VTP shaft critical speed calculation

[MECHENG60]

Dear Colleagues:

According to Dicmas book the shaft critical speed(fn) for Fixed-Fixed condition is fn (F/F) = 2.23 x fn(for Hinged/Hinged condition), for Fixed-Hinged condition fn (F/H) = 1.55 x fn (H/H), and according to L&B manufacturer fn (F/F) = 1,9 x fn (H/H) and fn (F/H) = 1.9 x fn (H/H)
What is the correct option?
Where can I get more information about this?

Thank You

 

[electricpete]

That form sounds like a beam equation with ideal infinite stiffness supports. Associated modeshape involves flexing of rotor only. Real machines usually have some flexibility in supports which cannot be neglected … i.e. the first modeshape will include some movement of bearing supports.

Edit - sorry I was thinking horizontal machine. Vertical pump I'm not so sure... if it was in the book on vertical pumps then he may have had a good reason to use that model as approximation for the particular machines he was looking at.

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(2B)+(2B)' ?