Measurement of waves

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granted by MTS Systems Corp.)

Measurement of waves

The wave gauges can be accurately positioned at any x-y location within the

testing region of the facility. The cross-shore position of the wave gauges can be

adjusted at the beginning of the experiment by manually relocating the gauges

along the length of the bridge. Figure 40 shows the wave gauges evenly

distributed every 1.5 m along the bridge, so that 10 wave gauges cover a total

range of 13.5 m in the cross-shore direction. However, rather than evenly

distributing the wave gauges, it may be important to position a few gauges more

densely in a certain region to provide sufficient cross-shore resolution to measure

changes in the wave height gradient in response to the changing moveable-bed

beach profile. Nonetheless, 10 wave gauges located along the length of the

bridge have provided sufficient cross-shore resolution to accurately document the

cross-shore distribution of wave height and mean water surface elevation.

During an experiment, waves are measured simultaneously with the 14 wave

gauges at a frequency of 20 Hz to provide sufficient temporal resolution to

accurately measure the profile shape of individual waves. For most wave

conditions generated in the LSTF, the shortest wave period in the irregular wave

spectrum is approximately 0.5 sec. Therefore, a sampling frequency of 20 Hz

provides 10 data points to delineate the profile shape of these shorter period

waves.

Chapter 8

Sensor Calibration, Measurement, and Data Analysis