Optimal maintenance of multi-component systems: a review

In this article we give an overview of the literature on multi-component maintenance optimization. We focus on work appearing since the 1991 survey "A survey of maintenance models for multi-unit systems" by Cho and Parlar. This paper builds forth on the review article by Dekker et al. (1996), which focusses on economic dependence, and the survey of maintenance policies by Wang (2002), in which some group maintenance and some opportunistic maintenance policies are considered. Our classification scheme is primarily based on the dependence between components (stochastic, structural or economic). Next, we also classify the papers on the basis of the planning aspect (short-term vs long-term), the grouping of maintenance activities (either grouping preventive or corrective maintenance, or opportunistic grouping) and the optimization approach used (heuristic, policy classes or exact algorithms). Finally, we pay attention to the applications of the models.literature review;economic dependence;failure interaction;maintenance policies;grouping maintenance;multi-component systems;opportunistic maintenance;maintencance optimization;structural dependence

Spletna aplikacija za optimizacijo hierarhične organizacijske strukture

Background and Purpose: In a complex strictly hierarchical organizational structure, undesired oscillations may occur, which have not yet been adequately addressed. Therefore, parameter values, which define fluctuations and transitions from one state to another, need to be optimized to prevent oscillations and to keep parameter values between lower and upper bounds. The objective was to develop a simulation model of hierarchical organizational structure as a web application to help in solving the aforementioned problem. Design/Methodology/Approach: The hierarchical structure was modeled according to the principles of System Dynamics. The problem of the undesired oscillatory behavior was addressed with deterministic finite automata, while the flow parameter values were optimized with genetic algorithms. These principles were implemented as a web application with JavaScript/ECMAScript. Results: Genetic algorithms were tested against well-known instances of problems for which the optimal analytical values were found. Deterministic finite automata was verified and validated via a three-state hierarchical organizational model, successfully preventing the oscillatory behavior of the structure. Conclusion: The results indicate that the hierarchical organizational model, genetic algorithms and deterministic finite automata have been successfully implemented with JavaScript as a web application that can be used on mobile devices. The objective of the paper was to optimize the flow parameter values in the hierarchical organizational model with genetic algorithms and finite automata. The web application was successfully used on a three-state hierarchical organizational structure, where the optimal flow parameter values were determined and undesired oscillatory behavior was prevented. Therefore, we have provided a decision support system for determination of quality restructuring strategies.Ozadje in namen: V kompleksnih striktnih hierarhičnih organizacijskih strukturah se lahko pojavijo neželene oscilacije stanj, kar do sedaj še ni bilo zadovoljivo naslovljeno. Da preprečimo neželene oscilacije je potrebno optimirati vrednosti parametrov, ki določajo prehode med stanji strukture in fluktuacije iz stanj. Hkrati je potrebno obdržati vrednosti parametrov znotraj določenih meja. Cilj je bil razviti simulacijski model hierarhične organizacijske strukture v obliki spletne aplikacije, ki bi pomagal pri reševanju prej omenjenega problema. Metodologija: Hierarhična struktura je bila modelirana po principih sistemske dinamike. Problem neželenih oscilacij je bil naslovljen z uporabo determinističnega končnega avtomata, medtem ko smo vrednosti parametrov pretoka optimirali z genetskimi algoritmi. Vsi omenjeni pristopi so bili implementirani kot spletna aplikacija z JavaScript/ECMAScript programskim jezikom. Rezultati: Genetski algoritmi so bili testirani na znanih problemskih instancah za katere so znane optimalne analitične rešitve. Deterministični končni avtomat je bil verificiran in validiran na hierarhičnem organizacijskem modelu s tremi stanji, kjer smo z njegovo uporabo uspeli preprečiti oscilacije v organizacijski strukturi. Zaključek: Rezultati nakazujejo, da smo uspešno implementirali hierarhični organizacijski model, genetske algoritme in deterministični končni avtomat z JavaScript programskim jezikom v obliki spletne aplikacije, ki se lahko uporablja na mobilnih napravah. Razvito spletno aplikacijo smo uspešno uporabili na hierarhičnem organizacijski strukturi s tremi stanji, kjer smo določili optimalne parametre pretoka in fluktuacij ter preprečili neželene oscilacije stanj. S tem smo zagotovili sistem za podporo odločanju, ki omogoča določanje kakovostnih strategij za prestrukturiranje organizacij

A greedy heuristic approach for the project scheduling with labour allocation problem

Responding to the growing need of generating a robust project scheduling, in this article we present a greedy algorithm to generate the project baseline schedule. The robustness achieved by integrating two dimensions of the human resources flexibilities. The first is the operators’ polyvalence, i.e. each operator has one or more secondary skill(s) beside his principal one, his mastering level being characterized by a factor we call “efficiency”. The second refers to the working time modulation, i.e. the workers have a flexible time-table that may vary on a daily or weekly basis respecting annualized working strategy. Moreover, the activity processing time is a non-increasing function of the number of workforce allocated to create it, also of their heterogynous working efficiencies. This modelling approach has led to a nonlinear optimization model with mixed variables. We present: the problem under study, the greedy algorithm used to solve it, and then results in comparison with those of the genetic algorithms

A model for cost efficient Workforce Organizational Dynamics and its optimization

This paper presents a workforce planning model scalable to an entire hierarchical organization. Its main objective is to design a cost optimal target which leverages flexible workforce solutions while ensuring an efficient promotional flux. The value of this paper lies in its proposal of an adequate flexibility rate using various solution types and in its discussion about external hiring ratios. The mathematical structures of the models are analyzed and numerical simulations illustrate the theoretical background

Aerospace design: a complex task

These lecture notes, prepared for the 1997 VKI Lecture Course on Inverse Design, identify some of the complexities inherent in the design of aeroengines and aircraft. It is argued that to handle the geometric complexities requires a computational representation which is hierarchical and based on parametric solids at the lowest level. On top of this can be built a tightly coupled two-level design system which uses an integrated set of multidisciplinary analysis packages which are also hierarchical, with differing levels of approximation and computational cost appropriate to preliminary design and detailed component design. \ud \ud A range of different numerical approaches to design are outlined, and their strengths and weaknesses are compared. Other related topics such as distributed computing, risk management and strategic research planning are also discussed

System and Decision Sciences at IIASA 1973-1980

This report contains a brief history of the past achievements of the System and Decision Sciences Area at IIASA, and a summary of its current and future research directions. There is a comprehensive list of the scientific staff of the Area since 1973, together with a list of their publications; abstracts of the most recent reports and biographies of the scholars working in the Area in 1980 are also included

Store-and-forward based methods for the signal control problem in large-scale congested urban road networks

The problem of designing network-wide traffic signal control strategies for large-scale congested urban road networks is considered. One known and two novel methodologies, all based on the store-and-forward modeling paradigm, are presented and compared. The known methodology is a linear multivariable feedback regulator derived through the formulation of a linear-quadratic optimal control problem. An alternative, novel methodology consists of an open-loop constrained quadratic optimal control problem, whose numerical solution is achieved via quadratic programming. Yet a different formulation leads to an open-loop constrained nonlinear optimal control problem, whose numerical solution is achieved by use of a feasible-direction algorithm. A preliminary simulation-based investigation of the signal control problem for a large-scale urban road network using these methodologies demonstrates the comparative efficiency and real-time feasibility of the developed signal control methods

Optimal maintenance of multi-component systems: a review

In this article we give an overview of the literature on multi-component maintenance optimization. We focus on work appearing since the 1991 survey "A survey of maintenance models for multi-unit systems" by Cho and Parlar. This paper builds forth on the review article by Dekker et al. (1996), which focusses on economic dependence, and the survey of maintenance policies by Wang (2002), in which some group maintenance and some opportunistic maintenance policies are considered. Our classification scheme is primarily based on the dependence between components (stochastic, structural or economic). Next, we also classify the papers on the basis of the planning aspect (short-term vs long-term), the grouping of maintenance activities (either grouping preventive or corrective maintenance, or opportunistic grouping) and the optimization approach used (heuristic, policy classes or exact algorithms). Finally, we pay attention to the applications of the models