Kim and Merciev 



cent) than in the absence of the model, probably because of the block- 

 age of flow within the nest of obstacles. 



Plans for Comprehensive Test Programs 



The results of the exploratory tests have not yielded an explan- 

 ation of the interaction effect, specifically the "tail-wagging" pheno- 

 mena, associated with the articulated model motions tests. The force 

 measurements reveal that a significant hydrodynamic interaction ef- 

 fect exists which would be expected to importantly influence the heav- 

 ing response even if the tail wagging behavior were not observed. Con- 

 sequently, it is necessary for design purposes to systematically in- 

 vestigate the effect of hydrodynamic interaction on the heave motions 

 response of resiliently connected arrays of floats. 



An experimental program to study the influence of float center- 

 to-center spacing, expressed in terms of waterline diameter, float 

 slenderness, deck rigidity, size of array, externally provided damp- 

 ing, and yaw-restraining spring-line restraint, has been developed and 

 will be carried out during August 19 72. 



Three sets of floats, having different spacing ratios (3 to 1, 

 3. 75 to 1 and 4.5 to 1) are being built. Each set will consist of seven- 

 teen rows fo ten floats each. The ten floats in each row will, in this 

 case, provide ample roll stability : these rows consist of sufficiently 

 stiff, yet very light weight, T-sections connected to the cylindrical 

 floatation tubes. 



The seventeen rows will be connected by two sets of plastic 

 splines, one pair at each gunwale, which provide sufficient pitch res- 

 traint for the otherwise unstable rows of floats, and which simulate a 

 specified deck elastic beam-like behavior. The full-size deck stiffness 

 is assumed to be equal to a plate El of 80 x 10 6 lb-ft 2 per ft of deck 

 width, a value recommended by GAC engineers. This stiffness scales 

 according to the 4th power of the scale ratio, which is taken to be 1/48, 

 with 1 1/2 -in diameter model floats corresponding to 6-ft diameter 

 full-size (waterline diameter). For the middle -spacing set of floats, 

 an additional simulated deck rigidity, twice as large as the nominal 

 value, will be tested by using plastic splines of the same thickness 

 and spacing but each twice as wide. 



The float attenuators to be used are thin-walled wax castings 

 with aluminum tubes at their upper ends. The shapes were selected so 

 that their calculated heave responses, assuming no interaction effects, 

 would be the same. The maximum diameters are 1.5 and 1.8 times 



846 



