فصلنامه مکانیک هوافضا
سال دوازدهم شماره 1 (پیاپی 43، بهار 1395)

In this article، free vibration analysis of thick functionally graded isotropic and transversely isotropic rectangular plates are investigated. Based on the higher-order shear and normal deformable plate theory of Batra and Vidoli، the governing equations are obtained using the principle of virtual work. The equations are then solved analytically، assuming the simply support boundary condition along all edges. In higher-order shear and normal deformable plate theory، the effects of the both transverse shear and normal deformations، are considered. Advantages of this theory compared to the shear theories is that، given that deflection of the plate along the thickness is not constant، for thick plate provides more accurate results. A power law distribution is used to explain the variation of mechanical، electrical and physical properties through the thickness of the functionally graded materials. Furthermore، after showing the accuracy of present analytical approach، the numerical results for different plate parameters has been listed and the different parameters effect on the plate natural frequencies has been studied in details. This investigation is shown that when fifth-order expansion is used، the results of this theory for natural frequencies of thick functionally graded rectangular plates are very close to those obtained from three dimensional elasticity theory.

one of the main concerns in the present navigation systems is their single-based. Navigation rely on one system will be very insecure and subjected to very high probability of errors. Therefore, having a navigation aid system or the use of two sensors at the same time can be the best way to reduce this very serious risk. In this research, simulation and software design to optimize movement and autopilot of small aircraft has been considered. At first, dynamic modelling of the aircraft with integrated inertial navigation and extended Kalman filter is developed. To obtain reliable results, the position and inertia sensors as well as actuator errors are modeled in simulation of the aircraft. Furthermore, to get closer to the reality, weather conditions for different wind speed also simulated and added to the PID control system. In order to increase the accuracy of the control system and ensure the precistion of performance, all commands and algorithms of the control system have been designed in three level and tested in two stages of open-loop and closed-loop simulations. The closeness of simulation results with of experimental tests indicates the correct choice of control algorithms, suitable modeling of components and precision simulation of the system.In this article, design and optimization of the nonlinear autopilot software of Desert Hawk hand launch UAV is reviewed using GPS and INS systems. To obtain more realistic results, the sensors and actuators of the autopilot have been modeled and installed in the control system. According to the complexity of the flight algorithm, PID controller is used in the series circuit. The comparison between the results of this method and experimental results approves the appropriate design and simulation of the system components.

Improvements in the level of autonomy of unmanned air vehicles (UAVs) are highly desirable and under pursuit by many researchers. The motion planning problem is one of the vital issues for autonomous vehicles. In motion planning, a trajectory is provided for the vehicle from a known location to a predefined target point. In order to provide feasible trajectories, one needs to consider the vehicle performance and dynamic constraints. In this regard, in the current research, by utilizing the nonlinear dynamic model and performance and dynamic capabilities of the vehicle, feasible trajectories are generated. Particle swarm optimization method is enhanced to handle the motion planning problem. Evaluation of the proposed algorithm, via simulating various scenarios, reveals its capability in generating optimal trajectories through terrain and threat obstacles.

This paper, provides tracking of moving targets in plane, based on observation angle data. Presented viewpoint is applicable in terrestrial and marine target tracking. Here, in order to overcome measurements noise, common estimation filters including, first and second order extended kalman filter(EKF1 & EKF2), unscented kalman filter(UKF) and smoothing filters is used, to achieve accurate estimation of target position. In order to demonstrate performance of mentioned filters, tracking of a marine target in the path of the Persian Gulf to Oman Sea is simulated. Monte Carlo simulations express identical performance of EKF1, EKF2 and UKF. Also it is revealed that using smoothing filters is resulted in more accurate estimation about three times. Finally due to system dynamic and considering accuracy and processing volume, EKF1 with smoothing filter is proposed for tracking of moving targets.

In this paper a method for online identification of moment of inertia tensor parameters of bodies based on recursive least squares method, with a 3 axis reaction wheel air bearing satellite simulator is presented. Dynamics of simulator is implemented in special manner. The only available sensor is a three axes rate gyro which measures the angular velocity of satellite in the body coordinate system. Due to existence of noise in this sensor, the regressor matrix that used in least squares method is not deterministic. So in this case, the classic least squares method cannot be utilized, and its convergence is not guaranteed. For solving this problem, a modified least squares method with robust scheme is presented and its stability is proved. Simulation Results have proved the success of this method in identification of inertia tensors using an air-bearing simulator.

Modal analysis is done periodically to ensure blades performance for non-occurrence of resonance obtained under various operating conditions. Since metal or composite helicopter blades have a certain flexibility at different speeds in different planes can lead to deformation of the structure that can have a great effect on the aerodynamic performance of the helicopter. In this paper, modal analysis of helicopter blade has been carried out by the lumped mass methods (myklestad and finite element method) and modal test on the rotor structure. The finite element analysis has been developed by two approach of analytical and software method. Modal testing was also performed in both static and dynamic states, with constant speed, to validate the lumped mass methods. Finally, the results of both methods are compared with each other. After ensuring there correspondence between lumped mass methods and experimental results, an analysis was done according to the operating conditions of the rotor and finally Campbell diagram has been generated. According to this diagram became clear there was not any problem with the resonance of the rotor blades, while the numerical result of case has an acceptable match with the experimental results.

In this article, free vibration analysis of thick functionally graded piezoelectric rectangular plates in closed circuit condition is investigated. Based on the higher-order shear and normal deformable plate theory, the governing equations are obtained using the principle of virtual work. The equations are then solved analytically, assuming the simply support boundary condition along all edges. In higher-order shear and normal deformable plate theory, the effects of the both transverse shear and normal deformations are considered and displacement, potentioal components are expanded in the thickness direction using the Legendre polynomials. Advantages of this theory compared to the shear theories is that given that deflection of the plate along the thickness is not constant, for thick plate provides more accurate results. A power law distribution is used to explain the variation of mechanical, electrical and physical properties through the thickness of the functionally graded materials. Furthermore, after showing the accuracy of present analytical approach, the numerical results for different parameters such as power of functionally graded piezoelectric material, various thickness to length ratio and piezoelectric effect on the plate natural frequencies has been studied.

Thermoelastic damping is recognized as a significant loss mechanism at room temperature in micro and nano-scale resonators. In this paper, the governing equations of coupled thermoelastic problems are established for axisymmetric out of plane vibration of rotating circular plate with constant angular velocity about its central axis. Then the Quality Factor obtained by finite element analysis using ANSYS software, as a function of rotation, environmental temperature and plate dimensions. The results for non rotating plate are verified based on the results obtained by the previous works. Then the effects of rotation, environmental temperature and plate dimensions on the thermoelastic damping are studied. The results show that, thermoelastic damping would be rise to a maximum value at specific sizes of plate, which is dependent on temperature and angular velocity.