Incoming Wave Research Articles

Control strategy of the MGR Wave Energy Converter (WEC)

This paper presents the control strategy proposed for a new wave energy converter (WEC) design, the MGR. The control aims to maximise the energy absorption from waves, adapting converter's resistance to the incoming wave size. The MGR is a near shore submerged converter that takes advantage of the oscillating water column created by the wave when it passes on the converter's platform. The wave column moves the platform, transmitting the force to a single acting cylinder, that pumps sea water to the coast, where is turbined generating electricity. The control strategy is based on adjusting the system pressure to the coming wave size to create the optimal resistance, absorbing the maximum energy from it. The pressure is controlled by the aperture of turbine jet, positioning jet needle. In addition, the PLC implements the synchronous generator's load (torque) in order to maintain the turbine working at the maximum efficiency rotation speed

A 3D BEM-Coupled Mode Model for the Performance Analysis of Wave Energy Converter Parks in Nearshore-Coastal Regions

Estimation on the production capacity of wave energy converter arrays (WECs) of the type of simple floaters deployed in nearshore locations highly depends on the evaluation of their performance. The latter also depends on various factors, including the dimensions and inertial characteristics of the devices, their relevant positioning, and the power take-off (PTO) system characteristics. Studying the system operation, based on the prevailing sea conditions in the region considered for deployment, can ensure that such WEC farms are sized and designed in an effective way. Furthermore, the wavelength and propagation direction of incoming wave fields can be significantly impacted by wave-seabed interactions in coastal areas, which can alter the WECs’ response pattern and ultimately the array’s power output. In this work, a 3D BEM hydrodynamic model is proposed aiming to assess the energy-capturing capacity of WEC arrays, accounting for the hydrodynamic interactions between various identical floating devices, as well as the local seabed topography. The model is supplemented by a Coupled Mode System (CMS) to calculate the incident wave field propagating over variable bathymetry, in order to simulate realistic nearshore environments. Finally, a case study is performed for an indicative geographical area, north of the coast of the island of Ikaria, located in the Eastern Aegean Sea region, where the wave potential is high, using long-term data. The latter study highlights the applicability of the proposed method and suggests its usage as a tool to support optimal WEC park design.

Experimental Study on Wave Transmission Coefficient of Double Cylindrical Floating Breakwater in a Wave Basin

Floating breakwater is a better alternative than the conventional method. It is an effective coastal engineering unit used to protect coastal regions such as harbours and marinas from erosive waves. It has many other applications such as offshore renewable energy generation, infrastructure preservation, temporary structure, and provides a controlled environment for aquaculture activities. The floating breakwater such as the double cylindrical floating breakwater (DCFB) is claimed to have effective wave attenuation characteristics. A lab scale investigation was done by placing the DCFB in a controlled wave basin in with wave generator to generate wave and wave gauge to quantify the wave transmission coefficient. The wave transmission coefficient represents the effectiveness of the breakwater system in attenuating incoming waves, where an effective breakwater system will result in a low transmission coefficient value. In this study, the DCFB’s effectiveness in terms of wave transmission coefficient was investigated with two different configurations where the spacing between the cylinders of the DCFB units are 0.2 m and 0.6 m respectively. Results show that the configuration of DCFB units with 0.5 m cylinder spacing are more effective in absorbing incoming wave height resulting in lower transmission coefficient. Furthermore, some prospective areas had been identified for future enhancement.

SItomo – A toolbox for splitting intensity tomography and application in the Eastern Alps

The tomographic inversion of shear wave splitting data for upper mantle anisotropy has been a longstanding challenge. This is due to the ray-based approximation of classical approaches and the near-vertical incidence of the core-mantle converted phases such as SKS that are often used. Recent developments include the calculation of finite-frequency sensitivity kernels for SKS splitting intensity observations, which allows us to accurately take into account the sensitivity to anisotropic structure with depth. A requirement of this tomographic technique is a dense station spacing, which results in overlapping sensitivity kernels at depth and allows for the localization of anisotropic structure. This is satisfied by a growing number of temporary seismic deployments, which motivates the desire to image anisotropic complexities with depth. Here, we introduce and make available a toolbox for the MATLAB environment that facilitates the application of finite-frequency splitting intensity tomography to dense seismic arrays. Our implementation includes several key features, including: 1) A forward calculation of splitting intensities and sensitivity kernels for a complex anisotropic model space. 2) Consideration of the dominant period of the wave, allowing for multiple-frequency analysis, as well as the incoming wave’s non-vertical incidence. 3) The inversion can be based on a classical gradient descent, on a form of the conjugate gradient method known as the BFGS algorithm, or on a gradient-informed stochastic reversible jump algorithm, allowing for a data-driven parametrization of the model space. 4) Importing splitting intensity measurements from waveforms processed in SplitRacer allows for fast pre-processing of large data sets due to its fully automatic design. To illustrate our method, we present both synthetic tests and an application to real data. We apply our inversion procedure to data from the Swath-D network, which densely covers the transition of the Central to the Eastern Alps. Previous studies showed evidence for an abrupt lateral change of layered seismic anisotropy that had been attributed to an opening for channeled asthenospheric flow. Using an SKS splitting intensity tomography approach, we can confirm previous inferences while providing additional constraints on the distribution of anisotropy laterally and with depth.

Determination of the seismic structure of the Earth based on joint analysis of gravimetric and seismometric data – a case study

The evolution of the Earth’s surface is driven by external and internal forces, the latter of which can only be studied indirectly. Knowledge about the structure of the Earth’s interior is very important for modeling and predicting the processes occurring at the surface. This study presents a new concept of joint analysis of the gravimetric and seismometric recordings of earthquakes for determining the seismic structure of the Earth down to the depth of 1250 km. The proposed method allows the use of gravimetric data without the known full transfer function of the instrument. Group velocity dispersion curves of the fundamental mode of Rayleigh waves up to the period of 550 s are measured based on the joint analysis of the recordings of superconducting gravimeter and broadband seismometers operating at the same location in five testing sites in Europe, allowing for the exploration of a broader response for incoming seismic waves. Averaged dispersion curves for earthquakes around the world for each site are inverted by the weighted linear inversion and Monte Carlo methods to estimate the distribution of shear-wave seismic velocity in the Earth’s mantle. A comparison of the deterministic and probabilistic inversion methods can excellently demonstrate surface waves’ ability to determine the Earth’s mantle structure. The inversion results are compared with the global ak135 seismic model (Kennett et al. 1995) to verify the proposed method.

Embayed beach configuration explained by wave sheltering

Embayed beaches, characterized by their distinctive planform curvature, are a common feature along coastlines worldwide. This study introduces a novel approach to describe bay shape that extends our understanding about the processes that control embayed beach development. The novel approach was thoroughly tested against one-line models and applied to real-world cases covering a wide range of spatial scales, wave climate conditions and geomorphological settings. Here we show that the equilibrium curvature of embayed beaches can be correctly described and explained by considering headland-provided offshore wave sheltering alone, without explicitly accounting for wave shoaling, refraction, diffraction, or longshore transport. This holds true as long as the offshore wave climate is accurately characterized, including complete information regarding the mean and the spread of the incoming wave direction. For narrow-banded dominant swell wave regimes, the inclusion of background wind sea components has been identified as crucial for predicting curvature in the more sheltered embayed domain. The presented model significantly contributes to the understanding of how waves shape embayed beaches.

Energy attenuation of seismic metamaterials composed of a periodic array of coated elliptical cylinders

Abstract We present a numerical study on energy attenuation of seismic metamaterials consisting of a periodic array of coated elliptical cylinders. The aim is to perceive the effect of aspect ratio for different wave modes so that the metamaterials can interact with the incoming wave causing them to interfere with each other destructively, especially for low-frequency seismic waves with relatively wide bandgap. Previous studies mainly focused on the configuration of coated circular cylinders or spheres, in which the metamaterial is composed of a hard inclusion surrounded by a soft coating layer and dispersed within a hard matrix. Here we utilize numerical simulations based on finite element calculation to analyze the local fields within the unit cell. Effective mass density, mass moment of inertia and shear modulus are analyzed through a homogenization procedure to characterize the macroscopic behavior of the effective medium. The effective behavior will be dependent for different aspect ratios and for different types of wave motions. To verify the effectiveness of energy attenuation, a full-scale model is adopted. Specifically, to identify optimal energy attenuation configurations, we illustrate the attenuation effects of elliptical metamaterials under longitudinal and shear horizontal types of waves. The present study demonstrates that elliptical metamaterials will have more reflexibilities to tune with the aspect ratio of the elliptical geometry as well as the directionality of incidence waves. Based on our simulations, we show the ability of the designed configuration in tuning local resonance frequencies and bandwidths for real implementations and applications of seismic metamaterials.

Printed graphene and its composite with copper for electromagnetic interference shielding applications.

Advances in mobile electronics and telecommunication systems along with 5G technologies have been escalating the electromagnetic interference (EMI) problem in recent years. Graphene-based material systems such as pristine graphene, graphene-polymer composites and other graphene-containing candidates have been shown to provide adequate EMI shielding performance. Besides achieving the needed shielding effectiveness (SE), the method of applying the candidate shielding material onto the object in need of protection is of enormous importance due to considerations of ease of application, reduced logistics and infrastructure, rapid prototyping and throughput, versatility to handle both rigid and flexible substrates and cost. Printing readily meets all these criteria and here we demonstrate plasma jet printing of thin films of graphene and its composite with copper to meet the EMI shielding needs. SE over 30 dB is achieved, which represents blocking over 99.9% of the incoming radiation. Graphene and its composite with copper yield higher green index compared to pure copper shields, implying reduced reflection of incoming electromagnetic waves to help reduce secondary pollution.

Resonant periodic structures for strong attenuation of surface water wave

Inspired by the local resonance mechanism, a resonant periodic structure (RS) constructed by an array of periodic floating oscillators is proposed for enhancing surface water wave attenuation. A hybrid frequency domain method is introduced for solving the linear or nonlinear initial-boundary value mixing problem. The numerical results show that the RS has a superior suppression effect on the propagation of waves in comparison with the Bragg periodic structure (BS) of the same scale. The incoming waves across the spectrum are substantially reduced by RS through the inverse propagation of radiation waves induced by the wave-driven oscillators. Furthermore, to achieve a better attenuation effect, a nonlinear resonant periodic structure which the periodic oscillators are integrated with the nonlinear stiffness mechanism (NSM) is proposed based on the idea of reducing equivalent stiffness. The motions of oscillators are regulated by the NSM, and the attenuation effect is further improved due to the modified radiation wave. The concept and results presented herein may provide forward-looking technical guidance for future coastal protection.

Engineered Materials, Machine Learning Enhance Carbon Storage Well Integrity

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 214844, “Engineered Materials and Machine Learning for Carbon Storage Well Integrity,” by Jacob Pollock, Oceanit Laboratories, and Hani Elshahawi, SPE, NoviDigiTech. The paper has not been peer reviewed. _ The success of CO2 injection operations, and the endurance of long-term storage, are partially dependent on well design and the materials used for well construction. The authors describe a stack of technologies they have developed that enable enhanced well robustness, monitoring of carbon-storage facilities, and modeling of their performance. The combination of these technologies enables the tracking of downhole and subsurface fluid distribution and flow. Furthermore, the scalable technologies can be used to exploit remaining reservoirs while preventing CO2-plume migration. Introduction Besides site selection and geological features that influence plume migration, well-construction design and materials have a major effect on successful storage. Injection wells are drilled into the storage site and completed with multiple cemented casing strings, with access to the reservoir through perforations or gravel packs. Cement supports and protects the metal casings from corrosive fluids while isolating the storage reservoir from freshwater aquifers by sealing off the wellbore annulus (Fig. 1). Cement integrity and durability are critical to successful carbon capture, storage, and use (CCUS) operations. Despite their importance, current cement-evaluation methods suffer from limited resolution, poor discrimination, and ambiguous interpretation. The authors have developed steel/cement interfacial bonding nanotechnology that enhances both mechanical bonding and acoustic coupling, along with acoustic metamaterials for sensing cement and tracking particles. The acoustic band gap of the materials was demonstrated to improve acoustic contrast and provide information about the cement environment based on frequency and amplitude. Furthermore, data-processing and machine-learning methods have been developed to interpret subsurface readings with more accuracy and deeper insight. Neural networks can be used to interpret the results of smart material detection and sensing, providing new information that was previously unattainable. Engineered Materials for Well Construction New classes of construction components with enhanced properties may be self-healing or passively sensing or may have outstanding physical properties such as mechanical strength. Nanoscale treatments can alter the surface characteristics of materials, endowing them with engineered interfacial behavior. Passive-sensing materials can alter incoming energy waves that can be detected to discern information about material condition and environment. These technologies can improve the properties of well-construction materials for carbon storage, increasing integrity and allowing monitoring of well and reservoir states. The results of successful laboratory and field trials of each technology described in this section are provided in the complete paper.

Assessing Empirical Components in Wave Breaking and Rollers Through Model Comparison of Radiation Stress and Vortex Force

AbstractAs incoming waves approach shallow water, they break and result in nearshore currents. The assessment of the wave‐induced nearshore currents often relies on the application of radiation stress (RS) and vortex force (VF) in circulation models, both of which incorporate empirical components to describe wave breaking and wave rollers. In this study, we compared a recent 3D RS formulation and a VF formulation by assessing the modeled cross‐shore velocities against the measured counterparts from the LIP11D and Duck’94 experiments. The comparison results indicate that the RS model performs better in LIP11D, whereas the VF model exhibits better with respect to Duck’94. Using momentum balance analysis, we found that the cross‐shore velocities were dominated by the breaking term (representing the RS terms and non‐conservative breaking term in the RS and VF models, respectively) and the roller term. The breaking term generates undertow currents across the entire surf zone. The roller term cooperates with the breaking term in the inner surf zone, but counteracts the breaking term and tends to trigger unrealistic offshore currents at the water surface in the outer surf zone. Further analysis reveals that the RS and VF formulations can simulate almost identical velocity results by adjusting the vertical distribution of the breaking and roller terms. Overall, this study indicates that both the RS and VF formulations are effective in evaluating wave effects on the cross‐shore currents, and empirical components in the breaking and roller terms are important for modeling cross‐shore velocities.

Reconfigurable Intelligent Surfaces for Beamforming in Upcoming Wireless Communications

Reconfigurable Intelligent Surfaces (RIS), also known as Intelligent Reflecting Surfaces (IRS), represent a groundbreaking advancement in wireless communication technology, enabling unprecedented control over electromagnetic (EM) wave propagation. Composed of numerous passive or active elements constructed from metasurfaces, RIS can dynamically alter their electromagnetic responses to optimize signal reflection, refraction, and scattering. These elements, capable of manipulating the phase, amplitude, and polarization of incoming waves, are centrally controlled through sophisticated algorithms that adapt to real-time environmental changes and communication requirements. RIS technology promises significant improvements in wireless communication by extending coverage, enhancing signal quality, managing interference, boosting energy efficiency, and improving security. Additionally, RIS can facilitate precise localization and sensing applications. Despite the high initial implementation costs and the need for complex control mechanisms and infrastructure compatibility, the potential benefits of RIS in creating efficient, secure, and adaptive wireless communication environments underscore its transformative impact on the field.

Characteristics of a two-dimensional periodic wave energy converter array

This study concentrates on the hydrodynamics of wave energy converters (WECs) consisting of an array of periodic buoys. The interaction between the bodies and waves was solved by a precise analytical method. The intrinsic relationships between wave propagation, energy capture, and array response are analyzed. Bragg resonance was found not only in scattering waves but also in radiation waves. The radiation wave is affected by different power take-off (PTO) damping, which could lead to incoming waves travelling freely through the array or being prevented through the array. The results show that Bragg resonance reduces the extraction efficiency significantly, and each device is affected to a different degree. In addition, this study reveals that there is collective behavior in the periodic WECs, all bodies in the array oscillate with identical amplitude at the Bragg resonance frequencies. Furthermore, the parametric effects on the hydrodynamic performance are investigated. The result of the study may provide useful guidance for the practical design of the WEC array.

Mitigation of side-to-side vibration of a 10MW monopile offshore wind turbine under misaligned wind and wave conditions by an active torque control

Large offshore wind turbines (OWTs) may encounter extreme misaligned wind and wave conditions throughout their lifetime, which could trigger side-to-side resonance of the OWTs and thus substantial reduction in fatigue life. This study aims to (1) understand the dynamic response of fixed-bottom OWTs under misaligned wind and wave conditions, and to (2) propose an active torque control algorithm for dynamic loading mitigation. For these purposes, an integrated aero-elastic model, coupled with an advanced soil-monopile interaction (i.e., p-y+M-θ model), is built in OpenFAST for the DTU 10MW OWT supported by a monopile in soft clay. The numerical results show that under misaligned wind and wave conditions, where the wave peak period is likely to approach the tower natural period, the dynamic loading along the side-to-side direction dominates the fatigue design of the OWT. To mitigate the side-to-side dynamic loading, an active torque control algorithm is designed with feedback from measured side-to-side tower vibration to enhance damping, as well as feedforward from measured incoming wave height to counteract external force. Through the use of the feedback-feedforward active torque controller, the side-to-side dynamic loading of the 10 MW OWT is significantly reduced, with the fatigue life extended from 19 to 39 years.

Jaynes–Cummings model in a weak gravitational wave background

Working in the framework of the linearized theory, we analyze the influence of a weak gravitational wave on the dynamics of the Jaynes–Cummings model, describing the interaction between a two-level quantum system and the electromagnetic field in a cavity. We show that the gravitational wave induces a small, time-dependent modulation in the generalized Rabi frequency Ω of the system. Such a modulation has the same frequency as the incoming gravitational wave. We also find that the atomic inversion acquires a similar time-dependent modulation. After a pulse of the electromagnetic driving field in the cavity, an atomic population N 0, previously prepared in its excited state, ends showing a small unbalance between the excited and the de-excited atoms. The unbalance amplitude is proportional to HN 0, with H being the gravitational strain. We briefly comment about possible astrophysical implications.

Gravitational partial-wave absorption from scattering amplitudes

We study gravitational absorption effects using effective on-shell scattering amplitudes. We develop an in-in probability-based framework involving plane- and partial-wave coherent states for the incoming wave to describe the interaction of the wave with a black hole or another compact object. We connect this framework to a simplified single-quantum analysis. The basic ingredients are mass-changing three-point amplitudes, which model the leading absorption effects and a spectral-density function of the black hole. As an application, we consider a non-spinning black hole that may start spinning as a consequence of the dynamics. The corresponding amplitudes are found to correspond to covariant spin-weighted spherical harmonics, the properties of which we formulate and make use of. We perform a matching calculation to general-relativity results at the cross-section level and derive the effective absorptive three-point couplings. They are found to behave as OGNewtons+1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{O}\\left({G}_{\ extrm{Newton}}^{s+1}\\right) $$\\end{document}, where s is the spin of the outgoing massive state.

Tiny stresses are capable of triggering earthquakes and tremors in Arunachal Himalaya

The Arunachal Himalaya has been hosting some notable events in the recent past. The tectonic history of Arunachal Himalaya is complex and has been influenced by several major tectonic events, including the 1950 Mw8.6 Assam-Tibet earthquake. In this study, we explored the effect of dynamic stresses generated by teleseismic events on the triggering of seismicity in the region. We analyzed 34 large teleseismic events since 2010 and found triggering during six events. The change in seismicity was also confirmed by analysis with the STA/LTA method. The triggering in the region occurred in the form of earthquakes and tremors. The dynamic stress as low as 1 kPa was found capable of triggering. The back-azimuth angle does not play an important role in the triggering. The angle direction of incoming waves with respect to the fault ~ 60° and ~ 120° is the possible reason for triggering in the region. The triggering occurred in the Mishmi and Main Central Thrust regions. The largest triggered event, ML2.3, was triggered 7.5 h after the 2012 Indian Ocean earthquake of Mw8.6. The region is tectonically very sensitive and tiny stresses are capable of triggering seismicity in Arunachal Pradesh.

Sea level oscillations spectra of a shallow coastal bay: Cost-effective measurements and numerical modelling in Kruglaya Bay

Seiches are long standing waves typical of enclosed and semi-enclosed basins. It is shown that they can be generated in bays by long-period waves coming from open sea through an entry. An interaction between adjacent bays may extend the number of seiche modes in these bays. Kruglaya Bay is widely used for recreational purposes. We measured sea level variations in Kruglaya Bay in August-October, 2022 by means of a cost-effective and robust autonomous sea-level recorder designed and assembled in Marine Hydrophysical Institute. Measurements were conducted based on an ultra-sound JSN-SR04T sensor. SWASH, a numerical high-resolution model, was used to simulate dissipating free oscillations in a system of connected shallow semi-enclosed bays initiated by long waves incoming from the open sea. A spectral analysis of measured sea level fluctuations was used to identify resonant periods of local seiches in Kruglaya Bay. Estimate periods of oscillations that correspond to incoming long waves from the neighbouring bays were obtained using the results of mathematical modeling. The performed wavelet analysis permitted to identify situations when local resonant oscillations were initiated before wind intensification (which manifested as an increase in energy at the high-frequency part of the spectrum). An intense fundamental mode (also known as the ‘Helmholtz mode’ of a semi-enclosed oscillating basin) of Kruglaya Bay (period around 14 min) was identified both in measurements and the numerical simulation. The power spectra of the sea level oscillations in Kruglaya Bay also showed significant peaks at the periods of fundamental modes of the neighbouring bays. Besides, periods of the Black Sea seiches (1.25 h and 2.5 h) were identified from the observations.

Nearly Ideal Transparency with Artificially Designed Meta-Atoms.

The ideal electromagnetic transparency refers to the ability of an object to remain scatteringless to any incoming waves, resulting in vacuum invisibility. However, natural solid substances can hardly be transparent in free space as they are responsive to external polarizations. Completely eliminating the polarization effect of an obstacle under arbitrary field illumination is a long-standing scientific challenge. Here, it is shown that a subwavelength meta-atom can be nearly ideally transparent in the vacuum. The overall vacuum-like property of the meta-atom is achieved through judiciously designing its internal polarization and magnetization. Remarkably, any large-scale objects made by stacking the meta-atoms inherit the vacuum-like property and are scatteringless in free space. By both the simulations and experiments, the meta-atom's peculiar property is reasonably verified. The proposed meta-atoms are excellent candidates for a wide range of applications, such as perfect radar radomes, scatteringless walls, filtering devices, and self-stealth materials.

Design of a compact filter integrated wideband and circularly polarized antenna array for K-band application

A compact filtering mechanism in the antenna system is required to avoid unwanted incoming electromagnetic waves in the working frequency band. A circularly polarized (CP), wideband, and high gain antenna array co-design with a wide bandpass filter (BPF) for a K-band satellite application at (17.7 to 21.2) GHz is studied in this paper. Antenna array elements with diagonal slots and BPF in the same frequency are compatible. For maximum radiation efficiency, the input impedance of the slotted 16 × 16 elements antenna array is matched to 50 Ω and equal to the output impedance of the BPF in the operating band. To implement the filtering concept, a co-design is modeled and simulated. The suggested wideband BPF and antenna array are integrated on a combined aperture, manufactured, and tested experimentally. Based on the results of the tests, it can be concluded that the suggested filtering antenna array is well matched (|S11| < −15 dB) throughout a wide frequency band of 17.7 GHz to 21.2 GHz. The final structure simulated and measured 3 dB axial ratio covers the functional spectrum with a maximum 25.3 dBi gain. High directive beams with a 20 dB cross-polarization suppression level in E & H planes are simulated and measured. Due to these advantages, the suggested antenna is an attractive option for use in K-band 3U satellite applications to minimize the requirement for extra filtering circuits in the RF system.