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711.
This paper presents a study on the numerical calculation of the friction resistance coefficient of an infinitely thin plate
as a function of the Reynolds number. Seven eddy-viscosity models have been selected: the one-equation turbulence models of
Menter and Spalart–Allmaras; the k-ω two-equation model proposed by Wilcox and its TNT, BSL and SST variants and the two-equation model. The flow has been computed at 14 Reynolds numbers in sets of seven geometrically similar Cartesian grids
to allow a reliable estimation of the numerical uncertainty. The effect of the computational domain size has been reduced
to negligible levels (below the numerical uncertainty). And the same holds for the iterative and round-off errors. In the
finest grids of each set, the numerical uncertainty of the friction resistance coefficient is always below 1%. Special attention
has further been given to the solution behaviour in the laminar-to-turbulent transition region. Curve fits have been applied
to the data obtained at the 14 Reynolds numbers and the numerical friction lines are compared with four proposals from the
open literature: the 1957 ITTC line, the Schoenherr line and the lines suggested by Grigson and Katsui et al. The differences
between the numerical friction lines obtained with the seven turbulence models are smaller than the differences between the
four lines proposed in the open literature. 相似文献
712.
B. Ruan G. Q. Li Y. Chen P. Mitrouchev B. He L. X. Lu 《International Journal of Automotive Technology》2016,17(6):1033-1043
As concerns of dynamic tensile measuring, a new tension mechanism driven by liner motor in high-speed tensile testing machine is presented. It satisfies the requirements for testing the dynamic tensile properties of plastic materials with strain rates from 1 to 100 s-1, which is relatively difficult to test for currently available machines. For this purpose the idle stroke principle is used to realize the dynamic load of plastic material with static grip. Computer aided engineering is used: i) to analyze and optimize the tension mechanism thus allowing reducing the system shock caused by collisions. ii) to avoid the influence of plastic materials specimen stress and strain uniformity on the measuring system. The analysis results agreed well with the established empirical relationships based on experimental evidence. Two sets of experiments for different strain rate tensile were conducted thus allowing proving the reliability and credibility of the designed tension mechanism. 相似文献
713.
Optimal toll design from a network reliability point of view is addressed in this paper. Improving network reliability is proposed as a policy objective of road pricing. A reliability‐based optimal toll design model, where on the upper level network performance including travel time reliability is optimized, while on the lower level a dynamic user‐equilibrium is achieved, is presented. Road authorities aim to optimize network travel time reliability by setting tolls in a network design problem. Travelers are influenced by these tolls and make route and trip decisions by considering travel times and tolls. Network performance reliability is analyzed for a degradable network with elastic and fluctuated travel demand, which integrates reliability and uncertainty, dynamic network equilibrium models, and Monte Carlo methods. The proposed model is applied to a small hypothesized network for which optimal tolls are derived. The network travel time reliability is indeed improved after implementing optimal tolling system. Trips may have a somewhat higher, but more reliable, travel time. 相似文献
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716.
从定量和定性角度系统地阐述了公路网的适应性评价的方法,在定量评价中列举了6个对公路网进行评价的指标,并结合山东省公路网的具体情况,用这6个指标进行了相应的评价,得出结论。在定性评价中主要对公路网的结构性问题进行了探讨,为了更好地解决车辆超载对公路造成的破坏,提出了公路建设标准应进一步改进的建议。 相似文献
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718.
基于面向对象技术的舰船综合电力系统电力网络故障模拟及拓扑跟踪 总被引:1,自引:0,他引:1
针对舰船综合电力系统电力网络结构特点,本文实现了基于面向对象技术的对舰船综合电力系统电力网络的拓扑建模。并针对电网故障的随机性特点,在面向对象环境中实现了对随机故障的模拟,同时用深度优先算法进行了快速的拓扑跟踪。算例分析证明了该方法的有效性。 相似文献
719.
无水港是近年来迅速发展的、与港口具有同样功能的"内陆港"。介绍了国内4个无水港港群发展的现状和我国目前无水港的通关模式。分析了无水港通关模式的优势和社会效益。指出了需要进一步解决的问题。 相似文献
720.
IntroductionIn recentyears,many FPGA technology map-ping algorithms for performance optimization havebeen presented[1~ 3 ] .Among them,DAG- MAP is arepresentative algorithm[3 ] .This algorithm is pro-grammed into a package and it mainly consists ofthree parts:1 preprocessing procedures transforman arbitrary Boolean network into a two- inputnet-work;2 the DAG- MAP algorithm maps the two-input network into a K- LUT FPGA network withminimum delay;3 postprocessing procedures per-form ar… 相似文献