Longitudinal Oscillations Research Articles

On Temperature Dependence of Longitudinal Electrical Conductivity Oscillations in Narrow-gap Electronic Semiconductors

On Temperature Dependence of Longitudinal Electrical Conductivity Oscillations in Narrow-gap Electronic Semiconductors

Evaluation of the vibration accelerations of drill bit for the well rotative-vibration drilling using the cavitation hydrovibrator

Cavitation hydrovibrator is one of the promising devices to intensify drilling of geological prospecting and production wells. Cavitation hydrovibrator transforms the stationary flow of drilling mud into a discrete-pulsed flow of increased power. The mud oscillating flow in hydrovibrator is converted into high-frequency (1,000 Hz - 20,000 Hz) vibrations of the drill bit. A method for determining the longitudinal vibrations of a drill string with bit has been developed. The method is based on the results of experimental studies of the dynamic interaction between longitudinal oscillations of the drilling string with rock massive by mathematical modeling this process with use of finite-element discretisation of drilling string. An obtained satisfactory convergence of the computed vibration accelerations of the drill bit and experimental data confirms the adequacy of the developed mathematical model and the ability with its help to determine the rational operational modes of the hydrovibrator.

Синтез закону оптимального керування одним класом об’єктів з параметрами, змінними у часі та просторі

The law of optimal control of one class of objects with parameters, variable in time and space, to which the crane electric drive system belongs, fragments in this electric drive system and change of characteristics of process of movement of cargoes in time caused by changes of the resulted moment of inertia of the electric drive system. the moment of loading during the movement of the load, and the influence of longitudinal oscillations that occur in the cable on which the load is suspended. As an optimization criterion, the functional in the form of an integral of the square of the deviations of the real angular velocity of the drive motor of the crane from its ideal trajectory is used. In synthesizing the law of optimal control, we used the mathematical model of load-moving processes of a crane created by us and published in our previous works, listed in the literature, the structure of which is constructed using as a normal differential equation with time-varying parameters. electric motor with the load moment and the reduced moment of inertia of the electric drive system and the differential equation in partial derivatives, which describes the process of longitudinal oscillations in the cable due to the mass of the load and the mass of the cable between the drum and the point of suspension. It is shown that the implementation of the synthesized law of optimal control of the electric crane drive achieves such characteristics of the cargo movement process that prevent the destruction of both cargoes and areas where these cargoes are installed, because the cargo movement process is carried out without their shock contacts due to longitudinal to which the load is suspended. An algorithm for the practical implementation of the synthesized law of optimal control of the crane electric drive system as a dynamic object with parameters variable in time and space is proposed.

Research into truck transmission torsion vibrations under longitudinal acceleration

The development of a modern motor vehicle is aimed at improving the performance in the field of dynamics (both longitudinal and lateral), economy, safety and ergonomic characteristics. Special attention is paid to passenger comfort. Torsional oscillations in transmission cause longitudinal vibrations of the vehicle, depending on inertial parameters, as well as on stiffness and damping of the transmission. Taking into account the complexity of the problem, it is estimated that it is useful to analyse the impact of the transmission design parameters on the longitudinal (fore and aft) vibrations of freight motor vehicle. For this purpose, the dynamic simulation method was used, and the analysis of the influence of certain constructive parameters on the longitudinal oscillations of the vehicle was performed using the sensitivity function.

Continual model and dynamic calculation of buildings under seismic impacts

Continuum plate model in the form of a cantilever anisotropic plate developed in the framework of the bimoment theory of plates describing seismic oscillations of buildings is proposed in this paper as a dynamic model of a building. Formulas for the reduced moduli of elasticity, shear and density of the plate model of a building are given. Longitudinal oscillations of a building are studied using the continuum plate and box-like models of the building with Finite Element Model. Numerical results are obtained in the form of graphs, followed by their analysis.

Erratum to: Identification of Cross-Section Defects of the Rod by Using Eigenfrequencies and Features of the Shape of Longitudinal Oscillations

Erratum to: Identification of Cross-Section Defects of the Rod by Using Eigenfrequencies and Features of the Shape of Longitudinal Oscillations

Evaluation of the vibration accelerations of drill bit for the well rotative-vibration drilling using the cavitation hydrovibrator

Cavitation hydrovibrator is one of the promising devices to intensify drilling of geological prospecting and production wells. Cavitation hydrovibrator transforms the stationary flow of drilling mud into a discrete-pulsed flow of increased power. The mud oscillating flow in hydrovibrator is converted into high-frequency (1,000 Hz - 20,000 Hz) vibrations of the drill bit. A method for determining the longitudinal vibrations of a drill string with bit has been developed. The method is based on the results of experimental studies of the dynamic interaction between longitudinal oscillations of the drilling string with rock massive by mathematical modeling this process with use of finite-element discretisation of drilling string. An obtained satisfactory convergence of the computed vibration accelerations of the drill bit and experimental data confirms the adequacy of the developed mathematical model and the ability with its help to determine the rational operational modes of the hydrovibrator.

Determination of Young’s Modulus by Specific Vibration of Basalt and Diabase

The elasticity is an important parameter for the evaluation of the mechanical behavior of a rock mass and a fundamental factor in the definition of the resistance characteristics, stability, and blastability in rock blasts, and it is an important parameter for the blastability equations like the Kuz–Ram method. This paper presents a comparison of the Uniaxial Compression Method (UCM) and the Impulse Excitation Technique (IET) in determining Young’s modulus. The IET is a static and nondestructive dynamic method of characterizing mechanical parameters of materials, while the UCM is a quasistatic and destructive method. We determined Young’s modulus of samples from nine basalt and diabase mines used as aggregates in the construction industry. Young’s modulus was determined by the acoustic response due to longitudinal oscillations caused by a mechanical impulse (IET) in the Sonelastic equipment and the stress‐strain curve (UCM). Young’s modulus values showed high repeatability and agreed with those reported in the literature for the same material. The work shows that the solnelastic is an innovate equipment and elucidated advantages of IET in comparison to the UCM such as shorter execution time, greater safety, and a lower cost ranging from 11.5% to 22.5% of the UCM.

A study of the influence deformation of the drilling riser on the longitudinal oscillations of the drill string

The article deals with the study of the effect of drilling riser transverse vibrations on the longitudinal vibrations of the drill string and the change of the dynamic component of weight on the bit when drilling wells from floating drilling vessel in deep sea conditions. The impact assessment was carried out by comparing the results of the simulation of the drilling system in the software based on the Modelica language. For this purpose, a simulation model has been created to enable the study of the operation of the «drill ship – riser wire tension system – drilling riser – drill string heave compensator – drill string» system in the case of irregular sea agitation obtained from decomposition the JONSWAP energy spectrum. The influence of the deformation of the drilling riser on the axial vibrations of the drill string is taken into account by introducing into the "classical" equation of the axial vibrations of the drill string the nonlinear term of the longitudinal-transverse strain. The drill string transverse deformation was determined based on the assumption that the axes of deformation of the drilling riser and drill string were coincident in the course of operation. A series of simulation experiments was carried out in the case from three to six WMO sea state code, absence of action of sea currents and active mode of work of the drill string heave compensator. The obtained results show that the greatest influence of the deformation of the drilling riser on the axial vibrations of the drill string is observed in the section at the level of the well head, where the amplitude of longitudinal vibrations increases up to 4 times. In general, the deformation of the drilling riser causes the growth of the dynamic impact factor of weight on the drill bit to increase by 4-7% for the investigated structure of the drilling system.

Simultaneous longitudinal and transverse oscillations in filament threads after a failed eruption

Context. Longitudinal and transverse oscillations are frequently observed in the solar prominences and/or filaments. These oscillations are excited by a large-scale shock wave, impulsive flares at one leg of the filament threads, or due to any low coronal eruptions. We report simultaneous longitudinal and transverse oscillations in the filament threads of a quiescent region filament. We observe a large filament in the northwest of the solar disk on July 6, 2017. On July 7, 2017, it starts rising around 13:00 UT. We then observe a failed eruption and subsequently the filament threads start to oscillate around 16:00 UT. Aims. We analyse oscillations in the threads of a filament and utilize seismology techniques to estimate magnetic field strength and length of filament threads. Methods. We placed horizontal and vertical artificial slits on the filament threads to capture the longitudinal and transverse oscillations of the threads. Data from Atmospheric Imaging Assembly onboard Solar Dynamics Observatory were used to detect the oscillations. Results. We find signatures of large-amplitude longitudinal oscillations (LALOs). We also detect damping in LALOs. In one thread of the filament, we observe large-amplitude transverse oscillations (LATOs). Using the pendulum model, we estimate the lower limit of magnetic field strength and radius of curvature from the observed parameter of LALOs. Conclusions. We show the co-existence of two different wave modes in the same filament threads. We estimate magnetic field from LALOs and suggest a possible range of the length of the filament threads using LATOs.

Complex frequency characteristic and Green’s function for cantilever beam under longitudinal oscillations

Relevant objective of this article is elaboration of methods of efficient determination of the dynamic characteristics of the materials both within the framework of well-known and classical models as well as within the advanced ones in the context of interaction with the environment under the impact of external dynamic loads. In the present work free and forced oscillations are studied with a help of spectral methods what allows to compare theoretical results with experimental data, obtained by other authors. The key point of the work is theoretical determination of the proper functions of the oscillatory system, its frequency characteristic using Green’s function. We examine longitudinal oscillations, caused by the substitute load, which provokes oscillations of a sound spectrum. Univariate character of the task is determined by the linearity organization of the longitudinal oscillations of a beam. The oscillations are modeled with a help of the substitute load, which is a subject to Dirac impulse function, which belongs to a class of generalized functions. The obtained solution makes it possible to use the proposed approach in order to determine frequency characteristics in the acoustic spectrum, taking into account that the oscillations are included in a full frequency spectrum and can be used for an adequate valuation of the possibility of the appearance of resonance phenomena.

Identification of Cross-Section Defects of the Rod by Using Eigenfrequencies and Features of the Shape of Longitudinal Oscillations

A method is proposed for solving inverse flaw detection problems for rods performing longitudinal oscillations. Based on the modeling of the cross-sectional defect as a known function, the main parameters characterizing it, such as the location and volume of the two lowest oscillation frequencies of the free and cantilevered rods, will be approximately determined. Using numerical simulations, it is shown that to satisfactorily determine the properties of a defect, it is sufficient to use several lower frequencies. A method for identifying a defect by one lowest frequency of a free rod is also proposed, provided the known location of the defect is applied, for which it is necessary to determine the characteristics of the oscillation modes. The results of an experimental study are presented.

Improving the Quality of Transmission Shifting Transients Due to Controlling Torque Redistribution

It is known that low-frequency torsion oscillations in the transmission, corresponding to the first one-node Eigen mode, are observed in the transient processes of starting from standstill and gear shifting. The power of these oscillations is sufficient to excite the longitudinal oscillations of the vehicle body (up to 2 ... 4 m/s2). Therefore, the problem of the scientific substantiation and development of new algorithms for controlling transient processes in the powertrain unit of the vehicle after locking friction elements of the shifted gear is actual. In the research the dynamic processes in powertrain of the vehicle are investigated numerically and experimentally. The development of the algorithm is based on the implementation of power redistribution of the control input. The control function is developed for a specific dynamic state of the system in accordance with the engaged gear and scheme of the driving axes switching (rear/forward/all). As a result of numerical simulation of the dynamic process, it was found that effectiveness of the proposed control system algorithm is determined by a complex of the transient process parameters - overshoot, response rate and robustness. In this case, Zero vibration derivative (ZVD) algorithm provides the highest efficiency in overshoot with acceptable response rate and robustness. From response rate point of Zero vibration (ZV) algorithm is the best solution. When the frequency of single-node Eigen mode is equal 4 Hz or above it is sensible to use the Ramp algorithm. Application of suggested algorithms of power control redistribution considering modal properties of the system allows to decrease dynamic loads in the powertrain and to increase comfortableness of the vehicle.

Numerical investigation of plasma heating during the entrance of an intense short laser pulse into a density profile

In this paper, plasma heating is numerically investigated using a 1D-3V particle-in-cell simulation code through the interaction between an intense short laser pulse with temporal duration, , and a plasma having a slightly overcritical bulk density and an exponential pre-plasma density profile. The aim is to identify, via suitable parametric analysis, the most relevant nonlinear mechanisms as a function of the system parameters. As key points of our research, simulation results revealed that, for pulse-lengths less than the local nonlinear plasma wavelength, , mechanisms such as vacuum–plasma interface wave-break and longitudinal plasma oscillations are the dominant mechanisms for the initiation of electron acceleration and plasma heating at earlier times. Further, for variable density scale lengths our results have proven that the heating mechanisms mentioned above can be ignored for the laser intensities less than a specific threshold value, , even for short density scale length, . Meanwhile, by increasing the laser intensity to higher values, it is observed that the trend of the time history curve for the mean temperature changed in a way that the total level of temperature increased. Also, by lengthening the scale length, at first the amounts of the mean temperature curve increased, and then smoothly decreased.

Solution of model boundary value problems on oscillations of mechanical systems with moving boundaries by the duhamel method

The Kantorovich – Galerkin method in conjunction with the Duhamel method is considered as applied to solving problems describing the oscillations of visco–elastic objects with conditions on moving boundaries. The mathematical formulation of the problem includes an inhomogeneous partial differential equation with respect to the desired displacement function, inhomogeneous boundary and initial conditions. By introducing a new function into the problem, the boundary and initial conditions are reduced to homogeneous. The solution is made in dimensionless variables with an accuracy of the second order of smallness with respect to small parameters characterizing the velocity of the boundary and viscoelasticity. Using the Kantorovich – Galerkin method and the Duhamel method, an approximate solution of the problem of forced longitudinal oscillations of a viscoelastic rod of variable length is found.

A longitudinal magnetoelastic wave in a rod with account of the damage of its material

For an electrically conducting rod that performs longitudinal oscillations, a self-consistent system is formulated that includes the equation of rod dynamics, the equation for the variation of the strength of the external magnetic field, and the kinetic equation for the accumulation of damages in the material of the rod. The linearized system and the system of equations, including geometrical and physical elastic nonlinearities, are consecutively considered. It is shown that the waves described by linearized system have dispersion and frequency-dependent damping due to the presence of two types of dissipation, one of which is caused by the damage of the material and the other by a magnetic field. In nonlinear case, an evolution equation is derived that generalizes the Burgers equation, known in nonlinear wave dynamics. Its solutions are found and analyzed.

Damping Mechanisms of the Solar Filament Longitudinal Oscillations in the Weak Magnetic Field

Abstract Longitudinal oscillations of the solar filament have been investigated via numerical simulations continuously, but mainly in one dimension, where the magnetic field line is treated as a rigid flux tube. Whereas those one-dimensional (1D) simulations can roughly reproduce the observed oscillation periods, implying that gravity is the main restoring force for filament longitudinal oscillations, the decay time in 1D simulations is generally longer than in observations. In this paper, we perform a two-dimensional (2D) nonadiabatic magnetohydrodynamic simulation of filament longitudinal oscillations, and compare it with the 2D adiabatic case and 1D adiabatic and nonadiabatic cases. It is found that, whereas both nonadiabatic processes (radiation and heat conduction) can significantly reduce the decay time, wave leakage is another important mechanism to dissipate the kinetic energy of the oscillating filament when the magnetic field is weak so that gravity is comparable to Lorentz force. In this case, our simulations indicate that the pendulum model might lead to an error of ∼100% in determining the curvature radius of the dipped magnetic field using the longitudinal oscillation period when the gravity to Lorentz force ratio is close to unity.

Coupling Instability of a Warm Relativistic Electron Beam with Ion-Channel Guiding

In this paper, the coupling instability of warm relativistic electron beam (WREB) propagating through the ion channel guiding is investigated in detail. Obtaining the equilibrium state of the system by considering the self-electric and azimuthal magnetic field, the fluid-Maxwell equations as well as linear perturbation theory are employed to derive the dispersion relation of the excited modes in the system. Numerical analysis of the obtained dispersion relation shows that the electromagnetic (EM) instability can be induced nearly the center of the beam through coupling between the fast electron plasma wave (FEPW), originated from the longitudinal oscillation of WREB, and fast forward electromagnetic wave (FFEW). In this sense, growing the perturbation amplitude occurs due to transport the kinetic energy of WREB to the EM wave at the specific frequency range, where the phase velocity of FEPW and FFEW is coincided. The results of the present investigation will greatly contribute to the understanding of the stability of the warm relativistic electron beam in laboratory experiments, such as in free electron laser experiments, where the ion-channel guiding is used to confine the electrons against the self-repulsive forces generated by the beam itself.

Feedback in Plasma Maser

A change in the operation mode of a plasma maser with a pulse duration of 40 ns from a noise amplifier to a feedback self-oscillator at a power level of up to 10 MW has been experimentally demonstrated for the first time. In the noise-amplifier mode, the radiation power is distributed almost uniformly in a frequency range from 3 to 9 GHz. In the self-oscillator mode, the emission spectrum contains characteristic frequencies of longitudinal oscillation modes of plasma—beam cavity.

Impact of piezoelectric fields on coherent zone-folded phonons in GaAs/AlAs superlattices

The amplitude decay of folded longitudinal acoustic phonon oscillations in GaAs/AlAs superlattices grown in the [100] and [111] directions is studied as a function of carrier excitation density. Time-resolved pump-probe measurements in reflection reveal decay times on the order of several tens of picoseconds, which are independent of the excitation density for all phonons in the [100] sample and for phonons at wave vectors $q\ensuremath{\ne}0$ in the [111] sample. In contrast, the decay time increases with carrier density for the phonon at $q=0$ in the [111] sample. This phonon couples to the photoexcited electron-hole plasma via the piezoelectric interaction. Friction in the carrier plasma induces a damping of the phonon oscillations. The impact of the piezoelectric phonon-electron coupling on the amplitude decay is reduced by screening at high carrier density, resulting in longer phonon decay times.