Evaluating policies to reduce greenhouse gas emissions from private transportation

This paper proposes a model system to forecast household greenhouse gas emissions (GHGEs) from private transportation. The proposed model combines an integrated discrete-continuous car ownership model with MOVES 2014. Four modeling components are calibrated and applied to the calculation of GHGEs: vehicle quantity, vehicle type and vintage, miles traveled, and rates of GHGEs. The model is applied to the Washington D.C. Metropolitan Area. Three tax schemes are evaluated: vehicle ownership tax, purchase tax and fuel tax. We calculate that the average GHGEs per vehicle is 5.15 tons of carbon dioxide-equivalent (CO₂E) gases. Our results show that: (a) a fuel tax is the most effective way to reduce vehicle GHGEs, especially for households with fewer vehicles; (b) a purchase tax reduces vehicle GHGEs mainly by decreasing vehicle quantity for households with more vehicles; and (c) an ownership tax reduces vehicle GHGEs by decreasing both vehicle quantity and miles traveled.     

The Hamilton–Jacobi partial differential equation and the three representations of traffic flow

This paper applies the theory of Hamilton–Jacobi partial differential equations to the case of first-order traffic flow models. The traffic flow surface is analyzed with respect to the three 2-dimensional coordinate systems arising in the space of vehicle number, time and distance. In each case, the solution to the initial and boundary value problems are presented. Explicit solution methods and examples are shown for the triangular flow-density diagram case. This unveils new models and shows how a number of existing models are cast as special cases.     

高架索航行补给中船舶在波浪中的运动性能研究

采用三维势流理论计算高架索航行补给中两船在波浪中的运动响应,将船体周围流场速度势分解为波浪入射势、自身绕射势、相邻船体的存在产生的绕射势、自身辐射势和相邻船体运动产生的辐射势,通过源汇分布法进行求解;对高架索索道上的恒定张力在耦合方程中表示为高架索瞬时张力系数矩阵;求解两船体在规则渡中的联立运动方程可得两船的运动响应.通过计算结果与高架索航行补给中两船运动响应的试验结果进行比较,吻合良好,说明文中的计算方法是可行的,在此基础上,对不同高架索恒定张力和不同浪向角条件下的接受船运动幅值响应进行计算并讨论.最后得出结论.     

Focusing of Spherical Nonlinear Pulses for Nonlinear Wave Equations Ⅲ. Subcritical Case

This paper studied spherical pulses of solutions of the system of semilinear wave equations with the pulses focusing at a point in three space variables. It is shown that there is no nonlinear effect at leading terms of pulses, when the initial data is subcritical.     

当代海军AIP技术发展动态

本文通过全球海军AIP技术发展的枚举,拟反映出依托技术进步的AIP艇装备在计划实施过程中所呈现出的动态性。     

粘塑性统一本构方程数值积分方法研究

本文提出了对粘塑性统一本构方程的隐式欧拉积分进行牛顿一拉夫森迭代的数值积 分方法.推导出该数值积分的统一迭代格式;给出自动选取步长以及迭代收敛的准 则;并对卜。uer的统一本构方程进行了数值求解。该法不但非常有效地克服了由于常 微分方程组的刚性带来的数值困难,而且还易于控制数值误差。计算结果表明:本文 所提出的方法是十分有效的.      

多周期稳定数值造波的参数设计方法

[目的]针对数值模拟中波浪随传播时间和距离发生波幅衰减及相位偏移的问题,提出一套可用于多周期稳定造波的参数设计方法。[方法]基于Navier-Stokes方程和流体体积（VOF）方法进行五阶Stokes波数值模拟,通过对一维波动方程的离散形式进行分析,研究几个重要参数对造波效果的影响。最后,应用所提参数设计方法对KCS船型在迎浪中的阻力和运动响应进行三维数值计算,并与模型实验结果进行比较。[结果]结果表明,将内迭代次数、网格分辨率、库朗数等参数按照一定规则设置,20个波周期内的波幅误差约5%,40个波周期的约10%。对KCS船型进行的三维数值计算结果与模型实验结果相比误差约10%。[结论]经此研究,验证了所提方法的可行性。     

铁路高桥墩的非线性动力分析

以铁路高桥墩为研究对象,导出了计轴力及内力素方向改变所致非线性项的高桥墩振动偏微分方程,在分析方程定解条件的基础上,讨论了高桥墩架梁前后的振动频率和墩顶位移的变化规律,并将其结果与线性结果和非自治系统受迫振动的非线性分析进行了比较。     

码头系泊船舶缆绳线力的混沌解法

码头系泊船舶缆绳张力的理论计算对于缆绳的选取、系泊设备的设计、系泊方式、缆绳预紧力的确定,以及船级社规范的制订都有着重要的指导意义。文中对小波浪水域码头系泊船舶缆绳张力的计算建立了数学模型,引入混沌优化的方法对非线性系泊方程组进行了求解,其结果与实验结果对比有较好的一致性。     

A structural equations analysis of commuters' activity and travel patterns

An exploratory analysis of commuters' activity and travel patterns was carried out using activity-based travel survey data collected in the Washington, DC metropolitan area to investigate and estimate relationships among socio-demographics, activity participation, and travel behavior. Structural equations modeling methodology was adopted to determine the structural relationships among commuters' demographics, activity patterns, trip generation, and trip chaining information. Three types of structural equations model systems were estimated: one that models relationships between travel and activity participation, another that captures trade-offs between in-home and out-of-home activity durations, and a third that models the generation of complex work trip chains. The model estimation results show that strong relationships do exist among commuters' socio-demographic characteristics, activity engagement information, and travel behavior. The finding that significant trade-offs exist between in-home and out-of-home activity participation is noteworthy in the context of in-home vs. out-of-home substitution effects. Virtually all of the results obtained in this paper corroborate earlier findings reported in the literature regarding relationships among time use, activity participation, and travel. This revised version was published online in June 2006 with corrections to the Cover Date.