Simscape simulation of Hydraulic/Gas chamber

Hello Community,

I need to simulate an atmospheric closed hydraulic chamber with several in/output ports. The chamber has to fullfill the following requirements:

• Signal output which shows the level of fluid
• The ports are able to push and pull water OR gas into the chamber
• The gas/fluid pressure balance decides about the fluid level
• When the chamber is getting filled but is not full: gas is pulled out trough open port until fluid level reaches the port
• If chamber is full, fluid shall be able to flow trough the former gas port
• Thermal effects are negnectable (room temperature)

I know that this requirements contain not allowed domain crossings in Simscape. But are there any workarounds?

What workarounds I already tried:

• Simulated the air as a fluid and separated it through a simple double piston with hard stop. The position of the stamp gave me the current level. I solved the water incompressibility issue with a gas loaded accumulator block. Problems: Only 'air-water' shall go in the air compardment of the piston trough the 'water-air port'. But real water could also come from that port, which should go in the water compardment of the piston to result in a correct level monitoring.
• Used the TL-G tank, placed perfect thermal insulators for the temperature independance. Problem: When fluid level crosses the limits the domain crossing drops a matlab error.

Do someone have any ideas or approaches how to reach such a model with Simscape/ Simscape Fluids.

Answer 1

[Yifeng Tang]

Maybe this will work:

Use the TL-G tank and the insulators you mentioned. It should be able to do 1-4 and 6 of your requirements.

You can "fake" No 5. to allow liquid flowing OUT of the gas port when it's full by using a check valve, whose opening pressure is set by the pressure differential imposed by the water when the tank is full. This way, the water will flow out, not through the gas port, but through the check valve. The picture/model below shows the idea. The pressure sensor on the gas side and the pressure source on the TL side is to make sure that the pressure differential on the check valve only comes from the water height and not the gas pressure.