فصلنامه مکانیک هوافضا
سال سیزدهم شماره 4 (پیاپی 50، زمستان 1396)

In this paper, extended sliding mode observer is used for estimating of target maneuver for applying of augmented proportional navigation in terminal guidance phase of homing interceptors. Implementation of augmented proportional navigation is dependent on estimation target acceleration. Nonlinear estimation of target acceleration is desired, because of nonlinear engagement geometry in terminal phase. Therefore in this paper, sliding mode observer has been used. This observer in the presence of nonlinearity and uncertainty is able to estimating of target maneuvers normal to line of sight. Simulation results show the good performance of proposed observer and augmented proportional navigation with this observer. The augmented proportional navigation with this estimation of target maneuvers, produce lower commanded acceleration in comparison with robust guidance laws such as sliding mode guidance law.

In this paper, tracking control of unmanned surface vessels by using the robust mode sliding control in the presence of fixed and moving obstacles are investigated. The mathematical model of vessels is in three degree of freedom (3DOF) and only contains the kinematics and dynamics of relevant to surge, sway and yaw. These vessels are controlled in under actuated manner; although they have (3DOF), but only are equipped to two actuators in direction of surge and yaw. Next, we are used the mode sliding control method and introduced the first and second order of sliding surfaces as a function of tracking errors in direction of surge and yaw. Based on Lyapunov stability method, stability of dynamics of error has been proven. Then, we have put the fixed and moving obstacles in the trajectory of vessels to examine the safe crossing ability of them. Finally, numerical simulations are implemented to demonstrate the validity of proposed controllers.

In present study, dynamic response of viscoelastic beams subjected to moving harmonic loads and mass flow is investigated. A semi-analytical solution composed of the Galerkin and fourth order Runge-Kutta methods is adopted to solve the governing equation of motion. The results of this analysis are obtained for four different boundary conditions, namely pinned-pinned, fixed- fixed, fixed- pinned and fixed- free. The moving force is assumed to move with accelerating, decelerating and constant velocity types of motion and the mass flow has a constant velocity. The beam is assumed to be initially straight and the applied harmonic force and mass flow pass suddenly over the beam. Then, the effect of simultaneous and non-simultaneous application of harmonic force and moving mass on the dynamic beam response is investigated. It should be noted that the effect of force is removed after crossing the beam. In the present work, the effects of various parameters such as mass ratio, various types of motions, effect of applying force and mass flow and effects of various boundary conditions on the dynamic displacement of the beam are elucidated. Without mass flow, results are compared with the data in the previous researches and a good agreement is achieved. Also, for another comparison, the results of deflection presented here are compared with the generalized differential quadrature method and excellent agreement is obtained.

In this paper static analysis of functionally graded piezoelectric thick rectangularplate is studied using the higher-order shear and normal deformable plate theory of Batra and Vidoli. Advantages of this theory compared to the shear theories is that, the effects of the both transverse shear and normal deformations are taken into account and the deflection of the plate along the thickness is not considered as a constant. Simple exponential function is used to explain mechanical and electrical properties through the thickness of the plate.Three displacement components are expanded in the thickness direction using the Legendre polynomials, and the governing equations are derived using the principle of virtual work. Finally, the effect of various electrical boundary conditions (closed circuit, open-closed circuit and electrical loading) on both surfaces of the plate is investigated.

In this paper, simultaneously attitude and orbit determination of satellites using only star tracker measurement is investigated. At first, the 6 D.O.F. governing equation of the system considering the gravity force and gravity gradient torque is obtained using the Newton-Euler equations. Next using a simplified star catalog, star tracker output in the desired orbit is calculated. To estimate variables of the attitude-orbital equations, an estimation algorithm based on the UKF is proposed. In each step using the governing equation, estimated parameter and star tracker output, satellite angular velocity and orientation of body against NED frame are estimated and these calculated parameters are used as input for the next step. According to Results after about one revolution of orbit, the estimation is converging and the ratio of filter’s solution error to dynamic’s solution error for the roll and yaw angles is about 2 percent and for the pitch angle and angular velocities are about 33 percent. In order to reduce position and linear velocity errors, the filter needs more time and at the end of 6 cycles, the performance shows 40 percent improvement in average.

In this article, for constructing a desired formation by a group of unmanned small helicopters, a novel control algorithm is presented. Firstly, by using Newton-Euler method, dynamics equations of motion of one helicopter is derived. Main rotor thrust, tail rotor thrust, longitudinal and lateral tilt angles of main rotor are four control inputs of each agent. Leader-follower method is used for controlling the formation of agents, for this purpose, motion of the follower relative to leaders is derived. Then, sliding mode control (SMC) method is used to design a lower level controller. Each agent does appropriate reactions and adjusts its relative distances and directions according to the information which are received from others. For evaluating the presented control algorithm, simulations results is shown at the end.

In this paper, forced vibration steady analysis of thick functionally graded isotropic and transversely isotropic rectangular plates has been investigated. Based on the higher-order shear and normal deformable plate theory which was introduced By Batra and Vidoli, the governing equations are obtained using the principle of virtual work. In this theory, both shear and normal deformation effects in the thickness direction are considered. Also, the deflection of the plate along the thickness is not constant. A power law distribution is used to describe the mechanical properties of the functionally graded materials through the thickness. The numerical results have been presented for first to fifth order shear and normal deformable theory in tables and diagrams. The effects of functionally graded material properties and the geometric parameters of the plate on deflection and stresses have been studied. This investigation is shown that this theory gives accurate results not only for thin and moderately thick plates, but also for functionally graded thick plates.

This paper focuses on modeling, simulation, and control of a vision-based target-tracker robot with active force control (AFC) capability. The direct and inverse kinematics of the target-tracker robot is first investigated and then, dynamic equations governing the robot system are extracted using Euler-Lagrange approach. Afterward, the robot control system is simulated by three controllers namely proportional-integral-derivative control, computed torque control, and active force control. Assuming a circle-like path for the movement of the target in camera coordinates, a circle trajectory is chosen as the reference input to the robot control system. One of the main challenging problems in such robotic systems is the existence of unwanted disturbance in military conditions, which results in deteriorating the performance of the control system. For instance, there is often a cyclic disturbance affecting the machine gun that reduces accuracy of the target tracking control system. In this work, the active force control method as an efficient disturbance rejection technique is proposed to remove the disturbance affecting the robot system and its performance is evaluated under a sinusoidal disturbance. Furthermore, the performance of the AFC method is compared to the rest of the controllers. The obtained results clearly demonstrate the priority of the AFC approach in comparison with PID and computer torque control methods when the robot system is under disturbance.