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The value of form factor k at different drafts is important in predicting full-scale total resistance and speed for different types of ships. In the ITTC community, most organizations predict form factor k using a low-speed model test. However, this method is problematic for ships with bulbous bows and transom. In this article, a Computational Fluid Dynamics (CFD)-based method is introduced to obtain k for different type of ships at different drafts, and a comparison is made between the CFD method and the model test. The results show that the CFD method produces reasonable k values. A grid generating method and turbulence model are briefly discussed in the context of obtaining a consistent k using CFD. 相似文献
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Traffic flow prediction is an essential part of intelligent transportation systems (ITS). Most of the previous traffic flow prediction work treated traffic flow as a time series process only, ignoring the spatial relationship from the upstream flows or the correlation with other traffic attributes like speed and density. In this paper, we utilize a linear conditional Gaussian (LCG) Bayesian network (BN) model to consider both spatial and temporal dimensions of traffic as well as speed information for short‐term traffic flow prediction. The LCG BN allows both continuous and discrete variables, which enables the consideration of categorical variables in traffic flow prediction. A microscopic traffic simulation dataset is used to test the performance of the proposed model compared to other popular approaches under different predicting time intervals. In addition, the authors investigate the importance of spatial data and speed data in flow prediction by comparing models with different levels of information. The results indicate that the prediction accuracy will increase significantly when both spatial data and speed data are included. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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With the real time and accurate information of motor torque and rotation speed of the four-in-wheel-motordrive electric vehicles, a slip based algorithm for estimating maximum road friction coefficient is designed using Lyapunov stability theory. Modified Burckhardt tire model is used to describe longitudinal slip property of the tire. By introducing a new state variable, a nonlinear estimator is proposed to estimate the longitudinal tire force and the maximum road friction coefficient simultaneously. With the appropriate selection of estimation gain, the convergence of the estimation error of the tire longitudinal force and maximum road friction coefficient is proved through Lyapunov stability analysis. In addition, the error is exponentially stable near the origin. Finally the method is validated with Carsim-Simulink co-simulation and real vehicle tests under multi working conditions in acceleration situation which demonstrate high computational efficiency and accuracy of this method. 相似文献
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碎石层缓冲差异沉降模拟试验研究 总被引:1,自引:0,他引:1
为研究碎石层对差异沉降的缓冲性能,设计了模拟差异沉降试验箱,通过模拟试验验证了碎石层缓冲差异沉降的效果;在碎石层缓冲差异沉降机理分析的基础上,提出了二次松散系数的概念及计算公式,设计了碎石层二次松散系数测试箱,并分析了粒径大小、颗粒形状、内摩擦角与二次松散系数的关系。根据常见的沉降曲线形状推导了相应的碎石松散边界方程,并由此分析了影响碎石松散区域大小的主要因素。研究表明:碎石模拟试验箱的设计及试验是成功的;碎石层散体材料可以缓冲差异沉降主要是由于其具有二次松散的性能;二次松散系数随碎石粒径及内摩擦角增大而增大,且同粒径卵石的二次松散系数总是低于碎石;沉降最大值及二次松散系数是决定松散区域厚度的主要因素。 相似文献
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对某船螺旋桨噪声进行了预报.高频噪声预报采用模型试验方法进行.在国家重点试验室大型循环水槽中完成了桨模高频噪声的测量,测试结果经量纲一的量方法换算至实船.采用面元法计算非定常力,通过力与声级的关系换算出低频离散谱噪声.求解出螺旋桨随机连续性力.然后换算出低频连续谱噪声.从预报结果总结出螺旋桨噪声随频率的变化规律以及速度对噪声的影响. 相似文献
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