Adept at Depth 



DISCUSSION 



Roy S. Rice 



Cornell Aeronautical Laboratory , Inc. 



Buffalo, New York 



The author has described several of the important considerations involved 

 in the development of vehicles able to perform the many functions required for 

 true agility in the depths of the sea. Each of these considerations is worthy of 

 extended discussion, but two of them are especially significant to this sympo- 

 sium because of the need for an understanding of low-speed hydrodynamics in 

 order to realize suitable vehicle configurations. 



The author has pointed out that emphasis on improving maneuverability in 

 submersible vehicles has been mainly concerned with the high-speed or cruise 

 regime. Indeed, until the formation of the Deep Submergence Systems Project, 

 very little work, either experimental or theoretical, had been done toward de- 

 termining the hydrodynamic coefficients and stability derivatives of underwater 

 vehicles operating at low speed. Now, with the extreme importance of estab- 

 lishing fundamental understanding of the stability and control characteristics of 

 the DSSP craft in order to assure ability to meet rescue, search, and recovery 

 mission requirements, the absence of an adequate body of knowledge of vehicle 

 dynamics in the near -zero speed range is creating substantial design problems. 



Most of you are familiar with the techniques developed at the Davidson Lab- 

 oratory and the David Taylor Model Basin for evaluating the hydrodynamic 

 characteristics of submarines when a dominant forward velocity exists. These 

 methods permit analysis of the nondimensionalized stability derivatives of the 

 vehicle in a convenient form and computation of the dynamic response charac- 

 teristics. Extrapolation of data to reasonably similar hulls may be made with 

 confidence, and preliminary design studies can result in obtaining substantial 

 insight into vehicle performance. 



The absence of a dominant speed in hovering operation means, of course, 

 that no established flow field exists from which perturbations for maneuvering 

 may be examined, and therefore the hydrodynamic characteristics must be 

 treated with respect to the motion of interest. This introduces many nonlinear - 

 ities which, coupled with the fact that the flow conditions range from laminar 

 through turbulent (with much of the operation in the transition region), pose se- 

 vere problems in theoretical studies. 



A second point of special interest brought out by the author has to do with 

 the generation of control forces. For the precision of location and attitude 

 needed for certain missions to be achieved, decoupled control of motion is in- 

 deed a necessity. Yet this capability must be attained within the constraints of 

 a design which is both energy and power limited on a vehicle having character- 

 istic response times severely mismatched with dynamic responses that the pilot 

 is well qualified to handle. Here, again, an understanding of the hydrodynamics — 

 the distortion of the flow field due to motions of the hull resulting in disorientation 



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