How to linearize SimHydraulics spool valve

I'm trying to linearize the simhydraulics circuit. It includes a simple 4-way spool valve. The linear system is zero.... I think this is because the valve is linearized to zero. The operating point is where all the orifices are closed, and piston is at the center of the cylinder. Both these specs are away from the deadband. does anyone have any idea how to linearize Simhydraulics model? Is there any demo/documentation specifically for SimHydraulics linearization? I would like to do it without predefining linearization for the block.

Answer 1

[Arkadiy Turevskiy]

Most probably the linearization is zero because you are computing it at the operating point where the orifice is closed. The tool "perturbs" the model a bit to calculate the difference between the operating point and the perturbed state. If the valve stays closed, you get zero linearization. One solution that often works in those cases is to run a model to a time where nothing is fully closed or fully open, and linearize at that time. For example, if you know that at 5 seconds into the simualtion, valves are partially open, in the Linear Analysis tool specify that you want to linearzie the model at simulation snapshot of 5 seconds, as discussed in the doc here.

Hope this helps. Arkadiy

Answer 2

[Punit]

The valve is closed at the operating point. But, the valve area curve has non-zero slope at that point, because there is no dead band. When we open the valve a little, unfortunately, it is not an equilibrium point, and I want to linearize at the equilibrium. Now, I think its the non-zero leakage area causing this problem. But, it should not give zero linearization with perturbation method, with perturbation higher than 10^-12.

Answer 3

[Arkadiy Turevskiy]

Hard to say without having the model. I just tried linearizing a shipping example with a 4 -way valve, sh_closed_loop_circuit_4_way_valve_cust_cyl.slx, and it linearizes fine.

Can you make your model available?