螺旋桨低频流噪声模拟方法研究

针对DTMB P4119螺旋桨在进速比为0.833时的流噪声进行研究,探讨螺旋桨低频流噪声数值模拟方法。首先采用大涡模拟方法模拟螺旋桨的非稳态流场,然后求解K-FWH方程预测低频流噪声。将计算得到的推力系数和扭矩系数与实验值比较,验证流场模拟的正确性。从流场仿真结果可以看出,螺旋桨表面存在连续的涡脱落现象。声场计算的结果表明:离散噪声远大于宽带噪声;宽带噪声主要由螺旋桨表面的涡脱落引起,宽带噪声引起螺旋桨近场总声压级的周向波动;在同一半径处总声压级沿轴向逐渐减小,在同一平面内总声压级沿径向先增加后减小。     

某矿车进气系统噪声的控制研究与分析

通过实验测试方法识别噪声源,确定降噪中心频率,针对中心频率进行降噪改进。采用有限元数值模拟的方法对改进前后的进气系统进行声学性能评价,以及流场特性分析。实际制造后进行实验测试,测试结果与仿真分析结果吻合较好,验证了设计结论。     

常州城市设计水位建议值研究报告

介绍了常州城市设计水位建议值研究中综合的各因素。常州城市河道通航、防洪、建桥、取水、供水、排水、农田水利及控制城市临介地坪标高等均具有统一要求,该水位建议值可统一常州城市设计水位,确保达到预期效果和所指定的安全标准,具有应用价值。     

一种正切调频与巴克码复合信号脉压性能分析

非线性调频信号和二相编码信号在脉冲压缩雷达中使用较为广泛,分别对其进行分析后推导出一类非线性调频-二相编码复合调制信号的时域表达式,这种信号兼有原两种信号的特点,仿真结果表明,该复合调制信号容易产生和处理,其匹配滤波结果对多普勒频移也不敏感,但由于该信号的特殊性,常规窗函数无法对其旁瓣进行抑制。采用延时线网络加权法抑制其旁瓣,效果十分理想。     

两种速度测量电路的原理及应用

介绍了速度(频率)/电压转换芯片LM2907/LM2917的工作原理、技术参数和应用电路,并介绍了基于555的速度测量电路和在柴油机测速上的应用。     

频率跟踪移相PWM控制下串联谐振式逆变器运行模式分析

结合DBD型臭氧发生器负载的特性,详细分析逆变器在各种运行模式下的工作过程。定性地分析了逆变器在各种工作模式中功率器件所受的电磁应力与开关损耗,由此得出适合于DBD型臭氧发生器负载和IGBT功率开关的逆变器运行模式,为确定DBD型臭氧发生器电源的运行方式提供了理论依据。     

不同约束条件下中低速磁浮道岔主动梁自振特性

为了探究中低速磁浮道岔主动梁自振特性,以清远磁浮旅游线道岔系统为对象,建立3台车和2台车道岔主动梁的有限元模型,对安装面刚性约束和弹性约束下道岔主动梁进行有限元模态分析,与道岔主动梁自振特性实测结果进行对比,研究结果表明:安装面位移约束下3台车和2台车道岔梁的低阶模态频率显著大于实测值,弹性约束下道岔梁模态分析结果与实测结果接近,故中低速磁浮道岔梁有限元建模时应施加弹性约束;相较于2台车道岔梁方案,3台车道岔梁的垂弯模态频率有明显提高,但10~30 Hz频率内的横弯和扭转模态频率变化不大,仅仅增加中间台车抑制和减缓磁浮车岔15~20 Hz耦合共振的效果并不理想,提高道岔梁阻尼和加强道岔梁约束是更合理的选择。     

轨道交通车辆空调系统智能控制与大数据应用

阐述了轨道交通车辆空调技术的发展历程,分析了智能化变频空调系统中智能控制与诊断、大数据技术应用的现状及发展前景。分析结果可为轨道交通车辆空调系统的智能化研究与应用提供技术参考。     

Direct and indirect influences on employed adults’ travel in the UK: New insights from the National Travel Survey data 2002–2010

Recent years saw a continuing shift in labour force composition, e.g. greater participation of women and a prominent rise in part-time workers. There are as yet relatively few recent studies that examine systematically the influences on the travel of employed adults from such perspectives, particularly regarding possible transport disadvantages of the fastest growing segments of workers. A robust analysis requires systematic data on a wide range of explanatory variables and multiple travel outcomes including accessibility, mobility and trip frequency for different trip purposes. The UK NTS data does meet the majority of this demanding data requirement, but its full use has so far been hampered by methodological difficulties. To overcome complex endogeneity problems, we develop novel, integrated structural equation models (SEMs) to uncover the influences of latent land use characteristics, indirect influences on car ownership, interactions among trip purposes as well as residents’ self-selection and spatial sorting. This general-purpose method provides a new, systematic decomposition of the influences on travel outcomes, where the effects of each variable can be examined in turn with robust error terms. The new insights underline two direct policy implications. First, it highlights the contributions of land use planning and urban design in restraining travel demand in the 2000s, and their increasing influence over the decade. Secondly, it shows that there may still be a large mobility disadvantage among the fastest growing segments of workers, particularly in dense urban areas. This research further investigates trend breaking influences before and after 2007 through grouped SEM models, as a test of the methodology for producing regular and timely updates regarding the main influences on personal travel from a system level.     

基于响应面法的汽车转向系统可靠性优化

针对结构参数的不确定性会导致确定性优化结果不可靠的问题,提出一种将可靠性分析与优化技术相结合的转向系统可靠性优化方法。该方法基于响应面方法构建转向系统优化近似模型,以1阶固有频率为约束,总质量为优化目标对转向系统进行可靠性优化。结果表明,采用该方法对汽车转向系统进行优化,减小了系统质量,提高系统的1阶固有频率,避免怠速共振,达到可靠性优化的目的。