Wave Amplitude Amplification Research Articles

Study on the Propagation and Focusing Mechanism of Long Waves over A Submerged Atoll

An analytical solution for long waves propagating over a submerged atoll is established. The atolls involved in this study are annular coral reefs with large lagoons in the middle, and the expression of the cross section is a trinomial function of the radial distance, i.e., h=ar2s−brs+h0, where s is the positive rational number. This analytical solution extends the theory by Wang et al. (2018) as s is no longer limited to s=2/m, where m is the positive integer. In addition, by adjusting the terrain parameters properly, the analytic solution can be degenerated to describe the wave propagation over topography with a hump or pit. According to the relationship between wave rays and wave energy, the distribution characteristics and formation mechanism of energy over the topography are expounded. When the lagoon is non-existent, all wave rays converge at the x-axis, which results in an abrupt amplification of the wave amplitude around the convergence point. When a lagoon is mounted on the top of the atoll, the rays are scattered due to the refraction of the lagoon, and only some rays converge at the symmetrical axis and the ridges on both sides, which results in the amplification of wave amplitudes in these areas.

Assessment of Risks Induced by Countermining Unexploded Large-Charge Historical Ordnance in a Shallow Water Environment—Part II: Modeling of Seismo-Acoustic Wave Propagation

The goal of this work presented in a two-companion paper is to pave the way for reliably assessing the risks of damage to buildings on the shore, induced by the detonation of large-charge historical ordnance (i.e., countermining) in variable shallow water environments. Here, we focus on the impact of the marine environment, more specifically the unconsolidated sedimentary layer, on detonation-induced seismo-acoustic wave propagation. We rely on a multidisciplinary cross-study including real data obtained within the framework of a countermining campaign, and numerical simulations of the seismo-acoustic propagation using a spectral-element method. We first develop a strategy relying on physical insights into the different kind of waves that can propagate in a coastal environment, to provide clues for a computational cost reduction. The geological surveys and the hydroacoustic measurements provide input data for the 3-D axisymmetric modeling of wave propagation. The numerical simulations, obtained for one specific source–receiver path with a variable sedimentary facies, are compared with the real seismic data induced by the detonation of a charge either on the seabed, or in the water column, and recorded on the coast. Numerical analysis sheds light on the strong interaction between surface waves and the sedimentary facies. The short-scale and deep sedimentary basins favor a local wave-amplitude amplification and a frequency shift toward the low-frequency domain. However, the seismo-acoustic waves are globally attenuated during their propagation because of intrinsic attenuation and geometrical spreading, which generally prevents any large damage to nearby buildings on the shore.

Effect of resonance and wave reflection in semi-enclosed moonpool on performance enhancement of point absorber arrays

This paper presents a novel means to enhance the energy generation of the wave energy converters (WECs) array by deploying it in a semi-enclosed moonpool. The resonance phenomenon in a moonpool and the wave reflection from the wall of the moonpool result in an amplification of wave amplitude thus increase the energy generation of the wave farm. The wave diffraction and radiation analyses, based on the boundary element method are used to assess the performance of the array. An array of five-point absorbers in a semi-enclosed moonpool is considered and the energy generation, interaction effect and wave climate surrounding the wave farm are investigated. The results show that the width of the moonpool opening affects the performance of the WEC array. The wave climate surrounding the moonpool platform is studied to assess the effectiveness of the moonpool platform as a floating breakwater. The results show that the proposed integrated wave farm and floating breakwater system (moonpool platform) could generate a substantial amount of wave energy and at the same time is effective in attenuating the wave forces. The characteristics of the WECs reveal that the energy generation bandwidth could be increased by deploying the WECs in the semi-enclosed moonpool.

Propagation of nonlinear waves in graded flexible metamaterials

Attenuation and amplification of wave amplitudes are the major concerns for the design of engineering structures subjected to dynamic/impact loadings. As a kind of special structures, flexible chains have been demonstrated to support solitary waves when they undergo impacts. Here we propose a method to harness graded flexible structures with stiffness gradient to realize the decrease and increase of the amplitude of the pulse or pulse-like signals, which contributes to the design of absorber and mechanical triode. By combining the positive gradient with the concept of amplitude gap, we find the pulse or pulse-like signals can be distorted and destructed, which paves a new way to implement impact mitigation.

Ferulic acid attenuates microglia-mediated neuroinflammation in retinal degeneration

BackgroundRetinal degeneration is often accompanied by microglia-mediated neuroinflammation. Ferulic acid (FA), an active ingredient of traditional Chinese medicines (TCMs), has been reported to have anti-inflammatory effects. This study explores the impact of FA on microglia-mediated neuroinflammation and associated retinal degeneration in rd10 mice.MethodsRd10 mice received different concentrations of FA every day from postnatal day (P)4 to P24. On P25, the visual function of the mice was evaluated by electroretinogram, and retinae were collected for further investigation. Microglial activation and the expression of relevant cytokines in the retina were evaluated by qPCR, western blotting and immunofluorescence staining. Retinal structure was assessed by haematoxylin and eosin (HE) staining.ResultsSupplementation with 50 mg/kg FA provided optimal protection against retinal degeneration, with treated mice exhibiting more photoreceptor nuclei as well as greater wave amplitude amplification on electroretinogram than untreated mice. FA suppressed microglial activation both in vivo and in vitro, and inhibited the expression of pro-inflammatory factors Tnfα, IL1β, and Ccl2 in the retinae of rd10 mice. Furthermore, FA suppressed the activation of STAT1 and subsequently inhibited IRF8 expression, potentially highlighting a role for these pathways in FA-mediated immunomodulatory activity.ConclusionsAttenuation of neuroinflammation by FA may be beneficial for retarding retinal degeneration.

On the model formulations for the interaction of nonlinear waves and current

We study the model formulations of wave–current interactions in the framework of Euler equations. This work is intrigued by a recent paper from Wang et al. (2018) (hereafter WMY), which proposes such a model for the evolution of nonlinear broadband surface waves under the influence of a prescribed steady and irrotational current without vertical shear. We show that WMY’s model can be derived from a more general model accounting for an arbitrary steady and irrotational current. Under further assumption of scale separation between waves and current (i.e. horizontally slowly-varying current), WMY’s model is equivalent to an earlier model, in contrast to WMY’s claim that their model includes additional higher-order effects in wave steepness. We demonstrate the usefulness of such models in a numerical study on wave blocking by opposing current, where the nonlinear effect on the caustic location and wave amplitude amplification is elucidated. We further show that the model formulation in the framework of Euler equations form a Hamiltonian system conserving the total energy of waves and current, justifying the theoretical significance of the model equations. Finally, we generalize the formulation to nonlinear wave evolution in the presence of a rotational current with constant vorticity, which overcomes a limitation of such models that has been overlooked in previous work.

Engineering bedrock depth estimation and ground response analysis of the northern Jeddah urban area, western Saudi Arabia

The engineering bedrock depth was determined in the northern Jeddah urban area via multichannel analysis of surface waves (MASW) conducted at 76 locations. Depths corresponding to the velocity ranges were estimated below the ground surface and mapped. The engineering bedrock depth was evaluated and it varies from 0 to approximately 36.23 m whereas the depth increased eastward. Further, ground response analysis was conducted to assess the seismic hazard in terms of peak ground acceleration, where it ranges from 3.37 to 17.71 cm/s2, considering the fundamental resonance frequency and amplification potential at the sites of measurement. These variations are due to differences in the soil profile at each location; ground surface acceleration increased at sites with thick layers of soft sediments. In addition, the spectral acceleration and response spectra were assessed at the ground surface with a 5% damping ratio for the identified lithological units. Peak spectral acceleration varies from 16.8 to 62.6 cm/s2. The eastern zone has a higher spectral acceleration than the western zone while the frequency corresponding to the spectral acceleration varies from 1.05 to 14.28 Hz. The spectral acceleration and response spectra are used for assessment the spectrum of structures. Ground response analysis shows that because of the soil condition, potential amplification of wave amplitudes is observed at the ground surface when compared to the engineering bedrock level acceleration. These results should be provided to civil engineers, land-used planners, and decision makers during the designing of either new buildings or rehabilitation of pre-existing structures.

Centrifuge modeling of seismic response and failure mode of a slope reinforced by a pile-anchor structure

Pile-anchor structures are now widely used in major slope reinforcement projects, but research on the seismic response of slopes reinforced by these structures has been very limited. This paper presents the results of a series of 50g dynamic centrifuge tests that reproduce the seismic response of a slope reinforced by a pile-anchor structure exposed to an earthquake-induced stress field. A silica gel model of a slope is used to conduct multiple tests. Long-period wave amplitude amplification and frequency filtering are observed after spectral analysis. Pile bending moments and anchor tensions were recorded before the earthquake, at the moment of peak ground acceleration, and after the earthquake and the data show that the pile is the main load-bearing structure. The anchor aids in keeping the pile from tilting outward to improve the durability of the pile. Pile-anchor structure failure is caused by anchor relaxation, pile bending, and slope displacement after the passage of multiple seismic waves. A suggestion for pile-anchor structure design is provided. This paper provides a useful reference for future research on the interactions between support structures and a slope during and after earthquakes. The conclusions provided by these tests lay the foundation for designing pile-anchor reinforcement structures for better dynamic performance.

Seismic effect assessment of the southern slope of Greater Caucasus (Azerbaijan) based on the earthquake scenarios: ground parameters and acceleration models

In this paper, earthquake scenarios parameters were assessed for deterministic seis-mic hazard of the southern slope of Greater Caucasus (Azerbaijan). Historically, there occurred strong earthquakes in the studied region. Series of soft and strong earthquakes occurred for the recent years on the southern slope of Greater Caucasus in Azerbaijan in Balakan (14.10.2012, M = 5,6; 29.06.2014, M = 5,3); Zagatala (07.05.2012, M = 5,7; 18.05.2012, M = 5,0; 05.06.2018, M = 5,5); Sheki (earthquake swarm 05.02.2004, M = 3,2 ¸ 4.6); Sheki-Oguz (04.09.2015, M = 5,9); Gabala 04.10.2014, M = 5,0); Ismailli (05.02.2019, M = 5,2) demonstrates the increase of seismic activity in the given region and proves once aga-in the necessity and actuality of continuation of the seismic hazard assessment resear-ches. For earthquake scenarios of various distances, average response spectrum (5 % attenuation) of surface ground fluctuation was plotted, peak ground acceleration were assessed at the maximum magnitude, series of peak ground acceleration models were simulated at respective MSK-64 intensity, and also amplification factor distribution map. The comparative analysis allows presuming that amplification occurs due to the resonance processes, that is, softer soils produce seismic wave amplitude amplification as a result of impedance differences of those layers and harder rocks. Seismic intensity increase is observed in the sites with soft-cemented sand-clayey soils, although with sands-tones, limestone and sandy marlstone of various thicknesses. It is demonstrated that ground displacements are various and not obviously oriented towards seismic source.

Nonlinear evolution of Benjamin-Feir wave group based on third order solution of Benjamin-Bona-Mahony equation

This study concerns on the evolution of trichromatic wave group. It has been known that the trichromatic wave group undergoes an instability during its propagation, which results wave deformation and amplification on the waves amplitude. The previous results on the KdV wave group showed that the nonlinear effect will deform the wave and lead to large wave whose amplitude is higher than the initial input. In this study we consider the Benjamin-Bona-Mahony equation and the theory of third order side band approximation to investigate the peaking and splitting phenomena of the wave groups which is initially in trichromatic signal. The wave amplitude amplification and the maximum position will be observed through a quantity called Maximal Temporal Amplitude (MTA) which measures the maximum amplitude of the waves over time.

An analytical model of the evolution of a Stokes wave and its two Benjamin–Feir sidebands on nonuniform unidirectional current

Abstract. An analytical weakly nonlinear model of the Benjamin–Feir instability of a Stokes wave on nonuniform unidirectional current is presented. The model describes evolution of a Stokes wave and its two main sidebands propagating on a slowly varying steady current. In contrast to the models based on versions of the cubic Schrödinger equation, the current variations could be strong, which allows us to examine the blockage and consider substantial variations of the wave numbers and frequencies of interacting waves. The spatial scale of the current variation is assumed to have the same order as the spatial scale of the Benjamin–Feir (BF) instability. The model includes wave action conservation law and nonlinear dispersion relation for each of the wave's triad. The effect of nonuniform current, apart from linear transformation, is in the detuning of the resonant interactions, which strongly affects the nonlinear evolution of the system. The modulation instability of Stokes waves in nonuniform moving media has special properties. Interaction with countercurrent accelerates the growth of sideband modes on a short spatial scale. An increase in initial wave steepness intensifies the wave energy exchange accompanied by wave breaking dissipation, resulting in asymmetry of sideband modes and a frequency downshift with an energy transfer jump to the lower sideband mode, and depresses the higher sideband and carrier wave. Nonlinear waves may even overpass the blocking barrier produced by strong adverse current. The frequency downshift of the energy peak is permanent and the system does not revert to its initial state. We find reasonable correspondence between the results of model simulations and available experimental results for wave interaction with blocking opposing current. Large transient or freak waves with amplitude and steepness several times those of normal waves may form during temporal nonlinear focusing of the waves accompanied by energy income from sufficiently strong opposing current. We employ the model for the estimation of the maximum amplification of wave amplitudes as a function of opposing current value and compare the result obtained with recently published experimental results and modeling results obtained with the nonlinear Schrödinger equation.

On the use of simultaneous measurements of OH and O<sub>2</sub> emissions to investigate wave growth and dissipation

Abstract. Simultaneous measurements of mesospheric OH (6–2) Meinel and O2 (0–1) Atmospheric band emissions from a low-latitude station, Maui, Hawaii (20.8° N, 156.2° W) are utilized to study the wave characteristics and associated processes. Deduced temperatures show large variability in both OH and O2 data. The seasonal variability in the temperature shows a well-defined, semiannual type of oscillation, which are comparable to the ground-based rocket sounding data. The "Wave Growth Factor", a ratio of normalized perturbation amplitude in O2 to the OH temperature variability, is estimated for principal as well as residual smaller period components of the nocturnal variability. It is noticed that smaller period waves (less than 12 h) occasionally have large growth factors of about 3–4 during equinox transitions, an indication of wave amplitude amplification within the 87–94 km altitudes while a strong wave-dissipation occurs throughout the year.

Revising the 1759 Kattegat earthquake questionnaires using synthetic wavefield analysis

In aseismic regions the lack of large earthquakes in modern times makes the study of historical earthquakes essential as such events often serve as the yardstick for estimating seismic hazards. Since the largest earthquakes with few exceptions took place hundreds of years ago we may claim that their recurrence times are very large or alternatively their magnitudes are biased upwards. Scandinavia is no exception in this regard and one interesting event in particular is the Kattegat earthquake of 22 December 1759. It is unique in the sense that a macroseismic questionnaire was circulated in Zealand within days of its occurrence. The puzzling feature here is that intensity ranges from VII to I across Zealand but then given I=III for Hamburg and other North German cities. We have chosen two avenues in reassessing the magnitude of the Kattegat earthquake, namely (1) 2D finite-difference (FD) waveform modelling to evaluate possible amplitude amplifications due to sub-surface basin structures and (2) re-assessing the intensity reports of the 1759 Kattegat earthquake in light of the new European Macroseismic Scale (EMS-98). Our 2D FD results show that the presence of the Danish and the North German basins led to shear wave amplitude amplification by factors of 10 and 5, respectively. This is equivalent to a significant increase or overestimation of the area of perception (tied to I=III). The re-assessment of the macroseismic observations in light of the above results and the EMS-98 downgrade the Kattegat earthquake MS magnitude from 5.6 to 5.1.

Shear waves in micro-faulted materials

We discuss two alternative models of wave propagation in materials with a continuous distribution of microscopic faults. Dissipation is explicitly taken into account, but special exchange relations between the macroscopic deformation and the microstructure may lead to the amplification of wave amplitudes.

Bi-orthogonal decomposition and Wavelet transform to analyse kinematics and dynamics of surface waves

A row of discrete vortices is superposed to an air-sea interface to modelize the generation of surface waves by wind. A numerical method is developed in order to take into account the nonlinear effects which occur in the evolution of surface waves with finite steepness. The shape of the excited surface waves range from quasi sinusoidal to asymmetrical profiles close to breaking. Bi-orthogonal decomposition shows that resonant excitation (amplification of wave amplitude) may occur both at the fundamental frequency and at its second harmonic. This deterministic physical model is compared with experiments conducted in an air-sea tunnel. A vortex street is artificially created in the air flow. Using Fourier analysis and Wavelet transform it is found, in agreement with the numerical formulation, that non-sinusoidal disturbances advected over the water surface can have harmonic components that interact resonantly to generate surface waves, even thought the basic (fundamental) scale is non -resonant.

Propagation and amplification of tsunamis at coastal boundaries

WHEN tsunamis hit a coastal area, they often cause substantial damage and loss of life at locations otherwise well protected from normal (even severe) wind-generated waves. An example of such a catastrophe took place on 12 December 1992, when an earthquake of magnitude Ms = 7.5 occurred in the eastern region of Flores Island, Indonesia1,2. One of the areas hardest hit by the resulting tsunamis was Babi, a small coastal island; two villages on the island were completely destroyed, even though both were located in sheltered areas where wave conditions are normally calm. Here we describe the results of numerical and laboratory experiments that show how, unlike wind-generated waves, tsunamis are capable of penetrating into sheltered coastal areas without significantly losing their energy. For the case of Babi Island, the original tsunami wave was split into two, with one wave propagating around each side of the island. The two waves met in the sheltered region, and the subsequent amplification of wave amplitude resulted in the destructive flow onto the beach.

A microzonation method based on uniform risk spectra

A method for seismic microzonation of a large metropolitan area is examined. It utilizes information on the location of active faults and their relative levels of seismicity, the three-dimensional source to station geometry, the frequency dependent attenuation, the effects of local amplification of wave amplitudes in terms of the depth of sedimentary deposits beneath the site, and the scaling in terms of earthquake magnitude. The method presented here does not require any new or difficult steps to gather data, when compared to other microzonation procedures employed in the United States or abroad. The advantage of the method lies in its ability to properly balance different contributing factors to the seismic risk at a point, in time, space and frequency of strong ground shaking.