排序方式： 共有23条查询结果，搜索用时 578 毫秒
1.
马幼童 《南京体育学院学报(社会科学版)》2000,(4):172-173
体育教学日益重视学生的心理特点，兴趣爱好，个人特点和个体差异，强调学生由同一目标的划一，被动的学习转为在教师的指导下自觉地、自主地进行探索性的学习．发展其个性和自我管理、自我锻炼、自我完善的能力，使学生毕业离校后．仍能坚持锻炼．真正起到终身受益的目的。 相似文献
2.
In this study, we present a thermal optimization method using the overall lumped parameter (LP) and partial computational fluid dynamics (CFD) modeling for a 600-kW permanent magnet traction motor developed for high-speed trains. The motor is totally enclosed forced ventilated to achieve high power density, high efficiency, and low maintenance requirements. Considering the electro-magnetic performance, bogie space, and thermal capacity, we propose a ventilation structure with zigzag plates in sector cross-section. We focus particularly on the ventilation channels and propose an overall LP model for thermal optimization, in which the full consideration of the influence of turbulent flow is given by using a partial CFD model. Given the specific critical parameters from the optimization results, we present a complete 3D CFD model of the whole motor to obtain an accurate temperature distribution and the maximum temperature rises in local points. The benefit of zigzag plates is studied extensively using both the LP and the complete CFD models and the results are verified by equivalent thermal experiments under rated operations. Experimental results indicate that the ventilation structure fulfills the normal operational demands of high-speed trains by improving thermal performance by more than 15%. Additionally, we propose an engineering method to estimate iron loss constraint with the complete CFD model to guide the control system design. 相似文献
3.
目的:提出一种适用于全封闭冷却结构的电机热性能优化模型,设计一台600 kW的高速列车用永磁牵引电机。创新点:1.通过耦合局部流体动力学模型的方法求解电机复杂冷却风道内的对流传热系数,并在全局热网络模型的框架内得到快速、准确的电机温升结果以用于结构优化;2.在冷却风道中引入栅格结构,采用热性能分析模型优化冷却结构,提升电机热性能;3.通过三维流体动力学模型计算电机局部温升最大值,并提山一种预测特定结构下电机铁损工作阈值的工程方法。方法:1.采用热网络法建立全局热网络模型(图3),并通过耦合局部流体动力学模型计算风道内的热网络参数(图4和6); 2.应用田口设计法对电机风道结构进行优化,并研制样机进行验证(计算与试验结果见表5); 3.假设铁损的谐波附加值与磁密值成正比,通过三维流体动力学模型计算给山端部绕组、永磁体温升值与铁损的预测曲线,并用样机试验进行验证。结论:1.采用全局热网络和局部流体动力学建模的方法可以快速、正确地计算复杂冷却结构下的电机温升分布,且优化后的冷却结构至少可以提升文中电机15%的热性能;2.本文提出的优化模型适用于全封闭风冷或者水冷等冷却结构相对独立且尚无经验公式可参考的电机热性能优化设计;3.铁损工作阈值的预测方法可以为电磁和控制系统设计提供参考。 相似文献
4.
5.
LIU Bao-you FANG You-tong WEI Jin-xiang WANG Yong-liang 《浙江大学学报(A卷英文版)》2007,8(3):495-500
In general, every system is in one of the three states: normal, abnormal, or failure state. When the system is diagnosed as abnormal state, it needs predictive maintenance. If the system fails, an identical new one will replace it. The predictive main- tenance cannot make the system “as good as new”. Under these assumptions, the reliability index and the inspection-replacement policy of a system were studied. The explicit expression of the reliability index and the average income rate (i.e., the long-run average income per unit time) are derived by using probability analysis and vector Markov process method. The criterion of feasibility for the optimal inspection-replacement policy under the maximum average income rate is obtained. The numerical example shows the optimal inspection-replacement policy can raise the average income rate when the optimal inspec- tion-replacement policy is feasible. 相似文献
6.
7.
The repairable system with preventive maintenance is one of the typical systems with wide useful applications in engineering. If the system can be made as good as new by preventive maintenance, both the life stochastic variable of different periods and fault correction time stochastic variable form monotonous stochastic process. Based on the above assumption and the available results, in this paper we discuss the maintenance and replacement policy of the repairable system with preventive maintenance. The intervals of preventive maintenance, T, and the times of system failure, N, are introduced and the vector Markov process method is used. The formulation of steady state average profit rate can be deduced to solve the optimization problem of the maintenance and replacement policy. 相似文献
8.
For an energy-efficient induction machine, the life-cycle cost (LCC) usually is the most important index to the consumer.
With this target, the optimization design of a motor is a complex nonlinear problem with constraints. To solve the problem,
the authors introduce a united random algorithm. At first, the problem is divided into two parts, the optimal rotor slots
and the optimization of other dimensions. Before optimizing the rotor slots with genetic algorithm (GA), the second part is
solved with TABU algorithm to simplify the problem. The numerical results showed that this method is better than the method
using a traditional algorithm.
Project (No. 601299) supported by the Science Foundation of Hebei Province, China. 相似文献
9.
FANG You-tong FAN Cheng-zhi 《浙江大学学报(A卷英文版)》2007,8(3):408-411
The paper deals with a new model of linear induction motor (LIM) to improve the reliability of the system. Based on the normal equation circuit of LIM considering the dynamic end effect, an equivalent circuit model with compensation of large end effect is constructed when the end effect force at synchronism is of braking character. The equivalent circuit model is used for secondary-flux oriented control of LIM. Single neuron network PI unit for LIM servo-drive is also discussed. The effectiveness of mathematical model for drive control is verified by simulations. 相似文献
10.
Reliability is a very important target of linear induction motors. In this paper, the reliability model of the motor is established, the reliability indexes are defined, the faults’ modes are analyzed and classified according to their effect and damage, the sequential sampling plan is discussed and its acceptable fault rate (ACFR) and refusable fault rate (REFR) are presented, and then, the detailed reliability compliance field test method is introduced with one case. With the method, engineers can verify the reliability of linear induction motors expediently. 相似文献