Kim and Mevoiev 



motions are given in Figure 43. The side forces are seen to be remark- 

 ably lower than the results without the hinge. The amount of angular 

 motion, which is greatest for low frequencies of course, is about 3° 

 per foot of wave elevation for a frequency of 0.0 7 Hertz. The resi- 

 lient model exhibits a resonance-like behavior at a frequency of about 

 0. 12 Hertz, somewhat higher than the calculated value of 0. 11 hertz, 

 as evidenced in both side force and pitch motions. This relatively 

 modest amplification of response occurs at a frequency at which signif- 

 icant wave energy exists and is consequently considered disadvantage- 

 ous. 



A variety of other tests also were carried out, using several of 

 these floats models and with various damping plates fitted. Besides 

 wave tests, forced heave and surge oscillation tests were carried out. 

 Results of these tests have not yet been analyzed in detail but are stor- 

 ed on magnetic tape for future processing. 



INTERACTION EFFECT TESTS 



Preliminary Wave Tests 



Although in previous experience with floating platforms such 

 as for drill rigs, hydrodynamic interaction between adjacent floats 

 was found to be negligible, the large numbers of floats planned for the 

 Floating Expandable Base are so closely packed in relation to their 

 size that it was considered vital to investigate the interaction between 

 floats at an early stage of this program. 



Wave-induced forces were measured on individual floats in an 

 array consisting of five rows of five floats each. The force-measuring 

 balance could be moved so that forces on any one of the floats could be 

 measured, as desired. The spacing of the floats was either three 

 times the water-plane diameter or five times. Two sets of floats, 

 shown in Figures 36c and 3 6d, having different proportions and drafts, 

 were tested with and without damping plates. 



Certain general findings of the tests can be given : the side 

 forces and pitching moments acting on the floats due to waves are prac> 

 tically un-influenced by proximity ; the vertical wave-induced force is 

 modified by an apparent increase in an added-mass type force com- 

 ponent which is significant for higher frequencies and accounts for 

 about a 30% increase above the isolated float results for the fatter of 

 the two floats studied. Further, damping plates attached in way of the 



836 



