نشریه مهندسی مکانیک ایران
سال بیست و چهارم شماره 2 (پیاپی 67، تابستان 1401)

Currently, one of the most important fields of scientific activity is building and sending satellites into space, which is one of the key needs of all countries. Satellites have great importance in the fields of telecommunications, research, weather, imaging and mapping, and military applications. Controllers are designed by considering some assumptions and simplifying the system that it can impose high costs of implementing the designed controllers on the real system without evaluating the designed controller on the simulator. Despite the discrepancy between the simulated system and the actual system model, testbed control simulator will help to achieve these goals. Determining this subsystem is responsible for the successful completion of the satellite mission. Any defect in this subsystem can cause the failure of the satellite mission. Therefore, testing and ensuring the correct operation of this subsystem before launching the satellite is so important. In this project, first, the hardware simulator is designed and built based on the 3 degree of freedom model. In the construction of this simulator, air bearings have been used to simulate the vacuum environment in space. To control the testbed model, the PID controller is implemented and the results are shown controller.

The present study investigates the effect of different insert inside the tubular heat exchanger on important thermal parameters and overall efficiency. In this regard, methods such as Design of Experiments (DOE) software and response surface methodology (RSM) Central composite design (CCD) were used to design experiments. Numerical methods and neural network modeling were also used to further strengthen the analysis and then the mentioned simulation methods were compared. In all cases, the results of this study indicate an increase in heat transfer coefficient and, consequently, an improvement in the Nusselt number due to the use of novel inserts. So that unlike the previous inserts of these inserts, in addition to rotating the current, it also has the ability to rotate. Finally, the average percentage of absolute error (MAPE) in the experimental design software modeling method and neural network is 10.77 and 0.94%, respectively, which indicates the high accuracy of the neural network method to determine the friction coefficient parameter.

The purpose of this paper is to investigate the heat transfer and entropy generated due to mixed convection of hybrid nanofluid inside the lid-driven semi-oval chamber. The magnetic field is applied uniformly and non-uniformly. The simulation is performed by MRT-LBM and by writing computer code in Fortran language. Effect of Richardson number (0.1, 1 and 10), nanoparticles volume fraction (0-0.06), Hartmann number (0-60), inclination angle of the chamber (-90, 0 and +90 degrees) and type of magnetic field applied (uniform and non-uniform) on the flow formed in the chamber is evaluated. The results show that increasing the volume fraction of nanoparticles increases the flow strength, average Nusselt number, total volumetric entropy and Bejan number and most of the effect is observed for Richardson number 10 and inclination angle +90°. In all cases, increasing the Hartmann number decreases maximum values of streamlines and heat transfer, and this effect decreases with increasing Richardson number. By applying a magnetic field non-uniformly, it can change the flow strength by more than 80% and increase the heat transfer to 35%. Increasing the Hartmann number makes the effect of the non-uniform magnetic field more obvious, and the heat transfer has the largest share in the total volumetric entropy.

Boiling is used in processes with high heat transfer rate given the large amount of heat flux involved in the phenomenon. Devising a groove on the surface can improve the bubble formation and increase the heat transfer of the boiling. Accordingly, the pool boiling phenomenon on a horizontal surface is numerically simulated using the Eulerian-Eulerian method in this study. Four surfaces: smooth, with rectangular groove, with triangular groove, and with circular groove are examined to this end. Numerical simulation results are compared with available experimental data. The results indicate that the surfaces with rectangular and circular grooves render approximately 50 and 90% more heat flux than the smooth surface, respectively. However, the surface with a triangular groove rendered approximately 37% less heat flux than the smooth surface.

In recent years, development and research on wheeled mobile tractor-trailer robots have been extensively increased. Development of such robot is due to increasing maximum load capacity and reducing fabrication and maintenance costs. In this paper, nonlinear dynamic modeling of the tractor-trailer and its motion control are performed. To do this, governing equations of the mobile tractor-trailer robot are firstly derived taken into account nonholonomic constraints of wheels. Assuming lateral and longitudinal non-slippage of the robot wheels, nonholonomic kinematic constraints of the mobile robot are obtained. For dynamic modeling, the Lagrange principle is implemented and the final form of the nonlinear equations of the tractor-trailer robot is derived. Also, the nonlinear dynamics of the system is presented in state-space form and the input-output linearization control method is employed to control point-to-point motion and trajectory tracking. Various simulations are done and the results demonstrate the correctness of the derived nonlinear dynamics and the applicability of the proposed method to control the wheeled mobile robot. Simulations show the nonholonomic constraints of wheels of the tractor and the trailer has a prominent effect on the point-to-point motion of the mobile robot. Moreover, the obtained results indicate the capability of the proposed modeling procedure for the future researches in this field.

A vortex tube is a mechanical device for separating a stream of compressed air into two streams of colder and warmer air than the inlet stream at the same time. Simple design, small volume and no need for repair, caused this dual-purpose device to be considered in the industry. In the paper, using simulation and computational fluid dynamics technique, the effect of inlet air pressure on the performance of a vortex tube device has been investigated. To solve the flow field equations, the k-ε turbulence model is used and the model geometry is considered constant. The results show that each vortex pipe has an optimal working pressure that is both economically and economically justifiable. This working pressure was 4.8 bar in the current project. The simulation results show that for cooling purposes, using a mass ratio of 0.3 will cause a higher separation in the cold output and for heating purposes, it is recommended to use a cold mass ratio of about 0.8.

This study focuses on evaluating the performance of sandwich beams under three-point bending test. Three sandwich beams consisting of transverse cores of Honeycomb, Beta, and Alpha with the same face sheets thickness are fabricated by employing a 3D printer. The extended high order sandwich beam theory has been used to carry out the static analysis of three-point bending behavior of the beams for the first time by this work. In order to compare the theoretical results, numerical simulations were implemented in ABAQUS software and experimental tests were performed. The theoretical results with less than 5% error follow the experimental ones. The tremendous achievements of the current investigation provide a novel insight into prognosticating the performance of the 3D printed sandwich beams.

A triple-tube heat exchanger composed of a condenser and evaporator was proposed in this study. Also, the heat exchanger is partly filled with metal foam for improving performance. So that in addition to heat transfer enhancement, the pressure drop does not exceed the value expected by the designer. A system of six differential equations is formed under the coupled interfacial boundary conditions; accordingly, the dimensionless relations of velocity and temperature for fluid and solid are analytically obtained using continuity, momentum, and energy equations in porous and clear regions. In the solution method, first by normalizing, linear combination, and the variable change method, the differential equations are decoupled, and then by forming the Bessel differential equations, the solutions are obtained in terms of the modified Bessel functions of the first and second kind. In the porous medium, the local thermal non-equilibrium and the Darcy-Brinkman models are used in the energy and momentum equations, respectively. Also, to validate the analytical solutions, numerical simulation using Ansys-Fluent software with UDF coding was employed. The results showed that at high values of pore density, the effect of porosity on pressure drop is relatively small. The porosity 0.97 as the optimum performance point and the dimensionless porosity radius 1.78 as the critical hydraulically point was obtained. One of the most important results of this research is that the performance of the partly porous triple-tube heat exchanger improves significantly nearly three times compared to the non-porous one.