مجله مهندسی مکانیک
پیاپی 148 (فروردین و اردیبهشت 1402)

Atomic force microscope is one of the new practical tools in the field of nanotechnology, which is used in nanomanipulation. The main goal of this research is to model the optimal routing of micro/nanoparticles in the second phase of manipulation and movement of particles u sing atomic force microscope images. For this purpose, in this research, firstly, experimental work and imaging of head and neck cancerous cell tissue has been done using an atomic force microscope. After that, these images are examined and analyzed and then using different routing algorithms, including particle swarm optimization algorithm, genetic algorithm and simulated refrigeration algorithm, the optimal path to perform the second phase of nanomanipulation is extracted. The obtained results indicate the optimization of the path in the second phase of nanomanipulation for the use of in-situ replacement of particles.

Downburst storms cause severe destruction by creating intense and unstable downdrafts. On the other hand, due to the difference in their structure from atmospheric boundary layer storms, it is essential to study and understand these flows under different conditions. Therefore, this study the effects of the impact angle of the downburst and the structure installation angle relative to the surface flow on a cube-shaped model investigates dynamically. The model is placed in front of the downburst in four angles of the storm colliding with the surface(θ), in two directions of the surface flow relative to the structure(α), and in the radial range of X/D=±1.5. Also, the ratio of horizontal displacement speed of this storm(VR) is considered to be 0.06 and 0.12. The results show that the increase of θ and VR caused the location of the maximum pressure coefficient to shift from the central point of the flow meeting the surface to the downstream. Also, increasing α has reduced the range of pressure and force changes by about 25% on the model. In addition, it was found that dynamic downburst caused stronger impacts on the structure and generally, these strong impacts occurred immediately after the downburst passed over the structure.

Micro energy harvester systems are a new technology that replaces batteries and energy storage devices that have limitations. Not needing to replace or recharge them periodically, very small volume and weight, as well as high accuracy are the characteristics of the micro energy scavenger system. This paper investigates the electromagnetic micro energy harvester system under random white noise excitation. The mechanical model considered for the micro energy harvester is in the form of a beam. In this system, the base acceleration is the input of the micro energy recovery and the induced voltage in the coil is the output of the system. The base excitation is assumed to be a weakly stationary Gaussian white noise random process. According to the mechanical motion equation of the system, the frequency response function can be obtained. The aim of this research is to calculate the mean power produced in the electromagnetic micro energy harvester under random excitation. Stress analysis is done using simulation in finite element software and numerical solution, and the results’ correctness is confirmed. Finally, the effect of the electromagnetic micro energy scavenger on the average parameters power produced is investigated.

In this paper, the combined convection heat transfer with radiation in the hot fuel rod of a pressurized nuclear reactor like the Bushehr reactor has been investigated. Generally, in the thermal analysis of a fuel rod, special attention is paid to the temperature distribution in the constituent parts of the fuel rod, as well as the effect of the fluid flow around it on the amount of heat removal. Therefore, in this study, using heat transfer equations in the fuel and its adjacent fluid, the intensity of convection and radiation heat transfer and the effect of different parameters have been investigated. In this modeling, the assumption of gray environment is used to model the radiation in the space between the fuel and the clad, as well as considering the opaque walls, and the radiation model used is the Discrete Direction Model (DOM). Ansys Fluent (CFD) software has been used for this simulation.

In this article, the thermal performance of microchannel heat sink containing a suspension of phase change materials with a porous elliptical cross-section has been investigated. Solving the basic equations governing the problem is based on the finite element method and the simulation is done using Comsol multiphysics software 5.6. ForschheimerBrickman-Darcy equations are used to describe the flow through the porous medium. In the present work, the analysis of the arrangement of porosity (ε) and the thickness of the porous area has been done on the thermal and hydraulic characteristics under different inlet velocities. The increase in the small diameter of the ellipse causes a decrease in the diameter of the porous section and the pressure drop decreases with the increase of the fluid inlet speed, so that at b = 0.275 mm and uin= 2 m/s, the pressure drop compared to b = 0.175 mm is 62.34 % decreased and the thermal resistance increased by 35.50 % At low inlet velocities, the coefficient of performance is less than 1, and the reason for this is the decrease in the momentum of the fluid elements due to the presence of the porous wall, and with the increase in speed, the coefficient of performance is greater than 1, because the increase in momentum and also the increase in the contact surface between the fluid and the solid matrix cause The thermal performance has been improved and this indicates the superiority of the porous microchannel heat sink compared to the microchannel heat sink without porous medium.

In this article, the simulation methods of multiphase flow in the presence of surfactants are classified into 3 categories based on Navier-Stokes, distribution function, and based on intermolecular forces, and each one is described separately. Navier-Stokes-based methods fall into two categories: interface tracking methods and interface capture methods. Methods based on intermolecular forces act as particle-based methods with a Lagrangian perspective in dealing with the flow field. The widely used models in the methods based on the distribution function are also introduced at the end. A wide range of numerical methods has put many choices in front of researchers. Knowing and understanding the capabilities and details of these methods will help to select the most appropriate numerical method and obtain reliable and cost-effective results according to the hardware facilities.