Newman 



Subsequently the International Towing Tank Conference has organized a 

 large concerted experimental program in which several model basins have par- 

 ticipated to compare experimental model and full-scale maneuvering data for a 

 Mariner hull. This activity has led to extensive progress in experimental meth- 

 ods, particularly in the widespread employment of mechanical oscillators or 

 "planar motion mechanisms" capable of exciting forced sinusoidal motions of 

 ship models and measuring the associated force response. There is evidence to 

 suggest that the results of this type of test can be applied in the prediction of 

 non-oscillatory motions, such as the steady turning of ships, with the same de- 

 gree of confidence as the prediction by a direct small-scale time-domain mod- 

 eling of the maneuver and with substantially more generality. 



In recent years there have also been a few investigators who dared to attack 

 with more fundamental techniques the hydrodynamic aspects of the motions of 

 ship hulls in the horizontal plane. Low aspect-ratio wing theory has been ap- 

 plied to yield predictions of the side force and moment on a yawed ship. Similar 

 analytical methods have been used to estimate the free surface effects associ- 

 ated with wave motion at the air-water interface. And a parallel experimental 

 investigation has been carried out to compare the side force on a yawed surface 

 ship model with that of an immersed geosim double-body. As a result of these 

 studies and of closely related developments in the field of aerodynamics, one 

 can claim to understand qualitatively most of the separate mechanisms which 

 contribute to the hydrodynamic force and moment acting on the hull. However, 

 as in the field of speed and powering, we are less certain of the interactions be- 

 tween the separate aspects of the problem. 



Reduced to its bare essentials, the analysis of ship maneuverability deals 

 with the motion of a rigid body on the free surface of a real fluid, subject to the 

 influence of the body's control surfaces and propellers. The dynamics of the 

 rigid body itself (i.e., the inertial characteristics of the ship) can be readily 

 treated with Newton's laws, but the dynamics of the surrounding fluid cannot be 

 described quantitatively unless severe idealizations are made. The difficulty 

 rests primarily with the complications of viscous and free surface effects. 

 Thus the classical description of a rigid body in an ideal unbounded fluid, which 

 is so elegantly developed in Lamb's "Hydrodynamics," is not applicable except 

 as a guide in setting up the equations of motion. And in principle not even this 

 is permissible since the generation both of vorticity and of surface waves will 

 give rise to "memory" effects of the fluid motion which will fundamentally affect 

 the form of the equations of motion. 



In view of the complexity of the flow phenomena involved, it is not surpris- 

 ing that most of the work in this field is semi-empirical. Nevertheless, avail- 

 able analytic methods can be relied upon for qualitative predictions and these 

 can serve the important role of supplementing and guiding the process of ex- 

 perimental investigation. It is hoped that this paper will help to advance that 

 role by surveying and collating some of the fundamental studies in the field. We 

 shall restrict ourselves to conventional ship hulls whose motion is primarily in 

 the horizontal plane and in otherwise calm water of infinite depth and horizontal 

 extent. Thus we will not discuss such topics as maneuverability in restricted 

 waters or in a seaway (including broaching!) or the behavior of high-performance 

 vessels such as planing boats, hydrofoils, or ground-effect-machines. 



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