移动车辆非定常气动力时域模拟及分析

为了在时域中考虑复数导纳函数,精细化模拟作用在移动列车上的非定常气动力,提出列车复数导纳函数时频变换方法,并建立同时考虑顺风向、横风向和竖向脉动风的移动列车非定常气动力数学模型.首先,推导出相对于移动列车的瞬时风速,并将瞬时风速代入到移动列车风荷载模型中,通过泰勒级数展开和忽略脉动风速、三角函数高阶项,将移动列车非定常...     

Re-parameterization of Bézier Curves by Square Approximation with Endpoint Constraints

In order to get an approximation with better effect of parameterization of Bozier curves, we proposed a method for arc-length parameterization and the corresponding algorithms by square approximation for the discrete even de-parameterization of the curves. This method is simple and easy to implement, and the property of the approximation has no change compared with the original curve. A quantitative criterion for estimating the effect of parameterization is also built to quantitatively characterize the parameterization effect of the algorithms. As a result, the nearly arc-length parameterized curve has a smaller relative deviation using either the algorithm with point constraint at endpoints or the algorithm with point constraint plus the first derivative constraint at endpoints. Experiments show that after re-parameterization with our algorithms, the relative deviation will have at least a 20% reduction.     

基于优化小波基的电力故障暂态数据压缩研究

在论述基于 辨分析的小波基构造方法和小波分解理论的基础上,针对电力故障信号富含瞬时性强、衰减快暂态成分的特点,研究了基于信号离用小波逼近品质,即离散逼近时域二范数最大的小波基优化方法。分析表明,基于优化小波基的离散小波变换对电力故障暂态数据具有较主的压缩比和较小的重构误差。     

A methodology to derive the critical demand density for designing and operating feeder transit services

Feeder lines are one of the most often used types of flexible transit services connecting a service area to a major transit network through a transfer point. They often switch operations between a demand responsive and a fixed-route policy. In designing and running such systems, the identification of the condition justifying the operating switch is often hard to properly evaluate. In this paper, we propose an analytical model and solution of the problem to assist decision makers and operators in their choice. By employing continuous approximations, we derive handy but powerful closed-form expressions to estimate the critical demand densities, representing the switching point between the competing operating policies. Based on the results of one-vehicle and two-vehicle operations for various scenarios, in comparison to values generated from simulation, we verify the validity of our analytical modeling approach.     

SVM在船舶柴油机故障检测系统中的应用研究

支持向量机(Support Vector Machine,简称SVM)是目前模式识别领域中最先进的机器学习算法,采用了核函数的思想,把非线性空间的问题转换到线性空间,降低了算法的复杂度.文中对SVM在船用柴油机故障诊断中的应用进行了论述,运用支持向量机理论对其进行了故障诊断的仿真研究和试验研究.     

Optimal transit service atop ring-radial and grid street networks: A continuum approximation design method and comparisons

Two continuum approximation (CA) optimization models are formulated to design city-wide transit systems at minimum cost. Transit routes are assumed to lie atop a city’s street network. Model 1 assumes that the city streets are laid out in ring-radial fashion. Model 2 assumes that the city streets form a grid. Both models can furnish hybrid designs, which exhibit intersecting routes in a city’s central (downtown) district and only radial branching routes in the periphery. Model 1 allows the service frequency and the route spacing at a location to vary arbitrarily with the location’s distance from the center. Model 2 also allows such variation but in the periphery only.The paper shows how to solve these CA optimization problems numerically, and how the numerical results can be used to design actual systems. A wide range of scenarios is analyzed in this way. It is found among other things that in all cases and for both models: (i) the optimal headways and spacings in the periphery increase with the distance from the center; and (ii) at the boundary between the central district and the periphery both, the optimal service frequency and line spacing for radial lines decrease abruptly in the outbound direction. On the other hand Model 1 is distinguished from Model 2 in that the former produces in all cases: (i) a much smaller central district, and (ii) a high frequency circular line on the outer edge of that central district.Parametric tests with all the scenarios further show that Model 1 is consistently more favorable to transit than Model 2. Cost differences between the two designs are typically between 9% and 13%, but can top 21.5%. This is attributed to the manner in which ring-radial networks naturally concentrate passenger’s shortest paths, and to the economies of demand concentration that transit exhibits. Thus, it appears that ring-radial street networks are better for transit than grids.To illustrate the robustness of the CA design procedure to irregularities in real street networks, the results for all the test problems were then used to design and evaluate transit systems on networks of the “wrong” type – grid networks were outfilled with transit systems designed with Model 1 and ring-radial networks designed with Model 2. Cost increased on average by only 2.7%. The magnitude of these deviations suggests that the proposed CA procedures can be used to design transit systems over real street networks when they are not too different from the ideal and that the resulting costs should usually be very close to those predicted.     

半导体Si和GaAs的GW近似能带结构与BSE吸收光谱的研究

基于密度泛函理论,采用平面缀加波的广义密度近似的PBE泛函和准粒子近似的GW方法对典型的半导体硅Si和砷化镓GaAs的能带结构进行了研究;同时研究了Si和GaAs的光吸收谱,并利用多体微扰理论的BetheSalpeter方程(BSE)进行了修正。计算结果表明,准粒子近似的GW方法对Si和GaAs的能隙预测结果和实验值符合较好,考虑了电子—空穴对激子效应的GW-BSE多体微扰方法计算的Si和GaAs的介电函数吸收谱与实验谱符合最佳;研究说明激子效应在半导体光谱性质分析方面十分重要。     

面向目标跟踪的传感器调度方法

针对传感器网络对目标的跟踪问题,提出一种传感器优化调度方法。该方法以传感器使用成本和允许激活的最大传感器数量为约束条件,把最小化目标位置误差作为优化目标,运用二进制凸规划技术对优化调度问题进行建模,采取逼近算法迭代求解规划模型。蒙特卡罗实验表明,对于节点数目小于70的传感器网络,优化调度方案可以获得高精度的目标跟踪结果。     

水流对浮体作用的SPH方法模拟

水流与浮体相互作用时,运动情况十分复杂,目前很难准确有效地模拟。而SPH作为一种纯拉格朗日方法,无需构建网格,用核函数近似粒子进行离散,能较好地解决一些自由面大变形问题。文章利用SPH法对溃坝时引起的高速水流冲击浮体以及水体晃动时破损浮体的运动过程进行模拟。模拟结果表明,SPH法能有效地进行水流对浮体作用的研究。     

Modeling the information flow propagation wave under vehicle-to-vehicle communications

Vehicle-to-vehicle (V2V) communications under the connected vehicle context have the potential to provide new paradigms to enhance the safety, mobility and environmental sustainability of surface transportation. Understanding the information propagation characteristics in space and time is a key enabler for V2V-based traffic systems. Most existing analytical models assume instantaneous propagation of information flow through multi-hop communications. Such an assumption ignores the spatiotemporal relationships between the traffic flow dynamics and V2V communication constraints. This study proposes a macroscopic two-layer model to characterize the information flow propagation wave (IFPW). The traffic flow propagation is formulated in the lower layer as a system of partial differential equations based on the Lighthill-Whitham-Richards model. Due to their conceptual similarities, the upper layer adapts and modifies a spatial Susceptible-Infected epidemic model to describe information dissemination between V2V-equipped vehicles using integro-differential equations. A closed-form solution is derived for the IFPW speed under homogeneous conditions. The IFPW speed is numerically determined for heterogeneous conditions. Numerical experiments illustrate the impact of traffic density and market penetration of V2V-equipped vehicles on the IFPW speed. The proposed model can capture the spatiotemporal relationships between the traffic and V2V communication layers, and aid in the design of novel information propagation strategies to manage traffic conditions under V2V-based traffic systems.