فهرست مطالب محمد مهدی نظری

Purpose of paper is to use a nonlinear dynamic absorber as beam with concentrated mass at its end to reduce the amplitude of resonant nonlinear oscillator vibration. Primary vibration system consists of mass, nonlinear spring, and viscous damping, and harmonic force is applied to it and causes the system to intensify. Nonlinear dynamic absorber has been used to reduce vibration amplitude. First, the kinetic energy and potential energy of system are calculated, and then governing equations of the system are extracted using Lagrange's equations. To solve the governing equations, the method of multiple scales is used. Numerical solution, in the negligible case of considering the mass of the absorber and the stiffness of the nonlinear Duffing spring, the validation of results is done. The effect of nonlinear dynamic vibration absorber on reducing the amplitude of resonant oscillator vibration can be seen well. Influence of the main parameters of the nonlinear dynamic absorber on vibration amplitude of primary system is investigated.

Micro energy harvester systems are a new technology that replaces batteries and energy storage devices that have limitations. Not needing to replace or recharge them periodically, very small volume and weight, as well as high accuracy are the characteristics of the micro energy scavenger system. This paper investigates the electromagnetic micro energy harvester system under random white noise excitation. The mechanical model considered for the micro energy harvester is in the form of a beam. In this system, the base acceleration is the input of the micro energy recovery and the induced voltage in the coil is the output of the system. The base excitation is assumed to be a weakly stationary Gaussian white noise random process. According to the mechanical motion equation of the system, the frequency response function can be obtained. The aim of this research is to calculate the mean power produced in the electromagnetic micro energy harvester under random excitation. Stress analysis is done using simulation in finite element software and numerical solution, and the results’ correctness is confirmed. Finally, the effect of the electromagnetic micro energy scavenger on the average parameters power produced is investigated.

A rotating composite shaft can be used with power transmission applications in the rotating machinery industry. A composite power transmission shaft usually has higher natural frequencies and critical speeds than a conventional metal power transmission shaft. Accurate determination of the natural frequency of the shaft is of great importance in its design, especially in the case of composite shafts due to the anisotropy of composite materials. In this paper, first in a rotating state, finite element results of a composite shaft of eight layers of carbon/epoxy in the case of two steel discs in the middle are symmetric with different diameters are compared with the results of previous research and the accuracy of the results is verified. A hollow composite shaft of eight layers of carbon/epoxy and glass/epoxy is modeled with two steel discs on the elastic supports. Applying the Lagrange equations, the equations of motion of the hybrid composite shaft are obtained using the modified equivalent modulus beam theory. By writing code in MATLAB software and numerical solution, the amplitude diagram in terms of frequency in the rotating state is obtained and compared with the results of the composite shaft simulation in Ansys software, and validation is performed. Finally, the effect of stacking sequence parameters such as fiber angle, arrangement of use carbon/epoxy, and glass/epoxy on natural frequencies is investigated.

Aerospace Launch Vehicles (ALV) are generally designed with high reliability to operate in complete security through fault avoidance practices. However, in spite of fault avoidance, fault occurring is inevitable. Hence there is a requirement for on-board fault detection and isolation (FDI) without significant degradation in the ALV performance. The robust observers are widely used in FDI due to reduction of the effect of disturbances in the FDI process. In this paper, the robust fault diagnosis observer is designed for an ALV subject to uncertainties. The linear sliding mode technique is used to design the observer for a linear time varying model of an ALV. The parameter estimation from the sliding mode scheme is compared with those generated by a nonlinear simulation and are found to provide good correlation. Then, a proposed linear sliding mode observer is employed to generate the residual as an indicator of predefined gyroscope faults.