Wave Gauge Measurements Research Articles

Preliminary Performance Assessment of the Wave Parameter Retrieval Algorithm from the Average Reflected Pulse

To obtain new information about surface waves, it is proposed to use an underwater acoustic wave gauge, and an assessment of its effectiveness can be performed using a numerical simulation and field experiment. A new device, an underwater acoustic wave gauge named “Kalmar”, was developed by the Institute of Applied Physics of the Russian Academy of Sciences for long-term, all-weather monitoring of wind waves. The instrument uses ultrasound to probe the water surface from underwater and can be used to verify remote sensing data. In this work, the capabilities of the device are tested and compared with ADCP data. Two independent methods for processing underwater acoustic wave gauge data are discussed and compared. One of them is completely new for acoustic measurements and is based on the analysis of the shape of the reflected acoustic pulse averaged over space and time. The other allows processing individual reflected pulses and calculating the time implementation of the distance to the water surface. It is shown that two independent methods of significant wave height retrieval from the acoustic wave gauge measurements are highly correlated. The “Kalmar” acoustic wave gauge and the RDI WH-600 acoustic Doppler current profiler operated simultaneously at the test site in Gelendzhik from 1 February to 10 February 2020. The significant wave heights measured by the two instruments are in good agreement.

Estimating ocean wave directional spreading using wave following buoys: a comparison of experimental buoy and gauge data

Directional spreading of ocean waves plays an important role in various aspects of ocean engineering, such as wave-induced loads, nonlinear wave evolution, and wave breaking. Wave following buoys, which are widely deployed across the oceans, offer the potential to measure directional wave properties. To assess the accuracy of directional spreading estimates made using buoy measurements, we compared estimates based on experimentally obtained buoy and wave gauge measurements, first presented in McAllister and van den Bremer (J Phys Oceanogr 50:399–414, 2020) Buoy and gauge measurements were recorded at the same locations and in identical sea states, allowing for a like-for-like comparison. We examine experiments with both following (unimodal in direction) and crossing (bimodal in direction) sea states. In addition to this, we use synthetic wave data to investigate the effects of wave generation and nonlinearity on spreading estimates. Our results show that while directional estimates produced using buoy measurements are reasonably accurate in following sea states, they struggle to identify distinct directional peaks in crossing sea states. We find that spreading estimates made using buoy measurements tend to underestimate the degree of directional spreading by approximately 9-14% in following sea states, which is most apparent in narrowly spread conditions.

Modulation of Wind-Wave Breaking by Long Surface Waves

This paper reports the results of field measurements of wave breaking modulations by dominant surface waves, taken from the Black Sea research platform at wind speeds ranging from 10 to 20 m/s. Wave breaking events were detected by video recordings of the sea surface synchronized and collocated with the wave gauge measurements. As observed, the main contribution to the fraction of the sea surface covered by whitecaps comes from the breaking of short gravity waves, with phase velocities exceeding 1.25 m/s. Averaging of the wave breaking over the same phases of the dominant long surface waves (LWs, with wavelengths in the range from 32 to 69 m) revealed strong modulation of whitecaps. Wave breaking occurs mainly on the crests of LWs and disappears in their troughs. Data analysis in terms of the modulation transfer function (MTF) shows that the magnitude of the MTF is about 20, it is weakly wind-dependent, and the maximum of whitecapping is windward-shifted from the LW-crest by 15 deg. A simple model of whitecaps modulations by the long waves is suggested. This model is in quantitative agreement with the measurements and correctly reproduces the modulations’ magnitude, phase, and non-sinusoidal shape.

Fully dispersive Boussinesq models with uneven bathymetry

Three weakly nonlinear but fully dispersive Whitham–Boussinesq systems for uneven bathymetry are studied. The derivation and discretization of one system is presented. The numerical solutions of all three are compared with wave gauge measurements from a series of laboratory experiments conducted by Dingemans (Comparison of computations with Boussinesq-like models and laboratory measurements. Delft Hydraulics memo H168412, 1994). The results show that although the models are mathematically similar, their accuracy varies dramatically.

Experimental Study of Turbulence and Entrained Air Characteristics in a Plunging Breaking Solitary Wave

The entrained air and turbulence characteristics under a breaking solitary wave on a 1:20 sloping beach are investigated through laboratory measurement. Free surface elevation is obtained from wave gauge measurements. Wave breaking process is captured in detail by a high-speed camera. The bubble image velocimetry (BIV) is used to measure the velocity and the fiber optic reflectometer (FOR) is used to capture instantaneous void fraction in the aerated region. The mean void fraction and velocities in the aerated region are obtained by ensemble averaging over 22 repetitions. Results show that the maximum mean void fraction is 0.6 in the collapsing cavity region and is 0.35 in the splash up region. The time series of the mean void fraction has good synchronization with the instantaneous images taken by high-speed camera. The maximum horizontal velocity occurs in the splash up region and reaches 1.17C shortly after the plunging jet hits the water surface, with C being the phase speed of the primary wave. The turbulence intensities over the entire aerated region are presented and discussed. The measured data can be used for the calibration and verification of the numerical model for aerated flows simulation under breaking waves in the surf zone.

Modeling of wave energy converters by GPUSPH and Project Chrono

This study presents a fully coupled numerical approach to study wave energy converters interaction with water waves. The open-source Smoothed Particle Hydrodynamics model GPUSPH is used to resolve wave dynamics and compute the hydrodynamic force on wave energy converters. The dynamics of wave energy converter is computed by the open-source physics engine, Project Chrono. The capability of the coupled numerical model to handle wave-body interaction is validated by considering a floating body in still water. The results show that the coupled model correctly predicts the balance between the floating body weight and the buoyancy force. Furthermore, the effectiveness of density diffusion method in reducing acoustic noise in a weakly compressible SPH model is also justified. In addition, the model is validated by laboratory experiment on floating body interaction with nonlinear wave packet. The model is then applied to simulate two types of wave energy converters. We conduct a thorough study of GPUSPH modeling of surface-piercing oscillating wave surge converter under waves. GPUSPH accurately predicts both wave gauge measurements and the device rotation as recorded in the laboratory. By virtue of the Project Chrono library we examine the power take-off scenario of the oscillating wave surge converter by introducing kinematic constraint into the system. The device performance under storm condition is further examined. We further present and simulate a conceptualized catenary mooring wave energy converter device, CSI-Device, under real sea states. We not only examine the interaction of CSI-Device with waves, but also we obtain the mooring force on the device that can facilitate the design of wave energy converters. We show that to maximize the energy extraction, it is important to design the device to have a natural frequency similar to the wave period of deployment site to maximize the swing motion of the pendulum. Finally the interaction of CSI-Device under different sea states with both relatively small and large wave heights are evaluated by placing the device in a directional spectral wave basin. Overall, this study shows that the open-source model GPUSPH is an efficient tool for modeling wave energy conversion devices in directional nonlinear sea states.

Resolving combined wave-current fields from measurements using interior point optimization

Complex wave and wave-current conditions exist in the natural world, and are increasingly emulated in advanced experimental facilities to de-risk the deployment, operation and maintenance of offshore structures and renewable energy devices. This can include combinations of ocean swell, multi-directional wind-driven seas, and reflected wave conditions interacting with a current field. It is vital to understand the full nature of these potentially hazardous conditions so they can be properly simulated in numerical models, to contextualize measurements made in field, and experimental programmes. Here, a numerical framework is presented for isolating both the wave systems and the mean current velocities from measured data using an interior point optimizer.A developed frequency domain solver is used to resolve, from experimentally obtained wave gauge measurements, two opposing wave systems on a collinear current, and used to effectively isolate the wave systems and predict the current velocity using only wave gauge measurements. Thirty five test cases are considered; consisting of five wave spectra interacting with seven different current velocities ranging from −0.3m s-10.3m s-1. Comparisons between the theoretical and derived wave numbers and current velocities show good agreement and the performance of the method is similar to that of existing methodologies while requiring no a priori knowledge of the current velocity impacting the wave field required.Although results are presented for the collinear problem, the presented method can be applied to a wide range of wave and current combinations, and provides a useful tool for increasing understanding of both ocean and experimental conditions.

Detailed Study on Breaking Wave Interactions With a Jacket Structure Based on Experimental Investigations

Wave breaking is one of the major concerns for offshore structures installed in shallow waters. Impulsive breaking wave forces sometimes govern the design of such structures, particularly in areas with a sloping sea bottom. Most of the existing offshore wind turbines were installed in shallow water regions. Among fixed-type support structures for offshore wind turbines, jacket structures have become popular in recent times as the water depth for fixed offshore wind structures increases. However, there are many uncertainties in estimating breaking wave forces on a jacket structure, as only a limited number of past studies have estimated these forces. Present study is based on the WaveSlam experiment carried out in 2013, in which a jacket structure of 1:8 scale was tested for several breaking wave conditions. The total and local wave slamming forces are obtained from the experimental measured forces, using two different filtering methods. The total wave slamming forces are filtered from the measured forces using the empirical mode decomposition (EMD) method, and local slamming forces are obtained by the frequency response function (FRF) method. From these results, the peak slamming forces and slamming coefficients on the jacket members are estimated. The breaking wave forces are found to be dependent on various breaking wave parameters such as breaking wave height, wave period, wave front asymmetry, and wave-breaking positions. These wave parameters are estimated from the wave gauge measurements taken during the experiment. The dependency of the wave slamming forces on these estimated wave parameters is also investigated.

Wave Run-Up Analyses Under Dissipative Condition Using X-Band Radar

An X-band nautical radar system was employed to examine wave run-up during a typhoon around the research pier HORS in Hasaki, Japan. Analyses on radar echo images were done to estimate the spatio-temporal variation of water fronts by manually digitizing cross-shore time stack images. Digitized instantaneous water fronts were validated with wave gauge measurements with an acceptable agreement. Longshore distribution of mean shoreline positions and inter-tidal foreshore slopes were then estimated using time-averaged images. Run-up, the height of discrete water level maxima, was estimated from the digitized water fronts with the help of foreshore profile. Run-up variations under dissipative condition were parameterized with surf similarity parameter. Low frequency variances in the run-up motion were observed, which travelled in the longshore direction.

Longshore Characteristics of Wave Run-up under Stormy Condition

An X-band nautical radar system was employed to examine wave run-up during a typhoon around the research pier HORS in Hasaki, Japan. Analyses on radar echo images were done to estimate temporal and spatial variations of water fronts by manual digitizing of cross-shore time stack images. Digitized instantaneous water fronts were validated with wave gauge measurements with an acceptable agreement. Long-shore distribution of mean shoreline positions and intertidal foreshore slopes were then estimated using time averaged images. Run-up, the height of discrete waterlevel maxima, was estimated from the digitized water fronts with the help of foreshore profile. Run-up variationswere parameterized with surf similarity parameter. Low frequency variances in run-up motion were observed, whichwere traveling in the longshore.

Two-dimensional periodic waves in shallow water. Part 2. Asymmetric waves

We demonstrate experimentally the existence of a family of gravity-induced finiteamplitude water waves that propagate practically without change of form in shallow water of uniform depth. The surface patterns of these waves are genuinely two-dimensional, and periodic. The basic template of a wave is hexagonal, but it need not be symmetric about the direction of propagation, as required in our previous studies (e.g. Hammack et al. 1989). Like the symmetric waves in earlier studies, the asymmetric waves studied here are easy to generate, they seem to be stable to perturbations, and their amplitudes need not be small. The Kadomtsev–Petviashvili (KP) equation is known to describe approximately the evolution of waves in shallow water, and an eight-parameter family of exact solutions of this equation ought to describe almost all spatially periodic waves of permanent form. We present an algorithm to obtain the eight parameters from wave-gauge measurements. The resulting KP solutions are observed to describe the measured waves with reasonable accuracy, even outside the putative range of validity of the KP model.

Shoaling and Decay of Two Wave Trains on Beach

Shoaling and decay of irregular wave trains with two distinct frequency peaks are simulated in a wave flume. The relative energy in each wave train, the closeness of the frequency peaks, and the total wave energy were varied over 12 cases. Wave-gauge measurements across the 1:30 plane slope in the flume show that linear superposition of single-peaked wave trains or lumping all energy into the dominant wave train are not satisfactory representations of multiple wave trains. The measurements also show that the wave train with the low-frequency peak dominates in the surf zone. Waves with the low-frequency peak appear unaffected by the second wave train, but the high-frequency wave train decays faster in the presence of the low-frequency waves. The variation of wave height through shoaling and breaking depends on the relative amount of energy in each of the wave trains and the closeness of the peak frequencies.