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Water represents 71% of the globe, of which 95% reserved by oceans and the rest is made out of seas and other water bodies. Communication among entities floating and diving underwater is not typically available or meets the acceptable level in most areas of water bodies, even though many underwater communication systems exist nowadays. However, the main issue of underwater acoustic and radio frequency (RF) wireless communication systems is the short communication distance between the transmitter and receiver without repeater due to the frequency dependence. Where in the optical wireless communication (OWC) the distance depends on the operating wavelength of the used light source. Recently, many researches have appeared in the field of underwater communication using visible light communications (VLC) and invisible OWC. Underwater optical wireless communication (UOWC) at 450 nm wavelength has proven to be better than at 680 nm and 860 nm due to the attenuation and dispersion mechanisms. In this paper, we will present a new design for a passive optical wireless code division multiple access (OW-CDMA) network based on a M-arry differential pulse position modulation (M-DPPM) with a new spreading code called double length modified prime code (DL-MPC) with distinct correlation characteristics to enhance the transmission distance, minimize the system latency, security of data transmission through the network, enhance the data rate per user, network capacity, improve the system signal to noise ratio (SNR) and consequently enhance BER performance at long transmission distance. The simulation results proved that the proposed system can accommodate about 500 users at a BER equals 10–9 using the proposed DL-MPC sequence at a transmission distance of 880 m under pure water. [ABSTRACT FROM AUTHOR]

The increasing interest in the use of renewable energy technologies is directing attention towards the potential contribution of marine energy technologies, especially ocean wave energy, to world energy demand. While open-sea demonstrations of full-scale devices have been carried out to validate several technologies, the focus now is shifting to optimising the components for efficiency and reliability. The efficiency of the electrical generator plays a crucial role in wave-to-wire numerical models for converting wave energy into usable electricity. It provides essential data that enables the industry to reduce technical risks and uncertainties. Wave-to-wire models typically simplify the generator's efficiency through assuming a single curve based on the load. This curve is usually provided by the machine manufacturers for the nominal rotational speed. However, the rotational speed varies in the case of air turbines used in OWC devices. Therefore, to accurately estimate decision variables derived from these models, a comprehensive efficiency map is necessary. This map should demonstrate the performance at different rotational speeds and loads, as it directly influences the estimation of key parameters. The main objective of the present work is to improve the generator behaviour of an OWC for different generator operation regimes. For this purpose, a numerical model of the generator's efficiency will be developed throughout the segregation of losses and validated experimentally. Finally, an optimal control law will be presented to maximise the electrical power output of the wave energy converter, considering the efficiency of both the generator and the turbine. [ABSTRACT FROM AUTHOR]

Energy, as an inexhaustible phenomenon, transforms various forms to meet human needs. Some forms of energy are challenging to harness for reuse, necessitating a combination of energy generators to enhance electricity production from renewable sources such as heat and water. The utilization of Ocean Wave Energy Converter (OWC) emerges as one solution, harnessing the phenomena of waves and air pressure to drive generators. The generated electrical output does not have to be large, as long as it can produce heat through coils. This heat is then used to warm thermoelectric materials, generating electricity that can be stored in the Powerhouse Storage. A holistic approach is employed to harness renewable energy efficiently and sustainably to meet electrical needs. [ABSTRACT FROM AUTHOR]

In this work, an oscillating water column (OWC) device is considered placed in front of a V-shaped vertical breakwater. The idea conceived, is based on the amplified wave power absorption due to the wave interactions originating from the presence of the breakwater. A theoretical analysis is presented in the realm of linear potential theory, based on the solution of proper diffraction, and radiation problems in the frequency domain, using the eigenfunction expansion method, the method of images, and the multiple scattering approach. Optimum absorption efficiency is examined taking into consideration the characteristics of the power take off (PTO) system and the air compressibility. Numerical results are presented and discussed in terms of the expected power absorption. The effect of the distance between the OWC and the vertical walls, the breakwater's forming angle, and the wave heading angle, is examined to demonstrate the enhanced absorption ability of the device. It is concluded that the device's efficiency is strongly dependent on the position of the OWC in front of the walls, as well as the angle of the wave impact, and should be taken into account when determining the optimum device parameters for maximization of its performance. [ABSTRACT FROM AUTHOR]

Marine energy still plays a marginal role in the current global energy scenario, despite the incessant effort by research for more than thirty years in the exploitation of the so-called blue energy. Among the wide range of marine technologies, wave energy harvesting can play a significant role in view of its potential and Oscillating Water Column (OWC) systems, coupled with Wells turbines, can be considered among the most mature wave energy technology. Due to the oscillating nature of the flow rate in this kind of applications, Wells turbines are affected by dynamic stall, which has significant effects in terms of performance, fatigue, noise and structural integrity of the turbine. Actually, during dynamic stall, the Wells turbine experiences evident high frequency torque fluctuations which overlay on the typical hysteresis loop, mainly during flow deceleration. The amplitudes of these fluctuations are damped as the flow rate decreases toward reattachment. Often these fluctuations are not evident because hysteresis loops are usually provided with phase-averaged data, which can significantly smoothen or even conceal them. Indeed, it is difficult to find in the literature high frequency torque measurements able to show these fluctuations. With the aim to better investigate how the stall triggers this phenomenon, a monoplane Wells turbine has been manufactured in 3D printing and tested in the open wind tunnel of the Polytechnic University of Bari, Italy. The interest of the experimental campaign has been mainly focused on the effects of main parameters of the oscillating inlet flow rate (mean flow rate, amplitude and period of the oscillations, modifying the controlling parameters of the inverter driving the squirrel cage blower) on the performance of the machine. The machine has been firstly investigated under steady state inlet flow conditions, then under dynamic stall conditions. As a result, unsteady torque fluctuations occur during the flow deceleration till the flow reattachment. After the stall, the investigated Wells turbine experiences a drastic reduction of the torque coefficient of about 90%. Moreover, the torque coefficient shows a number of peaks during deceleration phases ranging from 2 to 4. Specifically, the case with the maximum period of the flow rate under investigation (i.e., T = 20 s) shows a greater number of peaks (4) than those related to the other cases (3). Moreover, it has been found that this unsteady behavior is due neither to the mass flow rate crossing the turbine, nor to the stagnation pressure drop, nor to the rotational speed control, which is correctly performed keeping the rotational speed within 1% of the target value. Hence, detecting these oscillations can be relevant in the turbine design phase to enhance the structural strength of the turbine. [ABSTRACT FROM AUTHOR]

In this study, predictions by leading network technology companies and current literature on 5 G technologies have been investigated to shed a light on the foreseeable future of the developing communication systems infrastructure. Research has been carried out on the new-generation optical communication infrastructure, which is developing in parallel with the requirements of 5 G and beyond mobile communication systems, and optical-wireless communication (OWC), free-space optical communication (FSOC), visible-light communication (VLC), and optical-camera communication (OCC) is presented. Also, there is information about fiber-wireless (FiWi) and radio-over fiber (RoF) transmission systems and FSO system integration (RoFSO), which finds use as an infrastructure component in the next-generation high-frequency communication. [ABSTRACT FROM AUTHOR]

In high-speed wireless communication, visible light communication is considered an emerging and cutting-edge technology. A light-emitting diode can serve both as an illumination source in an environment and as a data transmitter. Nevertheless, plenty of complications stand in the way of developing VLC technology, including the low response time of waveguides and detectors and the field of view dependence of such devices. To cover those challenges, one approach is to develop a superior optical antenna that does not have a low response time related to phosphorescence materials and should also support concentrating light from the surroundings with a wide field of view. This research paper presents an optimized cylindrical optical antenna with benefits, such as affordable cost, fast response time due to high-efficient nanomaterials, and a wide field of view (FOV). The proposed structure avoids the need for intricate tracking systems and active pointing to the source, but it can also be integrated into portable devices. For the analysis of nanomaterials' characteristics, finite difference time domain simulations are used, and Monte-Carlo raytracing is used to study the proposed optical antenna. It was found that the antenna's optical efficiency varies from 1 to 29% depending on the size and the number of nanomaterials inside. Compared to other works, this paper shows higher efficiencies and wider FOV. [ABSTRACT FROM AUTHOR]

Integrating oscillating water columns (OWCs) into a row of closely-spaced hollow piles can form a wave farm, leading to cost reductions through cost-sharing with other structures and thus making the wave energy conversion more economically viable. It is important to understand the effects of the distance between the OWCs in the row on the performance of the wave farm. Using an air-water two-phase flow model, validated by a set of wave-flume test results, the hydrodynamic performance of the wave farm was investigated, with a focus on effects of the distance between OWCs on capture efficiency as well as wave transmission and reflection. The power takeoff (PTO) was represented by an orifice whose effects were parameterized by a porous media in the simulation. Sidewall effects that may be encountered in wave flume tests were also discussed. [ABSTRACT FROM AUTHOR]

The study investigates the structural characterisation of flexible membranes used in oscillating water column (OWC) wave energy converters (WECs). Four commonly utilised elastomers – natural rubber, nitrile rubber, silicone, and latex – were subjected to a novel hyperelastic model selection process. A custom bulge test setup enabled the selection of second-order Mooney-Rivlin (SOMR) and Yeoh models for relevant accuracy (RMSE<0.018 MPa), stability and numerical validation. A 1:20 scale OWC model with latex was tested in a water tank to examine the effects of waves with a frequency range of 0.25–1.4 Hz and up to 0.24m amplitude. Water tank experiments demonstrated smooth frequency responses for OWC with membrane, beneficial for consistent power generation. A dry test rig was designed and built to replicate OWC inflation conditions and apply cyclic loadings up to 1.5 Hz, overcoming pressure limitations of the water tank, exploring wider material options, and validating numerical simulation. An optical motion capture system, Qualisys, supported the validation process by providing precise data on membrane deformation during experiments. Furthermore, finite element analysis (FEA) was utilised to conduct stress analysis and parametric studies, assessing the suitability of these materials for flexible OWC application. [ABSTRACT FROM AUTHOR]

Vehicle-to-vehicle communication based on visible light communication has gained much attention. This work proposes a smart license plate receiver incorporated with a fluorescent concentrator, enabling a fast vehicle-to-vehicle communication with a large field of view and high optical gain. Communication performance is experimentally analyzed using off-the-shelf light-emitting diode-based headlamps for low-latency direct line of sight channel. Additionally, a blue laser diode-based beam-steering and tracking system, through image processing of taillights with a steerable mirror, is investigated. Data rates of 54 Mbps from the headlamps and 532 Mbps from the beam-steering channel with ±25° are demonstrated. In addition, real-time video streaming through the beam-steering channel is presented. [ABSTRACT FROM AUTHOR]

This article investigates outage statistics of double gamma–gamma random variable (RV) modeled as the product of two independent and identically distributed gamma–gamma RVs. The outage closed‐form statistics in terms of the first‐order statistical measures (probability density function and cumulative distribution function) and the second‐order statistical measures (level crossing rate and average fade duration) by Laplace approximation integral (LAI) and exponential LAI are derived. The statistical results are directly related to the performance evaluation of dual‐hop as well as cooperative dual‐hop optical wireless communications over moderate to strong turbulence‐induced fading channels. [ABSTRACT FROM AUTHOR]

This paper presents the viscous flow predictions for fixed, slender and cylindrical Oscillating Water Columns (OWCs). Comparisons with linear potential solutions indicate nonlinearities in the scattered wave and the internal water surface elevations. The predictions also confirm high-frequency contents and asymmetrical shapes in the forces acting on the water columns. To identify the physical causes of the nonlinearities, various geometries, excitation conditions and mechanisms experienced by the OWCs are considered. This study confirms that a nonlinear wave scattering by the cylindrical structures occurs yet has little implication for the nonlinearities in the internal water surface elevations and the forces. In contrast, the vortex shedding at the lower edges of the OWCs and the nonlinear inertia forcing instigate the nonlinear characteristics of the elevations. The vortex shedding also provokes the nonlinearities in the acting forces. While the influence of the vortex shedding on the second-harmonic air force diminishes, the role of the water column oscillation on the harmonics becomes increasingly important at large amplitudes of internal surface elevation. Given the improved physical understanding, practical implications concerning the guidance on developing an appropriate time-domain modelling and improving the hydrodynamic efficiency of an OWC arise in this study. • Fixed OWCs undergoing forced oscillations and wave excitations are studied. • Viscous flow and linear potential solutions are compared to investigate the OWCs. • Nonlinear inertia forces and vortex shedding cause nonlinear internal elevations. • Vortex shedding generates zeroth and second-harmonics in inline pressures. • Vortex shedding and water column oscillation drive nonlinearities in air forces. [ABSTRACT FROM AUTHOR]

This paper is concerned with the radiated wave and the rotational flow fields generated by the forced oscillations of the water columns within surface-piercing hollow cylinders. The present study utilised Open Foam as the viscous flow solver to numerically model the forced oscillations. An investigation of the radiated waves in the fields near the water columns confirms two distinct nonlinear characteristics. These are progressively reduced amplitude and progressively reduced phase difference. An evaluation of the rotational flow fields around the mouths of the water columns helps explain their origins. This study confirms that the nonlinear characteristics in the near-field are physically caused by the formation and motion of vortex ring at the bottom edge of the cylinder. Interestingly, the progressively reduced amplitude is not evident in the far-field. All these new findings support the confirmation regarding the appropriateness of linear radiation theory and the implication of the vortex motion on the effective draft of a fixed cylindrical Oscillating Water Column (OWC). • Wave radiations generated by forced oscillations of water columns are studied. • Near-field radiated waves have progressive reductions in amplitude and phase difference. • Vortex formation and motion cause nonlinear characteristics in near field. • Far-field radiated waves exhibit insignificant progressive amplitude reductions. • Location of vortex closest to the mouth affects the effective draft of water column. [ABSTRACT FROM AUTHOR]

To improve the adaptability in variable wave conditions, a novel oscillating water column (OWC) wave energy converter (WEC)-bottom mounted breakwater integrated system is proposed, in which the front-wall constrained by a torsional spring can oscillate in the pitch mode. In this study, an analytical model based on the eigenfunction matching method and technique of variables separation is developed to investigate the hydrodynamic performance (including energy conversion and structural safety) of the proposed integrated system. Taking the air compressibility and linear Power Take-off (PTO) system into account, the effects of the front-wall width, draft and spring stiffness on the performance are discussed, respectively. It shows that the interaction between the pitch motion of the front-wall and the air-pressure oscillation significantly broaden the frequency bandwidth of energy conversion efficiency (i.e., capture width ratio, C w), in comparison with the traditional OWC device with the fixed front-wall. It is also found that those frequency points corresponding to the peaks of C w satisfy the condition that the real part of complex air volume flux which is induced by unit air-pressure oscillation inside the chamber, is equal to zero, after decoupling and eliminating the influence of front-wall motion. • Hydrodynamics of an OWC WEC-breakwater integrated system is theoretically investigated. • Hydrodynamic efficiency is considerably enhanced when front-wall freely pitches. • The smaller the front-wall width, the wider the high-performance frequency bandwidth. • The front-wall draft exist an optimal value for the proposed system with pitching front-wall. [ABSTRACT FROM AUTHOR]

Explosive data rate requirements in the satellite communication for surveillance, military services, and broadcasting have put peer pressure on the optical wireless communication (OWC) systems. Secure data transmission against eavesdropper and performance enhancement at authentic user is major concern these days. In this work, performance and security analysis of spectral amplitude codes (SAC) in mode division multiplexed (MDM) OWC have been carried out and a novel zero cross correlation resultant weight (ZCCRW) code at 100 Gbps capacity has been presented. Random diagonal (RD), Enhanced double weight (EDW), Diagonal double weight (DDW) codes have been compared through simulations and also mathematical expressions are derived under the effects of eavesdropper. Hybrid modulations have been compared to check optimal modulation with combination of Laguerre-Gaussian (LG), and HermiteGaussian (HG) modes. Results have revealed that ZCCRW code with MD-DQPSK using LG modes provide best performance and least susceptibility to eavesdropper. [ABSTRACT FROM AUTHOR]

Sea wave characteristics could be the most crucial sloshing occurrence caused by OWCs. In this paper, an OWC with different inlet geometries has been investigated experimentally to optimize the performance and reduce sloshing. Eight wave gauges (WG) are applied to measure water free surface to determine the sloshing. The results showed that the converter performance decrease when sloshing occurs. To reduce sloshing, four inlet openings were installed at the inlet of OWC, and to achieve optimal efficiency in sloshing conditions, the geometry optimization done by genetic algorithm; then, the converter's performance with optimum inlet was experimentally investigated, sloshing phenomenon was observed in 4 frequencies in converter without opening; However, after installing the optimal opening, sloshing occurred in only one frequency, and also in this case, sloshing was 42 % reduced. The data correlation results showed a positive correlation between the frequency and the Top Free Surface of water inside the OWC (shown by a line called TFS) angle. At the same time, there is a negative correlation between the frequency and the flow rate, pressure difference, and power generated. The comparison of the converter results with opening and without opening shows that the correlation between frequency and other variables is always lower in the case with opening. Also, geometry optimization improved the sloshing frequency's 42.89 % performance. • Sloshing occurs in OWC and reduce the performance. • High frequency wave cause sloshing. • Inlet opening geometry optimization can reduce the sloshing. • Reducing sloshing can improve efficiency for 42.89 %. [ABSTRACT FROM AUTHOR]

Conventional Wave Energy Converters (WECs) are designed to extract the wave energy from the oceans with the wave power of 20–50 kW-per-meter. If these WECs are used where the wave energy is less than the mentioned values they cannot work in their maximum performance. Therefore it is proposed to optimize the WECs for the average wave power in each place. In this research, an Oscillating Water Column (OWC) is investigated to extract the maximum output power based on the characteristics of the Faroor island waves in the Persian Gulf. The average power of the Persian Gulf Waves is less than 10 kW-per-meter and using a conventional wave energy converter is not efficient. Numerical simulation is performed using ANSYS-Fluent software. In this study, waves are generated using nonlinear second order stokes theory. Also, the k- ω turbulence model and volume of fluid scheme are used for turbulence modeling and interface tracking respectively. Finally, with optimizing each parameter an optimum geometry with an efficiency of 41.5% is obtained to extract the Faroor Island waves' energy. This study emphasizes on this fact that one should design a new geometry to reach the best performance of the OWC in new wave characteristics. • The optimized OWC dimensionless parameters change with wave characteristics. • The optimized OWC increases the efficiency from 19.75% to 41.5%. • The bottom step can increase the hydrodynamic efficiency of the OWC. • The best length of the bottom step is equal to one wavelength. • The best front angle of the bottom step is 90 degrees. [ABSTRACT FROM AUTHOR]

This work aims to enhance the evidence base of extreme impact loads on the front (outer) wall and within the chamber of an oscillating water column (OWC) integrated into a vertical breakwater. Data are from large-scale physical model tests (at 1:9 scale) at the large wave channel (GWK). The paper shows that established prediction methods for nonimpulsive and impulsive wave loads for conventional vertical breakwaters can be applied to the front wall of OWC breakwaters. For the first time, impact loads within the OWC chamber have been quantified, on the rear in-chamber wall and on the chamber ceiling. These are found to reach magnitudes comparable to front wall wave impacts. Novel video records from within the OWC chamber provide new insight on water column behavior, including three different classifications identified as "single," "successional," and "water column" ceiling impacts. Conditions at risk of violent impacts within the chamber are also identified. These will be valuable in quantifying front (outside) design forces, in-chamber impacts, and in seeking to minimize in-chamber impacts occurrence, in construction and in operational phases. [ABSTRACT FROM AUTHOR]

Oscillating water column (OWC) device is one of the most promising wave energy converters (WECs). Besides the energy conversion efficiency, the survivability should also be considered for a design purpose in the process of wave energy exploitation. In the present study, by introducing the artificial viscous terms into the dynamic free surface boundary condition and Bernoulli equation, a fully nonlinear numerical model based on higher-order boundary element method (HOBEM) is adopted to model the wave dynamics of an OWC device. The viscosity effects on the wave force (i.e., Δ F) is investigated by comparing the predicted wave force by the numerical model with and without these viscous terms. The effects of the chamber geometry parameters, such as front wall draft, chamber width and opening ratio (i.e., air orifice width), on Δ F are investigated. The results indicate that the viscosity effect on the wave force on the seaside surface of the front wall is larger than that on its shoreside surface. The viscosity effect on the total horizontal wave force on the front wall increases with the increase of front wall draft in some extent. The influence of the viscosity on the horizontal wave force increases with opening ratio decreasing due to the increasing air pressure inside the chamber. • The viscosity effect on the wave dynamics of an OWC device is systemically studied. • Viscosity affects more on the wave force on the seaside surface than the other surface of the front wall. • Viscosity effect on the wave force is much influenced by the OWC chamber geometry. [ABSTRACT FROM AUTHOR]

• We present a methodology for assessing site-specific OWC converters' efficiency. • Turbine damping, air compressibility and important non-linear effects are considered. • We experimentally obtain the high-resolution efficiency matrices of the OWC. • We illustrate the methodology considering three study sites in NW Spain. • Efficient OWCs require a turbine damping matching the site-specific wave climate. The energy conversion performance of oscillating water column (OWC) wave energy converters at a specific site is often studied by means of analytical models. Based on linear theory, these models lose accuracy when viscous losses and turbulence become significant—more generally, when nonlinear effects play a role, as they often do in real operating conditions. In this work we apply a novel methodology based on a combination of numerical modelling and laboratory tests to investigate OWC performance without these shortcomings. First, high-resolution wave resource characterisation matrices are obtained by means of numerical modelling. Second, the resource matrices are combined with the OWC efficiency matrices obtained through laboratory tests and, importantly, including the effects of turbine-induced damping and air compressibility—usually disregarded in small-scale laboratory tests, but relevant for full-size (prototype) devices. The combined matrices thus obtained express, through a wave height-period distribution, the energy captured by the OWC for different values of the damping coefficient. On this basis, developers can select the most appropriate value of turbine-induced damping for a given site, based on performance values. The implementation of the novel methodology is illustrated through a case study in Galicia (NW Spain), in which three deployment sites are considered. We find that the turbine-induced damping must be matched to the wave climate of the site for an OWC device to achieve high performance; indeed, changes in damping cause variations in the total annual energy captured of up to 11%, which increase to 25% for specific sea states. [ABSTRACT FROM AUTHOR]

In this paper, a novel self-rectifying impulse turbine with U-shaped duct used for oscillating water column wave energy conversion is proposed. It has a pair of fixed, symmetrical and radial-flow guide vane rows, and an axisymmetric, U-shaped duct with increasing cross-sectional area from the rotor to the guide vane rows, therefore it is expected to be relatively simple, reliable and efficient. A three-dimensional (3D) steady-state numerical model and a fully transient model are established for the present turbine. These two models are validated by comparison with experimental results from the published works, respectively, and then used to investigate the steady performance and transient characteristics of the impulse turbine. Effect of the geometry of the guide vanes, the number of the guide vanes, and the hub-to-tip ratio on turbine performance under steady airflows and transient airflows are studied, and the difference between these two models in predicting turbine performance is discussed. • A novel high-efficiency impulse turbine with U-shaped duct for OWCs is proposed. • Steady-state and full transient models of the turbine are established and validated. • Effect of several parameters on steady and transient performance is studied. • Difference in turbine performance obtained using these two models is discussed. [ABSTRACT FROM AUTHOR]

Abstract The optimization of OWC devices has deserved much attention in the last few years. However, despite of this intense research activity, the most suitable turbine for OWC applications is still under debate. Recently, the twin-turbine configuration, where two unidirectional turbines are employed simultaneously, has emerged as a promising design. Although axial turbines are typically employed for those systems, the present paper demonstrates that the use of radial turbines can be also an interesting option. In this work a radial geometry, specifically designed to be used in a twin-turbine configuration, has been manufactured at a reasonable cost for a lab-scale facility taking advantage of 3D printing technology. Encouraging preliminary results were obtained in an aerodynamic database of the turbine. In particular, the total-to-static efficiency under stationary conditions (i.e. at constant flow coefficients) reached remarkable high values. Hence, the performance curve of the turbine under such stationary conditions has been used to make an assessment of its non-stationary performance in order to compare this optimized radial turbine with respect to impulse axial types available in the literature. The results revealed that radial turbines are clearly competitive against to axial ones when introduced in a twin-turbine configuration for OWC power plants. Highlights • Radial turbines are suitable for OWC devices with twin turbine configuration. • The performance of radial turbines when working as backflow preventer is good. • Performance of previous models clearly surpassed, both direct and reverse mode. • Leaking flow through the turbine not producing energy is lower than 20%. • The non-steady efficiency catches up with that achieved by axial turbines. [ABSTRACT FROM AUTHOR]

Optical wireless communication (OWC) technology is one of the most prominent alternative schemes for radio frequency (RF) communications. Flip-Orthogonal Frequency Division Multiplexing (Flip-OFDM) is a type of indoor OWC that transmits the positive and the absolute values of the negative parts of the signal in two consecutive OFDM symbols. The Flip-OFDM system exhibits better bit error rate (BER) performance than that of the DC-biased optical OFDM (DCO-OFDM). However, in Flip-OFDM, the recombination of the positive and negative sub-frames doubles the noise power, which causes distortion and degrades the BER performance. In this paper, a method to mitigate the noise effect using Convolutional and Turbo coders with Additive White Gaussian Noise (AWGN) and ceiling bounce channel models is proposed. Simulation results show that the Convolutional and Turbo coded Flip-OFDM system gives a better BER performance compared to that of the uncoded Flip-OFDM system. In addition, the Turbo coded Flip-OFDM system has a better BER performance than that of the Convolutional coded Flip-OFDM system. [ABSTRACT FROM AUTHOR]

Abstract Oscillating water column (OWC) is the most widely used wave energy converting technology for onshore structures. The interest in OWC wave energy converters (WECs) has been rising in the last decade because of its capability of long-term operation with high reliability and survivability. The impulse and Wells turbines, acting as axial-flow self-rectifying turbines and rotating unidirectionally in reciprocating airflows generated by the air chamber, play a key role in the pneumatic power conversion of OWC facilities. Although these turbines were developed based on theoretical analysis and steady-state laboratory tests, computational fluid dynamics (CFD) technologies have become a popular and convenient desktop tool for their design and optimization. This review aims to bridge the knowledge gap between engineering applications and CFD achievements for this type of turbine. Recent developments in the CFD modeling, geometry optimization, and performance enhancement have been summarized. Perspectives on the CFD model for OWC axial-flow turbines and its future trends are also proposed. Highlights • A comprehensive review of CFD studies on axial-flow OWC turbines are presented. • Detailed aspects of CFD models for both Wells and impulse turbines are summarized. • CFD achievements of geometry optimization and performance enhancement are reported. • Parameters of CFD models for steady-state analysis are recommended. • Future trends of CFD models for OWC turbines are discussed. [ABSTRACT FROM AUTHOR]

Power production levels at the Pico plant fall significantly short of pre-project estimates. Poor turbine performance compared to expectations from scale model testing accounts for much of this shortfall. Unanticipated chamber pressure skewness is also found to contribute to the deficit. This skewness manifests from wave shoaling because of the shallow chamber water depth from boulder collection and is worsened by intermittent chamber pressure losses caused by chamber wall defects. A passive non-return by-pass relief valve system for partially counteracting chamber pressure skewness is investigated. This functions by venting more of the unconvertible pneumatic over-power during the more intense but shorter duration exhalation half-wave cycles. At the same time, it retains more of the convertible pneumatic under-power in the weaker but longer duration inhalation half-wave cycles. This method reduces the degree of pressure skewness, which improves the system performance in higher energy excitation conditions. The passive relief valve specifications are optimised with a time-domain wave to wire model which is also used to project the expected plant performance enhancement in a range of wave conditions. Simulation results are compared to limited field tests results using a simple prototype passive valve system and good agreement is found. [ABSTRACT FROM AUTHOR]

Optical wireless communication (OWC) has recently gained much attention for addressing the increasing demand in the global broadband access market. Flip-orthogonal frequency division multiplexing (Flip-OFDM) is a type of OFDM that can be implemented in indoor OWC. Due to the ability of Flip-OFDM to keep the same bit error rate performance in asymmetrically clipped optical OFDM (ACO-OFDM) while saving 50% of the receiver hardware complexity, it can be used as an alternative to ACO-OFDM. However, the main drawback that can reduce the performance of the Flip-OFDM is the high peak-to-average power ratio (PAPR). So, in this article, partial transmit sequence (PTS) is applied to reduce the PAPR of Flip-OFDM over ceiling bounce model. Simulation results show that the proposed PTS-based Flip-OFDM achieves significantly lower PAPR values compared to Flip-OFDM. [ABSTRACT FROM AUTHOR]

This paper investigates the theoretical conclusions of a numerical analysis. The results are reproduced experimentally using a two-dimensional model in a wave flume. The experimental set-up is conducted by subjecting the model to waves with frequencies ranging from 0.2 to 2 Hz. The heave velocities of the structure and water column are calculated by differentiating the displacement of each with respect to time. The experimental results confirm that the extent of the parametric relationship between the structure heave velocity and oscillating water column heave velocity is linearly related to the power output potential of the system and hence, can be used as a design tool for floating offshore wave energy converters. It has also been determined that the extent of the parametric function is maximised when the forcing frequency is between 90 and 100% of the natural frequency of the water column of the system in question. This shows that the system efficiency is maximised when the waves cause resonance of the water column compared to the ocean wave. [ABSTRACT FROM AUTHOR]

Wave energy is a viable source of ocean renewable energy and research is being conducted worldwide. The Oscillating Water Column (OWC) device is recognised internationally as one of the most promising types of ocean Wave Energy Converters (WECs). To effectively utilize ocean waves for harvesting more energy, offshore OWC devices need to be deployed in deep–water where waves are more energetic. Therefore, the present paper experimentally investigated the hydrodynamic performance of a 3D offshore–stationary OWC device subjected to a wide range of regular wave conditions of different periods and heights and nonlinear power take–off (PTO) damping conditions simulated by an orifice. The experimental results were also employed to validate a 3D incompressible Computational Fluid Dynamics (CFD) model based on the RANS–VOF approach. It was found that the device capture width ratio decreased as wave height increased, especially for wave frequencies higher than device resonance frequency. However, for low–frequency waves under small PTO damping, there was a noticeable improvement in the device capture width ratio. More importantly, results of this study revealed that even with the changes in the device capture width ratio as wave height doubled, the OWC device could extract more wave energy throughout the whole frequency range tested by a maximum of about 7.7 times, particularly for long waves under small PTO damping. Furthermore, the numerical results from the 3D CFD model were in good agreement with the experiments, while the 2D model provided misleading (overestimating) results for high–frequency waves. [ABSTRACT FROM AUTHOR]

Renewable energy development could be an appropriate method to tackle the problems caused by fossil fuels. In this regard, an Oscillating Water Column (OWC) with a scale of 1:10 has been studied in this research. Sloshing is an unwanted phenomenon in OWC. Therefore in order to study sloshing, A Novel experimental approach for measuring free surface profile inside OWC by considering the effect of wave characteristics and sloshing was investigated experimentally in this paper. Eight wave gauges were installed at the top of the converter to study the hydrodynamic behaviour. The results showed that an increase in frequency raises the possibility of sloshing. However, up to the frequency of 0.37, the TFS (Top Free Surface) angle increase is insignificant. As frequency approaches 0.37, suddenly TFS angle rises, and sloshing occurs at frequencies of 0.37–0.80. Also, dead volumes are formed on TFS (some positive and negative volumes formed on free surface which cancel each other). Therefore if TFS angle is more than 3.85°, the sloshing is happened, and the converter's performance decreases severely. In the best conditions, efficiency and power are 53.7% and 192.2 W, respectively, and in sloshing area, efficiency and power are 8.3% and 35 W, respectively. • Sloshing in OWC has been studied experimentally. • Caspian sea with unique features has been cosidered. • Effect of wave characteristics on Sloshing has been studied. • In the resonance efficiency is 53.7%, however in sloshing is 8.3%. • Sloshing occurs whent TFS line angle touches 3.85°. [ABSTRACT FROM AUTHOR]

Oscillating Water Column devices are the most widespread among Wave Energy converters, with an efficiency that is closely related to the performance of its Power Take-Off element, usually a turbine. Using unidirectional turbines requires a system of valves to rectify the bidirectional flow, so self-rectifying turbines are more convenient for an OWC device. Another recent proposal is the use of a twin turbine configuration, where an arrangement of two unidirectional turbines could perform this task, with each turbine extracting the flow energy alternately. To date, all the twin turbine configurations studied in the open literature consider unidirectional axial turbines. In this paper, the use of a radial turbine to improve the system's efficiency by enhancing flow rectification is presented for the first time. An experimentally validated numerical model has been used to analyse the flow field of the radial turbine when working in both direct and reverse modes. Interesting conclusions are extracted. Finally, a performance comparison of the twin turbine configuration using axial or radial turbines has been carried out. It is concluded that the good performance of the radial turbine working as a flow preventer makes this kind of turbine an interesting option for twin systems. [ABSTRACT FROM AUTHOR]

The hydrodynamic performance of a fixed Oscillating Water Column (OWC) device is experimentally and numerically investigated. Based on the time-domain higher-order boundary element method (HOBEM), by introducing an artificial viscosity term in the dynamic free surface boundary condition, a fully nonlinear numerical wave model is used to simulate the hydrodynamic performance of an OWC device. A set of comprehensive experiments for regular waves is carried out to validate the numerical results as well as to investigate the nonlinear effects on the hydrodynamic performance of OWC. The mechanism of the nonlinear phenomenon is investigated based on the analysis of the experimental and numerical results. The influence of the wave nonlinearity and the viscosity on the hydrodynamic efficiency is quantified by comparing the linear and nonlinear numerical results. It was found that the hydrodynamic efficiency increases with the nonlinearity and viscosity when the incident wave amplitude is small. When the incident wave amplitude is large, the hydrodynamic efficiency is reduced by the weakened transmission of the second-order harmonic wave component due to the strong wave nonlinearity. However, when the wave amplitude is between these two regimes, the wave is weakly nonlinear, the efficiency decreases with the wave amplitude due to the combined effect of the nonlinearity and viscosity. [ABSTRACT FROM AUTHOR]

Mutriku has recently become the first commercial wave farm to release its operating data. The plant has 14 OWC operating turbines, and this study has conducted an analysis of hourly data corresponding to the 2014–2016 period. The plant's capacity factor has been calculated for this period, and its seasonal evolution characterized. Additionally, a plant efficiency index has been defined as the ratio between the wave energy flux at a reference buoy and the average power generation across the active turbines. The Mutriku wave farm's annual output in the period analysed has been 246,468.7 kW-h, with an average of around ten working turbines. The results indicate that Mutriku's average capacity factor is around 0.11, with higher values in winter than in summer. These values are below the capacity factors reported for other renewable energy sources. The plant efficiency index is 0.26, and further advances in regulation and control may also raise this parameter's values, as may lower rated power alternators. This will also help to improve the Mutriku wave plant's capacity factor, and OWC technology in general. [ABSTRACT FROM AUTHOR]

The emerging field of optical wireless communication (OWC) systems is seen as potential complementary technology to the radio frequency wireless communications in certain applications. It is deemed as a possible technology in the future 5th Generation communication networks to address the spectrum congestion and improve the system’s capacity. More research and developments in OWC is still needed in order for it to be adopted in current and future communication systems. This special issue brings together research papers on OWC covering free space optic, visible communications and ultraviolet communications. [ABSTRACT FROM AUTHOR]

In this paper, we propose a subcarrier-index modulation-based asymmetrically clipped optical orthogonal frequency division multiplexing (SACO-OFDM) scheme for optical wireless communication (OWC) systems, which benefits from the subcarrier-index modulation (SIM) and asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) techniques. SACO-OFDM conveys additional information via the subcarrier indexing, and the error rate of the bit transmitted by the subcarrier indexing is much lower than that of the conventional M -ary modulation scheme. On the other hand, as the signal constellation in M -ary modulation is relieved, SACO-OFDM has simple transceiver structure and low detection complexity. Moreover, considering the spectral, an enhanced SACO-OFDM (ESACO-OFDM) using even subcarriers is proposed. In this technique, the odd subcarriers are activated for SACO-OFDM, and the imaginary part of even subcarriers are activated for pulse-amplitude-modulated discrete multitone (PAM-DMT). Clearly, ESACO-OFDM achieves better spectral efficiency than the conventional optical OFDM, since all subcarriers are used for data transmission. Simulation results verify the significant bit error rate (BER) and peak-to-average power ratio (PAPR) improvement by the proposed ESACO-OFDM, especially for the medium-to-high signal-to-noise ratio (SNR) regime. [ABSTRACT FROM AUTHOR]

In this paper, wave forces on a 1:50 model–scale of an offshore stationary Oscillating Water Column (OWC) device are studied in 3D physical and numerical wave tanks. In total 310 physical experiments including repetition were performed in a wave tank for regular waves of different heights and periods, and several turbine–induced pneumatic damping conditions simulated via orifice plates. A Computational Fluid Dynamics (CFD) model based on the RANS equations and the VOF surface capturing scheme was constructed and validated against the tank measurements. The validated CFD model was then utilized to investigate the effects of tank sidewalls on the predicted wave forces. It was found that the horizontal wave force acting on the OWC device was always larger than the vertical force. The total horizontal and vertical forces were maximum and minimum, respectively at the intermediate wavelength. In addition, the pneumatic damping had a significant impact on the measured vertical force, whereas negligible effects were observed on the horizontal force. Increasing the wave height increased nonlinear effects on the forces measured, especially the vertical force. It was concluded that a tank width of less than five times the OWC device breadth will likely provide misleading wave forces due to blockage effects. [ABSTRACT FROM AUTHOR]

Wide aperture omnidirectional free-space optical (FSO) receivers using wavelength shifting (WLS) fibers that enable the use of small active area high-speed photodetectors in optical wireless communications, are presented. In particular, the influence of WLS fiber decay time in the bit rate is evaluated when receiving intensity modulated light generated with commercial off-the-shelf light-emitting diodes. The option of increasing the photon collecting area of a 7 mm 2 active area avalanche photodiode using WLS fiber, gave a 300% improvement in the bit rate, when compared with the option of using a bare 31 mm 2 active area avalanche photodiode. It was also experimentally verified, that a WLS spiral receiver mounted over a reflective base gave more gain than simulated Lambert‘s cosine law, proving that reflective optics can be used to increase the WLS-FSO receiver aperture. [ABSTRACT FROM AUTHOR]

Understanding the hydrodynamic performance of offshore Oscillating Water Column (OWC) devices is essential for assisting the development and optimization processes. The chamber underwater geometry is one of the paramount design aspects that strongly affect the wave–OWC interactions. This paper utilizes a well–validated two–dimensional, fully nonlinear Computational Fluid Dynamics (CFD) model to investigate the impact the underwater front and rear lips have on the hydrodynamic performance of an offshore stationary OWC. An extensive campaign of numerical simulations is performed to discover the relevance of the front and rear lip submergence and thickness to OWC performance. The key finding is that the overall hydrodynamic efficiency can be significantly improved over a broad frequency bandwidth by selecting suitable values for both the submergence ratio of asymmetric lips and the lip thickness. The device that is capable of absorbing a large amount of the incoming wave energy provides the maximum power extraction efficiency and the maximum energy losses. The optimal combination achieved a peak efficiency exceeding 0.79, which represents a massive enhancement over more simplistic, but commonly accepted, geometries that returned peak efficiencies of approximately 0.30. [ABSTRACT FROM AUTHOR]

Oscillating Water Columns (OWCs) are some of the most-studied wave energy converters (WECs). Previous work showed that the geometric characteristics of the OWC can play a significant role in the efficiency of the device. In this study, we investigate the behaviour of different designs of OWC making geometric modifications to the classic design of OWC and the U-OWC, initially suggested by Boccotti [1] . The multi-chamber OWCs examined here are fixed on the seabed and have a slit opening at the seaward side. The physical modelling was undertaken in the flume of the COAST laboratory of the University of Plymouth. The devices were tested in uni-directional regular and irregular wave conditions, with and without power take-off (PTO) mechanism, essentially also testing absorbing seawalls. The aim of the study is to present a preliminary comparison related to the geometry of OWCs under some typical wave conditions and suggest potential shape improvements towards an overall optimization of the devices that takes into account both the hydrodynamic efficiency of the OWC and other design aspects, such as the wave run-up. The present study also endeavours to highlight potential benefits from incorporating OWCs in coastal defence as absorbing seawalls. [ABSTRACT FROM AUTHOR]

Understanding the hydrodynamic interactions between ocean waves and the oscillating water column (OWC) wave energy converter is crucial for improving the device performance. Most previous relevant studies have focused on testing onshore and offshore OWCs using 2D models and wave flumes. Conversely, this paper provides experimental results for a 3D offshore stationary OWC device subjected to regular waves of different heights and periods under a constant power take–off (PTO) damping simulated by an orifice plate of fixed diameter. In addition, a 3D computational fluid dynamics (CFD) model based on the RANS equations and volume of fluid (VOF) surface capturing scheme was developed and validated against the experimental data. Following the validation stage, an extensive campaign of computational tests was performed to (1) discover the impact of testing such an offshore OWC in a 2D domain or a wave flume on device efficiency and (2) investigate the correlation between the incoming wave height and the OWC front wall draught for a maximum efficiency via testing several front lip draughts for two different rear lip draughts under two wave heights and a constant PTO damping. It is found that the 2D and wave flume modelling of an offshore OWC significantly overestimate the overall power extraction efficiency, especially for wave frequencies higher than the chamber resonant frequency. Furthermore, a front lip submergence equal to the wave amplitude affords maximum efficiency whilst preventing air leakage, hence it is recommended that the front lip draught is minimized. [ABSTRACT FROM AUTHOR]

Various studies investigated the behaviour and the performance of Oscillating Water Columns (OWCs) suggesting many alternative design concepts to improve the efficiency of the device. The OWCs examined here are fixed on the seabed and have a slit opening at the seaward side. The present study investigates the applicability of a multiphase Reynolds Averaged Navier-Stokes (RANS) numerical model for simulating the interaction between an OWC and regular and irregular waves. An initial validation of the open-source computational fluid dynamics (CFD) software package OpenFOAM with the wave generation and absorption toolbox waves2Foam is performed against experimental results obtained at the COAST laboratory of the University of Plymouth. The main aim of the study is to complement to the validation of RANS CFD models and later employ the broadly used numerical tool for further studies for better understanding the behaviour of the OWCs. A method based on mechanical damped oscillations for calculating the eigen frequency of the device from a decay test is presented and compared with the performance curve. The strength of CFD modelling for obtaining better insight to the hydrodynamics of OWCs is also demonstrated. [ABSTRACT FROM AUTHOR]

Understanding the hydrodynamic performance of an Oscillating Water Column (OWC) wave energy converter is essential for further improving the device efficiency. Most experimental measurements are performed at small scales where air compressibility can be ignored. In this paper, scaling and air compressibility effects on the performance of an offshore stationary OWC wave energy converter are studied in a 3D numerical wave tank. A Computational Fluid Dynamics (CFD) model based on the RANS equations and the VOF surface capturing scheme is developed and validated against physical measurements of a 1:50 model-scale OWC. Following the validation stage, the CFD model is utilized to investigate scaling and air compressibility effects on the performance of an OWC by comparing five different scales from 1:50 up to full-scale and modelling air as both compressible and incompressible. Other parameters that are considered include the impact of varying the power take-off (PTO) damping, wave height and period, underwater geometry, and the effect of air chamber height. Results reveal that at full-scale air compressibility is important and can induce about 12% reduction in the maximum efficiency predicted at model-scale under regular waves at the resonant frequency and the optimum PTO damping. Air compressibility effects slightly reduce as the extracted pneumatic power increases. In order to consider full-scale air compressibility effects while testing a small OWC model scaled using Froude’s similitude law, the full-scale air chamber volume is best scaled with the square of the scale factor rather than cubic to predict the device performance with errors of less than 1.2%. In this manner, this work contributes to the full-scale development of OWCs by better understanding the differences from small physical model-scales. [ABSTRACT FROM AUTHOR]

The hydrodynamic performance of Oscillating Water Column (OWC) wave energy converters depends mainly on the behaviour of the wave–OWC interaction. In this paper, a fully nonlinear 2D RANS–based computational fluid dynamics (CFD) model was used to carry out an energy balance analysis of an onshore OWC. Chamber differential air pressure and free surface elevation from published physical measurements were used to validate the CFD model. Additional validation was carried out via PIV data from available model–scale experiments to validate the CFD model's capability in capturing the flow field and the turbulent kinetic energy. The validated CFD model was then used in an extensive campaign of numerical tests to quantify the relevance of different design parameters such as incoming wave height and turbine pneumatic damping to characterise the hydrodynamic performance and wave energy conversion chain of the OWC. To capture the flow field inside the OWC in good agreement, additional refinement was required at the field of view together with utilizing either SST or RSM turbulence models rather than k-ɛ . It is found that the applied damping has crucial impacts on the energy conversion process. Also, increasing the wave height can lead to a massive drop in the system efficiency. Furthermore, both power take–off (PTO) damping and wave height play an important role in vortex formation around the upper and lower chamber's lips during the in–flow and out–flow stages. [ABSTRACT FROM AUTHOR]

In this paper, an ultra-high capacity inter-satellite optical wireless communication (OWC) system using different modulation is presented. The proposed system is achieved by using 64-channel dense wavelength division multiplexing (DWDM) by different modulation methods. The inter-satellite link has been designed for various distance and external modulation of carrier-suppressed return-to-zero (CSRZ), duo binary return-to-zero (DRZ) and modified duo binary return-to-zero (MDRZ) at different bit rate. The proposed system is simulated at different bit rates, 10, 20 and 40 Gbps by using atmosphere model. To show the good performance of the proposed system, its eye diagram, received power and Q -factor are shown. The comparative analyses show that at 10 and 20 Gbps, the proposed system has maximum quality factor, Q , and minimum bit error rate (BER) for all three modulations. Also, at 40 Gbps the MDRZ modulation has better performance in comparison to the CSRZ and DRZ modulations. [ABSTRACT FROM AUTHOR]

A numerical approach has been developed in this study for hydrodynamic analysis of complex-shaped oscillating water column (OWC) converters. Physically, in the circumstance when the device is free to move or moored in waves, the airflow movement inside the chamber is coupled tightly with the changing of the internal fluid surface and the hydrodynamic response of the device. By taking these coupling effects into account, appropriate boundary integral equations are formulated with supplemental theoretical relations. The boundary value problem is then solved using a higher-order boundary element method (HOBEM). After obtaining the wave force and dynamic air force, the coupled motions and hydrodynamic efficiency are evaluated by integration. In particular, unlike conventional methods limited to fixed OWCs, the proposed method is proved applicable to those floating with coupled rigid-body motions. An optimal turbine parameter is hence mathematically derived to maximise the wave power absorption. Besides the linear quantities, nonlinear wave drift loads are evaluated via a newly derived formulation that accounts for the far-field contribution and the oscillating air pressure over the internal fluid surface. Based on the above methodology and the resulting tool, numerical studies are carried out for three cylindrical OWC scenarios that are floating in waves, attached by a reflector and connected to a submerged caisson, respectively. Different modes of body motion and typical free-surface oscillation modes in the chamber are analysed and discussed. It is found that, for an OWC with an attached arc-shaped reflector or connected to a submerged caisson, its wave power absorption can be characterised by a series of apparent peaks which are associated with the resonant internal fluid and in close proximity to the resonance frequencies of body motions involving surge, heave or pitch. Numerical results also indicate the benefits of floating OWCs from the coupled rigid-body motion modes and OWC's resonance, expanding the frequency range of efficient conversion and improving the device's adaptability to variable oceanic environments. [ABSTRACT FROM AUTHOR]

Free-space optical links use modulated beam of light to transmit high amount of data from transmitter to receiver to get line-of-sight communication link. Free-space optical is cost effective solution to provide higher data rate to end-users. Free-space optical links are also considered as a better alternative to RF links due to their advantages of low power consumption and higher data rate of the range Gbps, and are highly secure to electromagnetic interference. Despite of having all these advantages free-space optical links are highly affected by the severe weather conditions like fog, rain, snow, smoke and dust or aerosol particles suspended in air. Fog is one of a major challenge for free-space optical to achieve carrier class availability and causes high amount of attenuation. In this paper we presented the performance analysis of free-space optical links by estimating signal-to-noise ratio, bit error rate, under fog conditions during winter season in Lahore, Pakistan. [ABSTRACT FROM AUTHOR]

The development of high-performance nano-luminophores based on luminescent nanomaterials, such as Carbon Nanotubes (CNT) and Quantum Dots (QDs), opens the doors for many potential improvements in luminescent systems and notably Optical Wireless Communication (OWC) systems. Other side, Cu 2 CdSnS 4 quaternary alloy nanostructure has attracted attention in solar cell applications owing to the high optical absorption in visible range. This work presents the feasibility of the infrared uplink Visible Light Communication (VLC) system using Near Infrared Light Emitting Diode (NIR-LED) operating at 780 nm. The used NIR-LED-based Cu 2 CdSnS 4 quaternary alloy nanostructure is to investigate the performance of NIR uplink transmission according to Line of Sight (LOS) channel model. In this transmission, the effect of transmitter orientation and transmitted optical power level with respect to Tx–Rx​ uplink distance are taken into consideration. For this purpose, performance evaluation will be achieved in terms of Bit Error Rate (BER) where we demonstrated satisfactory BER performance (B E R ≥ 1 0 − 9 ) over the entire typical room configuration. In addition, an optimal semi-angle interval and optimal Tx power level has been selected. We further investigated the performance improvement by using several transceivers, compared with a single one on the center of the ceiling. • Possible application of the Cu 2 CdSnS 4 quaternary alloy nanostructure is investigated. • Performance of the proposed system is considered. • Effect of transmitter orientation and transmitted optical power level is presented. [ABSTRACT FROM AUTHOR]

The efficiency of wave energy devices can be enhanced by positioning them at pre-defined locations of concentration of the energy flux which could be either by nature or through man-made methods. In shallow waters, energy flux density remains nearly uniform throughout the depth, while in intermediate and deep waters, it varies along with the depth with more energy being transferred nearer to the free surface. In the present study, a horizontal plate is used to concentrate the wave energy within a limited depth from the surface by inducing the waves to shoal. The plate length required for efficient shoaling is experimentally studied. An Oscillating water column, a proven wave energy extraction device, is fixed over the plate and its hydrodynamic efficiency is evaluated. The optimal distance between the leading edge of the plate and OWC is found. Through this method, it is observed that the hydrodynamic efficiency of OWC increases by about 10% compared to in the absence of the plate. • Frontal plates concept to a Oscillating water Coloumn (OWC) to harvest wave energy is introduced. • The plate length required for better wave amplification is experimentally studied and a predictor equation is arrived. • The plate of half the wave length is suggested for better wave amplification by shoaling. • The physics behind the dimensional requirement of the plate is detailly explained. • The hydrodynamic efficiency of OWC increase by 10% due to presence of plates. [ABSTRACT FROM AUTHOR]

The hydrodynamic performance of a fixed Oscillating Water Column (OWC) wave energy device under various wave conditions and geometric parameters was tested experimentally in a wave flume. The measured water surface elevation at the chamber center, the air pressure in the chamber of the OWC device and the hydrodynamic efficiency are compared well with the published numerical model results in Ning et al. (2015). Then the effects of various parameters including incident wave amplitude, the chamber width, the front wall draught, the orifice scale and the bottom slope on the hydrodynamic efficiency of the OWC device were investigated. It is found that the opening ratio ε ( ε = S 0 / S , where S 0 and S are the cross-sectional areas of the orifice and the air chamber, respectively) has a significant influence on the maximum hydrodynamic efficiency of the OWC device. The optimal efficiency occurs at the opening ratio of ε = 0.66%. Although bottom slope has little influence on the resonant frequency, the optimal hydrodynamic efficiency increases with the increase of bottom slope. A proper bottom slope can provide a work space in the OWC chamber almost independent on the sea wave conditions. The spatial variation of the water surface inside and outside the chamber was also examined. And the results indicate that the water motion is highly dependent on the relative wave length λ / B (where λ is the wave length and B is the chamber width). Seiching phenomenon is triggered when λ / B = 2 at which the hydrodynamic efficiency is close to zero. [ABSTRACT FROM AUTHOR]