جستجوی مقالات مرتبط با کلیدواژه "life cycle" در نشریات گروه "مکانیک"

The optimal insulation thickness is a function of the insulation initial cost and the cost of energy carriers for the internal space heating and cooling due to heat transfer from the wall. In Iran, by allocating subsidies to the energy sector, tariffs for energy carriers are sensibly lower than global prices. In order to determine the insulation optimal thickness, energy carrier tariffs were considered variable according to consumption. Electricity and gas costs were divided into 4 ascending tariffs for low, moderate, high, and very high consumption cases. In addition, the case of energy carriers without subsidies was also examined the 5 . The outer wall consists of a typical hollow with 20cm thickness, insulated with an expanded polystyrene layer, placed the outside. Heat load due to heat transfer from the external wall was calculated by using EnergyPlus simulation software in different geographical directions and different thermal insulation thicknesses in Tehran climate. The optimum insulation thickness was determined based on the total cost over the lifetime of 30 years. According to the results, in the first tariff, which refers to low-cost subscribers, the use of thermal insulation in some geographic directions does not allow the payback period over a lifetime. In other directions, economic savings are low and . For higher tariffs, the optimum insulation thickness increases. In the 2 5 , the thermal insulation thickness from 6 to 18 cm. Also, the calculated payback periods of these configurations are between 6 and 28 years.

In this paper, reliability of missile system in its total life cycle is evaluated in terms of its subsystems’ reliability, using Continuous Time Markov Chains (CTMC) and Monte Carlo simulation method, finally results of both methods are compared. Missile system’s life cycle includes storage, pre-launch and operation states. Missile system is composed of variety of components and materials, hence different environmental conditions and various stresses imposed on missile system in each state during its life cycle, stimulates diverse failure modes and mechanisms. Therefore, failure probability distribution function differs for each subsystem in each state. Flight control, mechanical parts and equipment, engine and warhead are four main subsystems of the missile system. They are linked in series therefore each one’s failure will result in system’s failure. Exponential, Weibull, Lognormal and Gompertz distributions are used for subsystems’ modeling in different life cycle states. Unlike many other researches in this field, failure rates are time variant. System is supposed to be unrepairable during life cycle. Finally, Continuous Time Markov Chain’s superiority in comparison with Monte Carlo method, both in accuracy and required amount of calculations is demonstrated and a few suggestions, based on obtained results, are presented for system reliability improvement.