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731.
Ⅰ型裂纹稳定扩展裂尖塑性区研究 总被引:2,自引:0,他引:2
运用FRANC2D/L软件分别对6.35 mm和2 mm两种厚度Arcan试件的Ⅰ型裂纹稳定扩展进行数值计算,研究了该软件的网格划分技术对计算结果的影响,发现该软件的计算精度主要受裂纹区的网格密度影响(当裂纹面单元与裂纹每步扩展单元尺寸一致时,计算精度好).通过分析有效应力,研究了材料、裂纹扩展长度及试件厚度对裂纹尖端塑性区尺寸的影响.研究结果表明,材料的屈服应力越大,其裂尖塑性区尺寸越小;塑性区尺寸随裂纹扩展长度的增加,先增大后趋于不变;塑性区的形状与板厚或边界有关,6.35 mm厚的母材及3种焊接板材塑性区成扩散型,2 mm厚的母材成Dugdale模型,25.4 mm以上厚度母材成平面应变模型;裂纹启裂时,塑性区随着厚度的增加而减小,最终不变. 相似文献
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为了研究适合中国城镇道路混合交通特点的道路养护优化策略,在总结已有研究的基础上,改进了机动车延误计算模型,提出了包括养护费用、机动车延误损失、非机动车延误损失和交通事故损失在内的总耗费目标函数.通过求解该函数的最小值来确定最优作业区长度及养护作业起始时间.利用"试错法"对模型进行了求解,并通过算例进行了分析.结果显示,养护作业区长度和作业起始时间是制定养护策略的关键因素,在养护路段长度一定的情况下,通过合理设定作业区长度和起始时间可使总耗费最省. 相似文献
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桂定一 《湖北汽车工业学院学报》2004,18(2):17-19
说明了最大、最小检测半径的计算,推证了双面啮合下节圆压力角(节点展角)的计算公式;解释了检测中心距公差带(径向综合测试公差带)的形成和作用,对个别代号的含义提出了看法;列举了保证功能齿厚测量精度的主要要求,给出了部分因素对测量精度影响的比率。 相似文献
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申江南路大治河桥主桥为120 m的大跨度简支下承式钢箱系杆拱组合体系拱桥。该桥吊杆与系梁锚固区为钢箱锚固体系,吊杆与系梁锚固区处钢板空间交汇。由于系梁采用钢混组合梁结构,该部位的构造和受力更为复杂。为了验证锚固区受力的合理性,采用混合有限元的计算方法有效模拟了吊杆与系梁锚固区局部的受力情况,计算了吊杆与系梁锚固区各板件的应力分布。计算结果表明,构件受力合理,吊杆与系梁锚固区处各板件应力情况满足设计要求。目前该工程已投入使用多年,运营良好。 相似文献
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This paper proposes a stochastic model to determine the yellow time according to the occurring probability of Type‐I dilemma zone (PDZ). Unlike the conventional methods generally based on the deterministic traffic flow theory, the proposed model fully accounts for the randomness of input variables such as approaching speed, deceleration rate, perception‐and‐reaction time, and distance to stop‐line at the yellow onset. A theoretical model is firstly established, and a computational program incorporating Monte Carlo Simulation is then developed to facilitate its general solution. These two alternative solution approaches to derive PDZ and Y are proposed, depending upon whether D/V and (τ + V/2d) follow certain analytical distributions or not. In addition, field data at a typical high‐speed highway intersection are collected to validate the model. Based on the validated model, comprehensive sensitivity analysis is conducted to look into the entire picture of the relationship between PDZ and the distributions as well as correlations of the input variables. To demonstrate the application of the proposed model, the required yellow times for various conditions are calculated based on the acceptable levels of PDZ, and representative application tables for typical cases are finally provided. With the aid of the proposed methodology, traffic engineers are capable of designing yellow time in a more sophisticated manner. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
737.
Integration of signal timing estimation model and dynamic traffic assignment in feedback loops: system design and case study 下载免费PDF全文
This paper presents an integrated framework for effective coupling of a signal timing estimation model and dynamic traffic assignment (DTA) in feedback loops. There are many challenges in effectively integrating signal timing tools with DTA software systems, such as data availability, exchange format, and system coupling. In this research, a tight coupling between a DTA model with various queue‐based simulation models and a quick estimation method Excel‐based signal control tool is achieved and tested. The presented framework design offers an automated solution for providing realistic signal timing parameters and intersection movement capacity allocation, especially for future year scenarios. The framework was used to design an open‐source data hub for multi‐resolution modeling in analysis, modeling and simulation applications, in which a typical regional planning model can be quickly converted to microscopic traffic simulation and signal optimization models. The coupling design and feedback loops are first demonstrated on a simple network, and we examine the theoretically important questions on the number of iterations required for reaching stable solutions in feedback loops. As shown in our experiment, the current coupled application becomes stable after about 30 iterations, when the capacity and signal timing parameters can quickly converge, while DTA's route switching model predominately determines and typically requires more iterations to reach a stable condition. A real‐world work zone case study illustrates how this application can be used to assess impacts of road construction or traffic incident events that disrupt normal traffic operations and cause route switching on multiple analysis levels. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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