Wave Propagation Process Research Articles

Local propagation of visual stimuli in focus of attention

Fast reactions to changes in the surrounding visual environment require efficient attention mechanisms to reallocate computational resources to the most relevant locations in the visual field. In this paper, we present a biologically-plausible computational model of focus of attention that exhibits spatiotemporal locality and that is very well-suited for parallel and distributed implementations. Attention emerges as a wave propagation process originated by visual stimuli corresponding to details and motion information. The resulting field obeys the principle of “inhibition of return” so as not to get stuck in potential holes. The proposed model is obtained as a hyperbolic regularization of the Poisson equation to which it reduces in the limit of high speed of propagation. According to the MultiMatch algorithm for scanpaths comparison, the proposed model achieves very competitive results when considering dynamical input stimuli.

Discrete element analysis of geogrid–aggregate interface shear behavior under cyclic normal loading

The stability of a geogrid-stabilized structure affected by cyclic normal loading (CNL) is significant but has not been fully revealed. Using the discrete element method (DEM), the effect of CNL on the microscale mechanical responses (i.e., stress states, contact evolution, fabric deformation) of the geogrid–aggregate interface direct shear test is first investigated. The complex shear behaviors at the interface with normal cyclic excitation at different frequencies and amplitudes are simulated. The DEM model is able to capture the macroscopic dynamic shear laws at the geogrid–aggregate interface in a similar way to those tested experimentally. The detailed behavior of the aggregate interacting with the geogrid under CNL is investigated. Compared with the simulation under static normal loading (SNL), CNL makes the stabilized layer more prone to failure, which could be quantitively evaluated by analyzing the local shear strain and the interparticle interlocking level. Microscale studies on the load wave propagation process and the confinement zone indicate that the present method can provide an applicable tool for dynamic service assessment and reliable forecasting of the undesirable effect of CNL on a mechanically stabilized layer.

Attenuation effect of a preset bubble on hydrodynamic ram induced by fragments impacting fluid-filled tank

When the fluid-filled structure is impacted by a high-velocity penetrator, the hydrodynamic ram (HRAM) will appear and may induce catastrophic damage. Based on the damage mechanism of HRAM, a countermeasure through presetting a bubble inside the fluid-filled tank is proposed to attenuate the HRAM loads and thus alleviate the vulnerability of the tank structure under the impact of high-velocity projectile. Experimental tests are performed to compare the tank’s damage considering the effect of bubble by the charge-driven preset fragments. The experimental results show that the peak pressure and impulse of the initial impact wave acting on the tank rear plate are reduced by 78% and 88%, respectively, and the cavitation collapsing pressure acting on the rear plate almost disappeared. Meanwhile, the maximum deformation of the front plate is reduced by about 15%. In addition, numerical simulation is employed to reproduce the experimental process. By comparing the structural dynamic response and the shock wave propagation process, the attenuation mechanism of the preset bubble on HRAM is revealed. Furthermore, the influence of the bubble position and size on the attenuation effect is investigated. Numerical results show that a smaller distance between the bubble and the front plate, and a larger bubble size lead to a better attenuation effect.

A simplified approach for efficiently simulating submarine slump generated tsunamis

A simplified approach was proposed to efficiently simulate the tsunamis generated by a submarine slump. The landslide tsunami generation process was simulated using a long-wave model, simplifying the wave generation problem as a slump traveling down a plane slope with a prescribed trajectory. As a result, the landslide tsunami generation process was parameterized by 11 input parameters. The wave profile at the end of the wave generation process can then be specified as the initial conditions in any numerical tsunami propagation model to study the subsequent tsunami propagation. To demonstrate the capability of this new landslide tsunami generation approach, we used it in combination with an existing Boussinesq wave solver to simulate the 1998 Papua New Guinea landslide tsunami. The results based on the newly calculated physics-based wave profile compare reasonably well with field measurements and the results based on an existing tuning-based wave profile. Sensitivity tests were performed to examine the sensitivity of the runup results to each of the 11 input parameters. Six sets of 100-case Monte Carlo experiments were conducted to investigate the propagation of uncertainty from the input parameters to the runup results. Runup uncertainty was found to be approximately 1.5 times the parameter uncertainty, highlighting the uncertain nature of landslide tsunamis.

Experimental and numerical investigations on the stress waves propagation in strain-hardening fiber-reinforced cementitious composites: Stochastic analysis using polynomial chaos expansions

The propagation of stress waves can result in spalling fractures in materials, which poses a threat to the safety of engineering structures. Hence, in-depth studies are necessary to mitigate such risks. Ultra-high toughness cementitious composites (UHTCC) with significant tensile strain-hardening properties are advanced engineering materials with great potential for impact engineering. The study used a combination of experimental and numerical methods to analyse the propagation and attenuation behaviour of stress waves in the UHTCC. The numerical model was developed using the Smooth Particle Galerkin (SPG) method and the Karagozian & Case concrete/cementitious (KCC) material constitutive model. Additionally, a quantitative global sensitivity analysis (GSA) using a polynomial chaos expansion (PCE) surrogate model and Sobol's method was conducted to analyse the stochastic input parameters of the numerical model. Results show that compressive stress waves undergo significant attenuation during propagation in UHTCC, and the developed numerical model accurately simulated the stress wave propagation process Furthermore, the PCE-Sobol GSA revealed that the selected stress wave propagation responses are most sensitive to the tensile strength of UHTCC. This study is expected to deepen the understanding of the propagation behaviour of stress waves in UHTCC and pave the way for promising applications of UHTCC in impact engineering.

Selection of Material and Thickness of the Protective Wall in the Conditions of a Hydrogen Explosion of Various Power

The main purpose of this study is a numerical assessment of the consequences of an explosion of a hydrogen-air cloud on the personnel of a hydrogen fueling station and the strength of a protective solid wall of certain dimensions. An explosive gas mixture is formed as a result of the destruction of high-pressure cylinders, the number of which determines the size of the cloud, the power of the explosion, and the scale of the consequences of environmental impact. To obtain the spatio-temporal distribution of the maximum overpressure and the impulse of the shock wave compression phase, a mathematical model of the dispersion of an active gaseous admixture is used, taking into account the chemical interaction with air oxygen. The probable consequences of the shock-impulse impact on the personnel at the control point are carried out using probit analysis. The values of the maximum bending moment and stress at the base of the protective wall, which result from the impact of the blast wave, are used to deterministically estimate the minimum wall thickness necessary for the safe operation of the protective device. The mathematical model takes into account the complex terrain and the three-dimensional non-stationary nature of the shock wave propagation process, and it is a source of data necessary to solve the problem of the strength of solid objects located in the area of baric perturbation of the gaseous medium. The developed methodology makes it possible to carry out a comparative analysis of the effectiveness of protective structures in relation to the power of the explosion.

Numerical Simulation of Acoustic Wave Generated by DC Corona Discharge Based on the Shock Wave Theory

The audible noise generated by corona discharge has the N-type characteristic at the initial generation stage, and it is a typical shock wave. This shock wave usually only exists around the corona source with a tiny range, making it difficult to obtain its characteristics through experimental measurements. An electrosound-combined simulation of the corona discharge based on the shock wave theory was conducted, and the development process involving the corona discharge, shock wave, and sound wave was simulated. First, the corona was numerically simulated based on the 2D pin–plate axisymmetric hydrodynamic model. It was found that the plasma was mainly distributed near the axis of the corona field where the electric field changed violently, and the maximum value of the electric field appeared at the head of the discharge channel. Then, the plasma energy was equivalent to the explosive energy, and a plasma explosion shock model was established. It was found that the shock wave pressure had obvious positive and negative pressure zones, and the propagation velocity decays to the sound velocity gradually. Finally, the shock wave pressure derived by the explosion model was used as the acoustic source, and the acoustic wave propagation process was simulated. The simulated sound pressure waveform had the same characteristics as the relevant experimental measurement results, proving that the developed method possessed strong applicability and gave rise to a new angle for the simulation of corona-generated audible noise.

Fault Location Study of Overhead Line–Cable Lines with Branches

A new fault location method based on the three-terminal travelling wave method is proposed for the fault location problem of multi-branch overhead line–cable transmission lines. Firstly, the process of fault travelling wave propagation in overhead transmission lines and the phenomenon of refraction are analysed, and an improved phase-mode transformation is introduced to decouple the electromagnetic coupling and perform fault phase selection. Secondly, the Pearson correlation coefficient is introduced to compare the similarity of the current travelling waveforms at different measurement points in order to implement fault segmentation. To solve the problems of the complexity of the fault travelling wave propagation process and the difficulty of identifying the travelling wavehead, the Hilbert–Huang transform is used to extract the fault signal characteristics, and the travelling wave arrival moment is accurately calculated by the sampling error correction method to determine the fault location. Finally, the accuracy and stability of the method are verified via a simulation test on the MATLAB/Simulink platform. The results show that the proposed positioning method combining the three-terminal travelling wave method with HHT and sampling error correction can locate the fault location more accurately, and it has good potential for application in the engineering field. It provides a new technical means for fault location in overhead transmission lines, which is expected to become one of the most important technologies in the future power system.

Flow and heat transfer through a porous tumor during high-intensity focused ultrasound

High-intensity focused ultrasound (HIFU) represents a non-invasive approach for localized treatment, wherein focused ultrasound waves are applied to specific tissues. However, accurately targeting the HIFU ablation area is still a challenge. The difference in the physical properties of the tumor being treated, compared to normal tissue, particularly, porosity, is an essential aspect that may influence the effectiveness of treatment. This study investigated the impact of tumor porosity, acoustic operating frequency, and the tumor acoustic absorption coefficient on fluid flow and temperature distribution in both the porous tumor and surrounding tissue during HIFU exposure using numerical models. Furthermore, the study examined the differences in porosity between normal and tumor tissues and the resulting phenomena. To determine the acoustic pressure, flow velocity, and temperature distributions in the porous tumor during HIFU treatment, researchers have employed numerical modeling to calculate acoustic wave propagation, fluid flow, and heat transfer processes. This study indicates that the maximal temperature increase might not always necessarily occur at the acoustic pressure focus, particularly, if the tumor does have a higher porosity than the neighboring normal tissue. This was because the flowing fluid of the tumor and adjacent tissues had a substantial impact on the strong convection in the focus area. These findings highlight the significance of this study in terms of precisely localizing the HIFU ablation target region and ensuring minimal thermal injury to the surrounding healthy tissue.

Numerical investigation of nonlinear effects in a standing wave thermoacoustic engine using the discontinuous Galerkin method

Understanding the nonlinear effects in thermoacoustic heat engines operating under high-pressure amplitude conditions plays a crucial role in improving their operational performance and efficiency. The discontinuous Galerkin (DG) method has several advantages, including high accuracy, adaptability, efficiency, and the ability to handle the coupling of multiple physical fields, making it suitable for accurately simulating the flow and heat transfer characteristics in thermoacoustic engines. The simulation code was developed based on MFEM, an open-source C++ library for modular finite element methods. The fully compressible Navier-Stokes equations and Fourier heat conduction equation were solved to investigate the nonlinear effects, which cannot be captured by the linear theory. To verify the accuracy of the simulation code, the numerical investigation of the thermoacoustic wave propagations induced by thermal effects in a square enclosure was first conducted. The simulation results presented the details of the generation and propagation of thermoacoustic waves, which were largely consistent with the results obtained using the flux-corrected transport (FCT) algorithm. Second, a quarter-wavelength standing wave thermoacoustic engine was simulated. The simulation results captured the process of pressure wave generation in the thermoacoustic engine, which was consistent with the pressure wave generation process in the enclosure. The results revealed the flow and heat transfer characteristics and nonlinear effects in the thermoacoustic engine under high-pressure amplitudes, which were consistent with the results obtained using finite volume method. The simulation results showed that the DG method is an effective numerical method for simulating thermoacoustic engines.

Dynamic Analysis for a Shallow Isosceles Trapezoid Depression Impacted by SH Waves

This paper presents a series solution of shear horizontal (SH) wave scattering by a shallow isosceles trapezoid depression in half-space. An appropriate multiregion-matching technique was adopted to divide the analytical model into three parts, which is necessary to meet the conditions of applying the wave function expansion method. Based on the complex function method, the wave field expressions, satisfying stress-free boundary conditions, were constructed. In addition, introducing complex variables avoided the redundant formula derivation for the implementation of coordinate transformation. The unknown coefficients in the wave field expressions were solved by Fourier series expansion in a complex field, and the convergence analysis was carried out to determine the number of traction terms of the series solution. Frequency-domain and time-domain results were presented to analyze the wave motion amplification and propagation process. The proposed method not only provides a benchmark for numerical simulation results but also makes up for the limitations of the theoretical research method of trapezoidal depression topography.

Influence of Excavation Pits on the Wave Hydrodynamics of Fringing Reefs under Regular Waves

Dredging materials from reef flats have become an important source of sand and aggregates for meeting the infrastructure needs of coral-lined shores in subtropical and tropical regions, especially for low-lying atoll islands. Dredging at the reef flats can generate artificial excavation pits, which not only have profound influences on coral ecological stability but also deeply affect the hydrodynamic characteristics of coral reefs. To deepen the understanding of the influence of excavation on the wave hydrodynamics of fringing reefs, the wave propagation, wave transformation, wave setup, and wave runup processes of regular waves on fringing reefs with artificial pits have been systematically analyzed using a non-hydrostatic numerical wave solver (NHWAVE). The effects of some significant factors have been carefully investigated. According to the study findings, the existence of artificial pits can result in a slight decrease in the wave height around the artificial pit. The time-mean maximum of wave runup height at the backreef slope can be reduced to some extent when the artificial pit is present. When placed close to the reef edge, the artificial pit can have noticeable effects on the hydrodynamic characteristics of fringing reefs, particularly the wave setup along the reef flat. It is hoped that the study findings can provide further reference for evaluation of the influences of artificial pits on the wave hydrodynamics of fringing reefs.

Numerical simulation of the coupled multiphysics fields and reactions during the microwave pyrolysis of wood particles

Microwave heating has gained significant attention as an alternative to conventional methods for biomass pyrolysis. To investigate the electromagnetic-thermal-hydraulic-chemical processes during biomass pyrolysis under microwave irradiation, a three-dimensional comprehensive pyrolysis model was developed. The model numerically described the physicochemical processes of the electromagnetic wave propagation in the reactor, heat transfer and fluid flow inside porous wood particles, pyrolysis reactions, and phase changes. The model was validated by comparing the temperature profiles of biomass samples under varying microwave powers against literature data. The modeling results demonstrated that there was a strong interaction between the distributions of the microwave electromagnetic fields in the cavity and that inside the wood particles; these distributions changed with the size, shape, and location of the biomass sample in the cavity. Using the model, the thermal response of wood particles to microwave radiation was determined. The predicted results showed that a millimeter-sized wood particle was large enough to straddle multiple high-energy microwave regions in the cavity, resulting in more than one intraparticle hotspots. The transient dielectric loss inside wood particles is nonuniform due to the enhancement of the local relative permittivity by the local hotspots. The maximum permeability within the wood particles increases by an order of magnitude during microwave pyrolysis at 1 kW. The hotspots have a considerable influence on the structural homogeneity and stability of biochar due to the formation of large thermal and expansion stresses around the hotspot locations. Moreover, the energy efficiency (ηe) of converting microwave electromagnetic energy into the thermal energy of wood particles is sensitive to the input microwave power and particle shape. For instance, ηe ranges from 12.44% to 36.15% under the microwave powers of 0.8–1 kW for the pyrolysis of a cylindrical wood particle with aspect ratios of 0.25–2. This work provides the fundamental technical support for the industrial application of microwave pyrolysis.

Infragravity waves at the Hambantota port located in the North Indian Ocean

Infragravity (IG) waves are the primary cause of harbor oscillations. The Hambantota port located in the North Indian Ocean is taken as an example to study the IG waves in the vicinity and interior of a complex-shaped real harbor and to reveal the energy transfer of IG waves toward the harbor. The research employs a combination of in-situ wave measurement and numerical simulations conducted using the spectral wave model WAVEWATCH III. The latter could provide a long-term estimation of the level of IG wave energy over a broad geographical region, though it cannot reflect the complex mechanism of IG waves near/at the shore. Results indicate that, at the sensor near the harbor entrance, the free IG wave heights HFIG generally exceeds the bound IG wave height HBIG. However, during energetic sea states (significant wave height HS > 2.5 m in this study), HBIG increases significantly and occasionally exceeds HFIG. The spatial distributions of HS, HBIG, and HFIG indicate that the narrow continental shelf surrounding Sri Lanka has a marginal effect on attenuating swell energy. Consequently, the Hambantota port experiences a substantial impact from both swell and accompanying IG waves. If solely considering the maximum acceptable HS, the downtime for large ships would be greatly underestimated. The process of wave propagation into the harbor enables the energy transfer from bound IG waves to free IG waves that finally excite harbor oscillations. Albeit the tidal range is low, the tidal level has a noteworthy impact on harbor oscillations. The IG spectral density during low tides is generally greater than that during high tides due to the enhanced nonlinear interactions of short waves under low-tide conditions.

Three-dimensional modelling of blur property for conventional optical microscopes

Intensity diffusion caused by optical diffraction limits the imaging resolution of conventional optical microscopes, therefore modelling and measuring the intensity transmission and distribution property of the light sources is a significant research topic in system development and pattern recognition. However, the complicated wave propagation process in optical imaging makes it difficult to provide a direct, analytical and simple mathematical model to measure the relationship between the blur degree and various camera parameters. In this study, an improved intensity transmission and distribution calculation method for conventional optical microscopes was proposed; furthermore, a simple mathematical relation between the blur degree and camera parameters was achieved based on the proposed method. First, the light intensity distribution and propagation characteristics of a conventional optical microscope were modeled based on the property of the Fresnel circular hole diffraction combined with the practical optical parameters. Second, by analyzing the property of intensity distribution and blurring imaging, a quantitative simplified mathematical relationship between the blur degree and camera parameters in optical microscope imaging was obtained, and the three-dimensional (3D) blur property in the optical imaging process was analyzed under different conditions. Third, the connection between diffractive optics and geometric optics was obtained by summarizing and generalizing the 3D blur property curve of each monochromatic light source. Finally, the proposed method was verified through a series of simulations and experiments.

Mesh-free simulation of height and energy transfer of landslide-induced tsunami waves

The landslide-induced tsunami wave poses a threat to human society and the living environment by causing disasters such as run-up of water surfaces and overtopping of dams. In this paper, we systematically investigated the relationship between landslide properties and induced tsunami wave characteristics as well as the energy transfer between the landslide and waves. A meshless smoothed particle hydrodynamics (SPH) framework was presented and validated with four experiments of different landslide types. The validations indicate that the SPH model is capable of reproducing the complex processes of tsunami wave generation induced by both rigid and deformable landslides. Then we perform numerical simulations of 162 landslide-induced waves scenarios with varying landslide deformability, relative initial positions, densities, landslide size, and downstream water depths using the validated SPH model. The results show that the effect of density and initial water depth on the maximum wave height can be disregarded, while the effective landslide volume has a significant effect. The analysis of the kinetic and potential energy of the induced waves reveals that energy transfer occurs rapidly, which mainly increases the potential energy of the water downstream. We also find an exponential relationship between landslide potential energy reduction and maximum wave height. These findings provide valuable insights into the landslide-induced tsunami waves and enhance risk assessment and mitigation efforts.

Research on the Rule of Explosion Shock Wave Propagation in Multi-Stage Cavity Energy-Absorbing Structures.

The propagation laws of explosion shock waves and flames in various chambers were explored through a self-built large-scale gas explosion experimental system. The propagation process of shock waves inside the cavity was explored through numerical simulation using Ansys Fluent, and an extended study was conducted on the wave attenuation effect of multiple cavities connected in a series. The findings show that the cavity's length and diameter influenced the weakening impact of shock waves and explosive flames. By creating a reverse shock wave through complicated superposition, the cavity's shock wave weakening mechanism worked. By suppressing detonation creation inside the cavity, the explosive flame was weakened by the cavity's design. The multi-stage cavity exhibited sound-weakening effects on both shock waves and explosive flames, and an expression was established for the relationship between the suppression rate of shock force and the number of cavities. Diffusion cavities 35, 55, 58, and 85 successfully suppressed explosive flames. The multi-stage cavity efficiently reduced the explosion shock wave. The flame suppression rate of the 58-35 diffusion cavity explosion was 93.38%, whereas it was 97.31% for the 58-35-55 cavity explosion. In engineering practice, employing the 58-58 cavity is advised due to the construction area, construction cost, and wave attenuation impact.

Multiple soliton solutions, lump, rogue wave and breather solutions of high dimensional equation for describing Rossby waves

In the past, we haven't paid much attention to higher-dimensional models, which are actually more consistent with the real atmosphere. In this manuscript, we derive a high-dimensional Kadomtsev-Petviashvili equation from a fluid system based on the Gardner-Morikawa transformation and the small parameter perturbation method, which is the first time to characterize the propagation process of Rossby waves in Large-scale atmospheric. The exact solutions such as soliton, lump, rogue wave and breather of this equation are achieved according to Hirota bilinear method and symbolic computation approach. Further we utilize the composite diagram of these solutions to observe the propagation properties of Rossby waves with assistance of Mathematica. The results enrich the analysis of Rossby waves in marine engineering and fluid dynamics.

Monitoring fatigue cracks in rib-to-deck joints of orthotropic steel deck using ultrasonic Lamb waves

Fatigue cracks in rib-to-deck joints of orthotropic steel decks (OSDs) endanger the safety of bridges and are difficult to detect. This paper proposes to monitor fatigue cracks using ultrasonic Lamb waves. An OSD specimen instrumented with ultrasonic sensors was fabricated and tested to crack under fatigue loads. Ultrasonic Lamb waves were measured to detect, locate, visualize, and evaluate fatigue cracks using a probabilistic inspection of damage method. A finite element model was developed to understand wave propagation and crack growth process, and utilized to perform parametric studies on the type, position, and severity of cracks. The results indicated that fatigue cracks were effectively monitored by ultrasonic Lamb waves. Errors of crack positions were less than 5 mm. The damage probability distribution increased with the crack depth and crack length. The ultrasonic Lamb waves are more sensitive to toe-deck and root-deck cracks than other modes of cracks in rib-to-deck joints.

Wave Generation by Fluidized Granular Flows: Experimental Insights Into the Maximum Near‐Field Wave Amplitude

AbstractTsunamis can be generated by an impulsive displacement of water resulting from the entrance of pyroclastic density currents (PDCs). The maximum wave amplitude is of primary interest regarding tsunami modeling and applications to hazard assessment. This study explores tsunami generation by fluidized granular flows and analyzes published relationships predicting maximum wave amplitudes from PDC characteristics. A fluidized column of glass beads is released from a reservoir, flows down an inclined plane and enters a water‐filled flume, generating waves. Fluidized flows of greater mass enter the flume with greater velocities; however, all the analyzed flows impact the water with a supercritical impact Froude number. Flows of greater mass generate a single, high‐amplitude wave, followed by a longer‐period trough. The solitary‐like leading wave propagates along the flume with a nearly constant amplitude. In contrast, the leading wave is followed by a low‐amplitude trough and a second low‐amplitude crest when generated by lower mass flows. Dispersive effects are stronger for waves produced by flows of lower masses, causing the decrease of the amplitudes with distance from the shore. Increased breaking and dissipation cause decreased amplitudes of the waves generated in shallow water depths. The predictive equations, determined based on the impact Froude number and the water depth in the constant‐depth section of the flume, provide relatively good predictions of the maximum wave amplitudes. A new approach is proposed, which calculates the impact Froude number considering the water depth value where the wave generation occurs, providing an improved understanding of the wave generation process.