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541.
This paper presents a comprehensive econometric modelling framework for daily activity program generation. It is for day-specific
activity program generations of a week-long time span. Activity types considered are 15 generic categories of non-skeletal
and flexible activities. Under the daily time budget and non-negativity of participation rate constraints, the models predict
optimal sets of frequencies of the activities under consideration (given the average duration of each activity type). The
daily time budget considers at-home basic needs and night sleep activities together as a composite activity. The concept of
composite activity ensures the dynamics and continuity of time allocation and activity/travel behaviour by encapsulating altogether
the activity types that are not of our direct interest in travel demand modelling. Workers’ total working hours (skeletal
activity and not a part of the non-skeletal activity time budget) are considered as a variable in the models to accommodate
the scheduling effects inside the generation model of non-skeletal activities. Incorporation of previous day’s total executed
activities as variables introduces day-to-day dynamics into the activity program generation models. The possibility of zero
frequency of any specific activity under consideration is ensured by the Kuhn-Tucker optimality conditions used for formulating
the model structure. Models use the concept of random utility maximization approach to derive activity program set. Estimations
of the empirical models are done using the 2002–2003 CHASE survey data set collected in Toronto.
相似文献
Eric J. MillerEmail: |
542.
机载布放式AUV是利用载机运送至特定海域上空,在一定条件下通过空投方式进入水下,完成预定工作的自主水下航行器。AUV入水时会受到巨大的载荷冲击,严重时会导致机体折断、元器件失灵,甚至引起弹道失控。为此,文章采用计算流体力学(Computational Fluid Dynamics,CFD)方法对机载布放式AUV的入水冲击问题进行了数值仿真研究。对不同入水速度、不同入水角度下AUV受力过程进行了计算,得出了不同入水条件下的速度响应曲线和压力响应曲线,可为机载布放式AUV的机体结构设计和投放条件研究提供参考。 相似文献
543.
系泊多体海上平台非线性动力特性研究 总被引:1,自引:1,他引:0
海上浮式平台通常由多个大型浮体模块柔性连接,组成一个典型的刚柔流耦合的多振子网络系统。本文从网络动力学角度研究多体浮式海上平台,通过龙格库塔法求解海上浮式平台运动微分方程,得到海洋平台运动响应随连接件刚度变化情况。数值结果表明,连接件刚度变化使得多体海上浮式平台表现出丰富的非线性动力特性现象,例如幅值跳跃、分岔、混沌等现象。为进一步揭示非线性浮式平台的集体动力学行为,作出浮块在各响应阶段对应的时域图和相图比较。本文得到的初步研究结果及研究方法,可为大型海上浮体结构初步设计提供理论参考。 相似文献
544.
545.
H. Nozaki 《International Journal of Automotive Technology》2008,9(3):307-315
Because Formula cars are lighter than ordinary cars, the optimal settings for this type of car are thought to be different
from those of a ordinary car. The front and rear weight distribution ratio of a vehicle is an important parameter that exerts
a significant influence on critical cornering. The tendency of a ordinary car to under-steer during critical cornering is
determined by the front and rear weight distribution ratio of the vehicle. Specifically, when the front of an ordinary FR
(front-engine, rear wheel drive) vehicle is slightly heavier than the rear, the car tends to understeer during critical cornering.
However, the optimal weight distribution ratio for critical cornering is not obvious for a formula car because of its lightness.
This observation was investigated using a driving course similar to a real driving course to perform a maximum speed cornering
simulations. It was found that a front to rear weight distribution ratio of 40:60 resulted in the fastest lap time. This ratio
also gave the best results in the maximum-speed driving experiment performed using a driving simulator. Moreover, the maximum
lateral acceleration during turning, the driving force, and the load movement of the inside and outside wheels was calculated
using experimental driving force data and the concept of a tire friction circle. As a result, driving mechanics have been
determined for a vehicle having a front/rear weight distribution ratio of 40:60 while traveling at maximum speed. 相似文献
546.
In order to prevent the uncontrolled release of seatbelt buckles due to high acceleration caused by pretensioners, anti-g
buckles that have pendulum-shaped g-masses to block the releasing motion are commonly adopted in seatbelt systems. However,
even with the wide applications of anti-g buckles, the underlying operational principles of anti-g buckles have yet to be
investigated. This work studies conditions for the engagement of the g-mass to prevent inertial release, and conditions for
maintaining a blocked state under very high acceleration. Using a multibody model of an anti-g buckle, the effects of various
design parameters on the performance of the anti-g buckle have been examined. It turns out that design variables associated
with the geometry of the g-mass and its contacting surface configuration play important roles. In order to account for the
dynamic interaction between driver and seatbelt, a multibody model of a seatbelt system is combined with a dummy model to
form a single dynamic system. Using the measured displacement of the buckle during the explosion of a pretensioner as the
driving condition for simulation, dynamic analysis of the seatbelt with driver interaction has been carried out. Through comparison
with measured and computed accelerations of webbing, which shows good agreement, the validity of the model has been demonstrated.
The dynamic model for seatbelt and driver can be used as a design tool for the development of anti-g buckles. 相似文献
547.
Because the characteristics of rubber bushing significantly affect the accuracy of vehicle dynamics simulations, they should
be accurately modeled in the vehicle suspension model. In this paper, a new nonlinear bushing model for automotive bushing
components is developed to improve the accuracy of vehicle dynamics analysis. Bushing components were first tested to capture
the nonlinear and hysteretic behavior of typical elements by using a MTS 3-axis elastomer tester. A simple Bouc-Wen hysteretic
differential model was modified to generate a more precise rubber bushing model. A sine wave, step input, and random excitations
are imposed on the bushing. The ADAMS program is used to calculate sensitivity and the VisualDOC program is employed to find
the optimal parameters for the bushing model. An error function is designed to find optimal parameters of the model. Parameter
identification is carried out to satisfy the static and dynamic characteristics due to sine and step excitation inputs. It
was proved that the proposed model could predict the bushing forces under sine, step, and random inputs well. The errors are
within 10% in the overall range. To show the validity of the proposed model, a numerical example was also carried out. Because
the bushing forces due to random excitation input show good agreement with experiments, the proposed bushing model is available
in the vehicle dynamics simulation. 相似文献
548.
549.
���н�ͨϵͳ��SDģ�ͼ���Ӧ�� 总被引:3,自引:1,他引:2
城市交通系统是一个多变量、多反馈、非线性的复杂系统,它的可持续发展受交通、社会、经济、环境等多种因素的制约,而传统的交通预测模型难以模拟这样一个复杂系统的动力机制。为此,本文采用系统动力学方法,在系统结构分析和因果反馈分析的基础上建立了城市交通系统的SD (System Dynamics) 模型,包括人口、经济发展、机动车保有量、环境影响、交通需求、交通供给和交通拥挤七个子系统。以大连主城区为对象,选取影响机动化发展的政策干预因素为调控参数进行仿真,分析了不同的机动化发展政策对城市发展和城市交通系统的影响,并提出了相应的建议和对策。 相似文献
550.
采用基于振动周期内平均功率相等的描述函数法,对重载货车转向架的非线性干摩擦力进行等效线性化,即将斜楔与摇枕间的垂向和横向非线性摩擦力线性等效为垂向和横向线性阻尼力,将旁承和心盘处的回转摩擦阻力矩线性等效为同转摩擦阻尼力,进而建立重载货车的等效线性动力学模型.以C80型重载货车为例,分别采用给出的等效线性动力学模型和非线性动力学模型进行重载货车动力学仿真计算.结果表明:等效线性动力学模型虽然小幅度增大了车体的垂向和横向平稳性指标、轮轨横向作用力、脱轨系数和轮重减载率,但是仍在GB/T 5599-1985标准范围内,满足其各项评价指标要求,验证了用描述函数法对非线性干摩擦力等效线性化的正确性和合理性;说明基于描述函数法的重载货车等效线性动力学模型可以替代复杂的非线性动力学模型进行重载货车通过既有桥梁的车桥耦合动力响应分析,为重载货车的非线性悬挂系统参数优化和车桥耦合动力学性能分析提供了新的有效途径. 相似文献