Nonlinear Control of Open-Channel Water Flow Based on Collocation Control Model

This paper is devoted to the nonlinear control of open-channel water flow dynamics via a one-dimensional collocation control model for irrigation canals or dam-river systems. Open channel dynamics are based on the well-known Saint-Venant nonlinear partial differential equations. In order to obtain a finite-dimensional model an orthogonal collocation method is used, together with functional approximation of the solutions of Saint-Venant equations based on Lagrange polynomials. This method can give a more tractable model than those obtained from classical finite-difference or finite-element methods (from the viewpoint of both state dimension and structure), and is well suited for control purposes. In particular it is shown how such a model can be used to design a nonlinear controller by techniques of dynamic input–output linearization with the goal of controlling water levels along an open-channel reach. Controller performance and robustness are illustrated in simulations, with a simulated model for the canal chosen as more accurate than the one used for control design.     

Simple Water Level Controller for Irrigation and Drainage Canals

A simple water level controller for irrigation and drainage canals is proposed; the proposed controller has a master-slave structure where the slaves control the flow rates through the control structures. The master controller consists of PI-based controllers for feedback, and a decoupler and feedforward controller that are based on the inversion of a simple dynamic model of the canal system. The applicability of the controller is demonstrated in field experiments.     

Modified Sliding Mode Control for Wind-Excited Benchmark Problem

Among promising control strategies, the sliding mode control is particularly robust with respect to structural uncertainty. In this paper, a modified sliding mode control (MSMC) strategy using dynamic output feedback is presented and demonstrated for the wind-excited benchmark building equipped with an ATMD (active tuned mass damper) control device. The main advantage of the MSMC presented is its ability to systematically modulate the control effort through the introduction of a prefilter prior to the control force. For practical implementation of a MSMC using acceleration measurements at strategic locations, a Kalman–Bucy filter type of observer is designed based on the augmented system. Hence the sliding surface design is composed of the observer state, and the modulation of control forces can be achieved by forming an optimization problem with a linear quadratic objective function. As shown by the simulation results of the wind-excited benchmark building, the modified sliding mode controller indeed has the capability of systematically modulating the control force. Moreover, the remarkable performance of the MSMC demonstrates that the strategy presented is suitable for the wind-excited tall buildings.     

Implementation of Modal Control for Seismically Excited Structures using Magnetorheological Dampers

This paper proposes an implementation of modal control for seismically excited structures using magnetorheological (MR) dampers. Many control algorithms such as clipped-optimal control, decentralized bang-bang control, and the control algorithms based on Lyapunov stability theory have been adopted for semiactive systems including MR dampers. In spite of good features, some algorithms have drawbacks such as poor performance or difficulties in designing the weighting matrix of the controller. However, modal control reshapes the motion of a structure by merely controlling a few selected vibration modes. Hence a modal control scheme is more convenient to design the controller than other control algorithms. Although modal control has been investigated for several decades, its potential for semiactive control, especially for the MR damper, has not been exploited. Thus, in order to study the effectiveness for a MR damper system, a modal control scheme is implemented to seismically excited structures. A Kalman filter is included in a control scheme to estimate modal states from measurements by sensors. Three cases of the structural measurement are considered by a Kalman filter to verify the effect of each measurement; displacement, velocity, and acceleration, respectively. Moreover, a low-pass filter is applied to eliminate the spillover problem. In a numerical example, a six-story building model with the MR dampers on the bottom two floors is used to verify the proposed modal control scheme. The El Centro earthquake is used to excite the system, and the reduction in the drifts, accelerations, and relative displacements throughout the structure is examined. The performance of the proposed modal control scheme is compared with that of other control algorithms previously studied. The numerical results indicate that the motion of the structure is effectively suppressed by merely controlling a few lowest modes, although resulting responses varied greatly depending on the choice of measurements available and weightings.     

一种增量式PID控制器在结晶器水温控制中的应用

结合酒钢CSP薄板坯连铸机实际生产过程,考虑到浇铸过程中的安全及可靠性、水温调节大惯性等因素,给出了一种基于预设定和前馈的增量式PID调节控制器设计和实际应用。实践表明,该控制器对薄板坯连铸机的水温控制是安全、有效的,并适用于其他连铸机结晶器冷却水水温控制。     

Simple Optimal Downstream Feedback Canal Controllers: Theory

A new class of downstream water-level feedback controllers is proposed that can vary from a series of individual proportional-integral (PI) controllers (each gate adjusted based on one water level) to fully centralized controllers (each gate adjusted based on all water levels) that include the effects of lag time. The controller design method uses discrete-time state-feedback control with a quadratic penalty function, physically based states, and no state estimation. A simple, linear model of canal pool response, the integrator-delay model, is used to define the state transitions. All controllers within this class are tuned for the entire canal using optimization techniques. This avoids the tedious task of manually tuning simple controllers. The relative performance of the various controllers within this class can be directly compared without simulation, since the same objective function is used to tune each controller. An example is provided which suggests that the fully centralized controller will perform better than a series of local controllers. However, reasonably good performance can be obtained for some intermediate PI controllers that pass information to one additional check structure upstream and downstream. This should limit some of the difficulties reported for full optimal controllers where all check structures respond to water-level errors in all pools (e.g., saturation of inputs). The results of simulation studies of these controllers are provided in a companion paper.     

Salt River Project Canal Automation Pilot Project: Simulation Tests

The feasibility of automatically controlling water levels and deliveries on the Salt River Project (SRP) canal system through computer-based algorithms is being investigated. The proposed control system automates and enhances functions already performed by SRP operators, namely feedforward routing of scheduled demand changes, feedback control of downstream water levels, and flow control at check structures. Performance of the control system was tested with unsteady flow simulation. Test scenarios were defined by the operators for a 30 km, four-pool canal reach. The tests considered the effect of imperfect knowledge of check gate head-discharge relationships. The combined feedback-feedforward controller easily kept water level deviations close to the target when dealing with routine, scheduled flow changes. Those same routine changes, when unscheduled, were handled effectively by the feedback controller alone. The combined system had greater difficulty in dealing with large demand changes, especially if unscheduled. Because feedback flow changes are computed independently of feedforward changes, the feedback controller tends to counteract feedforward control actions. The effect is unimportant when dealing with routine flow changes but is more significant when dealing with large changes, especially in cases where the demand change cannot be fully anticipated.     

模糊PID控制在工业锅炉控制系统中的应用

针对工业锅炉控制系统的特点,采用将常规PID控制与模糊控制相结合的控制策略,在常规PID调节器的基础上,采用模糊推理思想,根据不同的E、EC对PID参数Kp、Ki、Kd进行自校正。对锅炉汽包液位的控制表明这种模糊PID控制器可明显提高系统的性能。     

基于状态观测器的线性离散时间系统的最优预见控制

研究了带有预见信息的线性离散时间系统的状态观测器,并将其应用到预见控制系统.为了满足设计观测器的需要,首先导出了包含可预见的目标值信号和干扰信号的扩大误差系统,并由此得到最优预见控制器.在设计状态观测器时,通过改写输出方程充分利用了可预见的目标值信号和干扰信号.设计的状态观测器针对原系统是全维观测器,而针对扩大误差系统则是降维观测器.最后通过数值仿真证明了所设计的状态观测器的有效性.      

Simple Optimal Downstream Feedback Canal Controllers: ASCE Test Case Results

In a companion paper, a class of downstream-water-level feedback canal controllers was described. Within this class, a particular controller is chosen by selecting which controller coefficients to optimize (tune), the remaining coefficients being set to zero. These controllers range from a series of simple proportional-integral (PI) controllers to a single centralized controller that considers lag times. In this paper, several controllers within this class were tuned with the same quadratic performance criteria (i.e., identical penalty functions for optimization). The resulting controllers were then tested through unsteady-flow simulation with the ASCE canal automation test cases for canal 1. Differences between canal and gate properties, as simulated and as assumed for tuning, reduced controller performance in terms of both water-level errors and gate movements. The test case restrictions placed on minimum gate movement caused water levels to oscillate around their set points. This resulted in steady-state errors and much more gate movement (hunting). More centralized controllers handle unscheduled flow changes better than a series of local PI controllers. Controllers that explicitly account for pool wave travel times did not improve control as much as expected. Sending control actions within a given pool to upstream pools improved performance, but caused oscillations in some cases, unless control signals were also sent downstream. A good compromise between controller performance and complexity is provided by controllers that pass feedback from a given water level to the check structure at the upstream end of its pool (i.e., that used for downstream control of an individual pool) and to all upstream and one downstream check structures.     

Experiments on a Full-Scale Building Model using Modified Sliding Mode Control

This paper presents a modified sliding mode control (MSMC) method using acceleration feedback to reduce the response of seismic-excited civil buildings. A pre-filter is introduced prior to the control command so that a systematic trade-off between control and structural responses can be achieved. To demonstrate practical implementation of MSMC controllers, extensive shake table experimental tests have been conducted on a full-scale three-story building equipped with active bracing systems at the National Center for Research on Earthquake Engineering, Taiwan. To improve the effectiveness of active control, a nominal system that incorporates the control–structure interaction effect is used in the MSMC controller design. In addition, existing system uncertainties in the nominal system resulting from system identification are considered in the process of controller design and the robustness of control performance and stability is demonstrated through shake table experiments. Experimental results indicate that the MSMC strategy using acceleration feedback for the full-scale building is robust and its performance is quite remarkable. Furthermore, the numerical simulation based on an analytical model that was identified previously by taking into account the control–structure interaction effect was conducted and comparisons are made with the experimental results. It is shown that the correlation between numerical simulation results and experimental data is quite excellent.     

Hydraulic Modeling of a Mixed Water Level Control Hydromechanical Gate

This article describes the hydraulic behavior of a mixed water level control hydromechanical gate present in several irrigation canals. The automatic gate is termed “mixed” because it can hold either the upstream water level or the downstream water level constant according to the flow conditions. Such a complex behavior is obtained through a series of side tanks linked by orifices and weirs. No energy supply is needed in this regulation process. The mixed flow gate is analyzed and a mathematical model for its function is proposed, assuming the system is at equilibrium. The goal of the modeling was to better understand the mixed gate function and to help adjust their characteristics in the field or in a design process. The proposed model is analyzed and evaluated using real data collected on a canal in the south of France. The results show the ability of the model to reproduce the function of this complex hydromechanical system. The mathematical model is also implemented in software dedicated to hydraulic modeling of irrigation canals, which can be used to design and evaluate management strategies.     

Sequential ideal-observer analysis of visual discriminations.

Visual stimuli contain a limited amount of information that could potentially be used to perform a given visual task. At successive stages of visual processing, some of this information is lost and some is transmitted to higher stages. This article describes a new analysis, based on the concept of the ideal observer in signal detection theory, that allows one to trace the flow of discrimination information through the initial physiological stages of visual processing, for arbitrary spatio-chromatic stimuli. This ideal-observer analysis provides a rigorous means of measuring the information content of visual stimuli and of assessing the contribution of specific physiological mechanisms to discrimination performance. Here, the analysis is developed for the physiological mechanisms up to the level of the photoreceptor. It is shown that many psychophysical phenomena previously attributed to neural mechanisms may be explained by variations in the information content of the stimuli and by preneural mechanisms. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Control of Suspension Bridge Nonlinear Vibrations due to Moving Loads

The flexibility and low damping of the long-span suspended cables in the suspension bridges make them prone to vibrations due to wind and moving loads, which affect the dynamic response of the suspended cables and the bridge deck. This paper shows the design of two control schemes to control the nonlinear vibrations in the suspended cable and the bridge deck due to a vertical load moving on the bridge deck with a constant speed. The first control scheme is an optimal state feedback controller. The second control scheme is a robust state feedback controller, whose design is based on the design of optimal controllers. The proposed controllers, whose design is based on Lyapunov theory, guarantee the asymptotic stability of the system. A vertical cable between the bridge deck and the suspended cable is used to install a hydraulic actuator able to generate the active control force on the bridge deck. The MATLAB software is used to simulate the performance of the system with the designed controllers. The simulation results indicate that the proposed controllers are capable of significantly reducing the nonlinear oscillations of the system. In addition, the performance of the system with the proposed controllers is compared to the performance of the system controlled with a velocity feedback controller. It is found that the system with the proposed controllers can provide better performance than the system with the velocity feedback controller.     

基于前馈-串级控制的锅炉汽包水位控制系统

为改善设备控制效果、降低故障率,在某冶炼厂65 t/h锅炉汽包水位前馈-串级控制系统中,用变频水泵代替传统的流量调节阀,同时采用Profibus-DP现场总线技术构建整个控制系统,使之具有一定的先进性和实用性。本文主要介绍其实现方法及应用软件的开发,包括编程组态方法、监控界面设计、参数整定等。调试运行表明,该系统稳定可靠,控制效果良好。     

Case Study: Model to Simulate Regional Flow in South Florida

South Florida has a complex regional hydrologic system that consists of thousands of miles of networked canals, sloughs, highly pervious aquifers, open areas subjected to overland flow and sheet flow, agricultural areas and rapidly growing urban areas. This region faces equally complex problems related to water supply, flood control, and water quality management. Advanced computational methods and super fast computers alone have limited success in solving modern day problems such as these because the challenge is to model the complexity of the hydrologic system, while maintaining computational efficiency and acceptable levels of numerical errors. A new, physically based hydrologic model for South Florida called the regional simulation model (RSM) is presented here. The RSM is based on object oriented design methods, advanced computational techniques, extensible markup language, and geographic information system. The RSM uses a finite volume method to simulate two-dimensional (2D) surface and groundwater flow. It is capable of working with unstructured triangular and rectangular mesh discretizations. The discretized control volumes for 2D flow, canal flow and lake flow are treated as abstract “water bodies” that are connected by abstract “water movers.” The numerical procedure is designed to work with these and many other abstractions. An object oriented code design is used to provide robust and highly extensible software architecture. A weighted implicit numerical method is used to keep the model fully integrated and stable. A limited error analysis was carried out and the results were compared with analytical error estimates. The paper describes an application of the model to the L-8 basin in South Florida and the strength of this approach in developing models over complex areas.     

Active Control of Cross Wind Response of 76-Story Tall Building Using a Fuzzy Controller

This paper focuses on the benchmark problem application regarding the vibration control of tall buildings under cross wind excitation. The building under consideration is the 76-story, 306-m tall reinforced concrete office tower proposed for the city of Melbourne, Australia. The adopted control scheme consists of an active tuned mass damper (ATMD) where the control action is achieved by a fuzzy logic controller (FLC). The main advantage of the FLC is its inherent robustness and ability to handle any nonlinear behavior of the structure and the fact that its implementation does not require a mathematical model of the structure. This benchmark study is based on specified design constraints for the ATMD to be considered in the design of the proposed control scheme. The performance of the controller has been demonstrated through the uncertainty in stiffness (+15 and ?15% variation from initial stiffness) of the building. The results of the simulation show a good performance by the fuzzy controller for all cases tested. Also the results show that the fuzzy controller performance is similar to the linear quadratic Gaussian (LQG) controller, while possessing several advantages over the LQG controller.     

Case Study: Modeling Tidal Transport of Urban Runoff in Channels Using the Finite-Volume Method

A coupled flow and pollutant transport model based on the finite-volume method is developed and applied to predict the tidal transport of urban runoff in a southern California network of flood control channels that drain to near-shore bathing waters. Urban runoff in southern California contains elevated levels of indicator bacteria that signal the presence of fecal pollution and pose a risk to human health, and model predictions are used to understand the transport of these pollutants toward the coastline. The model is based on 1D conservation equations for fluid mass, momentum, and pollutant mass that are solved in integral form along channel reaches. A 2D formulation is solved at channel junctions. The model incorporates the monotone upwind scheme for conservation laws approach to give a high-resolution, nonoscillatory prediction of water level, velocity, and pollutant concentration. Model predictions and field measurements of water level, velocity, and a conservative urban runoff tracer are presented and compare favorably. This case study demonstrates that this finite-volume method–based scheme results in an accurate, stable, nonoscillatory and computationally manageable model. The nonoscillatory behavior is particularly beneficial in this study, since runoff enters the channels in pulses that create large gradients in pollutant concentration.     

Automatic Downstream Water-Level Feedback Control of Branching Canal Networks: Theory

Most of the research on the design of feedback controllers for irrigation canals has been concentrated on single, in-line canals with no branches. Because the branches in a network are hydraulically coupled with each other, it may be difficult to automatically control a branching canal network by designing separate feedback controllers for each branch and then letting them run simultaneously. Thus feedback control of an entire branching canal system may be more efficient if the branching flow dynamics are explicitly taken into account during the feedback controller design process. This paper develops two different feedback controllers for branching canal networks. The first feedback controller was developed using linear quadratic regulator theory and the second using model predictive control. Both algorithms were able to effectively control a simple branching canal network example with relatively small flow changes.     

确定性多变量自校正控制的稳定性、收敛性和鲁棒性

本文用基于传递函数概念的虚拟等价系统方法统一分析各种类型的多变量确定性自校正控制系统的稳定性、收敛性和鲁棒性,分别针对参数估计收敛到真值、参数估计收敛到非真值以及参数估计不收敛的3种情况给出若干定理、推论和注释.在各个判据的基础上,进一步深化对确定性多变量自校正控制系统的理解.所得结论说明:参数估计的收敛性不是确定性多变量自校正控制系统稳定和收敛的必要条件;系统自身的反馈信息对确定性多变量自校正控制是充分的,即外加激励信号不是必要的.