Numerical method for simulating tire rolling noise by the concept of periodically exciting contact force

For the numerical simulation of tire rolling noise, an important subject is the extraction of normal velocity data of the tire surface that are essential for the acoustic analysis. In the current study, a concept of periodically exciting contact force is introduced to effectively extract the tire normal velocity data. The ground contact pressure within contact patch that is obtained by the static tire contact analysis is periodically applied to the whole tread surface of stationary tire. The periodically exciting contact forces are sequentially applied with a time delay corresponding to the tire rolling speed. The tire vibration is analyzed by the mode superposition in the frequency domain, and the acoustic analysis is performed by commercial BEM code. The proposed method is illustrated through the numerical experiment of 3-D smooth tire model and verified from the comparison with experiment, and furthermore the acoustical responses are investigated to the tire rolling speed.     

Further study on the ultimate strength analysis of spherical pressure hulls

From a comparative study it is concluded that current design rules for the spherical pressure hull of manned submersible need to be updated and unified. In this paper, a series of spherical pressure hulls are calculated by nonlinear FEM. Based on these numerical results, the influence of critical arch length and the relationship of ultimate strength with t/R and structural imperfection are studied. Finally, empirical formulae for the ultimate strength of the titanium alloy spherical pressure hull of deep manned submersible based on numerical computations are given. The formulae can be used as the core equations to update current design rules.     

2和4的方程式

尽管中国曾经号称"自行车王国",但如今能为我们界定为自行车专家的人却并不算多。因为90%还在骑车的人不过是被迫仍然使用这种廉价的代步工具而已,而另一些人则在"升级"为四轮之后就患上了"汽油依赖症"。只有经历过从两轮到四轮,再重新回到两轮的资深人士,才有资格和我们一起计算这个算式……     

Modeling activity conflict resolution strategies using scheduling process data

Developments in activity scheduling process data have recently allowed for much improvement and validation of rule-based activity scheduling models. The use of actual scheduling process data allows for a potentially more realistic model in terms of how the travel episodes are actually derived. Since these types of models are simulations of the scheduling process, scheduling conflicts naturally arise in the creation of the final schedule. The handling of these scheduling conflicts is a critical component of all rule-based activity models. Many of these models rely on the concept of priority of the activities to resolve conflicts. However, recent research has shown that this is often not how conflicts are actually resolved. In order to more accurately model actual conflict resolution behavior, scheduling process data was used to estimate conflict resolution rules using decision trees. The use of a conflict resolution model allows the strategy chosen to depend on the attributes of the individual and the conflicting activities, rather than assuming a prior definition of precedence based on the activity types. The conflict resolution decision showed reasonable ability to predict the resolution strategy chosen in actual scheduling process survey data, and represents an important advance in developing a functional computational process model of activity scheduling.     

Modeling the structural relationships among short-distance travel amounts,perceptions, affections,and desires

Using structural equation modeling, the relationships among travel amounts, perceptions, affections, and desires across five short-distance (one-way trips of less than 100 miles) travel categories (overall, commute, work/school-related, entertainment/social/recreation, and personal vehicle) are examined. The models are estimated using data collected in 1998 from more than 1300 working commuters in the San Francisco Bay Area. A cross-model analysis reveals three robust relationships, namely: (1) myriad measures of travel amounts work together to affect perceptions; (2) perceptions are consistently important in shaping desires; and (3) affections have a positive relationship with desires. The second finding suggests that two individuals who travel the same objective amount may not have the same desire to reduce their travel: how much individuals perceive their travel to be is important. The third point argues that the degree to which travel is enjoyed is a key determinant of shaping desires to reduce travel: the more travel is enjoyed, the less the desire to reduce it.     

无损磁力检测仪的制造

据全俄铁路运输科学研究院1996年编的关于轮对轮箍轮缘的磁极-等离子强化工艺手册中称:当强化道宽度达到40 mm时,则硬化层深度为1.5～2 mm.在磁极-等离子强化区内其金属组织所发生的变化为:硬度为750 HV的马氏体组织深度约0.3 mm;硬度为580～660 HV的屈氏体-马氏体混合组织深度约0.3～0.9 mm;硬度为480～580 HV的屈氏体组织深度约0.9～1.3 mm;硬度为360～450 HV的索氏体组织深度约1.3～2.0 mm.     

迫导向货车转向架与标准三大件转向架性能的比较

对2种车型的迫导向转向架进行了试验，并与同等条件下的标准三大件货车转向架进行了性能比较，结果是迫导向转向架可节省燃料、降低质量、提高装载能力。     

Performance Index for a Preview Active Suspension Applied to a Quarter-Car Model

A simple and convenient matrix expression is derived for the performance index in the case of a linear vehicle model with two degrees of freedom and a preview active suspension, subject to a unit step road input and employing optimal control. The usual quadratic integral-type performance index is assumed and the effect of an additional form of constraint is described briefly. The effects of preview time on the performance index and the optimal feed-forward control are illustrated graphically for a particular example.     

提高电空制动机的可靠性

在机车车辆上采用电空制动机可以缩短制动距离,改善列车在制动过程中的动力作用.现有电空制动机的使用经验表明:其可靠性与现代要求相距甚远.其中原因之一是由于其控制件常常失灵导致电空制动机偏斜而引起不良后果.所以,为了保证列车运行安全,对电空制动机进行改进已成了特别迫切的任务.