CETN IV-19
March 1999
through a system of manifolds in the bay that may be adjusted for one, two, or three bay
channels or a uniform flow across the bay. Water is either released (flood flow) or taken from
(ebb flow) the ocean headbay to complete the circulation energized by the pumps located in the
right center region of Figure 1.
An 80-ft-long, unidirectional wave generator (see Figure 1) installed in the ocean produces either
irregular or monochromatic waves. Unscaled wave periods can be varied from 0.5 to about
3 sec, and long-crested wave heights to 10 cm can be generated (at the generator location, before
shoaling and refraction). Incident wave direction can be varied for specific experiments by
moving the generator to different locations.
INSTRUMENTATION AND CALIBRATION:
Wave height and period data are collected on electrical capacitance wave gauges that are
calibrated daily with a computer-controlled procedure incorporating a least-square fit of
measurements at 11 steps. This technique averages 21 voltage samples per gauge and minimizes
distortions introduced by slack in the gear drives and hysteresis in the sensors. Typical
calibration errors are less than 1 percent of full scale for the capacitance wave gauges. Wave
signal generation and data acquisition are controlled by computer. Wave data are evaluated with
a special analysis package for the frequency and time domains.
side-looking probe that is oriented to collect two components of velocity in a horizontal plane.
This model velocimeter is designed to work in the relatively shallow waters of an inlet. Samples
are collected at 10 Hz, though the instrument makes 250 pings per second and averages for each
output sample. Accuracy is 0.5 percent of the measured velocity, with resolution of 0.1
mm/sec and threshold of 0.1 cm/sec. The probe samples a 0.25-cm 3 volume located 5 cm from
the sensor heads. A gauge rack holds both the wave and current sensors, which can be moved to
collect data without interference in the processes to be measured.
Water-surface elevations are measured with a "bubbler system," where small-diameter plastic
tubing is mounted and placed at a given elevation below the water level at various locations
throughout the inlet region. A constant pressure is applied, and air is bubbled out of the tubes at
a bubble rate of 3 Hz. Pressures are measured with high precision, differential pressure
transducers and converted to elevation (0.015 cm). The pressures are sampled at a rate of 1 Hz
and include sampling of a calibration array of bubble tubes set at different elevations in a still-
water pit (located in the model facility).
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