50 



higher order solutions. 



3.5 Laboratory Measurements 



The following results use laboratory data collected by Murray Townsend and 

 John Fenton at the Australian Maritime Engineering Cooperative Research Center at 

 Monash University, Melbourne, Australia in June, 1996. The dynamic pressure, fluid 

 velocities and water surface were measured at the same horizontal location along the 

 flume; the pressure at a variety of elevations, and the horizontal and vertical velocities 

 at an elevation of -0.8 meters, with the origin at the mean water level. The still water 

 level was 1.55 meters, with the data sampled at 60 Hz. 



The wave flume is 52m long by 2.2m wide with two working sections 4m and 2.5m 

 long connected by a ramp. A false floor had been built into the shallower working 

 section to bring the depth to 1.55m. At one end of the flume is a hydraulically oper- 

 ated bottom hinged wave paddle and at the other a beach that absorbs a minimum 

 of 96% of wave energy across the range of operating frequencies. The measurements 

 were taken approximately 22m from the beach end of the flume. The beach length is 

 6m. 



The wave surface was measured with a capacitance wave probe with typical cali- 

 brations providing a correlation coefficient R^ greater than 0.999. The pressure was 

 measured with Druck PDCR35/D transducers located in the flume near the center 

 of a long (2.5m long by 2m high) plywood board aligned with the direction of wave 

 propagation. The measurement face of the probe was flush with the board surface 

 to eliminate local flow separation. The R^ values from calibrations were in all cases 

 above 0.999. Fluid velocities were measured with a factory calibrated Alec electronics 

 ACM250-A electromagnetic current meter which is capable of velocity measurements 

 in two dimensions. 



One of the difficulties encountered with pressure measurements is the question 

 of what has actually been measured. If the transducer itself is absolutely accurate, 

 the pressure recorded will be the actual pressure at the location of the transducer. 

 Unfortunately, the presence of the instrument is likely to alter the flow in its vicinity, 



