Wave Configuration Research Articles

219404 曲がり管を伝播するデトネーションの波面形態に関する数値解析(OS13 安全に寄与する熱工学2,オーガナイズド・セッション)

219404 曲がり管を伝播するデトネーションの波面形態に関する数値解析(OS13 安全に寄与する熱工学2,オーガナイズド・セッション)

A “Localized Pulse–Moving Front” Pair in a System of Coupled Complex Ginzburg–Landau Equations

A system of nonlinearly coupled complex Ginzburg–Landau equations, CGLEs, serves as a simple model for the dynamics of pulse propagation in dissipative, inhomogeneous media under the combined influence of dispersion, self and cross phase modulations, linear and nonlinear gain or loss. A solitary pulse (SP) is a localized wave form, and a kink or a front refers to a transition connecting two constant, but unequal, asymptotic states. Exact expressions for a “solitary pulse–kink” pair are obtained by a modified Hirota bilinear method. Parameters for these wave configurations are governed by a system of six algebraic equations, allowing the amplitudes, frequencies, and velocities to be determined. Exact solutions for special cases of the dispersive and nonlinear coefficients are obtained by computer algebra software.

Nonlinear Spline Method for Buckling Analysis of Steel Strip

The paper deals with numerical considerations of buckling phenomena in steel strip during rolling and leveling of sheet metal. The self-equilibrating stress states due to residual strains caused by the rolling process are calculated by the spline function method. The developed numerical model provides an estimation of buckling critical loads and wave configuration. It is shown how the waves observed on the strip sliding over or lying on a rigid plane, so one can provide information about the distribution of the differences in the plastic strains over the width of the strip which leads to the buckled configuration. The spline function method proposed in this paper is simpler and more convenient than traditional finite element method in the buckling analysis.

Reflection and transmission of atmospheric gravity waves in a stably sheared horizontal wind field

Applying a second‐order fully nonlinear numerical scheme, we have investigated the characteristics of reflection and transmission of atmospheric gravity wave packets in a vertically sheared horizontal wind. When the leading edge of incident wave arrives at the reflecting level predicted by the linear theory, the wave reflection begins to occur. In the reflection process, the reflection and incident waves are superposed with obvious phase staggering, which is different from the wave reflection in a meridionally sheared horizontal wind. In the evanescent region, the wave phase has only weak variation; the wave amplitude decays with the sheared wind growth and vice versa, which is in good agreement with the evanescent wave configuration predicted by the linear theory. Some spectral components of the incident wave can penetrate through the evanescent region and produce a transmitted wave. Both the reflection and transmission coefficients slightly decrease with the moderate increase of the initial amplitude of the incident wave, which is because a large‐amplitude wave can induce a strong mean flow; moreover, the wave‐induced mean flow plays a more significant role in transferring the energy from the waves to the background flow than in enhancing the transmission of the waves. This is distinguished from the wave reflection in a sheared flow under the wave propagation distance smaller than the density scale height, in which the mean flow induced by a larger‐amplitude wave significantly strengthens the transmission of the wave. The simulation shows that the reflection loop predicted by the linear theory is not a common phenomenon in the wave reflection. Several groups of simulated cases indicate that the reflection and transmission coefficients depend on not only the amplitude, frequency, and wavenumbers of the incident wave but also the strength and thickness of the evanescent region. The reflection coefficient increases but the transmission coefficient decreases with the relative evanescent thickness growth, and once the strength and thickness of the evanescent region are large enough, the wave hardly penetrates through the sheared wind zone, and the reflection coefficient approaches a constant value, too. Except for the disappearance of the evanescent region, the total sum of the reflection and transmission coefficients of the wave pseudoenergy flux is slightly <1 because of the interaction between the wave and flow. These results suggest that the effects of wave reflection and transmission should be correctly included in the parameterization of gravity waves to attain more realistic middle atmospheric climatology from general circulation models.

3D simulations and experiments of guided wave propagation in adhesively bonded multi-layered structures

Understanding guided wave propagation in multi-layered plates and interaction with discontinuities can be difficult, as well as the interpretation of the ultrasonic signals. Propagation of guided waves can be studied analytically solving the equations of motion with the proper boundary conditions; nevertheless analytical models can be difficult to solve for complex multi-layered structures or having inner discontinuities. The problem can be efficiently studied using numerical techniques. Simulation of guided wave propagation in multi-layered structures, for ultrasonic waves in the MHz range, is solved here with the finite element analysis based on an explicit integration rule to solve the equations of motion in a dynamic analysis. Simulation allows a better understanding of propagation and interference phenomena by creating a window of observation in the multi-layered plate. Numerical results determined for a three-layer Al plate, without or with discontinuities, matched very well with experiments, providing an efficient tool to visualize and extract significant information in the transmitted waves and to optimize wave mode and configuration for a rigorous ultrasonic inspection.

Shock wave configurations and flow structures in non-axisymmetric underexpanded sonic jets

An experimental and numerical study of underexpanded free sonic jet flows issuing from rectangular, elliptical and slot nozzles has been undertaken. Aspect ratios (AR) of 1, 2, and 4 are described at pressure ratios (exit plane pressure to ambient pressure), of 2 and 3. There is good qualitative agreement between the experimental observations and the numerical predictions. In the case of rectangular jets, a complex system of shock waves forming the incident shock system is identified. This shock wave system originates at the corners of the nozzle exits, and proceeds downstream. Mach reflections are found to occur on the incident shock wave surface as well as the presence of a Mach disk terminating the first jet cell. This Mach disk has the shape of a square, a hexagon, or an octagon depending on the nozzle shape. For slot and elliptical jets, the formation of the incident shock wave was not observed along the minor axis plane of the nozzle for AR > 2. The incident shock wave was observed to originate downstream of the nozzle exit in the major axis plane. This wave system undergoes a transition to Mach reflection as it propagates downstream of the nozzle exit. In all cases tested, the shape of the jet boundary is significantly distorted. In rectangular jets, the narrowing of the jet boundary along the diagonal axis of the nozzle exit is observed, and in the case of the elliptical and slot jets axis switching is noted.

Assessment of induced SAR in children exposed to electromagnetic plane waves between 10 MHz and 5.6 GHz

To avoid potentially adverse health effects of electromagnetic fields (EMF), the International Commission on Non-Ionizing Radiation Protection (ICNIRP) has defined EMF reference levels from the basic restrictions on the induced whole-body-averaged specific absorption rate (SARwb) and the peak 10 g spatial-averaged SAR (SAR10g). The objective of this study is to assess if the SAR in children remains below the basic restrictions upon exposure at the reference levels. Finite difference time domain (FDTD) modeling was used to calculate the SAR in six children and two adults when exposed to all 12 orthogonal plane wave configurations. A sensitivity study showed an expanded uncertainty of 53% (SARwb) and 58% (SAR10g) due to variations in simulation settings and tissue properties. In this study, we found that the basic restriction on the SARwb is occasionally exceeded for children, up to a maximum of 45% in small children. The maximum SAR10g values, usually found at body protrusions, remain under the limit for all scenarios studied. Our results are in good agreement with the literature, suggesting that the recommended ICNIRP reference levels may need fine tuning.

An applicability of dynamic response analysis of shear-failure type RC beams with lightweight aggregate concrete under falling-weight impact loading

In order to establish a simple and rational impact response analysis method for lightweight aggregate reinforced concrete (RC) beams, three-dimensional elasto-plastic finite element analysis was conducted for shear-failure type RC beams under falling-weight impact loading. The, tensile strength of concrete was assumed as 1/16th of the compressive one. An applicability of the proposed analysis method was confirmed by comparing with the experimental results of twelve beams. From this study, following results were obtained: (1) three response wave configurations: impact force; reaction force; and mid-span displacement, and crack patterns can be rationally predicted by using proposed analysis method; and (2) maximum response values of impact force, reaction force, and displacement can be estimated considering 20, 20, and 10% safety margin, respectively.

Thermal Wave Applications in Flow Fields With Steady Velocity Profile

This study explores the use of a thermal wave approach for flow field measurement applications, such as flow diagnostics near surfaces and in microfluidic systems. The basic mathematical characteristics of the governing equations of heat convection, with periodic heating boundary conditions in steady flow, are discussed and the validity of applying the complex combination method to this problem is illustrated. A scaling analysis of a two-dimensional thermal wave configuration with a linear velocity profile is performed to provide important insights into this type of heat transfer phenomena. A two-dimensional conjugate heat transfer model is developed and solved numerically with a finite difference method to demonstrate an example of imposing a thermal wave onto a flow field. The simulation results show that the temperature signal, especially the phase information, can be used for the measurement of flow properties near the surface, such as the wall shear stress.

HLLC-type Riemann solver for the Baer–Nunziato equations of compressible two-phase flow

We first construct an approximate Riemann solver of the HLLC-type for the Baer–Nunziato equations of compressible two-phase flow for the “subsonic” wave configuration. The solver is fully nonlinear. It is also complete, that is, it contains all the characteristic fields present in the exact solution of the Riemann problem. In particular, stationary contact waves are resolved exactly. We then implement and test a new upwind variant of the path-conservative approach; such schemes are suitable for solving numerically nonconservative systems. Finally, we use locally the new HLLC solver for the Baer–Nunziato equations in the framework of finite volume, discontinuous Galerkin finite element and path-conservative schemes. We systematically assess the solver on a series of carefully chosen test problems.

Shock wave interaction in a dusty gas and the appearance of fully dispersed waves

A problem of regular (symmetric and asymmetric) interaction of plane shock waves in a steady-state dusty-gas flow is considered. The possibility of the formation of wave structures is revealed, in which either all or some of the incident or reflected waves degenerate into fully dispersed waves, i.e. zones in which the parameters of both phases vary continuously. Using the Rankine-Hugoniot relations for a one-velocity “effective-gas” model, the ranges of nondimensional governing parameters (the Mach number, the angles between the incident waves and the free stream, the phase specific-heat ratio, and the particle mass concentration) are found, which correspond to different wave configurations. In the framework of a two-fluid dusty-gas model, the flow structure in the region of symmetric interaction of the shocks is calculated numerically for typical configurations containing fully dispersed waves. The flow in the region of a normal fully dispersed wave is also calculated. Good agreement between the calculated wave structure and the data known in the literature is obtained. A range of governing parameters in which the carrier-phase temperature has a local maximum inside the wave structure is found.

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.

Freeway Sensor Spacing and Probe Vehicle Penetration

Accurate travel time prediction–estimation is important for advanced traveler information systems and advanced traffic management systems. Traffic managers and operators are interested in estimating optimal sensor density for new construction and retrofits. In addition, with the development of vehicle-tracking technologies, they may be interested in estimating optimal probe vehicle percentage. Unlike most studies focusing on data-driven models, this paper extends some limited previous work and describes a concept developed from first principles of traffic flow. The goal is to establish analytical relationships between travel time prediction–estimation accuracy and sensor spacing by means of two basic travel time prediction–estimation algorithms, as well as to probe vehicle penetration rate. The methods are based on computing the magnitude of under- and overprediction–estimation of total travel time (TTT) during shock passages in a time–space plane by using the midpoint method for online travel time prediction and the Coifman method for offline travel time estimation. Three shock wave configurations are assessed with each method so as to consider representative traffic dynamics situations. TTT prediction–estimation errors are calculated and expressed as a function of sensor spacing and probe vehicle percentage. Optimal sensor spacing is calculated with consideration of the tradeoff between TTT estimation error and sensor deployment cost. The results from this study can provide simple and effective support for detector placement and probe vehicle deployment, especially along a freeway corridor with existing detectors. Optimal sensor spacing results are analyzed and compared for various methods of travel time estimation during different types of shock waves.

Analysis of the results of multifocal visual evoked potential examination in patients with anterior ischemic opticneuropathy before and after treatment

Objective To observe the results of multifocal visual evoked potential (mfVEP) examination in patients with anterior ischemic optic neuropathy (AION) before and ater treatment,and to probe its clinical significance.Methods A total of 90 patients (90 eyes) with AION were examined by mfVEP;the second-order reaction of mfVEP was analyzed.The reaction was divided into upper and lower hemi-field of visual field,or 1 / 4 quadrant visual field (superior nasal,inferior nasal,superior temporal,and inferior temporal).The sum of waves of each response was analyzed and the results in various regions were compared.The features of wave configuration was compared between the AION eyes and the contralateral eye,and between the AION eyes before and after treatment.Results The amplitude and latency of P-wave of mfVEP was 0.198±0.033 and 100.197±7.354 respectively in AION eyes before treatment,and was 0.271±0.024 and 98.567±6.794 in the contralateral eyes;the difference was significant (t=16.556,18.330;P＜0.01).The amplitude and latency of P-wave of mfVEP was 0.229±0.016 and 100.104±10.603 respectively in AION eyes after treatment,which differed much from that before the treatment (t=13.649,8.858;P＜0.01) and also from that of the contralateral eyes (t=13.649,8.858;P＜0.01).Conclusions The amplitude and latency of P-wave of mfVEP may accurately reflect the recovery of local optic nerve damage in AION eyes before and after treatment with good repeatability.AION can be used as a new method for AION diagnosis and detection of the prognosis. Key words: Evoked potentials; visual; Optic neuropathy; ischemic/therapy; Perimetry/utilization

И-Shaped surf beat understood in terms of transient forced long waves

The observed И-shape of the long wave generated by a single short wave pulse is explained qualitatively by including the free waves which are generated along with the well known bowl-shaped forced wave. Free waves of complicated shapes are generally formed as the wave group encounters gradual depth changes. However, the main qualitative feature, which has so far lacked a simple explanation, namely the long wave being И-shaped rather than a single bowl, can be explained through the simple free wave configuration which results from an abrupt onset of forcing at constant depth. И-shaped transient stages then occur between the initial flat surface and the final stage where free and forced waves have become completely separated from the forcing due to their different speeds. The И-shape is however also the shape of the gradually growing, resonant long wave due to a single short wave pulse, which travels with phase speed c and group velocity c g close to the long wave speed g h . The latter result is derived and compared with detailed laboratory experiments. It may explain the lack of observed H 2-dependence observed for some incident long waves, as well as the qualitative shapes of the long wave and of the cross correlation function between short wave envelope and long wave elevation.

Freak wave statistics on collinear currents

Linear refraction of waves on inhomogeneous current is known to provoke extreme waves. We investigate the effect of nonlinearity on this phenomenon, with respect to the variation of significant wave height, kurtosis and occurrence of freak waves. Monte Carlo simulations are performed employing a modified nonlinear Schrödinger equation that includes the effects of a prescribed non-potential current. We recommend that freak waves should be defined by a local criterion according to the wave distribution at each location of constant current, not by a global criterion that is either averaged over, or insensitive to, inhomogeneities of the current. Nonlinearity can reduce the modulation of significant wave height. Depending on the configuration of current and waves, the kurtosis and probability of freak waves can either grow or decrease when the wave height increases due to linear refraction. At the centre of an opposing current jet where waves are known to become large, we find that freak waves should be more rare than in the open ocean away from currents. The largest amount of freak waves on an opposing current jet is found at the jet sides where the significant wave height is small.

Two Dimensional Density Fluctuation Measurements During the Non-Inductive Current Ramp-up Phase in the Compact Plasma Wall Interaction Experimental Device CPD

Two-dimensional structure of density fluctuations is examined during the current jump phase, indicating a change from the open magnetic fields to the closed ones. During the smooth current ramp-up phase the two-dimensional contour of the LiI intensity shows vertically alignment, consistent with the magnetic surfaces. At the inflection point in Ip ramp-up the LiI intensity contour becomes flat in the observation regime and then suddenly a steep gradient and higher intensity regime are formed in the vertical direction. This higher intensity corresponds to a burst of LiI waveform. According to these changes in the contour, it is found that, within ±1 ms around the burst of LiI, a low frequency coherent wave with a long wavelength rapidly grows. The relations with other signals (magnetic flux and microwave stray power) are discussed with respect to the topological change in the magnetic configuration and mode conversion of the incident electromagnetic waves.

Determination of the minimum entropy configuration and velocity surfaces for elastic–plastic wave scattering at grain boundaries

A recent model based on full elastic anisotropy and crystal plasticity predicted the existence of multiple wave configurations during the interaction of stress waves with grain boundaries. Since the multiple wave configuration scenario cannot exist in nature, the principle of minimum entropy production is applied in the current work to find the most probable configuration. A large amplitude transmitted quasi-longitudinal wave is predicted for the given bicrystal orientation studied due to the wave propagating near a [001] direction and thus requiring large stress given the very low Schmid factor in this direction (for nickel aluminide (NiAl) as a model material). Anisotropic elastic–plastic velocity surfaces for quasi-longitudinal and quasi-shear waves in NiAl have also been constructed to gain an understanding of the general nature of plastic waves as a function of crystallographic direction.

Three-magnon splitting and confluence processes for spin-wave excitations in yttrium iron garnet films: Wave vector selective Brillouin light scattering measurements and analysis

Brillouin light scattering (BLS) has been used to observe and confirm the existence of nonlinear three magnon splitting and confluence processes for propagating spin waves in the magnetostatic backward volume wave configuration. Wave vector and frequency selective BLS techniques were also used to provide a quantitative map of the wave vector make-up for the parametrically excited half-frequency dipole-exchange spin wave (DESW) split magnons and the confluence magnons that result from the recombination of these DESW modes. The experimental wave vector maps for the product splitting and confluence magnons matched nicely with those expected from spin-wave theory. The data were obtained with (1) a strip line excitation/detection transducer structure, (2) forward-scattering BLS optics, (3) a fixed magnetic field of 352 Oe applied along the propagation direction, (4) pumping frequencies from 2.5 down to 2.1 GHz, (5) and cw input powers from $200\text{ }\ensuremath{\mu}\text{W}$ to 6 mW. The wave vector selective measurements utilized variable diameter circular diaphragms, rotatable slit apertures, and circular light blocks to access spin waves with wave numbers from about 100 to $3.6\ifmmode\times\else\texttimes\fi{}{10}^{4}\text{ }\text{rad}/\text{cm}$ and the full $360\ifmmode^\circ\else\textdegree\fi{}$ range of propagation angles.

Solution of the Riemann problem for irreversibly compressible media

AbstractThe Riemann problem for an irreversibly compressible medium has been solved. This solution introduces the maximum medium density that is attained in the process of active loading. To close the system of equations an extra equation is required to describe the transfer of this parameter through the Eulerian mesh. The possible wave configurations have been analyzed and the corresponding equations for the evaluation of the contact pressure and velocity have been obtained. The existence and uniqueness of the solution have been proven. The technique of the Riemann problem's solution for the arbitrary Lagrange Euler mesh was developed. Examples of the Riemann problem solution for various wave configurations show that neglecting the bulk elastic plastic deformations yields significant errors in the results both quantitatively and qualitatively. Copyright © 2009 John Wiley & Sons, Ltd.