Mechanical Wave Propagation Research Articles

A Pressure- and Frequency-Dependent Multiscale Model for Describing the Wave Propagation Characteristics of Fluid-Saturated Porous Media

Abstract The mechanism of wave propagation in fluid-saturated porous media is influenced by pressure and frequency. Pressure dependence is mainly dominated by the opening and closing of compliant and stiff pores in rocks, as well as nonlinear deformation respect to high-order elastic constants. Frequency dependence is mainly reflected in the dispersion and attenuation caused by wave-induced fluid flow (WIFF). Therefore, the propagation characteristics of seismic waves in subsurface rocks when pressure and frequency are coupled have broad practical significance, such as geofluid discrimination and in situ stress detection. A new equivalent elastic modulus applicable to fluid-saturated porous media has been established, which simultaneously considers the effects of pressure and WIFF. First, the dual-porosity model is incorporated to account for the changes in rock porosity under pressure and corresponding linear and nonlinear deformations. Then, based on the heterogeneity of rock at the mesocale and microscale, a unified pressure- and frequency-dependent elastic modulus over a wide frequency band is established using the Zener model. The wave equation of fluid-saturated porous media is constructed using the new model, and the pressure- and frequency-dependent phase velocities are derived. Rock physics and digital simulation experiments are applied to analyze the variation of elastic parameters and velocity with pressure and frequency. Comparison with experimental measurement data shows that the new model has higher accuracy than traditional models, especially in the low effective pressure region and the frequency band respect to seismic exploration.

Generation Mechanism of Oxygen Ion Cyclotron Harmonic Waves in the Inner Magnetosphere: Linear Instability Analysis Based on Observations

AbstractLinear kinetic instability analysis based on in situ observations for one typical oxygen ion cyclotron harmonic (OCH) wave event is performed to investigate the wave excitation mechanism. The observed partial‐shell velocity distribution of energetic O+s is fitted by the superposition of multiple ring‐beam distributions. The calculated linear growth rate shows that the observed OCH waves can be excited by energetic O+s with the partial‐shell velocity distribution, and the maximum growth rate occurs at the third harmonic, coinciding with the frequency associated with the maximum peak of the wave electric field power spectral density measured. In addition, it is found that cool heavy ions have a damping effect on the OCH waves near the corresponding heavy ion cyclotron frequency.

Experimental Study of Mechanical Wave Propagation in Solidifying Cement-Based Composites.

In this paper, a new measurement procedure is presented as an experimental study. In this experimental study, a measurement system using the pass-through pulsed ultrasonic method was used. The pilot application of the measurement setup was to monitor mechanical wave changes during the solidification and hardening of fine-grained cement-based composites. The fine-grained composites had different water-cement ratios. The measured results show apparent differences in the recorded mechanical wave parameters. Significant differences were observed in the waveforms of the amplitude increase in the passing mechanical waves. At the same time, the frequency spectra of the five most dominant frequencies are presented, where the frequency lines are clear, indicating the quality of the hydration process. Based on the results, it can be concluded that the new method is usable for fine-grained cement-based materials but is not limited to that. The advantages of this method are its high variability and non-destructive character. The experimental study also outlines the possible future applications of the pulsed passage ultrasonic method.

Deflecting incident flexural waves in a cylindrical shell metasurface

Nowadays, most research in metasurfaces focuses on flat plates, while curved plates widely used in engineering structures and lack sufficient corresponding research on elastic wave propagation mechanisms. In this paper, transmission properties of incident flexural waves in cylindrical shell metasurface with different curvatures are researched, and the flexural wave modulation is accomplished by accumulation of specific phase shifts. To start with, the metasurfaces cell model composed of curved cylinder is constructed in subwavelength range, the transmittance and phase of flexural wave at different curvatures were analyzed by using finite element method. Then, the supercells with special geometric dimensions are selected to combine into a complete cylindrical shell metasurfaces according to the generalized Shell law, and the approximate deflection formulas of flexural waves with different curvatures are obtained by curve fitting. Finally, the accuracy of incident flexural wave modulation is verified by the comparative results of simulation and experiment. The results show that there is a special functional relationship between curvature and phase, the deflection angle of flexural wave on metasurface is similar to the predicted values. From this paper, it is known that the change of phase shift decreases with the increase of curvature, the above formulas can not only be used for cylindrical shells with different curvatures, but also ensures high transmittance and full phase control. Therefore, this work may have a wide range of potential applications in the fields of vibration control, ultrasonic guidance, energy collection and sound stealth.

Study on stress wave propagation and failure characteristics of key parts in tunnel under blasting load

To investigate the propagation mechanisms of stress waves and the characteristics of crack distribution in tunnel structures subjected to explosive effects, an experimental model simulating rock mass using cement mortar was employed. Blasting experiments were conducted at various vertical locations relative to the tunnel. Utilizing ultra-dynamic strain monitoring alongside high-speed digital image recognition, we captured in real time the dynamic evolution of stress waves as well as the precise initiation and expansion paths of cracks. A comprehensive analysis was performed on both stress wave propagation and damage patterns within the refuge structure. Furthermore, the reliability of our numerical simulation algorithm was validated through an examination of fluid-structure coupling algorithms. The results indicated that peak strains at monitoring points within the tunnel increased as detonation points approached it, leading to heightened structural damage. Numerical simulations demonstrated a strong correlation between observed peak strains at critical locations and corresponding damage data from our experimental model. Additionally, it was found that decreasing height between detonation points and the tunnel resulted in increased dynamic response parameters—such as overpressure, velocity, and acceleration—at monitoring sites within the tunnel, thereby exacerbating damage to key areas including vaults and footwall structures. To mitigate potential structural instability within refuges, a full-section molded concrete lining support system was implemented along with supplementary anchor (mesh) spraying in critical regions to ensure long-term operational safety.

Ultra-wide low-frequency bandgap characteristics of auxeticity-based composite resonator for elastic wave manipulation and machine learning-based inverse structural design

Although auxetic metamaterials are generally light in weight, strong in compression and superior in energy absorption, less research has focused on their low-frequency bandgap realization and inverse structural design. Moreover, broadening the width of bandgap of auxetic metamaterials keep challenging as well in practical low-frequency applications. To broaden their applications, this work provides a new auxeticity-based composite resonator design by filling hard engineering material into the soft auxetic structure perforated by orthogonally-arrayed peanut-shaped holes to achieve ultra-wide low-frequency bandgap. The soft material is silicone rubber and the hard material may be concrete, steel or plumbum. Firstly, the wave propagation mechanics of the present composite structure is studied and then the bandgap characteristics are thoroughly investigated by parameter analysis. On this basis, a machine learning (ML) method combining the standard back-propagation neural network and genetic algorithm is proposed for bandgap prediction and inverse structural design. Results indicate that the present composite structure performs well in generating ultra-wide low-frequency bandgap, i.e. [11.35, 24.07] Hz, and the relative bandgap width reaches 71.76 %. Moreover, the present ML method is effective in the forward prediction of bandgap and the inverse structure design fitting the specific bandgap requirement. For the created optimal designs, the ML method and the finite element simulation can give similar results, and the maximum relative error between them is just about 5 %, which verifies the accuracy of the ML design method. This work provides a new way to realize the structural design of auxeticity-based acoustic metamaterials with low-frequency and broad bandgap.

Vibration-Based Diagnostics of Non-Ceramic Insulators: Characterization of Signals

This paper presents an experimental method for testing composite insulators based on vibration testing. The method used investigated the propagation, signal shape, and distortion of excited mechanical waves under the influence of defects. The aim of the method was to identify defects in the core of a composite insulator that cannot be economically detected by currently available diagnostic methods in field conditions. Therefore, this experiment aimed to distinguish between the mechanical waves’ characteristics of damaged and intact insulators using inexpensive tools. This article seeks to provide a basis for mechanical vibration diagnostics of composite insulators by demonstrating that damage to the core can result in a perceptible difference in the characteristics of mechanical waves when testing within the frequency range of audible sound.

On the Relationship Between the Banded Hiss Distribution and Plasmapause Location: A Survey of Van Allen Probes Observations

AbstractThe plasmapause is the outer boundary of the plasmasphere and plays a crucial role in the propagation of plasma waves. We statistically investigate the relationship between the distribution of banded hiss and plasmapause locations. Wave power distributions of banded hiss are analyzed in terms of two ways: (a) the distance away from the plasmapause (ΔL) and (b) the equatorial distance away from the Earth. Statistical results show both bands of banded hiss have larger wave powers and occurrence rates near the plasmapause. The frequencies of two banded hiss waves both decrease discernably with increasing L‐shell at most magnetic local time sectors and geomagnetic activities, but remain nearly constant with increasing ΔL. The highly consistent distribution suggests both bands may be generated in the plume region. The correlation between banded hiss waves and plasmapause locations sheds new light on the generation mechanisms of banded hiss waves.

Two types of interaction phenomena of the lump wave for nonlinear model of Rossby waves

In this paper, we show the interaction phenomena about the first-order lump wave and multiple solitons by four theorems. The interaction phenomena are divided into two types, one type is absorbing collision phenomenon and the other type is elastic collision phenomenon. Six sets of dynamic plots over time are showed the phenomenon of absorbing interactions with energy transfer process, the phenomenon of elastic interactions with restoration of the initial state after collision. We apply the four theorems to an equation which can characterize the Rossby waves’ amplitude, this equation can be used to describe the resonance phenomenon of Rossby waves. Different test functions with the same parameter values can present different wave-wave interaction properties. This study contributes to in-depth investigation of the mechanism of lump wave generation, evolution and interaction.

Nonlinear generalized piezothermoelasticity of spherical vessels made of functionally graded piezoelectric materials

The present study investigates the thermoelastic response of a heterogeneous piezoelectric sphere under thermal shock loading. Boundary conditions as well as loading are considered as symmetric; thus, the response of the sphere is expected to be symmetric. All of the properties of the thick-walled sphere, including mechanical, electrical and thermal properties, are considered dependent on the radial position, except for the relaxation time, which is considered a constant value along the radius. The governing equations of the sphere have been derived under heterogeneous anisotropic assumptions. The general form of the second law of thermodynamics, which is nonlinear in nature, and is called nonlinear energy equation is used. The number of the established equations is three, which includes the motion equation, energy equation and Maxwell electrostatic equation of Maxwell. These equations are obtained in terms of radial displacement, temperature difference and electric potential. The energy equation is derived based on Lord and Shulman theory with a single relaxation time. In the next step, by introducing dimensionless variables, the governing equations are provided in dimensionless presentation. Then these equations have been discretized using generalized differential quadrature method. Also, in order to follow the solution of the equations in time domain, Newmark method has been used. Since the system of equations is nonlinear, Picard algorithm is applied as a predictor-corrector mechanism to solve the nonlinear system of equations. Then numerical results are presented to investigate the propagation of mechanical, thermal and electric waves inside the heterogeneous sphere and also their reflection from the outer surface of the sphere. By examining the results, it can be seen that mechanical and thermal waves propagate with a limited speed, while the speed of electric wave propagation is infinite.

Assorted optical solitons of the (1+1)- and (2+1)-dimensional Chiral nonlinear Schrödinger equations using modified extended tanh-function technique

In this research article, the (1+1)- and (2+1)-dimensional Chiral nonlinear Schrödinger equations (CNLSEs) are studied, which play an important role in the development of quantum mechanics, particularly in the field of quantum Hall effect. Our primary goal is to obtain the analytical solutions utilizing novel methodology, particularly the modified extended tanh-function technique. We concentrate on the search to solitary wave solutions inside the (1+1)- and (2+1)-dimensional CNLSEs, which are relevant in domains such as optics, electro-magnetic wave propagation, plasma physics, optics and quantum mechanics. Our objective is to increase knowledge of this equation and give insight into the behavior of solitary waves by employing a novel mathematical technique. This will be accomplished by displaying our findings in 2D and 3D graphics. We believe that our results would pave a way for future research generating optical memories based on the nonlinear solitons.

The site-city interaction effect uncertainty on structural responses and its application to fragility analysis of buildings in Shanghai CBD

Seismic fragility analysis is a crucial tool for assessing the seismic performance of buildings. In areas with dense clusters of tall buildings, the significant site-city interaction (SCI) effect alters wave propagation mechanisms, influencing the seismic fragility of structures. However, a significant increase in computational workload results from the need for detailed modeling of sites and building clusters for the SCI analysis. To address this challenge, this work first investigates the minimum number of earthquake waves required to characterize SCI-induced response changes. The Central Business District of Shanghai is analyzed. A table for the recommended minimum number for a given accuracy requirement and prediction reliability is provided. Moreover, a seismic fragility analysis method considering the SCI effect is proposed for low-rise buildings. The case study indicates that, buildings with similar height will exhibit various fragility changes after considering SCI. For the complete damage state, the mean intensity value of the fragility curve can be 14.4 % smaller than that without SCI. In addition, this approach provides significant computational workload reduction. For the case study, the computational workload of the proposed method is roughly 1/50 of that using traditional IDA method.

Experimental Study on the Design and Cutting Mechanical Properties of Bionic Pruning Blades

This study focuses on existing pruning equipment; cutting blades show cutting resistance and lead to high energy consumption. Using finite element (FEA) numerical simulation technology, the branch stress wave propagation mechanism during pruning was studied. The cutting performance of the bionic blade was evaluated with cutting energy consumption as the test index and the branch diameter and branch angle as the test factors, respectively. The test results showed that the blades imitating the mouthparts of the three-pecten bull and the beak of the woodpecker performed well in pruning, and the energy consumption during cutting was reduced by 18.2% and 16.3% compared to traditional blades, making these blades significantly better. These two blades also effectively reduced the cutting resistance and branch splitting by optimizing the edge angle design and increasing the slip-cutting action. In contrast, the imitation shark’s tooth blade increased cutting energy consumption by 14.4% due to the large amount of cutting resistance in the cutting process when cutting larger-diameter branches, making it unsuitable for application in the pruning field. Therefore, the blades imitating the mouthparts of the three pectins and the beak of the woodpecker have significant advantages in reducing the cutting resistance and improving the pruning quality. These findings provide an important theoretical reference for the development of energy-efficient pruning equipment.

Application Practice of SHPB Experimental Technology in "Blasting Engineering" Teaching

The course of "Blasting Engineering" is a highly practical professional course in the field of civil engineering. In order to help students deeply understand and comprehend the propagation and attenuation mechanism of stress waves during rock blasting process, as well as the influence of rock dynamic characteristics on blasting rupture effect, SHPB impact compression experimental technology is introduced into the teaching of "blasting engineering". Firstly, the structure, experimental process, and principles of SHPB equipment were introduced, allowing students to have a better understanding of the experimental principles of SHPB and the theoretical calculation methods of rock dynamic parameters. Then, by combining SHPB experiments with the theoretical course of "Blasting Engineering", the teaching mode can solve students' difficulties in learning blasting theory, exercise their scientific research and exploration abilities, expand their innovative thinking, and cultivate their ability to propose and solve key scientific problems. This helps to unleash students' subjective initiative in conducting experimental research independently and improve teaching effectiveness.

Propagation of periodic director and flow patterns in a cholesteric liquid crystal under electroconvection

The electroconvection of liquid crystals is a typical example of a dissipative structure generated by complicated interactions between three factors: convective flow, structural deformation, and the migration of charge carriers. In this study, we found that the periodic structural deformation of a cholesteric liquid crystal propagates in space, like a wave, under an alternating-current electric field. The existence of convection and charge carriers was confirmed by flow-field measurements and dielectric relaxation spectroscopy. Given that the wave phenomenon results from electroconvection, we suggest a possible model for describing the mechanism of wave generation. The validity of the model was examined using the Onsager variational principle. Consequently, it was suggested that wave generation can be described by four effects: the electrostatic potential, mixing entropy, anisotropic friction due to charge migration, and viscous dissipation of the liquid crystal.

Elastic wave insulation and propagation control based on the programmable curved-beam periodic structure

AbstractCurved-beams can be used to design modular multistable metamaterials (MMMs) with reprogrammable material properties, i.e., programmable curved-beam periodic structure (PCBPS), which is promising for controlling the elastic wave propagation. The PCBPS is theoretically equivalent to a spring-oscillator system to investigate the mechanism of bandgap, analyze the wave propagation mechanisms, and further form its geometrical and physical criteria for tuning the elastic wave propagation. With the equivalent model, we calculate the analytical solutions of the dispersion relations to demonstrate its adjustability, and investigate the wave propagation characteristics through the PCBPS. To validate the equivalent system, the finite element method (FEM) is employed. It is revealed that the bandgaps of the PCBPS can be turned on-and-off and shifted by varying its physical and geometrical characteristics. The findings are highly promising for advancing the practical application of periodic structures in wave insulation and propagation control.

Analytic solutions for effective elastic moduli of isotropic solids containing oblate spheroid pores with critical porosity

AbstractAccurate characterization for effective elastic moduli of porous solids is crucial for better understanding their mechanical behaviour and wave propagation, which has found many applications in the fields of engineering, rock physics and exploration geophysics. We choose the spheroids with different aspect ratios to describe the various pore geometries in porous solids. The approximate equations for compressibility and shear compliance of spheroid pores and differential effective medium theory constrained by critical porosity are used to derive the asymptotic solutions for effective elastic moduli of the solids containing randomly oriented spheroids. The critical porosity in the new asymptotic solutions can be flexibly adjusted according to the elastic moduli – porosity relation of a real solid, thus extending the application of classic David‐Zimmerman model because it simply assumes the critical porosity is one. The asymptotic solutions are valid for the solids containing crack‐like oblate spheroids with aspect ratio < 0.3, nearly spherical pores (0.7 < < 1.3) and needle‐like prolate pores with > 3, instead of just valid in the limiting cases, for example perfectly spherical pores (= 1) and infinite thin cracks (0). The modelling results also show that the accuracies of asymptotic solutions are weakly affected by the critical porosity and grain Poisson's ratio , although the elastic moduli have appreciable dependency of and . We then use the approximate equations for pore compressibility and shear compliance as inputs into the Mori–Tanaka and Kuster–Toksoz theories and compare their calculations to our results from differential effective medium theory. By comparing the published laboratory measurements with modelled results, we validate our asymptotic solutions for effective elastic moduli.

Study on the evolution characteristics of coal mass spalling during coal and gas outbursts

The process of coal and gas outbursts (called outbursts for short) are commonly accompanied by coal mass spalling and fragmentation, but the formation mechanism of spalling is still unclear. To clarify this mechanism, this research constructs multi-layered combined coal-rock mass model. Based on the stress wave propagation mechanism, it’s found that outbursts initially start from ‘weak layer’. Besides, there are two significant results by analyzing the process of unloading waves formed by sudden pressure relief of the excavation face. Firstly, in the axial direction, due to the internal impact of the coal mass during the unloading wave propagation, the load shock wave is formed. The tensile stress is formed on the surface of the coal mass, resulting in rapid damage to the coal mass and even multi-layered spalling. Secondly, in the radial plane, permanent standing surfaces will be formed when the unloading wave catches up with the plastic load wave. Under effect of the unloading wave, internal impact will occur a series of load shock wave, resulting in the formation of multi-layered spalling in the radial plane. In addition, the attenuation law of the load shock wave generated by the internal impact in multi-layered coal mass is also analyzed, results showed that the thickness of coal mass spalling formed far away from the free surface will increase. Finally, the three-dimensional dynamic damage path and the spindle shape damage area formation mechanism in coal mass under external dynamic load are analyzed, which provides a new idea for elucidating the outbursts mechanism.

Non-Linear Plasma Wave Dynamics: Investigating Chaos in Dynamical Systems

This work addresses the significant issue of plasma waves interacting with non-linear dynamical systems in both perturbed and unperturbed states, as modeled by the generalized Whitham–Broer–Kaup–Boussinesq–Kupershmidt (WBK-BK) Equations. We investigate analytical solutions and the subsequent emergence of chaos within these systems. Initially, we apply advanced mathematical techniques, including the transform method and the G′G2 method. These methods allow us to derive new precise solutions and enhance our understanding of the non-linear processes dominating plasma wave dynamics. Through a systematic analysis, we identify the conditions under which the system transitions from orderly patterns to chaotic behavior. This investigation provides valuable insights into the fundamental mechanisms of non-linear wave propagation in plasmas. Our results highlight the dynamic interplay between non-linearity and variation, leading to chaos, which may be useful in predicting and potentially controlling similar phenomena in practical applications.

Interaction between the core and the edge for ion cyclotron resonance heating based on artificial absorption plasma model

In numerical simulations of the ion cyclotron range of frequencies (ICRF) wave heating scheme, core solvers usually focus on wave propagation and absorption mechanisms within the core plasma region. However, the realistic scrape-off layer (SOL) plasma is usually simplified, making it difficult to have deeper understanding of wave propagation and absorption within the SOL. In this work, we employ a cold plasma assumption and an artificial absorption mechanism based on the approach of reference (Zhang et al 2022 Nucl. Fusion 62 076032), to study wave propagation and absorption in the realistic SOL plasma of the EAST. During the exponential decay of the total coupled power with respect to the toroidal mode numbers, several fluctuations are observed in the case of low collisional frequencies. The fluctuations may be caused by the cavity modes associated with specific toroidal mode numbers. Due to the presence of cut-off densities, the edge power losses and the total coupled power exhibit different behaviors before and after the cut-off layer is “open”. Furthermore, the simulation results obtained from the kinetic model in reference (Zhang et al 2022 Nucl. Fusion 62 076032) is discussed. This suggests that both the core-edge combined model and the artificial mechanism are capable of simulating wave propagation and absorption.