Papers by Keyword: Forced Vibration

Abstract: The dynamic free and forced axial vibrations subjected to moving exponential and harmonic axial forces of a single-walled carbon nanotube (SWCNT) embedded in an elastic medium, are studied in this paper. Two different boundary conditions of SWCNT, including clamped-clamped and clamped-free, are taken into account. Eringen’s nonlocal elasticity theory is used to show the nonlocality for the model. The constitutive equations and their boundary conditions are derived by Hamilton’s principle. Employing the general solution, the derived equations are analytically solved to obtain two items. Firstly, the axial natural frequencies, secondly, the time-domain axial displacements at the middle of the carbon nanotube (CNT), and then the maximum axial displacements. The responses are validated with previous works, and the results demonstrates good agreement to them to verify the influence of the nonlocal parameter on the nondimensional natural frequencies for three various mode numbers. In the time-domain section, the effects of the nonlocal parameter, length, nondimensional stiffness of the elastic medium, and velocity of the moving load on the axial displacement are investigated. Also, the influences of the excitation frequency to natural frequency for the harmonic moving load, as well as the time constant for the exponential moving load on the axial displacement, are illustrated. Finally, the effect of the nonlocal parameter on the maximum axial deflection versus velocity parameter is schematically indicated.

Abstract: In the torque converter, a damper with a piecewise-linear spring is used to reduce the forced vibration, and the subharmonic vibration occurs when the spring restoring torque characteristics approach the switching point. This research analyzed the effect of stiffness ratio between the neighboring piecewise-linear springs on the occurrence of the subharmonic nonlinear vibration in automatic transmission powertrain. The powertrain is modeled with multi degree-of-freedom nonlinear system as an actual vehicle. The result shows higher value of the stiffness ratio between the neighboring springs creates larger value of the subharmonic vibration.

Abstract: Under driving force F(x,t)=Q*sinwt, a time-domain DQ (differential quadrature) method for dynamic problems of beams with initial-boundary value conditions is presented in this paper. On the basis of governing partial differential equation, the discrete DQ method adopted both in space domain and time domain in this method gives rise to new differential quadrature linear equations with complete initial-boundary value conditions for solving all parameters of the displacement-field. The numerical examples show that the computational accuracy and efficiency of time-domain DQ method is better than finite element method based on time-domain difference.

Abstract: The methods of piezoelectric energy harvest and detection based on forced vibration are introduced in this paper. Firstly, the mechanical energy of the forced vibration is converted into alternating current energy by using the piezoelectric harvester, and then the AC currents are rectified through the full bridge rectifier circuits, and finally the capacitor filter circuits are adopted to obtain the stable DC output. It also implements the voltage waveform detection during above energy harvesting process. The experimental results show that piezoelectric oscillator has the characteristics of simple structure and support stability, and its forced vibration frequency is independent of the structural natural frequency. The piezoelectric harvester forced with the vibration source can obtain an effective energy-harvested electric output.

Abstract: The time and frequency forced responses for the permanent magnetic planetary gear drive were computed and analyzed. The influence of magnetization intensity and pole pair number to frequency forced responses is discussed. Results show that the dynamic displacement when only considering output excitation is larger than that when only considering input excitation,and magnetic parameters have obvious effects on the low frequency vibration amplitude of elements. When magnetization intensity and pole pair number are too large or too small, they will seriously affect the dynamic performance of the system. So, selecting rational system structure parameters is very important, which can avoid system elements generating larger vibration.

Abstract: The presented article is focused on a theoretical dynamic analysis of the footbridge across the Opatovicka street in Prague, which acts as a simply supported beam. The structure was loaded by an ordinary pedestrian traffic, synchronous runners and vandals. The ordinary traffic was simulated by the Monte Carlo method as a stream of moving periodic forces with stochastic parameters. The synchronous runners and vandals were modeled as a combination of biomechanical models of human body, which influenced the structure vibration only passively, and driving forces, which loaded the structure in the contact points between the human body models and the structure. The driving force was the time – dependent function based on decomposition to the Fourier’s Series and periodic triangle function. The obtained theoretical results are compared with experimental data.

Abstract: The research object is hydraulic tool turret cabinet of CNC lathe. Building the hydraulic tool turret cabinet model by Pro/E, then meshing the cabinet by Hyper-mesh software, finally calculating by the ANSYS. Do modal analysis and harmonic response analysis for the cabinet, then make the second order frequency maximum as a target, use the Altair OptiStruct to improve its dynamic structure. The result shows: though the quality of optimized body is increased, but it avoids the resonance frequency, which greatly reduce the possibility of resonance, and greatly improve the dynamic performance of the cabinet.

Abstract: As a result of the trend towards lightweight construction in manufacturing, there has been a significant increase in the use of clinched joints in engineering structures and components. Mechanical structures assembled by clinching are expected to possess a high damping capacity. The aim of this paper is to provide an experimental measurement technique for the investigation of the forced vibration behavior of clinched joints. The dynamic test software and the data acquisition hardware were used in the experimental measurement of the dynamic response of the clinched joints. The frequency response functions of the clinched joints of different clinching point number were measured and compared.

Abstract: Generally, cross range resolution of a B-mode ultrasonic image is restricted by a point spread function of the measurement system. Although various super-resolution techniques are proposed, it is difficult to significantly improve the resolution with low calculation burden. In this paper, we propose a novel super-resolution technique in which the Doppler B-mode image is measured under forced vibration in the region of interest. The numerical simulation is carried out to demonstrate the validity of the proposed algorithm. It is shown that the cross range resolution is 3 times narrower than the original one.

Abstract: The main transportation pipelines are subjected to complex stresses resulting from the nature and state of the transported material, the operating conditions, and the environmental factors and so on. Thus, the stress in the pipe wall is generated and influenced by the pressure, the temperature and the mass of the transported fluid, by the weight of the pipe, the ambient temperature and in certain periods of time by the wind speed. In this paper are presented dynamic phenomena generated by wind flow and their effect on the magistrate transportation pipelines. The content of the paper presents an detailed analysis regarding the regimes in which is developing the force generated by Karman vortex and the situation when resonance phenomena are developed. The study presents a mathematical model that describes the dynamic phenomena generated by the wind action, determining the mathematical expression of the aerodynamic force that act on the normal direction to the wind speed. This force is having a periodic variation, its size and the frequency variation is dependent on the wind speed. Some methods are proposed in order to decrease the wind influence on the lifetime of transportation pipelines. The main results of the study are: determination of the speed range for which the dynamic phenomena have a high influence on the pipeline lifetime; determination of the real conditions that can lead to sharp rises of the pipe deformations; determination of the pipeline lifetime reduction under development of dynamic loads.