Wave Tank Research Articles

Real time water surface elevation using video camera

In recent years, image processing has become a popular tool in wave flume experiments. In Indonesia, the use of image processing methods for measuring instruments in wave flume experiments has not been widely used. Therefore, in this study, an image processing method using image data from a digital camera was used in real time to measure the water surface elevation in the wave flume. Regular and irregular waves were measured with this image processing technique. The measurement results using this video camera were calibrated with wave gauges. The results showed that the measurement method using video images has a small difference less than 7% in wave height and wave period error. Therefore, this method can be a solution as a low cost measuring tool in wave flume or in field observations.

Performance Characteristics of a Submerged Semicircular Breakwater Exposed to Regular Waves: An Experimental Study

Many mangrove replanting programs fail due to the drifting of the mangrove sapling by waves and coastal currents soon after the replanting. Hence, adequate wave protection for the mangrove planting site is required to enhance the survivability rates of the newly planted saplings. A small scaled modular submerged semicircular breakwater (SBW) is perceived to be a viable option to provide the required level of wave protection to mangroves. The study is set to investigate wave transmission, reflection, and energy loss by a SBW subjected to different immersion depths under a regular wave environment via physical modelling. The SBW model was tested in a wave flume and was subjected to relative immersion depth, i.e., a ratio of water depth to the height of the SBW, of 1.00 and 1.33, and wave steepness ranging from 0.02 to 0.06. The alternatively submerged SBW was found to be an effective breakwater design to provide the required level of wave tranquility to various coastal applications.

Non-intrusive measurements of wave nonlinearity over movable bed of sediment with different beach slopes

A series of laboratory experiments were undertaken to qualitatively investigate the evolution of wave nonlinearity over a movable bed of sediment with five different beach slopes under regular waves in a medium-scale wave flume. An innovative non-intrusive data collecting system, which mainly consists of three side-looking high-speed cameras, was developed to collect high-resolution and synchronous data on free-surface water elevation of waves and bed level changes without causing any disturbances to wave motions and the movable bed of sediment. On analyzing the collected experimental data, it is found that regular waves become nonlinear when they propagate to the shoaling zone and start breaking, and linear wave theory is quite accurate for calculating wave parameters such as orbital velocity with the correlation coefficient r2 = 0.8–0.95 before the waves break, but becomes less accurate after the waves break or are in the breaking zone with the smaller correlation coefficient r2 = 0.4–0.6. Four parameters, wave skewness Skη, asymmetry Ayη, Ursell number Ur, and Rocha number NP0, are introduced to describe the wave nonlinearity, of which Skη and Ayη are found to be of largest amplitudes at the wave breaking point and then start to decrease in the breaking zone and are almost unchanged for different beach slopes, while Ur further increases in the breaking zone and exceed the first larger value as waves approach to shoreline, but NP0 is almost linearly proportional to wave orbital velocity amplitude and quite sensitive to beach slope. The location of sandbar is found close to the wave breaking point in the wave flume and may be also considered as the point where wave nonlinearity becomes important for sediment transport in the surf zone, and the linear wave theory becomes less accurate.

Impact of Rainfall on 5G Millimeter Wave Channels

Impact of Rainfall on 5G Millimeter Wave Channels

The Roles of Bathymetry and Waves in Rip‐Channel Dynamics

AbstractThe behavior and predictability of rip currents (strong, wave‐driven offshore‐directed surfzone currents) have been studied for decades. However, few studies have examined the effects of rip channel morphology on the rip generation or have compared morphodynamic models with observations. Here, simulations conducted with the numerical morphodynamic model MIKE21 reproduce observed trends in flows and bathymetric evolution for two channels dredged across a nearshore sandbar and terrace on an ocean beach near Duck, NC, USA. Channel dimensions, wave conditions, and flows differed between the two cases. In one case, a strong rip current was driven by moderate height, near‐normally incident waves over an approximately 1‐m deep channel with relatively little bathymetric evolution. In the other case, no rip was generated by the large, near‐normally incident waves over the shallower (∼0.5 m) channel, and the channel migrated in the direction of the mean flow and eventually filled in. The model simulated the flow directions, the generation (or not) of rip currents, and the morphological evolution of the channels reasonably well. Model simulations were then conducted for different combinations of the two channel geometries and two wave conditions to examine the relative importance of the waves and morphology to the rip current evolution. The different bathymetries were the dominant factor controlling the flow, whereas both the initial morphology and wave conditions were important for channel evolution. In addition, channel dimensions affected the spatial distribution of rip current forcings and the relative importance of terms.

Effects of multi motion responses and incident-wave height on the gap resonances in a moonpool

The hydrodynamic characteristics of a free-floating moonpool encountering the gap resonances are investigated based on the constrained interpolation profile method in numerical wave tank. This paper mainly concentrates on the influences of the moonpool's motion responses and the incident-wave height on the gap resonances in the free-floating moonpool. Numerical results demonstrated that the heave response significantly changes the frequency and the magnitude of the linear gap resonance, while the roll motion influences more on the vertical wave loads and the wave responses in the fluid field. The heave and roll response of the free-floating moonpool are generally independent. Moreover, the magnitudes of the nonlinear gap resonances have the tendency of catching up and exceeding the linear gap resonance as the incident-wave height increasing for the free-floating moonpool, which is the consequence of the higher-order harmonics driven by the nonlinear processes and the linear secondary resonant region induced by the heave response. Based on the wavelet transform, it could be observed that the amplified harmonic component usually takes more time to be fully developed than other harmonic components during the development of its corresponding nonlinear gap resonance.

Multidimensional hybrid software-in-the-loop modeling approach for experimental analysis of a floating offshore wind turbine in wave tank experiments

Multidimensional hybrid software-in-the-loop modeling approach for experimental analysis of a floating offshore wind turbine in wave tank experiments

Performance Assessment of an ITU-T Compliant Machine Learning Enhancements for 5G RAN Network Slicing

Network slicing is a technique introduced by 3GPP to enable multi-tenant operation in 5 G systems. However, the support of slicing at the air interface requires not only efficient optimization algorithms operating in real time but also its tight integration into the 5 G control plane. In this paper, we first present a priority-based mechanism enabling defined performance isolation among slices competing for resources. Then, to speed up the resource arbitration process, we propose and compare several supervised machine learning (ML) techniques. We show how to embed the proposed approach into the ITU-T standardized ML architecture. The proposed ML enhancement is evaluated under realistic traffic conditions with respect to the performance criteria defined by GSMA while explicitly accounting for 5 G millimeter wave channel conditions. Our results show that ML techniques are able to provide suitable approximations for the resource allocation process ensuring slice performance isolation, efficient resource use, and fairness. Among the considered algorithms, polynomial regressions show the best results outperforming the exact solution algorithm by 5–6 orders of magnitude in terms of execution time and both neural network and random forest algorithms in terms of accuracy (by 20–40 %), sensitiveness to workload variations and training sample size. Finally, ML algorithms are generally prone to service level agreements (SLA) violation under high load and time-varying channel conditions, implying that an SLA enforcement system is needed in ITU-T's 5 G ML framework.

Experimental investigation into the effects of strong winds on the transport of overtopping water mass over a vertical seawall

ABSTRACT Hydraulic experiments using a wave flume with a wind tunnel at a scale of 1/40 were carried out to investigate the effect of wind on wave overtopping of a vertical seawall. To ascertain the possible effects of wave breaking, incident waves with various wave steepness (0.0102 to 0.0371) and three kinds of wind forcing (0 m/s, 6.84 m/s, 10.04 m/s) were used. The authors found that winds significantly increased the overtopping rate in general, and that there is a clear relationship between the overtopping rate and the wave steepness. Velocity fields obtained from PIV analysis revealed that the onshore winds directly enhanced the transport of overtopping water mass. The influence of the wind on the wave hydrodynamic processes that indirectly have an effect on the overtopping rate (such as the formation of a partially standing wave, breaker location, and breaker type) is also discussed. The perspective of treating wave overtopping as a transport of water mass could provide a novel understanding of complex fluid behavior, which would help to formulate countermeasures against future disasters influenced by intensive wind forcing.

Experimental Investigation of a Hybrid Device Combining a Wave Energy Converter and a Floating Breakwater in a Wave Flume Equipped with a Controllable Actuator

This paper presents a hydrodynamic investigation carried out on the “Wave Attenuator” device, which is a new type of floating breakwater anchored with piles and equipped with a linear Power Take Off (PTO) mechanism, which is typical for wave energy converters. The device is tested in the wave flume, under regular waves, in slightly non-linear conditions. The PTO mechanism, that restrains one of the two degrees of freedom, is simulated through an actuator and a programmable logic controller with preassigned strategy. The paper presents the system identification procedure followed in the laboratory, supported by a numerical investigation essential to set up a credible control strategy aiming at maximizing the wave energy harvesting. The maximum power conversion efficiency under the optimal PTO control strategy is found: it is of order 50–70% when the incident wave frequency is lower than the resonance one, and only of order 20% for higher frequencies. This type of experimental investigation is essential to evaluate the actual efficiency limitations imposed by device geometry.

Self-powered ocean buoy using a disk-type triboelectric nanogenerator with a mechanical frequency regulator

Triboelectric nanogenerator (TENG) systems have been demonstrated to generate power with high density. However, the electrical output power obtained from wave energy harvesting using TENG systems is typically limited to several milliwatts. To address this limitation and support various ocean buoy systems, an efficient method to scale-up TENG systems is required. In this paper, we present a self-powered ocean buoy (SPOB) incorporating a disk-type, soft-contact, mechanical frequency regulator TENG (DSMFR-TENG). The mechanical frequency regulator (MFR) enables the conversion of low-frequency wave energy to high-speed mechanical rotation, facilitating high power generation with the disk-type TENG. The SPOB was tested in a wave tank, reaching a peak power output of 470 mW and an average power output of 130 mW after the MFR released the rotational energy. To further enhance the functionality of the buoy, the DSMFR-TENG and a microcontroller, temperature sensor, and acoustic transmitter were integrated with the SPOB. The acoustic transmitter successfully transmitted signals 7, 23, and 30 times over a one-minute period at wave frequencies of 0.33 Hz, 0.5 Hz, and 1 Hz, respectively, thereby demonstrating the power supply capability of the TENG system for ocean buoys.

M4 WEC development and wave basin Froude testing

The M4 wave energy converter (WEC) is a moored, multi-float, multi-PTO (power takeoff), multi-mode, attenuator-type system designed to be capable of order MW capacity. The strategy is first described with technical requirements. Wave basin testing was undertaken to demonstrate the system and validate linear diffraction-radiation modelling, used for initial assessment and to generalise the configurations. Froude-scale modelling including power takeoff has been demonstrated for the first, possibly only, time. Further wave basin testing was undertaken to validate a multi-float generalisation. Moorings are a critical component with the elasticity of (synthetic) cables reducing snap loads markedly but with complex dynamics requiring wave basin testing and further model development. Preliminary results are presented. Limitations of wave basins with regard to the control of wave (and current) conditions and associated measurement are discussed along with suggested improvements. Computational modelling ranges from efficient linear diffraction-radiation modelling to massively resource-intensive computational fluid dynamics (CFD). The former extended to second order is of main practical importance and is well suited to generalise WEC configurations and model complexity, such as nonlinear power takeoff control and moorings, but are limited in accurately representing physics such wave nonlinearity, slamming and viscous effects. However, CFD has yet to become a practical tool for realistic irregular wave conditions. Wave basin modelling based on Froude scaling is of vital importance for both concept exploration and model validation.

The continuous transition from quantum channeling to the Bragg diffraction at the constant energy

It is well known that diffraction effects belong to the low-energy realm of wave physics, while the channeling effect resides in the high-energy realm of particle physics. The energy increase induces the transition between these two effects and is a well-understood singular semiclassical limiting process.In this paper, it will be shown that in the case of high-energy electron diffraction, the change of beam angular divergence can induce a continuous transition between the quantum planar channeling of electrons and Bragg's electron diffraction at the constant energy. In the described settings, the appearance of the diffraction maxima in the angular distribution of the transmitted electrons will be connected with the appearance of the quasi-stationary quai-periodic waves in crystal channels.

Backscattering reduction in a sharply bent water wave channel

Backscattering reduction in a sharply bent water wave channel

Experimental study on semi-active magnetorheological elastomer based isolation system for offshore platform using wave tank

Hydro-dynamic induced vibration is a major risk for offshore platform, which may cause fatigue damdage. The present work experimentally studies a smart isolation system for vibration mitigation of offshore platform utilizing magnetorheological elastomer (MRE). The principle of the proposed MRE-based smart isolation system is presented, in which a real-time decoupling between superstructure (deck) and the jacket structure is achieved by controlling MRE's horizontal stiffness. For a case study, a scaled simplified fixed offshore platform model is built. The prototype of MRE-based isolation system is manufactured and its field-induced dynamic performances are tested. A fuzzy logic controller is proposed for achieving real-time decoupling control. A wave tank testing for the offshore platform with MRE-based isolation system is conducted, in which wave loadings in different dynamic characteristics are considered (e.g., regular and random waves). The results show that the deck acceleration and its displacement, and isolation drift are greatly decreased by the controlled MRE isolation system. It is proven that the smart MRE-based isolation system is able to provide effectiveness vibration suppression for offshore platform structure over a wide range of wave loadings.

Experimental studies of the stability of wave-damping slopes to protect bridge supports from wave action

This article presents the results of experimental studies of the stability of wave-damping slopes to protect bridge supports from wave action. The object of the study is the construction of protective wave-damping slopes constructed to protect the supports of bridges designed and operated under wave action conditions (such as the bridge to Russian Island in Vladivostok, etc.) on the shores of the seas. The purpose of the work is to select the optimal design solutions for protective slopes that ensure reliable and safe operation of the bridge crossing during sea storms of rare frequency. The research was carried out by the method of physical modeling in a wave pool. Various variants of structural solutions of protective slopes are considered: from a stone outline and from gabions, as well as combined structures. According to the results of research on a physical model in the wave basin, the structures of the protective slopes of bridge supports that are most resistant to the effects of sea storm waves of rare frequency have been obtained. The results of the research are intended to select optimal design solutions for protecting bridge supports from wave action and can also be used to protect other transport structures, for example, the roadbed of railways designed on sea coasts. These results were used by the author in the development of the regulatory framework for the design and monitoring of engineering structures for the protection of transport structures from wave action.

Use of a spatially distributed in-phase antenna to increase the noise immunity of signal reception

Objectives. Radio-technical information transmission systems are widely used in various sectors of our life, not only for telecommunications and associated domestic needs, but also for the functioning of various special services, such as emergency response units, which increasingly use robotic complexes in the course of their work. In the event of an emergency, robot devices can be used to get in under rubble, in concrete pipes or other municipal facilities, which typically result in a sharp deterioration of the necessary conditions for the propagation of radio waves. In this regard, the problem of ensuring reliable communication with the robotic complex becomes rather acute. The aim of the present work is to reduce the effect of multipath propagation of radio waves in the communication channel under complex interference conditions.Methods. The methods of statistical radio engineering and mathematical modeling are used according to optimal signal reception theory.Results. The presented model for a multi-element, spatially-distributed, in-phase receiving antenna of various configurations, featuring an electronically adjustable radiation pattern, is designed to ameliorate the multipath nature of signal propagation. A simulation of a multipath communication channel was carried out in the presence of one main and three reflected beams of radio wave propagation, as well as with harmonic interference at two angles of its arrival and different frequency detuning relative to the frequency of the useful signal. The probability of a bit error when receiving discrete information using the proposed antenna is estimated.Conclusions. The proposed signal processing algorithm on the receiving side can be used to partially compensate for the influence of the multipath effect. As a result, the noise immunity of information reception in comparison with reception on an omnidirectional antenna with one antenna element increases: for a bit error probability of 10−3, the energy gain ranges from 2 dB for two beams to 7–10 dB for three or four beams. In the presence of concentrated harmonic interference in the radio channel, its simultaneous spatial (by the antenna) and spectral (by the demodulator) filtering is also observed, the effectiveness of which depends on the direction of arrival and the frequency detuning of the interference, which also leads to a significant decrease in the error probability.

A three‐dimensional wideband mmWave multiple‐input multiple‐output channel model for aerial reconfigurable intelligent surface‐assisted communication systems

SummaryThis paper presents a wideband millimeter wave (mmWave) channel model for aerial reconfigurable intelligent surface (ARIS) communications, in which the reconfigurable intelligent surface (RIS) is attached to an unmanned aerial vehicle (UAV) to enable intelligent signal reflections in the air. The model is established according to standard 3GPP channel models and considers important propagation factors, for example, large‐scale fading, small‐scale fading, and radiation pattern of reflection units (RUs). In addition, the model assumes three‐dimensional (3D) rotations of RIS and can capture its effects on channel characteristics. Based on the model, we propose a design method for RIS reflection phases. Statistics including channel amplitude, spatial, temporal, and frequency correlation functions (CFs), and space‐Doppler power spectral density (SD‐PSD) are obtained. The impacts of RU number, UAV height and speed, and RIS rotation on channel statistics are investigated. Results suggest that the designed reflection phases can effectively mitigate multipath fading and Doppler effect. Compared to the yaw angle of the UAV platform, channel characteristics are more sensitive to the roll and pitch angles.

Application of Seismic Channel Wave Technology on Small Structure Exploration in Coal Mine

At lane 20207 and lane 50207 of the 80207 working face of Sitai Mine, many small faults are exposed, and their extension is unknown, which causes great interference to safe and efficient mining and even normal production of the working face. In order to guide the rational transformation and safe and efficient production of the working face with science, Sitai Coal Mine commissioned Henan Polytechnic University to find out the extension of the exposed fault on the face and other geological anomalies by using geophysical exploration methods. According to the purpose of geophysical exploration in Sitai coal mine, combined with the geological conditions of the working face, the SUMMIT II EX type seismic channel wave exploration produced by DMT company of Germany is selected to explore the 80207 working face with the combined detection method of transmission and reflection. According to the detection results, combined with the existing hydrogeological data of Sitai mine, the relative channel wave anomaly area is delineated. The results show that the seismic channel wave exploration can provide a basis for the prevention and control of mine water disaster conveniently and effectively.

Neural Network calibration method for VARANS models to simulate wave-coastal structures interaction

This study develops a calibration method for the porous media to properly model the interaction between waves and coastal structures using VARANS models. The proposed method estimates the porosity, np, and the optimum values of the Forchheimer coefficients, α and β, that best represent the wave-structure interaction for a complete set of laboratory tests. Physical tests were conducted in a 2D wave flume for a homogeneous mound breakwater under regular wave conditions. Numerical tests were carried out using the IH-2VOF model to simulate the corresponding physical tests and incident wave conditions (HI, T). The numerical tests covered a wide range of Forchheimer coefficients found in the literature, α and β, and the porosity, np, with a total of 555 numerical tests. The results of 375 numerical tests using IH-2VOF were used to train a Neural Network (NN) model with five input variables (HI, T, np,α and β) and one output variable (KR2). The NN model explained more than 90% (R2 > 0.90 and RMSE <5%) of the variance of the squared coefficient of reflection, KR2. This NN model was used to estimate the KR2 in a wide range of np,α and β, and the error (εa) between the physical measurements with regular waves and the NN estimations of KR2 was calculated. The results of εa as function of np,α and β showed that for a given porosity, np, it was difficult to obtain a pair of α and β values that gave a common low error if few physical tests are used for calibration. Then to calibrate properly a VARANS model it seems necessary to check the results obtained for each combination of α and β with many laboratory {HI, T} tests. The minimum root-mean-square error of KR2 (εrms) was calculated to find the optimum values of porosity and Forchheimer coefficients: np = 0.44,α = 200 and β = 2.825 for the tested structure. Blind tests were conducted with the remaining 180 numerical tests using IH-2VOF to validate the proposed method for VARANS models. In this study, eight or more physical tests were required to find adequate values of np,α and β for VARANS models related to the best performance of wave-porous structure interaction.