Acoustic Velocity Meter Research Articles

Field measurements of shear stress and friction in the surf zone

AbstractMeasurements of near‐bed shear stress were undertaken in the shallow subtidal zone at Durras Beach, NSW, Australia using a sideways‐looking acoustic velocity meter installed within the wave boundary layer. The wave climate was swell‐dominated and wave conditions comprised shoaling and breaking waves as well as surf bores. The sediment at the field site was medium‐grained sand, and observations of bedform geometry were conducted using a pencilbeam‐sonar system. Using frequency‐filtering techniques, the measured stresses were partitioned into terms representing turbulent (Reynolds) stress, stresses due to gravity and infragravity‐scale oscillatory motions, and wave‐turbulence‐mean current cross‐terms. Gravity wave‐orbital scale motions contributed the largest fraction of the stresses, comprising 24% on average, followed by long‐wave advection of vertical orbital motion (16%). The presence of wave orbital‐scale motions near or at the water/sediment interface was likely due to the porous nature of the seabed, facilitating interfacial flow. Shear stresses did not scale with bed roughness but exhibited a linear relationship with the relative wave height. This indicates that for the experimental conditions, surf zone processes overwhelmed bed roughness effects on shear stress and friction. Calculations of the wave friction factor, fw, showed that in a natural surf zone, this was a factor 3–4 larger than conventional predictions. © 2020 John Wiley & Sons, Ltd.

Dynamic Analysis of the Acoustic Velocity Profile Observation Underwater Glider

Underwater gliders carried acoustic velocity meters can realize ocean profile observations of the acoustic velocity for long duration and large scale. This paper mainly studies the kinematics and hydrodynamics of the Slocum underwater glider carrying a acoustic velocity meter MINOSX with length 565mm and diameter 76mm. Thus, theory reference for optimal design parameters of the underwater glider is proposed. By establishing the kinematic equations and giving some related parameters, variations with time of the steady-state gliding velocity, pitch angle, gliding path and attack angle are simulated by using Matlab software; The simulation calculations of the hydro-drag and lift are completed by using Fluent software. Finally, this paper summarizes the dynamic characteristics in steady state of the underwater glider in longitudinal plane.

TRANSVERSE PROPAGATION CHARACTERISTICS OF SOUND AND MEASUREMENT OF CROSS-SECTIONAL AVERAGE VELOCITY IN TIDAL RIVER WITH A NEXT-GENERATION ACOUSTIC VELOCITY METER

An acoustic velocity meter (AVM) has been developed to measure river discharge continuously. The AVM has breakthroughs as follows : 1) accurate time with GPS clock signals, 2) high signalto-noise ratio with tenth order M-sequence, 3) thrifty power consumption, reduction in size and weight. The AVM installed at the Ohtagawa diversion channel, where the water level and salinity change significantly, successfully measured the cross-sectional average velocity and discharge for a spring tide. In addition, the intrusion of saltwater was detected from the sound speed data of the AVM. The cross-sectional average velocity and discharge give close agreement with those deduced from an acoustic Doppler current profiler.

Measurement of Freshwater Discharge in an Estuary by Acoustic Tomography

The freshwater discharge is an important hydrological quantity on coastal planning, management, and environment conservation. In order to monitor the discharge in real time, an acoustic velocity meter (AVM) has been developed and deployed at a tidal estuary. The AVM installed at a shallow tidal river, where water depth and salinity change significantly, successfully measured the cross-sectional average velocity and discharge in a spring tide. In addition, the mean salinity was measured from the sound speed data of the AVM. The freshwater discharge was deduced from the discharge and salinity data.

An acoustic current velocity meter for position instruments and probes

This paper considers the theoretical grounds for designing a new multi-component current velocity meter with a comprehensive beam pattern and minimum impact of structural elements on the measurement data. The effect of technological error on the sensor's ability to transmit acoustic signals is assessed. Information about the practical realization of the acoustic current velocity meter is provided, together with the results of its metrological tests.

Effect of Gradients on Acoustic Velocity Meter

The refraction of an acoustic path due to salinity and temperature gradients is usually neglected when making measurements with an acoustic velocity meter. This study shows that refraction of the path at a specific site in the Sacramento-San Joaquin River Delta causes multiple reflections off the water surface and the riverbed. Due to these extreme deviations, shorter acoustic paths are required. An error estimation is performed to evaluate the effects of refraction over a 400 m path length.