A question about Simscape component: gas-charged accumulator

Question

haonan He 2022-3-23

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https://ww2.mathworks.cn/matlabcentral/answers/1679069-a-question-about-simscape-component-gas-charged-accumulator

回答： Walter Roberson 2022-3-24

Hi,

I found a problem with Simscape component: gas-charged accumulator. The attached picture 'model' is a very simple model where there is only an accumulator. The paramter settings are also attached. For the initial conditions, I set the pressure of liquid volume to be 13.7 bar so according to the gas polytropic equation given in https://uk.mathworks.com/help/physmod/hydro/ref/gaschargedaccumulator.html the initial liquid volume can be calculated as 5.85e-4m^3 (Since I only set high priority for the pressure of liquid, I think the other two initial conditions can be ignored by Simulink). However, when I run the simulation, there was an error (please also see the attachment called 'error') saying that the volume of liquid must be less than total accumulator volume. But it is very evident that the initial liquid volume is 5.85e-4m^3 which is absolutely less than the total accumulator volume 1e-3m^3.

I appreciate it very much if someone could help me out.

Best regards,

Hao

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Walter Roberson 2022-3-23

You should take care of the base being negative from the warning message. You should assume that the condition that lead to that warning message caused a problem for you (or that the automatic handling of the condition was not suitable for your situation.)

haonan He 2022-3-24

Hi Walter,

Many thanks for your answer. It would be highly appreciated if you could give me more advice on this problem, since according to my initial condition, the base will never be negative.

The reason that the base will never be negative is that according to the gas polytropic equation given in the attached link in the above question, the liquid volume will not exceed the total accumulator volume under my initial condition (the initial pressure of liquid is 13.7bar).

It would be great if you could try my simulink model attached to the above question. It is a very simple model and you will see the problem. I am not sure whether it is a bug of this component.

Please let me know if more information is needed.

Many thanks, Haonan

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Answer 1

Walter Roberson 2022-3-24

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https://ww2.mathworks.cn/matlabcentral/answers/1679069-a-question-about-simscape-component-gas-charged-accumulator#answer_926359

I do not have any idea what the "real" answer is.. but

if you explore the Gas Charged Accumulator, and ask to look at the Variables, then there are three variables. At the moment you have the Priority of the Pressure of Liquid Volume marked as High and the other two marked as None.

If you set the Pressure priority to None, then the diagnostics do not occur.