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地面基站的几何布局方式是影响区域无线电定位系统定位精度的重要因素,水平几何精度递变因子(HDOP)是衡量地面基站几何布局对系统定位精度影响的基本指标。为求解区域无线电定位系统基站的最优几何布局,给出了区域无线电定位系统HDOP的计算方法,建立了求解区域无线电定位系统地面基站最优几何布局的数学模型;提出了应用惩罚函数对数学模型进行求解的方法,将约束优化问题转化为无约束优化问题;并针对求解过程中目标函数难于求导的问题,提出了采用模拟退火算法进行全局寻优,使求得的结果逼近全局最优解。仿真结果表明,这种结合惩罚函数法和模拟退火算法进行全局寻优的方法,对于区域无线电定位系统求解地面基站的最优布局方案具有工程实用价值。 相似文献
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An experimental investigation of a model forming fabric was conducted. The forming fabric was simplified and represented by a bank of two rows of cylinders. Particle image velocimetry (PIV), pressure drop, and hydrogen bubble visualization were used to evaluate the upstream and gross flow patterns for various diameter ratios and cylinder spacings at a Reynolds number of 65. It was found that for a row separation of 0.75 times the upstream cylinder diameter, the upstream flow matched that for a single row of cylinders. Further, it was found that when the pressure drop through the bank of cylinders was equal to the sum of the individual rows’ pressure drops, the upstream flow converged to that of a single row. 相似文献
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对比研究了货车心盘用ZG25MnNb钢、AAR-C级钢及经过表面强化处理的锻钢20Mn、锻钢Q345和铸钢ZG25的耐磨性能;采用金相显微镜分析了材料金相结构对其耐磨性能的影响。结果表明,对货车心盘用钢材进行表面强化能够显著改善其耐磨性能ZG25MnNb钢和经表面强化处理的锻钢20Mn的耐磨性较优;表面硬度高而组织细小的材料组成的摩擦副的耐磨性较好。 相似文献
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Analysis of transmission load of agricultural tractors 总被引:3,自引:0,他引:3
The objectives of this study were to analyze the load acting on the input shaft of the transmission of an agricultural tractor when it conducts plowing, rotovating and transporting operations under the Korean farming conditions. A survey was conducted to investigate the operational characteristics of such tractor works. To measure the load, a torque transducer was developed and installed on the input shaft of the transmission. A radio telemetry system was used to transmit the strain signals from the torque transducer to a data acquisition system. The time histories of the measured torque signals were digitized and analyzed using the rain-flow cycle counting method to determine their cyclic distributions. The load spectra thus obtained from the different operations were compared and their severeness to the transmission was discussed. 相似文献
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本文研究了黏弹性轴向运动梁横向受迫振动稳态幅频响应问题.在控制方程的推导中,对黏弹性本构关系采用物质导数.把多尺度法直接应用于梁横向振动的非线性控制方程,利用可解性条件消除长期项,得到系统稳态的幅频响应曲线.运用Lyapunov一次近似理论分析幅频响应曲线的稳定性.通过算例研究了黏性系数,外部激励幅值以及非线性项系数对稳态幅频响应曲线及其稳定性的影响.运用数值方法对两端固定边界下黏弹性轴向运动梁的控制方程直接数值解,分析梁横向非线性振动的稳态幅频响应,通过数值算例验证直接多尺度法的结论. 相似文献
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为了研究表面织构对聚四氟乙烯(PTFE)复合材料摩擦磨损性能的影响规律及其作用机理,采用BBD响应面法对试验进行设计与分析,利用LSR-2M往复摩擦试验机测试了复合材料的摩擦学性能,建立了织构参数与摩擦系数和体积磨损率之间的二次回归模型,研究了槽宽、间距和角度参数及其交互作用对复合材料摩擦学性能的影响. 结果表明:二次回归模型显著,拟合精度分别为82.9%和83.2%,预测出槽宽323.2 μm、间距295.4 μm、角度88.7°时摩擦系数存在最小值0.147,槽宽331.1 μm、间距307.6 μm、角度87.6°时体积磨损率存在最大值8.11×10?5 mm3/(Nm);织构增大了初始摩擦系数和体积磨损率,但有利于储存磨屑,在接触应力作用下磨屑中的纳米粒子与槽底及侧面的粗糙峰形成了机械互锁,提高了磨屑的附着力,促进了转移膜的生成. 相似文献
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Pinpoint calculation of tooth deflection on spur gear by means of method of complex variables in plane elasticity 总被引:1,自引:1,他引:0
This paper ineorporated and developed the method originated by AIDA.TERACCHI. and NAGAMUYA. to which a high value is set presently at home andabroad, in which the stress and deflection of tooth on spurgears are calculated by means ofthe method of complex variables in plane elasticity. In this paper, their approximatesolution was developed to become exact solution. The accuracy of the mapping shape oftooth was increased. It was mentioned that the mapping function was expressed by fivefractional terms. with the mapping error being less than 1%m.A calculating principle wasproposed to find out the displacement of contact point in relation to central line of theadjacent gear tooth affecting the quality of mesh of gears directly.The computer programwas made, and according to the computed results.the figures were given so that thedisplacement of the contact point in the normal direction can be calculated conveniently forengineering calculation. 相似文献
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This paper describes the work carried out to investigate the pore pressures occurring in secondary consolidation. A theoretical approach and an experimental technique was developed in order to conduct the study. By considering compression to occur only due to water leaving the soil it was possible to derive an expression for the dissipation of pore pressure in the secondary phase. By further simplified assumptions which are based on experimental observations, the above general solution was reduced to a simple formula which predicted the observed behaviour of pore water pressures during secondary consolidation. 相似文献
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针对混合澄清槽搅拌装置运行工况的特殊要求,以改善其滑动轴承使用性能及寿命为目标,选用和研制WC-VC-Ni-Cr-Mo金属陶瓷复合材料(WN20)和铁-镍-铬-石墨-二硫化钼自润滑复合材料(FC13). 考察了复合材料的微观组织、力学和摩擦学性能,结果表明WN20金属陶瓷复合材料具有优异的力学性能,FC13金属基自润滑复合材料在干摩擦状态下具有良好的自润滑和抗磨损性能,是滑动轴承组件摩擦副轴瓦的合适材料. 根据固体润滑滑动轴承的设计原则,设计滑动轴承组件结构及相应的润滑方式. 采用C13金属基自润滑复合材料制造轴瓦,并通过嵌入特种润滑剂的方式进行辅助润滑,与WN20金属陶瓷轴组成摩擦副时,滑动轴承组件表现出优异的摩擦磨损性能,经过250 h摩擦试验,摩擦系数和轴瓦温度无显著变化,摩擦系数为0.08,轴瓦径向磨损量为3.8 μm,均满足混合澄清槽搅拌装置的使用要求. 相似文献
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在线铁谱仪电磁装置磁场的有限元分析 总被引:1,自引:0,他引:1
针对在线铁谱仪中的一种新型的直流电磁装置,通过有限元分析揭示了其工作气隙中的磁场分布规律,采用正交设计方法确定了夹角方案条件下的最佳工作气隙尺寸,比较了磁场在夹角方案和倾角方案条件下的分布情况.结果表明,该装置在夹角方案条件下可以在油样流动方向上形成由弱到强的磁场分布,但效果不如倾角方案好. 相似文献
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Joost A. M. de Swart Rob J. M. Bastiaans Jeroen A. van Oijen L. Philip H. de Goey R. Stewart Cant 《Flow, Turbulence and Combustion》2010,85(3-4):473-511
In this paper we study the possibility to account for preferential diffusion effects in lean turbulent premixed flames in numerical predictions with reduced chemistry. We studied the situation when hydrogen is added to methane at levels of 20% and 40% by volume in the fuel, at lean combustion (??=?0.7) with air. The base case of pure methane was used as a reference. In this case preferential diffusion effects are negligible. First the sensitivity of the mass burning rate to flame stretch was investigated, in one dimensional computations with detailed chemistry, to set reference values. Then the framework of the Flamelet Generated Manifolds (FGM) was used to construct an adequate chemical method to take preferential diffusion into account, without the need for using detailed chemistry. To that end a generalization of the method was presented in which five controlling variables are required. For this system, proper transport equations and effective Lewis numbers where derived. In practice not all five variables are necessary to include and as a first step we limited the amount in the numerical tests in this study to two controlling variables. The method was then tested in configurations in which there was an interaction of coherent vortices and turbulence with flames. It was demonstrated that a minimum of two controlling variables is needed to account for the changed mass burning rate as function of stretch and curvature. It was shown that one-dimensional FGM as well as one-step Arrhenius kinetics can not describe this relation. 相似文献
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牙齿表面磨损一般通过显微镜进行形貌图像表征分析,而数值化分析牙齿表面磨损形貌的工作相对较少. 本研究中通过白光共聚焦显微镜,Solarmap Universal 软件和Tooth-Frax软件对牙齿咬合前后表面磨损形貌进行数值化分析,建立磨损前后表面尺度敏感曲线. 结果显示:牙齿表面磨损形貌可以通过轮廓分形分析法建立相应的表面尺度敏感曲线,形成表面磨损尺度敏感数字信号. 本工作的主要目的是寻求通过表面磨损数值化分析为研发牙齿磨损动态监测设备提供理论基础和技术支撑. 相似文献
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This study describes the experimental and numerical dynamic analysis of a kinematically excited spherical pendulum. The stability of the response in the vertical plane was analyzed in the theoretically predicted auto-parametric resonance domain. Three different types of the resonance domain were investigated the properties of which depended significantly on the dynamic parameters of the pendulum and the excitation amplitude. A mathematical model was used to represent the nonlinear characteristics of the pendulum, which includes the asymmetrical damping. A special frame was developed to carry out the experiments, which contained the pendulum supported by the Cardan joint and two magnetic units attached to the supporting axes of rotation, and this was able to reproduce linear viscous damping for both of the principal response components. The stability analysis of the system was compared with the numerical solution of the governing equations and experimental observation. The most significant practical outcomes for designers are also summarized. 相似文献
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镍钛记忆合金自补偿磨粒磨损性能研究 总被引:3,自引:3,他引:3
研究了高临界温度镍钛记忆合金一维自补偿磨粒磨损特性.结果表明,在一定温度下,镍钛记忆合金在摩擦过程中具有形状恢复能力,从而产生一维磨损自补偿作用.超弹状态镍钛记忆合金具有热弹性马氏体相变、高阻尼、应力感生马氏体、超弹性、高应变硬化指数和时效弥散析出强化等特性,这使得硬度较低的镍钛合金的耐磨性能远优于硬度较高的淬火45#钢.利用超弹状态镍钛记忆合金的磨损自补偿作用可望开发出新型抗磨形状记忆合金产品. 相似文献
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硅表面电沉积MoS2薄膜及其微观摩擦性能研究 总被引:2,自引:0,他引:2
以单晶硅片为基片,采用电化学沉积工艺通过阴极还原硫代钼酸根制备MoS2薄膜,利用光学显微镜、扫描电子显微镜、X射线衍射仪、俄歇电子能谱仪以及原子力显微镜表征薄膜结构,并研究其微观摩擦磨损性能.结果表明:所制备的薄膜为纳米/亚微米厚度,表面光滑致密,结构为非晶态,由钼、硫和氧元素构成;微米厚度的薄膜表面粗糙度增加,薄膜易开裂,结合性差;沉积MoS2薄膜的硅表面的最小摩擦力约为原始硅表面的1/2;沉积MoS2可以使硅表面的粘着能减少50%左右,从而使其微观摩擦力降低. 相似文献
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本文对动失速型非定常分离涡结构的控制方法,在低速风洞中应用相平均测压技术进行了实验研究。在二元平板模型中部安装一作俯仰振荡的扰流板产生动失速型分离涡,在其上游安装另一用作控制的小扰流板。实验结果表明,应用前置的振荡小扰流板可影响并改变动失速分离涡的强度和对流特性。在最有利的控制相位下,涡吸力峰可降低48%,涡对流时间可以推迟0.19周期。对于间歇式振荡扰流板,采用相位提前控制方式比相位滞后控制方式更有效。 相似文献