Scientia Iranica
Volume:30 Issue: 5, Sep-Oct 2023

In this paper, a multi objective model in which operation planning and tool assignment in a flexible manufacturing system (FMS) has been considered simultaneously. In this regard, the main characteristics of FMS have been analyzed. Then, a comprehensive model, including major system parameters and cost components have been designed and presented. The proposed model contains cost factors including machining cost, earliness and tardiness penalties, tool and part movement or switch costs and idle time costs of tools and machines. Then, a multi-objective model for the problem has been proposed, in which the relative importance of each cost through weighting these costs based on the decision making goals and sum of the mentioned costs have been considered simultaneously. Based on the complex nature of the problem, standard solution techniques have not been employed. Therefore, to reduce computational times, simulated annealing (SA) algorithm has been used for about 30 minutes (10,000 movements). The total production costs has been decreased from 7,000 to 4333 units using SA algorithm. Based on the results, 38% reduction in total production costs has been achieved. Computational results revealed that the proposed method is quite efficient in multi objective optimization of FMS within a short computational time.

In this study, we create an evolution function that assesses prosthetic hands in terms of their ability to grasp various objects like a human hand. It is required to evaluate the reachable workspace of prosthetic hands and grasp ability to assess it completely. The first one can be done by using forward kinematics. The Volume of the Grasp Wrench space, one of the grasp qualities indexes, is used to measure the second one. Randomization and grasp taxonomy are used to generalize the grasp quality to indicate the prosthetic hand functionality. Afterward, the created evaluation function is used to specify the importance of each finger and DOF. the results show that the most significant finger is the Thumb. The most crucial DOFs are the abduction movement of the Thumb's CMC joint and the Index's MCP joint. Finally, optimized hand configuration is created, considering limitations which are a number of actuators and stationery DOFs. Optimization has two steps. In the first step, the stationary joints and the joints that should be actuated independently from each other are chosen. In the second step, the remaining DOFs are specified to be coupled with which actuator using the Taguchi method.

Asbestos has been banned in many countries as a result of its negative effects on the environment and human health. As a result, a human-friendly friction material is required to replace asbestos in brake pads. Hence, the powder metallurgy technique was undertaken to develop friction material from locally sourced asbestos-free materials. Seashell was used as base elements with other additives. The filler material considered had a particulate size of 300 µm, and epoxy resin was used as a binder. The produced brake pads were evaluated and compared to commercial brake pads in terms of their physical, mechanical, and tribological properties. According to the investigated properties of the developed brake pads, increasing the seashell content in the formulated brake pads resulted in a decrease in wear rate, and compressive strength. Water absorption, hardness, oil absorption, density, and thermal conductivity all varied differently at the same time. The coefficient of friction of the produced friction material ranges between 0.311-0.353. The results showed that seashell particles could effectively replace asbestos in producing friction material for brake pads in an automobile.

An artery afflicted with multiple stenosis is the focus of this study, which emphasises the electro-osmotic effects. The artery's walls are porous and slip boundary effects are present. Blood flow problems are better modelled with a slip and porous border. It is examined extensively due to the wide range of applications in the medical field, especially in the diagnosis of drug delivery and handling of cellular irregularities. In this paper, we have visualised the non-Newtonian behaviour of blood by using viscoelastic fluids as a Williamson fluid model. A mathematical model for an incompressible fluid is being created, and the mathematical issue is then transformed into its dimensionless form by applying limitations in the case of mild multiple stenosis. As soon as the problem is put into a dimensionless form, the partial differential equations for the velocity profile and temperature profile can be found. Analytical solutions of the resulting system are calculated with the help of the Homotopy perturbation method (HPM). The visual representation of analytically obtained solutions is investigated for both symmetric and non-symmetric geometries of stenosis. For varied values of flow rate Q and electro-osmotic parameter m, the streamlines are examined in detail.

Dimensional synthesis of mechanisms to trace given points is an important issue in mechanism and machine science. Having no exact solution makes this issue an optimization problem. This study offers an optimization approach for the dimensional synthesis of planar mechanisms. Four-bar mechanisms having one degree of freedom (DOF) are chosen as the configurations. The proposed method is implemented by establishing the objective functions with specified constraints and searching for the results by using an optimization algorithm. Genetic Algorithm (GA) in Optimization Toolbox-Matlab® is selected as a solver. Different types of four-bar mechanisms like crank-rocker and double-crank including different target points are performed. Mechanisms are depicted by resulted parameters and a Matlab® script prepared plays their animations. As a result, it is proved that the mechanisms whose dimensional properties are obtained by the GA solver have a good tracing capability for the desired paths. This study has the property of being a design guide. Its application is not limited to four bar mechanism. Planar mechanisms with different configurations can be easily synthesized by using this technique.

In this study, the new mobile robot with N parallel axles were designed and developed as well as its motion equations derived. It uses several parallel axes, which, at different surface conditions, increase its mobility compared to similar ones. The number of parallel axes in such robotic systems makes studies the effect of slip mandatory due to the increase in the wheels contact area. These effects make a difference in the mobile robot kinematic constraints equations. The mobile platform requires a suspension system for reducing the effects of oscillations due to the floor. Finally, the dynamics model of a mobile robot obtains by considering the effect of wheels slips, suspension, and parallel axles using Lagrange equations. The concluded model is simulated for a two-axis mobile robot with four-wheels in different surfaces conditions. It can be seen that the deviation of the robot is eminent besides that the wheel's slips affect the system performance based on the floor conditions. Consequently, the robot deviation on ice is less than that on loose gravel, while the mentioned deviation on the loose gravel being twice. This robot can be used as space exploration, rescue robot and neutralizing due to its mobility efficiency and accuracy.

In recent decades, reverse flow analysis in mixed convection flow has attracted the attention of many researchers owing to its applications in the design of medical and engineering systems. The presence of reverse flow is unfavorable in many respects; therefore, it is crucial to find values of critical parameters affecting the reverse flow to eliminate it. In this paper, the thermal and hydrodynamic behavior of MWCNT-Fe3O4 hybrid nanofluid is explored in a vertical cylindrical annulus and in the adjacency of radial magnetic field by achieving the results of the exact solution. Furthermore, the effective factors on the reverse flow are investigated, considering the effects of wall movement and suction/injection on it. The range of changes of the governing parameters includes constant velocity of cylinders’ walls A=0−10, B=0−10, Mixed convection parameter η=-1500−1500, dimensionless temperature difference ratio ξ=0−1, Hartman number Ha=0−50, Suction/injection S=-6−6, nanocomposite particles concentration φ=0−0.3% and radios ratio λ=2−10. The results reveal that hybrid nanofluid enhances the heat transfer rate. Moreover, by changing the above-mentioned parameters and selecting the appropriate values for them, the flow, heat transfer and occurrence of reverse flow can be optimally controlled. Meanwhile, such parameters as Ha, S and ξ perform better in eliminating reverse flow.