WAVE INDUCED FORCES AND MOTIONS OF 

 TUBULAR STRUCTURES 



J. R. Paulling 



University of California 

 Bei^keley, California 



ABSTRACT 



Many types of stable ocean platforms consist of space- 

 frame assemblages of tubular structural and buoyancy 

 members. An approximate method of predicting the 

 hydrodynamic forces and resulting motions of such 

 structures is described. In this procedure, the force 

 on each member Is'computed by assuming that the 

 member is long and slender and all other members are 

 absent. Such forces for all members are summed and 

 introduced into the linear equations of motion of the 

 entire structure, which may then be solved for the re- 

 sulting platform motions. Reasonably good agreem.ent 

 is obtained between the results of such analysis and 

 model experiments with several different platform 

 configurations . 



I. INTRODUCTION 



Many of the stable floating platforms which have been pro- 

 posed or constructed for deep water drilling, mining, or emplace- 

 ment and recovery of heavy objects can be described as space- 

 frame assemblages of tubular members. R, H, Macy [1969] 

 describes and llluatrates several oil -drilling platforms of this type. 

 One of them, BLUE WATER II, consists of a square base configura- 

 tion approximately 200 feet square, made up of cylindrical members 

 14.5 feet in diameter, with four verticaJ. corner caissons 24.7 feet 

 in diameter supporting the main deck. This platform normally 

 operates at a draft of about 40 feet. A second platform, the SEDCO 

 135, consists of three main vertical caissons located approxlm.ately 

 at the vertices of an equilateral triangle, several diagonal tubular 

 truss members, and, at the bottomi of the main caissons, elongated 

 pontoons of oval planform. These platforms are moored by a spread 

 array of anchors, and operate in water depths of up to 600-1,000 feet. 



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