نشریه علوم کاربردی و محاسباتی در مکانیک
سال سی و چهارم شماره 1 (بهار 1401)

In this study, the effect of blowing jet parameters, which include location, blowing angle, momentum coefficient, and orifice area, on the average aerodynamic coefficients and aerodynamic performance parameter of the NACA0012 is investigated. The airfoil has a sinusoidal oscillating motion around a quarter of the chord. As a result of this movement, the angle of attack of the airfoil changes from -5 to 25 degrees. Five locations by 1, 4, 6, 10, and 20% of the chord length were examined and the results showed that the placement of the jet at 1% of the chord length is more appropriate than the other locations and significantly improves performance and have more impact on the flow control. Three angles of 30, 60, and 90 degrees were considered as the angles of the blowing jet and it was observed that the angle of 60 degrees is better in controlling the flow than the other two angles and this effective angle decreases when orifice length increases. The results show that there is no regular uptrend or downtrend for the angle effect. For the jet momentum coefficient, which actually aimed to investigate the effect of blowing jet velocity, the values of 0.14, 0.08, and 0.04 were considered while the orifice length is considered constants for these cases. The results showed that increasing the blowing jet velocity as well as increasing the jet orifice length improves aerodynamic performance, although increasing the orifice length at a constant momentum coefficient decreases the mean of lift coefficient.

In the present study, two geometries of microtube and microchannel are used simultaneously in a heatsink. The aim is to improve the performance of micro heatsink in cooling digital processors. ANSYS FLUENT software is employed to solve the governing equations. The second-order upwind method is utilized to solve the momentum equation and the SIMPLE method is employed for coupling the velocity and pressure fields. The results show that the fluid flow temperature changes less along with the micro heatsink by increasing the Reynolds number due to the high flow rate. Also, the surface temperature of the processor decreases significantly by enhancing the concentration of nanoparticles and improving the heat transfer performance. Hence, at Re =700 and a volume fraction of 0.5%, the average outlet temperature of the system is 316.1 K. It is equal to 319.03 K for a volume fraction of 1%. The addition of microtubes also causes a significant increment in the overall thermal efficiency of the system. For example, at Re = 300, the heat transfer coefficient for the base fluid flow with microtubes is approximately 58.4% higher than that for the system without microtubes. At Re =700 and 1500, this enhancement is 63.3% and 50.9%, respectively. This indicates that the presence of microtubes improves the performance of the heatsink and the access of heat transfer in different parts of the equipment to the cooling fluid flow. It reduces the thermal resistance of far points of the processor, leading to more heat absorption from the CPU surface.

Boron carbid (BC3) is a new two-dimensonal structure that exhibits unique chemical, thermal and mechanical peroperties. In this paper the mechanical properties of BC3 structure were investigated by using of molecular dynamics simulation. By using of Tressof potential and periodic boundry conditions, two elements of circular defect and followed temperature changes on BC3 structure were analyzed. The results of tensile test on boron carbide structure showed that the lowest young’s modulus as well as the failure stress and strain at the breaking point occurred in sample with central defect. Also, by changing the position of the defect towards the edges, the mechanical properties increased. By changing the position of the defect from the center of the structure to the edges, the values of young's modulus, stress and strain at the breaking point in th zigzag direction increased by 1.29%, 15.1% and 20%, respectively. Examination of temperature changes from 100K to 1000K showed that the increase in temperature reduced the mechanical properties, so that the value of the young's modulus decreased from 781.21 GPa at 100K to 616.19 GPa at 1000K. Also, the amount of stress and strain at the breaking point for the mentioned temperature compared to 100 K decreased by 43.05% and 51.08%, respectively.

In this paper, the effect of flower pattern design in the cold roll reshaping process, on the energy consumption and uniform distribution of force on the rollers at different forming stations, is investigated experimentally and numerically. Three-dimensional finite element simulations have been used to study the effect of variables and practical experiments have been performed to ensure the accuracy of the simulations. Dimensional and power consumption comparisons have been used to validate the simulation results. Along with the introduction of different design methods, the applied force on the rollers is studied in three different designs of the flower pattern and in each method, changes in external work and internal energy are studied. The distribution of force on the rollers in each method is also described. In addition to the minimum energy consumption, the uniformity of the force distribution on the rollers has also been introduced as a criterion for the design of the flower pattern It has been shown that using the criterion of uniformity of force applied to the rollers along with the criterion of minimum energy consumption, increases the dimensional accuracy of the product.

the flat solar heating transpired collector can be used for heat buildings and large spaces, industrial applications, and drying of agricultural products. The flow structure and convection heat transfer mechanisms are very important to the air performance of uncovered flat solar heating transpired collector. In these solar air heaters, the air is usually heated by a perforated absorber plate (metal). In this research, copper adsorbent plate has been used and numerical simulation has been performed for mass flow rate (0.007, 0.01, 0.0125, 0.015) kg/s. In order for the simulation to be consistent with the physical reality of the problem, the simulation is three-dimensional, non-continuous with a large computational range and continuous suction. Thermal efficiency, mass flow rate, and outlet temperature parameters were investigated. According to the obtained results, with decreasing mass flow rate, the temperature of the absorber plate and consequently the temperature of the outlet air increases; But increasing the temperature of the absorber plate is more than increasing the temperature of the outlet air. As the mass flow rate increases, the thermal efficiency of the flat solar heating transpired collector increases. The lowest efficiency in mass flow rate is 0.007 kg / s with 66.51 % and the highest efficiency in mass flow rate is 0.015 kg / s with 78.02 %.

The blank-holder force is an important and influential parameter in the sheet metal forming process. The size of this force around the part can be very effective in eliminating the defects of fracture and wrinkling in different points of the part. In symmetrical axial parts, a suitable uniform blank-holder force can prevent both defects, but for asymmetric axial parts, it is usually difficult to achieve a suitable uniform blank-holder force. In this case, the non-uniform blank-holder force can have a significant effect on improving the quality of parts. It is clear that simulation of the sheet metal forming process in finite element software and the effective use of optimization algorithms can be of great help in determining the amount of non-uniform blank-holder force. In this research, a method for automatic determination of non-uniform blank-holder force is presented. In this method, which has been created with the help of Catia, Abaqus, and Modefrontier software, various simulations and change of input parameters are performed completely automatically, until the appropriate conditions for sheet metal forming are determined. To show how this method works, two pieces with different geometries were examined. In these two geometries, it was not possible to achieve a piece without fracture and wrinkling with uniform blank-holder force, but the results showed that using this method, a suitable non-uniform arrangement of blank-holder force can be achieved automatically, which produces a flawless piece.