فصلنامه مکانیک هوافضا
سال شانزدهم شماره 2 (پیاپی 60، تابستان 1399)

The main purpose of this study is to present an algorithm of lateral guidance for the articulated vehicles. The possible lanes are extracted based on the kinematics of AV in terms of non - collision with the other vehicle. In order to determine the desired trajectory, the dynamic of the AV and specifically its tire must be considered. First, a sixteen-degrees-of-freedom nonlinear dynamic model of an articulated vehicle is developed. Then, the vehicle model is validated using TruckSim software during a standard maneuver. Also, in order to design the control system a three-degrees-of-freedom dynamic model of an articulated vehicle is used. The degrees- of-freedom are yaw rate and lateral velocity of the tractor unit and articulation angle. Tire dynamic is simulated based on nonlinear model of Duggof. Finally, lateral guidance of the AV is applied by sliding mode control method. The results show the effectiveness of the nonlinear sliding mode control method for lateral guidance of the AV.

In this paper, the dynamics and vibration analysis of cylindrical shells made of graphite epoxy layers with two piezoelectric layers at both internal and external surfaces are investigated. . Extraction of motion equations is based on sanders theory for thin shells. Equations of motion, obtained by partial derivatives, are solved by fourth order Runge Kutta method. First, we examine a number of geometric parameters of the problem, including shell thickness, radius and length of the shell, and the angle of the fiber in the change of the fundamental frequencies. Finally, the effect of piezoelectric parameters on the vibrational and dynamic response of cylindrical shells has been investigated. In all cases investigated, with increasing L / R ratio, the effect of piezoelectric coefficients has increased. The influence of other piezoelectric parameters has also been evaluated in relation to this parameter in a frequency response is negligible.

Controlling product weight before packing is one of the main quality control features of many manufacturing processes. Although this issue can be done by the usual methods such as measuring scale, it can reduce the speed of the product line which is equipped with fast machines such as the delta robot. This paper presents an online method for the identification of the payload mass in the delta robot during the packing process. For this purpose, the governing dynamic equations of the robot has been written and after validating them by the ADAMS software, they are rewritten in linear regression form for the identification process. Then, the recursive least square method is used for the online parameters identification. Moreover, since the assumption of constant friction coefficients during the robot operation can reduce the estimation accuracy, these parameters are also estimated in each step with the payload mass. The proposed method is implemented in MATLAB environment and the simulation results illustrates the sufficient accuracy of the suggested method even in the presence of the measurement noise. Furthermore, the simulations indicate that the method have high convergence rate and the payload mass can be estimated with a small number of data and in a short time.

In this study, an active steering system is proposed to control an articulated heavy vehicle during high-speed intelligent lane- change maneuver for obstacle avoidance. For this purpose, a simplified model of an articulated heavy vehicle is created in MATLAB/Simulink, then three control systems, i.e., model predictive controller (MPC), Linear quadratic integral (LQI) controller, and 2-DOF PID controller, are designed for its front axle steering system. Furthermore, the constraints associated with the vehicle lateral stability using the sideslip angles of the truck and the semi-trailer, and the reference articulation angle for the vehicle trajectory is defined, then the stability of the vehicle during moving on dry and slippery roads are investigated. In addition, in order to evaluate the performance of the control systems, two different scenarios, i.e., first, facing an obstacle on a dry road and second, the same situation on a slippery road, are taken into account and are fulfilled on the basis of a co-simulation between MATLAB and TruckSim. In the next step, to optimize the controllers' coefficients, some various tests are performed and implemented in TruckSim software and using an intelligent method, the optimal coefficients are obtained. Finally, the performance of the three controllers are compared to assess their strengths and weaknesses. The comparison shows that model predictive control (MPC) system is advantageous for this purpose.

Delamination is one of the common flaws in the composite plates, which may be created during manufacturing, boring or loading in the composite plate. This flaw has an impact on the flexibility, strength and performance of composite plates and structures and reduces them, which may even result in a layer fracture or complete fracture in the composite plate. In this study, a circular composite plate with the circular delamination under buckling load is considered. Given that the delamination grows and the delamination boundary is movable, the equilibrium equations governing the circular plate with circular delamination is produced by using Calculus of Variations method with moving boundary. The theory used in this paper for finding equilibrium equations governing the mentioned plate is the third order shear deformation theory. Ultimately, for isotropic and orthotropic materials, the critical buckling load is determined by using spectral homotopy analysis method and the results of the present paper is compared with the results of other studies. The results produced shows a good conformity with the other reference results.

In the present paper, a new systematic iterative analytical procedure for low-velocity impact analysis of composite plates is presented. In this method, assuming the exponential equation similar to the Hertzian contact law, using the principle of minimum potential energy and the energy-balance model between the indenter and the plate, the unknown coefficients of the exponential equation are obtained analytically. The elastic strain energy resulting from bending in the composite plate and external work due to indentation load is evaluated using an appropriate shape function for the composite plate deformation. Using the present method, in addition to reducing the runtime, the problem-solving process is carried out with appropriate convergence. Accordingly, contact coefficients for various types of composite plates with different boundary conditions have been calculated. The results are in good agreement with the experimental and numerical results. The force-time response and structure response to low-velocity impact with various boundary conditions are investigated. Also, considering the importance of physical and geometrical parameters such as mass and velocity of the impactor, the dimension of the composite plate, and the effect of these parameters on contact force history are studied. It has been shown that with increasing diameter and velocity of the impactor, exponent value in nonlinear equation contact will increase, while this parameter decreases with increasing mass of the impactor

In the present paper experimental study has been performed to investigate heat transfer under row of jets impinging to an asymmetric concave surface. In this regard two asymmetric concave surface with curvature radiuses of (8, 12) and (8 , 24) cm have been considered. Constant heat flux of 2000 W/m2 is applied on the concave surface using a silicon rubber heater mat. In the steady-state condition the temperature distribution of the concave surface is measured with an infrared camera. The studies of asymmetric flow and heat transfer in asymmetric surfaces have been carried out for three Reynolds numbers of 10000, 20000 and 30000. Results show that, the concave surface with lower curvature radius has more values of Nusselt number distributions. The present results confirm that the Nusselt distribution is asymmetry along the S axis. In the axial direction, symmetry distribution is observed for Nusselt number.

Defective pieces detection is one of the processes which is done by workers during production. In this article, a plan was offered for increasing the speed of dimensional controlling of the pin type pieces, before consuming in production line. For this purpose, pin dimensions were determined in the laboratory by computer and the coordinate measuring machine. Also, the dimensions of input pins were recorded by cameras, before using in production. These two groups of data were compared by Matlab software. In the next step, the desired tolerance dimensions were given to the software and the pins with mismatch dimensions were specified. It should be noted that the difference in the output from the software and the measurements by the coordinate measuring device was 0.2 mm. This difference could be decreased by increasing the resolution of the camera. Due to the position of the camera at the top of the work screen, the position of the pins is not limited in angle and shape. In this paper, the time period of control of pin dimensions has significantly decreased in comparison to manual control by manpower. It is also possible to examine the dimensions of several pieces simultaneously.