Newman 



On the other hand, the Model Basin has moved cautiously in applying the 

 planar-motion-mechanism technique to the case of surface (displacement) ships. 

 This was primarily due to concern over frequency effects which it was believed 

 would be caused by the waves generated by the oscillating hull. However, in 

 view of our experience with submarine forms and the authors assurances that 

 the viscous effects are more to be feared than the free-surface effects, plus the 

 recent experiences of other investigators, we should be able to proceed with 

 planar-motion-mechanism tests on surface ship models with full confidence. 



COMMENTS 



Roger Brard 



Bassin d'Essais des Carenes 



Paris, France 



The two main purposes of Dr. Newman's paper can be summarized as 

 follows: 



1. He wants to show that, in spite of the complexity of the flow surrounding 

 a maneuvering ship, it is possible to construct mathematical models taking into 

 account some of the principal characteristics of the flow; these mathematical 

 models lead to a better understanding of the phenomena involved in the maneu- 

 vering of ships. 



2. He discusses the analytical methods corresponding to the mathematical 

 models and he points out where further investigations are needed. 



In order to support his first point, Dr. Newman describes the flow over the 

 model of a Mariner class ship in yawed conditions. The observations were car- 

 ried out in the circulating water channel of the David Taylor Model Basin. They 

 show that the flow inside and outside the boundary layer differs substantially 

 according as the model is in straight or in yawed conditions. However, in yawed 

 condition, the areas of separation are of a limited extent. From that Dr. New- 

 man concludes that a theoretical inviscid fluid model based on the low aspect 

 ratio wing theory or on the slender body theory, should lead to an acceptable 

 description of the flow over the entire hull for angles of attack less than about 

 10 degrees. 



I personally believe that any application of theoretical views to the maneu- 

 vering of a surface ship or of a submarine requires preliminary observation of 

 the flow over the model. So I think that it is not sufficient to watch only the dis- 

 tribution of the flow over the hull surface in yawed condition. It is also neces- 

 sary to watch the flow in turning condition. For this reason, at the Bassin 

 d'Essais des Carenes, we closely examine the flow pattern around ship models 

 in yawed and in turning conditions. In Casal's thesis, which was prepared under 



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