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Expansion of pipelines installed on the sea floor due to the passage of high temperature and pressure hydrocarbons leads to lateral buckling. Interaction with a frictional sea floor can result in localization of such buckles, which must be controlled to ensure that the local bending is within acceptable limits. Periodic geometric imperfections introduced to a pipeline installed by reeling using the Residual Curvature Method are modeled and their effectiveness as expansion loops is evaluated. The imperfections are generated by allowing chosen lengths of the line to retain a small curvature by judicious action at the straightener. The model properly accounts for the complex interactions between geometric and material nonlinearities with frictional forces. It is demonstrated that as the temperature increases, the line can buckle in a snap-through manner, or can grow stably usually causing plastic deformation in its crest. The behavior is governed by the length, curvature, amplitude and periodicity of the imperfection, and by the lateral and axial frictional forces that develop. The effect of each of these variables is studied parametrically. Overall, the Residual Curvature Method is found to be a viable and effective method of controlling lateral buckling. The results provide guidance on the optimal periodicity, how to avoid snap-through buckling, and how to simultaneously minimize plastic bending. 相似文献
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ABSTRACTThe impacts of air transport on the economy arise both directly, via activity in the aviation sector; and indirectly, via increased spending and wider economic benefits associated with improved access to resources, markets, technology and economic mass. Economic activity, in turn, supports and generates demand for air transport. Despite its potential importance, the reciprocal nature of the causal relationship between air transport and economic performance has remained somewhat understudied. This paper provides a synthesis review of the channels the aviation sector interacts with regional economy. The review focuses on quantitative studies that contribute to the state-of-the-art understandings of the causality. We find that the reciprocal causal relationship is more likely to prevail in less developed economies. For more developed economies, only one direction of the causality is recognised, which runs from air transport to economic growth. Especially substantial is the effect of airline enplanement on service-related employment. The reverse direction of the relationship is, however, not as significant as believed in a causal sense within the developed world. Therefore, cautions need to be taken when applying income elasticities (such as the elasticity of air passenger demand with respect to GDP) in air travel demand forecasting, which implicitly assumes that economic growth causally leads to air traffic increment. Based on the fundamental links between air transport and economic growth, some typical imperfections and inefficiencies in aviation markets are discussed and promising avenues for future research are proposed. 相似文献
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破损船体极限强度非线性有限元分析 总被引:6,自引:0,他引:6
本文基于通用有限元系统,结合船体破损机理和初始缺陷处理方法,建立船体极限强度非线性有限元分析的完整框架.利用对水面舰船和双壳油船极限强度模型试验的比较验证,合理解决非线性有限元分析的关键技术,并对完整和破损船体极限强度进行非线性有限元法分析.然后,在模型试验和非线性有限元分析的基础上提出面向设计的适合破损船体和双向弯曲状态的船体极限强度分析的改进解析方法. 相似文献
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《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2012,50(6):753-770
Multibody dynamics and tyre models have made possible detailed analysis not only for ride and handling, but also for determining their effects on tyre nonuniformities. The aim of this paper is to analyse the steering wheel vibration, both shimmy and shake, excited by different tyre imperfections by using the commercial simulation package ADAMS/car 2005R2 and FTire. Different settings with respect to imperfection locations, amount, and the combined effects of defects have been studied. An interesting beat phenomenon is observed when all the wheels have imperfections. A procedure to determine the type of imperfections in the tyre from the results of the test rig has also been proposed. 相似文献
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陈敏 《武汉船舶职业技术学院学报》2013,(6):98-100,115
基于交际理论视角下的任务型教学模式在高职英语教学中的应用,能有效弥补高职英语存在的“以教师为中心”、“以书本为中心”的不足,以助推高职应用型人才培养主旨的实现。然而在任务型教学模式具体的实践过程中,存在任务与教材的适应性、任务难易确定性、师生能力与任务相匹配等问题的“缺憾”。基于此,必须对任务型教学模式进行更为深入的研究,并提出弥补任务型教学模式缺陷的创新性对策,进而继续发挥任务型教学模式在高职英语教学中的“正能量”。 相似文献
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加筋板屈曲和极限强度有限元计算方法研究 总被引:1,自引:0,他引:1
针对国际船级社协会双壳油船共同结构规范中加筋板屈吐和极限强度的计算要求,介绍了其技术背景和国内外相关研究现状,并通过分析各种因素对加筋板屈曲和极限强度的影响,研究国外相关技术文献,提出了一套完整的加强筋屈曲和极限强度有限元计算方法。与共同结构规范中要求的对标数据进行对比,验证了该方法的正确性。 相似文献
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This paper deals with vibration analysis of plates in marine structures. It is the main purpose of the paper to demonstrate that in order to obtain reliable frequency predictions it is necessary to include in the vibration analysis the effects of the unavoidable imperfections caused by welding or lateral fluid pressure. Furthermore, practical procedures for including these effects are presented. Simple algebraic expressions are derived for determination of small amplitude natural frequencies of vibration of initially imperfect rectangular plates subjected to uniaxial in-plane loads. The theoretical results show close agreement with experimental results available in the literature. For plating of marine structures with typical welding induced geometric imperfections and residual stresses it is shown that the lowest natural frequency of the unloaded imperfect plate can be twice as high as that of the perfect plate. For vibration analyses of plates submerged in a liquid the importance of taking into account deflections and membrane stresses caused by the hydrostatic pressure is demonstrated. 相似文献