Kim and Mercier 



The transfer functions previously presented by Mercier [5] 

 have now been used to obtain spectral information on performance in 

 irregular waves in accordance with Equation (7). Carpet plots showing 

 significant (average of the one-third highest) heave and pitch respons- 

 es as a function of significant wave height divided by (displaced vol- 

 ume)V3 and other parameters are shown in Figures 9 to 13. The de- 

 vice of carpet-plotting, which is common in aeronautical research 

 and testing, permits cross plots to be presented on a single sheet of 

 paper, and greatly facilitates performance comparisons and exhibit- 

 ing dependencies of results on various parameters. 



The effect of damping plate size on heave and pitch for a cru- 

 ciform array of floats (test runs 002,012 and 018, Table 1) are shown 

 in Figure 9. The same information is given in Figure 10 for platforms 

 with a different distribution of displacement among the "hull" and 

 "wing" floats ; hull float diam/wing float diam = 1.25 (rather than 1.5 

 for the results shown in Figure 9) (test runs 060,058 and 062, Table 

 1). In both cases, larger damping plates reduce heave response but 

 increase pitch response. For three float configurations, having some- 

 what more slender floats, the corresponding results are given in 

 Figure 11 (test runs 074,091, and 087) ; the influence on heave mo- 

 tions is similar but for pitching motions with low relative sea condi- 

 tions, HwJ y / < 0. 7 , a suitable selection of damping plate size ap- 

 pears to lead to minimum pitch motions. 



The effect of float slenderness on heave motions is exhibited in 

 Pig. 12 for the cruciform (test runs 02,047 and 032) and triangular 

 (test runs 074,096 and 083) float array models, both with damping 

 plate diam/float diam =1.6. Since the pitch response (but not the heave 

 response) is strongly dependent on metacentric height, and since the 

 tests with variations of float slenderness were not executed with uni- 

 form values of GM, the influence of float slenderness alone on pitch 

 motions is not presented. It is interesting to note the distinctly differ- 

 ent trends of heave response as a function of float draft-to-diameter 

 ratio j for the four-float configuration it appears that a maximum oc- 

 curs for T/D-p between 2 and 2.5, while for the three-float array a 

 minimum exists around T/Dj- = 5. These different behaviors may be 

 due to the different arrangements of floatation (three floats of four) as 

 well as the different ranges of slendernesses investigated. 



The influence of metacentric height on heave and pitch response 

 is shown in Fig. 13 for a four-float configuration (test runs 002,005 and 

 006). As was stated above, the heave motion is not importantly affect- 

 ed by GM. On the other hand, the pitching motion is greatly affected 

 by stability with excessively low metacentric height giving rise to large 

 angular motions which are not characteristic of well-designed float - 

 supported-platforms . 



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