Kim and Mercier 



measurements on individual element rows of this large array to de- 

 termine if the variation of wave force, with the model held fixed, is 

 sufficient to produce the motions obtained in the previous test. 



Possible scale effects were investigated briefly because of the 

 possibility of viscous wake interaction due to vortex shedding, separat- 

 ed flow, etc., being dependent on Reynolds number. Since large scale 

 model investigations are liable to be quite expensive, smaller scale 

 tests were undertaken. Although it is not at all clear in what way the 

 interaction effect in this unsteady flow situation depends on Reynolds 

 number (this dependence can only be established by extensive ex- 

 perimentation), it has been found that for many flow situations a mo- 

 dest reduction in size, or Reynolds number, can have as much effect 

 as a substantial increase in size. A model approximately one-third of 

 the size of the 1/57. 6-scale model, resulting in about one-fith of the 

 Reynolds number, was employed. 



Review of the wave-induced force measurements with the 

 1/57. 6-scale model indicated that the variations in forces correspond 

 reasonably with the variations in motions over the forward and middle 

 part of the island but do not exhibit a continuous increase toward the 

 trailing edge, which was felt to be called for to explain the tail- wagg- 

 ing. Since a suitable explanation in terms of elastic interaction is not 

 presently available, it was decided to re -test the articulated 6x35 

 array in the 75'x75'x4.5' deep wave test tank (No. 2) in order to as- 

 sure freedom from tank sidewall influences. 



An approach to an analytical description of the deck motion, 

 taking deck elasticity into account, is discussed but an explanation of 

 the tail- wagging does not appear to follow from this analysis. 



Plans for a comprehensive test program to determine the ef- 

 fects of variations in parameters such as float spacing and shape, 

 wave frequency and height, deck rigidity and number of floats on the 

 motions of the platform are described. 



Models 

 Articulated Model 



A preliminary design for float-attenuator shape was developed 

 on the basis of a simplified hydrodynamic analysis and a particular 

 limiting vertical motion criterion. The selected float had a relatively 

 shallow draft and large diameter near the lower end. No interaction 

 effect was anticipated in selecting the float shape. A scale ratio of 

 1/57.6 was selected ; the full-size float has 6-ft diameter at the water- 

 line while the model was fabricated with 1 l/ 4 ~in O.D. plastic tubing. 



838 



