Academic literature on the topic 'Mechanical Vibration'

There are lots of sources of disturbance in people’s surrounding environment - e.g. wind, sea, river flow, and intensive acoustic noise. These sources can cause auto vibrations of particular dynamic systems. Such phenomenon could be used for converting mechanical vibration energy to electrical energy. Solving this problem is topical because it could help to create autonomic sources of renewable energy. Dynamic model, described by a presumptive differential motion equation, of auto vibrating system, affected by airflow is made and inspected. Possible modes of vibrations and different states of nonlinear auto vibrating system are analyzed using methods of Newmark and Runge-Kutta. Auto vibration existence zones of the system are designated. Reliance on the existence of poly-solutions, stability or chaotic solutions of vibrating system is estimated. Consistencies of using electro dynamical principle of converting mechanical vibration energy to electric energy are inspected.

Vibration technology is widely used in mechanical engineering, construction, road building and different sectors of the manufacturing. In agriculture, it is used for dosing feed, cleaning and sorting seeds, digging up root crops, planting potatoes, and transporting bulk materials. Vibrations make the mechanical system more stable in relation to external force disturbances and do not change the technological properties of materials during its movement along the working surfaces. Also, the material passing through the vibration zone is not damaged. A wide range of frequency and amplitude of vibrations provides the possibility of vibration regime varying, and the characteristics of the movement of agricultural plant material on the vibrating working bodies. The analysis of possibility of application of vibrating hydraulic drives as elements of transmission of movement to working bodies of agricultural machines is executed. A historical excursion was conducted and the first mentions of the use of hydraulic drives were pointed out. The estimation of technological processes in agricultural production where it is expedient and possible to use vibration and vibrating drives is made. At the present stage of development of agricultural engineering, using vibrating hydraulic drive is accorded to the basic trends of agriculture machinery development. The stand for conduction of studies of amplitude-frequency characteristics of the vibrating drive with regulated perturbations is offered. A mathematical model is presented, which generally describes the course of the vibration process and estimates the stiffness of the mechanical system. The hydraulic parametric vibration exciter is recommended to use for studying and determination the conditions for the occurrence of parametric vibrations in working body of agricultural machines. Also, using a hydraulic drive makes it possible to simplify the kinematics, reduce metal consumption, increase accuracy, reliability and level of automation of working bodies of agricultural machines.

Carbon nanotubes (CNTs) have wide-ranging applications due to their excellent mechanical and electrical properties. However, there is little research on the nonlinear mechanical properties of thermal-electro-mechanical coupling. In this paper, we study the nonlinear vibrations of CNTs by a thermal-electro-mechanical coupling beam theory. The Galerkin method is used to discretize the partial differential equation and obtain two nonlinear ordinary differential equations that describe the first- and second-order mode vibrations. Then, we obtain the approximate analytical solutions of the two equations for the primary resonance and the subharmonic resonance using the multi-scale method. The results indicate the following three points. Firstly, the temperature and electric fields have a significant influence on the first-mode vibration, while they have little influence on the second-mode vibration. Under the primary resonance, when the load amplitude of the second mode is 20 times that of the first mode, the maximal vibrational amplitude of the second is only one-fifth of the first. Under the subharmonic resonance, it is more difficult to excite the subharmonic vibration at the second-order mode than that of the first mode for the same parameters. Secondly, because the coefficient of electrical expansion (CEE) is much bigger than the coefficient of thermal expansion (CTE), CNTs are more sensitive to changes in the electric field than the temperature field. Finally, under the primary resonance, there are two bifurcation points in the frequency response curves and the load-amplitude curves. As a result, they will induce the jump phenomenon of vibrational amplitude. When the subharmonic vibration is excited, the free vibration term does not disappear, and the steady-state vibration includes two compositions.

ABSTRACT The development of efficient machines for the mechanical harvesting of coffee plants requires the use of appropriate vibrational parameters. Thus, in order to detach less unripe fruits and decrease reharvesting, branch breakage and defoliation, it is important to choose the appropriate frequency, amplitude and vibration time. This study aimed at analyzing the detachment efficiency of fruits from coffee plants according to vibrational parameters and ripening stage. Fruit bunches were sampled at the green and mature stages and subjected to vibration, using a system composed by a signal generator, an amplifier and an electromagnetic vibrating machine. Tests combined different frequencies (16.4 Hz, 20.3 Hz, 24 Hz, 25.6 Hz, 30.0 Hz and 33.0 Hz), amplitudes (5.0 mm, 7.0 mm and 9.0 mm) and vibration times (10.0 s and 20.0 s). The vibration times did not affect the detachment efficiency. There was a trend for higher detachment efficiency in mature fruits than in green fruits. The detachment efficiency increased with increasing vibration frequency and amplitude.

The online frequency estimation of forced harmonic vibrations on a building-like structure, using a nonlinear flexible vibration absorber in a cantilever beam configuration, is addressed in this article. Algebraic formulae to compute online the harmonic excitation frequency on the nonlinear vibrating mechanical system using solely available measurement signals of position, velocity, or acceleration are presented. Fast algebraic frequency estimation can, thus, be implemented to tune online a semi-active dynamic vibration absorber to obtain a high attenuation level of undesirable vibrations affecting the main mechanical system. A semi-active vibration absorber can be tuned for application where variations of the excitation frequency can be expected. Adaptive vibration absorption for forced harmonic vibration suppression for operational scenarios with variable excitation frequency can be then performed. Analytical, numerical, and experimental results to demonstrate the effectiveness and efficiency of the operating frequency estimation, as well as the acceptable attenuation level achieved by the tunable flexible vibration absorber, are presented. The algebraic parametric estimation approach can be extended to add capabilities of variable frequency vibration suppression for several configurations of dynamic vibration absorbers.

Purpose. To formalize the dependence of the eigenfrequencies of translational and torsional vibrations of the structural elements of the vibrating machine articulated by the connection node on their design parameters and mechanical characteristics, as well as regulatory requirements for vibration activity, strength and accuracy. To develop a method for selecting the design parameters of the elastic band element of the package, taking into account the specified values of the amplitude and frequency characteristics of the dynamic loads reproduced by the supporting structure and the coefficient of variation of the natural frequencies of translational and torsional vibrations. Methodology. The research is based on fundamental approaches of applied mechanics, machine dynamics and vibration reliability. Findings. The dependences of the eigenfrequencies of torsional vibrations of the body parts of the vibrating machine connected by the connection node on their design parameters and mechanical characteristics are obtained and analyzed. Vibrations around an axis orthogonal to the working direction of the node are considered. A comparative analysis of the natural frequencies of the node in the direction of the transmitted vibration and its circular vibrations from the design parameters and mechanical characteristics of the elastic band elements, their number in the package and the number of packages in the connection node is performed. Originality. It is in the fact that for the first time the dependences describing the natural frequencies of translational and torsional vibrations of the body parts of a vibrating machine, articulated by a package of elastic band elements, are obtained. Also the paradigm for the choice of design parameters and mechanical characteristics of the elastic band element of the package, which is based on the results of a comparative analysis of the eigenfrequencies of vibrations in the working and connected directions through their coefficient of variation is innovative. This made it possible to include the criterion of vibration reproduction accuracy, which is formalized through the coefficient of frequency variation, together with the criteria of strength and rigidity, in the methodology of synthesis of the structural scheme of the vibrating machine. Practical value. The proposed methodological solutions for the calculation and selection of design parameters and mechanical characteristics of tape elastic elements ensure the achievement of vibration activity indicators of articulated parts, as well as the ratio of natural vibration frequencies in the working and related directions at the level of the requirements of normative documents when upgrading existing machines and creating new modern equipment. As a result, the reliability, durability, safety, productivity and load-bearing capacity of machines, equipment and mechanisms of mining engineering, aviation, transport and space technology are increased.

The paper shows that mechanical vibrations occur in a wide frequency range in the hydraulic systems operating in the real world. Hydraulic valves are also exposed to these vibrations. The paper gives examples of vibration sources and suggests that the influence of vibrations on hydraulic valves could be reduced. Particular attention was paid to the vibrating proportional distributor. The amplitude-frequency spectrum of pressure pulsation in a hydraulic system with a vibrating proportional distributor was analysed. During the tests, the frequency of external mechanical vibrations acting on the proportional distributor and their direction was changed.

Spring mechanical vibration motion system with a damped degree of freedom and influenced by external forces, is mathematically expressed as an ordinary differential equation of order of two linear constant coefficients that are not homogeneous. If an external force acts on a stationary system expressed as a continuous function f(t) for any time t, then the system will experience mechanical vibrational motion which mathematically the equation of motion can be expressed as a superposition. The equation consists of as a solution to a homogeneous form with mechanical vibrations as a solution to a particular form. In terms of the particular solution this article will show a mathematical way when f(t) is a continuous function section by part which is defined at an interval, such that the mechanical vibration motion equation is at the same time a special solution of the equation the mechanical vibration system.
 Keywords: Vibration, Impulse Functions, ConvolutionMSC2020: 34A37

Bone cells are deformed according to mechanical stimulation they receive and their mechanical characteristics. However, how osteoblasts are affected by mechanical vibration frequency and acceleration amplitude remains unclear. By developing 3D osteoblast finite element (FE) models, this study investigated the effect of cell shapes on vibration characteristics and effect of acceleration (vibration intensity) on vibrational responses of cultured osteoblasts. Firstly, the developed FE models predicted natural frequencies of osteoblasts within 6.85–48.69 Hz. Then, three different levels of acceleration of base excitation were selected (0.5, 1, and 2 g) to simulate vibrational responses, and acceleration of base excitation was found to have no influence on natural frequencies of osteoblasts. However, vibration response values of displacement, stress, and strain increased with the increase of acceleration. Finally, stress and stress distributions of osteoblast models under 0.5 g acceleration inZ-direction were investigated further. It was revealed that resonance frequencies can be a monotonic function of cell height or bottom area when cell volumes and material properties were assumed as constants. These findings will be useful in understanding how forces are transferred and influence osteoblast mechanical responses during vibrations and in providing guidance for cell culture and external vibration loading in experimental and clinical osteogenesis studies.

In order to achieve optimal physical and mechanical properties of hardened concrete, it is necessary to determine the right intensity and vibration time of fresh concrete during casting. Since concrete is considered as a polydisperse substance and various aggregate grains move randomly during vibration, it is very difficult to describe this stochastic phenomenon using exact physical equations and it is more advantageous to apply an experimental approach to verify the effects of vibration on fresh concrete. The effect of vibrations on fresh concrete increases the speed gradient of individual grains and thus reduces the viscosity of the cement paste. The intensity of vibration is determined mainly by the frequency, amplitude and centrifugal force of the eccentric of the vibrating machine. The optimal vibration time is generally considered to be the "minimum required". Insufficient vibration caused by an unsuitable vibrating machine or a short vibration time can result in insufficient compaction of the aggregate grains, non-release of accumulated air from the fresh concrete mixture, formation of cavities or poor-quality casting of parts of the structure with a higher degree of reinforcement. Vibration with excessive intensity or time can also be considered dangerous. The over-compaction of concrete is most often demonstrated by segregation of aggregates. The presented research deals with the determination of the optimal time and intensity of vibration of fresh concrete mixture to achieve the required physical properties of concrete, i.e. high compressive strength and modulus of elasticity of hardened concrete while reducing the negative effects of vibration, especially segregation of aggregates.