共查询到18条相似文献,搜索用时 156 毫秒
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《力学学报》2010,42(5):848
依据上海延安高架路段的交通流录像资料提取的26000余组实测数据,作出流量-密度图,发现即使在低密度时流密关系亦具有非线性二维区域特性。通过与Kerner提出的非线性二维流密关系模型进行比较,指出一些符合中国交通状况的现象可在图中得以体现。利用观测得到的大量数据,在按密度划分的不同区间内对已有的多个平衡函数进行最优筛选,得到分段平衡函数的表达式,使交通流模型更加贴近真实交通状况。最后提出了基于实测数据计算激进型驾驶者比例的方法,该方法的关键在于利用各种经过特征值变换后的平衡函数形式模拟已有数据的区域边界。关键词:交通流模型;实测数据;流量-密度图;分段平衡函数;激进型驾驶者 相似文献
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高压捕获翼前缘型线优化和分析 总被引:1,自引:0,他引:1
为分析翼前缘形状变化对高压捕获翼构型气动性能的影响,基于一种锥体组合捕获翼概念构型,采用幂次函数和余弦函数组合形式对翼前缘型线进行了参数化设计,在比较了多项式和径向基函数两种代理模型的拟合精度基础上,以飞行马赫数7,飞行攻角0° 为计算条件,结合使用均匀实验设计方法、计算流体力学、径向基函数代理模型方法和遗传算法,选择升阻比最大化为目标开展了数值优化,最后基于优化结果进行了单参数的灵敏度分析. 优化结果表明,相对于基准外形而言,优化后构型升力系数增大了约8.1%,阻力系数减小了约12.2%,升阻比提高了约23.4%. 此外,灵敏度分析结果表明升阻比与5 个设计参数均呈非线性关系,其中展向角度对升阻比影响最大,其次为幂次曲线的比例参数,其余3 个参数对升阻比的影响相对较弱. 相似文献
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关于交通流中扰动传播和发展的数值模拟 总被引:3,自引:3,他引:3
针对不同拥挤程度交通流中扰动的传播和发展,进行了系统的数值模拟研究.
讨论了PW模型、一维管流模型、单侧传播模型等几种典型交通流模型的不同特征;指出了
不同差分格式对数值结果的影响;也分析了数学模型中不同形式的平衡函数的作用. 结果发
现在适当的数学模型、平衡函数和离散格式下,能够对交通流中扰动的传播和发展,特别是
扰动波的传播速度,取得与实际测量数据相当接近的模拟效果. 建议了分别适用于不同密度
交通流的计算格式. 相似文献
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为了分析RC框架结构的非线性滞回性能,基于平面8节点单元,本文提出了一个新的针对受循环荷载作用钢筋混凝土的梁柱节点单元.单元中梁与节点交界面和柱与节点交界面被划分成“节点截面”和“梁柱截面”,节点核心区的力学性能由8节点单元描述,而梁柱受力钢筋与节点核心区的粘结滑移由存在于“节点截面”和“梁柱截面”之间的8根弹簧控制,梁柱与节点之间的剪切由4根剪切弹簧表示.单元具有4个外节点和8个内节点,每个内节点具有2个自由度,每个外节点具有3个自由度,该3个自由度与普通梁单元一致,从而确保本单元能够同普通一维梁柱单元一起进行钢筋混凝土结构平面非线性分析.通过将内节点上的自由度依附到外节点上,单元在数值表现上具有4个节点和28个自由度.通过对比试验和模拟分析结果,验证了本模型适合于循环荷载作用下平面框架结构的非线性响应分析. 相似文献
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Empirical test of a microscopic three-phase traffic theory 总被引:1,自引:0,他引:1
A review of dynamic nonlinear features of spatiotemporal congested patterns in freeway traffic is presented. The basis of
the review is a comparison of theoretical features of the congested patterns that are shown by a microscopic traffic flow
model in the context of the Kerner's three-phase traffic theory and empirical microscopic and macroscopic pattern characteristics
measured on different freeways over various days and years. In this test of the microscopic three-phase traffic flow theory,
a model of an "open" road is applied: Empirical time-dependence of traffic demand and drivers' destinations are used at the
upstream model boundaries. At downstream model boundary conditions for vehicle freely leaving a modeling freeway section(s)
are given. Spatiotemporal congested patterns emerge, develop, and dissolve in this open freeway model with the same types
of bottlenecks as those in empirical observations. It is found that microscopic three-phase traffic models can explain all
known macroscopic and microscopic empirical congested pattern features (e.g., probabilistic breakdown phenomenon as a first-order
phase transition from free flow to synchronized flow, moving jam emergence in synchronized flow rather than in free flow,
spatiotemporal features of synchronized flow and general congested patterns at freeway bottlenecks, intensification of downstream
congestion due to upstream congestion at adjacent bottlenecks). It turns out that microscopic optimal velocity (OV) functions
and time headway distributions are not necessarily qualitatively different, even if local congested traffic behavior is qualitatively
different. Model performance with respect to spatiotemporal pattern emergence and evolution cannot be tested using these traffic
characteristics. The reason for this is that important spatiotemporal features of congested traffic patterns are lost in these and many other macroscopic and microscopic traffic characteristics, which are widely used as the empirical basis
for a test of traffic flow models.
PACS: 89.40. + k, 47.54. + r, 64.60.Cn, 64.60.Lx 相似文献
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研究了在同一路段上非港湾式公交车站站点的分散式和集中式设置对道路 交通的影响. 在元胞自动机交通流NaSch模型上, 提出了考虑公交车站站点分散式和集中式 设置的双车道元胞自动机交通流模型, 通过计算机模拟和理论分析, 结果表明: 在开放边界条件下, 分散式公交车站点与集中式公交车站点相比, 影响道路交通通行能力作用显著的减小; 公交车站点之间的间隔、站台的长度、公交车停靠时间以及车流中公交车的比例对交通 流量有显著的影响. 相似文献
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R. G. Galiullin É. R. Galiullina E. I. Permyakov 《Journal of Applied Mechanics and Technical Physics》1998,39(3):404-410
An analytical theory of resonant oscillations of a gas in an open-ended tube is developed. The gas flow in the tube is assumed
to be turbulent. A model of gas flow near the open end of the tube is constructed. This model allows a boundary condition
that is free of empirical parameters to be obtained. Theoretical results are in reasonable agreement with experimental data
obtained by other authors.
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 39, No. 3, pp. 92–99, May–June, 1998. 相似文献
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R.M.C. So A. Sarkar G. Gerodimos J. Zhang 《Theoretical and Computational Fluid Dynamics》1997,9(1):47-63
Two-equation turbulence models are usually formulated for specific flow types and are seldom validated against a variety of
flows to account for near-wall and low-Reynolds-number effects simultaneously. In addition to low-Reynolds-number effects,
near-wall flows also experience wall blocking, which is absent in free flows. Consequently, near-wall modifications to two-equation
models could be quite different from low-Reynolds-number corrections. Besides, it is known that existing two-equation models
perform poorly when used to calculate plane wall jets and two-dimensional backstep flows. These problems could be traced to
the modeling of the dissipation rate equation. In this paper an attempt is made to improve the modeling of the dissipation
rate equation so that it could successfully predict both free and wall-bounded shear flows including plane wall jets and backstep
flows. The predictions are compared with experimental and direct numerical simulation data whenever available. Most of the
data used are obtained at low Reynolds numbers. Good correlation with data is obtained. Therefore, for the first time, a model
capable of correctly predicting free and wall-bounded shear flows, backstep flows, and plane wall jets is available.
Received: 12 December 1995 and accepted 12 November 1996 相似文献
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无壁面参数低雷诺数非线性涡黏性模式研究 总被引:3,自引:0,他引:3
建立了一个低雷诺数的非线性涡黏性湍流模式,该模式的一个显著特性是它不包含壁面参数(如y^ ,n等),因而特别适用于复杂几何流场的计算,本模式在几种包括回流、分离、激波等典型流动中进行了验证,结果令人满意。 相似文献
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The wicking height of a heated, evaporating meniscus formed by surface-wetting liquid in a vertical capillary tube with dynamic flow has been investigated. Previous experimental results and analytical models for measuring/predicting wicking heights in capillaries are also reviewed. An analytical model is presented that accounts for both major and minor vapor pressure losses along the vertical capillary tube. It is shown that during thermo-mechanical instability, vapor/meniscus interaction can become more prevalent due to increased vapor generation/pressure near the meniscus free surface. A relatively simple procedure for estimating onset of meniscus instability is presented and, when used with the vapor Reynolds number, can estimate whether vapor pressure loss is significant. By comparing the current model with the available experimental data, it is shown that the wicking height of an unstable, evaporating meniscus of n-pentane in a vertical, glass capillary tube is better estimated by considering vapor flow pressure losses – providing a 40% improvement over previous models that neglect vapor flow. In addition to vapor flow pressure loss, the dynamic contact angle and thin film profile must also be calculated to ensure accurate prediction of wicking height. Although the proposed model shows improvement, it is prone to under-predicting the actual meniscus wicking height for stable, evaporating menisci at lower relative heat loads. The proposed model can be used for predicting wicking behavior of heated, vertically-aligned liquid columns in capillary structures – which is relevant to the design of miniature heat transfer equipment/media such as wicked heat pipes, micro-channels and sintered/porous surfaces. 相似文献
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Similarly to the treatment of diluted gases, kinetic methods are formulated for the study of unidirectional freeway traffic. From these it is possible to construct fluid-dynamic equations which in comparison with heuristic fluid-dynamic models have the advantage of just some adjustable parameters although they have some other restrictions. In this work the comparison between two macroscopic models which are based on a kinetic traffic equation is shown. On the other hand, there will be presented some advances to attempt to generalize some restrictions of the kinetic formulation in order to study the synchronization phenomena, which is a very interesting transitory phase between free flow and traffic jams. 相似文献
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The three-dimensional problem of finite-depth stratified flow over a small bottom irregularity is considered in mixed Euler-Lagrange variables. The Brunt-Väisälä frequency is assumed to be constant and small, and the free surface condition is replaced by the rigid roof condition. Investigation of the far field showed that the principal wave perturbations lie within an angle which for large values of the internal Froude number is much less than theKelvin angle, while the wave amplitude at infinity is of the order of l/r, where r is the polar radius. The ring perturbations are exponentially damped. As distinct from point source models, the model in question does not lead to divergence of the integrals on the flow axis [1-3]. Appproximate expressions for the radial and ring waves in terms of certain universai functions were obtained for investigating the near and far fields when the bottom irregularity is hemispherical. For the radial waves a law of similarity was obtained for which the characteristic dimension in the direction of the flow axis is the ratio of the flow velocity to the Brunt-Väisälä frequency, and the characteristic dimension in a direction perpendicular to the flow axis the depth of the fluid. In the first approximation the ring perturbations do not depend on the Brunt-Väisälä frequency. It is shown that in the near field the zone of intense wave perturbations is of the order of the fluid depth and not of the dimensions of the obstacle as for Kelvin ship waves on the surface of a homogeneous fluid.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 86–94, September–October, 1987. 相似文献