Decay Of Waves Research Articles

Quasinormal modes of nonlinearly charged black holes surrounded by a cloud of strings in Rastall gravity

In this paper, we obtain the black hole solution for the Ayón-Beato–García (ABG)-type black hole surrounded by a cloud of strings in Rastall gravity and calculate the scalar quasinormal modes of it for a massless scalar field. To have a better visualization of the results, we also introduce a new nonlinear electrodynamic source and obtain a black hole solution surrounded by a cloud of strings in the Rastall gravity. We see that the quasinormal modes are affected by the type of nonlinear electrodynamic sources in case of higher magnitudes of charge [Formula: see text]. With increase in the magnitude of charge [Formula: see text], gravitational waves decay rapidly for the new black hole solution, while for the ABG black hole, the decay rate increases initially and finally starts to decrease near to [Formula: see text]. We also study the impact of the cloud of strings and other model parameters, including the Rastall parameter on the quasinormal modes for both of the black holes. The gravitational waves decay slowly with increase in the cloud of strings parameter for both of the black holes. Dependency of quasinormal modes on the Rastall parameter is different from a surrounding dark energy field and the decay of gravitational waves may be slow or rapid depending on the value of this parameter.

Performance of a coupled level-set and volume-of-fluid method combined with free surface turbulence damping boundary condition for simulating wave breaking in OpenFOAM

In the present study, an extension of the volume-of-fluid (VOF) method used in the open-source computational fluid dynamics (CFD) software OpenFOAM was developed, taking the advantages of the VOF and the level-set (LS) methods with an additional free surface turbulence damping (FSTD) boundary condition to restrict the overprediction of turbulence near the free surface. The coupled level-set and volume-of-fluid (CLSVOF) method has been developed, scripted, validated and proposed. The free surface elevation with the proposed CLSVOF method was validated in a developed numerical wave tank (NWT) against turbulence models used so far in OpenFOAM. Further, the validity of the present numerical model was evaluated for the case of plunging breaking waves against relevant experimental and numerical data. The outcome of this study demonstrates that the performance of the wave generation is improved with the proposed numerical model compared to existing turbulence models in OpenFOAM, creating a useful simulation add-on that generates long-term waves without unphysical dissipation, wave damping, and wave decay. The overprediction of turbulence created due to the significant difference in the fluid's density close to the free surface is limited by applying the FSTD boundary condition leading to a better representation of the flow field.

Wave Response of a Monocolumn Platform with a Skirt Using CFD and Experimental Approaches

This paper aims to investigate the nonlinear motion characteristics of a monocolumn type floater with skirts numerically and experimentally. Wave calibration, free decay, and regular wave tests were simulated using a computational fluid dynamics (CFD) code OpenFOAM. The experiments were carried out in a wave tank to validate the CFD results. First, wave calibration tests were performed to investigate wave generation, development, propagation, and absorption in the numerical wave tank. Second, the simulation input parameters were calibrated to reproduce the waves generated in the tank experiment. Third, free decay tests of heave and pitch were conducted to examine the natural period and the linear and quadratic damping of the floater. A verification and validation study was performed using experimental data for free decay tests. Finally, regular wave tests were performed to investigate the motion characteristics of the floater. The results were processed to obtain the response amplitude operator (RAO) for the heave and pitch motions. The RAOs of the floater was compared with the experimental data and numerical simulations based on the linear potential theory code WAMIT to investigate the performance of the CFD simulations. The comparisons made in this work showed the potential of the CFD method to reproduce the motion characteristics of a shallow-draft floating object with a skirt in waves and to visualize the nonlinear phenomena behind the oscillation of the floating object.

Viscoelastic Wave–Ice Interactions: A Computational Fluid–Solid Dynamic Approach

A computational fluid–solid dynamic model is employed to simulate the interaction between water waves and a consolidated ice cover. The model solves the Navier–Stokes equations for the ocean-wave flow around a solid body, and the solid behavior is formalized by the Maxwell viscoelastic model. Model predictions are compared against experimental flume tests of waves interacting with viscoelastic plates. The decay rate and wave dispersion predicted by the model are shown to be in good agreement with experimental results. Furthermore, the model is scaled, by simulating the wave interaction with an actual sea ice cover formed in the ocean. The scaled decay and dispersion results are found to be still valid in full scale. It is shown that the decay rate of waves in a viscoelastic cover is proportional to the quadratic of wave frequency in long waves, whilst biquadrate for short waves. The former is likely to be a viscoelastic effect, and the latter is likely to be related to the energy damping caused by the fluid motion. Overall, the modeling approach and results of the present paper are expected to provide new insights into wave–ice interactions and help researchers to dynamically simulate similar fluid–structure interactions with high fidelity.

Ultrasonic characterization of expanded polystyrene used for shallow tunnels under seismic excitation

Expanded Polystyrene (EPS) is used as an inclusion to mitigate stresses acting on tunnels. In this study, the efficiency of utilizing EPS in reducing dynamic loads acting on shallow tunnels was studied. To gauge this, dynamic modulus of elasticity ( E d ) and shear modulus ( G ) of EPS with densities equal to 25, 30, and 35 kg/m 3 were characterized based on series of ultrasonic tests, where E d ranged from 3500 to 6578 kPa, and G ranged from 1535 to 2741 kPa. A correlation was developed between EPS density and damping coefficient, which ranged from 1% to 2.3% based on G and the ultrasonic wave decay. A model was developed for a cut-and-cover tunnel with EPS along its side walls, and a parametric study was conducted using EPS thickness to tunnel depth ratio (t x /h 1 ) varying from 0.05 to 0.20. At tunnel critical sections, normal and bending were reduced by 30% and 46%, respectively.

Estimation of cavitation erosion area in unsteady cavitating flows using a modified approach

Estimation of cavitation erosion area remains a challenging issue. Only an accurate estimation of the erosion-sensitive area can effectively reveal the various mechanisms of cavitation erosion. In this study, large eddy simulation is applied to simulate the unsteady cavitating flows, and an energy approach is developed to estimate cavitation erosion area. This approach is modified by taking into account hydrodynamic efficiency, which is deduced from the perspective of shock wave decays. The numerical estimation is then validated based on an axisymmetric nozzle cavitating flow. The numerical simulation results indicate that the modified approach can reasonably estimate the cavitation erosion area. In addition, various hydrodynamic cavitation erosion mechanisms are numerically analyzed based on the cavitating flow around a NACA0015 hydrofoil. The numerical simulation is able to reproduce the experimentally observed U-shaped cavitation structure. The interaction between cavitation and vortex has an important influence on the distribution of cavitation erosion. The areas in which the U-shaped cavitation pass may be in high erosion risk.

Relaminarization of elastic turbulence

We report frictional drag reduction and a complete flow re-laminarization of elastic turbulence (ET) at vanishing inertia in a viscoelastic channel flow past an obstacle. We show that intensity of observed elastic waves and wall-normal vorticity correlate well with the measured drag above the ET onset. Moreover, we find that the elastic wave frequency grows with Weissenberg number, and at sufficiently high frequency it causes decay of the elastic waves, resulting in ET attenuation and drag reduction. Thus, this allows us to substantiate a physical mechanism, involving interaction of elastic waves with wall-normal vorticity fluctuations, leading to the drag reduction and re-laminarization phenomena at low Reynolds number.

A wave damping model for flexible marsh plants with leaves considering linear to weakly nonlinear wave conditions

Marsh plants protect the coasts and coastal communities by dissipating wave energy. The dissipation of wave energy depends on the geometric (leaf and stem dimensions) and mechanical (material rigidity) properties of the plants. First, flexible plants bend in response to hydrodynamic drag (called reconfiguration), which diminishes wave decay relative to a rigid plant of the same morphology. Second, mutual sheltering between plant leaves and stem can reduce the drag, and thus wave damping. This study connects the prediction of drag on an individual plant and the measurement of wave decay over a meadow of plants to build a physically-based wave-damping model that includes leaves, the impact of reconfiguration, and the impact of sheltering between plant elements. Model plants were constructed to be both geometrically and dynamically similar to Spartina alterniflora . The wave damping model assumed linear wave conditions, but was validated using a wide range of weakly nonlinear wave conditions within model plants, over a patch of live Spartina anglica in the laboratory, and over a meadow of Spartina alterniflora in the field. After validation, the model was used to explore the variation in wave decay over a range of wave parameters and plant geometric and bio-mechanic parameters, including stem length, stem diameter, number of leaves per plant, leaf length, leaf width, the rigidity of the stem and the leaf. • A physics-based prediction for wave dissipation by flexible marsh plants with leaves was developed and validated with laboratory experiments. • The dependence of wave dissipation on water depth, wave amplitude, and wave period was explored in detail with model predictions. • The impact of leaf and stem geometry and mechanical properties on wave dissipation were revealed by systematic model predictions.

Optimal economic scheduling of microgrids considering renewable energy sources based on energy hub model using demand response and improved water wave optimization algorithm

Unpredictable nature of renewable energy sources puts power system operators in different conditions in terms of maintaining the system reliability. Microgrids (MGs) can provide an effective solution for the problems of grid-connected renewable energy sources due to their tuning capability and flexibility. In this study, a stochastic optimization strategy was proposed for participating in energy market operations considering demand response (DR). The results indicated the operating cost decreased when the MG implemented DR programs. Also, DR program could shift energy consumption from on- to off-peak hours and flatten the load curve. Therefore, a scheduling model was presented for the operation of energy carriers and reserves considering security constraints of power and natural gas grids in interconnected hubs as well as responsive load participation using the developed water wave optimization (WWO) algorithm. The objective function of this model aimed to minimize the operating cost of sources to supply electrical and thermal loads applied to the proposed MG. WWO is a meta-heuristic algorithm inspired by the behavior of water waves. The waves formed on the sea surface have complex, but interesting, relationships that can be used to solve optimization problems. In this algorithm, each problem solution is encoded as a water wave and undergoes changes in the problem search space based on three behaviors of propagation, refraction, and decay of water waves or problem solutions. The simplicity of the structure of this method, elitism and the ability to escape from local points due to the existence of different search operators and the mutation of generations have led to the use of this method. The results indicated a decline in operating costs through electrical and thermal responsive load participation and thermal energy storage system. Results of the proposed model revealed a correlation between the electricity price and natural gas consumption, indicating multi-carrier energy grids should be examined and optimized simultaneously.

Third and Fourth Harmonics of Electromagnetic Emissions by a Weak Beam in a Solar Wind Plasma with Random Density Fluctuations

Electromagnetic emissions and at the third and fourth harmonics of the plasma frequency ω p were observed during the occurrence of type II and type III solar radio bursts. Two-dimensional particle-in-cell simulations are performed using a weak beam, high space and time resolutions, and a plasma with density fluctuations of a few percent, for parameters relevant to regions of type III bursts. For the first time, a detailed study of the different wave coalescence processes involved in the generation of and waves is presented and the impact of density fluctuations on the wave interaction mechanisms is demonstrated. Energy ratios between the second, third, and fourth harmonics , , and are consistent with space observations. It is shown that, in both homogeneous and inhomogeneous plasmas, the dominant processes generating () are the coalescence of () with a Langmuir wave, in spite of the random density fluctuations modifying the waves’ resonance conditions by energy transport in the wavevector space and of the damping of Langmuir waves. The role of the backscattered (forward-propagating) Langmuir waves coming from the first (second) cascade of the electrostatic decay of beam-driven Langmuir waves is determinant in these processes. Understanding such wave coalescence mechanisms can provide indirect information on Langmuir and ion acoustic wave turbulence, the average level of density inhomogeneities, and suprathermal electron fluxes generated in solar wind regions where the harmonics manifest. Causes for the rarity of their observations are discussed.

Decay of waves in strain gradient porous elasticity with Moore-Gibson-Thompson dissipation.

We study a one-dimensional problem arising in strain gradient porous-elasticity. Three different Moore-Gibson-Thompson dissipation mechanisms are considered: viscosity and hyperviscosity on the displacements, and weak viscoporosity. The existence and uniqueness of solutions are proved. The energy decay is also shown, being polynomial for the two first situations, unless a particular choice of the constitutive parameters is made in the hyperviscosity case. Finally, for the weak viscoporosity, only the slow decay can be expected. This article is part of the theme issue 'Wave generation and transmission in multi-scale complex media and structured metamaterials (part 1)'.

Accounting for super-spreader events and algebraic decay in SIR models

A central feature of pandemics is the emergence and decay of localized infection waves. While traditional SIR models for infectious diseases can reproduce such waves, they fail to capture two key features. First, SIR models are unable to represent short-duration super-spreader events which often trigger infection waves in a community. Second, SIR models predict exponential decay to an asymptotic state after the infection wave peaks. In contrast, observations suggest a slower algebraic decay. In this paper, we develop models for the basic reproduction number R0 to capture these features. To generate quantitative estimates for R0 during super-spreader events, we reconcile the SIR framework with the Wells–Riley model for airborne disease transmission. We also show that algebraic decay emerges naturally if models are modified to account for the behavioral tendency towards relaxing precautions as the infected fraction decreases. This approach merges for the first time behavioral with physicochemical aspects.

Bio-Physical Controls on Wave Transformation in Coastal Reed Beds: Insights From the Razelm-Sinoe Lagoon System, Romania

Coastal wetlands are dynamic bio-physical systems in which vegetation affects the movement of water and sediment, which in turn build and maintain the landform and ecosystem. Wetlands are an effective buffer against coastal erosion and flooding, enhance water quality and human health and wellbeing. Numerous field and laboratory experiments have quantified the reduction of waves by coastal ecosystems. Numerical models, however, are only able to capture observed reduction in wave energy when calibration coefficients are obtained by comparison with measured dissipation rates. A deeper understanding of how wave attenuation varies over time, with local flow conditions and ecosystem properties, is still lacking and should be acquired from a greater range of ecosystem types and geographical settings. Few studies have observed the detailed seasonal variations in how coastal wetlands function as wave buffers and how such seasonal variations might be explained. Equally, few studies have focused on the effect of coastal reed beds on wave dynamics. This study addresses both: i) seasonal variability in wave dissipation through reed vegetation and ii) intricate connections between reed vegetation and the physical context (meteorological and topographical) that might explain such variability. We present observations of wind generated wave transformation through two Phragmites australis reed beds in the Razelm-Sinoe Lagoon System, Danube Delta, Romania. We find that seasonal changes in vegetation density and biomass, as well as meteorological conditions, affect observed wave conditions within the first few meters of the reed beds. Our results also show a preferential reduction of higher frequency waves, irrespective of reed stem diameter or density and suggest the potential importance of seasonal vegetation debris to observed wave dissipation. Such complex and non-linear biogeomorphic effects on wave dissipation are not currently well understood or captured in the parameterisation of vegetation-induced wave dissipation. Our study highlights the importance of an accurate and temporally granular quantification of nearshore bathymetry, wetland topography, and vegetation to fully understand, model, and manage bio-physical interactions in coastal wetlands. More specifically, our results point towards the need for spatially and temporally explicit wave decay functions in emergent reed vegetation. This is particularly critical where the accurate evaluation of the flood and erosion risk contribution of any wetland is required as part of nature-based coastal protection solutions.

Evolution of weak shock waves in non-ideal magnetogasdynamics

Abstract In this article, a study concerning the growth and decay of weak shock waves in non-ideal magnetogasdynamic regime has been performed. One-dimensional plane and cylindrical symmetries are assumed. The flow medium is considered as a perfectly conducting non-ideal gas permeated with either axial or azimuthal magnetic field. The Generalized Wavefront Expansion (GWE) method used in this work provides a system of coupled non-linear transport equations which completely describe the evolution of weak shocks and first order discontinuities induced behind it. The solution obtained during the process agrees with the classical decay laws for weak shocks. A general criterion for steepening of compressive waves and flattening of expansion waves has been derived. Further, the effect of geometrical spreading, magnetic field, and non-idealness of the gas on steepening or flattening of waves is discussed and illustrated via figures. Also, a comparison between growth and decay of weak shocks in ideal and non-ideal magnetogasdynamic regimes has been made. It has been observed during the study that all compressive waves evolve into shock regardless of their initial strength, and expansive waves decay and damp out eventually.

Wave damping by seagrass meadows in combined wave‐current conditions

AbstractLaboratory experiments using an artificial seagrass meadow modeled after Zostera marina measured the impact of following currents on meadow‐induced wave decay as a function of the imposed current velocity , wave velocity , and wave Cauchy number , which is the ratio of hydrodynamic drag force to restoring force due to blade stiffness. For small wave‐induced reconfiguration of individual seagrass blades and the addition of current enhanced reconfiguration, which decreased wave decay relative to pure wave conditions. In contrast, when the wave‐induced reconfiguration was large , the addition of following current did not significantly enhance blade reconfiguration or impact wave damping. Due to canopy drag, the current velocity within the submerged meadow, , was significantly smaller than the depth‐averaged current , and a better prediction of wave decay was achieved using as the relevant velocity. The measured wave decay validated predictions based on a modified Cauchy number, defined for combined waves and current and using the in‐canopy velocity . Practical assumptions to facilitate the prediction of wave decay in the field are discussed and validated.

Achieving high aspect ratio in plasmonic lithography for practical applications with sub-20 nm half pitch

Plasmonic lithography, which exploits a bowtie nanoaperture (BNA) for the purpose of subwavelength near-field focusing, has the capability of high-resolution patterning. However, the ultra-small feature size is achieved at the price of sharply decay of the surface plasmon waves (SPWs) in the photoresist (PR) layer, which directly leads to some unfavorable patterning issues, such as non-uniformity and shallow pattern depth even over small exposure areas. In this work, a special hybrid plasmonic waveguide (HPW) patterning system, which is composed of the plasmonic BNA-PR layer-silver reflector, is designed to facilitate high spatial frequency selection and amplify the evanescent field in the PR layer. Theoretical calculations indicate that the antisymmetric coupled SPWs and plasmonic waveguide modes excited by the HPW structure can remove the exponential decay and ensure uniform exposure over the entire depth of the PR layer. Importantly, the hyperbolic decaying characteristic of the SPWs in the PR layer plays a noticeable role in the improvement of achievable resolution, depth-of-field, and line array pattern profile. It is worth to note that the uniform periodic patterns in sub-20 nm feature can be achieved with high aspect ratio. Additionally, further numerical simulation results are presented to demonstrate the achievement of spatial frequency selection of high-k mode in HPW structure by controlling the PR thickness and gap size. Our findings may provide a new perspective on the manufacture of surface nanostructures and broaden the potential promising applications of plasmonic lithography in nanoscale patterning.

Acoustic Shock Formation in Noise Propagation During Military Aircraft Ground Run-Up Operations

A distinctive feature of many high-amplitude jet noise waveforms is the presence of acoustic shocks. Metrics indicative of shock presence, specifically the skewness of the time derivative of the waveform, the average steepening factor, and a new wavelet-based metric called the shock energy fraction, are used to quantify the strength and prevalence of acoustic shocks within waveforms recorded 10–305 m from a tethered military aircraft. The derivative skewness is more sensitive to the presence of the largest and steepest shocks, whereas the average steepening factor and shock energy fraction tend to emphasize aggregate behavior of the entire waveform. These metrics are applied at various engine conditions, over a wide range of angles and distances, to assess the growth and decay of shock waves. This paper represents the first time that the development of these metrics is shown from the near field to the far field, out to 305 m. The responses of these metrics point to significant shock formation occurring through nonlinear propagation out to 76 m from the microphone array reference position. Although these strongest shocks decay past 35 m, continued shock formation and atmospheric absorption can make the steepened nature of the waveform more prominent out to 305 m.

Physical Drivers of Ocean Wave Attenuation in the Marginal Ice Zone

Abstract Despite a recent resurgence of observational studies attempting to quantify the ice-induced attenuation of ocean waves in polar oceans, the physical processes governing this phenomenon are still poorly understood. Most analyses have attempted to relate the spatial rate of wave attenuation to wave frequency, but have not considered how this relationship depends on ice, wave, and atmospheric conditions. An in-depth analysis of the wave-buoy data collected during the 2017 Polynyas, Ice Production, and Seasonal Evolution in the Ross Sea (PIPERS) program in the Ross Sea is conducted. Standard techniques are used to estimate the spatial rate of wave attenuation α, and the influence of a number of potential physical drivers on its dependence on wave period T is investigated. A power law is shown to consistently describe the α(T) relationship, in line with other recent analyses. The two parameters describing this relationship are found to depend significantly on sea ice concentration, mean wave period, and wind direction, however. Looking at cross correlations between these physical drivers, three regimes of ice-induced wave attenuation are identified, which characterize different ice, wave, and wind conditions, and very possibly different processes causing this observed attenuation. This analysis suggests that parameterizations of ice-induced wave decay in spectral wave models should be piecewise, so as to include their dependence on local ice, wave, and wind conditions. Significance Statement This work attempts to quantify how ice, wave, and wind conditions in polar oceans affect the way that ocean waves decay as a result of their interactions with sea ice. In situ wave data collected in the Ross Sea are analyzed along with several freely available ice, wave, and wind datasets. A simple relationship is shown to describe how wave attenuation due to sea ice depends on the wave period consistently across all data analyzed. However, the parameters of this relationship are significantly affected by sea ice concentration, mean wave period, and wind direction. This finding suggests that large-scale wave models need to account for this dependence on ice, wave, and wind conditions to improve wave forecast in ice-covered oceans.

Did the Tokyo Olympic Games enhance the transmission of COVID-19? An interpretation with machine learning

BackgroundIn the summer of 2021, the Olympic Games were held in Tokyo during the state of emergency due to the spread of COVID-19 pandemic. New daily positive cases (DPC) increased before the Olympic Games, and then decreased a few weeks after the Games. However, several cofactors influencing DPC exist; consequently, careful consideration is needed for future international events during an epidemic. MethodsThe impact of the Olympic Games on new DPC were evaluated in the Tokyo, Osaka, and Aichi Prefectures using a well-trained and -evaluated long short-term memory (LSTM) network. In addition, we proposed a compensation method based on effective reproduction number (ERN) to assess the effect of the national holidays on the DPC. ResultsDuring the spread phase, the estimated DPC with LSTM was 30%–60% lower than that of the observed value, but was consistent with the compensated value of the ERN for the three prefectures. During the decay phase, the estimated DPC was consistent with the observed values. The timing of the decay coincided with achievement of a fully-vaccinated rate of 10%–15% of people aged <65 years. ConclusionsThe up- and downsurge of the pandemic wave observed in July and September are likely attributable to high ERN during national holiday periods and to the vaccination effect, especially for people aged <65 years. The effect of national holidays in Tokyo was rather notable in Aichi and Osaka, which are distant from Tokyo. The effect of the Olympic Games on the spread and decay of the pandemic wave is neither dominant nor negligible due to the shifting of the national holiday dates to coincide with the Olympic Games.

A climatological-dynamical analysis of tropopause folds over Southwest Asia in the period of 1989–2018

Tropopause folding is believed to be connected to the development of cyclonic systems in midlatitudes as well as the larger-scale, lower-frequency processes in the lower latitudes. To investigate such connections, a statistical and dynamical analysis of tropopause folds occurred in Southwest Asia is carried out for the period of 1989–2018. Tropopause folds are identified using the Era-Interim reanalysis dataset from the European Centre for Medium-Range Weather Forecasts. The spatial–temporal distributions of tropopause folding show that the frequency of folding is higher in the winter hemisphere than in the summer hemisphere and greater values of the frequency are found mostly within an elongated zonal band which is situated between 20 and 40 degrees latitude. Southwest Asia also has strong positive anomalous values of tropopause folding frequency and achieves the values more than five times the average of the Northern Hemisphere in the summer, especially in the northern latitudes of this region including Afghanistan, Iran and the eastern Mediterranean. This can be attributed mainly to the formation of summer monsoon in the subtropical latitudes of the Indian Ocean. In this regard, the examination of the effects of El Niño and La Niña on the spatial–temporal distributions of tropopause folding reveals that the values of 3-month running average of tropopause folding frequency coincident with La Niña tend to be larger than those with El Nino in both the hemispheres and Southwest Asia. This result is consistent with the previous findings on the tendency for higher occurrence of anticyclonic (cyclonic) baroclinic wave life cycles during La Niña (El Niño). Dynamically, the folds occurred in the study area are associated with the formation of waves at 500 hPa level and subsequently the creation of surface cyclones. In areas of high frequency of folding events, strong meridional shear of the zonal winds and jet stream amplification are observed at 200 hPa level. The analysis of wave activity flux and its divergence for the selected month of June 2015 shows two regions of wave propagation, one with a wave-packet like signature of flux divergence/convergence centers in the upper troposphere and one over the lower troposphere. The upper-tropospheric wave packet ends with an area of flux convergence related with the receipt and decay of Rossby waves, while in the lower troposphere, a flux divergence region as a source of stationary waves associated with the Indian monsoon activity is identified.