جستجوی مقالات مرتبط با کلیدواژه « پیزوالکتریک » در نشریات گروه « مکانیک »

With the continuous improvement of integrated circuit technology and micro/nano electromechanical system technology, the development of small generator devices has become an inevitable trend in the development of microelectromechanical systems. Since the volume of electronic devices will be smaller and smaller on a daily basis, the demand for energy will be smaller and smaller, as a result, the energy needed by micro-devices can be easily supplied by using wind energy piezoelectric generators. In this research, while analyzing the behavior of piezoelectric transducers with the help of Abaqus finite element software, a method to increase the power extracted from wind generators has also been presented using auxetic structures. For this purpose, three different types of auxetic structures have been used and the effect of the type and thickness of the auxetic layer on the behavior of the structure has been analyzed. Examining the obtained results shows an acceptable increase in the output voltage of the piezoelectric layer by using auxetic structures, so that a 100% increase in output can be achieved by using this type of structure. Also, a drastic increase in the electric potential obtained with the help of similar-shaped auxetic structures made of steel compared to aluminum structures was observed, which confirms the effect of the geometric shape and material of these structures on the output power of the generator.

In this study, in order to harvest energy from vortex-induced vibration of fluid flow, piezoelectric beams mounted behind a circular cylinder are considered and effect of various arrangements of the beams are studied. To reach this goal, a three-way coupling model in the turbulent, unsteady and viscous flow regime is numerically investigated. The simulations are investigated for different values of electrical resistance and its effect on vibration amplitude, frequency ratio, voltage and power output are compared. It has been shown that the maximum oscillation amplitude and frequency ratio is occurred by a resistance value of 1000 Ω and its value decreases with the increase of resistance. Furthermore, by growing of the load resistance, the generated voltage goes up significantly and the maximum voltage is obtained in the load resistance as 100 MΩ, Contrastingly, maximum power is obtained at low values of the load resistance. Finally, it is found that in the parallel arrangement of beams, due to less damping ratio due to stronger interaction between beams and shear layers, larger vibration amplitude and much more electrical output occurs.

Energy harvesting from the existing vibrations in nature and converting it into electrical energy causes the recovery of wasted energies and their optimal use. The obtained electrical energy can be used as a cheap, continuous and clean source to power low-consumption equipment such as sensors, actuators, controllers, medical equipment, etc.This article contains a rigid horizontal cylinder that has only vertical movement and is bounded by 4 springs.As a result of the wind hitting to the cylinder, a vortex induction force acts to the cylinder and causes vibration in the direction of perpendicular to the wind flow. A piezo-elastic energy harvesting system is placed inside this cylinder, which is connected to the horizontal cylinder through the fixed part of the beam.In fact, with the movement of the horizontal cylinder and through the vibration of the base, the force is transferred to the fixed part of the beam and causes the vibration of the piezo-elastic beam. The induced nonlinear force of the vortex due to the impact of the wind on the horizontal cylinder is calculated by applying the Vanderpol equation and its effect on the vibration of the equivalent system is investigated.Then, by using the piezoelectric element installed on the beam, the electric energy will be collected as the voltage. Here, the optimal wind speed and also the optimal electrical resistance are calculated in order to maximize the output electrical power. At the end, the effect of different parameters on the output power is investigated.

Energy harvesting is the process of converting different kinds of energy, such as solar, thermal, kinetic energy of fluid, etc., to a usable form of energy. Different kinds of transduction mechanisms are used for energy harvesting. The piezoelectric mechanism has received considerable interest because of its advantages, such as ease of application and working over a wide range of frequencies. Simulation and investigation of energy harvesting from a piezoelectric plate, which is mounted on an elastic beam and located behind a cylinder through flow-induced vibrations, is the subject of the present research. First, the results of the lift and drag coefficients in the fluid flow around a stationary cylinder at Reynolds 200 are compared and validated with the previous studies. After that, by placing an elastic beam and a piezoelectric behind the cylinder, flow around the cylinder, and the fluid-solids interactions are investigated. Due to the vortex shedding phenomenon, which happens in the fluid flow past the cylinder, the elastic piezoelectric beam deforms periodically, and thus, the mechanical energy of the flow is converted into electrical energy. In this problem, the beam effect on both the drag/lift reduction and the amount of voltage extracted from the piezoelectric layer were investigated, and the optimal mode obtained was selected based on the extraction of more energy. In this regard, the process of finding the most optimal energy harvesting mode for the location of the elastic beam, the length of the beam, and the fixed point of the elastic beam in different geometries are carried out. The results of the optimal investigations are as the length of the elastic beam of 2D, the distance of the beam from the back of the cylinder 2.5D, and the state in which the beam is fixed from the right side, where D is the diameter of the cylinder.

In order to convert mechanical vibrations into useful electrical energy, is one of the goals of many researchers in today's science, and for this purpose, harvesting equipment with piezoelectric components has been used. To check the performance of this system, knowledge of the behavior and output of the vibration system, and the effect of different parameters of that system is of great importance. In the current research, it is tried to investigate the effects of different parameters on the performance of the harvester by modeling the vibration system as a two-degree-of-freedom model, in two different configurations. To check more closely and find a result closer to reality, using the theory of linear random vibrations, the stimulation in question was white noise type. In the mathematical modeling, two two-degree-of-freedom states have been investigated, in the first state, the piezoelectric between the base and the first mass, and in the second state, the piezoelectric between the base and the second mass has been assumed. After extracting the governing equations in each configuration and applying the input to the system with random excitation, the effect of all identified and introduced parameters in the system is studied, and the configuration with higher efficiency, in terms of the average energy harvester, is introduced and the results are expressed graphically.

This paper develops an intelligent attitude control and vibration suppression system for flexible spacecraft performing a single-axis maneuver with external disturbances and parameter uncertainties. Fully coupled nonlinear equations of motion are discretized by Hamilton's principle and the finite element method. The attitude control structure utilizes a fuzzy algorithm to control the attitude and vibration of the panel simultaneously. This algorithm uses a vibration criterion for flexible parts, attitude errors and time inputs. In order to evaluate the performance of such an approach, super twisting-non-singular terminal sliding mode (SNTSMC) and strain rate feedback (SRF) were used simultaneously. The proposed SNTSMC/SRF algorithm takes advantage of each as part of a hybrid algorithm that leads to increased targeting accuracy, faster convergence rate, reduced chattering, reduced residual vibrations, and reduced rigid-flexible bodies interactions. The Lyapunov theory demonstrates the system's overall stability. Simulation results as a comparative study demonstrate the effectiveness of both approaches in reducing control-structure interactions during large-angle maneuvers.

This paper deals with a robust active vibration and non-singular fast terminal sliding mode control design for flexible spacecraft attitude maneuvers. First, the fully coupled nonlinear rigid-flexible dynamic model of the spacecraft in the three-axis maneuver is derived using Lagrange's equations in terms of quasi-coordinates. Then, the attitude control law is designed based on a fast non-singular terminal sliding surface, which leads to the zero convergence of attitude tracking and angular velocity errors in a finite time in the presence of external disturbances and parameter uncertainties. Next, the flexible panels' residual vibrations during and after the maneuver have been reduced exponentially using a robust active vibration control algorithm through piezoelectric sensor/actuator patches. It has been proven that this algorithm ensures the stability of the closed loop system and eliminates the need for conservative assumptions regarding uncertainties and external disturbances at the upper limit. The finite-time convergence of the closed-loop system with a hybrid control approach is proved by the Lyapunov stability theory. The numerical simulations using 4th order Runge-Kutta approach show the simultaneous utilization of the proposed attitude and vibration controllers' performance compared to the classical approaches for dynamical systems with structural flexibility.

There are many engineering applications of pipes at different scales for conveying fluid. The dynamic characteristics of a spinning pipe conveying fluid in vertical configuration equipped with piezoelectric patches are analyzed in this study. Based on Euler–Bernoulli beam theory, the governing equations of the system are derived by applying Hamilton’s variational principle. In this equations, the gyroscopic coupling, electromechanical coupling and gravitational effects are considered. The Galerkin’s method is used to discretize the governing equations of motions. Numerical results are investigated to predict the influences of the piezoelectric layer spanning angle, spinning speed, pipe length and flow velocity, on the unbalance response of the system. The results indicate that, depending on excitation frequency, the vibration amplitude can be decreased or increased by increasing the piezoelectric layer spanning angle. The results of this research can be used to conduct piezoelectric pipe design and performance predictions for future pipe vibration control and energy harvesting applications.

An active vibration control algorithm and robust integral sliding mode control (SMC) are discussed to stabilize the attitude of the flexible spacecraft under external disturbances and actuator faults. As a coupled rigid-flexible dynamical system, the flexible spacecraft is modeled as a rigid hub with two solar panels equipped with piezoelectric (PZT) sensors and actuators. A passive fault-tolerant integral sliding mode control algorithm using a nominal proportional-derivative control algorithm and an improved fault-tolerant algorithm with time-varying additive fault is developed to increase system’s performance, prevent the system's flexible modes excitations in the phase of reaching the sliding surface. Therefore, when the system enters the sliding mode, the closed-loop dynamic behavior, including actuator faults, will be identical to that of the system without faults. It is possible to reduce the residual vibrations caused by the attitude dynamics and actuator faults by simultaneously activating the strain rate feedback (SRF) vibration control algorithm during the maneuver. The performance of the proposed integral fault-tolerant control in terms of the flexible modes excitation, the control effort, and achieving the desired attitude parameters in a comparative study demonstrated its advantage and superiority over the conventional integral sliding mode algorithms.

In this article, the Mori-Tanaka micromechanical approach is used to obtain the elastic and piezoelectric properties of a hybrid composite with a polyamide matrix and reinforced with piezoelectric particles of lead zirconate titanate and carbon nanotubes. Modeling consists of two steps, first, the effect of carbon nanotube distribution in the polyamide matrix is calculated, In the next step, the obtained results were used to calculate the addition of piezoelectric particles. The model has been validated with experimental results and previous studies. the increase in the volume fraction of piezoelectric particles causes an increase in the elastic and shear moduli and piezoelectric constants. Modeling for uniform and non-uniform distribution of carbon nanotubes has been done. The results show that by adding carbon nanotubes, the elastic moduli and piezoelectric constants increase. Also, the agglomeration of carbon nanotubes reduces these modules.

According to the direct relationship between the deformation due to vibration and the voltage generated at the Unimorph piezoelectric Surface, it is important to investigate the role of the geometric dimensions of these components in the voltage generated in a constant force application. In this study, in order to optimize the geometric dimensions of the piezoelectric Micro Electro Mechanic Systems (MEMS), the tool of MATLAB software genetic algorithm was used. For this purpose, first the analytical relationship governing a unimorph piezoelectric MEMS in Euler-Bernoulli model was extracted and considered as the objective function in the desired optimization. Then the variables of beam length, piezoelectric layer length, beam width, piezoelectric layer thickness and the thickness of the beam was selected as the optimal variables to maximize the product voltage in this optimization. To ensure the accuracy of the analytical relationship presented in ABAQUS software, the unimorph piezoelectric MEMS was modeled, that showed a 88% compliance between the analytical relationship and the finite element model. It was also observed that optimization using the genetic algorithm tool of MATLAB software, if the suitable population size is selected, can increase the generated voltage by up to 59% and at the same time reduce the dimensions of the unimorph by more than 50%..

This paper proposes robust hybrid sliding mode control with a time-varying sliding surface and active vibration control for a flexible spacecraft during attitude maneuver. The fully coupled nonlinear dynamic model of the rigid-flexible system includes the three-axis rotation of the rigid body in interaction with the transverse deformation of the smart PZT-mounted flexible appendages. The smooth control signal includes a hyperbolic tangent and a sharpness function to reduce the effects of chattering and high-frequency interactions of the flexible parts and external disturbances in interaction with the rigid body and controller. The structure of the variable sliding surface with time has made it possible to adjust the effect of attitude parameters (quaternions and angular velocities) on the control performance. Also, the residual vibrations during and after the reaching phase are suppressed using a robust active vibration control algorithm. The simulations in the form of a comparative study show the performance and superiority of the proposed approach compared to conventional sliding mode control approaches for systems with structural flexibility in the presence of external perturbations and uncertainties.

In this study, it is assumed that the outer shell of the sandwich has a core made of functional calibrated materials with piezoelectric patches and the inner shell is made of layered composites. Double-walled cylindrical shells have three external, internal and middle acoustic environments and are exposed to acoustic waves with a specific angle of effect. The dynamic equations of the structure are derived using the hypothesis of first-order shear displacement field of shells and Hamilton principle and together with the fluid / structure boundary conditions form the final equations. Using the Fourier series expansions of the input, return, and output sound pressures and shell displacements, the dynamic equations are discretized to form a state matrix. After validating the results with existing articles, finally the effects, voltage applied by piezoelectric patches, percentage of functional materials, angle of fibers used in composites, types of composite materials, number of piezoelectric patches and angle of impact on the structure of sound transmission behavior It has been evaluated in a certain frequency range. Finally, the voltage parameters applied by the piezoelectric patches, the percentage of functional materials, the angle of the fibers used in the composites, the types of composite materials, the number of piezoelectric patches and the angle of impact increased the sound loss.

In this research, the free vibration of rotating tapered Timoshenko beam with piezoelectric layer has been studied. It is assumed that the beam is made of Functionally Graded Materials (FGM) through the thickness direction and the boundary condition is a cantilever attached to the hub. The first-order shear deformation theory has been used to drive governing equations. At first, the total energy of the system such as potential and kinetic energies for the beam and piezoelectric layer has been derived, and then the natural frequencies of the beam have been determined by the Ritz approach based on minimizing the total system energy. After verifying the results by comparing them with other research, the effects of some parameters such as hub radius, rotational speed, taper ratios, rotary inertia, material gradient, piezoelectric voltage, and beam thickness on the natural frequencies of the tapered Timoshenko beam have been studied in detail. The results showed that with increasing the angular velocity of the beam, the natural frequency increases so that as the increasing velocity increases, the natural frequency increases with a steeper slope.

In this study, the effect of material imperfection on the free vibration response of FG sandwich panel with piezoelectric face sheets is studied. A new hyperbolic shear deformation function is presented in this paper. The properties of the FG core varied along the thickness according to power law. The material composition in production process cannot be completely in accordance with the expected pattern, which leads to the production of imperfect FG material. Hence in this research, one perfect model and two types of imperfect models have been considered. The governing differential equations are derived using the Hamilton’s principle and solved using the Navier method. The effects of important geometric and mechanical parameters of perfect model and two types of imperfect model including thickness to length ratio, length to width ratio, FGM core to piezoelectric layer thickness ratio and electrical potential on natural frequency response of imperfect FG sandwich panel with piezoelectric face sheets are investigated. To verification, the analytical results obtained in this study are compared with the results presented in the literature, and in this comparison, a good agreement was obtained, which shows the correctness theory, deriving and solving equations.

In this study, sound transmission loss of a cylindrical shell made out of functionally graded materials with an arrangement of piezoelectric patches is investigated in the framework of the first-order shear deformation theory. Also, power law model is utilized to take into account material characteristics distribution along the thickness of the shell. It is noteworthy that both outer and inner piezoelectric patches are used as actuator and sensor. The structure is immersed in an acoustic medium of air and is subjected to acoustic waves with certain incident angle. The derivation of vibroacoustic equations in the form of coupled relations is realized by implementing Hamilton’s principle in conjunction with fluid/structure compatibility conditions. An analytical method is exploited to solve the coupled vibroacoustic governing equations with Fourier series. After validation study, parameter studies reveal the effects of the functionally graded index, incident angles, external electric voltage, and characteristics of piezoelectric patches on the sound transmission loss behavior of the structure in a certain frequency domain. Results indicated that with increasing the power law index, sound transmission loss decreases in the low-frequency region. Also, the applied voltage is able to improve the sound transmission loss especially in high-frequency region.

New technologies such as ultrasonic systems and water extraction from fog using metal nets can improve the performance of solar still desalination systems. Experimental results of the current study show that the use of ultrasonic cold vapor generator module and using fog-harvesting technology by metal mesh are effective in increasing the rate of surface evaporation of saline water, dropwise condensation, and freshwater production in the solar still desalination system. Based on the performance evaluation of the improved system by ultrasonic unit and metal mesh, it was found that with increasing ambient temperature and solar radiation intensity, the atomized droplets evaporate quickly with ultrasonic waves and have a remarkable performance. The results show that the evaporative heat transfer coefficient of saline water increases by 22.90% and the energy efficiency and internal exergy increase by 56.21% and 29.14%, respectively. The modifications also increase the production of fresh water in the improved system with ultrasonic and metal net up to 18.75% compared to the base system.

In the current paper, the piezoelectric energy harvesting of inhomogeneous beams based on modified beam models is studied. Different classical boundary conditions, which are combination of free, simply and clamped, are contemplated for the structure. The beam mechanical properties are assumed to vary based on the power law along the thickness direction in which volume fractions of the ceramic and metal part can be adjusted using FG parameter. Here, various beam theories such as Euler-Bernoulli, exponential, trigonometric, hyperbolic and fifth-order are modelled using a unified formulation. These beam theories are capable of catching rotary inertia effects and transverse shear deformations. The vibrational performance of the beam is affected by the harmonic vibrations of the base. Additionally, two different dampings including structural damping and viscous damping are modelled in the current formulation. Transverse deflection of the beam is obtained using modal expansion and then electrical power, current and voltage outputs are calculated. Ultimately, in the discussion section, the impacts of different parameters on the vibration and energy harvesting of the beam are analyzed.

In this research, a energy harvesting system was introduced in which two console beams coupled with ‎piezoelectric layers are ‎connected to a rotating rigid disk. ‎First, the system equations were written using the ‎electromechanical Lagrange equations and then solved by exact solution and resonance ‎approximation of the exact solution methods. The energy harvesting system was also simulated ‎in software. The effect of angular velocity on resistance, voltage and optimal power was ‎investigated and observed that increasing angular velocity, the optimal resistance and voltage ‎first decrease and then increase, but the optimal power first increases and then decreases. ‎Optimal minimum resistance and voltage and maximum optimal power are obtained at 44 ‎rad/s. The results showed that in this system in order to produce absolute maximum power of ‎‎0.094 W, electrical resistance of 1115 Ω is required. Power were also evaluated versus ‎electrical voltage and resistance. Moreover, comparison of the results of the three methods ‎showed very good agreement between the results of solving equations and simulation and ‎resonance approximation solution responses are simpler than exact solution ones and have ‎negligible error.‎