Let us address your questions one by one.
1) The pressure at port B is constantly increasing (from 1400 psi to 3200 psi) while the pressure at port A is constant
Here, the “port A” of “fixed displacement hydraulic pump” Is connected to the reservoir. According to the documentation shown below,
A “reservoir” is a block that has constant pressure (in this case, atmospheric pressure) and infinite volume. This is the reason behind the pressure at “port A” being constant.
The “port B” of the hydraulic pump is connected to the “gas charged accumulator”. The “Gas-Charged Accumulator” block models a gas-charged accumulator that consists of a precharged gas chamber and a fluid chamber. The fluid chamber is connected to a hydraulic system. It has a parameter named “precharge pressure”. As the fluid pressure at the accumulator inlet becomes greater than the precharge pressure, fluid enters the accumulator and compresses the gas, storing hydraulic energy. Refer to the following documentation for “Gas charged accumulator”
Consider your system. When motor is energised, the hydraulic pump ensures constant flow of isothermal fluid (as mentioned in the “displacement” property of “fixed displacement pump”) which results in increased pressure of the “Gas charged accumulator”. Therefore, you can observe that the pressure of the “gas-charged accumulator” keeps on increasing and so is the pressure measured at “port B” of “fixed displacement block”.
2) How would I use the "Nominal Pressure Gain" field in the Fixed-Displacement Pump (IL) block?
Consider that the “pump” is ideal, that is, it has no leakage and friction present. Under this assumption, the pressure of the “Gas-charged pump” should keep on increasing , tending to a very large value. But this is not the case. Simulink also models the leakage and the friction present in the pump. Refer to the documentation:
When the “Leakage and friction parameterization” property of ”fixed-displacement” block is set to “Analytic”, the leakage flow rate is calculated by Simulink using the following formula:
We can see that the field “Nominal pressure gain” appears in the above formula and thus, decides the leakage flow rate. You already know the parameters (
) from the pump specifications. Therefore, you can select such a value of “Nominal Pressure Gain (
)”, which will yield your desired leakage flow rate.
) from the pump specifications. Therefore, you can select such a value of “Nominal Pressure Gain ()”, which will yield your desired leakage flow rate. 3) Discussion regarding the results:
I have created a similar Simulink model (attached with the answer) as shown by you in the attached image.
I simulated the system for a much longer time (2000s) so that the system reaches the steady state. I am attaching the “absolute pressure” waveform at “port B” of the “fixed-displacement pump”, capture by the scope. You can see that the pressure was initially increasing, but eventually it attained a constant value. This is due to the presence of “leakage flow rate”.
Now, I increased the value of “nominal pressure gain” which eventually decreased the leakage flow rate (refer to the above formula). After simulating the system, I got the following waveform:
Observe that the pressure at the “Gas-charged reservoir” has now increased as compared to the previous case. This is also makes sense because in this case, the leakage flow rate has decreased and so we can fill the “gas-charged reservoir” at higher fluid pressures.
I hope that the confusion regarding “nominal pressure gain” parameter is now resolved !
