TRACKING DOMAINS FOR UNSTABLE PLANTS WITH SATURATING-LIKE ACTUATORS

In many mechanical systems, the tracking control is one of the most important issues. Therefore for the unstable system subject to actuator saturation, the domain of the initial states corresponding to an arbitrary reference signal, within which tracking condition can be achieved, is interesting to be considered. In this paper, an approximate tracking domain is derived analytically. First in Theorem 1, for simple case, it is constructed by using the partial Lyapunov function and the absolute stability theory. In the following Theorems 2 and 3, a new idea is used to obtain larger domains. Finally in the last section, a simple numerical example is given.     

Switching‐based state tracking of model reference adaptive control systems in the presence of intermittent failures of all actuators

This paper investigates the state tracking problem for a class of model reference adaptive control systems with intermittent failures of all actuators. We consider the case that all actuators may suffer failures simultaneously. The concepts of failure frequency and unavailability rate are introduced to describe the failures. Because of the actuator failures, the error system is modeled as a switched system. Then, the notion of global practical stability of switched systems is presented, and sufficient conditions are provided to guarantee the global practical stability of the error system. An example of HiMAT vehicle and the simulation results demonstrate the feasibility and effectiveness of the proposed design method. Copyright © 2013 John Wiley & Sons, Ltd.     

住宅工程裂缝和渗漏的成因及防治

住宅工程质量关系人民群众的切身利益,关系社会和谐。文章针对目前合肥地区住宅工程存在的主要质量通病——裂缝和渗漏的情况进行了统计分析,着重就渗漏防治措施从材料、设计、施工、监理等方面进行了较为详细的阐述。     

Collapse of Suspended Portland Cement Plaster Stucco Soffit

The collapse of a suspended soffit consisting of portland cement plaster stucco on metal lath was investigated to determine the probable cause of collapse after over 30 years of service. Soffits of this type are often constructed with minimal, if any, details provided by the project architect or engineer. Without design guidance, the builder usually relies on typical industry practices and prior experience to construct these soffits. While experience may result in a safe installation in many instances, long-term performance without distress is no guarantee that no defects exist.     

Analysis of long flow lines with quality and operational failures

This paper presents approximation methods for the performance analysis of long manufacturing lines, i.e. lines with more than two machines and one buffer, that have both quality and operational failures. We describe three different versions of long flow lines that differ in the locations of the inspection stations and in the sets of machines that each inspection station monitors. We explain a transformation method that approximates long manufacturing lines that have quality and operational failures with long lines that only have operational failures. Such lines can be evaluated by decomposition methods. We introduce other approximations to quantify the effects of the separation of inspections from operations. Comparison with simulation shows that the solution methods provide reliable performance estimates.     

Analysis of Causes of Falsework Failures in Concrete Structures

A study of 85 major falsework collapses of bridges and buildings in the past 23 yrs has documented the types of collapsed falseworks and failed permanent structures, the construction stages at the time of collapse, and the causes of failures. Three causes of failure were identified: triggering; enabling; and procedural causes. Most failures occurred because of the interaction of the triggering and enabling events that were, in many cases, produced by inadequacies in the procedural methods. Impact forces resulting from concreting operations have repeatedly triggered falsework failures that were enabled by deficiencies in the falsework bracings, components, connections, foundations, and design. Inadequate review of falsework design and monitoring procedures were frequent problems that facilitated the occurrernce of these events. The findings emphasize the importance of proper delineation of responsibility of each party in the building process in order to reduce falsework failures in the future.     

具有不确定性的主从机械手自适应模糊控制

针对具有不确定性且存在执行器未知约束的遥操作机器人系统，研究自适应模糊轨迹跟踪控制方案。该方案无需精确建立机器人遥操作系统的动力学模型，也不需要测量机械臂末端的运动参数与末端受到的外力。通过自适应模糊系统逼近未知的机器人动力学模型，利用运动学参数线性化特性构建预估机器人雅可比矩阵，辅以参数更新律实现跟踪目标的近似表示。此外，通过采用Nussbaum函数处理执行器受到的输入约束实现输入约束补偿。针对遥操作机器人系统主从端受到的相互作用力，借助自适应模糊系统，在控制律中添加模糊项实现对相互作用力的逼近，从而实现更为稳定、精确的轨迹跟踪。通过李亚普诺夫稳定性理论证明了闭环动力学系统是有界的，且位置误差收敛于零，仿真试验进一步证明了理论方案的有效性。     

Latency and mode of error detection in a process industry

Licensee event reports (LERs) from an industry provide important information feedback about safety to the industry itself, the regulators and to the public. LERs from four nuclear power reactors were analyzed to find out about detection times, mode of detection and qualitative differences in reports from different reactors. The reliability of the codings was satisfactory and measured as the covariance between the ratings from two independent judges. The results showed differences in detection time across the reactors. On the average about 10% of the errors remained undetected for 100 weeks or more, but the great majority of errors were detected soon after their first appearance in the plant. On the average 40% of the errors were detected in regular tests and 40% through alarms. Operators found about 16% of the errors through noticing something abnormal in the plant. The remaining errors were detected in other ways. There were qualitative differences between the LERs from the different reactors reflecting the different conditions in the plants. The number of reports differed by a magnitude 1:2 between the different plants. However, a greater number of LERs can indicate both higher safety standards (e.g. a greater willingness to report all possible events to be able to learn from them) and lower safety standards (e.g. reporting as few events as possible to make a good impression). It was pointed out that LERs are indispensable in order to maintain safety of an industry and that the differences between plants found in the analyses of this study indicate how error reports can be used to initiate further investigations for improved safety.     

Transient behavior of time‐between‐failures of complex repairable systems

It is well known for complex repairable systems (with as few as four components), regardless of the time‐to‐failure (TTF) distribution of each component, that the time‐between‐failures (TBFs) tends toward the exponential. This is a long‐term or ‘steady‐state’ property. Aware of this property, many of those modeling such systems tend to base spares provisioning, maintenance personnel availability and other decisions on an exponential TBFs distribution. Such a policy may suffer serious drawbacks. A non‐homogeneous Poisson process (NHPP) accounts for these intervals for some time prior to ‘steady‐state’. Using computer simulation, the nature of transient TBF behavior is examined. The number of system failures until the exponential TBF assumption is valid is of particular interest. We show, using a number of system configurations and failure and repair distributions, that the transient behavior quickly drives the TBF distribution to the exponential. We feel comfortable with achieving exponential results for the TBF with 30 system failures. This number may be smaller for configurations with more components. However, at this point, we recommend 30 as the systems failure threshold for using the exponential assumption. Copyright © 2002 John Wiley & Sons, Ltd.