Water Wave Tank Research Articles

Breaking Undular and Breaking Surges Advancing in Still Water

The propagation of secondary surges can lead to unexpected interaction events with navigation ships and downstream hydraulic structures; hence, they may cause navigation accidents and structural damage. In the present study, physical experiments were performed in a long water wave tank to study the evolution of breaking undular and breaking surges advancing in still water. Both free-surface and velocity measurements were conducted. It was observed that the transition from a breaking undular surge to a breaking surge occurred as the ratio of the mean water depth behind the surge to the still water depth equal to 1.68–1.71. Empirical expressions based on the experimental data were proposed to predict the wave amplitude and wave steepness of breaking undular surges. The unsteady flow results demonstrated that the normalized longitudinal velocity component beneath the surge front was governed mainly by the normalized free-surface elevation, independently of the surge type. Moreover, the maximum vertical velocity component during the surge front passage had a linear dependence on the vertical location. The present result provided new quantitative information on breaking undular and breaking surges advancing in still water.

Atomic bright soliton interferometry

The properties of nonlinear interference pattern between atomic bright solitons are characterized analytically, with the aid of exact solutions of dynamical equation in mean-field approximation. It is shown that relative velocity, relative phase, and nonlinear interaction strength can be measured from the interference pattern. The nonlinear interference properties are proposed to design atomic soliton interferometry in Bose–Einstein condensate. As an example, we apply them to measure gravity acceleration in ultra-cold atom systems with a high precision degree. The results are also meaningful for precise measurements in optical fiber, water wave tank, plasma, and other nonlinear systems.

The evolution and runup of nonbreaking undular surges

Physical experiments were conducted in a long water wave tank over a wide range of still water depths to study the evolution and runup of nonbreaking undular surges generated by the release of a given volume of water. The results demonstrated that the wavefront of a nonbreaking undular surge closely matched that of the corresponding solitary wave of the same height. The wave celerity of the surge could be accurately predicted using the solitary wave theory. Two distinct wave stages existed in the evolution process of a nonbreaking undular surge based on the wave shape asymmetry. The wave stage transition could be approximated as a surge Froude number equal to 1.15. The wave amplitude and steepness of undular surges were in reasonable agreement with the linear wave theory for surge Froude numbers greater than 1.20. However, the wave length data presented a different pattern to that predicted by either the linear wave theory or the solution of the Boussinesq equation. Furthermore, the maximum surge runup on a vertical wall was in excellent agreement with the solitary wave theory. This study provided new insights into the quantitative behavior of nonbreaking undular surges.

Water wave decay and run-up in the numerical water wave tank

Water wave decay and run-up in the numerical water wave tank

Whirling‐Folded Triboelectric Nanogenerator with High Average Power for Water Wave Energy Harvesting

AbstractOcean wave energy, as one of the most abundant resources on the earth, is a promising energy source for large‐scale applications. Triboelectric nanogenerators (TENGs) provide a new strategy for water wave energy harvesting; however, its average performance in realistic water wave conditions is still not high. In this work, a whirling‐folded TENG (WF‐TENG) with maximized space utilization and minimized electrostatic shielding is constructed by 3D printing and printed circuit board technologies. The flexible vortex structure responds easily to multiform wave excitation with improved oscillation frequency. A standard water wave tank is established to generate controllable water waves to characterize the device performance. It is found to be determined by wave conditions and internal structure, which is also revealed by a theoretical dynamical analysis. The WF‐TENG can produce a maximum peak power of 6.5 mW and average power of 0.28 mW, which can power a digital thermometer to operate constantly and realize self‐powered monitoring on the TENG network to prevent possible damage in severe environments. Moreover, a self‐charge‐supplement WF‐TENG network is proposed to improve the output performance and stability. This study provides an effective strategy for improving the average power and characterizing the performance of spherical TENG towards large‐scale blue energy.

A highly-sensitive wave sensor based on liquid-solid interfacing triboelectric nanogenerator for smart marine equipment

Wave monitoring is essential for marine engineering construction, development and utilization of ocean resources, maritime safety and early warning of marine disasters. In this paper, a highly-sensitive wave sensor based on liquid-solid interfacing triboelectric nanogenerator is proposed and systematically investigated. The wave sensor is made of a copper electrode covered by a poly-tetra-fluoroethylene film with microstructural surface. The effects of substrate, wave height, frequency, and water salinity on the performance of wave sensor are systematically investigated. It is found that the output voltage increases linearly with wave height with a sensitivity of 23.5 mV/mm for the electrode width of 10 mm, implying that the wave sensor could sense the wave height in the millimeter range. The sensitivity could be further increased by widening the electrode and/or enhancing the surface hydrophobicity. In a water wave tank, the wave sensor is successfully used to monitor wave around a simulated offshore platform in real time. Therefore, the novel wave sensor could provide an alternative to monitor wave for smart marine equipment.

Solitons in nonlinear systems and eigen-states in quantum wells**Project supported by the National Natural Science Foundation of China (Grant No. 11775176), the Basic Research Program of Natural Science of Shaanxi Province, China (Grant No. 2018KJXX-094), the Key Innovative Research Team of Quantum Many-Body Theory and Quantum Control in Shaanxi Province, China (Grant No. 2017KCT-12), and the Major Basic Research Program

We study the relations between solitons of nonlinear Schrödinger equation and eigen-states of linear Schrödinger equation with some quantum wells. Many different non-degenerated solitons are re-derived from the eigen-states in the quantum wells. We show that the vector solitons for the coupled system with attractive interactions correspond to the identical eigen-states with the ones of the coupled systems with repulsive interactions. Although their energy eigenvalues seem to be different, they can be reduced to identical ones in the same quantum wells. The non-degenerated solitons for multi-component systems can be used to construct much abundant degenerated solitons in more components coupled cases. Meanwhile, we demonstrate that soliton solutions in nonlinear systems can also be used to solve the eigen-problems of quantum wells. As an example, we present the eigenvalue and eigen-state in a complicated quantum well for which the Hamiltonian belongs to the non-Hermitian Hamiltonian having parity–time symmetry. We further present the ground state and the first exited state in an asymmetric quantum double-well from asymmetric solitons. Based on these results, we expect that many nonlinear physical systems can be used to observe the quantum states evolution of quantum wells, such as a water wave tank, nonlinear fiber, Bose–Einstein condensate, and even plasma, although some of them are classical physical systems. These relations provide another way to understand the stability of solitons in nonlinear Schrödinger equation described systems, in contrast to the balance between dispersion and nonlinearity.

Performance of a model fish cage with copper-alloy net in a circulating water channel and wave tank

This study was aimed at establishing the load on of a circular fish cage with a chain-linked copper-alloy net under the action of ocean currents and waves. The test cage that was used for this purpose was a 1/15 scaled-down model of a real fish cage presently installed in the coastal area of Korea. The deformation and mooring line load of the model cage were observed under different current speeds of 0, 20, 40, 60, and 80 cm/s in a circulating water channel. The mooring line load and its pattern were also examined with respect to the gap between the cage and the supporting buoy (0 (no buoy), 0.5, 1, 1.5, and 2 m, respectively) under the action of a 0.15-m-high wave in the wave tank. Although the volume of the cage hardly changed, the mooring line load exponentially increased with increasing current speed. The addition of the supporting buoy to the cage decreased the maximum load and changed the loading pattern, with the peak load apparently reduced to less than half. The tank test observations were reproduced by computer simulation.

Erosion as a possible mechanism for the decrease of size of plastic pieces floating in oceans

A sea water wave tank fitted in an artificial UV light weathering chamber was built to study the behaviour of polypropylene (PP) injected pieces in close ocean-like conditions. In air, the same pieces sees a degradation in the bulk with a decrease of mechanical properties, a little change of crystal properties and nearly no change of surface chemistry. Weathering in the sea water wave tank shows only a surface changes, with no effect on crystals or mechanical properties with loss of small pieces of matter in the sub-micron range and a change of surface chemistry. This suggests an erosion dispersion mechanism. Such mechanism could explain why no particle smaller than about one millimeter is found when collecting plastic debris at sea: there are much smaller, eroded from plastic surfaces by a mechano-chemical process similar to the erosion mechanism found in the dispersion of agglomerate under flow.

Settling of dilbit-derived oil-mineral aggregates (OMAs) & transport parameters for oil spill modelling

The size and settling velocity of oil-mineral aggregates (OMAs) derived from diluted bitumen are primary constituents in predictive models for evaluating the potential fate of oil spilled in the aquatic environment. A series of low sediment concentration (15mg·L−1), colder water (<10°C) wave tank experiments designed to measure variability in these parameters in naturally-formed OMAs in response the presence or absence of chemical dispersant are discussed. Corresponding lab experiments revealed settling velocities of artificially formed OMAs on the order of 0.1–0.4mm·s−1. High-resolution imagery of settling particles were analyzed for particle size, density and settling velocity. In situ formation of OMAs in the wave tank was unsuccessful. Possible effects of chemical dispersant on natural sediment flocculation, the size of suspended oil droplets and clearance rates of suspended particles are discussed.

Bright and dark solitons on the surface of finite-depth fluid below the modulation instability threshold

Bright and dark solitons are usually considered from the perspective of modulation instability of the carrier wave train: bright solitons are observed when the carrier wave is unstable with respect to long-wave modulations, while dark solitons are observed when the carrier wave is modulationally stable. For the slowly modulated wave trains with narrow bandwidth on the surface of ideal finite-depth fluid, the corresponding modulation instability threshold is known to lie at kh≈1.363, k being the carrier wave number and h the undisturbed fluid depth. In this case, bright solitons are known to exist above the modulation instability threshold (kh≳1.363), while dark solitons are known to exist below this threshold (kh<1.363). We demonstrate for the first time that besides these classical results bright solitons can also be observed along with dark solitons in a certain water depth range around kh≈1.2 that lies below the modulation instability threshold. We provide initial conditions at which these new bright solitons can be generated in water wave tank experiments.

Modeling and parallel computation of the non-linear interaction of rigid bodies with incompressible multi-phase flow

A computational tool is developed to capture the interaction of solid object with two-phase flow. The full two-dimensional Navier–Stokes equations are solved on a regular structured grid to resolve the flow field. The level set and the immersed boundary methods are used to capture the free surface of a fluid and a solid object, respectively. A two-step projection method along with Multi-Processing (OpenMP) is employed to solve the flow equations. The computational tool is verified based on numerical and experimental data with three scenarios: a cylinder falling into a rectangular domain due to gravity, transient vertical oscillation of a cylinder by releasing above its equilibrium position, and a dam breaking in the presence of a fixed obstacle. In the first two validation simulations, the accuracy of the immersed boundary method is verified. However the accuracy of the level set method while the computational tool can model the high density ratio is confirmed in the dam breaking simulation. The results obtained from the current method are in good agreement with experimental data and other numerical studies. The applicability of the current computational tool for the interaction of a buoy in a water wave tank with two types of waves; symmetrical and asymmetrical waves; has also been studied.

401 底面形状を考慮したH_∞制御に基づく水槽内の定在波抑制制御(GS2-3 ロボティクス・メカトロニクス)

In this paper, conventional analysis and control methods on open- and closed-loop system of disturbance attenuation control in water-wave tank, is extended to consider variation in bottom surface geometry by additionally locating a submerged block. Frequency responses obtained by experiment and analyzed by the boundary element method (BEM) show good agreement in low frequency range, for various changes in block height, width, and position. Specifically, resonant frequencies are almost identical only with 2%error. The resonant frequency is decreased when the block height and width becomes larger. It is shown that the desired performance to attenuate standing-wave oscillation is provided by H_∞ control system design considering bottom shapes. Control experiment shows that sinusoidal disturbance with 1st to 3rd resonant frequencies are attenuated up to 40%, and random disturbance is attenuated up to 30% at 1st to 3rd resonant frequencies.

Disturbance attenuation for standing wave oscillation in a water wave tank based on feedback control with a vertical-vibrating plate

This paper proposes active control system based on feedback control and an wave generating actuator with a vertical-vibrating plate, in order to attenuate standing-wave oscillation by unkown disturbance contamination in water wave tank. The validity of the system is examined by control experiments. The water wave tank is about 0.9 m in length, and has two actuators symmetrically located in the tank (one for disturbance generation and one for attenuation control) and two water-level sensors (one for control measurement and one for performance evaluation). First, the plant model is identified based on frequency response experiments, and the validity of the model is shown by a numerical analysis with the boundary element method. Secondly, the feedback controller is systematically designed by H∞ control synthesis so that the robust stability is guaranteed against plant uncertainty, and the validity of the system is shown based on the symmetry locations of actuators. Finally, control experiments are examined by using sinusoidal and random signals as unknown disturbance. It has been shown that the frequency components of resonance from the 1st to 4th modes are reduced by 20%～60%,which shows the desired performance of the proposed system to attenuate standing-wave oscillation.

Rogue waves in a wave tank: experiments and modeling

Abstract. In past decades theoretical studies have been carried out with the double aim of improving knowledge of the main characteristics of the rogue wave and of attempting to predict its sudden appearance. We have tried to generate rogue waves in a water wave tank, using a symmetric spectrum (Akhmediev et al., 2011a) as input on the wave maker. The next step has been to apply a theoretical model to the amplitude envelope of these waves. After some considerations we agreed the best model to be an analog of the Ginzburg–Landau equation.

Shallow water waves generated by subaerial solid landslides

SUMMARY Subaerial landslides are common events, which may generate very large water waves. The numerical modelling and simulation of these events are thus of primary interest for forecasting and mitigation of tsunami disasters. In this paper, we aim at describing these extreme events using a simplified shallow water model to derive relevant scaling laws. To cope with the problem,twodifferentnumericalcodesareemployed:one,SPHysics,isbasedonaLagrangian meshless approach to accurately describe the impact stage whereas the other, Gerris, based on a two-phase finite-volume method is used to study the propagation of the wave. To validate Gerris for this very particular problem, two numerical cases of the literature are reproduced: a vertical sinking box and a 2-D wedge sliding down a slope. Then, to get insights into the problem of subaerial landslide-generated tsunamis and to further validate the codes for this case of landslides, a series of experiments is conducted in a water wave tank and successfully compared with the results of both codes. Based on a simplified approach, we derive different scaling laws in excellent agreement with the experiments and numerical simulations.

Observation of a hierarchy of up to fifth-order rogue waves in a water tank

We present experimental observations of the hierarchy of rational breather solutions of the nonlinear Schrödinger equation (NLS) generated in a water wave tank. First, five breathers of the infinite hierarchy have been successfully generated, thus confirming the theoretical predictions of their existence. Breathers of orders higher than five appeared to be unstable relative to the wave-breaking effect of water waves. Due to the strong influence of the wave breaking and relatively small carrier steepness values of the experiment these results for the higher-order solutions do not directly explain the formation of giant oceanic rogue waves. However, our results are important in understanding the dynamics of rogue water waves and may initiate similar experiments in other nonlinear dispersive media such as fiber optics and plasma physics, where the wave propagation is governed by the NLS.

Spectral properties of the Peregrine soliton observed in a water wave tank

The Peregrine soliton, which is commonly considered to be a prototype of a rogue wave in deep water, is observed and measured in a wave tank. Using the measured data of water elevation, we calculated the spectra of the Peregrine soliton and confirmed that they have triangular shapes, in accordance with the theory.

Observation of rogue wave holes in a water wave tank

Rogue waves in the ocean can take two forms. One form is an elevated wall of water that appears and disappears locally. Another form is a deep hole between the two crests on the surface of water. The latter one can be considered as an inverted profile of the former. For holes, the depth from crest to trough can reach more than twice the significant wave height. That allows us to consider them as rogue events. The existence of rogue holes follow from theoretical analysis but has never been proven experimentally. Here, we present the results confirming the existence of rogue wave holes on the water surface observed in a water wave tank.

Rogue Wave Observation in a Water Wave Tank

The conventional definition of rogue waves in the ocean is that their heights, from crest to trough, are more than about twice the significant wave height, which is the average wave height of the largest one-third of nearby waves. When modeling deep water waves using the nonlinear Schrödinger equation, the most likely candidate satisfying this criterion is the so-called Peregrine solution. It is localized in both space and time, thus describing a unique wave event. Until now, experiments specifically designed for observation of breather states in the evolution of deep water waves have never been made in this double limit. In the present work, we present the first experimental results with observations of the Peregrine soliton in a water wave tank.