نشریه مهندسی مکانیک ایران
سال بیست و چهارم شماره 3 (پیاپی 68، پاییز 1401)

Due to important role of composite materials in broad spectrum of applications, this paper focused on bending of a functionally graded graphene platelet reinforced composite porous circular/annular plates with various boundary conditions by employing state-space differential quadrature method (DQM). Equations of motion are established within the framework of theory of elasticity and are formulated along the thickness direction in the form of state-space. Applying DQM along the radial direction provides a semi-analytical solution to bending of the plate. The results of applying present approach are validated by comparing them with those reported in the literature. A thorough parametric investigation is conducted on the effects of different GPLs distributions integrated with various distribution patterns of internal porosity, thickness to radius ratio, graphene platelets (GPLs) weight fraction, porosity coefficient and edge boundary conditions on the bending behavior of FG-GPLRC circular/annular plates. The results reveal a very useful practical designing hint that locating more GPLs in the vicinity of the upper and bottom surfaces of the circular/annular plates with lower outer radius to thickness.

In most research on parallel cable robots, control input energy norm (with two-squared cost function), also known as the least-squares method is widely used, but in addition to the advantages of this method, such as smoothness and differentiable, in the case of the current cable robot, where the cable structure has a physical meaning only in the positive range, using the linear cost function is sufficient in terms of mathematical modeling. With this replacement, without compromising the convexity, the optimization problem on the robot is solved with the low tensile limit and the high rupture limit, and the equal constraint tensile strength of the cables and the moving platform. The simulation results show that while the mentioned the alternative in the cost function does not have a significant effect on solving the optimization problem with numerical methods, the reduction in the average elapsed time to achieve the optimal solution is about 3 times, compared to the analytical method with the two-squared cost function, and is obtained at least 80 times that of numerical methods.

This paper presents a new method of energy management (EM). The proposed method was defined as a reinforcement learning problem for a system consisting of solar panels, wind turbines, gas engines and batteries. The best corresponding energy managements for all the possible system states were found by employing the Q-learning algorithm to solve the EM problem. These results were then used for managing the power supply of four residential buildings in Negin Island Bushehr located in the southwest of Iran. The simulation was performed for 8760 hours of a year. The proposed energy management method was compared with the load following energy management, which resulted in a 2.4% reduction in annual operational costs and a 3.7% reduction in CO2 emissions. With the same quality of the results, the new EM method took about 2.5 times less computational time compared to the optimum energy management performed by genetic algorithm. The effect of iteration number on the convergence of algorithm was also investigated.

In this study, the effect of different depths on the performance and efficiency of a B-Wageningen series close to surface of water have been numerically investigated. For this purpose, the ANSYS-FLUENT commercial software has been used to solve the viscous, incompressible and two phase flow field. The rotation of the propeller has been implemented using the rotating reference frame model for steady flow and the sliding mesh for unsteady flow. For turbulent flow modeling and free surface simulation, the k-ω SST model and the volume of fluid method have been used, respectively. For validation of numerical results due to lack of access to experimental results of propeller close to surface, numerical solution in open water condition has been performed and performance coefficients have been calculated. Comparing the numerical results with the experiment ones shows good agreement. The results of the numerical solution show.

The purpose of this paper, is to investigate and provide robust PID control for flexible satellite considering thruster actuator dynamics. The flexibility of the satellite causes a change in the dynamics of the entire satellite. During the maneuver, stochastic disturbance torque and system inertia uncertainty are applied to the satellite. The thruster is an actuator used to execute control commands using a PWPF modulator optimized by a genetic metaheuristic algorithm Optimization of thruster and robust PID controller coefficients are other innovations of this paper. By adding angular velocity and control torque constraints, the designed robust control first performs well; And secondly, it is robust to internal and external uncertainties.

Although ECG signals contain rich enough information about the heart function, neither the clinical cardiologists nor researchers and engineers with their developed algorithms can illustrate all of this hidden information without some ECG pre-processing attempts. The standard 12- lead ECG signals represent the magnitudes of the heart's electrical activity at any instant in a cardiac cycle. Still, the direction of these signals is not clearly shown in ECG leads. On the other hand, in VCG, we have both the magnitude and direction of the heart's electrical signal, but the time is hidden. In this paper, a new approach has been proposed that, without requiring complicated calculations, represents and visualizes the magnitude and direction of the heart's electrical activity as a function of time. Unlike the normal 2-dimensional ECG for several leads, in this new 3-dimensional proposed ECG(Time Vector Electrocardiogram), any two arbitrary frontal leads are shown versus time. The resulting curve is independent of the selected leads; thus, only a single 3-dimensional curve is obtained, which contains and illustrates more information about the heart function. Some applications of the proposed method are presented in this paper by using the ECG data for patients from the G12EC database. If this new approach is welcomed by cardiologists and field experts, we believe that it would greatly assist them in diagnosing heart behavior and its possible abnormalities more clearly and much faster.

The application of the negative Poisson’s ratio materials (auxetic materials) is growing rapidly. Although these types of materials were found in nature, these materials are designed and made for industrial applications. The layout of the microstructure of auxetic has a big effect on their Poisson’s ratio. The present study aims to design the microstructure of auxetic materials by utilizing shape optimization of some moving components and by finding their position to minimize Poisson’s ratio. The shape of components is defined by a few variables explicitly which is a great advantage in the manufacturing of the final design. Due to the periodic structure of auxetic materials, the design problem is defined as the compliant mechanism topology optimization of one cell. A first-order method called the method of moving asymptotes (MMA) is utilized to solve the optimization problem. The core of the first-order methods is to find the gradient of the objective function and constraints with respect to design variables. The topological derivative for the compliant mechanism is utilized for this purpose. The obtained microstructure shows the efficiency of the proposed approach. Moreover, a sample of the designed structure is made using an additive manufacturing technique.