多相逆变系统数学模型及仿真研究

建立了多相逆变器的电路模型，并以此为基础，分别建立3相和6相逆变器——异步电机的matlab仿真模型，在不同的开关频率下，分别对三相逆变系统和六相逆变系统进行了仿真。仿真结果表明，在开关频率较低的情况下，多相逆变系统转矩脉动减小，系统效率和功率因数也有所提高。     

浅谈港口视频监控系统的防雷措施

介绍了雷电的形成过程及其对沿海港口视频监控系统的危害形式和途径，结合港口视频监控系统的工程实例，提出港口视频监控系统防御雷电灾害的措施。     

Differential Space Frequency Mapping Schemes and Norm Criterion

Introduction Since Hochwald and Sweldens[1], Hughes[2]independently invented differential unitary spacetime code, it aroused huge enthusiasm on the de-sign of differential modulation methods. No chan-nel state information (CSI) is needed at the trans-mitter and the receiver side, so the demodulation isvery simple. These works all concern the flat fad-ing environment and low data rate case, assumingthe channel is approximately constant for a coher-ent interval. But for the multi-path environ…     

传动轴弯曲固有频率理论计算方法研究

随着我国社会的快速发展,人们生活水平的提高,司乘人员对商用车的驾乘舒适性要求越来越高,商用车越发关注整车NVH性能。文章主要介绍与传动轴振动密切相关的弯曲固有频率的理论计算方法,并将理论计算结果与台架试验、CAE结果做比较,说明理论计算结果的准确性。     

安装边刚度对分动器振动特性的影响

提出一种考虑安装边支撑刚度对结构振动特性影响的分析方法,应用有限元模态分析方法计算分析了某分动器的振动模态。8种不同支撑刚度计算结果对比表明,随着安装边支撑刚度的增大,自然振动频率会随之增大,且对低阶的影响尤为明显;当安装边支撑刚度增加到一定值时,其变化所引起的自然振动频率变化不再明显,自振频率趋近于刚性支撑时结果。     

沥青混凝土超声波检测的衰减特征与影响因素研究

为有效获得沥青混凝土的超声波检测结果，基于压电换能器模拟和沥青砂浆Burgers黏弹性模型，建立三相介质的沥青混凝土有限元模型，在20~100 kHz频段范围内，比较9种入射频率下沥青混凝土中超声波细观的衰减特征及宏观的振幅变化，分析3种集料粒径（13.2，19.0，26.5 mm）及不同温度（-10℃~60℃）对沥青混凝土中超声波衰减的影响；针对数值模拟结果，使用超声横波成像仪MIRA-A1040进行室内试验验证，研究9种入射频率下实测振幅和断面重构图的衰减规律。研究结果表明：当温度为20℃时，在频段20~100 kHz内，入射频率每升高10 kHz，反射波振幅线性降低约3 dB；随着入射频率的升高，沥青砂浆中声压等值线的规则性、连续性及试件断面重构图的辨识度均大致呈线性降低趋势；当入射频率和温度不变时，集料粒径引起的散射衰减会引起振幅小幅度的降低；当集料粒径不变时，影响振幅降低速率的主要因素是温度，本质为沥青砂浆黏弹性引起的吸收衰减；以入射频率为30 kHz的沥青混凝土AC-13为例，温度每升高10℃，振幅约线性降低5 dB；2种衰减综合决定了反射波振幅的数值；沥青混凝土检测的入射频率不宜超过60 kHz，温度不宜超过40℃；用于沥青路面面层的检测时，建议入射频率范围为20~60 kHz；较低的入射频率与温度有利于沥青混凝土的超声波检测。     

基于神经网络/模糊逻辑系统的混合式特征提取器

特征提取是水声目标分类的关键环节之一，用以获取各类目标的一些可鉴别性特征。螺旋桨轴频、叶率和叶片数是目标的本质性、鉴别性特征，是分类的重要线索。本文提出了一个基于神经网络／模糊逻辑系统的混合式特征提取器，先利用侧抑制神经网络从目标辐射噪声的包络谱中提取线谱序列，再利用模糊逻辑系统从线谱序列中提取出螺旋桨轴频、叶率和叶片数。对目标数据的分析表明：该特征提取器能够为目标分类提取有效的鉴别性特征。     

ZPW-2000A无绝缘移频轨道电路监测系统

针对ZPW-2000A无绝缘移频轨道电路的系统结构和技术特点,提出一套切实可行的监测与维护解决方案.     

论天然河流设计最低通航水位两种确定方法的矛盾与统一

从理论及实际资料分析上论述了天然河流设计最低通航水位的两种方法的差异及内在联系,实质上两种方法只是一种水文事件中的两种表达形式而已。其根本差别只在于保证率频率法是人为地确定频率,而综合历时曲线法本身固有一个频率。因此,两者并无本质区别。     

Ride dynamic evaluations and design optimisation of a torsio-elastic off-road vehicle suspension

The ride dynamic characteristics of a novel torsio-elastic suspension for off-road vehicle applications are investigated through field measurements and simulations. A prototype suspension was realised and integrated within the rear axle of a forestry skidder for field evaluations. Field measurements were performed on forestry terrains at a constant forward speed of 5 km/h under the loaded and unloaded conditions, and the ride responses were acquired in terms of accelerations along the vertical, lateral, roll, longitudinal and pitch axes. The measurements were also performed on a conventional skidder to investigate the relative ride performance potentials of the proposed suspension. The results revealed that the proposed suspension could yield significant reductions in magnitudes of transmitted vibration to the operator seat. Compared with the unsuspended vehicle, the prototype suspended vehicle resulted in nearly 35%, 43% and 57% reductions in the frequency-weighted rms accelerations along the x-, y- and z-axis, respectively. A 13-degree-of-freedom ride dynamic model of the vehicle with rear-axle torsio-elastic suspension was subsequently derived and validated in order to study the sensitivity of the ride responses to suspension parameters. Optimal suspension parameters were identified using the Pareto technique based on the genetic algorithm to obtain minimal un-weighted and frequency-weighted rms acceleration responses. The optimal solutions resulted in further reduction in the pitch acceleration in the order of 20%, while the reductions in roll and vertical accelerations ranged from 3.5 to 6%.