I'm having trouble understanding hydrostatic pressure - please help?
I'm having trouble understanding hydrostatic pressure - please help?
(OP)
Good afternoon,
I'm having some trouble understanding how parts will behave when submerged under 3,000 psi of water pressure. One case in particular - if there's a annular disk and hub assembly (both steel) with an interference fit of 2,000 psi. so my question is: even though the interference fit pressure is less than the water pressure, will water seep through and into the interference surface? my first thought was this this is hydrostatic condition therefore there wouldn't be any deformation that would allow water to seep through. am i thinking about this the wrong way? is there any scenario that would cause water to seep through?
thanks and regards,
I'm having some trouble understanding how parts will behave when submerged under 3,000 psi of water pressure. One case in particular - if there's a annular disk and hub assembly (both steel) with an interference fit of 2,000 psi. so my question is: even though the interference fit pressure is less than the water pressure, will water seep through and into the interference surface? my first thought was this this is hydrostatic condition therefore there wouldn't be any deformation that would allow water to seep through. am i thinking about this the wrong way? is there any scenario that would cause water to seep through?
thanks and regards,





RE: I'm having trouble understanding hydrostatic pressure - please help?
Can you provide more information for example orientation of joint under water,is the joint held at this depth in water by an external force or is it in balance at this depth of water with the mass of the joint?
I think some water could get in the joint,imagine a cylindrical perfect interference fit equal distortion all the way round, now machine a small flat on one of the surfaces, you would still have an interference fit however the flat would allow fluid into the joint.
RE: I'm having trouble understanding hydrostatic pressure - please help?
This is pretty deep water you're talking about so would seem to be important to get it right, but hydrostatic pressure becomes important when there is a pressure difference.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: I'm having trouble understanding hydrostatic pressure - please help?
without a sketch the best you can hope for is motherhood, the worse sarcasm.
Quando Omni Flunkus Moritati
RE: I'm having trouble understanding hydrostatic pressure - please help?
RE: I'm having trouble understanding hydrostatic pressure - please help?
If the interference fit is 2000 psi with a 3000 psi stagnation pressure to water head, then the lid will pop off if the line of action forces the lid off it's bearing face. Otherwise it won't if it acts in a manner to force the lid into the bearing face, thus making a tighter seal.
Sounds like a homework assignment.
Regards,
Cockroach
RE: I'm having trouble understanding hydrostatic pressure - please help?
The first example i thought of was a press-fit of a disk onto a spinning rotor. This is a calculation that I'm comfortable doing.. i know how to calculate the radial and hoop stresses as well as the amount of pre-load loss due to the centrifugal forces. however, im trying to figure out how the presence of water pressure (on all sides) would or should change my approach.
In general, i'm trying to learn how to approach these problem. i havent started doing any work on the subsea applications but i wanted to get a head start and really understand the physics behind it. if you guys know of any good books out there or articles i can purchase, that info would be a big help as well.
the initial question i posted was hypothetical... if water pressure is higher than the interface pressure of the rotor and disk interface, will water contact the interface? I'll attach sketch shortly
RE: I'm having trouble understanding hydrostatic pressure - please help?
RE: I'm having trouble understanding hydrostatic pressure - please help?
In your example I can't see why water depth would be an issue.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: I'm having trouble understanding hydrostatic pressure - please help?
Your case is particularly interesting to me. I have just completed analysis on such a case resulting from collapse of a threaded joint in a downhole oilfield application regarding a frac application. The reservoir pressure was 4100 psi (28.3 MPa) with tubing string pressure roughly that of stagnation pressure of a brine solution with head of 1800 m. The joint collapsed from buckling of an external load, very similar to your case, except you have a flange.
Not the first time I've seen this or had projects relating to the phenonema. But over the industry, the usage of incorrect models to predict pressure vessel stress is particularly poor. So I decided to get some testing completed on a pressure vessel stringed with strain guages and complete a study for a white paper on the subject.
So I recommend Timoshenko - McCullough as classical literature on the subject. There are some excellent resource material on the subject regarding Von Mises with application to the Hencky model. I would start there and be careful to derive your model from first principles. It's very easy to misrepresent the triaxial state of stress subjected to external loads other than internal/external pressure. Lubricators for example are subject to axial compression from guide wires stabilizing what can be regarded as a Euler Column. Without FEA or similar type of analysis BACKED UP by an independent model for validation of output....well....God help us all.....
Good luck with it. Sounds like an exciting challenge!
Regards,
Cockroach
RE: I'm having trouble understanding hydrostatic pressure - please help?
RE: I'm having trouble understanding hydrostatic pressure - please help?
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way