基于位移反馈控制的主动增加时滞补偿方法及其试验验证

时滞是结构振动主动控制系统中普遍存在的现象,时滞不仅会降低控制系统的性能,严重时会造成系统失稳、控制发散。针对此问题,研究以下三方面内容:首先基于单自由度系统时滞的稳定性理论分析,确定系统最大允许时滞量的解析解,该阈值可以作为确定何时应用时滞补偿技术的一个评判指标;其次,当作动器实际时滞量大于最大允许时滞量时,常规时滞补偿方法将会失效,提出了基于位移反馈的主动增加时滞的补偿新方法,并定性结合定量详细分析了主动控制算法的参数影响规律;最后,以单层剪切型框架结构为被控对象,进行了多种输入激励下基于位移反馈的主动增加时滞补偿试验验证。大量仿真分析和试验结果表明所提方法能够在保证系统稳定性的同时获得一定可观的控制效果。

部分状态反馈的主动利用时滞补偿方法

时间滞后是结构振动主动控制系统中普遍存在的现象,时滞不仅会降低控制系统的性能,严重时会造成系统失稳、控制发散。常规时滞补偿方法大多是将时滞作为一种危害进行消减,而今提出了一种基于速度反馈的主动利用时滞的补偿新方法。研究分为以下三方面内容:首先以理论分析为基础,提出了基于速度反馈的主动增加时滞的补偿新方法;其次,结合大量仿真结果定性分析了主动控制算法的参数影响规律;最后,以单层剪切型框架结构为被控对象,进行了多种输入激励下基于速度反馈的主动增加时滞补偿试验验证。大量仿真分析和试验结果表明所提方法能够在保证系统稳定性的同时获得一定可观的控制效果。

基于吸振器控制的轧机辊系时滞反馈研究

考虑四辊轧机液压缸非线性弹簧力约束的因素,建立带有吸振器的两自由度轧机辊系模型。引入时滞反馈控制函数,设计带吸振器的轧机辊系振动位移、振动速度时滞反馈控制方程。通过分析轧机辊系振动极限环幅值和幅频特性的稳定性,得到不同反馈增益参数和时滞量参数对轧机辊系主系统的影响规律。适当地增大反馈增益系数g 1和g 2,减小时滞量系数τ1和τ2,可以改善系统的稳定性和收敛性。

基于时滞LQR算法的风洞模型振动控制试验研究

为有效抑制风洞试验中飞行器模型的振动,利用气动力学与机械动力学的观点分析了风洞模型的振动原因及特点,并建立了风洞模型—测力天平—风洞支杆所组成的悬臂梁系统的二阶模型。针对飞行器模型振动控制中的时滞问题,分析了时滞现象产生的原因及对风洞试验飞行器模型振动控制的影响,并利用基于所测振动信号与作动器信号的基频傅里叶变换方法实现了基频处的时滞量辨识。基于辨识出的时滞量分别分析研究考虑时滞问题与未考虑时滞问题的风洞模型振动控制状态方程,并设计时滞补偿线性二次型调节器控制算法。搭建地面试验系统,通过地面锤击试验验证得知,相比未考虑时滞问题的线性二次型调节器,时滞补偿线性二次型调节器控制算法具有较好的控制效果,能够更加稳定有效地对风洞模型振动进行控制。

非线性时滞反应-扩散方程向后欧拉方法的动力学性态(英文)

Hutchinson方程是涉及到反应-扩散量的非线性时滞方程.在给定初始值和周期边界条件,研究Hutchinson方程的不动点以及不动点的线性稳定性.通过数值例子证明不定点的线性稳定的正确性,并分析说明时滞量对数值方法稳定性的影响.

基于时滞的现代空防对抗兰彻斯特方程模型

针对现代战争中空防对抗过程的复杂,分析了现代作战条件下空袭与防空作战的主要特点,建立了基于时滞的现代空防对抗兰彻斯特方程模型,给出了该模型参数的求取方法,并进行了算例仿真分析,得到了有价值的仿真结果,为现代空防与防空作战提供了指导。

基于等效传递函数的多变量大滞后系统的内模控制方法研究

针对多变量大滞后系统存在的强耦合、控制困难等问题,文章提出了一种基于等效传递函数的内模控制新方法;该方法首先给出了具有内模结构的等效传递函数的计算方法,得到系统的等效传递函数;然后采用麦克劳林降阶法对得到的高阶传递函数进行降阶,进而根据降阶后的模型设计内模控制器,有效避免了超前项的出现,降低了控制器设计的复杂性;同时,为了消除稳态误差,在内模控制器上添加了一个由系统稳态响应获取的稳态增益;仿真结果表明,该方法能能够消除系统的稳态误差,实现系统的设定值跟踪;本方法具有设计简单、控制性能好等特点。

Multivariable Fuzzy Predictive Control Based on the Modified CPN Model

Through modifying the CPN model, a kind of multivariable fuzzy model is put forward, and the matching fuzzy multistep predictive control algorithm is deduced based on the model. The modified model works in a competitive output manner which results in its local representation property. While studying on line, only a few parameters need to be regulated. So the model has the merits of fast learning and on line self organizing modeling. The control algorithm is simple, adaptive and useful in multivariable and time delay systems. Applying the algorithm in a paper making system, simulation shows its good effect.

A low-power high-throughput link splitting router for NoCs

In this paper, we propose a technique for lowering the latency of the communication in a NoC （network on chip）. The technique, which can support two qualities of service （QoS）, i.e., the guaranteed throughput （GT） and best effort （BE）, is based on splitting a wider link into narrower links to increase throughput and decrease latency in the NoC. In addition, to ease the synchronization and reduce the crosstalk, we use the l-of-4 encoding for the smaller buses. The use of the encoding in the proposed NoC architecture considerably lowers the latency for both BE and GT packets. In addition, the bandwidth is increased while the power consumption of the links is reduced.

Detecting the Relationship Between Summer Rainfall Anomalies in Eastern China and the SSTA in the Global Domain with a New Significance Test Method

It is suggested that the multiple samples in a correlation map or a set of correlation maps should be examined with significance tests as per the Bernoulli probability model. Therefore, both the contemporaneous and lag correlations of summertime precipitation R in any one of the three regions of Northern China （NC）, the Changjiang-Huaihe River Valley （CHRV）, and Southern China （SC） with the SSTA in the global domain have been tested in the present article, using our significance test method and the method proposed by Livezey and Chen （1983） respectively. Our results demonstrate that the contemporaneous correlations of sum- mer R in CHRV with the SSTA are larger than those in NC. Significant correlations of SSTA with CHRV R are found to be in some warm SST regions in the tropics, whereas those of SSTA with NC R, which are opposite in sign as compared to the SSTA-CHRVR correlations, are found to be in some regions where the mean SSTs are low. In comparison with the patterns of the contemporaneous correlations, the 1 to 12 month lag correlations between NC R and SSTA, and those between CHRV summer R and SSTA show similar patterns, including the magnitudes and signs, and the spatial distributions of the coefficients. However, the summer rainfall in SC is not well correlated with the SSTA, no matter how long the lag interval is. The results derived from the observations have set up a relationship frame connecting the precipitation anomalies in NC, CHRV, and SC with the SSTA in the global domain, which is critically useful for our understanding and predicting the climate variabilities in different parts of China. Both NC and CHRV summer R are connected with E1 Nifio events, showing a ‘- -＇pattern in an E1 Nifio year and a‘＋ ＋＇ pattern in the subsequent year. Key words summer precipitation; eastern China; global sea surface

Robust H_∞ Filter Design for a Class of Uncertain Linear Systems with Time-delayed Measurement

A robust H∞ approach to filtering for a class of uncertain linear systems with time-delayed measurement is investigated. The parameter uncertainties are described by real time-varying norm-bounded form. A methodology is developed for designing linear filters such that the filtering process remains robustly stable and the transfer function from the disturbance inputs to error state outputs meets the prescribed H∞-norm upper-bound constraints. The filter can be obtained and parameterized by solving two Riccati equations based on the lemma of robust stability for control system with delay. Simulation example proves the method to be effective and feasible.

Stochastic resonance of coupled time-delayed system with fluctuation of mass and frequency and its application in bearing fault diagnosis

The stochastic resonance behavior of coupled stochastic resonance(SR)system with time-delay under mass and frequency fluctuations was studied.Firstly,the approximate system model of the time-delay system was obtained by the theory of small time-delay approximation.Then,the random average method and Shapiro-Loginov algorithm were used to calculate the output amplitude ratio of the two subsystems.The simulation analysis shows that increasing the time-delay and the input signal amplitude appropriately can improve the output response of the system.Finally,the system is applied to bearing fault diagnosis and compared with the stochastic resonance system with random mass and random frequency.The experimental results show that the coupled SR system taking into account the actual effect of time-delay and couple can more effectively extract the frequency of the fault signal,and thus realizing the diagnosis of the fault signal,which has important engineering application value.

模糊-动态高型控制方法在捷联反射镜稳定平台中的应用

针对捷联反射镜稳定平台处于跟踪状态时,机动目标及脱靶量时滞导致跟踪精度降低的问题,结合模糊控制及动态高型技术提出了一种改进的控制算法。传统动态高型控制方法在原有控制系统基础上动态并入积分环节以构成高型系统从而减小跟踪误差,但积分环节的并入和退出时机不易掌握,使得系统动态性能恶化,引入模糊控制理论建立系统跟踪误差及误差微分和积分环节系数之间的关系,使得动态调整积分策略为渐变而非"开关"。经仿真验证,该方法相较于普通PID控制方法跟踪精度提高了1个数量级,对工程实践具有指导意义。

Livestock Dynamic Responses to Climate Change in Alpine Grasslands on the Northern Tibetan Plateau:Forage Consumption and Time-lag Effects

Climate change and forage-intake are important components of livestock population systems,but our knowledge about the effects of changes in these properties on livestock is limited,particularly on the Northern Tibetan Plateau.Based on corresponding independent models（CASA and TEM）,a human-induced NPP（NPPH） value and forage-intake threshold were obtained to determine their influences on livestock population fluctuation and regrowth on the plateau.The intake threshold value provided compatible results with livestock population performance.If the forage-intake was greater than the critical value of 1.9（kg DM d^（-1） sheep^（-1））,the livestock population increased;otherwise,the livestock population decreased.It takes four years to transfer a disturbance in primary productivity to the next trophic level.The relationships between livestock population and NPP_H value determined population dynamics via the forage-intake value threshold.Improved knowledge on lag effects will advance our understanding of drivers of climatic changes on livestock population dynamics.

Singularly Perturbed Differential-Difference Reaction Diffusion Equations with Time Delay

A class of differential-difference reaction diffusion equations with a small time delay is considered.Under suitable conditions and by using the method of the stretched variable,the formal asymptotic solution is constructed.And then,by using the theory of differential inequalities the uniformly validity of solution is proved.

Weighing super-massive black holes with narrow Fe Kα line

It has been suggested that the narrow cores of the Fe Ka emission lines in Active Galactic Nuclei （AGNs） are likely produced in the torus, the inner radius of which can be measured by observing the lag time between the V and K band flux variations. In this paper, we compare the virial products of the infrared time lags, and the narrow Fe Ka widths for 10 type 1 AGNs, with the black hole masses from other techniques. We found the narrow Fe Ka line width is in average 2.6＋0.9-0.4 times broader than expected, assuming an isotropic velocity distribution of the torus at the distance measured by the infrared lags. We propose the thick disk model of the torus may explain the observed larger line width. Another possibility is the contamination by emission from the broad line region or the outer accretion disk. Alternatively, the narrow iron line might originate from the inner most part of the obscuring torus within the sublimation radius, while the infrared emission may be from the outer cooler part. We note the correlations between the black hole masses based on this new technique and those based on other known techniques are statistically insignificant. We argue that this could be attributed to the small sample size and the very large uncertainties in the measurements of iron K line widths. The next generation of X-ray observatories could help verify the origin of the narrow iron Ka line and the reliability of this new technique.

Full-Annulus Simulation of the Surge Inception in a Transonic Centrifugal Compressor

Full annulus simulations of the flow which develops in a transonic centrifugal compressor are performed at two stable operating points （peak efficiency and near surge） and during the path to surge. At stable conditions, the flow field properties are analyzed by comparisons with experimental data and numerical simulations using a phase lagged approach previously carried out. Regarding the stage overall performance, an excellent agreement is obtained between the numerical results （both with time lagged approach and full-annulus calculation） and the ex- periments. From the full-annnlus simulations, the change in flow pattern from peak efficiency to surge is found to be perfectly similar to that obtained from the simulations using the time lagged approach. In particular, pro- vided that the operating point is stable, the flow proves to be chorochronic. The full-annulus simulations were continued after a unique small change in the throttle law applied at the exit of the numerical domain. The mass flow, pressure ratio and efficiency then significantly drop all the more the time progresses. The simulation becomes unstable and the surge inception well underway. The path to surge is found to be due to the enlargement of the boundary layer separation on the suction side of the diffuser vanes in accordance with the conclusions drawn from the chorochronic simulations and experiments. But as the time progresses, the flow loses its chorochronic character. Stall cells rotating at around 7% of the rotor speed develop and lead to surge in around 5 revolutions.

Subspace-based identification of discrete time-delay system

We investigate the identification problems of a class of linear stochastic time-delay systems with unknown delayed states in this study. A time-delay system is expressed as a delay differential equation with a single delay in the state vector. We first derive an equivalent linear time-invariant(LTI) system for the time-delay system using a state augmentation technique. Then a conventional subspace identification method is used to estimate augmented system matrices and Kalman state sequences up to a similarity transformation. To obtain a state-space model for the time-delay system, an alternate convex search(ACS) algorithm is presented to find a similarity transformation that takes the identified augmented system back to a form so that the time-delay system can be recovered. Finally, we reconstruct the Kalman state sequences based on the similarity transformation. The time-delay system matrices under the same state-space basis can be recovered from the Kalman state sequences and input-output data by solving two least squares problems. Numerical examples are to show the effectiveness of the proposed method.

Approximate Controllability of Neutral Functional Differential Systems with State-Dependent Delay

This paper deals with the approximate controllability of semilinear neutral functional differential systems with state-dependent delay. The fractional power theory and α-norm are used to discuss the problem so that the obtained results can apply to the systems involving derivatives of spatial variables. By methods of functional analysis and semigroup theory, sufficient conditions of approximate controllability are formulated and proved. Finally, an example is provided to illustrate the applications of the obtained results.