebuilding it. Running an Eigenfrequency solver gives the first
real mode as a sheer mode, indicating that a normal meshing may be insufficient, but finer meshes result in an out of memory during LU factorization error |
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Tue Jun 25 15:18:41 2013, Emory Brown, Optics, General, A new boundary condition to attempt to avoid the relative residual error
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I contacted COMSOL support about our difficulties with the relative residual error and was told "Typically for solid mechanics this error
is because you have not constrained the body enough. So any solution + a rigid body transformation is also a solution. To remove this non-uniqueness, you
need a solutions modulo the rigid body transformations. So try and constrain the body somehow." This is what the gravitationally balanced body |
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Wed Jun 26 16:46:32 2013, Emory Brown, Optics, General, A convergent stationary solution
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By adding additional constraints as described in the previous eLog to the model I was able to get a convergent solution using the stationary solver.
I cleared meshes, solutions, and history and uploaded the file in its current form. Using the stationary solver, we get Umax=1.51646*10^-10
J instead of the 1.52887*10^-10 J obtained using the rigid back constraint. This is less than a 1% difference, so it is still off from the analytic |
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Thu Jun 27 11:26:18 2013, Emory Brown, Optics, General, Missing factor of 4 and a comparison of analytic and simulated Brownian noise
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In our calculation of Sx(f) from Umax prior to this, we were missing a factor of 4. The correct formula
from Liu and Thorne's formula 58 is Sx[f] := 4*Kb*T*Umax*Phi/Pi*f*F0^2). When we correct this formula, we get results which agree fairly well with |
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Fri Jun 28 11:54:10 2013, Emory Brown, Optics, General, Maintaining a constant volume while modifying the radii of the test mass faces
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When changing the dimensions of the mirror, we want to keep a constant volume. To do so, we must modify the height of the test mass. The area
of the test mass if R is the radius of the front mirror face and r the radius of the back mirror face is (1/3)*pi*h*(R^2+R*r+r^2)=area, so using the values
currently in our model, R=r=0.17 m and h=0.2 m, area=0.0181584055 m^3=pi*0.2*0.17^2 m^3, so to ensure that the volume of the test mass remains constant, |
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Tue Jul 2 13:32:30 2013, Emory Brown, Optics, General, Using Matlab to run our COMSOL simulations
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We want to be able to test a number of values for the ratio of the radii of the frustum which will be much easier once we can get Matlab to
automate running our COMSOL model. I have been able to output the COMSOL model to a .m file and was able to figure out a way to export the Umax value
we want to Matlab (see the attached .m file). |
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Mon Jul 8 15:47:23 2013, Emory Brown, Optics, General, Meshing error when varying geometry
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I attempted to run the Matlab code built last week, but received an error that the mesh failed to generate on the inner domain/failed to respect
edge element on geometry edge. The error occurred on the second computation with ratioR=0.2, but for ratioR=0.1 the simulation completed successfully.
I reproduced the error in COMSOL and noted that for meshes with size at least as course as "course" or extremely fine, a mesh could be |
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Tue Jul 9 14:45:04 2013, Emory Brown, Optics, General, Meshing error when varying geometry
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I tried removing the constraints and applied force and was able to get close to the same frequencies for the butterfly modes as the simple model. By
also removing the interior cylinder from our model I was able to restore the butterfly modes as well. I can see why removing the constraints and
forces would make a difference, but I don't understand how the interior region which was only used to aid in making the meshing in the central region more |
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Wed Jul 10 14:15:20 2013, Emory Brown, Optics, General, Comparison of Umax and the frequency of the lowest eigenmode against ratioR
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I was able to run the looper program designed last week over the interval ratioR=[0.5, 0.9] with a step size of 0.01 and obtained the plot below
with a minimal value of Umax=1.4723e-10 J obtained for ratioR=0.71, which is about 3.2% less than the value of Umax=1.5202e-10 J when ratioR=1. This
is not very significant, but the shifting upward of the frequencies of the lowest eigenmodes as described in the previous post is. Additionally, |
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Fri Jul 12 00:09:17 2013, Emory Brown, Optics, General, Analysis of substrate Brownian noise in a silicon test mass with changing ratioR value
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I performed the same analysis we previously did on a test mass made of silicon (using the built-in silicon within COMSOL) and obtained the attached
plots. The plots show more of a difference between the two solutions optimal points than for fused silica, but they are still quite close. All
data is included in the attached tarball. The values for ratioR=1 or a cylindrical test mass place the frequency of the lowest real eigenmode at |
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Fri Jul 12 00:31:11 2013, Emory Brown, Optics, General, Reversed face mirror design
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We had noticed that when we ran an eigenfrequency analysis, there was often a node (see attached screenshot) on the face opposite the applied force.
This indicated that the noise might be lowered by reversing the face the force was applied to, but it also seems like this would be equivalent to
increasing the ratioR value and making the primary face smaller while retaining the mass of the test mass. It seems worthwhile to see how the Umax |
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Mon Jul 15 13:14:30 2013, Emory Brown, Optics, General, Umax curves for varying height test masses
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I ran sweeps over the ratioR range from 0.5 to 0.9 for test masses with modified height, and thus mass, which were otherwise equivalent to our
previous test mass. The attached plot was generated and indicates that the optimal ratioR value for the test mass was shifted significantly, for
the half mass test mass into lower frequency regions, and for the 10x mass test mass into higher frequency ranges. I took the data collected from |
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Mon Sep 16 10:07:32 2013, Evan, General, Configuration, COMSOL 4.3 on the OS X command line
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If you're running Matlab scripts that iterate over simulation parameters (à la Tara),
you might find it useful to be able to run everything from the command line (instead of launching the "Comsol with Matlab" GUI application).
First, the comsol command wasn't in my path, so I symlinked it to someplace where bash could |
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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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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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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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Thu May 2 14:00:36 2013, Koji, General, Configuration, test mass TR with Levin's approach
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Thermo-refractive noise in a finite cylindrical/infinite test mass with Levin's approach
Location of the codes: 40m SVN repository
comsol/thermo-refractive/ |
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Sun Jun 23 14:29:04 2013, Koji, Optics, General, Differences on using a coarser mesh in calculating TR noise
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What about the dependence on the size of the time slice?
It is unclear what the unit fo the frequency. Hz? ot logHz (which should be expressed as 10^1, 10^2, ...)?
Can you combine the result of the caluculation and the error together? |
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Wed Jul 3 00:04:46 2013, Koji, Optics, General, Using Matlab to run our COMSOL simulations
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Please use zipped files instead of uploading extremely long text files on the elog.
Or use wiki or svn instead of elog for uploading them.
And appropriate word wrapping so that we can read the entries. Please. |
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Wed Jul 10 17:52:18 2013, Koji, General, General, How to force time steps for a time dependent simulation
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A common trap in COMSOL:
When you run a time series simulation, COMSOL tries to be "clever" by skipping some time steps
and returns you an interpolated result in order to accelerate the calculation. |
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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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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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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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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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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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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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Wed Jun 5 13:31:41 2013, Matt A, Optics, General, Analytic Calculation of Thermal Noise due to Brownian Motion using Levin and Thorne's Methods
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Nice Work Emory,
Can you make a plot with both of the lines on the same plot, with a legend, units, and everything? I'd like to see these compared side-by side.
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Wed Jun 5 16:56:53 2013, Matt A., Optics, General, Difference in the Levin and Liu & Thorne results for thermal noise
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Good Work Deep,
Can you include the equations that you used to calculated these expressions?
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Wed Jun 5 16:59:51 2013, Matt A., Optics, General, Matlab code for calculating the zeros of Bessel functions from GWINC
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For calculating the Liu and Thorn U_0 + DU, you need to sum over the first N zeros of the first-order Bessel function. Unfortunately, Matlab doesn't
seem to come with a function to do this.
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Thu Jun 6 12:40:07 2013, Matt A., Optics, General, Conventional Thermal noise (Sec V) from Liu & Thorne
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Good work Deep,
Can you write more on what this is and why you're doing it? We want our elog entries to be easy to understand for anybody who reads it.
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Mon Jun 10 18:37:09 2013, Matt A., General, General, Response to question in: Disscussion of the code of a 'comsol with matlab' model file (partially complete).
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trange = ['range(0,' num2str(dt) ',' num2str(t_end) ')'];
**There is however a query regarding the keyword range which in Matlab returns the difference between the maximum and minimum of the list |
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Thu Jun 20 10:26:38 2013, Matt A., General, General, The Relative Residual Convergence Error
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Emory:
I don't understand how you're getting the strain energy from the eigenvalue solver. It is my understanding that the eigenvalue solver will only
give you the strain energy at a particular eigenfrequency. We're interested in the strain energy from the beam deformation at frequencies below the first |
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Mon Jul 8 18:39:31 2013, Matt A., Optics, General, Meshing error when varying geometry
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Quote:
I attempted to run the Matlab code built last week, but received an error that the mesh failed to generate on the inner domain/failed |
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Mon Jul 8 19:04:35 2013, Matt A., Optics, General, Meshing error when varying geometry
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Quote:
I attempted to run the Matlab code built last week, but received an error that the mesh failed to generate on the inner domain/failed |