جستجوی مقالات مرتبط با کلیدواژه « rail » در نشریات گروه « عمران »

Rapid transportation and delivery large volumes of equipment to combat operational and support units, especially in recent wars, clearly shows the necessity of using all transportation capacities in the country. In addition to speed, safety and reliability and other criteria affect the modes of transport. This study analyzes the rail transport selection decisions in the logistics of a defense organization by gathering the opinions of experts through the Analytical Hierarchy Process (AHP) and attempts to analyze the items and criteria for the transport of each of them through rail transport. Therefore, it is applied in terms of purpose and exploratory in terms of nature and method. The innovations of this research include analyzing the application of rail transport in defense organizations, the use of the Analytical Hierarchy Process and the presentation of the same prepared classes between military and civilian organizations. According to the findings, transportation safety was the most important criterion and dangerous items among the movable items in the five categories, according to the transportation safety criterion was extracted as the first option. The results of the research can be used in the logistics policy of defense organizations.

One of the most important factors influencing mode choice in freight transport between rail and road is travel time reliability, which has been researched in the world more around the stated preferences [SP] data also to the best knowledge of the authors there is no research formed with revealed preferences data in Iran.  The present study intends to conduct this research using the data of the revealed preferences of the registered bill of lading of rail and road and the travel time of freight trains and in terms of various variables of reliability. In this article, the choice of mode between rail and road for 10 groups of goods is examined. Initially, the various variables of reliability that were previously introduced in the sources related to freight and passenger transport, in addition to the new variables of this study were made based on the travel time information. In most groups of goods, the variable of shipments ratio in the range of 10% of the average travel time was more significant. One of the outstanding results of this research is that the group of containerized goods and foodstuffs are the most sensitive to reliability, respectively, and on time delivery of shipments can play an effective role in attracting these loads from the road. The group of mineral goods is less sensitive to the reliability of travel time, and in this group, variables such as cost play a more important role in the choice of transport mode.

Rail transportation system plays an important role in the development of the economies of the countries. This system will be worn over time by operation and weather conditions and will require maintenance. One of the goals of this operation is to keep the tracks in an acceptable condition and prevent their excessive deviation from the optimal situation. Railways maintenance and repair management system has been studied and implemented to optimize activities and reduce related costs. Such systems have used various techniques to predict the future state of failure. Choosing the best maintenance policy is the goal of these systems. For policy making, the best and most cost-effective option, life-cycle cost analysis is required. In the following, with the help of the Markov prediction model, the life cycle cost (LCC) model is suggested for rail and ballast. In the end, it was found that the main costs in the ballast part are renewal costs and the track unavailability costs. The effect of renewal tonnage on these two costs is far higher than other costs. As you can see, the lowest ballast life cycle cost in the range of 100 to 150 million gross tons. In this study, assuming annual tonnage (16 million gross tonnages) as previously mentioned, it results a renewal life of about 6 to 10 years. This value for the rails is from 500 to 540 million gross tons, which is equivalent to 30 to 35 years.

In the rail fleet Sizing problem, it is aimed to determine the optimal number of each vehicle type in transportation fleet, while optimizing system objectives. This issue has been investigated as a single-objective problem in the context of rail transportation with the assumption of homogeneity in the fleet, despite the existence of different goals in real systems. In this paper, a dual objective function is adopted after studying real-world consideration. According to the experts at the IslamicRepublic of Iran Railway Company (IRIR), reduction of the number of delays in response to requests during the course of planning is an important additional objective function, which is included in our model. The solved problem is dynamic and demands for wagons and the transportation times are assumed to be deterministic. In this paper, after presenting the mathematical model, the importance factor of each objective function is calculated taking into account theprescriptions of the experts at the IRIR Research Center and based on aggregate weighting method. In order to solve the model and find the solutions on the Pareto front, three methods based on Genetic Algorithms, Simulated Annealing, and a hybrid of those are designed and their parameters tuned, by which the rail transportation system of the IRIR is solved and the results are discussed.

Nowadays، modeling methods by using petrinets in broad and complex networks، especially by developing computer science and the increasing the computers speed، has got a wide range of use. The graphic capability of petrinets has caused that these networks be utilized broadly in industry. In this study a closed rail-road network in which Normal and Express trains، by using petrinets can move has been considered as a model. By dint of analyzing the computerized model network، the total reachable space state that exists in rail-road network، has been drawn and the network will be analyzed from the point of view of Safety and Free dead-lock. By means of Supervisory control designed based on petrinets، not only it removes the dead-lock situation revised network، with the allowed number of Normal and Express trains، but also its safety would be guaranteed.

In this paper, wheel-rail contact problem in presence of rail surface crack is investigated. The reason for investigating this problem is significant effect of wheel-rail contact on stress intensity factors and also the effect of crack on contact pressure. ..

Nowadays, railway has been identified as the safest and most proper transportation system. Failure of rails, as one of the most importance elements of railway systems, can cause accidents and affect its safety. In this study, 55 steel samples extracted from UIC60 rail have been tested by Charpy impact test equipment in different temperatures ranged between -40 and 60 C. Then, fracture toughness of rail in different temperatures has been calculated by using known experimental relation between fracture toughness and measured fracture energy. Finally, the rail critical crack length has been determined by replacing calculated fracture toughness in formula of stress intensity factor. In order to restrict rail fracture and increase service life of the rail, critical crack length, in addition to none destructive tests for maintenance process of rails

Although the current analysis and design of railway track systems are based on theassumption of continuous and linear behavior of the rail support system, repair andmaintenance plans have considerable influences on the structural behavior of thetrack support system, particularly after accumulative loading or track tamping.Recent experimental investigation indicated the behavior of the track support systemis time and stress dependent. The amount of traffic passed and the quality andquantity of maintenance activities can considerably influence the track responsefunctions. Although some experimental investigations have been carried out to studythe time and stress dependent characteristics of the ballast and subgrade materials,the effects of the consideration of these characteristics on the track analysis anddesign, need further evaluations. Furthermore, the recent extensive increases in axleloads, speed and traffic volumes in rail transport systems, require more preciseanalytical and mechanistic approaches for railway track system. This research is aresponse to this need. In this paper, the current practices in the analysis and design ofrailway track system are discussed. A mode of track support system withconsideration of discrete supports is developed. By comparison of the analysesresults obtained from track models with continuous and discrete support systems, theaccuracy of the assumption made in the Winkler model, used in the current designapproach, are evaluated. The nonlinear behaviors of the track support system werestudied and the influences made by the consideration of the non-linearity of the tracksupport system on the rail design criteria were investigated. Rail bending momentsand rail deflections as the main rail design criteria are obtained form track with alinear support and nonlinear behaviors. Obtaining large discrepancies between theresults obtained from linear and non-linear analyses, the importance of the trackregular and systematic repairs, in particular tamping and stabilizing the ballast, areproved. It is shown that the consideration of regular repairs of the track supportsystem improves the long term reliability and accuracy of the current track designapproach. Recommendations are made on the track maintenance and repairs in orderto keep the track support system in the linear conditions.