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System Performance Measure (system + performance_measure)

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Engineering50%

Selected Abstracts

Robust quadratic performance for time-delayed uncertain linear systems

INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 2 2003
Fen WuArticle first published online: 20 DEC 200
Abstract In this paper, the analysis and control synthesis problems were studied for a general class of uncertain linear systems with variable time delay. It is assumed that the structured time-varying parametric uncertainties enter the system state-space description in a linear fractional fashion. The generic quadratic performance metric encompasses many types of dynamic system performance measure. In the context of delay-independent stability, it was shown that the analysis and state-feedback synthesis problems for such time-delayed uncertain systems can be formulated equivalently as linear matrix inequality (LMI) optimization problems using the mechanism of full block multipliers. However, the solvability condition to output-feedback problem was given as bilinear matrix inequality (BMI), which leads to a non-convex optimization problem. A numerical example is provided to demonstrate the advantages of newly proposed control synthesis condition for time-delayed uncertain systems over existing approaches. Copyright © 2002 John Wiley & Sons, Ltd. [source]

A new approach to solving problems of multi-state system reliability optimization

QUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 2 2001
Gregory Levitin
Abstract Usually engineers try to achieve the required reliability level with minimal cost. The problem of total investment cost minimization, subject to reliability constraints, is well known as the reliability optimization problem. When applied to multi-state systems (MSS), the system has many performance levels, and reliability is considered as a measure of the ability of the system to meet the demand (required performance). In this case, the outage effect will be essentially different for units with different performance rate. Therefore, the performance of system components, as well as the demand, should be taken into account. In this paper, we present a technique for solving a family of MSS reliability optimization problems, such as structure optimization, optimal expansion, maintenance optimization and optimal multistage modernization. This technique combines a universal generating function (UGF) method used for fast reliability estimation of MSS and a genetic algorithm (GA) used as an optimization engine. The UGF method provides the ability to estimate relatively quickly different MSS reliability indices for series-parallel and bridge structures. It can be applied to MSS with different physical nature of system performance measure. The GA is a robust, universal optimization tool that uses only estimates of solution quality to determine the direction of search. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Analyzing the Trade-off Between Investing in Service Channels and Satisfying the Targeted User Service for Brazilian Internet Service Providers

INTERNATIONAL TRANSACTIONS IN OPERATIONAL RESEARCH, Issue 3 2002
Gisele C. Fontanella
The computer connection to the Internet is provided by firms known as internet service providers (ISPs). The simplest mode of physical connection is when the user connects to an ISP's service channel by an ordinary telephone line (dial-up). Finding an available channel may not be an easy task, especially during the peak hours of many Brazilian ISPs. This results in a problem for the ISPs, which is how to achieve the most appropriate trade-off between investing in capacity and satisfying the target user service level. This paper analyzes this trade-off based on a three-step approach: (i) determine user arrival and service processes in chosen periods, (ii) select an appropriate queueing model using some simplifying assumptions, and (iii) generate trade-off curves between system performance measures. To illustrate the application of this approach, some results derived from a case study performed at an ISP in Sao Paulo state are given. [source]

Modelling a general standby system and evaluation of its performance

APPLIED STOCHASTIC MODELS IN BUSINESS AND INDUSTRY, Issue 2 2008
Ji Hwan Cha
Abstract Redundancy or standby is a technique that has been widely applied to improving system reliability and availability in system design. In this paper, a general method for modelling standby system is proposed and system performance measures are derived. It is shown that the proposed general standby system includes the cases of cold, hot and warm standby systems with units of exponential distribution, which were studied in the literature, as special cases. An optimal allocation problem for a standby system is also discussed. Copyright © 2007 John Wiley & Sons, Ltd. [source]