نشریه مهندسی مکانیک ایران
سال بیست و ششم شماره 3 (پیاپی 76، پاییز 1403)

In this study, the dynamic response of an annular sector plate in contact with incompressible fluid under harmonic load is investigated. The governing equations of the plate are derived based on First-order Shear Deformation Plate Theory (FSDT) with consideration of rotational inertial effects and transverse shear stresses and using the Hamilton’s principle. In addition, the governing equation of the oscillating behavior of the fluid is obtained by solving the Laplace equation as a function of velocity potential and satisfying the boundary conditions of the fluid. The differential quadrature (DQ) and Newmark methods are used to determine the vibrational behavior of the plate. The results of this study are compared and validated with results of other works and Finite Element Method (FEM) software. Finally, the effects of the different geometrical parameters such as the inner radius to outer radius ratio, the height to Thickness ratio, thickness to outer radius ratio of plate, fluid density and fluid height to plate thickness on the dynamic response of the plate are investigated.

Controlling a humanoid robot is a complicated task because it deals with a high degree of freedom, a non-holonomic and underactuated system. Many model-based control strategies have been implied on humanoid robots. Over time model-free and AI-based strategies have taken place. Among AI strategies, Reinforcement Learning has the largest share. Many complex systems have successfully controlled to perform complicated tasks such as jumping and running. Toe joints is almost missing in all of these systems and does not have the application it performs in humans. Toed robots can outperform, so implementing Reinforcement Learning algorithms on a humanoid with an active toe joint has been studied. Two algorithms, DDPG, and TD3 were applied and compared. A customized RL framework was designed to teach a humanoid to walk. Simulations showed that the task of controlling a humanoid to walk was accomplished. Learned robot was able to gait on a flat surface at the average speed of 0.9 m/s.

In the current study, with the help of Adams and MATLAB software, a seven-degree-of-freedom wheeled autonomous robot with a mechanism of adaptation to the passive pipe diameter and benefiting from a fuzzy controller to guide the movement path was designed and simulated. The control system of this robot consists of two inputs, which are the difference between the desired speed and the actual speed of the robot (error) and its rate of change (acceleration) and an output, which is the voltage of direct current motors. In this research, the dynamic simulation of robot movement in different geometrical conditions such as straight and vertical pipes, elbows, pipes with reducer, sediments and corrosion was investigated through the design of the fuzzy controller, and the obtained results show that the modeled robot was able to Standard pipes with a diameter of 20-32 inches, as well as pipes with a diameter change or a 90-degree bend with a radius of curvature between 408-763 mm can pass successfully. In addition, the use of a spring instead of a motor in the design of this robot, in order to adapt to the diameter of the pipe, has been a solution to reduce production costs. Therefore, instead of using a motor and two separate controllers (one to adjust the adaptation mechanism to the diameter of the pipe and the other to supply the torque of the robot's wheels), this robot was able to advance its movement using only one controller and from this point of view, it has shown the economic potentials for making real samples, product commercialization and responding to the needs of some industries in the country.

The current research has studied the piezoelectric blade sensor from different views in order to control the oscillations of the circular cylinder present upstream of the piezoelectric blade and to control the fluctuating fluid flow around the blade using the force on the piezoelectric blade. The desired arrangement of a piezoelectric blade is placed downstream of a circular cylinder and with the help of a certain limit of blade oscillations, the hardness coefficient of the cylinder spring is applied from 65 (N/M) in normal condition to 100 (N/M) in the necessary condition. The controller as well as in other cases, the damping rate increases from zero to 0.02 (Nm/S) and in this way, the oscillations of the cylinder are controlled. In the same way, by controlling the oscillations of the cylinder, its effect on the oscillations of the blade, which is located downstream, has been investigated under the title of feedback effects. By controlling the feedback of the force on the piezoelectric blade in a closed loop, it is possible to monitor the displacement of the tip of the blade and the force on the piezoelectric blade. In these studies, it has been determined that in the case where the specific limit of the controller is 0.7 mm of the oscillations of the piezoelectric blade tip, due to the earlier application of the controller compared to the specific limit of 1 and 2 mm of the oscillations of the blade tip, the oscillations of the cylinder are Also, by comparing the state where the controller is included in the circuit compared to the state without the controller, it is clear that the oscillations of the blade and cylinder have been controlled to some extent.

One of the most significant operational aspects of vehicles is their safety in critical braking maneuvers. Proper braking performance occurs when the stopping distance is minimized while the vehicle’s steerability is maintained. To meet these objectives, the tire slip ratio should be regulated at its optimum value. In this study, a control system is designed for simultaneously controlling the brake torque of the front and rear wheels using the nonlinear prediction-based control method. In the control design process, the pitch dynamics have been considered which plays an important role in braking maneuvers. Moreover, the instantaneous optimum wheel slip is determined via an artificial neural network (ANN) to improve the performance of the system and achieve the maximum possible brake deceleration. The performance of the designed control system is investigated through conducted simulations in the CarSim and Matlab/Simulink software environments. The obtained results confirm the enhancement in the braking performance along with a considerable reduction in the stopping distance.

This paper determines the buckling load of an axisymmetric cylindrical shell of homogeneous and isotropic materials analytically using the first-order shear deformation theory (FSDT). To describe the kinematics of the shell, the FSDT, and von Karman relations are used. The equilibrium equations, which are a system of nonlinear coupled differential equations, are determined from the principle of virtual work. The nonlinear equilibrium equations are solved analytically using the perturbation technique and then the stability equations are derived from them by employing the adjacent criterion method. The resulting equations are a system of coupled linear differential equations with variable coefficients that are solved analytically to find the buckling load of the structure. The effects of geometrical properties have been investigated by a parametric study on buckling load results. Also, the buckling load is determined using the finite element method (FEM) and classical theory (Lorenz) and compared with the analytical solution results.