The wave-induced forces on the model pipe section were measured by 

 a wave force meter designed and built by Al-Kazily (1972) . A few modi- 

 fications were made to make the instrument more suitable for this inves- 

 tigation. The same transducer unit was used in all of the experiments, 

 but fittings of different sizes were made to accommodate test cylinders 

 of various diameters. 



The force transducer consists of a strain bar mounted between two 

 supports. The model pipe section is mounted to the strain bar in such 

 a way that forces on the pipe induce bending stresses on the strain bar. 

 Tliese forces are measured by four strain gages mounted to the strain 

 bar at sections of maximum strain, with two gages in compression and the 

 other two in tension. The strain gages are wired in a IVheatstone bridge, 

 which is connected to a carrier amplifier which amplifies the output from 

 the strain gages. The signal is then recorded on a strip-chart recorder. 



The original strain gages were Bean-type BAB-13-125DD-120S, and were 

 mounted to the steel strain bar with EPY-150 two-part epox , and then 

 coated with Dow Coming Silastic RTV silicon rubber for waterproofing. 

 Shortly after the beginning of the three-dimensional tests, problems 

 were encountered in the operation of the transducer. The^e problems 

 were caused by the deterioration of the original strain gage adhesive 

 and coating, so new strain gages were installed on the transducer unit. 

 The new gages were Micromeasurement-type EA-06-125AD-120, bonded to the 

 strain bar with Micromeasurement M-Bond 610 two-part strain gage adhesive, 

 and then coated with Micromeasurement M-Coat D and M-Coat G for water- 

 proofing protection. About halfway through the three-dimensional tests, 

 further problems were encountered in the operation of the transducer unit, 

 probably due to water leakage into the waterproof coating. There was 

 also evidence of corrosion on the steel strain bar, so it was decided 

 to build a new force transducer using a stainless-steel strain bar to 

 minimize corrosion, and encapsulated strain gages to minimize problems 

 with water leakage. The new strain gages were Micromeasurement-type 

 CEA-06-125UW-120. The same strain gage adhesive and waterproof coatings 

 were used, with Micromeasurement M-Coat B along the lead wires to mini- 

 mize the change of water "wicking" along the lead wires to the inside 

 of the coating materials. 



The transducer mounting arrangement was different for the two- 

 dimensional and three-dimensional experiments. The test cylinder and 

 transducer unit for the two-dimensional tests were mounted between two 

 support brackets on each side of the 1-foot wave channel. For the 

 three-dimensional experiments, the test cylinder and transducer unit 

 were mounted between two long dummy pipe sections, which were in turn 

 mounted to a steel base. The force meter and mounting arrangement is 

 shown in Figures 9 and 10 for the two-dimensional tests, and in Figures 

 11 to 15 for the three-dimensional tests. 



A parallel -wire resistance-type wave gage was used to record the waves 

 passing over the model pipe section. The gage was mounted directly over 



37 



