علی حاج نایب

Nowadays, piezoelectric transducers are widely applied because of their capability to convert environmental energies (e.g. mechanical vibrations) into the electrical energy. In an energy harvester structure, not only piezoelectric characteristics but also properties of the non-piezoelectric part of the energy harvesting structure are highly important. Therefore, in the present research, electrical energy generation from forced vibrations of a composite beam with the piezoelectric layer is considered. For this purpose, firstly, the governing equations of the system are obtained using Euler-Bernoulli beam theory. Then, Kantorovich method was used to calculate the output voltage for a composite beam with the piezoelectric layer. To verify the analytical method, the results were compared to the finite-element modeling results. Furthermore, the effects of fiber orientation angle and layup arrangement in the composite beam with piezoelectric layer on the amount of harvested energy were investigated. According to the obtained results, by increasing the elastic modulus of the composite beam and its effect on the damping ratio of the structure, considerably higher energy is harvested. Then, the effects of composite beam dimensions, the ratio of composite beam thickness to the piezoelectric layer thickness, the concentrated mass, and the damping ratio on the amount of harvested energy were studied. The results show that using the composite materials and by proper design of layup and fiber orientation angle in each layer, it is possible to get different equivalent elastic modulus in the composite beam, and consequently alter natural frequency of the system and output voltage amplitude of the circuit

In this paper, the nonlinear free vibrations of a bimorph piezoelectric nanoactuator is studied based on nonlocal elasticity. The Euler-Bernoulli beam theory and Hamilton’s principle are used to derive the equation of motion of the actuator. In order to obtain the reduced-order form of equations, the Galerkin method is used. The mode shapes of a multi-span beam are used for a faster convergence. The nonlinear natural frequencies are obtained by using He’s variational approach. Equations are solved for clamped-clamped boundary conditions, and the effects of values of DC voltage, actuator length and thickness, length of piezoelectric layers and nonlocal parameter on the nonlinear natural frequencies are studied. The results show that applying a DC voltage induces a static deflection and an increase in the stiffness of the actuator. Therefore, the natural frequency increases. Moreover, increasing the nonlocal parameter decreases the rate of change in frequency variation. An increase in the nonlocal parameter or the length of the actuator increases the nonlinear to nonlinear natural frequency ratio. Finally, the effect of the middle layer material of the actuator on the frequency ratio is studied.

The inseparable parts of any industrial unit are usually the rotary machines. Fans are categorized as a common type of rotary machines, which play an important role in the industry. In order to decrease the repairing costs and energy consumption, Fans have to operate without vibration. However, if the fan unit with an acceptable level of vibrations is installed on a huge structure, the vibration caused by the fan can develop complications for the structure as well as serious problems for the fan itself. A long-time operation of a faulty fan can cause failure in the fan motor and fatigue in the structure. Therefore, investigating the root causes of the vibrations of the fan and decreasing the vibrations is vital for increasing the operating time and the efficiency of the fans.This study is focused on identifying the root causes of excessive vibrations of one of the air fans in BualiSina petrochemical company. First, the main frequencies which are responsible for the increase in vibration levels are identified, by using ODS analysis. Then, the natural frequencies of the structure are derived using the operational modal analysis (OMA). Also, the finite element model of the fan unit and the structure is developed based on the most possible compatibility with the experimental data. Finally, a number of suggestions for reducing vibration amplitudes of the fan are proposed.