جستجوی مقالات مرتبط با کلیدواژه "life cycle" در نشریات گروه "فنی و مهندسی"

Nanocomposites are widely used in dental restorative materials and medical equipment, among the most important of which, polymer-based nanocomposites can be mentioned. One of the most useful biocompatible polymers in this field is polymethylmethacrylate (PMMA). In the present study, the numerical analysis of the fatigue behavior of polymethyl methacrylate nanocomposite reinforced with hydroxyapatite nanoparticles has been investigated. For this purpose, standard samples of nanocomposite were made and their mechanical properties were investigated. To study the fatigue behavior and life cycle, a notched model was simulated in Abaqus and Fe-Safe software, and the data obtained from the tensile test were used as the mechanical properties of the material. By adding nanoparticles to the pure polymer, Young's modulus and tensile strength of the part, as well as the life cycle, were improved; However, it was observed that with the addition of more nanoparticles, the mechanical properties and the life cycle decreased slightly, which was caused by the accumulation of nanoparticles on the surface of the nanocomposite, which leads to a decrease in the strength of the samples.

Examining the technical, social, environmental, geographic, and economic features is necessary in the process of water and sewage projects on a large scale. The purpose of this research is to identify and rank water and sewage risks in Ilam province. In this research, using in-depth library studies to identify risk in the life cycle and using CVR content validity to remove irrelevant factors. Then, by designing a questionnaire and a statistical community of 40 water and sewage experts, which was determined using Cochran's formula, the effect of the importance of risk factors in the life cycle of the project was investigated. . In this research, the internal reliability of the structure is 0.76, which has established a good internal consistency, then using the Friedman test, the risks have been ranked, and in this research, the risks of lack of plans and executive details, lack of proper design, and the need The changes in the implementation phase compared to the plan have the most important risk and changes. Then, in order to prioritize the life cycle stages of the project, using the AHP technique and a community of experts (5 to 7 people), the life cycle stages have been examined with safety-cost-time alternatives, and the results show that design and planning have the highest priority and They have attributed the least importance to the establishment in this research.

The main aim of this study is to reduce costs and improve the efficiency of the Tehran subway project. The approach to this research is a system engineering with life cycle methodology. Needs analysis is the first phase of the life cycle and the next phases are Design, production, operation, support, and retirement. Needs analysis, which is the first and most important phase of the life cycle, has been performed in this research. For this purpose, a questionnaire including 42 questions was distributed and collected from 220 customers of Tehran Subway. 10 factors that have more than 70% of the variance of customer needs were discovered through exploratory factor analysis and named subway quality indicators. In addition, 39 customer needs with specific values greater than one and operating loads greater than 0.5 were identified and selected as customer needs. Then, using the network analysis process method and the MATLAB software, the importance of each of the subway quality indicators and the importance of customer needs indicators was achieved. And finally graded. Based on the findings of this study, in the implementation of the design phase of the Tehran subway life cycle, all 10 indicators of subway quality should be considered, but the availability of vehicles and station facilities need more attention. Also, all 39 subway customers need indicators that should be considered in the design, but the top 10 requirements indicators are much more important than the other 29 indicators.

Corrosion of rebar is a complex process and one of the most important factors of failure of reinforced concrete structures which reduces the strength and serviceability of the structures. The crack width is an important parameter for designing and evaluating the performance of concrete structures. This paper presents an analytical model to calculate the crack width caused by corrosion. Crack propagation due to corrosion product expansion was investigated at different stages across the concrete cover starting from the reinforcing bar-concrete interface through to the surface. A merit of this model is that it is directly related to the factors that affect the corrosion induced cracking process. Then, the predicted crack width was chosen as a random variable in the calculation of structural failure probability using a stochastic gamma process, after which life cycle costs and the optimum repair period were determined using a renewal process. Furthermore, the effects of structural parameters, including rebar diameter and corrosion rate, on the probability of failure and maintenance costs were investigated, indicating that crack width and life cycle costs are most significantly affected by corrosion rate. That is, a 16-times increase in corrosion rate results in 32 percent reduction in repair time. Moreover, it is to be noted that increasing the allowable fracture limit by 10 percent resulted in the doubling of optimum repair time. In other words, the optimum repair period is significantly affected by the allowed fracture limit which indicates the threshold for structural repair.

With regard to the strong position of the infrastructural projects specially petroleum refinery projects, in development of countries, and negative environmental, social, an even economic effects whether in short-term or long-term, this study develops a sustainable development framework based on the literature review and evaluate its adaption to different phases in the project life-cycle and petroleum refinery parts. So that, in addition to ensure the development of comprehensive sustainability framework, sustainability priorities will be achieved in different phases of the targeted project. The study outputs will help managers at different levels in their decision makings by reducing the ambiguity of the decision environment and demonstrating the critical path by a long-term viewpoint. Hence, it will be a powerful tool in different areas of decision making for different managers and experts in this industry.

Fatigue is one of the most effective parameters on the life cycle of the railway slab track. In this paper, a simple method is developed to estimate the life cycle of railway slab track based on the concrete fatigue. For this purpose, a mathematical/analytical model consists of two layered beams laid on elastic foundation is used to calculate the time history of stress induced in the concrete slab. Rain-flow counting method was used to count the stress cycles of the obtained time history. Finally, the life cycle of railway concrete slab track has been calculated according to the tensile fatigue behavior of concrete and stress cycles. The results obtained in this research indicate that as thickness of concrete slab and 28 days compressive strength of the concrete are increased, the life cycle of concrete slab track is increased. When the subgrade stiffness of concrete slab is increased, the life cycle of slab track is raised negligibly. Moreover, when the traffic volume passed over the track is increased, the life cycle of slab track is decreased dramatically.

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.

Using appropriate variables that can consider individual, family and trip attribute effects on transportation decision is known as one of the most important part of transportation modeling. The goal of this study is using life cycle variables to have more accurate describing of family structure. For example life cycle can discriminate between families with similar number of children and adult but different children’s age, adult’s age and employment status and this discrimination will bring more accuracy for family attribute. This study use life cycle variables in trip mode choice modeling for different trips purpose. One of the most important results of this paper is substantial rule of life cycle variables compared with household size variable in educational, social-recreational and personal trips.

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.

Management model desirable to establish the life cycle of various commodities in different organizations is a closed-loop supply chain.In this paper, according to classic models in white and brown goods, a unified framework is used to implement in a military logistics company. It seems that using this model, improved lifecycle management, environmental conservation and improvement of services provided to stakeholders and customers.

The best way to reduce highway noise is predicting measures in order to reduce the noise at sound source place. This research is about the changes of traffic noise emission given by asphalt pavement over the time cause of traffics made by any vehicle types, according to accomplished observation the asphalt pavements noise level normally increases by its longevity. For porous pavements, it is a known phenomenon that the voids of the pavements tend to clog (compress) which leads to increase noise-generated from air compaction. But for other types of dense pavements or patulous graded one (not real porous) because of continuous changes in surface structure noticing atmospheric and traffic conditions in pavements life cycle the noise increases. Physical changes like raveling, cracking, etc are noted. That causes this increase in noise in the period in between when the bitumen film is warn off and when the pavements begins to deteriorate with distresses like raveling, cracking etc. The increase of noise has normally been analyzed in relation to the age of pavements. In this research this is supplemented by also using the traffic load as well as an artificial indicator defined as the change of noise predicted as a combination of actual physical age and traffic load.

Turn of the third millennium, the role of human resources so highlighted that some referred to as the only source of sustainable competitive advantage. This is especially true as more and more in knowledge based businesses. For a start up company, human capital is the most important. The quality of this investment is more, probability of survival, success, and promotion of the business will more. In today's highly competitive and changing environment, creative and innovative human resource can help to achieve a competitive advantage. Organizations need to become learning and dynamic organizations. So their employees can develop the ability to adapt to changes in competition fields. Commitment, in brief is a person's inner feelings and attitudes towards the organization that influences on performance, judgment and loyalty towards the organization. As a result of continuous study and research on the factors of organizational commitment essential ingredients, managers can reconstruct, rehabilitate and restore of positive behaviors and organizational commitment or modify or eliminate damaging parts of this phenomenon.One of the concepts that can be used for analysis of entrepreneur team durability and the business survival is organizational commitment. In this article we attempt to discussed about the role of organizational commitment in possibility of work team integrity in the early stages of forming a business, based on a comparative study and by combining the concepts of organizational commitment and human resources in startup businesses.The purpose of this paper is to establish a correspondence between the importance of human resources in start-ups and their role in business survival and functions of organizational commitment in fulfilling these requirements.

The importance of products lifetime and determining the necessary methods appears to be obvious. Therefore, logistic organizations in the armed forces have been paying a close attention to the longevity and durability of material and consuming items (such as ammunitions) in the projects. Accordingly, good financial resources have been allocated to these projects.According to the recent research and study, appropriate operation of ammunition and explosives during the consumption are depends on variable factors. One of these factors is the effects of environmental situation within longevity (during producing and consuming time). In this study after introducing the component and process of environmental profile of ammunition and explosives in replacement, transportation, storage and utilization, we will consider necessary methods of optimizing this process. Moreover, the statistical diagram of appearing the ammunition flaws from delivery till consumption will be mentioned.Last but not least, it is highly recommended to utilize methods of time management in different levels (mellowing level, natural life level and erosion level) and design different experiments during the different period of the lifetime in order to make it possible to optimize the consumption and storage of ammunitions.