جستجوی مقالات مرتبط با کلیدواژه « چاه غیرخطی انرژی » در نشریات گروه « مکانیک »

In this paper, to reduce the energy of an underwater beam, a vibro-impact nonlinear energy sink is used and the force due to water is considered as a sinusoidal harmonic force and a constant load. A nonlinear energy sink consists of a cavity and a ball in the cavity. First, the governing equations for the beams and the nonlinear energy sink are obtained. With optimization, the minimum time to transfer 95% of the energy of the beam to the absorber is obtained. To optimize the four parameters of cavity length, the mass ratio of the nonlinear energy sink and the beam, restitute coefficient, and adsorbent position on the beam, which is the first time that all parameters of vibro-impact nonlinear energy sink are considered for optimal design. In the following, each of these parameters is considered, and the optimal value for each of these parameters is calculated. Finally, it is shown that the dynamic response of the system with two impacts per cycle (symmetric) is the most optimal response of the system.

Recently, modern turbines are designed close to their critical operating points with lower stability margin. Therefore, accurate dynamic analysis and using advanced vibration control systems are required. In this paper, the application of nonlinear energy sinks (NESs) for indirect vibration reduction of the blades in a flexible shaft-disk-blades system of a real steam turbine is conducted. 37 packets of seven-connected blades are mounted on the perimeter of the disk. The cyclic finite element analysis is employed to obtain mode shapes and frequency diagram. For the second combined mode of system, which is a combination of the second bending mode of shaft and the third bending mode of disk-blades, a two degrees of freedom (2DOFs) reduced order model (ROM) is identified for each sector. The cyclic symmetry of ROM reduces the size of the studied model to 2 DOFs. NESs with a small mass, an essential nonlinear stiffness and a linear damping are installed on the ROM in the antinode position of desired mode. The Runge-Kutta method is used to solve the nonlinear equations numerically. Optimum stiffness and damping of the NESs are determined to minimize the vibration amplitude of the blades.The results show the occurrence of strongly modulated response around the resonance, and hence, the desired vibration reduction of the blades is take placed. If the NESs have large nonlinear stiffness or low damping, a saddle-node bifurcation and a large island form near the resonance, and the blades could experience large amplitude periodic motion in the negative detuning frequencies.

This paper investigates vibration analysis of a clamped-clamped beam attached to a nonlinear energy sink (with nonlinear stiffness and damping) under an external harmonic force. The bream is modeled using the Euler-Bernouli beam theory. Different locations for nonlinear energy sink are chosen and the effects of various parameters on behavior of the system are considered. Required conditions for occurring the Saddle-node bifurcations and the Hopf bifurcations in the system are studied. In vibration analysis, the frequency response diagram of the system is very important because it shows the best regions for attenuation of vibration and is a good criterion for designing nonlinear energy sinks; hence Complexification-Averaging method is used to find simply the amplitude of oscillation in terms of excitation load. For validation and comparison, numerical simulation (Runge-Kuta method) is used. The results demonstrate that by approaching the position of nonlinear energy sink to the beam supports, probability of occurrence of the Hopf and the saddle-node bifurcations decreases and increases, respectively, detached response curve will be formed in smaller range of external amplitude force. Moreover, by increasing external amplitude force, the steady state amplitude of the system increases smoothly.