Use ideal gas in SimHydraulics

Hi everyone!

If someone wanted to use simply and ideal gas inside a model of SimHydraulics, would it be enough to just set the "Custom Hydraulic Fluid Block - relative amount of trapped air" into a big ratio, lets say 999 and then just set the density of the fluid to the ideal gas equation?

I wanted the model to know that at different pressures there will be different densities automatically.

Thank you for your help!

Best Regards,

David

Answer 1

[Sebastian Castro]

Hmm... probably not. That parameter just tweaks the bulk modulus characteristics of the fluid as its pressure changes. You should use the Pneumatic modeling domain, which follows the Ideal Gas law.

All those blocks are under "Simscape > Foundation Library > Pneumatic", and contain basic elements like orifices, resistive tubes, volume chambers, etc. Furthermore, this domain accounts for temperature changes while the hydraulic domain assumes constant temperature fluid. This is not a good assumption for gases.

Also, SimHydraulics has a Pneumo-Hydraulic Actuator block if what you're seeking is to model is a system with an ideal gas/isothermal liquid interface.

- Sebastian

[David Yu]

I know that the Pneumatic Blocks are the most appropriate ones but I wanted to use the "Jet Pump" block which is in the SimHydraulics section. Do you know any way I could adjust the parameters of the hydraulic fluid to simulate air as precise as possible?

Thanks for the reply!

[Sebastian Castro]

I think the best approach would be to take the equations from the Jet Pump block help and re-implement them in a custom pneumatic domain block. You can do this with the Simscape language.

To get started, I'd recommend looking at some example components from the pneumatic library. If you double-click any block in the Simscape Foundation Library, you should see a "Source code" hyperlink which shows you the Simscape language file.

- Sebastian