三相桥式全控整流电路反相序工作的仿真

三相桥式全控整流电路反相序工作是调试中常见状态。为了对此状态下整流电路的工作过程进行分析,采用Matlab/simulink软件对此进行了仿真。结果表明,在控制角(α)从0°到180°的增加过程中,反相序输出电压波形出现了反复,输出电压平均值(Ud)出现两次最大值。通过分析反相序对触发信号的影响,对此现象进行了解释,并得到Ud的计算公式。     

Experimental and numerical analysis of non-symmetric breakage of liquid columns in an axial gravitational field rotating around an eccentric axis

An experiment in microgravity conditions aboard the TEXUS-23 mission was performed to obtain the deformation up to breakage of a cylindrical liquid column in isorotation around an eccentric axis. In previous work, breakage rotation speed was predicted by a numerical method. This method was validated by comparison with analytical and experimental results. The non-symmetric breakage of the liquid column observed in the experiment, however, was not explained by the combined effect of rotation and eccentricity.     

Structural Design and Control Strategy Analysis of Micro/Nano Transmission Platform

A fully flexure micro/nano transmission platform(MNTP)which has five degrees of freedom is designed on the basis of bridge type amplification mechanism.According to the kinematic theory and the elastic beam theory,the theoretical output displacement equation of the platform is derived,and then piezoelectric actuator(PZT)is calibrated.Meanwhile,a full closed-loop control strategy of the platform is established using the feedforward proportional-integral-derivative(PID)compound control algorithm based on the Preisach model.Moreover,the total transfer function of the micro positioning system is derived,and the calculation method of output signal is acquired.Finally,the theoretical output displacement is verified by finite element analysis(FEA)and positioning experiments.     

AH2500A电容电桥比对实验结果

20 0 3年 9月在四个校准实验室对AH2 5 0 0A电容电桥进行了比对实验 ,取得了宝贵的实验数据 ,并对实验数据进行进一步分析 ,提出成组稳定性考核和间接溯源的设想 ,并用实例说明。实验数据由 4家单位共享。     

舰面流场下的直升机平衡特性分析

主要分析了舰载直升机在母舰甲板上方悬停时的平衡特性。采用CFD方法计算了母舰甲板上方的气流场,建立了适用于舰载环境的直升机飞行动力学模型,计算了UH-60A直升机在流场悬停位置处的配平值。在此基础上,计算了旋翼入流、载荷、功率以及机体姿态状态量的响应。仿真结果表明,舰面流场的非线性、不均匀等特点对计算值影响较大。通过与无离散模型计算结果的对比,表明了流场对直升机旋翼的垂向载荷影响较大,对机体姿态角速率的影响更为显著,破坏了直升机的平衡,对直升机在舰面流场环境下的飞行控制系统提出了更高的要求。     

舰载飞机拦阻钩载荷实测方法研究

为完成某舰载飞机飞行试验任务,采用应变法实测了其拦阻着舰时的拦阻钩载荷。在分析着舰拦阻过程中拦阻钩受载状态的基础上,建立了拦阻钩纵向、侧向和垂向这3个方向上的载荷模型;对拦阻钩钩臂进行内力分析,设计了载荷测量应变电桥,并进行了载荷校准,建立了载荷方程。给出并详细分析了典型拦阻过程中的拦阻钩载荷,计算了拦阻功量及拦阻系统的效率。最后,通过与常规单向载荷模型的对比,探讨了采用三向载荷模型的意义。分析表明,建立的模型和采用的方法正确,结果合理可信,可供相关工程参考。     

某桥梁独立施工控制网高程复测技术研究

建立独立施工控制网是桥梁施工和安全运营的保证,而控制网的定期复测也很重要。本文以某大桥为例,就桥梁独立施工控制网高程部分的复测方法、数据平差方法、水准点稳定性探查等关键技术给予详细介绍。     

Stability of liquid bridges subject to an eccentric rotation

A cylindrical liquid bridge supported between two circular-shaped disks in isorotation is considered. The effect of an offset between the rotation axis and the axis of the two supporting disks (eccentricity) on the stability of the static liquid bridge is investigated. A numerical method is used to find stable and unstable shapes and to determine the stability limit for different values of eccentricity. The calculated stability limits are compared with analytical results, recovering the same behavior. Numerical results have been also compared with the results of an experiment aboard TEXUS-23, recovering the stability limit and the equilibrium shapes.     

直流电源输出阻抗测量技术

直流电源输出阻抗是新的特性参数,一些电源产品开始把它列入技术指标手册中。本文分析了电源阻抗的定义,总结了电源阻抗的特点,综述了当前电源阻抗测量技术的现状,提出了基于数字电桥的一种测量方法,提出了直流电源阻抗测量中的技术难点和尚待解决的技术问题。     

Dynamic particle accumulation structure (PAS) in half-zone liquid bridge – Reconstruction of particle motion by 3-D PTV

Three-dimensional (3-D) velocity field reconstruction of oscillatory thermocapillary convections in a half-zone liquid bridge with a radius of O (1 mm) was carried out by applying 3-D particle tracking velocimetry (PTV). Simultaneous observation of the particles suspended in the bridge by two CCD cameras was carried out by placing a small cubic beam splitter above a transparent top rod. The reconstruction of the 3-D trajectories and the velocity fields of the particles in the several types of oscillatory-flow regimes were conducted successfully for sufficiently long period without losing particle tracking. With this application the present authors conducted a series of experiments focusing upon the collapse and re-formation process of the PAS by mechanically disturbing fully developed PAS.