Wave Processes Research Articles

NON-STATIONARY WAVES IN A FUNCTIONALLY GRADED VISCOELASTIC PLANE-PARALLEL LAYER2

The propagation of nonstationary disturbances in a plane-parallel layer of infinite extent, which arise as a result of normal dynamic loading of one of its surfaces when the other surface is stationary, is investigated. The material of the layer is assumed to be functionally graded and, at the same time, viscoelastic. The hereditary properties of such a material are taken into account using linear integral Boltzmann–Volterra relations with regular kernels in the form of partial sums of the Prony's series. The peculiarity of this work is that here the parameters of the relaxation kernels are considered continuous functions of the transverse coordinate in the same way as other physical and mechanical characteristics. A method was used for the study, which consists in replacing a functionally graded material with an approximating layered homogeneous structure with continuity conditions at the contact of homogeneous layers. The solution of the nonstationary dynamic linear viscoelasticity problem for a package of plane homogeneous viscoelastic layers is presented in a special form, which greatly simplifies its numerical implementation, especially with a large number of layers with different hereditary properties. This made it possible to successfully apply this method and carry out a series of calculations using an efficient algorithm. Transient wave processes are investigated in the case when the parameters of a functionally graded material are non-monotonic functions of the transverse coordinate, symmetrical with respect to the middle surface of the layer. A comparison of transient wave processes for different types of these functions is carried out. The convergence of the calculation results with an increase in the number of approximating homogeneous layers with a continuous dependence of the external load on time is confirmed. The significant influence of both heterogeneity and viscosity of the material on nonstationary wave processes has been established.

ОДИН ИЗ МЕХАНИЗМОВ ВОЗНИКНОВЕНИЯ ВЫСОКОЧАСТОТНЫХ КОЛЕБАНИЙ ПРИ ТОЧЕНИИ

The article presents the results of theoretical studies of the mechanism of high-frequency oscillations in the cutting zone based on wave processes accompanying the change in the elastic deforming state of the material during its destruction along the shear plane. Based on the studies carried out, it was confirmed that the source of high-frequency self-oscillations generated in the cutting zone is the dynamics of deformation of the material during its destruction along the shear plane. This plane represents the interface of the two media initiating wave processes propagating into the body of the workpiece and chips. Their character and parameters largely depend on the properties of the material being treated (modulus of elasticity and density), the haracteristics of the tool (material, front angle and quality of the front surface) and such operating parameters as the supply to the revolution and the width of the cut. It is noted that the cutting speed affects them indirectly, through the shear angle and the main component of the cutting force. Analytical dependence is proposed, establishing their relationship. It will allow a priori assessment of frequency ranges of possible self-oscillations in order to exclude modes that lead to deterioration of the quality of the treated surfaces.

Solitary deformation waves in two coaxial shells made of material with combined nonlinearity and forming the walls of annular and circular cross-section channels filled with viscous fluid

The aim of the paper is to obtain a system of nonlinear evolution equations for two coaxial cylindrical shells containing viscous fluid between them and in the inner shell, as well as numerical modeling of the propagation processes for nonlinear solitary longitudinal strain waves in these shells. The case when the stress-strain coupling law for the shell material has a hardening combined nonlinearity in the form of a function with fractional exponent and a quadratic function is considered. Methods. To formulate the problem of shell hydroelasticity, the Lagrangian–Eulerian approach for recording the equations of dynamics and boundary conditions is used. The multiscale perturbation method is applied to analyze the formulated problem. As a result of asymptotic analysis, a system of two evolution equations, which are generalized Schamel– Korteweg– de Vries equations, is obtained, and it is shown that, in general, the system requires numerical investigation. The new difference scheme obtained using the Grobner basis technique is proposed to discretize the system of evolution equations. Results. The exact solution of the system of evolution equations for the special case of no fluid in the inner shell is found. Numerical modeling has shown that in the absence of fluid in the inner shell, the solitary deformation waves have supersonic velocity. In addition, for the above case, it was found that the strain waves in the shells retain their velocity and amplitude after interaction, i.e., they are solitons. On the other hand, calculations have shown that in the presence of a viscous fluid in the inner shell, attenuation of strain solitons is observed, and their propagation velocity becomes subsonic.

Rapid-Transfer Matrix Method for Analysis of Electromagnetic Properties of Uniaxial/Biaxial Biaxially Anisotropic Media

The employment of uniaxial/biaxial bianisotropic materials in the field of optical device manufacturing is widespread due to the distinctive electromagnetic response characteristics exhibited by such materials. To effectively analyze the electromagnetic properties of uniaxial/biaxial bianisotropic materials, rapid-transfer matrix method (R-TMM) is proposed to investigate the propagation process of plane waves in the media. Starting from the Maxwell’s equations in the time domain, the homogeneous differential equation about the electric field is constructed by processing the matrix containing dielectric and magnetic conductivity, electric and magnetic loss, tellegen and chirality carrier parameters, and the complex matrix operation is applied to that equation to get the booker quartic equation, and then the formulae method are utilized to obtain the eigenvalues in the uniaxial/biaxial bianisotropic media. Subsequently, the tangential continuity of layered media at the interface is employed to establish a transfer matrix for single-layered media. In the case of multi-layered media, the transfer matrix of plane waves propagating in multi-layered uniaxial/biaxial bianisotropic media can be obtained by means of a continuous iteration process based on the transfer matrix of single-layered media. The formula for calculating the propagation coefficient of uniaxial/biaxial bianisotropic materials can be derived based on the different upward and downward waves in the reflection/transmission region. Finally, the reliability and efficiency of R-TMM is verified from two numerical experiments with the plane waves incident at different angles on a uniaxial/biaxial bianisotropic media. The first experiment is designed as a single-layered biaxial bianisotropic model with more general electromagnetic parameters, and the second experiment is designed as a double-layered uniaxial and biaxial bianisotropic model consisting of common optical materials, which are composed of two non-magnetic materials, lithium niobate (LiNbLO<sub>3</sub>) and cadmium sulfide (CdS). The experimental results demonstrate that, in comparison with the conventional conventional-transfer matrix method (C-TMM), the R-TMM reduces the computational memory and CPU time required for calculating the reflection and transmission coefficients of the uniaxial/ biaxial bianisotropic model by over 98%, while maintaining the accuracy of the reflection and transmission coefficients calculation. Therefore, R-TMM provides an efficient and dependable approach for the design of complex optical devices and the analysis for uniaxial/biaxial bianisotropic propagation characteristics.

Application of Plane Wave Imaging and Processing for Measurement of Reflectors in Concrete

Application of Plane Wave Imaging and Processing for Measurement of Reflectors in Concrete

Nonlinear Mechanisms of Oceanic Wave and Mixing Processes

Nonlinear Mechanisms of Oceanic Wave and Mixing Processes

Wave and Littoral Processes at Thengapattanam Coast, Kanyakumari District, Tamil Nadu State, SW India

The field investigations were carried out on the beach profiles, breaking wave parameters and longshore currents for a period of 25 months from December 2006 to December 2008 to study the beach dynamics of Thengapattanam coast, Kanyakumari district, Tamilnadu state, SW India. The Thengapattanam beach is well known for its long history, estuary, tourism, manmade structures and fishing activities. Monthly measurements were prepared on littoral environmental observations (LEO) and beach level variations. Longshore sediment transport rates were estimated based on the observed data. The estimated annual gross longshore sediment transport rate was higher due to recent manmade structures and the net transport was towards southerly direction . The beach profile level was lowest in July and high in April and the variation was 35 m. The total volume of sand transported was 840 m3/yr during 2007 and 710 m3/yr during 2008. The wave heights varied between 0.4 to 2.5 m during 2007 and 0.45 to 1.8 m during 2008, whereas wave period was between 8 sec to 15.5 sec and 7 sec to 21 sec for 2007 and 2008 respectively. The study concluded that the beach is experiencing significant erosion. Thengapatanam beach is being subjected to erosion phase during both monsoon seasons and get stable profiles by fair weather seasons. Longshore currents were stronger in June, July and August and steady during rest of the year. The net southerly transport was 1.2*106 m3/yr during 2007 and 0.577*106 m3/year during 2008. The volume variations of the sediments, an account of accretion/erosion were estimated considering the January 2007 profile as the base reference over which the values of other months were compared. The study area is highly vulnerable due to its erosion and other factors.

Calculation Algorithm for Electromagnetic Wave Processes in Multi-wire Intersystem ETL

Calculation Algorithm for Electromagnetic Wave Processes in Multi-wire Intersystem ETL

Modelling algorithms for learner interaction with training courses

This paper considers learning as a process of mastering a knowledge domain, investigating the interaction of learners with courses of study and the influence of learner actions on the state of mastery of the knowledge space in order to define a learning control function and to model algorithms for constructing the knowledge space. Key aspects of the interaction process, variables that can be changed to customise the learning model, are given. A threshold to mastery of a course element is formulated and a scale of mastery level for a particular knowledge element is described. As a result, algorithms for forming, expanding and segmenting the knowledge space were created. The research presented the concept of learning as a guided wave process of knowledge mastery, where the learner's actions correspond to the structure of the knowledge space and are determined by its properties.

Modeling of Wave Processes in Hydraulic Drive Systems of Technological Equipment

The article, based on the performed theoretical research, solves the essential scientific and technical problem of increasing the accuracy of identification of wave processes in a hydrodynamic system (pipeline) by developing a generalized method of mathematical designing of the dynamics of a continuous viscous and weakly compressed fluid in the hydrodynamic system pipeline based on the Navier-Stokes equation. Amplitude-frequency characteristics represent parameters of wave processes in the hydraulic drive system. A partial solution of Navier–Stokes equations, under zero initial conditions, is proposed in the form of four-pole equations, the components of which are represented in the form of the Laplace image of the corresponding relative pressure and flow coordinates and the the hydraulic line parameters determine the four-pole elements themselves It is also proposed to determine the values of the four-pole elements based on time constants and relative damping coefficients on the frequency characteristics of hydraulic lines with distribution parameters based on the condition of equality of the first resonant frequencies and amplitudes (at these frequencies). With the help of the developed methods, the primary dynamic parameters of the amplitude-frequency characteristics of continuous viscous and weakly compressed liquid in the pipeline of hydraulic systems for different flow ranges. This made it possible to achieve the following practical results: the high degree of adequacy of the developed mathematical model indicates an increase in the reliability of determining the operating characteristics when designing a hydraulic drive. The high accuracy of determining the first resonant frequencies and amplitudes allows for creating a hydraulic pump with improved operational characteristics.

Improvement of transmission-line-based fault locating for typical traveling-wave accelerator with constant-gradient structures

Since RF breakdown is one of the primary limitations to improving the performances of RF accelerators, extensive efforts have been dedicated to locating the breakdowns. However, most existing methods rely on specialized techniques, resulting in high financial burdens. Although the method based on transient response of transmission line (TL) is suitable for facilities with sporadic recoverable breakdowns, practical operations are susceptible to notable errors. This study revisits the fundamental theories of lossless TL and investigates the wave process to understand the characteristics of the reversed pulse induced by the breakdowns. By utilizing steady-state response of the TL and employing phasor method, we derive analytical formulas to determine the exact location of breakdowns within the faulty cell for constant-gradient TW accelerator. Furthermore, the derived formulas demonstrate their independence from RF phase, thereby distinguishing them from traditional phase-based methods. Additionally, experimental validations are conducted at the HUST injector, and the results confirm the consistency of the analysis. Thus, the proposed method represents a promising improvement over the TL-based approaches and serves as a valuable complement to current techniques. Importantly, this method demonstrates particular advantages for constructed TW accelerators seeking to achieve a balance among high performance, low costs, and compact layouts.

Mathematical model for the management of the wave processes in three-winding transformers with consideration of the main magnetic flux in mining industry

Mathematical model for the management of the wave processes in three-winding transformers with consideration of the main magnetic flux in mining industry

Numerical study of the interaction of a shock wave with a layer of particles using the Baer–Nunziato model

The work is devoted to the application of the Baer–Nunziato model to study shock wave processes in particle beds. The numerical algorithm is based on an HLLC-like solver and takes into account the processes of establishing equilibrium at the interface, taking into account the effect of particle compaction. The problem statement corresponds to the full-scale experiment of B.C. Fan et al. As part of the work, qualitative and quantitative agreement was obtained with the results of natural experiments and calculations of other authors, and an explanation was proposed for the experimentally observed phenomena.

EXPERIMENTAL AND THEORETICAL STUDY OF SPACE DEBRIS IMPACTS ON SHIELDED TARGETS

A comprehensive study is reported on highand hypervelocity impacts of a steel ball simulating a space debris particle on shielded targets. Experimental studies of high-velocity impact of a steel ball were performed in the velocity range up to 2500 m/s. The obtained data were used to verify the mathematical model and numerical algorithm. Numerical modeling of space debris impact on a shielded target was carried out in the impact velocity range of 1400-7000 m/s using the finite element method implemented in the original EFES software package. The proposed failure algorithm can describe the fragmentation of the material and the formation of new contact boundaries without computational mesh distortion. The specific features of shock wave processes and the destruction of the target and impactor at different impact velocities were investigated.

INFLUENCE OF PARAMETERS OF OPERATING CONDITIONS OF SELECTIVE LASER MELTING ON SPALL FRACTURE KINETICS OF 12Cr18Ni10Ti STEEL

The results are presented with regard to experimental studies of dynamic strength characteristics of samples made of 12Cr18Ni10Ti steel powder. They were obtained through selective laser melting with various parameters of a technological process at shock-wave compression up to pressures of ~7 GPa. Critical parameters of a process, in addition to powder characteristics, include laser operating conditions: a laser spot diameter, laser power, a laser beam scanning velocity, as well as a powder layer thickness, protective atmosphere, etc. It has been demonstrated that an increase in the scan laser power and a decrease in a powder layer thickness bring about a decrease in a number of internal defects in initial structures of samples. The results are given, which compare strength characteristics of these steels with properties of steel produced by a traditional technique of hot rolling. Shock-wave experiments were carried out using a light gas gun-type facility, which makes it possible to accelerate flat impactors to speeds of ~700 m/s; internal wave processes in samples were reproduced when recording a rate of movement of the sample's free surface via a PDV laser interferometer; a degree of spall fracture was determined by the help of a metallographic analysis of samples recovered in tests. It has been showed that steel samples made through a selective laser melting technique have high spall strength and a lower degree of damage compared to hot-rolled steel under the same conditions of high-speed shock loading. According to the results of the metallographic studies, the presence of internal defects in initial structures of samples associated with a choice of operating conditions of a manufacturing process does not affect a degree of their spall damage. At the same time, a wave pattern of shock wave propagation differs significantly for samples with and without defects.

Unsteady wave processes in a cylinder made of a functionally graded viscoelastic material

Рассмотрена задача о распространении нестационарных волн в поперечном сечении бесконечного полого цилиндра из вязкоупругого функционально-градиентного материала с немонотонно изменяющимися вдоль радиуса свойствами. Цилиндр заменен кусочно-однородным с большим количеством коаксиальных однородных слоев, аппроксимирующих свойства исходного материала. На основе построенного ранее решения для слоистого цилиндра исследованы волновые процессы в цилиндре из вязкоупругого функционально-градиентного материала с разными видами неоднородностей немонотонного характера.

Properties of Indium Antimonide Nanocrystals as Nanoelectronic Elements

By measurements on single nanocrystals of indium antimonide in the interelectrode nanogap of a scanning probe microscope, current-voltage characteristics with quasiperiodic current pulsations, are explained in the model of Bloch oscillations in a perfect nanocrystal, and individual sharp peaks - conductivity resonances, explained in the model of quantum-size limitation of the wave process of electron transport in a deep potential hole. The mutual influence of radiation from two statistical ensembles of nanocrystals from the same batch was experimentally studied and established. It is assumed that this radiation is entangled photons. It is proposed to use nanocrystals in nanoelectronics as a single-electron memristor, a single-photon bolometer, and a source of microwave radiation.

Experimental study on gas and coal dust explosive overpressure and flame dynamic characteristics in an engineering-level test roadway

The continuous development of coal science and technology has made gas and coal dust explosion disasters an important factor that restricts efficient and intelligent coal mining, which seriously threatens the safe production process of coal mines. To explore the gas and coal dust explosive overpressure and flame propagation characteristics in an actual roadway, the dynamic characteristics of gas and coal dust mixed explosion propagation and evolution laws of explosion flames were investigated using an integrated explosion test system and a high-speed image acquisition system in an engineering-level test roadway with a length of about 700 m and a cross-sectional area of 7.2 m2. Experimental results showed that the peak overpressure measured at each measuring point during the propagation process of explosion shock wave in the roadway did not rise or fall monotonously but fluctuated. The power of explosion shock wave was significantly strengthened by adding coal dust, while the flame propagation speed sharply increased in a certain zone, which generally showed a first increasing and then declining trend. In addition, the flame was blue white after the gas in the roadway was ignited, developed in an irregular shape, and ignited the surrounding combustible gas soon, which further ignited the coal dust under the combined action of pressure wave and flame front. In this case, the flame was deep yellow on the whole. The gas and coal dust explosion flame propagated along the longitudinal section above the roadway, and the flame propagated at an accelerated speed on the transverse section due to the disturbance of obstacles. The study results will provide an important theoretical basis for the R&D of technical active explosion suppression equipment in coal mines and the improvement in their installation technologies.

Combined storm surge and wave overtopping inundation based on fully coupled storm surge-wave-tide model

Inundations in low-lying coastal areas are commonly caused by compound flooding due to the combination of surge overflow and wave overtopping. The increasing frequency of strong tropical cyclones accompanied by high waves is exacerbating flooding risks. In recent studies, wave-induced flooding (i.e., wave run-up and overtopping) has been reported as a critical component of coastal inundations. However, no clear standard has been established for estimating compound flooding caused by the nonlinear interactions of each component. The present study developed a fully coupled model of surge, wave, tide, and wave overtopping to propose a framework for assessing compound coastal inundations. A series of numerical experiments were conducted in an idealized coastal area to analyze flooding risk comprehensively. The experimental results revealed that the conventional decoupled calculation processes for wave overtopping/run-up tend to overestimate the inundation. The advanced approaches provided stable estimations of offshore wave characteristics that change dynamically under extreme wave conditions, resulting in a reliable wave overtopping calculation. Furthermore, a considerable amount of inundation can occur even when typhoons make landfall during low tidal conditions due to the prolonged occurrence of wave overtopping. The proposed framework can be considered an optimal method for practical flooding risk assessments in coastal areas by estimating compound inundations and including transition processes of surge overflow and wave overtopping/run-up.

Eigenfrequency Shift of Piezoelectric Backplate in Vibro-Acoustic Energy Harvesting

Noise is increasingly recognised as a serious, worldwide public health concern. Noise is a type of occupational hazard that can cause damage to hearing and other health effects in workers who are exposed to high levels of noise in their work environment. Traditionally, noise can be controlled and suppressed but recently, noise can be useful and converted into electrical energy. The process of converting noise or acoustic waves into electrical energy by using a quarter wavelength resonator tube embedded with a flexible piezoelectric backplate was used in this study. The results show the maximum output voltage of 1.41 V/Pa at 112 Hz and 0.44 V/Pa at 225 Hz in the experiment, and 1.44 V/Pa at 106 Hz and 0.41 V/Pa at 226.5 Hz with incident sound waves at 90 dB. A parametric study was then performed by adjusting the lumped pointed mass at the piezoelectric backplate to tune the resonant frequencies of the system and the optimal power output. The point mass has given significant change in the acoustic properties. The maximum output power increased from 20.4 at 112 Hz using a flexible back plate to 711 at 119.75 Hz. Various small power applications can benefit from the approach by reducing and absorbing specific low-frequency bandwidths of continuous noise in the environment.