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961.
The practical use of fracture mechanics has been established for use on large turbine and electric generator rotor components used in the atomic power generation and the aircraft industry. Application areas in the offshore industry have also been identified. Fracture mechanics is currently used at the design stage of offshore facilities. It provides the basis for fatigue life prediction, steel selection and tolerance setting on allowable weld imperfections. Fracture mechanics is also used during the operational stage of a structure to make important decisions on inspection scheduling and repair strategies and as a tool for establishing limits on operational conditions. Linear elastic fracture mechanics relies on the use of the stress intensity factor concept. The stress intensity factor is a very important fracture mechanics parameter. Therefore, the accuracy of any fracture mechanics model for the prediction of fatigue crack growth in offshore structures for example will depend very much on the accuracy of the stress intensity factor solution used. Several empirical and semi-empirical solutions have been developed over the years with varying degrees of accuracy. This paper presents a review of some of these methods and attempts to assess their accuracy in predicting Y factors for welded tubular joints by comparing predicted results with experimental data obtained from fatigue tests conducted on large scale welded tubular joints. The experimental results were conducted under simulated service conditions, using a jack-up offshore standard load history (JOSH). A comparison between the experimental and predicted results shows that there may be other factors, which influence fatigue crack growth under variable amplitude conditions. Some of these factors have been identified and discussed in this paper. 相似文献
962.
963.
Richard W. Stoffle Jessica Minnis Amanda Murphy Kathleen Van Vlack Nathan O'Meara Tavarrie Smith 《Coastal management》2013,41(5):501-517
This article recommends the parallel but separate modeling of nature-based and people-based marine protected areas (MPA) before the design and siting stages of establishing an MPA. Separate but simultaneous modeling of ideal nature and people MPAs permits each to be maximized for its own variables and subsequently compared to identify conflicts and agreements. The case that supports this recommendation is in the Commonwealth of the Bahamas, where the study conducted 572 interviews with people from six traditional settlements in the central Exumas Islands and Cays. The research is focused on why members of these settlements differentially responded to three nearby national MPA proposals. 相似文献
964.
Inseok Park Seungwoo Hong Myoungho Sunwoo 《International Journal of Automotive Technology》2017,18(4):579-587
This paper presents a model-based gain scheduling algorithm of a PI-based EGR controller for light-duty diesel engines. In order to capture nonlinear characteristic of the EGR system, we have proposed a new scheduling variable to illustrate the static-gain of the plant model as a linear function. The proposed scheduling variable is composed of the air-tofuel ratio of the exhaust gas and the pressure ratio between the exhaust and intake manifolds. Using the scheduling variable, a static-gain model achieved 0.94 of the R-squared value with 810 of steady-state measurements which include key engine operating conditions. Based on the model of the static-gain parameter, the gains of the PI controller are decided by Skogestad internal model control (SIMC) tuning rule in real-time. Through various scenarios of engine experiments, the proposed gain scheduling algorithm represented that the PI gains were successfully adapted according to the changes of the engine operating conditions. 相似文献
965.
Anthony T.H. Chin Joyce M.W. Low 《Transportation Research Part D: Transport and Environment》2010,15(8):483-488
Atmospheric and water pollution are two main sources of negative environmental externalities generated by shipping. This study recognizes the negative externalities in the production of port services in East Asia by explicitly incorporating environmental impacts of shipping. Programming techniques are used to analyze 156 Origin–Destination pairs between 13 major East Asian ports, to derive the externality-augmented measures of port productivity and efficiency at the waterside. The results suggest that the inclusion of externality mitigation strategies can exert a considerable influence on efficiency performance. 相似文献
966.
W. S. Homburger 《运输规划与技术》2013,36(3):187-201
This study analyzes data of traffic crossing San Francisco Bay and passing through the Berkeley Hills via Caldecott Tunnel to determine the effect of the opening in 1974 of the Bay Area Rapid Transit System (BART) transbay line. There was a sudden shift in trend lines in 1974; vehicle volumes dropped, transit patronage jumped, but total person trips in the short run followed roughly the trends of the previous eight years. Since 1974, the growth rate in person trips through the Berkeley Hills appears to have remained about the same, while transbay vehicle and transit traffic have increased at a more rapid rate. The increase in transit patronage is particularly noticeable between the morning and afternoon peaks and probably represents new trips by shoppers and sightseers. Whereas other factors, such as the increase in the price of gasoline between October 1973 and July 1974 may have contributed a little to the sudden change in the long‐range trends in 1974, it is believed that the major cause was the opening of the BART network to transbay travel. 相似文献
967.
文章针对农村公路水泥稳定类基层建设采用集中厂拌法面临的用电困难、运输距离远、易离析以及传统路拌法水泥撒布不均匀、水泥剂量、含水量与混合料的均匀性不易准确控制、能耗大、劳动强度大、粉尘污染严重等不足之处,经过实验室模拟研究与现场试验,提出了利用碎石撒布车均匀撒布矿料、粉料撒布车均匀撒布水泥、冷再生机现场拌和、碾压、整平的机械一体化"现场均匀拌和法"施工工艺,现场质量检测结果表明这种工艺具有可行性。本研究对于我国新农村公路建设的迅速发展具有一定的参考价值。 相似文献
968.
970.
通过分析国内部分城市轨道交通项目的融资、财务分析等问题,建议通过降低资金成本,合理控制运营成本,进而提高项目的经济效益,最终达到吸引社会投资、多元化融资渠道的良性循环。 相似文献