مجله مهندسی مکانیک
پیاپی 135 (بهمن و اسفند 1399)

The rapid advancement of marine science and military technology in the field of production of offensive weapons by developed countries and the ability of other countries to keep step with the issue of defense by developed countries has received serious attention. The use of impact absorbers in ship bodies, ship body reinforcement against bullets, military vehicle bumper, nuclear reactors retrofitting against aircraft and missile collisions are some of the applications of impact mechanics. The ballistic penetration performance of a projectile with kinetic energy will be more affected by the deformation of the projectile during the impact process; Among the effective factors of structural behavior against projectile penetration are their density and resistance; As these characteristics increase, so does the resistance to penetration. In this paper, using the modified theory of Bernoulli equation and expansion of the spherical cavity expansion in the target, the axial momentum equation, the analytical model of Walker and Anderson penetration are presented. The aimed analytical model, according to the available hypotheses, agrees quite well with different experimental values.

Numerous factors such as duct fouling, corrosion and wear of blades and internal return currents affect the performance quality and efficiency of the centrifugal compressor and can change vital variables such as pressure ratio, mass flow rate and energy consumption of the device that in turn affect the profitability and safety of the operating unit. In this study, the performance of compressor C-661 of Abadan Oil Refining Company, which is of centrifugal type with two operational stages and an intermediate cooling, has been investigated with the aim of evaluating its deviation from the manufacturer’s predicted conditions. Components that indicate the quality of compressor performance such as pressure ratio, mass flow rate, efficiency and power consumption have been measured. The results showed that this compressor after eight years of continuous operation, had a decrease of less than 1% of polytrophic efficiency in the first stage and a decrease of nearly 4% of polytrophic efficiency in the second stage. The average pressure ratio of the device has decreased by about 9% and the average mass flow rate has decreased by about 14% compared to the design point. The main cause of this decrease is the fouling of the device. The mechanical efficiency drop was close to 25%, which could be due to the decrease in steam turbine efficiency. Therefore, by using health coefficients, the performance diagram of this compressor was modified to show the current operating conditions and the overall equipment Effectiveness of the compressor was calculated with a new method. The economic survey also showed an 18% drop in productivity for the device.

In this paper, the energy consumption of a household freezer is compared with a constant speed compressor and a variable speed compressor. The highest grade of energy consumption in household freezers is related to household freezers with variable speed compressors. To compare energy consumption in household freezers, a single speed compressor with a cooling capacity of 185 watts and a performance factor of 1.92, and a multi speed compressor with different speeds in terms of revolutions per minute 1300, 1600, 2000, 3000, 4500 and with a cooling capacity of 85, respectively., 108, 130, 200, 260 watts and performance coefficients of 1.80, 1.88, 1.90, 1.80, 1.60 were used respectively. In both compressors, one type of hydrocarbon gas is used and the amount of refrigerant in both types is almost equal. The experimental results showed that variable speed systems, in addition to more stable temperatures and reduced energy consumption, also cause rapid freezing due to their different speeds. A variable speed compressor reduces energy consumption by 24% per day compared to a constant speed compressor.

Intersections play a key role in reducing the congestion and road traffic and are the bottleneck of traffic on urban thoroughfares. The capacity of intersections determines the volume of vehicles passing through the entire transportation network, and it is essential to prevent any disruption to vehicle traffic, such as traffic jams and accidents. Accordingly, in this paper, the importance of the topic of intersection management is discussed. Then, a general classification of the types of intersection management methods is presented. The conventional and classic methods are based on the use of traffic lights, which applies the appropriate command to the traffic light by investigating the traffic conditions in the intersection. With the advancement of communication technologies, the method of cooperative intersection control, which works without the use of traffic lights, has been emerged. This system, not only reduces the delay in crossing the intersection but also improves the passengers’ and pedestrians’ safety.

The use of driver assistance systems in cars is increasing since it helps the driver and reduces his/her activities and fatigue. Among these systems, the Adaptive Cruise Control (ACC) system with longitudinal dynamic automatic control is at the center of attention. With such automation, the role of the driver changes from an operator to a supervisor. Therefore, providing safety and passenger comfort in these systems is of particular importance. It should be noted that ACC can greatly affect traffic flow and can perform better than a human driver. In this paper, various control functions will be examined focusing on their application in the ACCs control section. By analyzing the advantages and disadvantages of each of the studied functions, their effects on various components such as safety and comfort of vehicle passengers are studied. Moreover, the ACC sensitivity road and weather conditions are also addressed. At the end, the horizons ahead of this topic are presented which helps to improve the past works as much as possible.

To realize the development and exploitation of space, it is necessary to develop low-cost space transportation systems. The development of systems that are fully or partially reusable has been the subject of extensive study since the 1960s. These types of systems are categorized into two main groups: SSTO and TSTO. The TSTO launcher has fewer requirements than the SSTO because the responsibility for achieving a successful mission will be divided into both stages; therefore, the dry-mass of the TSTO second-stage has been reduced compared whit the SSTO for delivering a payload with the same weight. In this paper, a first-time launcher is introduced; then describes how the launcher completes the mission. The following are basic subsystems of this launcher are introduced, and a brief explanation is given to each other. Finally, some of the most important examples of this type of launcher are named and the characteristics of each are presented.

In this paper, the numerical method of heat transfer and fluid flow in the fuel cell of polymer membranes and cooling channels, with the parallel channel pattern and the use of liquid water in separate channels embedded in the bipolar plane, is investigated and the performance of four different field designs Gas flow and cooling, based on the absence of the need for an external thermal boundary condition, the temperature uniformity is simulated and compared using Ansys-Fluent software. The results showed that by increasing the Reynolds number of the cooling flow from 40 to 800, the pressure drop in the cooling flow channel path reaches from 40 to 640 Pascals. On the other hand, the Nusselt number of the cooling flow increases exponentially from 350 to about 700 by changing the Reynolds number from 40 to 400, and then it is fixed. The results also showed that the best cell performance was obtained at Reynolds number 60, because with increasing Reynolds number, the cooling flow and increasing pressure drop of the system’s noise power increases.