Hello everyone.
It is decided to perform an EMA on a dry-hull of an experimental model of a ship hull. The question is, where should the fixed points on the experimental model be considered to gain the best result?
* Fixed points are the points that the ship experimental model should be fixed on as a support points to perform the modal test.
I speak of aerospace experience, when people do an EMA/GVT they tend to mount the aircraft on something very soft, so its stiffness doesn't affect the modal behaviour, effectively simulating a free-free boundary condition. This can be achieved by for example reducing the tyre pressures so the contact with the ground softens or hanging the aircraft.
When you attempt to do this on a ship model, you can follow the same approach, mount it on some soft rubber or hang it with rubber chords (size/weight permitting). If that is not possible, you can do a preliminary FEA to determine the mode shapes and choose the mounting points where they have little effect of the mode shapes of interest; typically near nodes.
Dear Dr. David Sziroczak
Thank you so much for your detailed reply and also your proposed method which seems so be definitely useful.
Dear Hamid Hokmabady you can look at this texts mentioned below
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