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Abstract:
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Submerged recovery of small submersibles by means of surface
tethered platforms offers the possibility of operations in sea
states higher than is now possible using surface recovery means.
The Woods Hole Oceanographic Institution's submersible support
catamaran LULU has such a tethered system. The system consisting
of cradle, chains, and hoist is designed to recover DSRV ALVIN
at a depth of 100 feet, and then lift the submersible rapidly
through the air-sea interface. Scientific commitments as well as
possible damage to the cradle and/or ALVIN, and danger to personnel
have prevented full scale recovery experiments. A 1/40 scale model
of the catamaran, chain and cradle was constructed to investigate
cradle heave and pitch response in regular sinusoidal waves. Model
tests were conducted at the Massachusetts Institute of Technology
Tow Tank Facility and data was recorded electronically and photographically.
Test runs were made at various ship speeds, cradle
depths, wave heights, wave lengths, and cradle suspension modifications.
Results indicate that for the existing system, cradle pitch
and heave is only slightly attenuated over catamaran response at
speeds less then 3 knots (full scale). By decreasing the number
of cradle suspension points, and varying hoist resiliency and cradle
added mass characteristics, cradle motion can be substantially reduced
over catamaran motion. |