مجله مهندسی مکانیک
پیاپی 136 (فروردین و اردیبهشت 1400)

In this paper, the performance of direct expansion ground source refrigeration cycle has been investigated. CO2 in transcritical cycle has been used as the refrigerant and the effects of the refrigerant pressure drop in the heat exchangers have been considered. Using this simulation, system characteristics such as length of ground heat exchanger, refrigeration capacity and COP are investigated. In this study, it was found that at the peak refrigeration load, by increasing the thermal conductivity of the soil from 1.1 to 3.4W/m.C and the ground heat exchanger diameter from 6 to 13 mm, the loop length of the ground heat exchanger is decreased by 66.5% and 10%, respectively. Also, in choosing the number of ground heat exchanger loops, there is an optimum value for which the length of the heat exchanger is the smallest. The increase in the compressor’s speed and the incoming temperature leads to an increase in the refrigeration capacity of the system.

Optimizing the window surface is very effective in saving energy. The natural light in the living room, a multi-purpose collective space, must meet the users’ different needs. This study aims to optimize the north and south windows’ surface in a residential building’s floors. Simulation steps have been done with simultaneous attention to thermal and lighting performance. For this purpose, window optimization based on parametric modeling has been done using Grass Hopper software to minimize thermal energy consumption with Energy Plus engine and lighting with Radiance and Daysim engine. Optimization operations have been performed for all available modes to minimize the thermal target function and maximize the lighting target function. The results show that the optimal window surface is different on each floor and face of the building. With the window optimization in the northern unit, the dynamic daylight index has increased from about 50% to more than 80%. The percentage of improvement of the dynamic light index in the southern unit floors has been between 2% to 9%. Based on results, designers can ensure optimal heating and lighting throughout the year in similar buildings while saving energy consumption.

Energy absorbers have various applications in vehicles, military industries, ships, trains, aerospace industries, etc. In recent years, with the development of science and technology, multiple absorbents have been invented to absorb impact energy and ensure the safety of structures against impacts. Among absorbents, foams have significant advantages such as lightweight and high energy absorption per unit mass. Synthetic foams have a higher energy absorption capacity than conventional metal foams; For this reason, in this study, the energy absorption of synthetic foams at high-speed impact is investigated numerically using Abaqus finite element software. Also, the force-displacement diagram, the amount of energy absorption per unit mass, the initial maximum force, and the samples average force are investigated. Models are low carbon steel synthetic foam, aluminum-6061, and aluminum-6063 synthetic foam. According to the results, it is observed that the amount of energy absorption, maximum strength, and the average strength of low carbon synthetic foam is higher than aluminum synthetic foams, but the amount of energy absorption per unit mass of aluminum synthetic foam-6063 is higher than others.

Modeling and analyzing the problem of impact and penetration of projectiles in the targets and the effects are also among the practical issues that can be used to design bulletproof panels and military equipment, construction of impact and impact resistant structures, design of projectiles with appropriate penetration power and high efficiency noted. In this paper, the analytical model is used to predict the performance of a long rod eroding projectile that normally penetrates metal targets at speed of 2 km/s, and this model predicts the hole diameter, penetration of depth, and penetration velocity as functions of the projectile velocity. X-ray evaluation shows that the nose of the projectile becomes mushroom after penetrating the target and retains almost its hemispherical head shape in all the early stages of quasi-constant penetration. For the final ballistic evaluation, steel and tungsten projectiles penetrated the aluminum target at a speed between 1.3 to 2 km/s and then the results of spherical cavity expansion analysis on nondeformable projectiles were used to calculate the target resistance to erosive projectiles. The aimed analytical model, according to the available hypotheses, agrees quite well with different experimental values.

The accuracy of the initial design of the gears can significantly ensure the proper function of the gearbox as a part of the transmission systems. This paper discusses the economic impact of performing a virtual process, which includes computer-aided design and rapid prototyping, on reverse engineering of a Honda CB-125R motorcycle gearbox to modify existing traditional trends and examines the reduction of production costs. For this purpose, the gears were disassembled from the motorcycle gearbox and examined in terms of dimensions. Then, calculations were performed to find the modulus of each pair of gears involved. After extracting the dimensional characteristics of the gears, a computer model of each was drawn, and then physical samples of them were produced layer by layer by fused deposition modeling method. To ensure the dimensional accuracy of the gears for mass production, the produced samples were used to test with assembly in the gearbox. After the approval of the initial design, the mass production of gears with the determined parameters was performed by the hobbing machine. The results of monitoring the application of the virtual process in reverse engineering of the studied gears in the five months of mass production prove that the virtual process reduces the costs of the production errors, assembly defects, and waste parts to 100%, 55%, 71% respectively. Hence, the virtual process reduces the total mass production costs by 36%.

Congestion of vehicles in metropolitan areas has increasingly raised concerns about the negative consequences for human health, the environment and the economy. The movement of public and private vehicles in the city to send goods, urban traffic or public transport, intensifies traffic and result in social anomalies, release of pollutants, increasing the psychological impact and cost of urban living, waste of fossil fuels, and ultimately degrading quality of urban life. In this regard, many researches have addressed this problem amongst, the Computational Intelligence (CI)-based algorithms are in the center of attention. In this paper, we have reviewed the most recent and influential CI-based methods presented for solving the Vehicle Transportation Routing System (VTRS) problem.

Laser cladding technology , creates the ability to produce, repair and optimize parts with high accuracy and complexity. Laser cladding exhibits highly complex heat transfer and thermoelastic-plastic-flow with multi-physics field coupling changes, which are accompanied by such physical phenomena as melting, solidification and phase transitions in the metal and non-metal powders. This process involves high thermal gradients and heating and cooling rates that cause residual stresses, torsion, and distortion. The temperature rates and flow fields in the molten pool affect convection, heat transfer, mass transfer, and solidification, which ultimately affect the quality of the cladding layer. The quality and properties of the cladding can be determined by many factors such as cladding geometry, microstructures, dilution ratio, defects, distortion, surface smoothness and metallurgical changes in the substrate and process efficiency. These factors, regardless of their degree of importance, are affected by the parameters of the cladding process and the physical phenomena that occur during the process. In this research, a landscape review on the process of laser cladding, type and methods, characteristics of process and effective parameters on process are studied and presented.

The evacuation time of occupants from the building is one of the most important issues in fire safety design. Fire safety is designed in two ways, prescribed based on building codes and standards, and the performance basis is based on engineering judgment. In many special buildings, such as high-rise and complex buildings, the performance method is more applicable. Most performance-based methods require computer models that require cost and time. The purpose of this paper is to provide a simple analytical method that allows the study of evacuation by considering the speed of movement of occupants and the limitations of the capacity of the exit doors. One of the advantages of this method is that it considers simple algebraic equations of traffic at exit doors. To evaluate the accuracy of the method, this method has been compared with an approved computer model. The results show that this method can be used in designing escape routes for initial designs.