Elastic Vibration Research Articles

Исследование различных подходов к управлению двухмассовыми объектами

The reasons for elastic oscillations occurring in the mechanisms of multi-mass objects are considered. Various control systems for complex two-mass objects are analyzed. A mathematical description of a twomass system interconnected through an elastic drive belt is provided. According to the given system of equations, a block diagram of the object under consideration has been constructed in the mathematical environment of MatLab and Simulink. The synthesis and comparative analysis is conducted for the following control systems for a two-mass object: slave control with external feedback on the speed of the first mass; multiloop slave regulation; modal control; subordinate regulation using a correction factor and a neurocontroller with a reference model. The resulting graphs of transient processes in terms of moment and speed of the driven pulley of the considered twomass system with an elastic replacement belt are presented and analyzed. The simulation results have shown that control systems with a modal controller and a neurocontroller show good results in the problem of damping elastic vibrations of a two-mass system in comparison with other considered control systems.

INVESTIGATION OF THE PASSAGE OF VIBRATIONS THROUGH A FIXED SECTION OF AN ELONGATED PLATE CAUSED BY THE ACTION OF THE AXIAL FORCE AT THE END

A method has been developed for the experimental study of forced elastic vibrations of a cantilevered thin-walled structural element in the form of a rod-strip, excited due to the passage of vibrations through the section of a finite length fixed along one of the surfaces caused by axial loading by a harmonic force applied to the end of the fixed section. The experimental dependence of the amplitude values of the vibration accelerations of the point at the end of the console on the frequency of the excited bending vibrations of the end of the rod is obtained, indicating the passage of vibrations through the fixing section of the finite length, which occurs due to the transformation of longitudinal vibrations in the loading zone into longitudinal-transverse-shear vibrations of the rod-strip in the fixing zone, followed by their transformation into predominantly bending vibrations of the cantilever part of the rod. For the theoretical study of the described phenomenon, a transformational model of deformation of the rod-strip is constructed, taking into account the deformability of the fastening section of finite length on the basis of the refined model of S. Timoshenko. The cantilever part of the rod is represented by the classical Kirchhoff-Love model, taking into account geometric nonlinearity in determining axial deformations. The kinematic conditions of coupling of the fixed and cantilever parts of the rod are formulated. On the basis of the Hamilton-Ostrogradsky variational equation, the equations of motion of the non-fixed and fixed parts of the rod, as well as the boundary conditions for them and the force condition of conjugation of the marked parts of the rod are obtained. Numerical experiments have been carried out for a rod-strip made of aluminum alloy D16AT, showing a noticeable passage of vibrations through the fixing section of the final length into the cantilever part of the rod with a decrease in the dynamic shear modulus of the material to a certain value.

Influence of Short Wave Irregularity on Elastic Vibration Characteristics of ATP Antenna Beam of High-speed EMU

Influence of Short Wave Irregularity on Elastic Vibration Characteristics of ATP Antenna Beam of High-speed EMU

Mathematical modelling of elastic vibrations arising from four-body impact interaction

This paper presents a mathematical model of elastic vibrations arising from shock interaction in a four-body system. The resulting model has two applications: the study of linear elastic interaction and the study of nonlinear elastic interaction. The linear elastic body model is presented in analytical form. In the transition to nonlinear interaction, it is difficult to represent the model in analytical approximation. The application of numerical algorithms has made it possible to obtain solution of a nonlinear problem with a specified accuracy sufficient for the simulated process. The model is intended for the description of the behavior of the device for measuring the modulus of elasticity of soil by the stamp method. An algorithm is developed to obtain the displacement and acceleration of the falling load and the loading die. Under laboratory conditions, an experiment with a test rig capable of measuring the acceleration of a loading die during shock-elastic interaction with the falling load is conducted. The measuring part is a three-axis accelerometer sensor connected to a four-channel analog-digital converter, which transmits the data to a mobile device with the developed specialized software. The sampling frequency of the measuring system is 12 kHz for each of the four channels. Polyurethane was used as a nonlinear element of the system, the approximate stiffness of which was determined experimentally by measuring deformations under a given load. When comparing the experimental results with the simulation results, the numerical model parameters were optimized by an algorithm based on gradient descent, which was based on maximizing the correlation coefficient between the theoretical and experimental data.

Numerical study on the effect by the structural characteristics of carbody shell faces on elastic vibrations of railway vehicle carbodies

Numerical study on the effect by the structural characteristics of carbody shell faces on elastic vibrations of railway vehicle carbodies

Сенсорні системи з оптичним відгуком

This paper is a review of the scientific works of the co-authors. In the paper, the basic principles of action of sensor systems with optical response of two types are considered. In particular, two spectroscopic technologies for probing some objects or events in non-living (synthetic) or biological environments are considered. In the first part of the work, sensor technologies related to the use of probes with optical response specially introduced into the sensor system are analyzed. As a rule, these probes are specially developed systems, the spectral properties of which change significantly under interaction with the object of probing. In the first part of the work, sensors of the first type are considered. In particular, the main ideas used in this type of sensors are given and specific examples of the use of such sensors are analyzed: specially created molecules that have a low fluorescence quantum yield due to a significant number of mechanical intramolecular degrees of freedom. The intercalation of such probes to large biomolecules leads to a change in the spectral characteristics of these probes, in particular, to a significant increase in fluorescence (up to 1000 times). The case of two-photon absorption of molecular probes in the transparency window of biological tissues is examined. Semiconductor and metal nanoparticles whose absorption and fluorescence spectra depend on their sizes were also proposed as probes of the first type (as sensors of elastic vibrations of the environment).The second part of the paper is devoted to the mechanisms of autosensing (the case when the medium's own optical centers are used to detect processes occurring in biological or synthetic systems). The main ideas that underlie the operation of sensors with optical response of this type were analyzed, and examples of such use were also given. In particular, the use of the own spectral properties of biomacromolecules and some coenzymes for changes in the external environment is considered. The use of the optical response of synthetic macromolecules on the value of their molecular weight was also analyzed.

Wave technologies for intensifying oil and gas extraction for fields at a late stage of development

One of the promising areas of research in the field of increasing oil recovery from reservoirs is the study of the influence of elastic vibrations on the productive reservoir. Research on the influence of elastic vibrations on stagnant oil zones in an oil reservoir in order to increase the oil recovery factor is at an early stage. The purpose of this work is to evaluate the effectiveness of using one of the wave methods to increase oil recovery. theoretical and experimental studies of the influence of elastic vibrations on changes in the parameters of the bottomhole zones of the formation and, as a consequence, increasing the productivity of oil wells and the oil recovery factor in oil fields. The work will analyze the wave method of influencing reservoir systems, such as acoustic, and evaluate the effectiveness of this method on changing the characteristics of the reservoir system. The work will conduct various studies on the practical application of wave methods. The effect of the wave method on the components and viscosity of heavy crude oil will also be studied. The proposed wave action creates the opportunity to exploit fields at later stages of development, which are characterized by a high content of asphaltenes, resins and paraffins. The results of the wave impact confirmed the effectiveness of this technology, which made it possible to double the turnaround time.

Влияние структурного состояния на упругие и микропластические свойства алюминиевого сплава AД1

The results of a study of aluminum alloy AD1 in four structural states before and after severe plastic deformation are presented. Both the initial coarse-grained state (supply state) and three fine-grained states, which differ from each other in the method of obtaining, are considered. Elastic and microplastic properties (modulus of elasticity, decrement of elastic vibrations, microplastic deformation) were determined by the acoustic method of a composite vibrator. It is shown that the modulus of elasticity changes to a large extent under the influence of the evolution of internal stresses; the attenuation of ultrasound after severe plastic deformation increases due to an increase in the area of grain boundaries. Key words: AD1 aluminum, modulus of elasticity, microcrystalline aluminum, decrement of elastic vibrations, microplastic deformation.

A novel vibration analytical model for thin-walled box-like long cylindrical structures combining elastic plates and straight and curved beams

This paper proposes a novel analytical model for elastic vibrations of thin-walled box-like long cylindrical structures, commonly observed in railway vehicle carbodies, aircraft, and buses. Here, we focus on railway vehicle carbody, where three-dimensional elastic vibrations are a significant problem for improving ride quality. The carbody is modeled as a box-like structure consisting of elastic plates and beams. The condition to connect those structural members is satisfied by introducing artificial springs at their joints. From observations of some actual carbody's elastic vibration modes, it has already been found that the relative vertical deformation between the roof and floor interacts with lateral deformation of side structures. To express this three-dimensional deformation simply, the authors introduce curved elastic beams as pillars in the side structures in this study; therefore, the newly proposed model is called the curved box model. The free vibration of the curved box model has been investigated in this paper by applying the Ritz method to derive the eigenvalue problem. The modal characteristics (natural frequencies and mode shapes) of elastic vibrations are calculated. The vibration analysis procedure is validated by comparing those results with those obtained from a finite element model. As some numerical examples, the effects of cross-sectional shape changes on the natural frequencies of elastic vibration modes are presented.

A novel vertical elastic vibration reduction for railway vehicle carbody based on minimum generalized force principle

Aiming at the vertical elastic vibration reduction of a railway vehicle carbody, the traditional technology mainly focuses on the design of modal frequency, the method of increasing damping and the design of dynamic vibration absorber (DVA), with little attention to the design of modal shape. In this paper, a novel vertical elastic vibration reduction method based on the minimum generalized force principle (MGFP) is proposed, i.e., the vertical elastic vibration of carbody is reduced by adjusting its own parameters (weight distribution and stiffness distribution) to control the first-order vertical bending (FVB) modal shape nodes to the carbody–bogie interface positions. Firstly, to better apply MGFP, a factor called generalized force factor (GFF) that can determine the level of generalized force (GF) is proposed. By improving theoretical model of a railway vehicle carbody, the traditional uniform cross-section Euler–Bernoulli beam (UCEB) is replaced by variable cross-section Euler–Bernoulli beam (VCEB) model, and the influencing factors of modal frequency and modal shape node locations can be investigated by the VCEB model. Then, the vertical vehicle system dynamics model is established based on the VCEB carbody model, and the influence of weight distribution, stiffness distribution and carbody–bogie interface positions on the elastic vibration is analyzed under a sweep frequency signal and track irregularities. Finally, the vibration reduction method is verified by a full-scale roller rig test. The theoretical analysis and experimental results show that: by changing the weight distribution or stiffness distribution of the carbody, the FVB modal shape node locations can be effectively controlled, and then combined with the design of carbody–bogie interface positions, the vertical bending elastic vibration of the carbody can be reduced. The vibration reduction method proposed in this paper can be applied to the design of new carbodies or the layout optimization of carbody subsidiary mass.

Aeroelastic Behavior of Long Blades of Last Stage of a 220 MW Steam Turbine

The phenomenon of flutter in steam turbines is quite rare, but when it occurs, the risk of damaging the blades and putting the whole unit out of service increases significantly. Currently, there is a tendency to increase the length of the blades of the last stages of powerful steam turbines, as a result of which the amplitude-frequency characteristics of the blade oscillations change, which can lead to the occurrence of uncontrolled self-excited oscillations. The paper presents the results of a numerical analysis of the aeroelastic characteristics of blade row of the last stage rotor of a 200 MW steam turbine, in which, during modernization, the length of the blades increased to 1200 mm, which made it necessary to check the resistance to flutter in operating modes. The analysis used the method of solving the coupled problem of unsteady aerodynamics and elastic blade vibrations, which allows to predict the amplitude-frequency spectrum of unsteady loads and blade vibrations in a viscous gas flow. The results of the calculations showed the absence of flutter and self-oscillations on the first five natural forms of blade oscillations in the nominal mode of operation of the steam turbine.

Numerical analysis of wave propagation and vibration attenuation effects of periodic scattering piles in unsaturated poroviscoelastic ground

ABSTRACT The elastic wave propagation and vibration attenuation zones for periodically scattering piles in unsaturated ground were investigated using Finite-Element Method (FEM) and Bloch periodic theory. The unsaturated ground was modelled by unsaturated poroviscoelastic medium with the weak form governing equations derived from the mass and momentum conservative equations using Galerkin method and Fourier transform. The quadratic polynomial eigenvalue equations for the unsaturated medium were obtained using the Bloch periodic theory, and solved by FEM for the complex eigenvalues to evaluate the band gaps of the pile-soil system. The eigenvalue bands combined with the frequency response function were used to analyse the mitigation effects of piles in unsaturated ground with different soil properties and piles parameters. This research found that the pile-soil system has three propagational waves, in which the shear wave and the slow longitudinal wave carry low-frequency vibrations that undermine the attenuation effects of the piles barrier. The increasing soil saturation degree affects the attenuation effects by reducing the soil modulus and increasing the fluid content. And both of those two mechanisms reduce the frequency of the attenuation zones (AZ), which improves the low-frequency vibration attenuation, and reduces the width of AZ that could reduce the vibration mitigation effects.

Dynamics of the Rotor System of a Vibrational–Centrifugal Separator with an Elastic Vibration Limiter

Dynamics of the Rotor System of a Vibrational–Centrifugal Separator with an Elastic Vibration Limiter

Algorithm for Damping Elastic Vibrations of a Distributed System with an Excessive Number of Sensor-Actuator Pairs

Algorithm for Damping Elastic Vibrations of a Distributed System with an Excessive Number of Sensor-Actuator Pairs

Attitude Stabilization of Rocket Elastic Vibration Based on Robust Observer

This paper proposes an approach to suppressing the elastic vibration and propellant sloshing in attitude control of a high slenderness ratio rocket. The main method is to combine a variable-gain robust observer with a variable structure controller for the purpose of attitude stability and elastic vibration suppression. A variable-gain robust observer is designed to reconstruct the attitude variable and complex multi-order elastic state. In this way, each order elastic vibration can be transformed into an additional attitude with the attitude characteristics of the rocket, which is easy to control. The reconstructed rocket body with an additional attitude is treated as the input of the designed variable structure controller to output the control signal. Under the simultaneous action between the variable-gain robust observer and variable structure controller, attitude stability is achieved for the rocket considering multi-order elastic vibration, and the propellant sloshing in the launch vehicle storage tank can be suppressed simultaneously. According to the simulation results, the proposed method produces a satisfactory stabilization outcome on each order of elastic vibration (especially low-order elastic vibration) and is better than a single variable structure controller.

Review and prospects of metamaterials used to control elastic waves and vibrations

Acoustic metamaterials, artificial composite structures with exotic material properties used to control elastic waves, have become a new frontier in physics, materials science, engineering and chemistry. In this paper, the research progress and development prospect of acoustic metamaterials are reviewed. Related studies on passive acoustic metamaterials and active acoustic metamaterials are introduced and compared. Additionally, we discuss approaches to material structure design, including topology optimization approaches, as well as bio-inspired and fractal geometry-based approaches to structure design. Finally, we summarize and look forward to the prospects and directions of acoustic metamaterial research. With the development of additive manufacturing technology, the research potential of acoustic metamaterials is huge.

Experimental Consideration on Suppression Effect of Elastic Vibration in Electromagnetic Levitation System for Flexible Thin Steel Plate with Curvature

Recently, research on non-contact conveyance systems using electromagnetic levitation technology has accelerated. We have constructed an electromagnetic levitation control system that keeps the relative distance between the electromagnet and steel plate constant. To investigate the levitation stability of thin steel plates, we performed magnetic levitation experiments on a thin steel plate with curvature. A physical disturbance was applied to the electromagnet units by vibrators. The electromagnet units were vibrated up and down by a vibrator. We investigated whether the bending magnetic levitation improved the levitation performance even if the magnetic levitation system was in a vibrating environment. We determined that it was possible to realize stable levitation for a steel plate under external disturbances during levitation at the optimal bending angle.

Modal properties of fractal sympodial trees: insights and analytical solutions using a group tree modeling approach

This study examines the intricate relationship between the hierarchical architecture of fractal trees and their dynamic properties, namely modal frequencies and mode shapes. It focuses on idealized sympodial trees under small, linear elastic lateral vibrations. This study proposes a group tree modeling approach that condenses the branches into simple structures, reducing the complexity of the model as appropriate. With the aid of a renormalization technique, the analysis proves that the sympodial tree is characterized by two families of vibration modes, i.e., the “emerging” and the “self-similar” modes. It further shows that the sympodial tree inherits all modes from the previous tree order (i.e., fractal level). Crucially, these inherited modes are self-similar, and beneficial in mitigating the vibration of the trunk by localizing the vibration of the tree at higher order branches. The study derives recursive closed-form solutions for both self-similar modal frequencies and mode shapes. Further, the analysis of sympodial trees with infinite tree order shows that their modal frequencies converge to stable values as the tree order increases. Accordingly, the study proposes analytical formulas to estimate these frequency limits from the fractal parameters of the sympodial trees. Results reveal that the natural frequency of a sympodial tree with infinite tree order and infinite branching number approaches asymptotically to that of a branchless tree. The proposed approach is then validated with numerical simulations and compared with independent studies. These findings are promising towards new bio-mimicking design concepts for civil engineering structures with improved dynamic behaviour.

Visual Servoing of Flexible-Link Manipulators by Considering Vibration Suppression Without Deformation Measurements.

Visual servoing and vibration suppression of spatial flexible-link manipulators with a fixed camera setup are addressed in this article. The singular perturbation method is adopted to decouple the dynamic equations of the flexible manipulator; hence, two subsystems that represent the rigid robot motion and flexible-link vibration are obtained, respectively. Then, for the slow subsystem related to the rigid motion, an image-based controller is designed to converge the image errors with the consideration of compensating for the errors of approximating the Jacobian matrix. For the fast subsystem corresponding to the elastic vibration, to eliminate the requirements of measuring the vibration states, an observer is designed to estimate the fast states and then a feedback controller of the fast subsystem is presented to suppress the vibration of the flexible manipulator by using the estimation values. The closed-loop stabilities of the slow and fast subsystem are both proved by employing the Lyapunov theory. Numerical simulations demonstrate the effectiveness of the proposed controller, which shows that the image errors approach zero with the vibration of the flexible manipulator damped out simultaneously.

Free damping vibration of functionally graded porous viscoelastic nonlocal microbeam with thermal effect

Combining classic Kelvin–Voigt viscoelastic model and two-phase local/nonlocal integral models (TPNIM), two-phase local/nonlocal integral viscoelastic models (TPNIVM) are proposed to study the free thermo-damping vibration of functionally graded porous microbeam with four different porous distribution patterns. The differential governing equations, boundary conditions, and constitutive constraints are formulated. The axial stress due to environmental temperature variation is derived explicitly. Several nominal variables are introduced to simplify the mathematical formulae. Laplace transformation is applied to obtain the explicit expression for bending deflection and moment. On considering the boundary conditions and constitutive constraints, a complex coefficients nonlinear equation is obtained to determine the complex characteristic frequency. A two-step numerical method is proposed to solve the elastic vibration frequency and damping ratio. The influence of nonlocal parameters, porous distribution parameters, and environmental temperature variation on the elastic vibration frequency and damping ratio is investigated numerically for different boundary conditions. The numerical results show that, under different boundary conditions, the compressive thermal stresses lead to the decrease of nominal vibration frequencies, and the increase of critical viscos coefficient and the damping ratio. With the increase of and the decrease of , the damping ratio increases and decrease for strain-driven (εD) and stress-driven (σD) nonlocal models, respectively.