Hello,
I want to use Molflow to calculate the Brownian noise generated by gas. Taking this cylinder as an example, I have obtained the force and forcesqr of the gas on this facet. How can I use these data to obtain the Brownian noise generated by the gas on this surface?
I would be extremely grateful,If anyone can give me some guidance.
Hello Wang,
We had a problem with notifications and I’m only reading this now.
I’m afraid that Molflow can’t calculate Brownian noise in static simulations. The idea would be to set up a time-dependent simulation, inject a small amount of gas, then look at the force evolution on a surface. Please note that it’s quite advanced use.
If this problem is still of interest, can you tell us a bit more about the underlying physical problem?
Hello Marton,
I’m very happy you can reply to my question! Currently, I’m working on calculating Brownian force noise in gravitational wave observatories. Here is a simplified model of a test mass ™ and its electrode housing. I assume the TM moves along the x-direction, and I’m trying to calculate the gas damping noise acting on the TM.
When I read papers, all of them mention conducting experiments to obtain the gas-damping coefficient (beta) and then applying beta in the fluctuation-dissipation theorem to derive the Brownian force noise. I want to simulate the gas force acting on the TM and use FFT to obtain the power spectral density (PSD).
Here are a few questions that have been confusing me:
- What causes the Brownian force noise?
Is the resultant force of all gas molecules acting on the surface perpendicular to the direction of motion considered as the force noise, or is it the small variation in this resultant force that constitutes the force noise? - In static simulations, using a formula tool, I can observe the force change in the formular tool window and convergence plot (1 second record once). I have exported the data and used an FFT tool to obtain a PSD. Is PSD the Brownian force noise?
(Facet44 and Facet 46 are two Facets along move direction.)
Overall, I’m not fully understanding which data I should record. Should I record the force along the movement direction (x-direction) or the data from all facets? If you could provide any tutorials or guidance, I would be very grateful.Here is the molflow file of my simulation.
test paper.zip (264.2 KB)
Lastly, please forgive me for my poor English; it may not fully express my questions. I hope you can understand.
Best wishes!