bottom was 15.84°. The most reliable information on these data is for a value 

 of kd greater than approximately 0.45; i.e., for wave period somewhat less 

 than about 13 seconds. The dominant feature of these data is the extreme 

 mooring line forces experienced in the region of 12-second waves (kd = 0.5) 

 with the forces dropping significantly for shorter wave periods. The maximum 

 mooring force for the 10-foot wave is about 160,000 pounds, which is approach- 

 ing the breaking strength for this particular line. For small wave heights 

 from 2 to 6 feet, the mooring force appears roughly linear with wave height, 

 although for larger waves the nonlinear ity becomes quite apparent. 



(3) Effect of Mooring Location on Transmission Coefficient. The var- 

 iation of the transmission coefficient is presented as a function of kd for 

 three mooring arrangements (Fig. 59). There appears to be some fundamental 

 difference in the transmission coefficient for cases A and C, shown in the 

 figure, compared to case B for the region of kd between 0.7 and 1.0. In the 

 region of interest to both Navy and Corps operations (wave periods about 7 

 seconds or values of kd about 0.9), the transmission coefficient varies from 

 approximately 0.35 to 0.45, depending on the mooring system. Raichlen (1978) 

 did not entirely expect such differences; he recommended that, since the curve 

 of case B was obtained by interpolation and cases A and C were actual data, 

 more confidence could be placed on the data points than on the interpolated 

 curve. 



(4) Effect of Mooring Location on Mooring Forces . The effects of 

 variation of the mooring position on the mooring forces, as a function of kd, 

 are presented in Figure 60. Except for experimental scatter, there appears to 

 be little such effect for values of kd greater than approximately 0.5. 

 There is a large deviation of the data of cases A and C from those of case B 

 for values less than 0.5; it is probable that the curve for case B may be in 

 error for this region. In general, the mooring force is largest for long 

 waves and decreases with an increase in the depth-to-wavelength ratio. This 

 is reasonable considering the variation in the velocity distribution under a 

 wave with increasing kd. For small kd values, the pressures will be 

 positive along one side of the barge; for large values of kd, the pressure 

 would reverse sign along one side of the barge, perhaps leading to a smaller 

 total force and moment. 



(5) Effect of Bow Angle on Transmission Coefficient . From prelimi- 

 nary experiments, it was concluded that a part of the wave transmission past 

 the barge was due to overtopping of the structure by some waves. To increase 

 the freeboard and minimize the effect of overtopping, Raichlen (1978) added a 

 perpendicular wall extension to the seaward face of the inclined pontoon. He 

 termed this vertical distance the "bow angle," although in reality there is no 

 angle associated with this distance. For the two cases, the height of the 

 extension was 2.5 feet in one set and 5.0 feet in another set, both conducted 

 with 6-foot-high waves; the corresponding attenuation results are presented in 

 Figure 61, as well as for the case of zero bow angle. Also, for the case of 

 no bow angle, two mooring line restraints (a nonlinear spring and an inexten- 

 sible mooring line) were evaluated. Generally, it appeared that the transmis- 

 sion was largest for the condition of greatest restraint. For the case with 

 the dynamic restraint, the transmission was the smallest when the bow angle 

 was the largest. However, the effect of the bow angle was smaller than 

 expected. In the region near a value of kd = 0.9, the bow angle reduces the 

 transmission from approximately 0.47 to 0.35. Significant transmission must 



102 



