滚珠自动控制转子系统强迫振动研究(1/2次分数谐波振动)

应用两个滚珠在线自动平衡转子系统,并控制转子系统的强迫振动。目前相关研究主要集中在线性转子系统,然而实际的转子系统大多属于非线性系统,特别是在常见的滚动轴承等支承的转子系统中,由于装配误差等原因出现弱非线性弹性恢复力。对具有弱非线性弹性恢复力作用的转子系统,在已完成的对主振动控制研究的基础上,通过理论解析与数值模拟,研究了两滚珠平衡制振时转子系统的1/2次分数谐波振动的响应特性及滚珠质量对振动响应大小的影响规律等。研究表明平衡滚珠在高速区域能够完全平衡非线性转子系统,对系统的1/2次分数谐波振动具有良好的制振性能。

电力系统分数谐波的测量方法

分析了电力系统传统谐波分析方法不能检测分数谐波的根本原因 ,提出了一种分析分数谐波且能提高整次谐波检测精度的方法 ,通过仿真实验 ,验证了这是一种高精度的整数。

低频参激下具有分布时滞分数阶Duffing系统的振动分析

针对受到低频参激和低频外激驱动且包括分布时滞的分数阶Mathieu-Duffing系统,该文研究了在任意分数阶谐波共振下的振动机理。在数值格式方面,该文采用一种基于Caputo导数定义的精确数值算法,将传统振动系统中的渐进解析分析方法拓展到分数阶振动系统,从理论上给出了各谐振频率处稳态响应幅值的统一解析结果,以揭示低频参激对共振频率项的影响机制,并给出2种参激频率影响模式。研究发现,外激频率会引起系统稳态响应幅值的鞍节分岔现象,在数值结果中呈振幅跳变现象,确定了由分数阶阻尼阶次诱导的三重鞍结分岔现象。此外,该文进一步考虑将分布时滞参数作为控制参数,成功预测并验证了由时滞强度系数诱导的跨临界分岔现象。

Operational Modal Analysis of a Ship Model in the Presence of Harmonic Excitation

A ship is operated under an extremely complex environment, and waves and winds are assumed to be the stochastic excitations. Moreover, the propeller, host and mechanical equipment can also induce the harmonic responses. In order to reduce structural vibration, it is important to obtain the modal parameters information of a ship. However, the traditional modal parameter identification methods are not suitable since the excitation information is difficult to obtain. Natural excitation technique-eigensystem realization algorithm （NExT-ERA） is an operational modal identification method which abstracts modal parameters only from the response signals, and it is based on the assumption that the input to the structure is pure white noise. Hence, it is necessary to study the influence of harmonic excitations while applying the NExT-ERA method to a ship structure. The results of this research paper indicate the practical experiences under ambient excitation, ship model experiments were successfully done in the modal parameters identification only when the harmonic frequencies were not too close to the modal frequencies.

Electromagnetic Zero-Sequence Harmonics Blocker： Modeling and Experimental Analysis

This paper reveals new contributions to the analysis and development of devices for harmonic distortion mitigation. Considering the sequential distribution of harmonic currents, zero-sequence components could be diminished using electromagnetic devices, particularly the eZSB （electromagnetic zero-sequence blocking）. One important characteristic of this device, which has received particular attention on this research, is its robustness and low cost of construction. Theoretical and experimental results related to the behavior of the electromagnetic blocking devices are presented. The results illustrate the consistence of the theoretical aspects related with the model in the frequency domain, as well as the performance of the blocking devices, reducing zero-sequence harmonic currents, mainly by the conjunct action of the eZSF （electromagnetic zero-sequence harmonic filter）, working as a impedance coupler. In this context, aiming the evaluation of the reliability of the results obtained through mathematical modeling, experimental tests have been carried out using a low-power prototype, highlighting particular aspects related to its function as a zero-sequence harmonic blocker.

Influence of wave normal angle on gyroresonance between chorus waves and outer radiation belt electrons

In this paper, using a Gaussian distribution of wave normal angle X=tan0, and considering contributions of harmonic resonances n up to ＋5, we analyze the effect of normal angle on diffusion coefficients induced by gyroresonance between chorus waves and electrons with energies 0.1 and 1.0 MeV on the dayside and nightside at L=4.5. When pitch angle a~〉10~, for 0.1 and 1,0 MeV electrons on the dayside and nightside, diffusion coefficients of five orders （-2, -1, 0, 1, 2） decrease with in- creasing normal angle peak, leading to the total diffusion coefficients decreasing with increasing peak. When ae〈10~, for 1.0 MeV electrons on the dayside and 0.1 MeV electrons on the dayside and nightside, the positive order diffusion coefficients are generally smaller than the same negative order ones; in the meanwhile, diffusion coefficients of orders （-2, 1, 2） are very small, the dominant order n=-I diffusion coefficients change very little, hence the total diffusion coefficients almost remain un- changed. However, for 1.0 MeV electrons on the nightside, diffusion coefficients of orders （-2, 1, 2） which are larger than those of the order （-1） resonance increase with increasing peak, hence the total diffusion coefficients increase with increasing peak. The current results show that the wave normal angle plays an important role in the quantitative analysis of gyroresonance between chorus waves and electrons in the outer radiation belt.

Stochastic stability of the harmonically and randomly excited Duffing oscillator with damping modeled by a fractional derivative

The stochastic stability of the harmonically and randomly excited Duffing oscillator with damping modeled by a fractional derivative of Caputo's definition is analyzed.First,the system state is approximately described by It equations through the stochastic averaging method based on the generalized harmonic function.Then,the associated expression for the largest Lyapunov exponent of the linearized averaged It is derived,and the necessary and sufficient condition for the asymptotic stability with probability one of the trivial solution of the original system is obtained approximately by letting the largest Lyapunov exponent be negative.The effects of fractional orders and random excitation intensities on the asymptotic stability with probability one determined by the largest Lyapunov exponent are shown graphically.