is defined to describe the flow about the same body in an unbounded fluid, 

 i.e., in the absence of channel boundaries. The fluid speed on a body 

 surface in general increases due to the blockage effect when compared with 

 that of unbounded fluid. However, the speed increment on the body surface 

 is not uniform over the entire surface. For example, the forward stag- 

 nation point of an axisymmetric body remains the same whether in an un- 

 bounded fluid or in a wind tunnel of circular cross section. Nevertheless, 

 a mean speed correction has been traditionally employed for the blockage 

 correction mainly due to its simplicity. To describe a mean-speed incre- 

 ment, speed increment due to blockage locally on the body surface is 

 defined as 



Au = V ($-$ ) • T 

 o 



= V (<M> o ) * T (3) 



where T = (t.. ,T„,T.O is a unit tangential vector on the body surface; T.. 

 is the component along the x-axis, i.e., the longitudinal direction, and 

 x and t_ are, respectively, the normal and tangential components in the 

 cross sectional plane of the body. Then the "exact" mean speed increment 

 averaged over the entire submerged body surface is given by 



■ ; ■ k « 



V (<Hf> ) • T ds (4) 



where S is the wetted surface area, and T is specified. One natural way 





 of specifying T would be as the unit potential flow streamline vector on 



the body. However, streamlines on a body in bounded and unbounded flows, 



described by $ and $ , respectively, do not coincide in general, except in 



the special case of an axisymmetric body in a flow facility of circular 



cross section. In the case of a ship hull, if T = (1,0,0), and S = 



2 • L • T under the assumption that the ship is thin, Equation (4) can be 



reduced to 



