SIMULINK How to connect gas charge accumulator to a pump/motor?

How can I simulate a reversible pump/motor that draws fluid from a gas charged accumulator and dispenses the fluid to a reservoir afterwards, and for the reverse so the pump uses a source of torque to draw fluid from the reservoir through the pump to the gas charged accumulator?

Answer 1

[Sebastian Castro]

SimHydraulics comes with blocks for all of those already: Pumps, gas-charged accumulator, tanks, valves, etc. A typical diagram could look as follows:

The real challenge is getting all the parameters right :)

- Sebastian

[greeneapps]

Thanks Sebastian, i'm a beginner here so my questions may seem silly but why have you used a variable head tank instead of a reservoir? and also will the same principles apply for a variable pump/motor, I have the idea of using a variable hydraulic machine, would it make sense to use it?

[Sebastian Castro]

I used the Tank block only because the Reservoir block has 2 ports, but our circuit is only connected to one port. You could use a Reservoir block and put a Hydraulic Cap block on the 2nd port, I suppose.

Also, sure -- you can absolutely use a variable-displacement pump/motor. There are plenty other pump/motor blocks in SimHydraulics. I just wanted this example to be simple.

- Sebastian

[greeneapps]

Thanks again Sebastian, I have been trying to configure the parameters for a while now but I keep getting this message 'Unable to reduce the step size without violating minimum step size....This usually may be caused by the high stiffness of the system' How may i go about solving this issue?

[Sebastian Castro]

Yeah, this is common when you have hydraulic components. The zero-crossings fired deal with rapid "mode switching" -- for example, if your accumulator is constantly switching between charging and discharging.

I like this blog's explanation of how you can deal with zero-crossings: http://blogs.mathworks.com/seth/2013/04/26/zero-crossing-detection-what-are-your-options/

Another approach which is particular to using Simscape/SimHydraulics/etc. is the use of the Local Solver , which prevents these small time-steps at the cost of (some) accuracy. You typically want to run your model with all those zero-crossings, and then enable local solver to see if your speed increases without sacrificing accuracy.

- Sebastian