Virtual mass
Virtual mass
(OP)
We are dealing with vibration in a ship propeller. This is a thruster. Consider a baseball with propeller wings in one end. The CofG is in the baseball centre. What would be the lowest natural frequency based on added mass influence? Along the long axis, or the short axis?
Thanks a lot!
Thanks a lot!





RE: Virtual mass
RE: Virtual mass
And, sorry. I mean a football (american football, not soccer) of course, not a baseball. The housing has something like a football shape with the propeller coming out at the "long end". The housing is suspended from the hull with a cylinder-shaped structure. I need to optimise the hull attachment area, but I am uncertain in which direction I will get my lowest natural frequency.
As I said, my stiffness in the propeller housing an suspension is symmetrical. What about my added mass from water? That will not be symmetrical, but which direction will have most added mass? Longitudinal or transverse?
RE: Virtual mass
RE: Virtual mass
Cheers
Greg Locock
RE: Virtual mass
Thanks EnglishMuffin for your input. I dont't have Blevins book available, but your suggestion would mean that my lowest natural frequency is perpendicular to the propeller thrust! Which is, of course, good news.
RE: Virtual mass
RE: Virtual mass
Cheers
Greg Locock