Appendix D 

 SUMMARY OF DRAG COEFFICIENTS 



INTRODUCTION 



In an analysis of the motions of o body through water, whether the body is 

 falling freely or being lowered by cable, one of the most important effects which 

 must be considered is the resistance, or drag, experienced by the body. 



The purpose of this appendix is to summarize existing information on drag 

 forces and indicate areas of work which must be covered in order that such forces 

 may be included in calculating the motions of a load being lowered to the deep 

 ocean. 



DRAG IN UNIFORM FLOW 



On the front of every solid body moving through water, there is at least one 

 point where there is no relative motion between the water particles and the body; 

 i.e., there is a stagnation point. The pressure at this point, termed the dynamic 

 pressure, is given as 



P, = ypV^ (D-1) 



stag I 



where p is the density of water and V is the relative velocity of the body to the 

 water. It is convenient to express the total drag due to pressure forces relative to 

 this stagnation pressure by defining 



^(J-PV2)S (D-2) 



D = C 



where D is the drag force due to pressure, Cq is the coefficient of drag, and S 

 is a representative area of the body — either Its frontal or cross-sectional area. 

 Equation D-2 is essentially a definition of Cq. 



The total drag on any body consists of the "pressure drag," defined above, 

 plus drag forces due to skin friction. However, for angular bodies such as those 

 envisaged as loads to be lowered to the deep ocean floor, the skin friction drag 

 may be assumed small compared to the pressure drag. 



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