Paulling 



From Fig. 3 it is seen that instrumentation was provided 

 for measuring model motions, tension variations in the mooring legs, 

 and incident wave amplitude. The surge motion was sensed and con- 

 verted to an electrical signal by a miniature low torque potentiometer 

 driven by the model through a string and pulley arrangement. Yaw 

 was sensed by a rate gyroscope mounted on the model, the output 

 of which was integrated electronically to give the yaw displacement. 

 Tension meters were installed in each mooring leg. These consisted 

 of small proving rings fabricated from seamless stainless steel 

 tubing and mounted with etched foil strain gages. Four gages on 

 each ring were connected to form a four-arm Weatstone bridge, the 

 output of which is proportional to the applied force. The bridge was 

 balanced initially to bias out the initial static tension. Therefore 

 only the time dependent variations are recorded. 



The outputs of these force and motion transducers, as well 

 as the output of a resistance wire wave meter, were recorded, using 

 a multichannel oscillograph. During experiments in random waves, 

 a simiultaneous recording was made of the same quantities in digital 

 form on magnetic tape for processing by electronic computer. 



Single Cylinder Experiments 



The first group of experiments were conducted using a single 

 circular cylindrical model having hemispherical ends and moored 

 by two legs, one at each end. Only the incident regular waves and 

 tension variations were recorded. The model dimensions and test 

 conditions were: 



Length 3,44 ft 



Diameter 0, 28 2 ft 



Depth of model 0, 792 f t = 2,8 X dia. 



Weight 6,5 lbs 



Water depth 4,17 ft 



For this configuration, the computed tension variations in the 

 mooring legs will be equal to the hydrodynamic forces expressed in 

 Eq, (7), i,e, , there will be no linear coupling between the tension 

 variations and the motions of the model. These results, for regular 

 waves of 1.45 second period, and several different amplitudes striking 

 the model at , 45, and 90 degrees, are shown in Fig, 4. Experimen- 

 tal points show the amplitudes of force variations which were measured 

 in the two mooring legs. The theoretical lines have been determined 

 by the method described here and by Havelock [ 1954] . Havelock's 

 procedure gives the wave force and moment on a spheroid having its 

 long axis horizontal, moving beneath a train of regular waves. For 

 the present computation the approximating spheroid was assumed to 

 have the same length and diameter as the cylinder model. The 

 dashed curve labelled "present work" was computed by Eq. (7) 

 assuming the infinite fluid value of unity for the added mass coefficient 



1102 



