Analyses of Multiple-Float-Supported Platforms in Waves 



fat lower parts of the floats may result in severe interaction influence 

 on the drag-type force component but plates may be attached to the 

 slender upper part of the float without important interaction. When the 

 spacing of floats was five times the water-plane diameter, no measur- 

 able interaction influence was observed. 



Some results for vertical (heave) force on the full float of fig- 

 ure 36d, both in the middle of the 25 float array and isolated, are 

 exhibited in Figure 3 7, which shows the increase in force at high fre- 

 quency. The introduction of a ten-foot diameter damping plate at the 

 junction of the conical transition piece and the upper float produced 

 only a minor increase in lift force at high frequency. Rather similar 

 results were obtained with the deeper, more slender float of Pig. 36c; 

 but when damping plates having 13. 5 -ft diameter were fitted to the 

 lower end of the floats, the wave forces were dramatically increased, 

 evidently because of a drag-type component in phase with the vertical 

 wave velocity. The forces on the interior float elements of the array 

 were found to be virtually the same as one another while the floats in 

 the forward row (near the wave generator) and in the aft row were 

 close to the results for isolated floats. 



Horizontal forces measured on the full float of Figure 3 6d, 

 isolated and in array, are shown in Figure 39. It is found (somewhat 

 surprisingly) that little or no interaction occurs for this component of 

 force and the floats in array experience essentially the same side force 

 as the isolated floats. 



Large -Array Investigations 



A freely- floating model of a substantial segment of a Floating 

 Expandable Base, having 35 rows of 6 floats each like those of Fig.36d, 

 with rows connected to each other by parallel motion linkages which 

 are intended to permit freedom to heave while restraining against 

 pitch motions, was tested in regular waves in Davidson Laboratory 

 Tank No. 3, which is 300-ft long x 12-ft wide x 6-ft deep. 



A particular, unexpected result of this model test program 

 with the 35 by 6 array of floats (which have a nominal scale ratio of 

 1/57.6) was a "tail-wagging" phenomena where the heave motions in- 

 creased from front to rear of model. This is an especially significant 

 feature of the performance of arrays of large numbers of such floats. 

 A variety of experiments have been carried out in order to study cer- 

 tain aspects of the hydrodynamic interaction observed in the motions 

 response tests of the 35 by 6 array of floats. These include wave force 



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