3 Experiment Procedures and 

 Data Analysis 



This chapter provides information on data collection and analysis. Some 

 selected sample plots of data are shown. 



Sequence of Events and Data Sampling 



Following daily calibration of the wave gauges (Chapter 2), the ebb flow was 

 first set in the proper range using a flowmeter installed in the pipeline downstream 

 of the pump location. The flow setting then was refined by bringing the current to 

 its proper level by using a reference current meter in the inlet channel. With a 

 stable flow in the chaimel, current velocities were collected at all locations for 

 about 70 s (700 data samples), then the wave generator was turned on and botii 

 current and wave data were collected. The wave generator was operated for 

 1,020 s. Wave gauge sampling rate was 20 Hz, so 20,400 water elevation data 

 points were collected at each gauge and 10,200 velocity data samples (10-Hz 

 sampling rate) for each sensor were collected during a run. 



Figure 4 compares target and measured spectra at a wave gauge location in 

 front of the wave generator. Figure 5 is a snapshot of waves over a portion of an 

 experiment at some of the gauges, first for a waves-only experiment test (upper 

 two panels), and then a wave-current experiment (lower 2 panels). 



Data Analysis 



The velocity data were analyzed in the time domain. The pre-wave velocity 

 record was averaged over the initial 7(X) samples. Velocity records after the wave 

 generator was in operation were examined individually to determine when a 

 steady-state average was reached and a long-as-possible record was averaged, 

 usually on the order of 8,000 to 9,000 samples (up to 900 s of data). Figure 6 

 shows the ciurents at stations for a particular run. Initially, there is steady state 

 flow without waves, then once wave activity has begun, there is a transitory 

 period for the adjustment to a near steady state with oscillations superimposed due 

 to wave orbital velocities. 



Chapter 3 Experiment Procedures and Data Analysis 



