Kim and Mevciev 



motions where linearity of forces and moments is in question. Five to 

 ten complete cycles of the wave forms were "averaged" in determining 

 the Fourier coefficients except when the test period was very long, 

 when no less than three cycles were used. 



Forces oscillation tests were carried out by adjusting the crank 

 offsets of the several motion-producing linkages so that either pure 

 heave, surge, or pitch were produced. Yaw motion was not tested. A 

 cosine potentiometer was coupled to the drive shaft of the mechanism. 

 A constant (battery) voltage was applied to this potentiometer whose 

 output was consequently proportional to the cosine of the shaft rotation 

 angle and thus was suitable for use as a phase reference for the motion. 



For some tests, both in waves and with forced oscillations, a 

 hinge was used to permit the lower end of the attenuator to oscillate 

 like a pendulum under the action of waves. In this way, the periodic 

 side loads due to the waves are not completely transmitted to the float- 

 ing base connecting structure by way of bending moments in the float 

 but are rather absorbed by the pendulum-like motion of the attenuator. 

 This reduces the strength requirements of the inflated float and, con- 

 sequently, weight and cost. 



A rotary variable differential transducer was connected to the 

 attenuator by a system of strings to permit the measurement of ang- 

 ular motion. 



Scaling 



The periodic hydrodynamic forces and moments are assumed 

 to follow Froude's scaling law. Thus the full-size force and moment 

 are related to model quantities by 



F. .. . ■ F A . x " ful1 size x V 3 (44) 



full size model p , , 



model 



tut twt Pfu11 size x» 4 iak\ 



M . - M x x V (45) 



full size model , , 



naaodel 



where 



F = Force 



M = Moment 



P = F luid density 



X = Scale ratio 



834 



