Stiffness of hydraulic oil

[boek]

I am trying to estimate the stiffness from the oil inside a hydraulic system. For a simple piston it is possible to estimate the stiffness using two springs, which gives a total stiffness for the oil as: k[sub]oil[/sub]=E[sub]1[/sub]A[sub]1[/sub][sup]2[/sup]/V[sub]1[/sub]+E[sub]2[/sub]A[sub]2[/sub][sup]2[/sup]/V[sub]2[/sub], where E is the bulk modulus of the oil, A the piston area and V the volume of the oil, see the figure below.

However, I have a different system which could be simplified according to the figure below. I need to estimate the stiffness of the oil for this system. Since there is no relative volume change in V[sub]1[/sub], my idea is to neglect the stiffness contribution in the this region, such that: k[sub]oil[/sub]=E[sub]2[/sub]A[sub]2[/sub][sup]2[/sup]/V[sub]2[/sub].
Is this reasonable?

 

[Stick.]

It's probably reasonable, but it also wouldn't be hard to check. Since the fluid in cavity 1 and the piston rod are basically springs in parallel, you could just calculate the spring constant for each and compare them to see if one dominates the stiffness of the system.

 

[PNachtwey]

It looks good but what are you going to do with the stiffness value? I usually compute the natural frequency.



Peter Nachtwey
Delta Motion

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