Wave Propagation Process Research Articles

High-Frequency Electrodynamics of Slow Moving Media Taking into Account the Specular Reflection

The paper presents the results of constructing the physical and mathematical model of high-frequency electromagnetic waves propagation in slowly moving media of finite dimensions, which takes into account the phenomena of specular reflection of these waves. The constructed model is based on formulas designed to determine the speed of electromagnetic waves propagation in slowly moving media of finite dimensions, as well as on equations designed to describe these waves. The advantageous feature of these equations is that they take into account the Fresnel drag coefficient for electromagnetic waves propagation speed. The approach to solving of these equations, as well as the approach to modeling of the process of electromagnetic waves propagation in slowly moving media of finite dimensions, based on the use of a difference scheme, in which the motion of these media is taken into account, is proposed. It has been determined that the proposed model and approaches can be used in solving problems related to the construction of receiving-transmitting paths, as well as in solving problems of aeroacoustics.

Compacting nanopowder materials by a pulse pressure generated by expanding plasma channel of a spark ignited by wire electrical explosion

The purpose of the article is to explore the possibilities of powder material compaction by the pressure pulse of an electric explosion of a conductor, establish a functional relationship between the parameters of the pressure pulse and an electrical technological installation for powder material compaction, select the parameters for pulse pressure amplitude and duration adjustment, and specify the design options of the working tool for powder material compaction. Analytical studies have been carried out on the basis of the method of formalized representation of the development of the process of pulse pressure wave formation and propagation where the latter is created by an expanding plasma channel of an electric spark in a transmitting medium initiated by an electric explosion of a wire. The simulation of high-speed de formation of the pipe wall under the action of the pulse pressure is carried out in the MATLAB software package. A scanning electron microscope is used to study the microstructure of the breakage of the compacted material with nanomodifiers. Based on the experimental studies on powder material compaction by the pulse pressure created by the expanding plasma channel of a spark initiated by an electric explosion of a wire when the current pulse f rom an electrotechnological installation is supplied to it, it has been determined that the magnitude and shape of the pressure pulse are most influenced by the parameters of this installation. Based on the obtained model studies, the optimal modes for compaction of nanomodified powders have been selected. The relationship is obtained between the parameters of the pulse pressure (Pm amplitude and pressure wave propagation form) and the electrotechnological installation (voltage, inductance, capacitance). It is proposed to use an acoustic-electric wave model to estimate the pressure that provides high-speed deformation of metal pipes, and to plot a deformation profile of metal pipes used for compaction. Analysis of SEM images of the fractures obtained in compact experiments has showed a high degree of particle compaction with the formation of a solid composite.

Numerical investigation of wave steepening and shock coalescence near a cold Mach 3 jet.

Wave steepening and shock coalescence due to nonlinear propagation effects are investigated for a cold Mach 3 jet. The jet flow and near pressure fields are computed using large-eddy simulation. The near acoustic field is propagated to the far field by solving the linearized or the weakly nonlinear Euler equations. Near the angle of peak levels, the skewness factors of the pressure fluctuations for linear and nonlinear propagations display positive values that are almost identical. Thus, the positive asymmetry of the fluctuations originates during the wave generation process and is not due to nonlinear propagation effects. Compressions in the signals are much steeper for a nonlinear than for a linear propagation, highlighting the crucial role of nonlinear distortions in the formation of steepened waves. The power transfers due to nonlinear propagation are examined for specific frequencies by considering the spatial distribution of the Morfey-Howell indicator in the near and far acoustic fields. They are in good agreement with the direct measurements performed by comparing the spectra for nonlinear and linear propagations. This shows the suitability of the Morfey-Howell indicator to characterize nonlinear distortions for supersonic jets.

Improvement of Automatic Calculation Method of CASE Bearing Capacity

Because of the reliance on the empirical parameter CASE damping coefficient Jc, the high‐strain CASE method is not recommended. The automatic bearing capacity calculation method RAU can avoid this, but it cannot be applied to friction piles. Based on the analysis of the automatic calculation method of bearing capacity RAU, considering the influence of pile side soil resistance unloading, this paper improved the RAU method through the influence of pile side soil damping on the velocity of the pile mass point during the stress wave propagation process. In this paper, we compare the collected static load test results of test piles with the improved automatic method results. The unary linear regression analysis is carried out with the help of statistical tools. The unary linear regression of the improved automatic method bearing capacity results on the static load test bearing capacity results is established. The improved automatic method solves the problem that the RAU method is only applicable to end‐bearing piles and can be applied to the quality analysis and bearing capacity calculation of the high‐strain curve of the driven pile.

Correction of Radio Wave Propagation Prediction Model Based on Improved Seagull Algorithm in Tunnel Environment

In the urban rail transit (URT) environment, the radio wave propagation prediction model and communication system planning are very important. However, due to the complexity of the tunnel propagation environment, the current prediction model can not fully cover the radio wave propagation process in the tunnel. In this paper, the propagation mechanism area is divided based on the segmentation approach. Different propagation models are used for different propagation mechanism areas to predict path loss more quickly and accurately. To improve the accuracy of the prediction model, this paper proposes an improved seagull optimization algorithm (ISOA). First, to address the shortcomings of the seagull optimization algorithm (SOA) such as easy premature convergence and slow convergence speeds, two improved methods of random search and periodic disturbance are proposed. Then, in order to verify the effectiveness and feasibility of the improved algorithm, the benchmark function is used to test the optimization performance of the ISOA and gray wolf optimization, the SOA, and particle swarm optimization. The results show that the optimization performance of ISOA is the most significant. Finally, the ISOA is used to fit and correct the continuous wave test data for a rectangular tunnel and an arch tunnel. The results show that the corrected propagation model has a higher degree of fit with the measured data than the single standard propagation model (SPM) model. The modified propagation model thus has guiding significance for the deployment of time-division long-term (TD-LTE) evolution networks in the tunnel environment.

Research on the Seam Formation Mechanism of Elliptical Bipolar Linear Directional Blasting Based on the SPH‐FEM Coupling Method

Rock mass blasting is a complex process that involves the coupling of both discontinuous and continuous media. This paper aims to reveal the dynamic failure process between adjacent boreholes under an elliptical bipolar linear charge structure using the SPH‐FEM (smooth particle hydrodynamics and finite‐element method) coupling algorithm numerical simulation method. The numerical simulation results are compared with the existing experimental results, which proves the rationality of the algorithm. According to the numerical simulation results, the shaped jet will first shock the hole wall and form a stress concentration zone that will guide the formation of cracks during the stress wave propagation process. In the case of double‐hole blast loading, there is a tendency for cracks coalescence to develop between adjacent boreholes due to the superposition of stresses between the double holes and the increase in damage and plastic strain. The best blasting results will be achieved with this structure when the distance between adjacent holes is 110 cm. Finally, the superiority of elliptical bipolar linear blasting in engineering blasting was verified through field experiments. The results of this study provide a reference for subsequent applications of elliptical bipolar structures in the field of rock blasting.

Numerical study of shallow-water equations using three explicit schemes - application to dam break flood wave

The numerical method to solve dam break problem on regular bathymetry was developed. Two cases of dam break wave propagation on wet and dry bottoms were selected to verify the numerical model elaborated. Three numerical schemes of Lax-Friedrichs, Adams-Bashforth and Adams-Bashforth-Adams-Moulton are applied to simulate this phenomenon using the 1D Saint-Venant equations. An artificial viscosity is added to these numerical schemes to provide stability and reduce numerical diffusion. This viscosity makes the numerical scheme robust (very powerful) for the simulation of this phenomenon. The results obtained show that these developed models are able to simulate dam break wave propagation process. The relative error in the L1 norm between the computed results and analytical solutions is calculated. The L1 norm indicates that the Adams-Bashforth-Adams-Moulton scheme has better accuracy than the other two schemes. It is shown that the technique used is simple, accurate, robust and stable for the simulation of the dam break wave propagation on wet and dry bed conditions.

Research on Seismic Input Method of Layered Ground Foundation

The seismic input of layered foundation is an essential part of seismic analysis of structure- foundation system. Most of the traditional seismic input methods only consider the first reflection process of seismic waves at the interface of different media, ignoring the subsequent reflection and refraction propagation process, which can not truly reflect the wave propagation process in the layered foundation. This paper proposes a new seismic input method for layered foundation, considering all reflected and refracted waves. Firstly, the viscous-spring artificial boundary model of the layered foundation is established, which can simulate the absorption of scattered waves and the elastic recovery capacity of semi-infinite foundation at the same time. Then, based on the wave mechanics theory, the equivalent nodal force calculation formula is derived to realize the vibration input of layered ground. Finally, the calculation results of the layered foundation and two-way surge tower engineering are verified. The results show that: compared to the traditional input method, the method proposed in this paper has a significant influence on the seismic response of layered foundation, and the method in this paper can better meet the accuracy requirements of engineering earthquake resistance, which provides an effective and practical calculation method for seismic analysis of layered foundation structure.

Vibrations Induced by Mechanical Rock Excavation on R.C. Buildings in an Urban Area

The paper describes the numerical approach adopted to investigate the effects of vibrations induced on reinforced concrete (R.C.) buildings by the excavation works needed to bury an existing railway line crossing an urban area in the south of Italy. The construction works are carried out in dolomitic rocks, characterized by a high resistance to excavation. Therefore, they may have a great impact on the surrounding environment in terms of induced vibrations. The study is conducted through an uncoupled approach, investigating the dynamic response of the geotechnical system and the above-surface structure, separately. The impulse force equivalent to the dynamic action of a breaker hammer is used as input motion for 2D finite element (FE) geotechnical simulations of the wave propagation process occurring during the excavation. Then, the acceleration time histories obtained from the geotechnical analyses are adopted to study the dynamic performance of an “index” R.C. building, representing the most recurrent structural typology in the examined area, through a 3D FE model. The results show how the adoption of a mitigation strategy consisting in the execution of a preliminary vertical cut followed by a rock crushing treatment allows to significantly reduce the vibrations induced by the excavation processes on existing buildings.

WAVE GENERATION DUE TO DEBRIS FLOW INTO A SMALL AREA OF WATER

It is known that the tsunami is generated by the debris flow due to slope collapse into the sea. The huge waves may cause damage to coastal structures and residents. Because of heavy rain in northern parts of Kyushu Island, Japan, in July 2017, many reservoirs were damaged and were destroyed. It has been reported that the huge waves may have been caused by debris flow due to the heavy rain. Many laboratory experiments and numerical simulations of the landslide-generated tsunami into the sea have been carried out to clarify the process of wave generation. However, there are a few studies of wave generation by debris flow into a small area of water such as a reservoir. In this study, model experiments of debris flow were conducted in a two-dimensional flume and numerical models based on the depth-averaged shallow water equations have been per-formed in order to clarify the hydraulic characteristics of the waves.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/r6r72KtkvL4

Multiscale simulation of terahertz radiation process in benzimidazole crystal by impulsive stimulated Raman scattering.

Comprehensive dynamics of coupled light wave and molecules in the terahertz wave generation process in an organic molecular crystal solid, 5,6-dichloro-2-methylbenzimidazole (DCMBI), induced by impulsive stimulated Raman scattering has been described by our previously developed multi-scale simulation, Maxwell + polarizable molecular dynamics method, where the propagation of macroscopic electromagnetic fields and microscopic molecular dynamics based on the force field model are numerically solved in the time domain. It has shown the behaviors of the excitation of Raman-active phonon modes by the irradiated pulse and terahertz radiation by molecular motions of infrared-active modes. Simulations of terahertz absorption and Raman spectroscopies of the DCMBI solid have also been performed to verify the applicability of the method to the terahertz optics. The calculated spectra are compared with the experimental measurements, showing good agreement. The detailed motions of the interacting electromagnetic fields and molecules occurred in the terahertz spectroscopies have also been provided, and the analyses have shown that rotational motions of the DCMBI molecules play key roles in the terahertz wave generation.

Creation of magnetic rogue waves

Rogue waves, first discovered in the ocean, are extraordinarily large amplitude waves which can form in relatively calm environments. Magnetic materials also support waves, but with a completely different set of underlying physics. We demonstrate the possibility of generating magnetic rogue waves by applying an abstract form of time reversal. Magnetic systems have important differences from the other media which admit rogue waves; they are inherently anisotropic and have many tunable parameters such as the magnitude and direction of an applied field. We investigate the role of anisotropy and these tunable parameters in the formation and properties of magnetic rogue waves. Through analytic calculations, we identify the important wave vectors and frequencies, typically ranging from 10 to 25 GHz, of the spin waves involved in the creation of magnetic rogue waves. We then correlate this information with the overall efficiency of the rogue wave generation process.

The Role of Micro Breaking of Small-Scale Wind Waves in Radar Backscattering from Sea Surface

The study of the microwave scattering mechanisms of the sea surface is extremely important for the development of radar sensing methods. Some time ago, Bragg (resonance) scattering of electromagnetic waves from the sea surface was proposed as the main mechanism of radar backscattering at moderate incidence angles of microwaves. However, it has been recently confirmed that Bragg scattering is often unable to correctly explain observational data and that some other physical mechanisms should be taken into consideration. The newly introduced additional scattering mechanism was characterized as non-polarized, or non-Bragg scattering, from quasi-specular facets appearing due to breaking wave crests, the latter usually occurring in moderate and strong winds. In this paper, it was determined experimentally that such non-polarized radar backscattering appeared not only for rough sea conditions in which wave crests strongly break and “white caps” occur, but also at very low wind velocities close to their threshold values for the wave generation process. The experiments were performed using two polarized Doppler radars. The experiments demonstrated that a polarization ratio, which characterizes relative contributions of non-polarized and Bragg components to the total backscatter, changed slightly with wind velocity and wind direction. Detailed analysis of radar Doppler shifts revealed two types of scatterers responsible for the non-polarized component. One type of scatterer, moving with the velocities of decimeter-scale wind waves, determined radar backscattering at low winds. We identified these scatterers as “microbreakers” and related them to nonlinear features in the profile of decimeter-scale waves, like bulges, toes and parasitic capillary ripples. The scatterers of the second type were associated with strong breaking, moved with the phase velocities of meter-scale breaking waves and appeared at moderate winds additionally to the “microbreakers”. Along with strong breakers, the impact of microbreaking in non-polarized backscattering at moderate winds remained significant; specifically the microbreakers were found to be responsible for about half of the non-polarized component of the radar return. The presence of surfactant films on the sea surface led to a significant suppression of the small-scale non-Bragg scattering and practically did not change the non-Bragg scatterer speed. This effect was explained by the fact that the nonlinear structures associated with dm-scale waves were strongly reduced in the presence of a film due to the cascade mechanism, even if the reduction of the amplitude of dm waves was weak. At the same time, the velocities of non-Bragg scatterers remained practically the same as in non-slick areas since the phase velocity of dm waves was not affected by the film.

Generating shallow- and intermediate-water waves using a line-shaped mass source wavemaker

The mass source wavemaker in Navier–Stokes equations, which is a frequently used wave generation method, is relatively difficult to control. To resolve this problem, a line-shaped mass source wavemaker is proposed for generating shallow- and intermediate-water waves. Via employing reasonable simplifications, only the enhanced factor, which is introduced to compensate for the energy loss, is unknown during the wave generation process. It is derived that the enhanced factor depends on a weighted combination of wave steepness and relative water depth. Furthermore, the velocity field inside the source region is adjusted at each time step to eliminate the undesirable downward velocity which could contaminate the result via inducing strong and persistent vortical activities near source regions. With the undesirable velocity eliminated, the vortical activity in the vicinity of the source region is weakened significantly. Compared with other mass source wavemakers, the proposed method yields better results when it is used for simulating waves of large steepness. Compared with piston-type wavemakers, the proposed method yields satisfactory results when it is used for generating high-order waves although it is derived under the linear theory. Further simulations indicate that the proposed method is competent to reproduce the process of wave-structure interactions precisely.

About the nonlinear acoustic parameter during deformation of AMG61 alloy

Various acoustic effects are used in the study of deformation processes. Acoustic emission is most often mentioned in such studies, and the effects due to nonlinear properties of a deformable metal are the subject of the present work. These properties of real solids lead to nonlinear acoustic effects of the interaction elastic waves forbidden by the theory of elasticity of a homogeneous isotropic body. The work solves the problem of using the principles of nonlinear acoustics in studying the deformation of AMg61 alloy samples. A surface elastic wave is used to control the alloy condition. The process of the elastic wave propagation in the deformed AMg61 alloy due to nonlinear effects is accompanied by generating the double frequency, both of the longitudinal component of the wave and the shear one, the latter is forbidden by equations of the classical elasticity theory. Excitation and reception in the samples was carried out by piezoelectric converters (PES). A wedge converter with a resonance frequency of 1MHz was used to excite the surfactant. The passing surfactant was recorded by a wedge converter with a resonance frequency of 2 MHz. We justified the control technique of the nonlinear acoustic parameter with respect to amplitudes of the first and second harmonics measured during the whole deformation process. An experimental device has been developed to control the nonlinear acoustic parameter in the process of changing the structural state of the sample metal. The pilot study results of the nonlinear acoustic parameter under Amg61 alloy deformation are given. It is shown that the nonlinear acoustic parameter, as well as the acoustic emission activity, is sensitive to changing mechanisms of the defective structure evolution. The non-linearity jump formation during deformation of alloy AMg61 is recorded, which may indicate adjustment of the metal structure. The presented data demonstrate the increase of acoustic nonlinearity in metal at various deformation stages, both at early stages of elastoplastic deformation and at pre-destruction stage, which can be used as the prognostic criterion.

Wave Dissipation Characteristics of A Mountain-Type Breakwater

One mountain-type breakwater consisting of two inclined plates and one vertical plate is proposed based on several types of traditional free surface breakwaters, including the horizontal plate, curtain wall, and trapezoidal barriers. The interaction between the regular waves and the fixed free surface mountain-type breakwater is measured in one wave flume (15.0 m×0.6 m×0.7 m). The wave propagation, reflection, and transmission process are simulated using the VOF method and the hybrid SAS/laminar method. The simulated wave profiles are consistent with the experimental observations. For waves with a length smaller than four times width of the mountain-type breakwater, the reflected wave amplitudes are slightly larger than those of the vertical-plate breakwater, while the wave transmission coefficients are all smaller than 0.5, and the wave loss coefficients are larger than 0.7. The wave energy is dissipated by wave breaking on the windward inclined plate, and turbulent flow around the vertical plate and the leeward inclined plate.

Typhoon wave modelling application for planning the harbor in Danang city, Viet Nam

Analysis of wave propagation in shallow water is considered as one of the important keys in assessing the shoreline evolution, as well as an important basis for assessing the impact of waves on coastal structures. With the purpose of simulating the wave propagation process in the area of Danang Bay, as a basis for assessing the impact of waves and wind on the shoreline evolution as well as giving appropriate construction measures, the study has analysed wave propagation in an area of about 60.3 × 103 km2. Using the MIKE 21/3 module of the Danish Hydraulics Institute, and simulating under the most extreme wave conditions, under the impact of hurricanes level 10, level 13 and level 16 (conditions and storm trajectories based on Nari storm in 2013) as well as the influence of the flow of the Cu De and Han rivers, the study initially showed changes in velocity fields over time, changes in water level and waves in Danang Bay. These results are expected to become the basis for consultation with local authorities in coastal management and disaster prevention, especially in the context of increasingly complex climate change and sea level rise.

Peculiarities of wave propagation processes in poroelastic media

During analyzing of wave propagation processes in the fluid-saturated porous media unlike the theory of elasticity should be applied proposed by Biot the two phase model of media in which porous the solid elements are belonging to the first phase and the elements of pores fluid filler are belong to the second phase. Sometimes, for solving problems three phase model are used in which porous skeleton is partially saturated by fluid and partially saturated by gas. For the elastic porous media are introduced parameters such as: the porosity, the fluid viscosity, the permeability, the Biot coefficient of effective stress, the shear modulus and the bulk modulus, the mass densities and the total density of the porous material. Also the fundamental characteristic of the porous media is propagation of three different compression waves: the longitudinal fast wave, the second longitudinal slow wave, and the third transversal slow wave. One of the methods that are used for solving problems of poroelasticity is the Boundary Integral Equation Method. The algorithmic bases of it are the boundary analogues of Somiliani’s formulas for the solid displacements and the fluid pressure. The boundary integral equations and the fundamental solutions that are comprised in the poroelastic equations are different from the theory of elasticity analogues because the body with fluid-saturated pores is differ from the continuous homogeneous elastic media. Figures show that the graphs for the poroelastic region may be gradual approximated to the elastic analogues during changing some parameters. The biggest influence for displacements functions has change of the parameter R especially gradual increase of it for the some order. When for changing the functions graphs of the generalized derivatives one gradual increase of the parameter Q for one order is enough.

Experimental investigation of tsunami waves generated by granular collapse into water

Abstract

Estimates of spectral wave attenuation in Antarctic sea ice, using model/data inversion

A model-data inversion is applied to an extensive observational dataset collected in the Southern Ocean north of the Ross Sea during late autumn to early winter, producing estimates of the frequency-dependent rate of dissipation by sea ice. The modeling platform is WAVEWATCH III® which accounts for non-stationarity, advection, wave generation, and other relevant processes. The resulting 9477 dissipation profiles are co-located with other variables such as ice thickness to quantify correlations which might be exploited in later studies to improve predictions. An average of dissipation profiles from cases of thinner ice near the ice edge is fitted to a simple binomial. The binomial shows remarkable qualitative similarity to prior observation-based estimates of dissipation, and the power dependence is consistent with at least three theoretical models, one of which assumes that dissipation is dominated by turbulence generated by shear at the ice-water interface. Estimated dissipation is lower closer to the ice edge, where ice is thinner, and waveheight is larger. The quantified correlation with ice thickness may be exploited to develop new parametric predictions of dissipation.