Prediction-based Iterative Learning Control (PILC) for Uncertain Dynamic Nonlinear Systems Using System Identification Technique

Prediction-based Iterative Learning Control (PILC) is proposed in this paper for a class of time varying nonlinear uncertain systems. Convergence of PILC is analyzed and the uniform boundedness of tracking error is obtained in the presence of uncertainty and disturbances. It is shown that the learning algorithm not only guarantees the robustness, but also improves the learning rate despite the presence of disturbances and slowly varying desired trajectories in succeeding iterations. The effectiveness of the proposed PILC is presented by simulations.     

一类不确定性广义非线性系统的鲁棒控制

考虑一类上有不确定性广义非线性系统Ｅｚ＝（Ａ＋ΔＡ）ｚ＋Ｂｖ＋ｆ（ｚ）的鲁棒控制问题,这里Ｅ是奇异的ｆ（ｚ）系统的非线性部分,在适当的假设下,得到了基于状态反馈作用的鲁棒控制存在的条件。     

一种复杂非线性系统的智能变结构控制方法

采用一种智能结构方法实现复杂非线性系统的控制,给出了设计原则,并用第四代歼击机飞行控制系统设计一个复杂实例来说明方法的有效性,实例系统中包含了两种控制律：增益调参和非线性动态逆控制律,两种控制律都包括了对发动机推力矢量喷管的控制。文中采用了一种基于状态的控制律切换算法进行两类控制律的切换,考虑了变结构系统切换瞬态问题和强迫振荡问题,并给出了简便的解决方法。     

A three-year longitudinal assessment of changes in office activities following the introduction of microcomputers into a multinational bank

A longitudinal assessment of the introduction of new office technologies into a multinational bank was conducted using both task diaries and semi-structured interviews. Task diaries were administered prior to the introduction of microcomputers, several months after the introduction and several years later. Semi-structured interviews were completed after the second task diary. The assessment provides evidence of how offices adapt to changing electronic tookits. The asssessment provides ergonomists with a usable list of taks activities and the effects on task variability of the adoption of microcomputers into the work routine. It shows that when support staff are asked to use a new computer they must choose what other tasks to cut back on, which has consequences for the overall work process. Overtime increased 170% after the introduction of the computer. In a culture where professional staff have high expectations of support staff this has consequences for working relationships in terms of perceptions of the computer's utility. Support staff and professional staff differ in perceptions of control, time-saving and ability to make corrections. The assessment demonstrates the importance of multiple measurement instruments in tracking the effects of technological change on the work process. In conclusion, it is noted that the introduction of new technologies into the office must be considered in the broader office context to avoid the unintended consequences often reported in other case studies.     

Response-time simulation of multivariate point process models for multiprogrammed jobstreams

We consider simulation methods for particular marked multivariate point processes, calledR-processes, which have recently been proposed as models for multiprogrammed jobstreams. Using workload marks on events, such models facilitate the incorporation of realistic workload characteristics into computer system performance predictions. We consider R-processes in which workload marks for an individual jobstream form a stationary sequence of discrete random variables having a (generally non-Markovian) mixed moving average-autoregressive dependency structure. For such models we provide a method for obtaining from a single simulation run point and interval estimates for general characteristics of job response times.     

Optimal design of butterfly-shaped linear ultrasonic motor using finite element method and response surface methodology

A new method for optimizing a butterfly-shaped linear ultrasonic motor was proposed to maximize its mechanical output. The finite element analysis technology and response surface methodology were combined together to realize the optimal design of the butterfly-shaped linear ultrasonic motor. First, the operation principle of the motor was introduced. Second, the finite element parameterized model of the stator of the motor was built using ANSYS parametric design language and some structure parameters of the stator were selected as design variables. Third, the sample points were selected in design variable space using latin hypercube Design. Through modal analysis and harmonic response analysis of the stator based on these sample points, the target responses were obtained. These sample points and response values were combined together to build a response surface model. Finally, the simplex method was used to find the optimal solution. The experimental results showed that many aspects of the design requirements of the butterfly-shaped linear ultrasonic motor have been fulfilled. The prototype motor fabricated based on the optimal design result exhibited considerably high dynamic performance, such as no-load speed of 873 mm/s, maximal thrust of 27.5 N, maximal efficiency of 43%, and thrust-weight ratio of 45.8.     

Energy flux characteristics of seismic waves at the interface between soil layers with different saturations

Based on the multiphase poroelasticity theory describing the propagation of waves in the unsaturated fluid-saturated porous medium, the reflection and transmission coefficients of the seismic waves at the interface between soil layers with different saturations are obtained. Our unsaturated model consists of a deformable skeleton in which two compressible and viscous fluids (i.e., water and gas) flow in the interstices. Three compressional waves (i.e., P1, P2, and P3 waves) and one shear (i.e., S wave) wave exist in the unsaturated soils. The expressions for the energy ratios of the various reflected and transmitted waves at the interface during the transmission and reflection processes are presented in explicit forms accordingly. At last, numerical computations are performed and the results obtained are respectively depicted graphically. The variation of the energy ratios with the incident angle, wave frequency and saturation degrees of the upper and lower soil layers is illustrated in detail. The calculation results show that the allocation of incident seismic waves at the interface is influenced not only by the angle and frequency of the incident seismic waves, but also by the saturations of the upper and lower soil layers. It is also verified that, at the interface, the sum of energy ratios of the reflected and transmitted waves is approximately equal to unity as was expected. This study is of importance to several fields such as geotechnical engineering, seismology, and geophysics.     

Dynamics of polymer electrolyte fuel cells undergoing load changes

Numerical simulations are carried out for a single-channel polymer electrolyte fuel cell (PEFC) undergoing a step increase in current density. The objective is to elucidate profound interactions between the cell voltage response and water transport dynamics occurring in a low-humidity PEFC where the membrane hydration and hence resistance hinges upon the product water. Detailed results are presented to show that a step increase in the current density leads to anode dryout due to electroosmotic drag, while it takes several seconds for water back-diffusion and anode humidified gas to re-wet the anode side of the polymer membrane. The water redistribution process is controlled by water production, membrane hydration, electroosmotic drag, and water diffusion in the membrane. The anode dryout results in a substantial drop in cell voltage and hence temporary power loss. Under extreme situations such as dry anode feed, large step increase in the current density, and/or lower temperatures, the cell voltage may even reverse, resulting in not only power loss but also cell degradation. Finally, the dynamics of current distribution after a step change in gas humidification is numerically examined.     

Some spectral response characteristics of ZnTe thin films

Zinc telluride thin films have been grown at room temperature and higher temperature substrates by thermal evaporation technique in a vacuum of 10^-6 torr. A main peak in the photocurrent is observed at 781 nm (1.58 eV) with two lower amplitude peaks on the lower wavelength side and one on higher wavelength side. The evaluated thermal activation energy is found to correspond well with the main spectral peak. From these studies it can be inferred that temperatures up to 453 K is still in the extrinsic conductivity region of the studied ZnTe thin films. The paper was presented at the 6th Asian Thermophysical Properties Conference (6th ATPC), held at Gauhati University, during 8–11 October 2001.     

时间最优开关控制的非线性规划方法

提出单输入非线性时间最优开关控制的非线性规划算法．针对不同的开关控制划分未知时间段，以时间段为变量建立与最优控制等价的非线性规划模型．构造每个未知时间段的等分龙格库塔格式，该格式不但不增加未知变量，而且可构造出不含导数的非线性规划算法．利用龙格库塔格式的收敛性和非线性规划的一阶最优性条件证明该方法的收敛性．最后以实例验证该算法．