Water Wave Energy Research Articles

Robust Swing‐Structured Triboelectric Nanogenerator for Efficient Blue Energy Harvesting

AbstractOcean wave energy is a promising renewable energy source, but harvesting such irregular, “random,” and mostly ultra‐low frequency energies is rather challenging due to technological limitations. Triboelectric nanogenerators (TENGs) provide a potential efficient technology for scavenging ocean wave energy. Here, a robust swing‐structured triboelectric nanogenerator (SS‐TENG) with high energy conversion efficiency for ultra‐low frequency water wave energy harvesting is reported. The swing structure inside the cylindrical TENG greatly elongates its operation time, accompanied with multiplied output frequency. The design of the air gap and flexible dielectric brushes enable mininized frictional resistance and sustainable triboelectric charges, leading to enhanced robustness and durability. The TENG performance is controlled by external triggering conditions, with a long swing time of 88 s and a high energy conversion efficiency, as well as undiminished performance after continuous triggering for 4 00 000 cycles. Furthermore, the SS‐TENG is demonstrated to effectively harvest water wave energy. Portable electronic devices are successfully powered for self‐powered sensing and environment monitoring. Due to the excellent performance of the distinctive mechanism and structure, the SS‐TENG in this work provides a good candidate for harvesting blue energy on a large scale.

Mechanical Regulation Triboelectric Nanogenerator with Controllable Output Performance for Random Energy Harvesting

AbstractRecycling of random mechanical energy in the environment has become an important research hotspot. The triboelectric nanogenerators (TENGs) were invented to harvest energy, and have been widely applied due to their simple structure, small size, and low cost. This paper reports a mechanical regulation triboelectric nanogenerator (MR‐TENG) for the first time with controllable output performance used to harvest random or irregular energy in the environment. It comprises a transmission unit, switch structure, generator unit, flywheel, and shell. Random linear motion or rocking motion is transferred via the transmission unit to the flywheel. The rotor of the generator unit fixed on the flywheel and the stator of the generator unit fixed on the shell combine. By controlling the storage and release of energy in the flywheel, the switch structure assists the flywheel to convert random or irregular energy into a controllable and stable energy output. The MR‐TENG can generate an open‐circuit voltage of 350 V, a short‐circuit current of 12 μA, a transfer charge of 130 nC, and a peak power of 2.52 mW. Furthermore, a thermometer and more than 300 light emitting diodes (LEDs) are separately powered by this MR‐TENG in simulated water waves, demonstrating its potential application in water wave energy harvesting.

Square-shaped structures can topologically guide water waves

Due to its dispersive nature, the topological confinement of water waves is a difficult feat, though it may lead to the development of highly efficient water-wave energy harvesters.

Water wave transmission and energy dissipation by a floating plate in the presence of overwash

A numerical model, based on the two-phase incompressible Navier–Stokes equations, is used to study transmission of regular water waves by a thin floating plate in two dimensions. The model is shown to capture the phenomenon of waves overwashing the plate, and the generation of turbulent bores on the upper plate surface. It is validated against laboratory experimental measurements, in terms of the transmitted wave field and overwash depths, for a set of incident wave periods and steepness values. Corresponding simulations are performed for a thick plate that does not experience overwash, which are validated using experiments where an edge barrier prevents thin-plate overwash. The model accurately reproduces (i) the linear relationship between the transmitted and incident amplitudes for the thick plate, and (ii) the decrease in proportion of incident-wave transmission for the thin plate, as incident steepness increases. Model outputs are used to link the decreasing transmission to wave-energy dissipation in the overwash, particularly where bores collide, and in the surrounding water, particularly at the plate ends. It is shown that most energy dissipation occurs in the overwash for the shortest incident waves tested, and in the surrounding water for the longer incident waves. Further, evidence is given that overwash suppresses plate motions, and causes asymmetry in plate rotations.

Spherical triboelectric nanogenerator integrated with power management module for harvesting multidirectional water wave energy

A spherical TENG with a spring-assisted multilayered structure was power-managed to effectively harvest multidirectional water wave energy.

A fully packed spheroidal hybrid generator for water wave energy harvesting and self-powered position tracking

Water waves are a promising source of renewable energy. Their kinetic energy can potentially drive energy harvesters. Herein, we describe a fully packed spheroidal smart buoy hybrid generator (SB-HG) composed of triboelectric nanogenerator (TENG) and an electromagnetic generator (EMG) for scavenging water-wave energy. Each of the energy harvesting components generated electrical outputs from the same wave motion. A position-tracking long-range (LoRa) device placed in the buoy enabled identification of the buoy location when it was placed in the sea for energy harvesting, navigation, and fishnet tracking purposes. A solar cell placed on the top of the buoy powered the device under calm wave conditions. The TENG and EMG components generated maximum electrical outputs of 100 V/2 μA and 20 V/15 mA, respectively. Combining the devices efficiently converted the kinetic energy of the waves into useful electrical energy, which was used to charge a commercial capacitor and lithium-ion battery. The charged battery drove the position-tracking LoRa device for a positioning application and demonstrated that the SB-HG device is an inexpensive and reliable candidate for ocean navigation systems. Our water-wave energy harvester is highly promising as a clean energy power source and as a self-powered sensor for various environmental monitoring systems.

Stretchable shape-adaptive liquid-solid interface nanogenerator enabled by in-situ charged nanocomposite membrane

Wearable and portable electronics for water environment application are of paramount significance, however restricted by its power source component. It remains a great challenge to simultaneously achieve ultra stretchability and high electric output performance for most energy harvesters in water. Herein, we report a high-performance stretchable liquid-solid contact electrification-based nanogenerator (S-LSNG) that enables water wave energy harvesting and subtle motion monitoring in water by an in-situ charged nanocomposite membrane. Notably, the effectively charged PTFE nanoparticles (100 nm) in this novel membrane can highly promote the output of S-LSNG. For the first time, the excellent stretchability (tensile strain, 200%), high output performance (open-circuit voltage of 120 V and short-circuit current of 18 μA) and ultra-thin device structure (300 μm) were achieved simultaneously for a liquid-solid contact electrification-based nanogenerator. Besides, the output performance of S-LSNG barely changed even after 100000 submerging-emerging cycles. In addition, the application of motion monitoring for human body in water was also demonstrated, such as single finger motion sensing and complex motion sensing of multiple-fingers. Because of the excellent stretchability, output performance and durability, the S-LSNG would be extensively applied to a sustainable energy supplier for the stretchable and wearable electronics in water.

Investigation of the energy of wave motions in a three-layer hydrodynamic system

In this paper, the propagation of the energy of internal waves in a three-layer hydrodynamic liquid system ‘a layer with a solid bottom–a layer–a layer with a lid’ is investigated. The problem statement is executed in a dimensionless form. Using the method of multidimensional development, the first three linear problems were obtained. For the first approximation problem, a dispersion equation of the first order is derived, and two pairs of independent solutions are obtained. The dependence of total energy on the wave number and thickness at different values of physical parameters were graphically illustrated and analyzed. The limiting case in which the obtained results are compared with the calculation of the energy that transferring the wave in the hydrodynamic system ‘liquid layer–a layer with a lid’, which was investigated earlier is considered. Graphically illustrates the transition of this system to a two-layer one. Data obtained as a result of the study of the problem of propagation of internal wave energy in a liquid three-layer hydrodynamic system can be used in the study of similar areas in the ocean and in the development of appropriate technologies and devices using the energy of water waves or converted into electricity.

Numerical Simulations of Non-Breaking, Breaking and Broken Wave Interaction with Emerged Vegetation Using Navier-Stokes Equations

Coastal plants can significantly dissipate water wave energy and services as a part of shoreline protection. Using plants as a natural buffer from wave impacts remains an attractive possibility. In this paper, we present a numerical investigation on the effects of the emerged vegetation on non-breaking, breaking and broken wave propagation through vegetation over flat and sloping beds using the Reynolds-average Navier-Stokes (RANS) equations coupled with a volume of fluid (VOF) surface capturing method. The multiphase two-equation k-ω SST turbulence model is adopted to simulate wave breaking and takes into account the effects enhanced by vegetation. The numerical model is validated with existing data from several laboratory experiments. The sensitivities of wave height evolution due to wave conditions and vegetation characteristics with variable bathymetry have been investigated. The results show good agreement with measured data. For non-breaking waves, the wave reflection due to the vegetation can increase wave height in front of the vegetation. For breaking waves, it is shown that the wave breaking behavior can be different when the vegetation is in the surf zone. The wave breaking point is slightly earlier and the wave height at the breaking point is smaller with the vegetation. For broken waves, the vegetation has little effect on the wave height before the breaking point. Meanwhile, the inertia force is important within denser vegetation and is intended to decrease the wave damping of the vegetation. Overall, the present model has good performance in simulating non-breaking, breaking and broken wave interaction with the emerged vegetation and can achieve a better understanding of wave propagation over the emerged vegetation.

Wave energy attenuation in fields of colliding ice floes – Part 1: Discrete-element modelling of dissipation due to ice–water drag

Abstract. The energy of water waves propagating through sea ice is attenuated due to non-dissipative (scattering) and dissipative processes. The nature of those processes and their contribution to attenuation depends on wave characteristics and ice properties and is usually difficult (or impossible) to determine from limited observations available. Therefore, many aspects of relevant dissipation mechanisms remain poorly understood. In this work, a discrete-element model (DEM) is used to study one of those mechanisms: dissipation due to ice–water drag. The model consists of two coupled parts, a DEM simulating the surge motion and collisions of ice floes driven by waves and a wave module solving the wave energy transport equation with source terms computed based on phase-averaged DEM results. The wave energy attenuation is analysed analytically for a limiting case of a compact, horizontally confined ice cover. It is shown that the usage of a quadratic drag law leads to non-exponential attenuation of wave amplitude a with distance x, of the form a(x)=1/(αx+1/a0), with the attenuation rate α linearly proportional to the drag coefficient. The dependence of α on wave frequency ω varies with the dispersion relation used. For the open-water (OW) dispersion relation, α∼ω4. For the mass loading dispersion relation, suitable for ice covers composed of small floes, the increase in α with ω is much faster than in the OW case, leading to very fast elimination of high-frequency components from the wave energy spectrum. For elastic-plate dispersion relation, suitable for large floes or continuous ice, α∼ωm within the high-frequency tail, with m close to 2.0–2.5; i.e. dissipation is much slower than in the OW case. The coupled DEM–wave model predicts the existence of two zones: a relatively narrow area of very strong attenuation close to the ice edge, with energetic floe collisions and therefore high instantaneous ice–water velocities, and an inner zone where ice floes are in permanent or semi-permanent contact with each other, with attenuation rates close to those analysed theoretically. Dissipation in the collisional zone increases with an increasing restitution coefficient of the ice and with decreasing floe size. In effect, two factors contribute to strong attenuation in fields of small ice floes: lower wave energy propagation speeds and higher relative ice–water velocities due to larger accelerations of floes with smaller mass and more collisions per unit surface area.

Study of thin film blue energy harvester based on triboelectric nanogenerator and seashore IoT applications

Water wave energy, also known as blue energy, is a promising clean and renewable energy to solve global energy crisis. Recently, triboelectric nanogenerator (TENG) is considered as one of the most efficient approaches for harvesting water wave energy. Here we introduced a thin film blue energy harvester based on liquid-solid contact triboelectric mechanism. With novel external Ū electrode including a bar electrode (B electrode) and a U-shape electrode (U electrode), the shielding effect from water is hugely minimized, and outputs are effectively improved. Moreover, a series of IoT applications aiming seashore area is studied and realized, such as functions of wave level warning, continuously powering and a wireless signals transmission.

Matryoshka-inspired hierarchically structured triboelectric nanogenerators for wave energy harvesting

There is a tremendous interest to harvest ocean wave energy due to its promising advantages of high-power density, wide distribution, independence of time of day, weather or seasons, and sustainability. However, most of the current energy harvesters or converters based on electromagnetic generators are suffering from unsatisfactory efficiency at low ocean wave triggering frequency and have the drawbacks of complex design, high cost and ease of corrosion in seawater. In this work, we report a matryoshka-inspired hierarchically structured triboelectric nanogenerator (HS-TENG) by nest-assembling multiple shells with decreasing sizes for effectively harvesting low-frequency wave energies with low-cost, high power density and high efficiency. As a proof-of-concept, we have fabricated a three-hierarchical-level HS-TENG by nesting three spherical acrylic shells filled with polytetrafluoroethylene (PTFE) balls into the gap spaces between the neighboring shells. The important factors that may affect the energy harvesting performance of the HS-TENG are studied, including the size and number of moving balls, the diameter of the holding shell, the amplitude and frequency of wave actuation, as well as the orientation angle between wave motion direction and electrode gap. It is demonstrated that the HS-TENG has superior output performance over the traditional single ball TENG (SB-TENG), with a maximum output peak power of 544 μW at a low frequency of 2 Hz, more than 6.5 times of that obtained by a SB-TENG with the same size, capable of driving different wearable electronics. Based on the optimized design, we further demonstrate that a HS-TENG network formed by a 3 × 3 device array can directly lighten dozens of light-emitting diodes and power an electronic thermometer for monitoring water condition, indicating its capability in effectively harvesting water wave energy for potential large-scale deployment in the ocean. This study provides an innovative hierarchical structure that can effectively improve the output performance of TENGs and paves the way for developing next-generation high-performance TENGs for blue energy harvesting.

Stacked pendulum-structured triboelectric nanogenerators for effectively harvesting low-frequency water wave energy

The invention of triboelectric nanogenerators (TENGs) provides an effective approach for harvesting water wave energy that is clean and renewable. Here, stacked pendulum-structured triboelectric nanogenerators for harvesting low-frequency water wave energy is proposed. The device works based on a pendulum-like principle through a compact disk-track structure that enables area contact instead of point contact while maintaining the susceptible rolling motion. Thus the tribo-electrification and the output are greatly enhanced in slow water waves. While only considering the volume of the TENG units, charge output density of 4622 μC m−3 can be achieved, which is more than 13.2 times of a typical ball-shell structured device. A peak power density of 14.71 W m−3 and an average power density of 1.05 W m−3 are obtained in low-frequency water waves below 0.5 Hz. The device shows great potential of the rolling area-contact design to enhance the output of TENG-based wave energy harvester with excellent low-frequency performance, which is crucial to the development of TENGs for effectively exploiting abundant water wave energy.

A High-Power Density Triboelectric Nanogenerator for Harvesting Wave Energy

The global power by waves breaking around the coastlines worldwide has been estimated to be 2-3TW, and if wave energy is collected on open oceans, the global wave power is estimated to be one order of magnitude larger[1]. The water wave energy could turn out to be an even more benign source of power than wind, due to its abundance in the ocean [2]. Although it is a promising prospect for harvesting wave energy, most technologies for capturing wave power still remain in the testing phase. Currently, traditional devices usually harvest wave energy with complex hydraulic or mechanical structures and they drive an electromagnetic generator by transforming the energy from the water waves into rotary motion or linear reciprocal motion. However, these current oceans wave energy apparatuses exhibit unsatisfactory energy harvesting efficiency, high cost, and other methods of harvesting energy would have to be implemented [3-4]. In this work, a high-power density triboelectric nanogenerator (HPD-TENG) is designed and systematically investigated.This HPD-TENG is designed to be built by multiple units made of PTFE balls and 3D printed arc surface coated with melt adhesive reticulation nylon film. The integration of power generation model together with the kinetic model for the HPD-TENG is proposed and studied. The HPD-TENG can effectively transform arbitrary directional wave energy into electrical energy by utilizing charged balls rolling on optimized arc surface induced by ocean wave excitation. Furthermore, with the power generation units increases from 1 to 10 in one block, the power density increases linearly from 1.03 W/m3 to 10.6 W/m3. This indicates that the power density of the HPD-TENG increases proportionally with the number of units connected in parallel without rectifiers due to its distinctive mechanism and structure. Hence the design of HPD-TENG can be regarded as an innovative and effective approach for large-scale blue energy harvesting through integrating more units to form HPD-TENG networks.

(Invited) Triboelectric Nanogenerators for Internet of Things and Self-Powered Systems

Self-powered system is a system that can sustainably operate without an external power supply for sensing, detection, data processing and data transmission. Nanogenerators (NG) were first developed for self-powered systems based on piezoelectric effect and triboelectrification effect for converting tiny mechanical energy into electricity, which have applications in internet of things, environmental/infrastructural monitoring, medical science, environmental science and security. NGs are the applications of Maxwell’s displacement current in energy and sensors. NGs have three major application fields: micro/nano-power source, self-powered sensors and blue energy. We will present the applications of the NGs for harvesting all kind mechanical energy that is available but wasted in our daily life, such as human motion, walking, vibration, mechanical triggering, rotating tire, wind, flowing water and more. Then, we will illustrate the networks based on triboelectric NGs for harvesting ocean water wave energy, for exploring its possibility as a sustainable large-scale power supply. Lastly, we will show that NGs as self-powered sensors for actively detecting the static and dynamic processes arising from mechanical agitation using the voltage and current output signals. This presentation will cover not only the fundamental science of triboelectric nanogenerators, but also will focus on the technology innovation and perspective industrial applications as well as business opportunities. Z.L. Wang, Materials Today, 20 (2017) 74-82.“Nanogenerators for Self-Powered Devices and Systems”, by Z.L. Wang, published by Georgia Institute of Technology (first book for free online down load): http://smartech.gatech.edu/handle/1853/39262 Z.L. Wang, L. Lin, J. Chen. S.M. Niu, Y.L. Zi “Triboelectric Nanogenerators”, Springer, 2016. http://www.springer.com/us/book/9783319400389L. Wang “Triboelectric Nanogenerators as New Energy Technology for Self-Powered Systems and as Active Mechanical and Chemical Sensors”, ACS Nano 7 (2013) 9533-9557.Z.L. Wang, J. Chen, L. Lin “Progress in triboelectric nanogenertors as new energy technology and self-powered sensors”, Energy & Environmental Sci, 8 (2015) 2250-2282.

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

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

A Nonencapsulative Pendulum‐Like Paper–Based Hybrid Nanogenerator for Energy Harvesting

AbstractThe newly invented triboelectric nanogenerator (TENG) is deemed to be a more efficient strategy than an electromagnetic generator (EMG) in harvesting low‐frequency (<2 Hz) water wave energy. Various TENGs with different structures and functions for blue energy have been developed, which can be roughly divided into two types: liquid–solid contact electrification TENGs and fully enclosed solid–solid contact electrification TENGs. Robustness and packaging are critical factors in the development of TENGs toward practical applications. Furthermore, for fully enclosed TENGs, the requirements and costs of packaging are very high, and they can difficult to disassemble after enclosed, if there is something wrong with the devices. Herein, a nonencapsulative pendulum‐like paper based hybrid nanogenerator for energy harvesting is designed, which mainly consists of three parts, one solar panel, two paper based zigzag multilayered TENGs, and three EMG units. This unique structure reveals the superior robustness and a maximum peak power of zigzag multilayered TENGs up to 22.5 mW is realized. Moreover, the device can be used to collect the mechanical energy of human motion in hand shaking. This work presents a new platform of hybrid generators toward energy harvesting as a portable practical power source, which has potential applications in navigation and lighting.

Super-robust and frequency-multiplied triboelectric nanogenerator for efficient harvesting water and wind energy

Mechanical energy in ambient, such as water wave, wind, vibration, and human activities, is a green energy that is widely distributed and universally achievable. However, this type of energy has ultra-low frequencies and variable amplitudes, so it is rather challenging to collect them at high efficiency. Here we report a pendulum inspired triboelectric nanogenerator (P-TENG), which could not only boost the output frequency multiple times using a pendulum structure, but also hugely improve the harvesting efficiency through a transformation of impact kinetic energy into potential energy. The P-TENG also has ultrahigh sensitivity and active response to mechanical triggering from a random direction and superior durability for long time operation. A single trigger from the environment, the P-TENG shows a continuous electrical output for 120 s at a frequency of 2 Hz, and its output energy of which is 14.2 times larger than the energy of conventional free-standing TENG. Owing to the air gap between the triboelectric layer and electrodes and the mechanism of electrostatic induction, the P-TENG can work with little frictional resistance and surface wearing, largely enhancing its robustness and durability. The network of P-TENGs was successfully demonstrated to scavenge water wave or wind energy as sustainable power sources. Given the features of exceptional output performance, unprecedented robustness and universal applicability resulting from distinctive mechanism and structure, the P-TENG is a promising method to efficiently harvest energy from the ambient environment with possibility contributing to the blue energy.

Self-powered intelligent buoy system by water wave energy for sustainable and autonomous wireless sensing and data transmission

Harvesting ocean wave energy is a killer application of triboelectric nanogenerator (TENG) for advantages in simple mechanism, high power density and high efficiency at low frequency. Here we report a self-powered intelligent buoy system (SIBS), in which a high-output multilayered TENG is used for water wave energy harvesting. With a power management module, the output voltage can be converted and regulated as a steady DC voltage of 2.5 V for the operations of a microprogrammed control unit (MCU), several micro sensors and a transmitter. With the intelligent monitoring mechanism of the MCU, the harvested energy can be deployed for each sensor with different priority and data transmission cycle, and the SIBS can be at standby and active status by itself at different energy levels. At a wave frequency of 2 Hz, the SIBS can provide an average output power density of 13.2 mW/m2 and realize sustainable and autonomous wireless sensing for acceleration, magnetic intensity and temperature in range of 15 m, with amount of 19 bytes every 30 s. The SIBS has first demonstrated a complete TENG-based micro-energy solution for self-powered intelligent system, including energy harvesting, management, deployment and utilization, with an unattended manner and infinite lifetime. As a significant milestone for the TENG, this work has provided a universal platform for self-powered wireless sensor network nodes and exhibited broad prospects in internet of things, big data, artificial intelligence and blue energy.

Prediction of interface states in liquid surface waves with one-dimensional modulation

We theoretically study the interface states of liquid surface waves propagating over the heterojunctions formed by a bottom with one-dimensional periodic undulations. By considering the periodic structure as a homogeneous one, our systematic study shows that the signs of the effective depth and gravitational acceleration are opposite within the band gaps whether the structure is symmetric or not. Those effective parameters can be used to predict the interface states which could amplify the amplitudes of liquid surface waves. These phenomena provide new opportunities to control the localization of water-wave energy.