STUDY ON THE RELATIONSHIP BETWEEN ADJUSTABLE OPERATIONAL PARAMETERS AND NOISE OF SINGLE-CYLINDER DIESEL ENGINE

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Squeal noise in hydraulic poppet valves

The poppet valve is a fundamental component in fluid power systems. Under particular conditions, annoying “squeal” noises may be generated in hydraulic poppet valves. In the present study, the frequency spectrum of the squeal noise is obtained by analyzing the sampling data from the accelerometer mounted on the valve body. It is found that the flow velocity, pressure, and structural parameters have crucial effects on the properties of squeal noise, especially frequency. Larger valve chamber volume or lower backpressure leads to lower fundamental frequency of the squeal noise. An explanation for the squeal noise, as a result of Helmholtz resonance, is suggested and proved by experimental results.     

Effect of a semi electro-mechanical engine valve on performance and emissions in a single cylinder spark ignited engine

In this study, an electro-mechanical valve （EMV） system for the intake valve ofa fottr stroke, single cylinder, overhead valve and spark ignition （SI） engine was designed and constructed. An engine with the EMV system and a standard engine were tested to observe the effects of the EMV on engine performance and emissions at different speeds under full load. The EMV engine showed improved engine power, engine torque and break specific fuel consumption （BSFC）. A 66% decrease in CO emissions was also obtained with the EMV system, but hydrocarbons （HC） and NOx emissions increased by 12% and 13% respectively.     

基于电控发动机氧传感器闭环反馈机制的研究

通过对电控汽油机燃油反馈系统中起关键作用的氧传感器的故障实验,在不同工作条件下,研究氧传感器正常工作或模拟失效时对汽油机的各项运行参数及排放物的影响。通过对实验结果的统计与分析,提出基于氧传感器的燃油反馈系统在电控汽油机不同运行阶段的控制方法和控制策略。     

电容式硅微加速度计系统的性能分析

介绍了微加速度计的工作原理,得出了不同方向上的加速度计的等效刚度.基于加速度计的集总模型分析,从能量和运动角度推导得出了加速度计的等效质量、精度和灵敏度的具体表达形式.从力学观点,总结了加速度计阻尼的影响因素.对开环和闭环加速度计系统的机械热噪声的特性和它们各自检测的动态范围进行研究后发现,电容式微加速度计的噪声主要由机械热噪声决定,并取决于加速度计系统的温度和阻尼.对闭环加速度计系统的测量结果表明,系统的精度可以达到mg数量级,量程为±50g的范围.     

Development of lanthanum strontium cobalt ferrite composite cathodes for intermediate- to low-temperature solid oxide fuel cells

Solid oxide fuel cells(SOFCs) offer high energy conversion,low noise,low pollutant emission,and low processing cost.Despite many advantages,SOFCs face a major challenge in competing with other types of fuel cells because of their high operating temperature.The necessity to reduce the operational temperature of SOFCs has led to the development of research into the materials and fabrication technology of fuel cells.The use of composite cathodes significantly reduces the cathode polarization resistance and expands the triple phase boundary area available for oxygen reduction.Powder preparation and composite cathode fabrication also affect the overall performance of composite cathodes and fuel cells.Among many types of cathode materials,lanthanum-based materials such as lanthanum strontium cobalt ferrite(La1-xSrxCo1-yFeyO3- have recently been discovered to offer great compatibility with ceria-based electrolytes in performing as composite cathode materials for intermediate-to low-temperature SOFCs(IT-LTSOFCs).This paper reviews various ceria-based composite cathodes for IT-LTSOFCs and focuses on the aspects of progress and challenges in materials technology.     

随机参数反对称层合板响应的灵敏度分析及优化设计

工程结构中的复合材料层合板的几何参数往往具有随机性质.如何研究随机参数层合板的灵敏度, 并对参数进行优化分析,这对正确估计结构设计的可靠性有着非常重要的意义.本文用随机摄动法,导出了求反对称层合板响应灵敏度的计算公式,研究了随机参数反对称层合板响应的灵敏度和优化设计,并用网格法计算出最佳铺层角.     

Numerical investigation of cavitating flow behind the cone of a poppet valve in water hydraulic system

Computational Fluid Dynamics (CFD) simulations of cavitating flow through water hydraulic poppet valves were performed using advanced RNGk-epsilon turbulence model. The flow was turbulent, incompressible and unsteady, for Reynolds numbers greater than 43000. The working fluid was water, and the structure of the valve was simplified as a two dimensional axisymmetric geometrical model. Flow field visualization was numerically achieved. The effects of inlet velocity, outlet pressure, opening size as well as poppet angle on cavitation intensity in the poppet valve were numerically investigated. Experimental flow visualization was conducted to capture cavitation images near the orifice in the poppet valve with 30° poppet angle using high speed video camera. The binary cavitating flow field distribution obtained from digital processing of the original cavitation image showed a good agreement with the numerical result. Project supported by the National Natural Science Foundation of China (No. 59835160) and Scientific Research Foundation for Returned Overseas Chinese Scholars, State Education Ministry of China (No. 50175097)     

Simulation investigation on fluid characteristics of jet pipe water hydraulic servo valve based on CFD

Simulation investigation on fluid characteristics of the water hydraulic jet pipe servo valve (WHJPSV) is conducted through a commercial computational fluid dynamics (CFD) software package FLUENT. In particular, the factors to fluid characteristics of WHJPSV are addressed, which include diameter combination of jet pipe and receiver pipe, jet pipe nozzle clearance, angle between two jet receiver pipes and deflection angle of the jet pipe. It is concluded from the results that: (i) Structural parameters have ...     

基于Mega 64的燃料电池控制系统设计

针对目前燃料电池控制系统设计复杂、能耗高、价格贵等问题,提出一种基于Mega 64单片机作为核心控制单元的5 kW质子交换膜燃料电池控制系统设计与实现方案。该方案采用工业传感器采集燃料电池的各项参数,采取闭环PID控制保证输出电压稳定,实现了对燃料电池的氢气供给系统、氧气供给系统、水温控制系统及逆变并网供电系统的检测与控制。系统具备在线设置运行参数,保存历史数据等功能,并且具有良好的人机交互界面,方便进行实时监控。现场运行结果表明,该系统设计可靠,运行稳定。     

基于结构健康监测系统的悬索桥运行模态识别(英文)

介绍了联合应用峰值法和互谱法的模态参数识别方法,并提出了一种新的主梁振型优化方法.将上述方法应用于润扬大桥悬索桥的运行模态识别系统中,利用结构健康监测系统采集的振动响应数据获取结构的模态参数.作为应用实例,对台风麦莎作用下的主梁、主缆和桥塔振动响应数据进行了模态参数识别.结果表明:主梁部分振型的模态频率不仅能从主梁的振动响应识别出来,而且能够从主缆和桥塔振动响应中识别,主粱、主缆和桥塔之间存在较强的耦合振动.此外,将运行模态的识别结果和成桥之初的现场测试结果进行了对比,二者识别结果整体上吻合较好,但运行模态系统识别的部分振型模态频率,如L1和L2,发生了较明显的下降.     

Study of a GaAs MESFET model with ultra-low power consumption

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心电放大器PSPICE辅助设计

以CMOS运放LMC6035构成的前置放大器和有源高通-低通滤波器为主要部件的心电放大器,可实现输出电压高增益、低噪声、高灵敏度,保证心电信号清晰稳定,满足临床监护以及病理分析的要求。在设计过程中运用电子线路CAD仿真软件对心电放大器进行功能分析,获得电路的技术指标,再进行参数修改和电路优化设计,从而可快速、精确地评价电路设计的正确性,节省实际测试费用,缩短设计开发周期。     

增程式混合动力洗扫车控制与仿真分析

针对目前国内传统双发动机洗扫车在作业工况下带来的高排放、高油耗、高噪音问题,以现有的洗扫车为原型,采用增程式混合动力系统结构,实现驱动系统与上装作业系统完全解耦,对动力系统主要部件的参数进行选型。通过AVL-Cruise软件对增程式混合动力洗扫车与传统双发动机洗扫车进行参照对比,在Matlab/Simulink平台搭建功率跟随控制策略进行联合仿真。仿真结果表明:APU能在电池SOC下降到设定的最低值开启,APU在设定的SOC上限值关闭,保证车辆的续航,使电池SOC维持在一定区间内,防止电池过充过放,延长电池寿命。在能耗方面,通过与传统双发动机洗扫车对比,增程式混合动力洗扫车在市区转场工况下节油51.5%,作业工况下节油22.2%,验证了混合动力洗扫车的燃油经济性。     

基于SVM的中频感应电炉自动浇注系统设计

针对中频感应电炉金属液手工浇注误差大的缺点,根据电炉的结构参数、倾斜运动的角速度、已经倾斜的角度和比例调节阀的电流,建立浇注流量的数学模型,并通过支持向量回归机算法预测每个时刻浇注系统的流量值,控制电炉的浇注流量进行误差补偿,实现精确的闭环反馈自动浇注控制.     

基于公理设计的产品结构分析

对公理设计理论进行了简单的描述.以国内某企业生产的闸阀为例,从实际应用角度,详细描述了闸阀的公理设计过程,并从公理设计角度对现有的闸阀结构进行了分析.     

Analysis on fused deposition modelling performance

Fused deposition modelling （FDM） is one of rapid prototyping （RP） technologies which uses an additive fabrication approach.Each commercially available FDM model has different types of process parameters for different applications.Some of the desired parts require excellent surface finish as well as good tolerance.The most common parameters requiring setup are the raster angle,tool path,slice thickness,build orientation,and deposition speed.The purpose of this paper is to discuss the process parameters of FDM Prodigy Plus （Stratasys,Inc.,Eden Prairie,MN,USA）.Various selected parameters were tested and the optimum condition was proposed.The quality of the parts produced was accessed in terms of dimensional accuracy and surface finish.The optimum parameters obtained were then applied in the fabrication of the master pattern prior to silicone rubber moulding （SRM）.These parameters would reduce the post processing time.The dimensional accuracy and surface roughness were analyzed using coordinate measuring machine （CMM） and surface roughness tester,respectively.Based on this study,the recommended parameters will improve the quality of the FDM parts produced in terms of dimensional accuracy and surface roughness for the application of SRM.     

番木瓜芹菜复合果蔬汁澄清工艺研制

复合果蔬汁澄清处理工艺的好坏直接影响其品质,添加澄清剂是常用的处理方法,壳聚糖作为常用的澄清剂,便宜且处理效果好又快。本文以壳聚糖为澄清剂,首先通过单因素实验,确定了四个单因素的最佳值：壳聚糖添加量0.08-0.12g/L,澄清温度40-50℃,澄清时间50-60min,复合果蔬汁pH值3.3-3.75,每个单因素各自处于最佳值时,复合果蔬汁的透光率和出汁率均在97%以上。在单因素实验基础上通过正交试验,确定了最佳工艺参数为：壳聚糖用量0.1g/L,澄清温度48℃,澄清时间55min,果蔬汁pH值3.5,在此条件下复合果蔬汁的透光率为98.8%。     

SHAFER 气液联动阀远控开关工作原理

通过对SHAFER气液联动阀原理图进行仔细研究和分析,总结归纳出了SHAFER气液联动阀远控开关的工作原理,包括普通远程开关阀和ESD开关阀,为日常运行维护提供了必要依据。当生产运行中发生意外开关阀情况时,可根据开关原理迅速定位和排除故障。     

公务员招聘的一种优化录用方案

文章针对2004年全国大学生数学建模竞赛专科组D题所涉及的公务员招聘问题进行分析,利用求两空间向量夹角及Hadamard积的方法,得出每个应聘人员在各用人单位的选拔参数,然后根据用人部门的优先权、选拔参数的大小并辅以逻辑判断给出录用分配方案.该数学模型原理简单,实施简便,具有普遍适用性,是一种通用的优化录用方案.