Fluid inertia in Simscape hydraulic
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Hi,
I have had the impression that Simscape does not account for the fluid inertia in an hydraulic cylinder.
For example when the piston is at the end of its stroke, does Simscape account for the effect of inertia forces on the piston caused by the deceleration of the fluid?
I saw there is a "Fluid Inertia" block but it seems specific for fluid aceleration/deceleration in pipes.
Any help is much appreciated.
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Yifeng Tang
il 24 Giu 2024
Hi Amodio,
I don't think the actuator blocks model the inertia of the fluid inside. The "cushion" can be used to model some end-of-stroke behavior from flow restriction devices, but not the fluid inertia itself.
That said, I think there may be a trick we can play to mimic some effect from the mass of the fluids inside the cylinder. How about adding the mass of the fluid to a mass/inertia block attached at the R port, where the piston mass/inertia is usually also attached to? Something like this:
The piston position is used to calculate the fluid mass (*area*density), and it's added to the total mass at the R end. It assumes the fluids inside is moving at the same velocity of the piston (good assumption?).
Do you think this may work? I'm not sure what a good test case would be so I can't verify.
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Amodio
il 28 Giu 2024
1 Commento
Yifeng Tang
il 28 Giu 2024
That will be very difficult :(
Wild guesses and things to try:
(1) does the poppet valve has an opening dynamics option? If yes, enable it and use a reasonable time constant.
(2) use a fluid property block and make the entrained air fraction non-zero, e.g. 0.005.
(3) replace a long pipe with a few shorter pipes, to capture the propagation of pressure wave.
Do you have access to MathWorks' account team at your company/university/institute? If there is an NDA in place, you may share the model with MathWorks' application engineering team for more relevant advice. You can also try Tech Support, if you don't know who to reach out to initially.
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