Cruising and Hovering Response of a Tail-Stabilized Subnnersible 



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Fig. 14 - Effect of longitudinal current velocity on hovering 

 heave maneuver for otherwise standard run conditions 



current velocity of 1 knot, the vessel attains a pitch angle 6 and longitudinal 

 displacement of almost 80 degrees and 4 hull lengths, respectively, before the 

 maneuver is completed. At slightly higher positive currents than 1 knot the 

 maneuver cannot be completed at all because the pitch angle exceeds the limit 

 value. On the other hand, for a negative current velocity of 1 knot, both the re- 

 sponse time 1 2 and the heave overshoot are significantly reduced and the cou- 

 pling effects are negligible in comparison with those obtained for the positive 

 1 knot current. 



It is noted that attempts to improve hovering response in positive longitudi- 

 nal currents by large reductions in tail appendage size were unsuccessful. 

 These reductions did not improve heave response significantly for u^ > 0, and 

 also had large detrimental effects on performance for u^ < 0. 



Because the pitch and surge motions of the tail-stabilized submersible are 

 so sensitive to the action of a pure vertical force z^ , some amelioration of 

 these coupled motions can be obtained by reducing the magnitude of z^. Figure 

 15 shows this effect for otherwise standard conditions with u^ = 0. Decreasing 

 Z^ also reduces the heave overshoot and causes large increases in response 

 time. Therefore, if the slower response can be accepted, small vertical control 

 forces (50 or 100 lb) could be used to move the vessel vertically. This will per- 

 mit the hydrodynamic pitch moments arising from the vertical motion to be 

 counteracted by a pure control moment M . 



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