Broadband water wave reflector with customisable frequency range enabled by floating metaplates

This paper is about how the uses of computer software's are such valuable tools for undergraduate engineering education, specifically in the design and analysis of renewable energy systems. Right now, there are many programs in the area of design of renewable energy systems, some more complexes, others user-friendlier and others too simple. For this work, the software HOMER (Hybrid Optimization Model for Electric Renewable) has all the tools necessarily to make a good work and it is not too complicated for undergraduate engineering students without previous knowledge in the area of energy systems. As part of this work, three educational modules were developed. The first module is about how to use and interact with HOMER. Second, how to design a residential photovoltaic system to lower energy cost. The last module can be considered as a guide on how to use renewable energy to secure a sustainable grid. The paper presents the technical skills gained by the students using the software HOMER. Finally, undergraduate students had the exposure to non-technical engineering skills, like economic feasibility, logistic and decision on energy security.

The subject of seismic metamaterials, inspired from novel ideas in optics and acoustics, has attracted great attention in the last decade for potential applications in earthquake engineering. Simple structure systems, like beams and plates, with periodically attached mechanical resonators provide a simple physical model to interpret the existence of certain frequency bandgap in dispersion relations and to simulate the mechanism of flexural energy attenuation. In this work, we consider simple structure systems of beams and plates with periodically attached resonators. The resonator is composed of a spring, a damper and a mass attached along the beam direction. We utilize the Timoshenko beam model and the Mindlin plate theory to incorporate the shear effect. The plane wave expansion method together with the Bloch theorem is used to expand the governing field into an eigenvalue problem of an infinite complex system, allowing us to characterize the band structures of the dispersion relations. Local resonance and Bragg bandgaps are identified and examined. The effect of thickness ratios, the damping ratio and the shear modulus are exemplified to demonstrate how these factors will affect the formation of bandgaps. This formulation demonstrates a feasibility that a periodic array of mechanical resonators together with suitable material and geometric parameters of beams and plates can be designed to tune with the dispersion behavior in the control of flexure waves. This study may open up new potential in the control of wave propagation in complex continuum systems through the interaction of adequately designed resonators.

Geometric phase is a far-reaching concept in quantum and classical physics, revealing deep connections between topology and wave dynamics in diverse systems. The Pancharatnam-Berry (PB) geometric phase, which arises from 2D optical polarization evolution, has revolutionized light manipulation by enabling optical metasurfaces. The PB phase is commonly regarded as a unique property of light waves. Generalizing this concept to other classical waves can uncover new geometric phase properties and enable novel wave control mechanisms. Here, the first observation of the PB phase in surface water (gravity) waves is reported, achieved through the interaction with symmetry-engineered scatterers. In contrast to the optical PB phase, the water-wave PB phase is an intrinsic higher-order geometric phase induced by 4D evolution of spin-orbit states. It exhibits remarkable properties, including unbounded phase values, spin-momentum-locked unidirectional channels, and a Poincaré hypersphere representation. PB metasurfaces are further realized for versatile manipulation of water wavefronts, including steering and focusing. This work reveals the universality of the PB phase across different wave systems and generalizes it to higher-dimensional state evolutions. The results open new avenues for exploring the geometric and topological properties of water waves, with potential applications in coastal protection and wave energyharvesting.

Based on analytic derivations and numerical simulations, we show that near a low resonant frequency water waves cannot propagate through a periodic array of resonators (bottom-mounted split tubes) as if water has a negative effective gravitational acceleration g(e) and positive effective depth h(e). This gives rise to a low-frequency resonant band gap in which water waves can be strongly reflected by the resonator array. For a damping resonator array, the resonant gap can also dramatically modify the absorption efficiency of water waves. The results provide a mechanism to block water waves and should find applications in ocean wave energy extraction.

Waves propagating over oscillating periodic structures can be reflected and attenuated either by Bragg scattering or by local resonance. In this work, we focus on the interplay between surface gravity waves and submerged resonators, investigating the effect of the local resonance on wave propagation. The study is performed using a state of the art numerical simulation of the Navier–Stokes equation in two-dimensional form with free boundary and moving bodies. A volume of fluid interface technique is employed for tracking the free surface, and an immersed boundary method for the fluid–structure interaction. A wave maker is placed at one end of the flume and an absorbing beach at the other. The evolution in space of a monochromatic wave interacting with up to four resonators coupled only fluid mechanically is presented. We evaluate the efficiency of the system in terms of wave amplitude attenuation and energy transfers between the fluid and the solid phase. The results indicate that, near resonance conditions, both wave reflection and energy dissipation increase significantly. Conversely, far from resonance, waves can propagate through the system with minimal dissipation, even in the presence of numerous resonators. Moreover, when the time scale associated with the resonator’s restoring force is longer than the wave period, the resonators tend to follow the wave motion, oscillating with an amplitude comparable to that of the wave. In contrast, when the two time scales are similar, the resonator motion becomes amplified, resulting in stronger velocity gradients and enhanced viscous dissipation.

Renewable energy and storage systems are widely discussed to minimise the impact of global warming. In addition to the temporal resolution of simulation tools, also the chosen input data might have a strong impact on the performance of renewable energy systems, and energy storage systems in particular. This study analyses the impact of probabilistic weather data on the design of renewable energy systems. The main objective is hereby the determination of the robustness of a recently state-of-the-art design process of a 100% renewable energy and storage system with varying probabilistic input data. The island of La Gomera, Canary Islands, is taken as a case study. Although all analysed systems show some variance in their results, the combination of vehicle-to-grid and power-to-hydrogen shows the best economic performance. Hereby, small island energy systems depending heavily on wind energy show higher variations than those with high shares of solar energy. This analysis illustrates clearly that the choice of one historical reference year is not suitable to determine the expected performance of an energy system. To learn about their sensitivity, synthetic probabilistic inputs as applied in this study are a good way to determine both the expected mean values and their variance.

A design model for sustainable and clean power system integrated with reverse osmosis water treatment/desalination unit to meet the challenges of climate change, water shortage and energy while producing organic and healthy food is presented. The main objectives of the optimized design of renewable energy system are: (1) decrease the CO2 emissions, (2) reduce the energy consumption from the grid by adding more renewable resources such as solar, and (3) fresh water production for irrigation using underground or sea water reverse osmosis water treatment/desalination system. The goal is to integrate sustainable power and water systems to meet the challenges of climate change and water shortages especially in desert regions. Modeling and simulation for the optimized design of renewable energy system for the agriculture farm was used in this study. The results show that the grid-tied solar PV energy system has the best performance compared to the grid and standalone renewable power system. The solar energy system connected to the grid is a good option for the agriculture farm with respect to the cost (85$/MWh), renewable fraction (67%), and greenhouse gas emissions (208 kg of carbon dioxide per MWh of energy produced).

Water wave energy is one important source of renewable energy worth further exploitation to help reduce global carbon emission. To aid in such exploitation, we have designed and constructed a water wave energy harvester, and tested it in the towing tank at NCKU. The wave energy harvester has three major systems: a mechanical mechanism driven by wave motion through an oscillating buoy, a generator system converting the mechanical energy of the buoy into electric energy, and an energy storage system. Meanwhile, to optimize the performance of mechatronic components and energy storage electronics of our wave energy harvester to be tested in the towing tank, a small-scale apparatus also is built, which includes an actuator system and an energy harvesting system that mimics the full-scale wave energy harvester. Through dynamical similarity analysis, nearshore wave data collected on the west coast of Central Taiwan are used to determine the system parameters, such that the tested system can be thought of as a 1/6 model of a prototype that hopefully can be built and deployed nearshore. Results of the towing tank tests indicate that, for water waves of period 1.4 s and height 10 cm, and when the moment of inertia of the harvester is 6.14 x 10 - 3 kg-m 2 , a maximum energy conversion efficiency of 14.2% can be achieved. This preliminary study demonstrates the feasibility of our wave energy harvester design, and helps identify how its efficiency can be further improved.

A theory is developed for the diffraction of light by two spatially separated parallel ultrasonic progressive waves of different frequency. The preliminary theories ofRaman andNath [C. V.Raman and N. S.Nath, Proc. Indian Acad. Sci. A2, 406–412; 413–420 (1935)] for normal and oblique incidence are taken to be valid. The resulting equations are extensions of earlier results of R.Mertens, Z. Physik160, 291–296 (1960). The predicted periodicity of the diffraction spectrum with increasing sound beam separation agrees with the well known periodicity of the light intensity distributions in the Fresnel zone of the phase grating formed by the first ultrasonic wave. Results of numerical calculations are presented to illustrate features of the theoretical results, as reflected in the first order of diffraction for 3.0 and 6.0 Mc ultrasonic waves in water.

Review of application of AI techniques to Solar Tower Systems

This article explores how a submerged elastic plate, clamped at one edge, interacts with water waves. Submerged elastic plates have been considered as potentially effective design elements in the development of wave energy harvesters but their behaviour in a wave field remains largely unexplored, especially experimentally. Positioned at a fixed depth in a wave tank, the flexible plate demonstrates significant wave reflection capabilities, a characteristic absent in rigid plates of identical dimensions. The experiments thus reveal that plate motion is crucial for wave reflection. Sufficiently steep waves are shown to induce a change in the mean position of the plate, with the trailing edge reaching the free surface in some cases. This configuration change is found to be particularly efficient to break water waves. These findings contribute to understanding the potential of elastic plates for wave energy harvesting and wave attenuation scenarios.

<p>Propagation of gravity waves (GWs) is studied in the troposphere and thermosphere/ionosphere. The investigation of GW propagation in the troposphere is based on measurements by large scale array of absolute microbarometers with high resolution that is located in the westernmost part of the Czech Republic. On the other hand, the propagation of GWs in the thermosphere/ionosphere is observed remotely, using multi-frequency and multi-point continuous HF Doppler sounding system operating in the western part of the Czech Republic. The reflection heights of sounding radio waves of different frequencies are determined from ionospheric sounder, located in Pruhonice in the vicinity of Prague. Propagation velocities and directions are in both cases calculated from time/phase delays between signals recorded at different locations. The investigation of propagation of GWs in the ionosphere is performed in three dimensions as the observation points (reflection points of radio signals) are separated both horizontally and vertically. It is shown that GWs in the ionosphere usually propagate with wave vectors directed obliquely downward, which means upward propagation of energy. In addition, seasonal and diurnal changes of propagation directions were found. Typical propagation velocities of GWs observed at ionospheric heights are much higher (~100 to 200 m/s) than those observed on the ground (several tens of m/s).        </p>

Effect of a porous sea-bed on water wave scattering by two thin vertical submerged porous plates

Investigation of a new magnetorheological elastomer metamaterial plate with continuous programmable properties for vibration manipulation

A resonator assembly consisting of a two-dimensional periodic array (mass-screws) mounted to a thin homogenous plate was used to investigate the vibration characteristics of locally resonant (LR) phononic plates. The numeric simulations employed the finite element method to calculate the band structures of the proposed periodic plates and to analyze the effect of geometry parameters on the evolution of the flexural band gap behavior. To experimentally validate the predictions for these theoretical examinations, two measurements with the LR phononic plates were obtained with respective lattice constants a = 40 and 50 mm. The tested plate was clamped on one side to a shaking table to generate a plane wave, propagating in the Ox-direction. Obtained experimental measurements of the wave attenuation in this direction are in good agreement with the theoretical frequency of both complete and directional band gaps.