Incident Wave Characteristics Research Articles

Enhanced Mild-Slope Wave Model with Parallel Implementation and Artificial Neural Network Support for Simulation of Wave Disturbance and Resonance in Ports

Ensuring sea surface tranquility within port basins is of paramount importance for safe and efficient port operations and vessels’ accommodation. The present study aims to introduce a robust numerical model based on mild-slope equations, capable of accurately simulating wave disturbance and resonance in ports. The model is further enhanced by the integration of an artificial neural network (ANN) to address partial reflection, and its efficiency is optimized by developing a parallel algorithm based on OpenMP, allowing for a reduction in the required simulation times for real port areas spanning several kilometers horizontally. Numerous numerical experiments focusing on wave reflection against a vertical wall were conducted to develop the ANN. This neural network was designed to determine the appropriate value of the eddy viscosity coefficient, a crucial parameter in the momentum equation of the mild-slope model, tailored to incident wave characteristics. The model’s validity was confirmed through rigorous validation against experimental measurements, covering wave disturbance, rectangular harbor resonance, and Bragg resonance. The model consistently demonstrated a more than satisfactory performance across all considered scenarios. In a practical application, the model was deployed in the Port of Rethymno, Crete Island, Greece, effectively capturing and describing dominant phenomena within the port area. The implementation of a parallel algorithm significantly reduced the simulation times by ~92%, compared to the serial algorithm, thereby enhancing the model’s efficiency and applicability in real-world port environments.

Dynamic BEM analysis of elastic anisotropic nano‐sheet with surface imperfections and cavities

AbstractThe paper considers elastic anisotropic nano‐sheet with nanotopography and containing embedded nanocavities under time‐harmonic in‐plane wave motion. The mechanical model is based on the classical elastodynamic theory for the anisotropic bulk solid and the nonclassical boundary conditions along its boundary derived by Gurtin and Murdoch. A localized constitutive equation for the half‐plane boundary is considered in the frame of surface elasticity theory. The computational tool is an efficient direct displacement boundary element method (BEM) based on the frequency‐dependent elastodynamic fundamental solution for elastic generally anisotropic material. To show the versatility of the proposed methodology, wave propagation in an elastic anisotropic heterogeneous nano‐sheet with nanorelief presented by hill‐canyon nanotopography is studied. The simulations illustrate the dependence of the wave field on the material anisotropy, on the surface elasticity properties, on the nanorelief peculiarities, on the nanocavities existence and their dynamic interaction, and on the incident wave characteristics. The obtained results reveal the potential of the developed mechanical model based on the boundary integral equations in the frame of surface elasticity theory to produce highly accurate results by using strongly reduced discretization mesh in comparison with the domain‐based methods.

Fast Transceiver Design for RIS-Assisted MIMO mmWave Wireless Communications

Due to high bandwidth and small antenna size, millimeter-wave (mmWave) integrated line-of-sight (LOS) multiple-input-multiple-output (MIMO) systems have attracted much attention. Reconfigurable intelligent surfaces (RISs), which have the potential to change the characteristics of incident electromagnetic waves with low power cost, can improve the performance for the MIMO mmWave wireless communications. Uniform circular array (UCA) is an effective antenna structure with low complexity transceiver. In this paper, UCA based RIS-assisted MIMO mmWave wireless communications with transmit UCA, the RIS UCAs, and receive UCA are investigated. Since the rotation angles between the transceiver make the channel matrix noncirculant, an algorithm is developed to derive the ranges of the rotation angles based on an acceptable error and reduce the impact of rotation angles on channel matrix. Then, we propose a low-complexity precoding scheme at the transmitter, phase designs at the RIS UCAs, and a phase compensation scheme at the receiver, which can convert the channel matrix into an equivalent circulant channel matrix with a small error. Then, a fast symbol-wise maximum likelihood (ML) detection scheme is proposed to recover the signals with low computational complexity. Simulation results are presented to illustrate the theory.

Structural and optical properties of triple-layer for high-uniformity beam division

In this paper, a triple-layer grating beam splitter with three-port output is designed. Through the combination of rigorous coupled-wave analysis (RCWA) and simulated annealing algorithms (SAA), the calculation and optimization of each parameter of the grating is carried out to make the diffraction efficiency of the grating meet the conditions. At the incident wavelength of 800[Formula: see text]nm, the diffraction efficiencies of 0th order and ±1st order under TE polarization are 31.6% and 31.4%, respectively. The diffraction efficiencies of 0th order and ±1st order under TM polarization are 32.7% and 32.5%, respectively. It can be seen that not only the total diffraction efficiency under TE polarization and TM polarization exceeds 90%, but also the uniformity of diffraction efficiency at each order exceeds 99%. Finally, the influence of grating parameters and incident wave characteristics on diffraction efficiency is discussed.

Experimental study of an oscillating water column converter to optimize nonlinear PTO using genetic algorithm

The characteristics of incident waves, draft depth, and orifice diameter significantly affects the performance of the OWC. This paper evaluated the hydrodynamic response of an OWC with nonlinear PTO imposed on the Caspian Sea wave conditions experimentally. Experimental tests have been done in two stages; first, considering the incident wave frequency constant in 0.4 Hz, two main variables, area ratio, and depth ratio, have considered optimizing the performance by genetic algorithm. The experiments for three area ratios of the orifice equal to 0.5%, 0.75%, and 2%, and the three depth ratio equal to 0.05, 0.14 0.33 have been done. The optimal values of the area and depth ratios are equal to 1% and 0.24, respectively. In the next step, the tests were carried out for a wide range of conditions of the Caspian Sea, and four area ratios and depth ratios, including the optimal values, repeated in the form of 800 tests. The results showed that the converter performance would be optimum for the other frequencies considering the optimal values. The optimal converter can generate 191W, while before the optimization, the highest recorded power was 132W, an increase of 45%. After optimization, the converter pneumatic efficiency has increased to 53.74%.

Water Level Modulation of Wave Transformation, Setup and Runup Over La Saline Fringing Reef

AbstractCoral reefs represent an efficient natural mechanical coastal defense against ocean waves. The focus of this study is La Saline fringing coral reef, located in the microtidal West of La Réunion Island in the Indian Ocean, frequently exposed to Southern Ocean swell and cyclonic events. The aim is to provide a better understanding of the reef's coastal defense characteristics for several Southern Ocean swell events. Pressure sensors were placed across the reef to measure water level fluctuations and to study wave transformation. A numerical model (XBeach surfbeat), validated using field observations, was used to deepen understanding of wave transformation, wave setup and runup. Field measurements and model outputs show that as gravity waves dissipate over the reef, and frequency‐dependent dissipation of infragravity waves by bottom‐friction occurs, the reef acts as a low‐pass filter. Wave‐induced setup is found to be the dominant hydrodynamic component. Setup and runup are each 98% and 79% driven by the offshore significant wave height, and 2% and 21% driven by the tide. The modulation of the water level by setup is the main contributor to runup in the fringing reef. At semidiurnal timescales, setup and runup are in antiphase with tidal variations as lower water levels result in higher gravity wave energy dissipation, setup and runup. Simple‐to‐use transfer functions relating incident wave characteristics to these hydrodynamic components are proposed. The effects of bottom friction and water level on the defensive capacity of the coral reef highlight future implications of structural damage and sea level rise.

Large-eddy simulations of gravity currents in the presence of waves

Simulations are performed to investigate gravity currents in the presence of free surface waves using the open-source computational fluid dynamics programme REEF3D with the concentration equation, and the large eddy simulation model for turbulence closure. Simulations show that the period of the oscillation front relates only to the period of the incident waves and the oscillation amplitude increases with wave height. The average velocity of the density current increases with increasing wave height and wavelength. The surface waves change the generation position and combination direction of the turbulence structures in the pycnocline. The oscillatory motion of the waves stabilizes the pycnocline earlier and reduces the turbulent mixing. The instability zone is reduced faster with higher wave heights with well-ordered K-H billows, but not for longer wavelengths. The instantaneous velocity and concentration fields are highly influenced by the incident wave characteristics when compared to that in the absence of waves.

An analytical study of the effects of a circumferentially corrugated core on sound transmission through double-walled cylindrical shells

Corrugated structures are widely being used in industrial applications, which raises the demand for careful analysis of their behavior. To fill the gap for vibroacoustic characteristics, this paper focuses on proposing a model to investigate sound transmission through double-walled cylindrical shells with a circumferentially corrugated core. The structure is composed of outer and inner isotropic layers and a corrugated core. The outer layer is subjected to an oblige plane wave, and also a subsonic flow is traveling outside the double-walled shell. An equivalent method is applied to replace the corrugated core as axial, radial, and rotational springs with specific stiffness coefficients. The first-order shear deformation theory (FSDT) is applied to describe the behavior of isotropic shells. A considerable parametric study is established concerning both the incident wave and structural characteristics. The results show that the presence of the corrugated core improves sound transmission loss (STL) of the structure in the mass-controlled region, and it has a negative effect on STL in the coincidence-controlled region; therefore, using such a core for sound insulation depends on the desired frequency domain.

High-resolution perfect imaging of micro/nanojet

A systematic theoretical study on elimination of imaging distortion for realization of perfect imaging of a micro/nanojet in THz, visible and infrared regions has been performed on the basis of a two-layer structure formed by an exterior hexagonal prism and a cuboid (cube) or cylinder embedded in it. The study concentrates on effects of scatterer’s geometry, propagation direction and polarization characteristics on ellipticity of the micro/nanojet. The geometry of scatterer involves height, side length, relative position of the exterior and interior layers. The study shows that imaging distortion can be eliminated in all spectral regions considered, and perfect images with an ellipticity of ∼ 1.0 can be obtained on the basis of an optimal scatterer structure proposed. Meanwhile, high wave intensity (I/I0 > 23) and high imaging resolution (<0.30λ) beyond the diffraction limit are expected. The study also shows that the imaging and hence the morphology of micro/nanojet shows considerable effects of polarization state and direction of incident wave, and the effects are associated with both structure features of scatterer and polarization characteristics of incident wave. The perfect imaging of micro/nanojet shows great potential for its application in the field of high-resolution imaging at different frequency regions.

Dynamic interaction between complex defect and crack in functionally graded magnetic-electro-elastic bi-materials

This paper aims to develop an effective theoretical method for analyzing the interaction of interfacial crack and complex defect in functionally graded magnetic-electro-elastic bi-materials with exponential variation under the action of anti-plane incident SH-wave. The boundary value problem of interest is solved by Green’s function method. The mechanical model of the cracks is constructed through interface conjunction and crack deviation techniques, thereby simplifying the crack problem to solving a series of the first kind of Fredholm’s integral equations, from which the dynamic stress intensity factor (DSIF) at the crack tips of the left crack are expressed. The validity of the present method is verified by comparing with a single crack model in previous work. Through the analyses of numerical cases, it can be concluded that the DSIF is related with 3 factors：the geometry of complex defect and crack, the characteristics of incident wave and the inhomogeneity of materials. Comparing with dual integral equations in dealing with asymmetric defects, the method in this paper is relatively more flexible and applicable, also it comes up with a new way to study fracture problems in functionally graded magnetic-electro-elastic materials with more complex defects.

Transmission electromagnetic beam splitter based on double-sided all dielectric microstructure

We propose a transmission type dual beam splitter based on all-dielectric encoded metasurface. In order to improve the efficiency of the device, we propose to construct the coding metasurface using double-sided all-dielectric cylindrical cell structure. Based on the electromagnetic dipole resonance characteristics of the all-dielectric resonator, two all-dielectric elements with transmission phase difference π were obtained, and 1-bit coded metasurface was constructed to achieve beam splitting characteristics of incident waves. Based on the finite integral method, we numerically simulate the far-field scattering characteristics of coded metasurface beam splitter. It is found that the number of digital repeats of coding unit particles has a great influence on beam splitting when constructing coding metasurface due to the coupling effect between particles. The energy ratio of double beam splitting can be continuously regulated by changing the incident angle. The dual-beam splitter we designed also has broadband characteristics.

An experimental investigation into the effects of front wall geometry on OWC performance for various levels of applied power take off dampings

Despite the achieved progress, exploiting wave energy in a competitive and efficient manner is still a grand challenge problem. This study aims to improve the performance of an Oscillating Water Column (OWC) by experimentally testing different streamlined front wall underlip geometries. Results show that the proposed geometries have an important bearing on OWC hydrodynamic performance provided that OWC does not operate in sloshing mode. Relative to rectangular front wall plate, underlip geometry with a circular cross-section, provided a maximal increase of 21.2% in capture width ratio via reducing vortex shedding and increasing conveyed amount of incident wave energy into the chamber. Observations indicate that the value of Power Take-off (PTO) damping has a crucial impact on the amount of acquired performance improvement. Therefore, applied PTO damping is a key parameter that has to be determined with care. All tested geometries failed to diminish the sloshing present in the chamber which highlights the fact that sloshing phenomenon is only associated with incident wave characteristics independent of wave-structure interaction. Introduced front wall shapes are also found significant from structural design point of view as they are beneficial in attenuating large vortex induced shear stresses that OWC front wall has to endure.

Fluid-structural analysis of modular floating solar farms under wave motion

Floating solar farms (FSFs) are emerging to be a viable option for large scale solar power production. The present study develops an original approach for the design assessment of the maximum stress/strain and displacement of massively connected modular FSFs under wave action. The scope includes two parts: (1) numerical simulations for the fluid structural analysis with two-way coupling of a global array of connected modular floaters that hold the massive number of solar panels; and (2) experimental validation of the numerical predictions for the dynamic response of the global array under wave action. The numerical approaches are based on finite element simulations. Both static and dynamic simulations are carried out with and without using the Fluid Structure Interaction (FSI) method, under different incident wave characteristics, rheological properties of the global array, and mooring configurations. The experiments were performed with a flexible perforated sheet using Froude scaling for dynamic similitude, with ultrasonic measurements to quantify the wave profile as well as the displacement responses of the array under wave action. The comparison shows reasonable agreement between the predictions and measurements at discrete locations along the array. Finally, a summary is provided on how the new approach can aid in the design assessment of modular FSFs under wave motion.

Sound Wave Insulation Performance of Cylindrical-type Acoustic Metamaterials

In recent years, acoustic metamaterials have been attracting attention as a noise control measure, and various studies have been conducted. They are structures with artificially adjusted characteristic values that contribute to the propagation of the sound. In this study, we devise an acoustic metamaterial with a simple structure that can significantly change the sound propagation characteristics. We fabricated a metamaterial consisting of an array of solid cylinders and investigated the transmission characteristics of incident sound waves propagating through the material both by the finite element analysis. As a result, the insulation effect on sound waves by the material was observed. It was also found that the insulation effect depended on the fill rate and diameter of the cylinder.

Design of metasurface beam splitter based on polarization characteristics of incident wave

A transmissive metasurface polarization beam splitter (MPBS) with three-layer dielectric substrate was designed to meet the application requirements of polarization beam splitting devices. The microstructure unit cell was composed of an elliptical patch and a square resonant ring, and the phase and amplitude responses to the x- and y-polarized incident waves were independent. Here 16 transmissive unit cells designed with a 90° phase difference and more than 0.8 transmission coefficient could be used to realize different functions by pre-designing distribution of “00”, “01”, “10”, “11” encoding particles in x- and y-direction. We experimentally demonstrated a 2-bit encoding MPBS that separated x- and y-polarization incident waves into two different directions at 15 GHz respectively using specially designed encoding unit cells. The work may alleviate the shortage of advanced multifunctional devices and provide important application prospect in imaging, MIMO system, etc.

Predicting Crenulate Bay Profiles from Wave Fronts: Numerical Experiments and Empirical Formulae

For crenulate-shaped bays, the coastal outline assumes a specific shape related to the predominant waves in the area: it generally consists of a tangential zone downcoast and a curved portion upcoast. Many coastal engineers have attempted to derive an expression of the headland bay shapes that emerge when a full equilibrium is reached (stable or dynamic). However, even though models for static equilibrium bays exist, they are merely of an empirical kind, lacking further insight on relationships between incident wave characteristics and beach shape. In addition, it is commonly believed that shoreline profiles tend to follow wave fronts, but this has been never fully verified. In this paper, we investigate a possible correlation between static equilibrium profiles and wave front shapes. Numerical experiments have been performed using the MIKE 21 Boussinesq Wave module, and the generated wave fronts have been compared to the hyperbolic-tangent equilibrium profile. A thoughtful analysis of results revealed that a single-headland equilibrium profile is merely the wave front translated perpendicularly to the wave direction at the headland tip, without any influence of wave period or in wave direction. A new function called the “wave-front-bay-shape equation” has been obtained, and the application and validation of this formula to the case-study bay of the Bagnoli coast (south-west of Italy) is described in the paper.

An in depth experimental investigation into effects of incident wave characteristics front wall opening and PTO damping on the water column displacement and air differential pressure in an OWC chamber

Efficiency of an OWC depends solely on the water column heave motion and air pressure differential in the chamber. In this study, an extensive experimental campaign is conducted to investigate the displacement of water column surface (WCS) and chamber air pressure under different incident waves, chamber underwater opening heights and applied PTO dampings. It is found that, transmitted wave height (μ) and transmitted wave pressure (Pw) exponentially decay with the dimensionless wave frequency (Kh) irrespective of the relative opening (α) and orifice ratio (τ) (PTO damping), however, the decay rate slows down as the orifice ratio decreases. Effects of orifice ratio on μ and Pw heavily depend on the value of the Kh such that as Kh increases transmitted wave height, μ and pressure, Pw become less sensitive to variations in the orifice ratio, τ. Pw increase with the relative opening in a linear fashion but the upward trend declines for larger dimensionless wave frequencies. An almost perfect linear association is detected between transmitted wave height and pressure, and, captured wave length (δ) (incident wave length divided by chamber length). In the design stage, in order to prevent sloshing in the chamber δ smaller than approximately 4 should not be selected. Negative pressure peaks are always found to be larger than positive pressure peaks in magnitude. Further, a novel dimensionless pressure number NPR is proposed, which is found to be proportional to μ. Proportionality constant is also presented. Accordingly, prediction of μ or Pw yields the value of the other in an accurate manner. Despite the complex wave-energy conversion processes the most important aspects and the related parameters can be described using very accurate simple analytical models.

Progression of Wave Breaker Types on a Plane Impermeable Slope, Depending on Experimental Design

AbstractThe objective of this research was to analyze the progression of breaker types on plane impermeable slopes. This study used dimensional analysis to demonstrate the relative water depth is a key explanatory quantity. The dominant breaker types depend on the incident wave characteristics at the foot of the slope. Accordingly, it is possible to combine values of H, T, and m. The physical experiments of Galvin, recent numerical results, and new experiments, performed on an impermeable 1:10 slope, were used to verify the result. It was thus possible to obtain the progression of breaker types in different sequences of pairs of combined wave H and T values. Once a sequence is defined, the expected progression of breaker types is predictable, and is well approximated by the log‐transform of the alternate similarity parameter. Since the classification of breaker types is discontinuous, the data assigned to each type were placed in horizontal lines, based on the value of log(χ). Given that the breaking of a wave train on a slope should be considered a continuous process, the location of some data was corrected to satisfy this assumption. There is thus a functional relationship between the sets of the experimental space and of the breaker types. This research also derives the non‐dimensional energy dissipation on the slope, considering the wave‐reflected energy flux on the slope. It is proportional to a dimensionless bulk dissipation coefficient which depends on the breaker type and, therefore, on the value of χ at the toe of the slope.

Classification and Comparison of Wave Impact Modes on Semi-Submersibles

Semi-submersibles for offshore oil exploration and exploitation often suffer from severe wave impacts in extreme ocean environments. Owing to the complex wave interactions among structural components of semi-submersibles, in-depth analyses on the characteristics of wave impact events are of significance for both industry and academia. An experimental study was carried out to investigate the local wave impact loads on a semi-submersible, with focus on understanding the wave impacts by identifying typical impact modes. Quantitative criteria are proposed to classify major wave impacts on the semi-submersible into six modes and two types. The results show that the classification is reasonable and provides valuable information for studying wave impacts on semi-submersibles. The incident wave characteristics at the fore column of the semi-submersible have important influence on the wave impact mode. The fore-column dominating wave impacts exert the most intense loads on the fore column and feature well-developed breaking waves or slightly breaking waves at the fore column. However, the aft-column dominating wave impacts exert the most intense loads on the aft column or the deck bottom and feature non-breaking waves at the fore column. Energy loss during the fore-column impact weakens the impact severity on the aft column in the fore-column dominating wave impacts. The shoaling effect of the submerged pontoon and different motion configurations of the platform result in higher occurrence rate of the aft-column dominating wave impacts. Different impact modes are also distinguished by different spatial distributions of wave impact loads.

Wave climate and power distribution around a rocky island: Alcatrazes, Brazil

We investigate the distribution of the wave power around the Alcatrazes island, a protected marine reserve in southeastern Brazil, located at 20 nautical miles from the coast of São Sebastião/SP. A 14-year wave time series (2005-2018) extracted from the global WaveWatch III model, was used to obtain the offshore wave climate. Based on the wave climate, a wave propagation model (Delft3D) was applied in order to obtain nearshore information. The most frequent waves are from the east, southeast and south, with heights between 1.0 and 2.0 m and periods of 7 to 10 s. Due to dominant wave direction incidence, the wave power is higher at the more exposed eastern side of the island, with its lee side becoming shadowed from the main wave trains. Magnitudes vary seasonally, with winter and autumn presenting more energetic southerly waves and consequent higher wave power along the rocky island. The wave power distribution is a consequence of the incident wave characteristics and the geomorphology of the island. Our findings are the first assessment of the local wave climate and wave power distribution along the rocky shores of Alcatrazes island, providing important background information for understanding different aspects of its functioning and management.