Excitation Of Waves Research Articles

Detecting bolt looseness of flanged joint based on multiple-mode conversion

This article detects the bolt looseness of a flanged joint based on the energy conversion between multiple wave modes. The mode conversion introduced by the flange carries abundant information referring to the bolt looseness, but it requires precise sensing technology to capture each mode. The mode transducer for cylindrical shells was first proposed based on the orthogonality of mode shapes. The distribution scheme and electrode function enable the piezo transducer array to selectively control multiple modes. Both the simulated and experimental validations were subsequently conducted to check the design scheme. We examined the shapes and mode signals of the excited wave field to ensure that the energy was concentrated in the target mode. Finally, two-stage detection was conducted for eight bolts: the first stage detected the initial looseness of a single bolt using two indicators; the second stage trained the machine learning classifiers to recognize the location of the loose bolts. The results exhibited a high sensitivity of mode conversion in detecting initial looseness, with an accuracy of [Formula: see text] in recognizing the loose location.

A Laterally Excited Bulk Acoustic Wave Resonator Based on LiNbO3 with Arc-Shaped Electrodes

High frequency and large bandwidth are growing trends in communication radio-frequency devices. The LiNbO3 thin film material is expected to become the preferred piezoelectric material for high coupling resonators in the 5G frequency band due to its ultra-high piezoelectric coefficient and low loss characteristics. The main mode of laterally excited bulk acoustic wave resonators (XBAR) have an ultra-high sound velocity, which enables high-frequency applications. However, the interference of spurious modes is one of the main reasons hindering the widespread application of XBAR. In this paper, a Z-cut LiNbO3 thin film-based XBAR with arc-shaped electrodes is presented. We investigate the electric field distribution of the XBAR, while the irregular boundary of the arc-shaped electrodes affects the electric field between the existing interdigital transducers (IDTs). The mode shapes and impedance response of the XBAR with arc-shaped electrodes and the XBARs with traditional IDTs are compared in this work. The fabricated XBAR on a 350 nm Z-cut LiNbO3 thin film with arc-shaped electrodes operating at over 5 GHz achieves a high effective electromechanical coupling coefficient of 29.8% and the spurious modes are well suppressed. This work promotes an XBAR with an optimized electrode design to further achieve the desired performance.

Anisotropy of acoustic properties in thin-sheet rolled low-carbon manganese steel

Thin-sheet rolled low-carbon manganese steel 09G2S with a thickness of 0,8 mm which has strong property anisotropy due to texture and residual stresses, was experimentally studied using SH-wave with horizontal polarization and zero-order symmetric Lamb wave mode. The velocities of elastic wave propagation along the sheet were analyzed as their direction and polarization varied relative to the rolling direction in the range of angles from 0 to 180 degrees. The excitation and reception of normal waves in the sheet were carried out by piezoelectric transducers with dry point contact, providing tangential force application. The results of the research on the anisotropy of acoustic properties, X-ray structural analysis of residual stresses and inverse pole figures, and metallographic studies were obtained.

The Phase Structure of Wave Disturbances Excited by a Pulsating Source at the Interface of a Liquid Flow of Finite Depth and an Ice Sheet

The floating ice sheet determines the dynamic interaction between the ocean and the atmosphere, affects the dynamics of the sea surface and subsurface waters, since the ice sheet and the entire mass of liquid under it participate in the general vertical movement. The paper investigates the phase structure of wave fields arising at the interface between ice and a flow of homogeneous liquid of finite thickness when flowing around a localized pulsating source of disturbances. The ice sheet is modeled by a thin elastic plate, the deformations of which are small, and the plate is physically linear. An integral representation of the solution is obtained, and the results of calculations of dispersion dependencies and phase patterns for various parameters of wave generation are presented. It is shown that the main parameters determining the characteristics of the amplitude-phase structure of wave disturbances of the ice sheet surface are ice thickness, flow velocity, and pulsation frequency. Numerical calculations demonstrate that when the flow velocities, ice thickness, and frequency change, there is a noticeable qualitative restructuring of the phase patterns of the excited long-range wave fields at the ice-liquid interface.

Studies of stationary features in jets: BL Lacertae II. Trajectory reversals and superluminal speeds on sub-parsec scales

High-resolution very long baseline interferometry observations have revealed a quasi-stationary component (QSC) in the relativistic jets of many blazars, which represents a standing recollimation shock. VLBA monitoring of the BL Lacertae jet at 15 GHz shows the QSC at a projected distance of about 0.26 mas from the radio core. We study the trajectory and kinematics of the QSC in BL Lacertae on sub-parsec scales using 15 GHz VLBA data of 164 observations over 20 years from the MOJAVE program and 2 cm VLBA Survey. To reconstruct the QSC's intrinsic trajectory, we used moving average and trajectory refinement procedures to smooth out the effects of core displacement and account for QSC positioning errors. We identified 22 QSC reversal patterns with a frequency of $ 1.5$ per year. Most reversals have an acute angle $<90 and a few have a loop-shaped or arc-shaped trajectory. Where observed, combinations of reversals show reversible and quasi-oscillatory motion. We propose a model in which a relativistic transverse wave passes through the QSC, generating a short-lived reverse motion, similar to the transverse motion of a seagull on a wave. According to the model, relativistic waves are generated upstream and the reverse motion of the QSC is governed by the amplitude, velocity, and tilt of the wave as it passes through. The apparent superluminal speeds of the QSC ($ 2\,c$) are then due to the relativistic speed of the jet's transverse wave ($<0.3\,c$ in the host galaxy rest frame) combined with the relativistic motion towards the observer. The measured superluminal speeds of the QSC indirectly indicate the presence of relativistic transverse waves, and the size of the QSC scattering on the sky is proportional to the maximum amplitude of the wave. We find that most of the transverse waves are twisted in space. In the active state of the jet, the directions of the twisting waves are random, similar to the behaviour of the wave in a high-pressure hose, while in the jet stable state, the wave makes quasi-oscillations with regular twisting. The study of QSC dynamics in BL Lac-type blazars is important for evaluating the physical characteristics of relativistic transverse jet waves. The latter have important implications for jet physics and open up possibilities for modelling the physical conditions and location in the jet necessary for the excitation of relativistic transverse waves.

Resonant Excitation of Kelvin Waves by Interactions of Subtropical Rossby Waves and the Zonal Mean Flow

Abstract Equatorial Kelvin waves can be affected by subtropical Rossby wave dynamics. Previous research has demonstrated the Kelvin wave growth in response to subtropical forcing and the resonant growth due to eddy momentum flux convergence. However, the relative importance of the wave–mean flow and wave–wave interactions for the Kelvin wave growth compared to the direct wave excitation by the external forcing has not been made clear. This study demonstrates the resonant Kelvin wave excitation by interactions of subtropical Rossby waves and the mean flow using a spherical shallow-water model. The use of Hough harmonics as basis functions makes Rossby and Kelvin waves prognostic variables of the model and allows the quantification of terms contributing to their tendencies in physical and wave spaces. The simulations show that Kelvin waves are resonantly excited by interactions of Rossby waves and the balanced zonal mean flow in the subtropics, provided the Rossby and Kelvin wave frequencies, which are modified by the mean flow, match. The resonance mechanism is substantiated by analytical expressions. The Kelvin wave tendencies are caused by velocity and depth tendencies: The velocity tendencies due to the meridional advection of the zonal mean velocity can be outweighed by the zonal advection of the Rossby wave velocity or by the depth tendencies due to Rossby wave divergence. Identifying the resonant excitation mechanism in data should contribute to the quantification of Kelvin wave variability originating in the subtropics. Significance Statement This study seeks to understand how Kelvin waves, which are eastward-propagating disturbances in the tropical atmosphere, are connected to Rossby wave dynamics in the subtropics. Using idealized simulations, the Kelvin wave excitation is explained as a resonance effect due to interactions of Rossby waves and the zonal mean flow. The mechanism contributes to the understanding of atmospheric wave interactions and extratropical effects on the tropics. Further work searching for evidence of the new mechanism in atmospheric data may shed a new light on subseasonal variability in the tropics, such as the Madden–Julian oscillation.

Plasma response to pulsed ion acoustic wave excitation

Plasma response to pulsed ion acoustic wave excitation

Solving an internal problem for finite regular two-dimensional lattice spiral elements, excitable plate electromagnetic wave

Background. The work is aimed at developing and researching rigorous methods for solving internal problem of electrodynamics for multi-element structures (metastructures) consisting from the final number of elements, as well as to study the physical processes occurring in them. A special case of such structures are two-dimensional lattices with a fixed interelement distance, consisting of identical elements having the same spatial orientation (regular lattices). Aim. In this work, based on an iterative approach, the internal solution is solved. problems of electrodynamics for a finite regular two-dimensional lattice of spiral elements. In order to obtain a priori information about the electrodynamic characteristics of elements lattice and justification for the choice of projection function systems are analyzed spectral characteristics of the integral operator of the internal problem for a single spiral element. Then the currents on the structure elements are calculated, their spectral characteristics are determined. The results of spectral analysis allow increase the efficiency of solving an internal problem. Methods. The research is based on a strict electrodynamic approach, within the framework of which, for the specified structure in the thin-wire approximation, an integral representation of the electromagnetic field is formed, which, when considered on the surface of conductors together with boundary conditions, is reduced to a system of Fredholm integral equations of the second kind, written relative to unknown current distributions on conductors (internal task). The solution of the internal problem within the framework of the method of moments is reduced to solving a SLAE with a block matrix. Results. A mathematical model of a finite two-dimensional lattice of spiral elements is proposed radiating structure. For the specified structure, in the case of its excitation by a flat electromagnetic wave, based on the iterative approach, the internal problem of electrodynamics was solved. The following were carried out in a wide frequency range: analysis of the convergence of the iterative process, spectral analysis of the integral operator of the internal problem for a single spiral element, as well as spectral analysis of external field and current functions functions on lattice elements. Conclusion. The feasibility of determining the spectral characteristics of integral operators is shown internal task for the elements forming the metastructure. A relationship has been identified between the frequency dependence eigenvalues of the integral operator of the internal problem of single elements, forming a metastructure, with resonance phenomena arising in the metastructure, the influence of resonances on the convergence of the iterative process was confirmed. The feasibility of considering averaged amplitude current spectra is shown. It was revealed that the averaged spectrum of current functions is close to degenerate, especially near resonant frequencies. This allows for use as projection functions a compact set of eigenfunctions that have significant amplitudes in the vicinity of the frequency under study, which significantly simplifies the solution of the internal problem.

Hemodynamic cortical ripples through cyclicity analysis

Abstract A fine-grained understanding of dynamics in cortical networks is crucial to unpacking brain function. Resting-state functional magnetic resonance imaging (fMRI) gives rise to time series recordings of the activity of different brain regions, which are aperiodic and lack a base frequency. Cyclicity analysis, a novel technique robust under time reparametrizations, is effective in recovering the temporal ordering of such time series, collectively considered components of a multidimensional trajectory. Here, we extend this analytical method for characterizing the dynamic interaction between distant brain regions and apply it to the data from the Human Connectome Project. Our analysis detected cortical traveling waves of activity propagating along a spatial axis, resembling cortical hierarchical organization with consistent lead-lag relationships between specific brain regions in resting-state scans. In fMRI scans involving tasks, we observed short bursts of task-modulated strong temporal ordering that dominate overall lead-lag relationships between pairs of regions in the brain that align temporally with stimuli from the tasks. Our results suggest a possible role played by waves of excitation sweeping through brain regions that underlie emergent cognitive functions.

Application of Graphene in Acoustoelectronics.

An interdigital transducer structure was fabricated from multilayer graphene on the surface of the YZ-cut of a LiNbO3 ferroelectric crystal. The multilayer graphene was prepared by CVD method and transferred onto the surface of the LiNbO3 substrate. The properties of the multilayer graphene film were studied by Raman spectroscopy. A multilayer graphene (MLG) interdigital transducer (IDT) structure for surface acoustic wave (SAW) excitation with a wavelength of Λ=60 μm was fabricated on the surface of the LiNbO3 crystal using electron beam lithography (EBL) and plasma chemical etching. The amplitude-frequency response of the SAW delay time line was measured. The process of SAW excitation by graphene IDT was visualized by scanning electron microscopy. It was demonstrated that the increase in the SAW velocity using graphene was related to the minimization of the IDT mass.

Magnetic ordering and dynamics in monolayers and bilayers of chromium trihalides: atomistic simulations approach

We analyze magnetic properties of monolayers and bilayers of chromium iodide, \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {CrI}_3$$\\end{document}, in two different stacking configurations: AA and rhombohedral ones. Our main focus is on the corresponding Curie temperatures, hysteresis curves, equilibrium spin structures, and spin wave excitations. To obtain all these magnetic characteristic, we employ the atomistic spin dynamics and Monte Carlo simulation techniques. The model Hamiltonian includes isotropic exchange coupling, magnetic anisotropy, and Dzyaloshinskii-Moriya interaction. As the latter interaction is relatively weak in pristine \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {CrI}_3$$\\end{document}, we consider a more general case, when the Dzyaloshinskii-Moriya interaction is enhanced externally (e.g. due to gate voltage, mechanical strain, or proximity effects). An important issue of the analysis is the correlation between hysteresis curves and spin configurations in the system, as well as formation of the skyrmion textures.

ELECTROPHYSICAL CHARACTERISTICS OF TiO2 SAMPLES IRRADIATED WITH 0.12 MeV HELIUM IONS

The main parameters of samples irradiation on the linear helium ions accelerator are presented as well as of TiO2 irradiated characteristics. It is experimentally shown that with irradiation dose increasing, helium ion energy of 0.12 MeV, the volume electrical resistance and surface electrical resistances on the front and back sides of samples decrease, the loss angle tangents and relative dielectric permittivities increase. The primary processes, namely: the sputtering, ionization, phonons and vacancies formation, segregation, damage have been calculated. The analysis of experimental and calculated data has shown that a model based on processes of the excitation and propagation of elastic waves in a concept of the long-range effect most physically correctly describes the changes in electrophysical characteristics of the irradiated samples.

Modeling the Effects of a Light Bridge on Properties of Magnetohydrodynamic Waves in Solar Pores

Solar pores are ideal magnetic structures for wave propagation and transport of energy radially outwards across the upper layers of the solar atmosphere. We aim to model the excitation and propagation of magnetohydrodynamic waves in a pore with a light bridge modeled as two interacting magnetic flux tubes separated by a thin, weaker-field layer. We solve the three-dimensional magnetohydrodynamic equations numerically and calculate the circulation as a measure of net torsional motion. We find that the interaction between flux tubes results in the natural excitation of propagating torsional Alfvén waves but find no torsional waves in the model with a single flux tube. The torsional Alfvén waves propagate with wave speeds matching the local Alfvén speed where wave amplitude peaks.

SH guided wave excitation in rails for defect and stress monitoring

Monitoring rail defects and thermal stress is imperative in ensuring the safety of railway transportation. Guided-wave-based inspection techniques emerge as a promising solution for concurrently detecting both the defects and thermal stress in rails. However, the substantial multimodal and dispersive nature of guided waves in the rail poses limitations on the application and advancement of this technology. This study systematically investigates the propagation characteristics of the SH0-like wave (the lowest-order shear horizontal-like wave) in the rail and its effectiveness in defect and axial stress monitoring through finite element simulations and experiments. A method based on dual opposite polarization active elements, and the corresponding piezoelectric transducers are proposed to excite SH0-like wave in the rail web and rail foot. Results show that SH0-like wave can travel stably across a broad frequency range in the rail web and rail foot. Additionally, both the simulations and experiments confirm that the SH0-like wave in the rail web is suitable for monitoring axial stress, as its velocity changes linearly with axial stress variations. Furthermore, the ability of the SH0-like wave to detect cracks and hole defects in the rail web is experimentally demonstrated. Given that the SH0-like wave is quasi-nondispersive in a broad frequency range and an SH0-like wave with high SRN can be effectively generated using the proposed method, this research aims to offer a practical technical solution to overcome the challenges of multimodal and dispersive effects in the guided-wave-based rail inspection techniques. It also sets the stage for developing a comprehensive system capable of simultaneously monitoring the defects and thermal stress in rails.

Phonon-polariton Bragg generation at the surface of silicon carbide

Phonon-polaritons are known to emerge at the surface of solids under infrared (IR) irradiation at frequencies close to the optical phonon resonance. Metal, patterned on the top of the polariton-active surface, locally blocks the excitation of surface waves due to plasmonic screening and can be used for the design of wave patterns. We excite polaritonic waves at the surface of SiC under the irradiation of a CO2 laser (λ∼10μm) and visualize them using apertureless near-field interference scanning probe microscopy. From the near-field scans in the vicinity of gold film periodical strip structures, we identify the Bragg scattering (diffraction) outside the grating with the contribution from separate strips coherently summed up, provided that the wavelength matching condition is fulfilled. The observed phenomena agree with wavefield calculations. Our observations demonstrate the potential of metal-patterned silicon carbide for the fabrication of on-chip polaritonic IR circuits.

Tidal Spin-up of Subdwarf B Stars

Hot subdwarf B (sdB) stars are stripped helium-burning stars that are often found in close binaries, where they experience strong tidal interactions. The dissipation of tidally excited gravity waves alters their rotational evolution throughout the sdB lifetime. While many sdB binaries have well-measured rotational and orbital frequencies, there have been few theoretical efforts to accurately calculate the tidal torque produced by gravity waves. In this work, we directly calculate the tidal excitation of internal gravity waves in realistic sdB stellar models and integrate the coupled spin–orbit evolution of sdB binaries. We find that for canonical sdB (M sdB = 0.47 M ⊙) binaries, the transitional orbital period below which they could reach tidal synchronization in the sdB lifetime is ∼0.2 day, with weak dependence on the companion masses. For low-mass sdBs (M sdB = 0.37 M ⊙) formed from more massive progenitor stars, the transitional orbital period becomes ∼0.15 day. These values are very similar to the tidal synchronization boundary (∼0.2 day) evident from observations. We discuss the dependence of tidal torques on stellar radii, and we make predictions for the rapidly rotating white dwarfs formed from synchronized sdB binaries.

Parametric Excitation and Instabilities of Spin Waves Driven by Surface Acoustic Waves

AbstractThe parametric excitation of spin waves by coherent surface acoustic waves in metallic magnetic thin film structures is demonstrated experimentally using Brillouin light scattering spectroscopy. Complementary micromagnetic simulations and analytical modeling reveal that, depending on the experimental conditions, the spin‐wave instabilities originate from different phonon‐magnon and magnon‐magnon scattering processes. This opens novel ways to create micro‐scaled nonlinear magnonic systems for logic and data processing that profit from the efficient excitation of phonons using piezoelectricity.

Scotch yoke structure inspired piezoelectric-electromagnetic hybrid harvester for wave energy harvesting

This paper presents a piezoelectric-electromagnetic hybrid harvester for wave energy harvesting inspired by a scotch yoke structure for obtaining energy from irregular and low-frequency waves. Through simplification of the energy harvester model, the kinematic equations of the scotch yoke are established. One of the advantages of the harvester is that the wave energy can be harvested by an up-conversion mechanism, The piezoelectric transducer (PZT) and electromagnetic generator (EMG) transform the wave excitation into electricity, and by utilizing the frequency up-conversion mechanism, the PZTs’ harvesting efficiency is increased, the influencing factors of the output power of the harvester are explored by simulation and experimental studies, The results of the experiment demonstrate that this harvester could generate an ultimate output power of 286.36 mW at ultra-low frequency (1.4 Hz) operating frequency. This study offers a practical solution for harvesting low-frequency and disordered wave energy and makes significant progress in harvesting low-frequency and irregular wave energy.

Nonlinear harmonic resonant behaviors and bifurcation in a Two Degree-of-Freedom Duffing oscillator coupled system of Tension Leg Platform type Floating Offshore Wind Turbine

The surge-heave coupled motion model of a Tension Leg Platform type Floating Offshore Wind Turbine (TLP FOWT) is first established. By taking the tendons stretching and platform set-down motion into consideration, the nonlinear model is a Duffing oscillator coupled system. We analyze the nonlinear feature in the surge-heave coupled motions by the semi-analytical algorithms in nonlinear dynamics. The harmonic balance method is applied to obtain the analytical solutions of the nonlinear system under wind and wave excitations. The analytical solution verifies the excellent accuracy. To further achieve the heave motion response, we organize the bifurcation analysis and discuss the effects of the dynamic parameters on the heave responses. The results reveal the multi components of heave motion, which consist of constant, primary harmonic resonate and higher order harmonic resonate. In addition, the change of dynamic parameters has various effects on the response. The increment of wave load leads to the expansion of heave response, and an instantaneous expansion appear. Both linear surge and heave damping only affect the amplitudes of heave motion. The nonlinear surge stiffness and heave stiffness can barely affect the primary harmonic resonance amplitudes, but they present different effects on the higher order harmonic resonance component.

Nonlinear analysis of hydrodynamics of a shallow-draft floating wind turbine

AbstractThis study investigates numerically the dynamic responses of the T-Omega Wind novel concept of Floating Offshore Wind Turbine. The turbine is light-weight, has a shallow-draft and a relatively high centre of gravity that allows it to glide over harsh marine environments. The turbine responses are studied under regular wave excitation, considering most probable ranges of discrete sea wave heights and periods representative of real ocean conditions. A multibody virtual model is developed, simplified to a rigid 6 DOF system and experimentally validated in the state-of-art Marine Simulator to define the types of dynamical responses for both “Low” and “High” Sea States. The dynamics of coupled heave and pitch DOFs are evaluated with time histories, phase-plane portraits, Poincaré sections and FFT analyses to conclude that period-1 stable solutions exist for all studied cases of “Low Sea States”, whereas period-2, period-3 and period-4 periodic responses are identified for short wave periods of excitation under “High Sea States” conditions. Simulation results show that regions where period-1 responses exist are highly sensitive to wave height and can widen as the wave amplitude reduces. Finally, the turbines’ nonlinearities generated by the floats’ geometry are observed in this dynamical system, which are identified to be related to variation in float waterplane area and particularly observable for “High Sea States”.