1. ANSYS simulation of LIGO ITM
Frequency shifts with time
(dynamic surface heating)

2. Simulation parameters
2D axysimmetrical model
Absorbed power in the coating: 10mW
Waist of the gaussian heating beam: 3.4 cm
Radiation into 295K
Coating modeling included in the simulation
We chose 295K because the measured temperature into Virgo towers is (22.0±0.1)°C

3. Modal analisys results
2D axysimmetrical with coating, T=295K:
f0= Hz breathing mode
f0= Hz drum mode
2D axysimmetrical with coating, T=300K:
f0= Hz breathing mode
f0= Hz drum mode
Difference with your simulation:
( )/14465=8.5·10-5
( )/9524.8=8.6·10-5
We think this difference may be due to a non perfect match of our elastic parameters and different eigensolvers in Ansys and Comsol.

4. Thermal-modal analisys steady state
10mW absorbed into coating T=295K:
Δf/f0_breath=1.534·10-6
Δf/f0_drum=1.633·10-6
10mW absorbed into substrate T=295K :
Δf/f0_breath=1.651·10-6
Δf/f0_drum=1.614·10-6
10mW absorbed into coating T=300K:
Δf/f0_breath=1.283·10-6
Δf/f0_drum=1.324·10-6
10mW absorbed into substrate T=300K :
Δf/f0_breath=1.380·10-6
Δf/f0_drum=1.306·10-6
The differences with your results are of the order of 12-14%, these may be due to the fact that we used different temperature dependances of the elastic parameters. Anyway we cannot exclude that the temperature distribution inside the ITM is different as calculated by Ansys and Comsol...

5. Time dependent solution
We read your data files. There are 121 points in both files, if sampled every 5 minutes,
it means the time span is 10 hours. If we plot them against time, they look ok.
But if we zoom the last hours....
Are we missing something?

6. Ansys data (T0=295K)
Next step will be the solution for 10 mW absorbed into the substrate.