软开关变流器的稳态分析(一)

讨论软开关变流器的稳态分析.由于分别由软开关变流器的Lr-Cr单元和大的L-C滤波器单元决定的快、慢固有频率的共存,通过启动瞬态仿真程序寻找软开关变流器的稳态解可能会造成繁琐的计算和收敛失败.由于采用了基于暂态分析的换相检测技术和基于补偿原理的换相分析技术,文章所提出的数值法显示了高可靠性和快速收敛性.对两个直流变换器、一台逆变器和一台功率因数补偿装置作的稳态分析,突出显示了仿真算法的良好性能.     

TTB or not TTB, that is the question: a review and analysis of the empirical literature on travel time (and money) budgets

This paper summarizes and analyses findings from more than two dozen aggregate and disaggregate studies of travel time (and sometimes money) expenditures, exploring the question of the existence of a constant travel time budget. We conclude (with prior researchers) that travel time expenditures are not constant except, perhaps, at the most aggregate level. Nevertheless, individuals’ travel time expenditures do show patterns that can be partly explained by measurable characteristics. Travel time expenditure is strongly related to individual and household characteristics (e.g., income level, gender, employment status, and car ownership), attributes of activities at the destination (e.g., activity group and activity duration), and characteristics of residential areas (e.g., density, spatial structure, and level of service). To the extent that travel time expenditures are constant at the aggregate level, the underlying mechanisms explaining that regularity are not well understood. Consequently, further research into explaining travel time and money expenditure patterns is justified.     

Dynamics of the railway track and the underlying soil: the boundary-element solution, theoretical results and their experimental verification

A combined finite-element boundary-element method is presented in detail to calculate the dynamic interaction of the railway track and the underlying soil. A number of results are shown for ballasted and slab track, demonstrating the influence of the stiffness of the soil and the rail pads on the vertical compliance of the track. The compliance of the track is combined with a simple model of the vehicle giving the transfer function of vehicle-track interaction. An experimental verification of the theoretical results is achieved by harmonic and impulse excitation with and without static (train-) load and by combined measurements of train-track-soil interaction. A clear vehicle-track resonance is found for the slab track with elastic rail pads and for higher frequencies at highspeed traffic, the dynamic axle loads due to sleeper passage are reduced.     

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.