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排序方式: 共有775条查询结果,搜索用时 234 毫秒
51.
52.
This paper discusses stochastic analysis of the ash handling system in a thermal power plant. The system consists of four subsystems Ai, Bj, C and Dk in series, with three possible states: good, reduced and failed. Failure and repair rates for each subsystem are taken to be constants. Using a probabilistic approach, the differential equations are generated and the expression for steady state availability is computed. Taking data from the thermal power plant, situated in North India, the behaviour of each working unit is analysed. Problems and remedies with appropriate maintenance schedules have been discussed. The results are discussed with the plant personnel and are helpful to the management in predicting the behaviour of each operating unit, so that timely decisions can be taken for maintaining the system in upstate for a long duration. 相似文献
53.
54.
Wavelength Conversion Placement in WDM Mesh Optical Networks* 总被引:1,自引:0,他引:1
Wavelength conversion helps improve the performance of wavelength division multiplexed (WDM) optical networks that employ wavelength routing. In this paper, we address the problem of optimally placing a limited number of wavelength converters in mesh topologies. Two objective functions, namely, minimizing the average blocking probability and minimizing the maximum blocking probability over all routes, are considered. In the first part of the paper, we extend an earlier analytical model to compute the blocking probability on an arbitrary route in a mesh topology, given the traffic and locations of converters. We then propose heuristic algorithms to place wavelength converters, and evaluate the performance of the proposed heuristics using the analytical model. Results suggest that simple heuristics are sufficient to give near-optimal performance. 相似文献
55.
P. B. Thanedar J. S. Arora C. H. Tseng O. K. Lim G. J. Park 《International journal for numerical methods in engineering》1986,23(12):2187-2203
This paper describes the basic ideas of sequential quadratic programming (SQP) algorithms for design optimization. There are two fundamental differences between the various algorithms: (i) the difinition of the QP subproblem solved at each iteration, and (ii) the descent function used during step size determination. The performances of the algorithms can change dramatically depending on how the two steps are executed. Numerical implementation details of various computational steps are discussed. Three programs based on SQP algorithms are used to solve 17 structural design problems having 7 to 96 design variables and 10 to 1051 performance constraints besides design variable bounds. Based on the performance of these programs, efficient procedures to execute various steps of the SQP methods are determined. It is concluded that the potential constraint strategy, where only a subset of the constraints is used to define the QP subproblem, is essential for large scale engineering design applications. With this strategy the SQP methods are quite robust and have great potential for routine application in engineering design. 相似文献
56.
Ashok D. Belegundu Jasbir S. Arora 《International journal for numerical methods in engineering》1985,21(9):1583-1599
A comprehensive study of various mathematical programming methods for structural optimization is presented. In recent years, many modern optimization techniques and convergence results have been developed in the field of mathematical programming. The aim of this paper is twofold: (a) to discuss the applicability of modern optimization techniques to structural design problems, and (b) to present mathematical programming methods from a unified and design engineers' viewpoint. Theoretical aspects are considered here, while numerical results of test problems are discussed in a companion paper. Special features possessed by structural optimization problems, together with recent developments in mathematical programming (recursive quadratic programming methods, global convergence theory), have formed a basis for conducting the study. Some improvements of existing methods are noted and areas for future investigation are discussed. 相似文献
57.
Charu Mathur Melissa H Stigler Cheryl L Perry Monika Arora K Srinath Reddy 《Nicotine & tobacco research》2008,10(1):109-116
This study examined whether the distribution of tobacco use and related psychosocial risk factors among youth in urban India vary by socioeconomic status (SES). Data were derived from a cross-sectional survey of students enrolled in the 6th and 8th grades in 32 schools in Delhi and Chennai (N = 11,642). The survey was conducted in 2004, before the implementation of a program designed to prevent and reduce tobacco use (MYTRI). Mixed-effect regression models were used (a) to determine the prevalence of tobacco use among private (higher SES) and government (lower SES) school students, (b) to investigate whether certain psychosocial factors were associated with increased tobacco use, and (c) to determine how these factors varied by school type. Ever-use of multiple forms of tobacco (e.g., gutkha, bidis, and cigarettes) was more prevalent among government school students than private school students. After adjusting for city, gender, grade, and age, we found the prevalence rate for ever-use of any tobacco product to be 18.9% for government school students, compared with 12.2% for private school students (p<.01). Students in government schools scored lower than private school students on most psychosocial risk factors for tobacco use studied here, indicating higher risk. Government school students scored the lowest for refusal skills, self-efficacy, and reasons not to use tobacco. Social susceptibility to chewing tobacco and social susceptibility to smoking were strong correlates of current tobacco use among government school students. Exposure to tobacco advertising was also a strong correlate of current tobacco use for government school students but not private school students. In two large cities of India, students attending government schools are using many forms of tobacco at higher rates than private school students. The psychosocial risk profile of government school students suggests they are more vulnerable to initiation and use and to outside influences that encourage use. 相似文献
58.
A practical approach towards mathematical modeling of deposition rate during twin-wire submerged arc welding 总被引:1,自引:1,他引:0
Abhay Sharma Navneet Arora Bhanu K. Mishra 《The International Journal of Advanced Manufacturing Technology》2008,36(5-6):463-474
The present paper deals with a shop floor applicable mathematical model for deposition rate during twin-wire submerged arc
welding. The salient features of this model are (1) instead of melting rate, as modeled during past investigations, it quantifies
the deposition rate, which is the actual outcome of the process and always remains smaller than the melting rate because of
evaporation or spatters losses and (2) it estimates electrode extension in order to predict the deposition rate which makes
the proposed model more practical than the models constituted with the help of experimental measurement of electrode extension.
The model is more scientific than the simplified models where contact tube to work-piece distance has been considered as the
electrode extension. A critical review of the relevant past investigation is given and a mathematical model is developed for
deposition rate during the twin-wire welding with both the polarities, i.e., direct current electrode positive and direct
current electrode negative. The model is calibrated using the results of 200 experimental runs and it is found to be very
accurate with very high coefficient of regression and admissible standard error. The developed model is further validated
with extra experimental runs. The practicality of the considered approach for prediction of deposition rate can further be
used in future research for other consumable arc welding processes. 相似文献
59.
60.
Rakesh Kumar Soni Harjeet Singh Krishna Dutt Priyanka Arora 《Journal of Polymer Research》2010,17(3):411-427
The mixing torque behavior of ter blends of isotactic-polypropylene (iPP) with ethylene-propylene diene rubber (EPDM)/Nitrile
rubber (NBR) was studied with the help of Rheometer using resole type phenolic resin as a cross-linking agents. Systematic
changes with varying blend composition were observed in stress-strain behavior in the yield region viz., width of yield peak,
work of yield, yield stress and yield strain. Analysis of yield stress data was made on the basis of various mathematical
expressions of first power and two-thirds power laws of blend composition dependence and the porosity model. It led to consistent
result from the expressions about the variation of stress concentration effect in both uncross-linked and cross-linked blend
systems. With the aid of scanning electron microscopy (SEM) shapes and sizes of dispersed elastomer phase (EPDM / NBR) domains
at varying blend compositions were studied. 相似文献