Science and Technology in Mechanical Engineering
Year:2023 | Volume:2 | Issue:2|Papers Count:10

In the current research, the effect of the inclination and the rotation speed of the pelletizing disc, besides moisture and bentonite on the efficiency of the production process, has been studied with the experimental approach. The median size estimate (size index) and falling number (strength index) are considered as the main characteristics of the green pellets. The number of necessary experiments and the amount of their variables were determined by implementing the design of experiments (DoE) process with the response surface type. In order to obtain explicit mathematical functions, curve fitting was performed on the experimental results and four-variable functions were extracted for the two characteristics of mean size and falling number. In order to find out the details and effects of each of the factors on the results, the necessary graphs were prepared and in addition to identifying their individual roles, the concurrent impacts of each pair of them was also investigated. Moreover, the observed results were discussed in physical view point. In conclusion, it was found that there is an optimal range for the two factors of rotation speed and disc inclination, which leads to obtaining the desired pellets from both the size and strength perspectives. It was found that moisture and bentonite do not necessarily have a positive simultaneous impact on the size and strength of the product in the studied range. The results of the present research can be useful in practical respect for the factories that produce iron pellet.

In this article, the problem of controlling the attitude of a spacecraft with integral pulse width and frequency integrator is investigated and the said integrator is developed as a fractional order. The spacecraft is controlled by a two-state on-off thruster actuator with a combination of proportional-derivative law and integrator. In order to focus more on studying the behavior of the proposed integrator, the operator model is ideally considered, although it is due to the use of a nonlinear control system integrator. Average fuel consumption and operator activity are included as two main evaluation indicators, and on the other hand, the absolute average value of the sign error on spacecraft status is also included as another important indicator in the study of the behavior of the proposed integrator. In order to compare the results fairly, the situation control problem has been done for the same assumed conditions and for the integrator of integer order and fractional order. The comparative results for changing the fractional power of the fractional order integrator filter and checking the three performance criteria have been done. Also, the influence of the uncertainty of the moment of inertia of the spacecraft, the uncertainty of the reference entry angle and the range of external disturbances have also been studied. The obtained results indicate the change of the performance criterion for changing the order of the fractional combiner filter and show the more appropriate performance of the proposed combiner for a range of fractional powers.

Nowadays, energy saving in oil and gas refineries is of special importance, so saving and optimizing energy (fuel) consumption can have many positive economic and environmental effects. Based on this, in this research, optimization of fuel consumption in Bo Ali Refinery has been discussed. In this way, Bo Ali Refinery was first simulated in the Aspen Hysys software environment, then it was modified and redesigned through the sensitivity analysis of parameters effective in the energy consumption of the refinery. According to the title of the research, in order to minimize the consumption of external heat sources, pinch technology has been used. Also, considering the comprehensive combination diagram and its results, a four-stream converter is proposed for this refinery. The results showed that this redesign saved the heat transfer rate (34829042 kJ/h) and reduced the consumption of the refinery by about 7%.

In the present work, the performance of a case study screw conveyor in Shahrebabak copper complex has been studied. The design of screw based on the standard design codes, especially CEMA code, has been investigated to determine the design problems. The variation graphs of the screw speed, material rate and the upper bin discharge have been recorded to use in evaluations. Data collection revealed that the screw conveying rate of material did not match with the evaluations which given by the standard codes for the conveying capacity of screw. The data were used to derive a correction factor between the operational data and theoretical relations of conveying capacity. By the obtained correction factor, the relation for evaluation of the case screw capacity was derived and by with, the maximum screw capacity was determined. Redesign of screw, according to the material conditions and required capacity (of about 72 t/h) has been performed.

Thermal conductivity and contact thermal conductivity play an important role in the design of engineering thermal products. To date, various types of solid and thin film measurement techniques are known. In general, these methods are divided into two categories: stable and transient, each of which is used according to the nature and accuracy required of the measurement, relative to the target test sample. In general, the most common challenge of the techniques for measuring the conductive heat transfer coefficient is related to achieving an error of less than 5%, which is caused by bulk or contact heat transfer. For this reason, choosing the appropriate measurement method for quantitative and accurate measurement of the target sample requires knowledge in the field of thermophysical characteristics, geometry and sample preparation method. It is also important to understand the principles and limitations of testing methods and possible sources of error that affect the final results. In this regard, in the present study, after examining the various aspects of stable and transient measurement methods, including the type of sample, achievable accuracy, costs, activities required for preparation, and other related matters, a comparison has been made between them; finally, the appropriate method has been recommended according to the target sample considering the parameters of measurement time, appropriate sample size, cost, and complexity of the technique.

Extreme plastic deformation methods are methods that can be used to produce materials with a high strength-to-weight ratio. Grooving process is an intense plastic deformation method used to produce metal sheets with very fine grain structure. In this research, numerically and using the finite element method, the process of limited groove pressing up to one complete pass is studied on a pure copper sample. Therefore, numerical modeling was done by ABAQUS 14 6 software, and by using this method, the output results of each stage are transferred as input to the next stage. Numerical results showed that by applying each stage of the process (Constrained Groove Pressing), the amount of plastic strain increases and also along the length of the sample, the amount of effective plastic strain changes in an oscillating manner. By examining the changes in the forming force during the process, it was observed that The changes in force in individual steps include three parts, and in the third part, the slope of force changes increases sharply, which is due to the increase in contact surfaces and the effect of friction in order to fill the corners of the mold. By examining the effect of the friction coefficient on the forming force, see As the friction coefficient increases, the maximum value of the forming force increases.

In this paper, a robust and reliable optimization approach has been used to reduce the effect of sensor noise on the performance of the spacecraft attitude control system with reaction wheel actuators. The absolute mean value of the pointing error on the satellite attitude has been chosen as the main control performance criterion. The optimizer algorithm is based on the genetic method and based on Monte Carlo successive iterations to include the effect of noise and obtain control coefficients. The first-order dynamics was used to model the reaction wheel as the main control operator, taking into account the practical limits of the maximum production torque, and a proportional-integral-derivative (PI-D) controller modified by the method, the observer is used to control the satellite. Gaussian white noise signal after passing through a first-order filter is added to the angle and angular velocity feedback path signals and applied to the control circuit. In order to compare the results fairly, the control coefficients for the same simulation conditions were obtained for the two approaches of deterministic optimization and robust and reliable optimization, and the performance criteria in terms of the noise power spectral density function were investigated for the two optimization approaches. The comparative results show that the control system adjusted by robust and reliability optimization method, its performance criterion is more robust in the face of noise and its performance reliability number is higher than the results of deterministic optimization. The results indicate the preference of using a robust and reliable optimization approach

In this research, with the help of commercial software called AVL BOOST, the performance of the EF7 gasoline engine has been simulated numerically, and the effect of compression ratio and spark timing on power, torque, and thermal efficiency has been investigated. The error of the current modeling compared to the results of experimental tests was reported in the range of 3%. Also the simulation results showed that at high speed (5000 rpm) if the spark starts 25 degrees before the top dead point and the spark duration in the range is 55 degrees, the maximum output power is obtained from the engine, and as the spark duration increases, the ignition speed decreases and the output power decreases. Besides, with the greater advance of the ignition angle, a greater percentage of the input energy is lost as heat to the engine wall and the output power decreases. It is noteworthy that in the optimal conditions of spark timing at 5000 rpm, the thermal efficiency of about 38% can be achieved, which is increased by about 11% compared to the default spark timing mode.

Amidst the continuous expansion of global commerce and the urgent need for expedited order delivery within distribution networks and online customer service platforms, the demand for air cargo transportation has reached unprecedented levels, complementing traditional distribution channels such as land and sea. Consequently, this sector has garnered considerable attention in recent years. One of the primary challenges encountered in aerial distribution networks pertains to the routing problem for unmanned aerial vehicles (UAVs), which necessitates considerations of enhanced customer satisfaction and network constraints. To address this challenge, this paper commences by introducing the routing problem alongside customer and network constraints, subsequently presenting their mathematical formulations. Notably, the dynamic behavior of aerial robots poses a significant constraint in this context, which has been inadequately addressed in existing research on routing problems within distribution and customer service networks. This deficiency is attributed to the involvement of flight dynamics equations, complicating the problem significantly. In this study, the nonlinear equations governing aerial robots for customer service are reformulated in state space representation. Subsequently, the routing problem, incorporating the state space equations of flying robots and considerations of customer and network constraints, is tackled using a genetic optimization algorithm—an optimal solver. Following the solution process using the genetic algorithm, the results are elucidated in terms of optimal routes. Simulation outcomes validate the efficacy of the proposed approach in meeting all problem requirements and objectives, thereby presenting a viable solution for routing large-scale aerial networks.

Under adverse weather conditions, distance measuring equipment (DME) must be optimally positioned to reduce landing errors. Interval type-2 fuzzy logic is employed as an effective method for determining the optimal placement of DME. This approach evaluates factors such as weather conditions, flight paths, and other relevant variables fuzzily to determine the optimal DME positioning. When there are unequal distances from the normal landing strip for each sensor, identifying the optimal location for secondary sensor placement is crucial. This system operates dynamically, identifying the presumed central landing line based on the initial placement of each sensor, and ultimately determining the optimal position for the secondary sensor. In our experiments, the ideal distances from the aircraft to the sensors were 131.5 meters and 132 meters, respectively, allowing the system to accurately determine the appropriate landing spot. In non-ideal conditions, with distances of 134 meters and 129.4 meters, the system indicated that closer proximity to the second sensor led to an unsuitable central landing line. The results demonstrate that using interval type-2 fuzzy logic can accurately identify and optimize sensor placement, thereby reducing the likelihood of landing errors in adverse weather conditions.