Modes Of Wave Propagation Research Articles

Identifying elastic wave polarization and bandgaps in periodic solid media

We present a new computational method to accurately identify the elastic wave propagation modes and polarizations in periodic solid structures and metamaterials. The method uses the eigenvectors associated with each propagating wave solution to calculate the contribution of each translational and rotational component of the total mass-in-motion. We use this information to identify the dominant wave propagation mode by defining a relative effective modal mass vector. Then, we associate each wave solution with its correct polarization by defining a polarization factor that quantifies the relative orientation between the wave propagation and lattice motion directions and provides a positive numerical value between 0 (pure S-wave) and 1 (pure P-wave). Further, we suggest a graphical representational scheme for easier visualization of the wave polarization within traditional dispersion plots. To validate the method, we compare our predictions against previously published results for various elastodynamic problems. Finally, we use the proposed method to analyze the effect of various lattice and structural parameter perturbations on the elastic wave propagation and polarized bandgap behavior of a square planar beam lattice. Our analysis reveals the emergence of previously unobserved dynamic characteristics, including various polarized bandgaps, fluid-like behavior, and ultralow-frequency SH- and SV-bandgaps that extend to 0 Hz. Our proposed method provides an alternative computational approach to the typically employed visual mode inspection technique and provides a robust method for analyzing the elastic wave response of periodic solid media.

Fiber-Optic Airplane Seismology on the Northeast Greenland Ice Stream

Abstract We present distributed fiber-optic sensing data from an airplane landing near the EastGRIP ice core drilling site on the Northeast Greenland Ice Stream. The recordings of exceptional clarity contain at least 15 easily visible wave propagation modes corresponding to various Rayleigh, pseudoacoustic, and leaky waves. In the frequency range from 8 to 55 Hz, seven of the modes can be identified unambiguously. Based on an a priori firn and ice model that matches P-wave dispersion and the fundamental Rayleigh mode, a Backus–Gilbert inversion yields an S-wavespeed model with resolution lengths as low as a few meters and uncertainties in the range of only 10 m/s. An empirical scaling from S wavespeed to density leads to a depth estimate of the firn–ice transition between 65 and 71 m, in agreement with direct firn core measurements. This work underlines the potential of distributed fiber-optic sensing combined with strong unconventional seismic sources in studies of firn and ice properties, which are critical ingredients of ice core climatology, as well as ice sheet dynamics and mass balance calculations.

Failure mode and stress wave propagation in concrete target subjected to a projectile penetration followed by charge explosion: Experimental and numerical investigation

The earth penetration weapons (EPWs) usually penetrate into protective structures firstly, and then detonate the charge to induce high-intensity blast stress waves to cause further damage. Existing investigations on the destructive effect caused by the following charge explosion after penetration of EPWs are very limited. To clarify the combined destructive effect in concrete material caused by an EPW, an experimental and numerical investigation on failure mode and stress wave propagation in concrete target subjected to a projectile penetration followed by charge explosion was conducted in the present study. Firstly, two field tests on high strength fiber-reinforced concrete targets subjected to a projectile penetration followed by charge explosion were conducted, in which the failure and blast waves in concrete targets were comprehensively obtained. Then two-step numerical models based on the Kong-Fang concrete material model and SPG method were developed and validated against the experimental data. Finally, based on the validated numerical models, the influences of projectile penetration on the destructive effect caused by following charge explosion were analyzed. The numerical results demonstrated that the damage caused by projectile penetration has significant influences on the final failure mode and stress wave propagation in concrete targets. The research results can provide an important reference for the design of protective structure against EPWs.

Surface waves at a fluid/double-porosity medium interface

SUMMARYWe consider surface-wave propagations at an interface separating a fluid layer and a double-porosity medium embedded with cracks. The theory is based on a generalization of the Biot-Rayleigh model from spherical cavities to penny-shaped cracks randomly embedded into a host medium, where mesoscopic local fluid flow (LFF) plays an important role. We derive closed-form dispersion equations of surface waves, based on potentials and suitable boundary conditions (BCs), to obtain the phase velocity and attenuation by using numerical iterations. Two special cases are considered by letting the thickness of the fluid (water) layer to be zero and infinity. We obtain pseudo-Rayleigh and pseudo-Stoneley waves for zero and infinite thickness and high-order surface modes for finite nonzero thickness. Numerical examples confirm that the LFF affects the propagation at low frequencies, causing strong attenuation, whereas the impact of BCs is mainly observed at high frequencies, due to the propagation of slow wave modes. The crack density mainly affects the level of attenuation, whereas the aspect ratio the location of the relaxation peak. The fundamental mode undergoes a significant velocity dispersion, whose location moves to low frequencies as the thickness increases. In all cases, there also exist two slower surface modes that resemble the two slow body waves, only present for sealed BCs.

Controlling the Modes of Spin Wave Propagation in an Yttrium Iron Garnet Waveguide by Local Laser Heating

Controlling the Modes of Spin Wave Propagation in an Yttrium Iron Garnet Waveguide by Local Laser Heating

Control of spin wave propagation modes in the yttrium iron garnet waveguide by means of local laser heating

The results of micromagnetic modeling of the magnetic structure on the surface of a film of yttrium iron garnet (YIG) are presented, where a region of altered saturation magnetization was created by focused laser radiation. Based on the constructed amplitude-frequency characteristics of signal transmission through a magnon structure with a heating region, the possibility of implementing spin-wave signal filtering modes with a change in the diameter of the heated region on the YIG surface is shown.

Wave resonances in the presence of current and the frequency and time-domain interconnection

The current work investigates the relationship between frequency and time domain problems associated with flexural gravity wave motion with oblique incidence and current. Different types of wave resonances such as buckling resonance, primary and secondary blocking resonance, Bragg resonance and interaction among them are discussed. Three propagating wave modes are observed between the primary and secondary blocking points, two of which are associated with positive group velocities and the third one is related to negative group velocities. Again, the Bragg resonance is analyzed for wave scattering problems. The complex porosity parameter is found to have a significant effect on the buckling and blocking resonance but does not affect Bragg resonance. The discontinuity of Bragg reflection is observed at primary and secondary blocking points and the peak values of Bragg reflection increase in the blocking zone. Again, we establish the interconnection between the frequency and time domain by deriving the time-domain solution from the frequency-domain solution and vice versa. The derivation of time-domain solutions using the dispersion relation and method of stationary phase is an intriguing finding. Wave energy and wave packets move faster in co-propagating waves than in counter-propagating waves and shallow water than in finite water depth. To validate the results, time-domain simulation and spectral methods are used.

Macro Meso Response and Stress Wave Propagation Characteristics of MCT High-Voltage Switch Under Shock load

In order to study the dynamic and electrical coupling response characteristics of Metal Oxide Semiconductor Controlled Thyristor (MCT) high-voltage switch under the synergic action of mechanical load and high voltage, the separated Hopkinson pressure bar (SHPB) test system was used to simulate different impact load environments, and combined with the multi-layer high-voltage ceramic capacitor charging and discharging system, the instantaneous electrical signals of MCT high-voltage switch were collected. Combined with numerical simulation and theoretical analysis, the failure mode and stress wave propagation characteristics of MCT high voltage switch were determined. The mechanical and electrical coupling response characteristics and failure mechanism of MCT high voltage switch under dynamic load were revealed from macroscopic and microscopic levels. The results show that the damage modes of MCT high-voltage switches can be divided into non-functional damage, recoverable functional damage, non-recoverable damage and structural damage. Due to the gap between the metal gate and the oxide layer, the insulating oxide layer was charged. After placing for a period of time, the elastic deformation of the metal gate partially recovered and the accumulated charge disappeared, which induced the recoverable functional damage failure of the device. In addition, obvious cracks appeared on both sides of the monocrystalline silicon inside the MCT high-voltage switch, leading to unrecoverable damage of the device.

Acoustic Path Filtering for Improved Multimode Total Focusing Method Inspection

Total focusing method (TFM) is an ultrasonic testing (UT) technique that provides nondestructive testing (NDT) inspectors with new imaging modes, enabling more accurate detection, sizing, and representation of challenging defects. While TFM may offer convenient, nearly true-to-geometry imagery as the inspection result, it is often detrimentally affected by mode conversion artifacts. Current standards, such as ASME Section V, place the burden on the inspector to explain the origins of those artifacts, impacting the productivity and reliability of the inspection. A method enabling direct control of the ultrasonic wave propagation modes—that is, transverse wave (T) or longitudinal wave (L)—through each interface of the acoustic path is proposed and evaluated in this paper. This control is achieved after the full matrix capture acquisition by modulating, according to the desired propagation mode, the gain applied on the individual paths within the summation process. This leads to the formation of a Path-Filtered Total Focusing Method image. Empirical results on various use cases show considerable improvement of the signal-to-noise ratio through the almost complete elimination of signals originating from undesired paths.

Comparative Study of Dispersion Curves for LAMB Waves Using Analytical Solutions and Semi-Analytical Methods

Lamb wave dispersion curves are useful for optimizing the inspection scanning distance that can be covered with good sensitivity in many current applications. However, one of the main problems concerning this calculation lies in selecting a numerical method that is computationally accurate and efficient. In this paper, Lamb waves dispersion curves are generated by the Scaled Boundary Finite Element Method, and by the Rayleigh–Lamb equation. For the semi-analytical case, waveguide cross-section discretization was performed using isoparametric elements and high-order spectral elements. The semi-analytical formulations lead to an eigenvalue problem that can be solved efficiently by calculating the couples of wavenumbers and frequencies that guarantee the wave mode propagation, the basis for generating the dispersion curves. These are compared with those obtained from the analytical solution for the symmetric and antisymmetric modes; in both cases, homogeneous plates of constant thickness are considered. The numerical results show good agreement when using a low number of isoparametric elements, or a single spectral element with shape functions of the order of six for computing the dispersion curves and wave structure. The calculation is given with low computational effort, and the relative variation with respect to the analytical reference values is less than 2%.

Bragg scattering of flexural-gravity waves by a series of polynyas in the context of blocking dynamics

Flexural-gravity wave scattering due to an array of polynyas is investigated from the perspective of the blocking dynamics. The canonical eigenfunction expansion method is generalized to account for multiple propagating wave modes within blocking frequencies. Bragg scattering occurs due to the presence of multiple gaps in the floating ice sheet, and the number of sub-harmonic peaks in wave reflection becomes one/two less than the number of gaps as the reflection coefficient varies with a change in gap/ice-sheet length. In addition, the amplitudes of harmonic peaks in wave reflection increase with an increase in the number of gaps. The variation of wave reflection with an increase in wavenumber/length of the ice sheet depicts that common zero minima occur for an even number of gaps, while common sub-harmonic maxima occur for an odd number of gaps. The scattering coefficients vary between zero and unity within the blocking frequencies, despite the individual amplitudes of the scattered waves becoming more than unity for certain frequencies. Noticeably, higher amplitudes of the scattered waves are associated with lower energy transfer rates and vice versa. Extrema in wave reflection occur for higher values of frequency within the primary and secondary blocking points. In addition, removable discontinuities are found in the scattering coefficient at the blocking frequencies, whereas a jump discontinuity is observed for certain frequencies within the blocking limits due to the incident wave mode conversion. Moreover, irregularities in the ice sheet's deflection are observed for any frequency within the blocking limit due to the superposition of three propagating wave modes.

Influence of electron temperature anisotropy on wave mode propagation and power deposition characteristics in helicon plasma

As the core issue in helicon discharge, the physical mechanism behind the high ionization rate phenomenon is still not fully understood. Based on the warm plasma dielectric tensor model which contains both the particle drift velocity and temperature anisotropy effect, by employing the general dispersion relation of electromagnetic waves propagating in magnetized and uniform plasma with typical helicon discharge parameter conditions, wave mode propagation characteristic and collisional, cyclotron and Landua damping induced wave power deposition properties of azimuthally symmetric mode are theoretically investigated. Systematic analysis shows the following findings. 1) Under typical helicon plasma parameter conditions, i.e. wave frequency <i>ω</i>/(2π)=13.56 MHz, ion temperature is one tenth of the electron temperature, and for a given magnetic field <i>B</i><sub>0</sub> (or wave frequency <i>ω</i>), there exists a critical wave frequency <i>ω</i><sub>cr</sub> (or magnetic field <i>B</i><sub>0,cr</sub>), above which (or below <i>B</i><sub>0,cr</sub>) the damping of the <i>n = </i>1, 2, 3 cyclotron harmonics begins to increase sharply. 2) For the electron temperature isotropic case, the attenuation constants of different harmonics start to increase significantly and monotonically at different thresholds of magnetic field, while the phase constant abruptly increases monotonically from the beginning of the parameter interval. On the other hand, for the electron temperature anisotropic case, both the phase constant and attenuation constant have peaking phenomenon, i.e. the attenuation constant begins to increase sharply at a certain value of <i>B</i><sub>0</sub> and meanwhile the phase constant presents a maximum value near the same value of magnetic field, thus the phase constant starts to keep constant at a certain value of <i>B</i><sub><i>0</i></sub> and meanwhile the attenuation constant has a maximum value near this same value of magnetic field. 3) For the wave power deposition properties, under electron temperature anisotropy conditions, power deposition due to collisional damping of Trivelpiece-Gould (TG) wave plays a dominant role in a low field (<i>B</i><sub>0 </sub>= 48 Gs) (1 Gs = 10<sup>–4</sup> T); by considering the electron finite Larmor radius (FLR) effect, the power deposition of TG wave presents a maximum value at a certain point of parallel electron temperature<i> T</i><sub>e,</sub><sub>//</sub>; with the decrease of <i>T</i><sub>e,⊥</sub>/<i>T</i><sub>e,</sub><sub>//</sub>, the maximum value of power deposition increases gradually. All these findings are very important in further revealing the physical mechanism behind the high ionization rate in helicon plasma.

On the wave propagation modes and operation range in rotating detonation combustor with varied injection and outlet throat

The rotating detonation combustor (RDC) has received remarkable attention in the aerospace community. In this work, an experimental RDC model supplied by liquid kerosene and oxygen-enriched air is established. A parametric survey is performed with different injection throats, outlet restrictions, and equivalence ratios to analyze the rotating detonation wave propagation modes comprehensively. Dynamic pressure transducers and a high-speed camera are both employed to identify wave modes synchronously. Overall, the propagation modes are found to be highly dependent on the injection throat and combustor outlet restriction. With a large injection to annulus area ratio of 0.3, a single-wave mode is characterized when no restriction is added at the combustor outlet. Reducing the outlet area leads to a decrease in the wave frequency and a narrower steady rotating detonation propagation regime. The propagation stability of the rotating detonation is strengthened when the injection to annulus area ratio decreases to 0.2. A dual-wave collision mode and a four-wave collision mode are observed, depending on the outlet restriction. A preliminary stable RDC operation range correlated with outlet to injection throat area ratio and equivalence ratio is achieved. Furthermore, an interval value of the outlet to injection throat area ratio is proposed to reach the potential positive total pressure gain. These findings should serve as the reference for RDC configuration design in air-breathing and gas-turbine propulsion systems.

Autoignition of DME/DMM Fuel Blends: Part II: Reaction Wave Propagation Modes in the Presence of Temperature Gradients

Autoignition of DME/DMM Fuel Blends: Part II: Reaction Wave Propagation Modes in the Presence of Temperature Gradients

Numerical and experimental investigation of guided ultrasonic wave propagation in non-uniform plates with structural phase variations

The article presents the results of numerical and experimental investigations of guided wave propagation in aluminum plates with variable thickness. The shapes of plate surfaces have been specially designed and manufactured using a CNC milling machine. The shapes of the plates were defined by sinusoidal functions varying in phase shift, which forced the changes in thickness variability alongside the propagation path. The main aim of the study is to analyze the wave propagation characteristics caused by non-uniform thickness. In the first step, the influence of thickness variability on the time course of propagating waves has been analyzed theoretically. The study proves that the wave propagation signals can be determined based on knowledge about the statistical description of the specimen geometry. The histograms of thickness distribution together with the a priori knowledge of the dispersion curves were used to develop an iterative procedure assuming that the signal from the previous step becomes the excitation in the next step. Such an approach allowed for taking into account the complex geometry of the plate and rejecting the assumption about the constant average thickness alongside the propagation path. In consequence, it was possible to predict correctly the signal time course, as well as the time of flight and number of propagating wave modes in specimens with variable thickness. It is demonstrated that theoretical signals predicted in this way coincide well with numerical and experimental results. Moreover, the novel procedure allowed for the correct prediction of the occurrence of higher-order modes.

Cool flame wave propagation in high-pressure spray flames

Cool flame has an important impact on the performance and emission of advanced low-temperature combustion (LTC) internal combustion engines (ICEs) in which the liquid fuel is injected earlier at a lower ambient temperature (Tam) than that in the conventional diesel combustion engines. However, the cool flame characteristics of spray combustion under ICEs conditions are not fully understood, e.g., the effect of cool flame on the spray ignition and flame stabilization is not well studied. In this paper, the so-called cool flame wave propagation (CFWP) in the Engine Combustion Networks Spray A flames at three ambient temperatures Tam (800 K, 900 K and 1000 K) is analyzed using the data from large eddy simulation with an improved Eulerian based transported probability density function sub-grid combustion model. A good agreement between the LES results and experimental data is obtained for the spray liquid penetration length, vapor fuel penetration length, mean pressure rise profile, and flame liftoff length. It is shown that CFWP in the spray ignition process promotes the ignition of the fuel-rich and cold reactant mixture, leading to the most reactive mixture shifting toward fuel-richer locations due to the spatial stratification of temperature and concentration, and turbulent mixing. As a result, the high temperature ignition (HTI) can be shortened compared to the ignition in the homogeneous mixture. At Tam = 800 K, the HTI kernels are consistently formed following the CFWP propagating toward the spray head region. However, as Tam increases, the spatial correlation between HTI kernels and CFWP fronts is weakened. On the other hand, the turbulent mixing (quantified using local scalar dissipation rate) contributes more to the formation of HTI kernels at higher Tam. The present results indicate that CFWP is more profound at lower Tam in the spray ignition process. Finally, it is found that cool flame propagates mainly into pre-reacted fuel-rich mixture in an ignition wave propagation mode from the spray upstream region toward downstream region, whereas the ignition assisted flame mode is found in the spray upstream region where the combustion heat release is negligible.

Gravity wave interaction with an articulated submerged plate resting on a Winkler foundation

Surface gravity wave interaction with an articulated flexible submerged plate in the presence of lateral compressive force is investigated within the framework of blocking dynamics, assuming that the submerged plate is resting on a uniform Winkler foundation. The problem is studied considering small-amplitude plate response and linearised water wave theory in finite water depth. The loci of the dispersion relation reveal the occurrence of wave blocking in the submerged plate mode for a range of wave frequency and compressive force when the submerged plate is resting on a Winker foundation. However, in the absence of the Winkler foundation, no wave blocking occurs in the plate mode irrespective of the values of compressive force, and plane wave propagation in plate mode does not happen for particular values of compressive force. Four propagating wavenumbers exist within the blocking frequencies, of which one is in the surface mode, and others are in the submerged plate mode. Thus, to account for the four propagating wave modes, the existing solution approach for a pair of propagating wave modes is modified in an appropriate manner within the limit of blocking frequencies. Consequently, the energy relation is obtained using Green’s identity, in which the reflection and transmission coefficients are a combination of the amplitudes of different reflected and transmitted wave modes and the associated energy transfer rates. The reflection coefficient in the submerged plate mode jumps from one to zero for very small values of frequency due to the introduction of the Winkler foundation in the presence of compressive force. In addition, zero wave reflection occurs for a higher frequency range with an increase in the values of the Winkler constant. Removable discontinuities are observed at the blocking and saddle points, whilst jump discontinuities occur in the reflection and transmission coefficients due to the change of incident wave mode within the blocking frequencies. Linear time-dependent displacements in surface and submerged plate modes are presented prior to the blocking limit.

Experimental study on wave propagations in a rotating detonation chamber with different outlet configurations

To improve the propulsive performance, exhaust nozzles are desired for rotating detonation engines in practical applications. Therefore, their effects on the upstream behaviors inside the combustion chamber are required to be clarified. This study focuses on the characteristics of rotating detonation waves influenced by different outlet configurations. Three types of aerospike nozzle configurations are developed with different throat areas. Ethylene and oxygen-enriched air with an oxygen volume fraction of 50% are utilized in this study. When nozzles are employed, five wave propagation modes (i.e., the single-wave mode, the counter-rotating wave mode, the self-adjustive mode, the periodic oscillation mode, and the deflagration mode) are observed with the equivalence ratio ranging from 0.33 to 1.39, while only single-wave mode appears in the nozzle-less case under the same operating conditions. When increasing the equivalence ratio or reducing the nozzle throat area, those unstable propagation modes are more likely to happen and three boundaries of the equivalence ratio for the wave propagation transformation are clarified. On the contrary, the standard deviations of propagation velocities in the stable propagation process are smaller when employing nozzle configurations compared to the nozzle-less cases, which indicates a more stable state of the wave propagation although the stable propagation range is narrowed. Besides, the pressure rise and specific thrust are analyzed under different outlet configurations.

Ethanol blending effects on auto-ignition and reaction wave propagation under engine-relevant conditions

Ethanol as an attractive oxygenated fuel is often blended with gasoline to yield beneficial anti-knocking performance. Due to the distinctions in fuel chemistry, the combustion behavior of gasoline-ethanol blends is not fully understood. This study investigated ethanol blending effects on auto-ignition and reaction wave propagation under engine-relevant conditions covering the negative temperature coefficient (NTC) region. Three ethanol blending levels (i.e., E10, E20, and E30 on a volume basis) were introduced into gasoline surrogates. Characteristic timescale analysis for homogeneous auto-ignition was conducted, and localized hotspot auto-ignition and reaction wave propagation was investigated for different gasoline-ethanol blends. Meanwhile, ethanol blending effects on detonation development were comparatively explored. The results show that ethanol addition significantly suppresses fuel reactivity for homogeneous scenarios, especially in low-temperature regions, manifesting prolonged timescales and diminishing NTC behavior. Despite this, different reaction wave propagation modes can be identified during transient auto-ignition and reaction wave propagation, including deflagration, detonation development, and thermal explosion. The detonation wave is always at an underdeveloped status under engine-relevant conditions, and the induced pressure characteristics are sensitive to initial temperatures, hotspot sizes, and fuel reactivity. Meanwhile, ethanol addition tends to promote transient detonation development by elevating the reaction front propagation speed inside the hotspot and enhancing the deflagration to detonation transition outside the hotspot. Such observations are not contrary to that ethanol yields beneficial anti-knocking performance because only chemical effects of ethanol blending are addressed, without considering vaporization cooling effects. The present work demonstrates that ethanol addition globally suppresses engine knocking, but it may induce stronger knocking intensity once end-gas auto-ignition and detonation development are initiated. The current study provides useful insights into ethanol perturbative effects on auto-ignition and reaction wave propagation from chemical perspectives.

A New Lattice Boltzmann Scheme for Photonic Bandgap and Defect Mode Simulation in One-Dimensional Plasma Photonic Crystals

A novel lattice Boltzmann method (LBM) with a pseudo-equilibrium potential is proposed for electromagnetic wave propagation in one-dimensional (1D) plasma photonic crystals. The final form of the LBM incorporates the dispersive effect of plasma media with a pseudo-equilibrium potential in the equilibrium distribution functions. The consistency between the proposed lattice Boltzmann scheme and Maxwell’s equations was rigorously proven based on the Chapman–Enskog expansion technique. Based on the proposed LBM scheme, we investigated the effects of the thickness and relative dielectric constant of a defect layer on the EM wave propagation and defect modes of 1D plasma photonic crystals. We have illustrated that several defect modes can be tuned to appear within the photonic bandgaps. Both the frequency and number of the defect modes could be tuned by changing the relative dielectric constant and thickness of the defect modes. These strategies would assist in the design of narrowband filters.