sponse of the gauges in regular waves. The capacitance gauges were placed 

 side by side in the wave tank with commercial resistance wire wave gauges of 

 known reliability. In all cases, the capacitance gauges performed identically 

 to the commercial resistance wave gauges in nonbreaking waves. The gauges 

 were not tested in breaking waves where the foaming water surface with 

 entrained air bubbles might affect the gauge response. Static calibrations were 

 also performed at the Naval Academy in wet and saturated sand. It was con- 

 firmed that the gauges could record the wet sand/water surface if the sand was 

 fully saturated. Some degradation of the response was found if the sand was 

 not fully saturated. 



Data collection and storage were performed on a personal computer (PC) 

 that was separate from the main Oregon State University, O. H. Hinsdale 

 Wave Research Laboratory (WRL) data collection system, the system used for 

 the other hydrodynamic measurements. Lack of data channels on the main 

 SUPERTANK data collection system prevented use of this common system for 

 the swash data. The PC-based system used a MetraByte 12-bit, 16-channel 

 Analog-to-Digital interface board. Data sampling was controlled using the 

 LabTech Notebook data acquisition software package. 



Experiment Procedures 



Calibration 



Capacitance wave gauges were calibrated once each week, but additional 

 gauge calibrations were performed more frequently if a gauge was reposi- 

 tioned or if the length of the sensing wires was changed. Gauge calibration 

 differed from that used for the resistance wave gauges because it was too 

 time-consuming to frequently raise the channel water level high enough to 

 activate the capacitance gauges that were near the runup limit. Instead, a 

 separate calibration tank was built and placed outside the wave tank. The 

 swash gauges could be removed from the wave channel and placed in the 

 calibration tank without disconnecting the power supply or signal cables. To 

 facilitate calibration, the stainless steel support rods mat held the gauge elec- 

 tronics housing and sensing wire were pre-drilled with 1/8-in.- (3.2-mm-) 

 diameter holes spaced every 2 in. (5.08 cm). This support rod could then be 

 moved up and down in the calibration tank in 2-in. (5.08-cm) intervals over 

 the entire length of the sensing wire. The gauges were found to be linear 

 over almost the entire length of the sensing wire. 



Calibration of the capacitance gauges was accomplished by adjusting the 

 gain or sensitivity potentiometer of the power supply /signal conditioning unit 

 to give an output of 0.1 V/in. (0.04 V/cm) change in water level. This value 

 was adopted as a standard calibration value for all gauges. Based on the rated 

 resolution of the data acquisition board, water surface measurements could in 

 theory have been resolved to the nearest 1/400 of an inch (0.006 cm), 

 although data storage was limited to the nearest 1/100 of an inch (0.025 cm). 



Chapter 4 SUPERTANK Swash Measurements 



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