3. Procedure for Three-Dimensional Experiments . 



a. Calibration. The wave gage and force meter were calibrated 

 before each set of experimental runs. The wave gage was calibrated in 

 the same manner as the two-dimensional tests, but 0.1-foot (3.05 centi- 

 meters) increments were used rather than 0.05-foot increments, since 

 larger waves were used in these experiments. 



The force transducer was calibrated in the upward direction in the 

 same manner as the two-dimensional tests, by hanging weights over a 

 pulley to a string attached to the pipe test section. However, because 

 the three-dimensional model was mounted to a base with a small bottom 

 clearance, it was impossible to calibrate the transducer in the down- 

 ward direction by using a system of pulleys, since there was no room 

 for a pulley between the pipe section and the base to which it was 

 mounted. Rather, the force meter was calibrated in the downward direc- 

 tion by placing the weights directly on top of the center of the sub- 

 merged test section and using the submerged weight of the weights in 

 calculating the calibration curve. Weight increments of 50 grams were 

 used in calibrating the transducer. The calibration method is shown in 

 Figure 20. 



b. Procedure . An overhead crane was used to lower the pipeline 

 model and base into the wave tank. The assembly was first submerged to 

 a depth of about llg feet (45.7 centimeters). The model was tilted at 

 both ends to remove all air bubbles from the system, and the ends of 

 the dummy pipe sections were stoppered to prevent waterflow through the 

 pipeline model. The bottom clearance between the base and the pipe 

 model was adjusted by placing spacers on the support rods between the 

 base and the dummy pipe sections, and then tightening the nuts on the 

 support rods above the dummy pipe sections. The test section was tnen 

 centered and adjusted carefully to the exact bottom clearance desired 

 with the aid of 10 adjusting screws. The calibration string was 

 attached to the test section, and the assembly was lowered to the 

 bottom of the tank. 



The calibration string and pulley system was alined directly over 

 the center of the test section with a plumb bob, and the pulley sup- 

 ports were then clamped to the sides of the wave tank. The transducer 

 was first calibrated in the upward direction, after which the calibra- 

 tion string was removed, and the transducer was calibrated in the down- 

 ward direction, as described above. 



The pipeline model was positioned at the desired angle of orienta- 

 tion on the tank bottom by lining up one of the long edges of the model 

 base parallel to the correct line marked on the bottom of the wave tank. 

 Lines were marked on the tank bottom in 15° increments from 0° to 75°, 

 where 0° corresponds to a pipeline parallel to the approaching wave 

 crests. After the model was calibrated and placed in position, the 

 wave gage was lined up directly over the center of the test section with 



