Simulation and experimental investigation on a dynamic lateral flow mode in trepanning electrochemical machining

An appropriate flow mode of electrolyte has a positive effect on process efficiency, surface roughness, and machining accuracy in the electrochemical machining(ECM) process. In this study, a new dynamic lateral flow mode, in which the electrolyte flows from the leading edge to the trailing edge, was proposed in trepanning ECM of a diffuser. Then a numerical model of the channel was set up and simulated by using computational fluid dynamics software. The result showed that the distribution of the flow field was comparatively uniform in the inter-electrode gap. Furthermore, a fixture was designed to realize this new flow mode and then corresponding experiments were carried out. The experimental results illustrated that the feeding rate of the cathode reached 2 mm/min, the best taper angle was about 0.4°, and the best surface roughness was up to Ra= 0.115 lm. It reflects that this flow mode is suitable and effective, and can also be applied to machining other complex structures in trepanning ECM.     

γ–TiAl金属间化合物加工的国内外研究现状

介绍了γ–TiAl金属间化合物的主要特点。塑韧性较差、导热率较低等特点是导致加工γ–TiAl时切削温度高、切削力大和加工表面质量差的主要因素。从工具寿命、加工效率和加工表面质量等几方面对γ–TiAl金属间化合物的典型机械加工和特种加工方法进行了总结。认为磨削、高速铣削和电解加工是现阶段加工γ–TiAl比较适用的加工方法,但仍缺乏能兼顾效率、成本和表面质量的加工工艺。     

Nonlinear Interactions between the Quasi 5-day Wave and Tides Based on Meteor Radar Observations at Maui

Nonlinear interactions between the quasi 5-day wave and tides based on meteor radar observation in the Mesosphere and Lower Thermosphere(MLT) at Maui are studied in this paper.Strong sum interaction between quasi 5-day wave and diurnal tide,and evident difference interaction between quasi 5-day wave and semidiurnal tide are observed during the time of attention.However,their difference and sum counterparts are clearly weaker.The secondary waves generated from those interactions beat with the tide and show intense modulation at the period of 5 days which confirms the existence of their interactions.Additionally,correlation coefficients among these waves are calculated to further explore their interactions and find that they can persist for several days although they are highly intermittent.The energy exchange among these waves can be reversible during the observational time.The periods when the significant difference interaction between the quasi 5-day wave and semidiurnal tide occur are much shorter than those when the significant sum interaction between the quasi 5-day wave and diurnal tide occur.Moreover,these two strong interactions can take place simultaneously.In generally,this study provides the proof of nonlinear interactions between quasi 5-day wave and tides which were seldom reported before.     

IIR滤波器在芯片原子钟中的应用

芯片原子钟是具有小体积,低功耗特点的原子钟。本文采用了IIR滤波器方案对芯片原子钟物理系统输出信号进行处理,该方案有利于减小芯片原子钟的体积、提高芯片原子钟短期频率稳定度。实验结果表明,与FIR滤波方案相比,IIR滤波器使用的FPGA资源减小了约58%;与现有模拟滤波方案相比,使用IIR滤波器方案的芯片原子钟频率稳定度提高了1.4×10~(-10)τ~(-1/2)(τ=1s-100s),电路面积减小了10%。     

河北省大型钢铁企业可持续发展战略

本文通过研究河北省大型钢铁企业的发展现状,深入分析了此次全球性金融危机对我省大型钢铁企业的影响及深层根源,并探讨其实现可持续发展的基本路径。     

飞机座舱人机工效评定实验台研制

为解决飞机人机界面设计在新形势下面临的问题,研制了一套基于飞行模拟器的驾驶员工效评定实验台,以便在更加实际的飞行情况下对飞行员的认知特性进行研究.该实验台由飞机座舱、仿真软件、计算机系统和生理参数测量系统等组成,能开展座舱优化布局、界面信息显示适人性、脑力负荷的综合评定等研究.该实验台的研制为飞机人机界面的工效设计和评定提供了一种新的方法.     

偏转弹头导弹控制系统设计与仿真

根据弹头的可偏转特性,利用无根多刚体系统动力学方法建立了偏转弹头导弹的动力学模型,并对通道间的耦合特性及弹头偏转对弹体运动的影响进行了分析。在此基础上,将通道间的耦合及弹头偏转对弹体运动的影响作为干扰项处理,将气动参数的非线性变化等效为标称参数的摄动,利用变结构控制理论设计了偏转弹头导弹的控制器。仿真结果表明,所设计的变结构控制器能够有效地减小和消除俯仰、偏航通道对滚转通道的耦合作用以及弹头偏转对弹体运动的影响,较好地抑制了导弹气动参数的摄动,具有较高的稳态精度和良好的动态性能。     

Flight Safety System Evaluation and Optimal Linear Prediction

The complexity of flight safety system is usually affected by a variety of uncertainties.The uncertainty of overall security situation of flight safety system are hardly determined. In this work,flight safety assessment index system is firstly established based on software hardware environment liveware management(SHELM)model. And flight safety assessment is also carried out with matter-element theory algorithm to obtain safety state. According to correlation degree values of each evaluation index,key indexes affected flight safety are obtained. Under the assumption that the flight safety system is a linear dynamic system and combining the above evaluation analysis,Kalman filter algorithm is used to carry out prediction analysis on security situation. A simulation analysis is carried out based on an actual flight safety situation of an airline. The results show that the security state of airline flight safety system in a short period of time can be obtained,and main factors affecting flight safety are found out. This provides a viable way for airlines to further strengthen flight safety management.     

基于落点预测的高旋火箭弹弹道修正算法

高旋火箭弹的修正控制是基于等效力实现的二维弹道修正控制，由于弹体存在陀螺进动和马格努斯效应，在控制力作用下产生的附加攻角引起的升力与控制力的矢量合为等效力，其大小与方向在控制过程中不断变化，不能简单根据偏差量（修正量）的比例关系来确定控制力的方向。基于此，分析了控制力与等效力的关系，提出了一种基于弹道落点预测的控制算法。首先利用弹道落点预测模型实时预测落点与目标的偏差量，然后利用小扰动法构造偏差量对控制量的敏感系数矩阵，通过偏差量与敏感系数矩阵解算出纵、横两个方向的需用控制量。采用修正前后速度矢量的位置关系得到控制量的合矢量及其方位角，并利用控制量的合矢量与等效力计算出控制周期，在控制周期内按照等效力方位角调整控制力的方向实现对高旋火箭弹的精确控制，解决了非线性耦合问题。仿真结果表明该算法具有较高的控制精度，为工程应用提供理论依据。     

直升机金属结构缺陷容限验证技术研究

直升机结构的缺陷容限验证在FAR／CCAR27／29．571条适航条款中有明确的要求。文章提出了全尺寸结构缺陷容限验证思路，对验证的各个环节，包含缺陷的类型及参数、缺陷容限特性曲线基本参数及安全系数、真实缺陷下载荷或应力的修正、结构的缺陷容限性能、检查周期的确定等进行了探讨，为开展直升机结构缺陷容限验证工作提供了技术支持。