Incident Wave Amplitude Research Articles

Hybrid simulation of mode conversion at the magnetopause

Two‐dimensional hybrid simulations are used to investigate how fast‐mode compressional waves incident on a magnetopause current layer mode convert both linearly and nonlinearly to short wavelength (k⊥ρi ∼ 1) kinetic Alfvén waves near the Alfvén resonance surface. The background magnetic fields on both sides of the current layer are parallel to each other and perpendicular to the magnetopause normal, corresponding to a northward interplanetary magnetic field. The simulations are performed in a 2‐D plane (xz), where x is normal to the magnetopause and z is tilted by an angle, θ, relative to the magnetic field. We examine how the mode conversion depends on wave frequency ω0, wave vector, Alfvén velocity profile (particularly the magnetopause width, D0), ion β in the magnetosheath, electron‐to‐ion temperature ratio, and incident wave amplitude. Kinetic effects resolve the resonance, and KAWs radiate back to the magnetosheath side of the current layer. The compressional wave absorption rate is estimated and compared with linear theory. Unlike the prediction from low‐frequency theory of the Alfvén resonance, KAWs are also generated in cases with θ = 0°, provided ω0 > 0.1Ω0, with Ω0 being the ion cyclotron frequency in the magnetosheath. As the incident wave amplitude is increased, several nonlinear wave properties are manifested in the mode conversion process. Harmonics of the driver frequency are generated. As a result of nonlinear wave interaction, the mode conversion region and its spectral width are broadened. The nonlinear waves provide a significant transport of momentum across the magnetopause and are associated with significant ion heating in the resonant region.

Residual circulation due to internal waves shoaling on a slope

We describe the residual circulation induced in a two‐layer system when internal waves, with a wave length equal to or longer than the slope length, propagate over a sloping bottom and either reflect or break. For the case of no wave breaking, scaling is used to derive Boussinesq‐type equations, the solution of which leads to an expression for the residual circulation adjacent to the sloping bottom. This residual circulation is maintained by a weak slope on the density interface. For breaking waves, laboratory experiments and numerical modeling were used to ascertain the details of the residual circulation arising from the formation of gravitational intrusions. Results from these three investigative tools were used to determine, as a function of bottom slope and incident wave amplitude, the internal wave reflection coefficient and the strength of the residual circulation pattern with and without wave breaking.

Acoustic Properties of Porous Coatings for Hypersonic Boundary-Layer Control

Numerical simulations are performed to investigate the interaction of acoustic waves with an array of equally spaced two-dimensional microcavities on an otherwise flat plate without external boundary-layer flow. This acoustic scattering problem is important in the design of ultrasonic absorptive coatings for hypersonic laminar flow control. The reflection coefficient, characterizing the ratio of the reflected wave amplitude to the incident wave amplitude, is computed as a function of the acoustic wave frequency and angle of incidence, for coatings of different porosities, at various acoustic Reynolds numbers relevant to hypersonic flight. Overall, the numerical results validate predictions from existing theoretical modeling. In general, the amplitude of the reflection coefficient has local minima at some specific frequencies. A simple model to predict these frequencies is presented. The simulations also highlight the presence of resonant acoustic modes caused by coupling of small-scale scattered waves near the coating surface. Finally, the cavity depth and the porosity are identified as the most important parameters for coating design. Guidelines for the choice of these parameters are suggested.

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

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.

Hysteresis jumps of the surface reactance of a layered superconductor as the incident wave amplitude varies

The nonlinear response of a layered superconductor to symmetric (in magnetic field) electromagnetic excitation has been theoretically investigated. An ambiguous dependence of the phase of the reflected signal on the amplitude H0 of the irradiating wave is predicted. This causes hysteresis jumps in the dependence of the surface reactance of the superconductor on H0. If the frequency of the irradiating field is close to the Josephson plasma frequency, this unusual nonlinear effect can be observed when the amplitudes of the ac field are not very strong. The conditions for the appearance of hysteresis are obtained. Expressions for the phase shift of the reflected wave are derived, using the coupled sine-Gordon equations. Moreover, a class of solutions of these equations that are discontinuous in the coordinate are studied that correspond to a continuous spatial distribution of the magnetic field in the superconductor. Such solutions result in the appearance of additional branches in the dependence of the phase shift of the reflected wave on the incident wave amplitude.

S0302-2-1 非線形超音波計測のための8chフェイズドアレイシステム([S0302-2]超音波非破壊評価の高精度化(2))

In industrial ultrasonic inspection, closed defects (cracks) result in misdetection or underestimation in sizing of the defects. Nonlinear ultrasound especially sub-harmonic ultrasound has been expected to detect closed defects due to the large displacement of incident wave. However, applicable displacement of incident ultrasound at defect is 100 nm peak-to-peak at most which considered insufficient comparing to the industrial crack tip displacement. In this study, we focused on phased array technique, and fabricated an 8ch phased array system which can excite 600Vp-p successive wave. We observed the fundamental travelling behavior of ultrasound combined with the prototyped transducers and investigated the availability of the phased array techniques to enhance the amplitude of incident waves.

Resonance induced by a bound state in the continuum in a two-level nonlinear Fano-Anderson model

We consider the transmission through a nonlinear media in the framework of a two-level nonlinear Fano-Anderson model. The model is realized in photonic crystal waveguide coupled with two off-channel defects with the instantaneous Kerr-type nonlinearity. We reveal a resonance and argue that it is a result of excitement of bound state in the continuum (BSC) by transmitted wave. The resonance induced by BSC is located at the energy of BSC with a width proportional to the amplitude of incident wave. The BSC exists at any distance between energy levels of the two-level nonlinear Fano-Anderson model that is fundamentally different from the linear case.

Nonlinear Internal Wave Run-Up on Impermeable Steep Slopes

Laboratory experiments were conducted to investigate the run-up of internal solitary waves (ISWs) on steep uniform slopes in a two-layered fluid system with a free surface. A 12 m long wave flume, which incorporated a movable vertical gate for generating ISWs, was used in the experiments. A steep uniform slope was modeled at one end of the flume. In the present study we looked at internal waves with small and large amplitudes using a steep uniform slope (from one of θ=30, 50, 60, 90, 120, and 130 deg) much longer than those previously published in the literature. Results collected from a wide range of experimental runs show that the run-up height depends on the planar slope, while the breaking depth is only antecedent to the amplitude of an ISW. The overall quantitative agreement with the linear feature aspects of the incident wave amplitude is encouraging.

Effects of stiffness on reflection and transmission of micropolar thermoelastic waves at the interface between an elastic and micropolar generalized thermoelastic solid

The reflection and transmission of micropolar thermoelastic plane waves at the interface between an elastic solid and micropolar generalized thermoelastic solid is discussed. The interface boundary conditions obtained contain interface stiffness (normal stiffness and transverse stiffness). The expressions for the reflection and transmission coefficients which are the ratios of the amplitudes of reflected and transmitted waves to the amplitude of incident waves are obtained for normal force stiffness, transverse force stiffness and welded contact. Numerical calculations have been performed for amplitude ratios of various reflected and transmitted waves. The variations of amplitude ratios with angle of incident wave have been depicted graphically. It is found that the amplitude ratios of reflected and transmitted waves are affected by the stiffness, micropolarity and thermal distribution of the media.

Coupling Between Waveguide-Fed Planar Slot Arrays

Coupling between two waveguide-fed planar slot arrays is investigated using full-wave analysis. The analysis employs the method-of-moments solution to the pertinent coupled integral equations for the aperture electric field of all slots. From the TE10 mode scattered by the slots, the complex coefficient of the wave incident at the input port of each array is computed. By exciting the input port of one of the arrays and match-terminating the other, we determine the incident wave amplitude at the input port of the second array, thereby determining the coupling. Computed coupling values are presented for different array geometries.

Numerical Simulation of Long-Shore Currents Induced by Regular Breaking Wave

The hydrodynamics of coastal zones are extremely complicated, being influenced greatly by shallow water waves and currents induced by wave breaking. This paper presents numerical simulations of long-shore currents induced by the breaking of oblique incident waves in shallow coastal zones. The wave numerical model is based on parabolic mild slope equation, and so the wave radiation stress required for the generation of wave-induced currents are calculated based on the variables in the parabolic mild slope equation, and the long-shore currents have been numerically simulated based on these. The numerical models are validated against experimental data, and the results suggest that the long-shore current velocity and wave set-up increase with the increasing incident wave amplitude and offshore slope steepness, as well as the wave set-up increase with the increasing incident wave period.

Abstract 1196: Endogenous Nitric Oxide Synthase Inhibitors, Arterial Hemodynamics And Subclinical Vascular Disease: A Population-based Study

Background: Asymmetric dimethylarginine (ADMA) and NG-monomethyl-L-arginine (NMMA), endogenous nitric oxide-synthase inhibitors (End-NOSI), have been associated with cardiovascular risk factors (CVRF) and atherosclerosis. In addition, acute administration of NOSI cause hypertension through hemodynamic effects, but whether circulating End-NOSI are associated with these abnormalities is unknown. Methods: We studied 922 adults in a population-based study (PREVENCION study). We examined the correlation between End-NOSI/L-arginine and CVRF, as well as the relationship between these biomarkers and arterial hemodynamics, carotid-femoral pulse wave velocity (cf-PWV) and carotid intima-media thickness (c-IMT). We used general linear modeling for statistical analyses. Estimates (β) are standardized. Results: In multivariate analyses, LDL-cholesterol and C-reactive protein (CRP) were independent predictors of ADMA, whereas LDL-cholesterol and gender independently predicted NMMA. Age, gender, HDL-cholesterol and CRP were independent predictors of L-arginine. ADMA (β=0.09;p=0.008) and NMMA (β=0.11; p=0.001), but not L-arginine, were strong predictors of c-IMT, even after adjustment for CVRF, CRP and renal function. In contrast, ADMA and NMMA were not predictors of cf-PWV, blood pressure or hemodynamic abnormalities. Higher L-arginine independently predicted higher central (aortic) pulse pressure (β=0.09; p=0.002), incident wave amplitude (β=0.11; p<0.001) and late systolic augmented pressure from wave reflections (β=0.07; p=0.003), but not systemic vascular resistance or cardiac output. Conclusions: ADMA and NMMA are differentially associated with CVRF, but both End-NOSI are independently predictors of carotid atherosclerosis. In contrast, they are not associated with large artery stiffness, hypertension or hemodynamic abnormalities. Our findings are consistent with a role for End-NOSI in atherosclerosis, but not in large artery stiffnening, hypertension or long-term hemodynamic regulation. L-arginine is independently associated with abnormal pulsatile hemodynamics, which may reflect abnormal L-arginine transport, leading to decreased intracellular bioavailability for NO synthesis.

Endogenous Nitric Oxide Synthase Inhibitors, Arterial Hemodynamics, and Subclinical Vascular Disease

Endogenous NO synthase inhibitors (end-NOSIs) have been associated with cardiovascular risk factors and atherosclerosis. In addition, end-NOSIs may directly cause hypertension through hemodynamic effects. We aimed to examine the association between end-NOSI asymmetrical dimethylarginine (ADMA) and N-guanidino-monomethyl-arginine (NMMA), subclinical atherosclerosis, and arterial hemodynamics. We studied 922 adults participating in a population-based study (PREVENCION Study) and examined the correlation between end-NOSI/L-arginine and arterial hemodynamics, carotid-femoral pulse wave velocity, and carotid intima-media thickness using linear regression. ADMA, NMMA, and L-arginine were found to be differentially associated with various classic cardiovascular risk factors. ADMA and NMMA (but not L-arginine) were significant predictors of carotid intima-media thickness, even after adjustment for cardiovascular risk factors, C-reactive protein, and renal function. In contrast, ADMA and NMMA did not predict carotid-femoral pulse wave velocity, blood pressure, or hemodynamic abnormalities. Higher L-arginine independently predicted systolic hypertension, higher central pulse pressure, incident wave amplitude, central augmented pressure, and lower total arterial compliance but not systemic vascular resistance or cardiac output. We conclude that ADMA and NMMA are differentially associated with cardiovascular risk factors, but both end-NOSIs are independent predictors of carotid atherosclerosis. In contrast, they are not associated with large artery stiffness, hypertension, or hemodynamic abnormalities. Our findings are consistent with a role for asymmetrical arginine methylation in atherosclerosis but not in large artery stiffening, hypertension, or long-term hemodynamic regulation. L-arginine is independently associated with abnormal pulsatile (but not resistive) arterial hemodynamic indices, which may reflect abnormal L-arginine transport, leading to decreased intracellular bioavailability for NO synthesis.

Beyond ray tracing for internal waves. II. Finite-amplitude effects

We examine the transmission of small and moderately large internal gravity wavepackets through uniformly and nonuniformly stratified fluids using fully nonlinear numerical simulations. The simulations of finite-amplitude waves in a uniformly stratified fluid show that the weakly nonlinear theory developed for horizontally periodic wavepackets extends well to the dynamics of wavepackets with horizontal extent comparable to the horizontal wavelength. In simulations of small-amplitude wavepackets in a nonuniformly stratified fluid the transmission coefficient is found to be comparable to that computed analytically for horizontally periodic waves that radiate continuously (nontransiently) on a reflection level. Simulations of finite-amplitude waves in a nonuniformly stratified fluid show little dependence of transmission coefficient on the wavepacket extent. However, for a wide range of incident wave frequencies the simulations exhibit a monotonic increase in the transmission coefficient as a function of the incident wave amplitude.

Third order approximation to capillary gravity short crested waves with uniform currents

A third-order analytical solution for the capillary gravity short crested waves with uniform current (the main current direction is along the vertical wall) in front of a vertical wall is derived through a perturbation expanding technique. The validity and advantage of the new solution were proved by comparing the results of wave profiles and wave pressures with those of Huang and Jia [H. Huang, F. Jia, The patterns of surface capillary gravity short-crested waves with uniform current fields in coastal waters, Acta Mech. Sinica 22 (2006) 433–441] and Hsu [J.R.C. Hsu, Y. Tsuchiya, R. Silvester, Third-order approximation to short-crested waves, J. Fluid Mech 90 (1979) 179–196]. The important influences of currents on the wave profiles, wave frequency, the ratio of maximum crest height to the total wave height, and wave pressure are investigated for both small-scale (for example, the incident wave wavelength is 9.35 cm) and larger-scale (for example, the incident wave wavelength is 5 m) short crested wave. By numerical computation, we find wave frequency of short crested wave system is greatly affected by incident wave amplitude, incident angle, water depth, surface tension coefficient and the strength of the currents for small-scale incident wave. Furthermore, for the larger-scale short crested wave system, the higher-order solution with uniform current is particularly important for the prediction of wave profile and wave pressure for different water depth and incident angle. Computational results show that with the increase of the current speed, the crests of wave profile and wave pressure become more and more steep. In some cases, the crest value of wave pressure with strong current would be larger about six times than that of no current. Therefore, ocean engineers should consider the short crested wave-current load on marine constructs carefully.

Reflection and Transmission of Micropolar Elastic Waves at an Imperfect Boundary

A problem concerning with the reflection and transmission of micropolar elastic plane waves at an imperfect interface between two homogeneous, isotropic micropolar elastic half‐spaces of different micropolar elastic properties has been investigated. The expressions for the reflection and transmission coefficients which are the ratios of the amplitudes of reflected and transmitted waves to the amplitude of incident waves are obtained for an imperfect boundary and deduced for normal couple stiffness, transverse couple stiffness, transverse force stiffness and welded contact. Numerical calculations have been performed for amplitude ratios of various reflected and transmitted waves. The variations of amplitude ratios with angle of incident wave have been depicted graphically. Some special cases have also been deduced from the present investigation. It is found that the amplitude ratios of reflected and transmitted waves are affected by the stiffness and micropolarity of the media.

Simulation of field bifurcations in electrodynamic structures containing a nonlinear semiconductor medium exhibiting instability

A strip-slot guiding structure (GS) containing a distributed semiconductor inclusion with a negative differential conductivity is considered. Instabilities and nonlinear effects observed during propagation of electromagnetic waves in such a structure are investigated via numerical analysis of branching points of solutions to the nonlinear Maxwell equations. The method of universal autonomous blocks with Floquet channels is applied to solve the 3D problem of diffraction of electromagnetic waves by a nonlinear semiconductor irregularity in a strip-slot GS. The solutions obtained describe frequency multiplication and generation of the GS fundamental mode near a branching point. The generation process is described as a function of the incident-wave amplitude. The bifurcation points of the nonlinear Maxwell operator are found numerically with allowance for bounding geometries. These points specify the self-oscillation frequencies in planar Gunn effect diodes in a strip-slot GS.

Propagation of plane waves in thermoelastic cubic crystal material with two relaxation times

A problem concerned with the reflection and refraction of thermoelastic plane waves at an imperfect interface between two generalized thermally conducting cubic crystal solid half-spaces of different elastic and thermal properties with two relaxation times has been investigated. The generalized thermoelastic theory with two relaxation times developed by Green and Lindsay has been used to study the problem. The expressions for the reflection and refraction coefficients which are the ratios of the amplitudes of reflected and refracted waves to the amplitude of incident waves are obtained for an imperfect boundary and deduced for normal stiffness, transverse stiffness, thermal contact conductance, slip and welded boundaries. Amplitude ratios of different reflected and refracted waves for different boundaries with angle of emergence have been compared graphically for different incident waves. It is observed that the amplitude ratios of reflected and refracted waves are affected by the stiffness and thermal properties of the media.

506 円筒介在物による弾性散乱波の位相・振幅に関する理論解析(セラミック/セラミック基複合材料2)

Changes in amplitude and phase of incident waves due to scattering by cylindrical inclusions contained in an isotropic matrix are considered. These changes relate to changes in apparent sonic velocity and attenuation coefficient obtained by the ultrasonic method. The integral equation suggested by Lavrov for scattering waves due to single inclusion gives the changes in amplitude and phase. In order to consider the cases that the number of inclusions contained in the matrix is more than two, the frequency response function corresponding to the frequency response when the incident waves passed through the single inclusion in the matrix was introduced.

Interaction of a characteristic shock with a weak discontinuity in a non-ideal gas

The Lie group of point transformations, which leave the equations for plane and radially symmetric flows of a non-ideal gas invariant, are used to obtain an exact solution that exhibits space-time dependence. We consider the propagation of a weak discontinuity through a state, characterized by this solution. Further, the evolution of a characteristic shock and its interaction with the weak discontinuity are studied. The properties of reflected and transmitted waves and the jump in shock acceleration, influenced by the incident wave amplitude and the van der Waals excluded volume, are completely characterized, and certain observations are noted in respect of their contrasting behaviour.