I. SUMMARY 



A. PURPOSE AND SCOPE 



This report relates to the operational aspect of lowering heavy array 

 structures to the bottom of the deep ocean. Because of the weight of the array 

 and the depth to which it will be lowered, the lowering cable can be expected to 

 be under a high stress. Ocean currents, surface waves, and motions of the 

 lowering vessel will also contribute to the stress placed on the lowering cable. 

 Therefore, a critical design problem may exist for the lowering cable. 



The objective of this report is to develop a reasonable theory on 

 which to base the ultimate design of the lowering cable. The study is limited 

 to the case of a single cable lowering the array vertically. Each factor con- 

 tributing to the stress on the cable is considered separately, and the conditions 

 under which the analyses are valid and of practical significance are given . 

 From the results of this theory some general conclusions are drawn as to the 

 feasibility of the operation with regard to dynamically optimum array configu- 

 rations, stability of the lowering platform in a rough sea and degree of rough- 

 ness of the sea (sea state). The results of the study are presented in plot form 

 involving a non-dimensional maximum (djTiamic) stress versus a non-dimensional 

 frequency for various mass and drag parameters . 



Other methods of operation, which are not treated in this report, but 

 which will be considered in later investigations, are. 



(1) Cancel out most of the dynamic inputs to the cable by an auxiliary 

 mechanical system on the vessel. There are two crucial problems here: the 

 horsepower of the driver of such a system and the rapidity with which the over- 

 all system can respond. 



(2) Introduce considerable damping along the cable, which will have 

 the effect of flattening out resonant peaks. This can be effected by attaching 

 bluff bodies to the cable at certain intervals. The drag of the water on them 

 will give the desired friction. This idea seems quite attractive, since these 

 bodies can also provide buoyancy to reduce the rather high static stresses in 

 the cable, but its plausibility must be investigated quantitatively. 



artbur a.lLittlcJnt. 



S-7001-0307 



