Vibrations Of Mechanical Systems Research Articles

Hydraulic elements in reduction of vibrations in mechanical systems

This work presents non-classical method of design of mechanic systems with subsystem reducing vibrations. The purpose of this paper is also introduces synthesis of mechanic system with reducing vibrations understand as design of this type of systems. The synthesis may be applied to modify the already existing systems in order to achieve a desired result. Elements which reduce vibrations can be constructed with passive, semi-active or active components. These considerations systems have selected active items. A hallmark of active elements it is possible to change the parameters on time of these elements and their power from an external source. The implementation of active elements is very broad. These elements can be implemented through the use of components of electrical, pneumatic, hydraulic, etc. The system was consisted from mechanical and hydraulic elements. Hydraulic elements were used as subsystem reducing unwanted vibration of mechanical system. Hydraulic elements can be realized in the form of hydraulic cylinder. In the case of an active vibration reduction in the form of hydraulic cylinder it is very important to find the corresponding values of hydraulic components. The values of these elements affect the frequency of vibrations of this sub-system which is related to the effective vibration reduction [7,11].

Global Cooperative Control Framework for Multiagent Systems Subject to Actuator Saturation With Industrial Applications

This paper proposes a global cooperative control framework to address leader-follower consensus of constraints subsystems of industrial plants, in which each subsystem is modeled as an agent and all the subsystems and networks of information flow construct a multiagent system. The focus of this paper is to solve the global leader-follower consensus for multiagent systems with input saturation via low-high gain feedback approach and parametric algebraic Riccati equation approach, in which the feedback gain design is distributed and decoupled from network topologies. By introducing appropriate assumptions, a class of low-high gain feedback protocol is designed based on the states of local neighbors to reach the global stability. It is proved in the sense of Lyapunov that, if the dwell time is larger than a positive threshold, the global leader-follower consensus for the closed-loop linear multiagent systems with input saturation under the derived topology containing a directed spanning tree can be achieved. The results are further extended to leader-follower consensus for nonlinear multiagent systems with the design of nonlinear low-high gain feedback protocol. As industrial applications of the proposed low-high gain scheduling approaches, the controller design of vibration in mechanical systems and satellite formation systems are revisited. Numerical simulations with cooperative control of industries subsystems show the effectiveness of the proposed approach.

Vibrations of mechanical systems with energy dissipation hysteresis

A phenomenological approach which we refer to as kinematic is proposed to describe hysteresis; according to this approach, the force and kinematic parameters of a mechanical system are related by a first-order ordinary differential equation. The right-hand side is chosen in the class of functions ensuring the asymptotic approach of the solution to the curves of the enveloping (limit) hysteresis cycle of steady-state vibrations. The coefficients of the equation are identified by experimental data for the enveloping cycle. The proposed approach permits describing the hysteresis trajectory under the conditions of unsteady vibrations with an arbitrary starting point inside the region of the enveloping cycle. As an example, we consider the problem on forced vibrations of a pendulum-type damper of low-frequency vibrations.

On establishing equations of motion of mechanical vibration systems placed on moving bases

The first author has been teaching the postgraduate course, “The Dynamics of Mechanical Systems” in The ITU Faculty of Mechanical Engineering for nearly 20 years. He has observed that students frequently have problems in obtaining the equations of motion of the vibrating systems which were placed on moving bases. Starting from this observation, he has found that the homework stated below, which was given to the students occasionally, was very helpful in learning the subject. The main idea of the homework is the derivation of the equations of motion, with the help of formulating the Lagrange’s equations with respect to a moving set of axis for a vibration system with two degrees of freedom which consists of a horizontal table rotating with a constant angular velocity around a vertical axis. The students were also asked to solve the same problem with a different method of their choice and to determine the reaction forces as well. We want to share this problem with the reader, which we have assessed as very instructive and appropriate from the viewpoint of applicability of different methods.

Broadband signal response of thermo-acoustic devices and its applications.

Thermo-acoustic (TA) transducers are generation of sound speakers without any mechanical vibration system which exhibit an extremely wide frequency response range. In this paper, acoustic field responses to broadband input signals applied to both free-standing and nano-thinfilm-substrate thermo-acoustic devices are developed theoretically by using the Fourier transformation. A series of signals, including single-frequency signal, square root signal, periodic triangle wave signal, and periodic rectangular pulse signal, are applied to these TA devices in simulations and the acoustic pressure responses are investigated. The reproducibility of input signals is predicted. The single frequency results show good agreement with previously published experimental results. Alternative methods for reproducing the original signals with small distortion and low power consumption are introduced. The excellent performance of the TA devices on broadband signal responses will provide a design approach for sound parametric array and underwater communication equipment.

Investigation of the Ring Vibration Isolator, the Characteristics of which are Regulated by Changing the Radius of Curvature and Angle of Coverage

All-metal vibration isolators made from ribbons and ropes widely distributed and effectively reduce the harmful effects of the vibrations in mechanical systems. However, in modern literature is poorly understood issue of regulation of such vibration isolators taking into account the non-linearity of its characteristics. The paper established the method for calculating the load characteristics of controlled all-metal vibration isolators with adjustable change in the radius of curvature and angle of coverage. The calculation method is based on the joint use of Mora method, the finite element method and the method of minimum strain energy. Created full-size model of the design, which shows the possibility of significant regulation of stiffness and damping characteristics, which allows you to create adaptive systems of protection against vibration. The method allows to precisely determine the parameters of vibration isolator, thus reducing the time and cost of designing.

Vibration of Mechanical System with Higher Degrees of Freedom: Solution of the Frequency Equations

The solution of the motion equation of the rigid body systems with higher degrees of freedom 2 ≤ p° ≤ 10 is difficult. The presented method allows solving the motion equations of such systems by its transformation to higher degrees’ algebraic characteristic equations. The vibration of the system is then described by frequencies obtained from solution of characteristic equations. The proposed method follows Bezout's factor theorem, Bairstow-Hitchcock's method, method of synthetic division and other presuppositions given in the article. The solution is based on the determination of the complex zeros of polynomials.

Selection of active elements in system reduction of vibration

This work presents non-classical method of design of mechatronic systems. The purpose of this paper is also introduces synthesis of mechatronic system understand as design of mechatronic systems. The synthesis may be applied to modify the already existing systems in order to achieve a desired result. The system was consisted from mechanical and electrical elements. Electrical elements were used as subsystem reducing unwanted vibration of mechanical system. Electrical elements can be realized in the form of coils with movable core. The system was modelled in Matlab Simulink.

Comparison of adaptive algorithms for the control of tonal disturbances in mechanical systems

This paper presents a study on the performance of adaptive control algorithms designed to reduce the vibration of mechanical systems excited by a harmonic disturbance. The mechanical system consists of a mass suspended on a spring and a damper. The system is equipped with a force actuator in parallel with the suspension. The control signal driving the actuator is generated by adjusting the amplitude and phase of a sinusoidal reference signal at the same frequency as the excitation. An adaptive feedforward control algorithm is used to adapt the amplitude and phase of the control signal, to minimise the mean square velocity of the mass. Two adaptation strategies are considered in which the control signal is either updated after each period of the oscillation or at every time sample. The first strategy is traditionally used in vibration control in helicopters for example; the second strategy is normally referred to as the filtered-x least mean square algorithm and is often used to control engine noise in cars. The two adaptation strategies are compared through a parametric study, which investigates the influence of the properties of both the mechanical system and the control system on the convergence speed of the two algorithms.

Suppressing self-excited vibrations of mechanical systems by impulsive force excitation

In this contribution, self-excited mechanical systems subjected to force excitation of impulsive type are investigated. It is shown that applying force impulses which are equally spaced in time, but whose impulsive strength depends in a certain manner on the state-variables of the mechanical system, results in a periodic energy exchange between lower and higher modes of vibration. Moreover, in the theoretical case of Dirac delta impulses, it is possible that no energy crosses the system boundary while energy is transferred across modes, i.e. neither external energy is fed to the mechanical system, nor energy is extracted from the mechanical system. Shifting energy to higher modes of vibration, whose natural damping is larger compared to lower ones, results in a faster dissipation of energy. An analytical stability investigation is presented using the assumption of impulsive forcing of Dirac delta type, which allows deciding easily about the stability by evaluating the eigenvalues of the coefficient matrix of a corresponding set of difference equations. It is shown that the developed impulsive forcing concept is capable to suppress self-excited vibrations of mechanical systems. Some numerical results of a simple mechanical system with two degrees of freedom underline the presented approach.

Combining blind separation and cyclostationary techniques for monitoring distributed wear in gearbox rolling bearings

This work seeks to study the potential effectiveness of the Blind Signal Extraction (BSE) as a pre-processing tool for the detection of distributed faults in rolling bearings. In the literature, most of the authors focus their attention on the detection of incipient localized defects. In that case, classical techniques (i.e. envelope analysis) are robust in recognizing the presence of the fault and its characteristic frequency. However, when the fault grows, the classical approach fails, due to the change of the fault signature. De facto, in this case the signal does not contain impulses at the fault characteristic frequency, but more complex components with strong non-stationary contents. Moreover, signals acquired from complex machines often contain contributions from several different components as well as noise; thus the fault signature can be hidden in the complex system vibration. Therefore, pre-processing tools are needed in order to extract the bearing signature, from the raw system vibration. In this paper the authors focalize their attention on the application of the BSE in order to extract the bearing signature from the raw vibration of mechanical systems. The effectiveness and sensitivity of BSE is here exploited on the basis of both simulated and real signals. Among different procedures for the BSE computation, the Reduced-Rank Cyclic Regression algorithm (RRCR) is used. Firstly a simulated signal including the effect of gear meshing as well as a localized fault in bearings is introduced in order to tune the parameters of the RRCR. Next, two different real cases are considered, a bearing test-rig as an example of simple machine and a gearbox test-rig as an example of complex machine. In both examples, the bearings were degreased in order to accelerate the wear process. The BSE is compared with the usual pre-processing technique for the analysis of cyclostationary signals, i.e. the extraction of the residual signal. The fault detection is carried out by the computation of the Integrated Cyclic Modulation Spectrum on the extracted signals. The results indicate that the extracted signals via BSE clearly highlight the distributed fault signature, in particular both the appearance of the faults as well as their development are detected, whilst noise still hides fault grow in the residual signals.

Non-classical method of modelling of vibrating mechatronic systems

This work presents non-classical method of modelling of mechatronic systems by using polar graphs. The use of such a method enables the analysis and synthesis of mechatronic systems irrespective of the type and number of the elements of such a system. The method id connected with algebra of structural numbers. The purpose of this paper is also introduces synthesis of mechatronic system which is the reverse task of dynamics. The result of synthesis is obtaining system meeting the defined requirements. This approach is understood as design of mechatronic systems. The synthesis may also be applied to modify the already existing systems in order to achieve a desired result. The system was consisted from mechanical and electrical elements. Electrical elements were used as subsystem reducing unwanted vibration of mechanical system. The majority of vibration occurring in devices and machines is harmful and has a disadvantageous effect on their condition. Harmful impact of vibration is caused by the occurrence of increased stresses and the loss of energy, which results in faster wear machinery. Vibration, particularly low-frequency vibration, also has a negative influence on the human organism. For this reason many scientists in various research centres conduct research aimed at the reduction or total elimination of vibration.

Nonlinear time-varying vibration system identification using parametric time–frequency transform with spline kernel

In real-life applications, mechanical vibration systems are not linear time invariant. Time-varying pattern arise, for instance, during deployment, aging, deformation, load variation, etc. In the absence of a complete physics-based description of a system, system identification (SI) is able to obtain the missed information of nonstationary pattern for the unknown system. The SI will face difficulty when the time-varying system involves the nonlinearity, which makes the system solution have both the nonlinear and nonstationary time–frequency patterns. This paper aimed to identify the system with linear and nonlinear time-varying characteristics using parametric time–frequency transform with spline kernel, which is known for offering great energy concentration in time–frequency domain and allows the accurate extraction of model feature. The efficacy of the proposed method is demonstrated on SDOF systems comprised of three types of nonlinear time-varying stiffness, including time-varying periodic modulation of stiffness, time-varying piecewise modulation of nonlinear stiffness and time-varying periodic modulation of nonlinear stiffness. Comparisons with the conventional time–frequency methods and the Hilbert transform-based SI validated that the proposed method is more robust in characterizing the nonlinear time-varying stiffness of the system with the presence of noise.

A REVIEW OF IDENTIFICATION OF COULOMB, VISCOUS AND PARTICLE DAMPING PARAMETERS FROM THE RESPONSE OF SINGLE DEGREES OF FREEDOM SYSTEM

Mechanical vibration systems with viscous and Coulomb friction are of importance in the applications of dynamics and control problems. Friction dampers are used in gas turbine engines, high speed turbo pumps, large space structures which are flexible in nature and placed under carriage of railway bogie, vehicle suspension systems etc. These dampers are used for reduction of resonant stresses by usage sliding contact in between two points experiencing relative motion due to vibration, thereby dissipating resonant vibration energy.

Instrumentation for mechanical vibrations analysis in the time domain and frequency domain using the Arduino platform

In this paper, we use the Arduino platform together with sensors as accelerometer, gyroscope and ultrasound, to measure vibrations in mechanical systems. The main objective is to assemble a signals acquisition system easy to handle, of low cost and good accuracy for teaching purposes. It is also used the Python language and its numerical libraries for signal processing. This paper proposes the study of vibrations of a beam, which is measured by position, velocity and acceleration. An experimental setup was implemented. The results obtained are compared with analytical models and computer simulations using finite elements. The results are in agreement with the literature.

SPECIALTY OF ROTOR’S DRIVE MECHANISM OSCILLATIONS

Purpose. Scientific work is devoted to study the influence of dynamic coefficients of bearings segment (coefficients of resistance and recirculating power) on stability and subharmonics self-oscillating components of the rotor vibration in unstable region of rotational speeds. Methodology. The study is based on the methods: the theory of vibrations of mechanical systems with lumped parameters; Lagrange functions; linear algebra. Findings. The researchers made: a) justification of the discrete two-mass model of an unbalanced rotor, which takes into account the influence of rotation on dynamic coefficients; b) analysis and improvement of methods for engineering analysis of stability and parameter subharmonic self-oscillations in the unstable range of frequencies of rotation of the rotor; c) installation and classification of the main rotor causes of vibrations constructive or those arising in the manufacture, assembly and operation of the machine, and on the other hand, rotary systems specific for non-conservative forces, that lead under certain conditions to the self-oscillation; d) determination (identification) the characteristics/differences of rotor vibration, which lies in the fact that in most cases they are associated with the transverse vibrations of the rotors, while torsional or longitudinal oscillations play the incomparably smaller role, and therefore the last in this study were rejected; e)it is shown that the characteristic feature of the functioning of rotor systems of modern machines and units have no direct relationship with the level of vibration with amount of power that is transmitted through them or produced engine. Originality. In this paper the authors first considered the nonlinear response bearing lubrication layer, namely the coefficients of resistance and circulating forces that determine the dynamic coefficient of segment bearings. Practical value. The engineering calculations subharmonic stability and self-oscillations of the rotor (unbalanced) in unstable frequency of rotation are adjusted and significantly improved. The results of this work can be used to analyze rotary systems which under certain conditions can cause vibration that is not caused by some external periodic loads (or imperfections of the rotor) and the conditions of occurrence of which is not associated with some (any) resonant ratio (i.e., the system with self-excitation or self-oscillations). The latter are caused by the action of nonconservative forces of circulation type (circulation strength associated with the displacement vector of the rotor, not the velocity vector, as in systems with «negative» friction). As the circulating force vector is perpendicular to the vector displacement of the rotor, resulting in such a force can manifest themselves only in mechanical (rotary) systems with many degrees of freedom of movement greater than one. In addition, an important feature of the circulation of forces there should not be conservative, so the results can be used to study non-conservative rotor systems with asymmetric (skew-symmetric) matrix of coefficients.

Investigating the effect of vibration on corrosion rate of crude oil storage tanks

The present paper, deals with the influence of vibration and temperature on corrosion rate of ASTM A537 carbon steel used for crude oil storage tanks of Basrah oil fields in south Iraq. A mechanical vibration system equipped with temperature controller according to ASTM G32 standards test method was used to test and study the effect of vibration and temperature on the corrosion rates using immersion test method. Three types of crude oils: light, medium, and heavy crude oils were collected from tanks in southern Iraq. The experimental immersion test results demonstrated that the vibration increases the corrosion rate compared to static case. The light crude oil show larger values of corrosion and heavy crude oil show smaller values, while medium crude oil show moderate values.

分散制御型多点加振による音響固有振動の計測

This paper describes measurement of natural vibration of acoustic space by multi-point excitation using decentralized control. A set of acoustic excitation system consists of a speaker, a microphone, and a local feedback controller. The acoustic excitation system handles the frequency range from 100Hz to 500Hz higher than a mechanical vibration system does. So the phase lag of an actuator, the dead time by propagation of sound, and the dead time by sampling of a controller influence the local feedback control. First, the various phase lag in the acoustic excitation system are identified. The speaker has the second vibration property derived from mechanical resonance, and the first delay property derived from induced voltage of coil. The propagation of sound from the speaker to the microphone causes the dead time. Sampling time of the controller also causes the dead time from the input signal to the output signal. Second, the way to compensate these phase lag in the acoustic excitation system is proposed. Resonance of the speaker makes the phase decrease 180 degree at the resonant frequency. To suppress a change in the phase in the frequency range from 100Hz to 500Hz, the resonant frequency moves to less than 100 Hz. The phase lead and the phase lag after the resonant frequency movement are compensated by the second order phase lag-lead element. The natural vibration of one-dimensional/two-dimensional acoustic space is self-excited by the acoustic excitation system with the phase compensation. By closing the feedback loop, the first mode natural vibration is excited. By adding sinusoidal signal from outside, all natural vibration in the frequency range from 100Hz to the 500Hz is self-excited (forced entrainment).

Multi-Domain Modeling Based on Modelica

With the application of simulation technology in large-scale and multi-field problems, multi-domain unified modeling become an effective way to solve these problems. This paper introduces several basic methods and advantages of the multidisciplinary model, and focuses on the simulation based on Modelica language. The Modelica/Mworks is a newly developed simulation software with features of an object-oriented and non-casual language for modeling of the large, multi-domain system, which makes the model easier to grasp, develop and maintain.It This article shows the single degree of freedom mechanical vibration system based on Modelica language special connection mechanism in Mworks. This method that multi-domain modeling has simple and feasible, high reusability. it closer to the physical system, and many other advantages.

Friction vibration modeling with detachment and adhesion by Cellular Automata

Friction vibration in a dynamical system composed of a slider supported by a spring on a belt was modeled and simulated by Cellular Automata (CA). Friction vibration in mechanical systems has been studied for a long time and various models have been proposed to understand its physical phenomena, but dynamical behavior of an elastic body on friction surface has not been revealed yet. This may be caused by the complexity of friction between two surfaces, and CA can be used as a strong tool of modeling physical phenomena introducing local neighbor and transition rules based on observation of phenomena. It may not be easy to derive the governing equation of motion including the precise mechanism of friction. In this study, a modeling procedure of friction dynamics by CA was discussed. The new model was based on a two-dimensional spring-block model proposed by Olami, Feder and Christensen, but an additional layer of internal surface was introduced to consider the contact area of sliding surfaces. The self-excited vibration, including the stick-slip vibration and the damped free vibration could be simulated in the proposed CA model.