نشریه مهندسی مکانیک ایران
سال بیست و سوم شماره 1 (پیاپی 62، بهار 1400)

Modeling mechanical and thermal properties of nanocomposites is usually carried out via multi scale modeling, where the Finite Element approach is more common in homogeneous. Which can be used with identified properties of the components as a numerical approach. The use of nanoparticles significantly affects the mechanical, thermal, electrical, and mechanical strength properties. Coiled carbon nanotubes, due to their high flexibility, tolerate more strains and have recently attracted the attention of researchers. The purpose of this study is to modeling of the effective thermal conductivity of coiled carbon nanotube reinforced polyethylene nanocomposite through finite element approach. Coiled carbon nanotubes are distributed using the Monte Carlo algorithm in a uniform manner with different aspect ratios, volume fractions, and different geometries of nanoparticles in polyethylene via developing script codes. Using finite element algorithm, thermal analysis is conducted. According to the results, it is shown that increasing the volume fraction, aspect ratio, inner or outer diameter of the Coiled nanoparticles, the thermal conductivity coefficient grows, which for 0.71% volume fraction, the thermal conductivity increases by 9.35% while for the inner or outer diameter of the CCNT, has a minimal effect on the thermal conductivity of the nanocomposite by 1%. By increasing the radius of Coiled carbon nanotube from 15 to 30 nm, the thermal conductivity coefficient decrease by 2.7%.

People suffering from neuromuscular diseases, may also face certain abnormalities in their walking pattern. Drop foot patients suffer from some restrictions in dorsiflexion as well as in controlling their plantarflexion during the gait cycle because of abnormal stiffness pattern of the ankle joint. The two major complications of drop foot are slapping of the foot after heel strike (foot slap) and dragging of the toe during swing (toe drag). The current treatment options like Ankle Foot Orthosis (AFO) while offering some biomechanical benefits, do not adapt to different walking conditions and fail to eliminate significant gait complications. This study proposes a passive Ankle Foot Orthosis design which combines an AFO and torsional spring. The required moment to reproduce the stiffness of a normal ankle joint is calculated using the OpenSim software package in conjunction with the data collected from the motion analysis of each patient. Torsional spring was then used to reproduce the calculated moment for different levels of muscles weakness. It is shown that by designing patient-specific orthosis, the stiffness profile of normal joint for each patient with distinct level of muscles weakness can be reproduced.

New forming processes should be capable of manufacturing complex and high quality components in addition to low production costs and high production speeds. The gas pressure forming process is one of the methods used in forming these parts. In this research, the formation of Al-A356 alloy sheet in incomplete cone with gas pressure process has been studied numerically and experimentally. In general, it can be said that the purpose of this study is to investigate the effect of parameters such as the ratio of diameter to height of the die, angle, temperature and pressure. In order to determine the effect of parameters, filling the corners of the die and distributing the thickness of the parts under different pressures has been investigated. Also, for simulating validation, the simulation results were first compared with experimental tests. The results show that the mold filling will improve around 15% by increasing the pressure from 1 bar to 8 bar. However, is reduced to less than 0.5 mm. Although, the mold filling increased by decreasing of the ratio of diameter to height but the critical thickness of the sheet is decreased around 14%. It was also found that for having a proper mold filling, it is necessary to increase the pressure value around 25% when the cone angle decrease from 30º to 0º. The results also showed that by increasing the temperature from 350°C to 550°C, the required pressure for filling the mold decreased from 8 to 2 bar.

Steel sheets are used in various industries such as automotive, aerospace, and … . The issue of impact and penetration in steel sheets has been the main focus of many studies. In this study, Laboratory and numerical studies of flat and reinforced steel sheets by steel reinforcement have been performed under the of impact caused by free fall of the weights. Steel sheets used are steel St12. The material and thickness of the pendentive used are similar to the sheet and have a width of 2 cm. The parameters have evaluated include the amount of impact acceleration on the sheet, the rate of permanent deformation, and the amount of energy absorption for simple and reinforcer flat sheets. The numerical modeling of Abaqus finite element software is used. The results show that the use of reinforcer causes a slight increase in the acceleration of the sheet and a significant reduction in its permanent deformation.

In this paper, a new adaptive control system is presented for suppression of boring bar chatter in internal turning process. The vibration control system is consisted of electromagnetic actuator, boring bar, accelerometer and a novel adaptive control algorithm. The controller gain is adaptively adjusted according to the operating condition of actuator and the level of boring bar vibrations. Such that the consumed actuator power always remain proportional to the intensity of chatter vibrations due to cutting process. As a result, the gain adaptation algorithm is indirectly developed by using the dynamic characteristics of actuator-boring bar assembly. Firstly, the tunable parameters of adaptive controller are optimally identified by conducting impact tests. Secondly, the performance of adaptive controller is investigated during the internal turning of Aluminum alloy 6063-T6. The presented adaptive control system can improve the dynamic stiffness of boring bar as well as the critical limiting depth of cut on stability chart by at least 10 folds. Due to optimal performance of the adaptive controller, the dominant magnitude of boring bar’s power spectral density is successfully attenuated up to 78 dBs. Also, the roughness of cut surface is reduced from above 40 micrometers in control-off cutting test to below 5 micrometers in control-on test. Moreover, the actuator cost is considerably reduced for adaptive controller, in comparison to the optimal constant-gain integral controller. As a result, by using the proposed adaptive control algorithm, a smaller electromagnetic actuator with lower power capacity can be used for chatter suppression at the same cutting conditions.

Quadrotor is an underactuated and nonlinear coupled system. in this paper for controlling the dynamic of the system, feedback linearization (FL) method is used to convert the nonlinear model to a simple linear one. Moreover, a combination of fractional order PID (FOPID) with FL is used to improve the tracking ability. Tuning the parameters of NFOPID, because of two more orders of integral and derivation is a complicated task; therefore neural networks (NNs) method is used to cope with this duty. Back propagation (BP) algorithm is used to train the weights of the NNs. Because of the flexibility and online learning of the NNs, the proposed controller can be robust against uncertainties and disturbances. The fractional order operator has infinite dimension and for practical implementation modified Oustaloup's method is used in this paper. and finally the results of the simulations also validate the effectiveness and robustness of the proposed scheme.

Recent developments in control and the use of automatic agents result in attracting attention to the cooperative systems and their abilities in performing efficient missions. Optimal task assignment of multiple cooperative agents is among the most important factors in effective performing of robots and UAVs' cooperative missions. Uncertainty and dynamic conditions are some of the most essential criteria during the simulation of mechanical phenomena.In this paper, the task assignment of a fleet of cooperative heterogeneous UAVs in a dynamic environment including moving targets was examined. An appropriate architecture was applied by using a hierarchical mixed-integer linear programming in order to solve task assignment problems within the reasonable range. To enhance the outlook of solution architecture and therefore achieving some near optimum assignments, a combination of the proposed architecture and a TSK-type Fuzzy inference system was introduced. The results approved a conflict-free and optimal solution in the task assigning problems. Efficiency increase of the proposed innovative architecture in existence of Fuzzy inference systems ranges from 10 to 35 percent. In order to evaluate the proposed approach in experimental and practical terms, a user panel has been designed and used and with the help of this panel, the capability of practical implementation of this approach has been presented.

Insulated rail joints are one of the most important components of the railroad and their failure, deals a massive financial loss for our country. Usually, these joints are bearing different dynamic and quasi-static loads such as tensile load and bending moment. In this research, design and construction of insulated rail joints from composite material was examined, due to their optimized performance rather than conventional materials. The composite epoxy/glass fiber was chosen as a material for insulated rail joints, based on the failures accrued for conventional insulated rail joints. To evaluate the mechanical properties of composite samples, the tension, three point bending and hardness experiments were carried out based on ASTM standards. The results showed that the improvement of mechanical and flexural strength of composite insulated rail joints in comparison with conventional insulated rail joints. In addition, the estimated cost of composite insulated rail joints was decreased by 40 percent to European companies.

In the nearly six decades, exoskeletons have progressed from the stuff of science fiction to nearly commercialized products. In addition, the main part in usage of these robots in the medical sciences and particularly for the rehabilitation, specially disabled and elderly people is to help them to do their basic routine activities like walking, sitting and etc. This article represents the design process of a lower limb exoskeleton robot for helping disable people in gait cycle. First, the conceptual design of 7 Degrees of Freedom (DoFs) robot, consist of 3-DoFs in each leg and 1-DoF in hip joint, is presented. Then the dynamic modeling of mechanical system is shown by Lagrange Method. In addition to producing an optimized mechanical model of the exoskeleton, it was necessary to ensure the strength of each component. So that after the force analyzing of the robot components which are designed for the lower limb extremities, the physical output information of the modeling software (CATIA) is used as the dynamic model input and also in order to obtain motion equation in the gait cycle always needed to choose an appropriate coordinate for simulating closer to reality. In continuation of discussion a combined controller is designed to investigate its performance. Finally the system results are shown the maximum torque of 1st joint is 32 N.m, the 2nd joint is 13 N.m and the 3rd joint is 3 N.m. The maximum torques lead to select the suitable actuator for each link of robot.

Magnetic suspension system as an appropriate mechanism for non-touch maintaining the objects through magnetic force has become very important in many applications. Due to their instability and high nonlinearity, such systems pose a challenge to many researchers attempting to design high-performance and robust tracking control. This paper proposes a sliding mode control strategy for a nonlinear magnetic suspension system with one degree-of-freedom. In conventional sliding mode control systems, insensitivity to uncertain parameters and external disturbances is achieved when the bounds of the uncertainty and disturbance are known. In this regard, the proposed control structure is the inertial delay control being concentratedly estimated the uncertainties of the system and unknown disturbances. The main purpose of this paper is to implement the robust output tracking through centralized uncertainty and its estimation in which, by considering the suspension system coil current as the control input, the position of the suspended object is maintained and the estimation error tends to zero. Simulation results indicate the designed controller on the magnetic suspension system has a good performance compared to the other methods. In addition, the proposed method is effective and the output robust tracking, as well as the estimation of system uncertainties, are realized.