scholarly journals Dasar Laut Sinusoidal Sebagai Reflektor Gelombang

2011 ◽  
Vol 2 (1) ◽  
pp. 441
Author(s):  
Viska Noviantri
Keyword(s):  
Asymptotic Expansion ◽  
Incident Wave ◽  
Large Amplitude ◽  
Wave Amplitude ◽  
Transmitted Wave ◽  
Bragg Resonance ◽  
Multi Scale ◽  
Reflected Wave ◽  
Incident Waves

This article discusses about the influence of sinusoidal sandbars towards the amplitude of incident wave. sinusoidal sandbars may lead to Bragg resonance. Basically, when a wave meets a different depth, it will scatter into a transmitted wave and a reflected wave. Bragg resonance happens when the wavelength of incident wave is twice of the wavelength of the periodic bottom disturbance. We apply the multi-scale asymptotic expansion to obtain the results. Eventually we find that a larger amplitude disturbance leads to larger reflected wave amplitude. This result explains that the sinusoidal sandbars indeed can reduce the amplitude of incident wave and protect a beach from large amplitude incident waves. 

Nonlinear Interaction of Acoustical Waves Due to Cracks and Its Possible Usage for Cracks Detection

1995 ◽  
Vol 1 (3) ◽  
pp. 335-344 ◽  
Author(s):  
V. Yu. Zaitsev ◽  
A.M. Sutin ◽  
I. Yu. Belyaeva ◽  
V.E. Nazarov
Keyword(s):  
Acoustic Wave ◽  
Nonlinear Interaction ◽  
Crack Detection ◽  
Wave Amplitude ◽  
Acoustic Pulse ◽  
Transmitted Wave ◽  
New Method ◽  
Nonlinear Properties ◽  
Reflected Wave ◽  
Crack Type

An interaction of a CW acoustic wave and a powerful acoustic pulse due to nonlinear properties of a crack-type discontinuity in a solid is considered. Characteristics of nonstationary variations of the reflected wave amplitude and the phase of the transmitted wave, which are induced by the powerful pulse, are determined. The effects should allow one to distinguish cracks from other scatterers and can be used as a base of a new method of crack detection and positioning. Demonstrative signal estimates based on two simplified crack models are presented.

Generation and radiation of second harmonics by s-polarized electromagnetic waves incident on a narrow inhomogeneous plasma layer

1974 ◽  
Vol 12 (1) ◽  
pp. 15-20 ◽  
Author(s):  
V. V. Dolgopolov ◽  
N. M. El-Siragy ◽  
Y. A. Sayed
Keyword(s):  
Incident Wave ◽  
Electromagnetic Waves ◽  
Plasma Layer ◽  
Inhomogeneous Plasma ◽  
Normal Incidence ◽  
Transmitted Wave ◽  
Wave Radiation ◽  
Isotropic Plasma ◽  
Basic Frequency ◽  
Reflected Wave

We investigate radiation of waves at double the frequency from an arbitrary inhomogeneous, isotropic plasma layer, when 8-polarized electromagnetic waves are obliquely incident on it and their lengths are considerably greater than the width of the layer. We calculate the amplitudes of the radiated waves. We show that, in general, the second harmonics are radiated in the direction of propagation of both the reflected and the transmitted wave being at the basic frequency. At small plasma densities, the second harmonics are emitted practically only in the direction of propagation of the reflected wave at the basic frequency. For normal incidence, there is no wave radiation at double the frequency of the incident wave.

scholarly journals SUBHARMONIC GENERATION OF TRANSVERSE OSCILLATIONS INDUCED BY INCIDENT REGULAR WAVES

2012 ◽  
Vol 1 (33) ◽  
pp. 11 ◽  
Author(s):  
Gang Wang ◽  
Jin-Hai Zheng
Keyword(s):  
Numerical Investigation ◽  
Incident Wave ◽  
Growth Rates ◽  
Wave Amplitude ◽  
Threshold Value ◽  
Steep Slope ◽  
Regular Waves ◽  
Constant Slope ◽  
Incident Waves ◽  
Transverse Oscillations

It is generally accepted that there are transverse oscillation, which are concentrated and confined to the backwall and decay asymptotically offshore, existed in the harbor of constant slope, however, whether these oscillations can be induced by the normally incident waves is not clear. This numerical investigation aims at providing the subharmonic generations of transverse oscillations within the harbor of a plane slope by waves normally impacting on. For the harbor of perfectly plane slopes, the subharmonic transverse oscillations are small on the mild and moderate slopes but evident on the steep slope. This instability can take place only if the incident wave amplitude exceeds a threshold value, and transverse oscillations can even grow up to a larger value than that of longitudinal oscillations. The magnitudes of transverse oscillations are approximately the same, only their growth rates are affected by the incident wave amplitude.

scholarly journals Oblique sub- and super-harmonic Bragg resonance of surface waves by bottom ripples

2010 ◽  
Vol 643 ◽  
pp. 437-447 ◽  
Author(s):  
MOHAMMAD-REZA ALAM ◽  
YUMING LIU ◽  
DICK K. P. YUE
Keyword(s):  
Perturbation Theory ◽  
Incident Wave ◽  
Special Importance ◽  
Bragg Resonance ◽  
Class Iii ◽  
Spectral Evolution ◽  
Resonant Wave ◽  
Continental Shelves ◽  
Special Cases ◽  
Incident Waves

We consider a class of higher order (quartet) Bragg resonance involving two incident wave components and a bottom ripple component (so called class III Bragg resonance). In this case, unlike class I/II Bragg resonance involving a single incident wave and one/two bottom ripple components, the frequency of the resonant wave, which can be reflected or transmitted, is a sum or difference of the incident wave frequencies. In addition to transferring energy across the spectrum leading to potentially significant spectral transformation, such resonances may generate long (infragravity) waves of special importance to coastal processes and engineering applications. Of particular interest here is the case where the incident waves are oblique to the bottom undulations (or to each other) which leads to new and unexpected wave configurations. We elucidate the general conditions for such resonances, offering a simple geometric construction for obtaining these. Perturbation analysis results are obtained for these resonances predicting the evolutions of the resonant and incident wave amplitudes. We investigate special cases using numerical simulations (applying a high-order spectral method) and compare the results to perturbation theory: infragravity wave generation by co- and counter-propagating incident waves normal to bottom undulations; longshore long waves generated by (bottom) oblique incident waves; and propagating–standing resonant waves due to (bottom) parallel incident waves. Finally, we consider a case of multiple resonance due to oblique incident waves on bottom ripples which leads to complex wave creation and transformations not easily tractable with perturbation theory. These new wave resonance mechanisms can be of potential importance on continental shelves and in littoral zones, contributing to wave spectral evolution and bottom processes such as sandbar formation.

Study on Nonlinear Motion Behavior of Coupled Heave-Pitch for the Classic Spar Platform Based on AQWA

2012 ◽  
Vol 170-173 ◽  
pp. 2170-2174 ◽  
Author(s):  
Song Sang ◽  
Yuan Zhou ◽  
Xue Liang Jiang
Keyword(s):  
Incident Wave ◽  
Wave Amplitude ◽  
Wave Period ◽  
Critical Periods ◽  
Spar Platform ◽  
Natural Period ◽  
Nonlinear Motion ◽  
Motion Characteristic ◽  
Instability Parameter ◽  
Motion Behavior

This paper used AQWA software to research the nonlinear motion characteristic of heave-pitch coupling of classical Spar platform in regular waves. With classic Spar platform as an example, the wave amplitude and periodic changes’ effect to the nonlinear motion behavior of coupled heave-pitch is researched. After calculation, the critical periods corresponding to the different incident wave amplitude are obtained, based which, gets the instability parameter domain of coupling resonance of platform in the wave period-amplitude plane. The results in this paper show that the heave-pitch coupled resonance of platform depends on the wave amplitude and the ratio of the natural period of heave and pitch, and the incident wave period.

An Improved Body-Exact Method to Predict Large Amplitude Ship Roll Responses

2018 ◽  
Author(s):  
Rahul Subramanian ◽  
Naga Venkata Rakesh ◽  
Robert F. Beck
Keyword(s):  
Incident Wave ◽  
Large Amplitude ◽  
Nonlinear Models ◽  
Body Position ◽  
Computational Cost ◽  
Offshore Structures ◽  
The Body ◽  
Surface Boundary ◽  
Strip Theory ◽  
New Formulation

Accurate prediction of the roll response is of significant practical relevance not only for ships but also ship type offshore structures such as FPSOs, FLNGs and FSRUs. This paper presents a new body-exact scheme that is introduced into a nonlinear direct time-domain based strip theory formulation to study the roll response of a vessel subjected to moderately large amplitude incident waves. The free surface boundary conditions are transferred onto a representative incident wave surface at each station. The body boundary condition is satisfied on the instantaneous wetted surface of the body below this surface. This new scheme allows capturing nonlinear higher order fluid loads arising from the radiated and wave diffraction components. The Froude-Krylov and hydrostatic loads are computed on the intersection surface of the exact body position and incident wave field. The key advantage of the methodology is that it improves prediction of nonlinear hydrodynamic loads while keeping the additional computational cost small. Physical model tests have been carried out to validate the computational model. Fairly good agreement is seen. Comparisons of the force components with fully linear and body-nonlinear models help in bringing out the improvements due to the new formulation.

scholarly journals GROIN LENGTH AND THE GENERATION OF EDGE WAVES

1976 ◽  
Vol 1 (15) ◽  
pp. 85 ◽  
Author(s):  
Michael K. Gaughan ◽  
Paul D. Komar
Keyword(s):  
Incident Wave ◽  
Wave Length ◽  
Critical Length ◽  
Beach Erosion ◽  
Rip Currents ◽  
Edge Waves ◽  
Normal Waves ◽  
Wave Basin ◽  
Incident Waves ◽  
Selection Of

A series of wave basin experiments were undertaken to better understand the selection of groin spacings and lengths. Rather than obtaining edge waves with the same period as the normal incident waves, subharmonic edge waves were produced with a period twice that of the incoming waves and a wave length equal to the groin spacing. Rip currents were therefore not formed by the interactions of the synchronous edge waves and normal waves as proposed by Bowen and Inman (1969). Rips were present in the wave basin but their origin is uncertain and they were never strong enough to cause beach erosion. The generation of strong subharmonic edge waves conforms with the work of Guza and Davis (1974) and Guza and Inman (1975). The subharmonic edge waves interacted with the incoming waves to give an alternating sequence of surging and collapsing breakers along the beach. Their effects on the swash were sufficient to erode the beach in some places and cause deposition in other places. Thus major rearrangements of the sand were produced between the groins, but significant erosion did not occur as had been anticipated when the study began. By progressively decreasing the length of the submerged portions of the groins, it was found that the strength (amplitude) of the edge waves decreases. A critical submerged groin length was determined whereby the normally incident wave field could not generate resonant subharmonic edge waves of mode zero with a wavelength equal to the groin spacing. The ratio of this critical length to the spacing of the groins was found in the experiments to be approximately 0.15 to 0.20, and did not vary with the steepness of the normal incident waves.

scholarly journals Bragg Resonance around the Coast of Hardwall

2016 ◽  
Vol 7 (4) ◽  
pp. 275
Author(s):  
Viska Noviantri ◽  
Ro’fah Nur Rachmawati
Keyword(s):  
Wave Length ◽  
Expansion Method ◽  
Wave Transmission ◽  
Bragg Resonance ◽  
Incoming Wave ◽  
Approximation Solution ◽  
Multi Scale ◽  
The Right ◽  
Asymptotic Expansion Method ◽  
Transmission And Reflection

Basically, when waves pass an uneven basis, then this wave will be split into transmission and reflection waves. First of all, it will be shown that a sinusoidal seabed can lead to the phenomenon of Bragg resonance. Bragg resonance occurs when the wave-length comes at twice the wave-length of a sinusoidal basis. The method used to obtain approximation solution is a multi-scale asymptotic expansion method. A research on the effect of Bragg resonance on sinusoidal basis had been studied. Sinusoidal basis can reduce the amplitude of the incoming wave so that the amplitude of the wave transmission is quite small. In these researcher, the coast is assumed ideal and can absorb all the energy of the wave transmission. If the beach can reflect waves, this indicates that the existence of sinusoidal basis is more harmful to the coast. This mechanism relies on the distance between the base sinusoidal and beaches. The present research will examined the influence of the base, when there was a beach of hard-wall on the right, which was perfectly capable of reflecting waves. Having regard to the phase difference, from super positioned waves when they hit the beach, so it can determine the safert and the most dangerous distance.

scholarly journals Lab Non Destructive Test to Analyze the Effect of Corrosion on Ground Penetrating Radar Scans

2019 ◽  
Vol 11 (23) ◽  
pp. 2814 ◽  
Author(s):  
Sossa ◽  
Pérez-Gracia ◽  
González-Drigo ◽  
Rasol
Keyword(s):  
Ground Penetrating Radar ◽  
Wave Amplitude ◽  
Metallic Surface ◽  
Non Destructive Testing ◽  
Destructive Testing ◽  
Accurate Analysis ◽  
Reflected Wave ◽  
Dense Grid ◽  
Ground Penetrating ◽  
Non Destructive

Corrosion is a significant damage in many reinforced concrete structures, mainly in coastal areas. The oxidation of embedded iron or steel elements degrades rebar, producing a porous layer not adhered to the metallic surface. This process could completely destroy rebar. In addition, the concrete around the metallic targets is also damaged, and a dense grid of fissures appears around the oxidized elements. The evaluation of corrosion is difficult in early stages, because damage is usually hidden. Non-destructive testing measurements, based on non-destructive testing (NDT) electric and magnetic surveys, could detect damage as consequence of corrosion. The work presented in this paper is based in several laboratory tests, which are centered in defining the effect of different corrosion stage on ground penetrating radar (GPR) signals. The analysis focuses on the evaluation of the reflected wave amplitude and its behavior. The results indicated that an accurate analysis of amplitude decay and intensity could most likely reveal an approach to the state of degradation of the embedded metallic targets because GPR images exhibit characteristics that depend on the effects of the oxidized rebar and the damaged concrete. These characteristics could be detected and measured in some cases. One important feature is referred to as the reflected wave amplitude. In the case of corroded targets, this amplitude is lower than in the case of reflection on non-oxidized surfaces. Additionally, in some cases, a blurred image appears related to high corrosion. The results of the tests highlight the higher amplitude decay of the cases of specimens with corroded elements.

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