Optimization of stochastic maintenance policies

The present study examines various inspection policy models, also known in reliability literature as preparedness models. These types of models deal with stochastically failing systems, in which failure is detected by inspection only. The present study deals with two yet unsolved problems in the field of maintenance preparedness models. The first is the analysis of various models and various objective functions while taking into consideration a positive discount factor. The second is the analysis of those models while the maintenance costs are varying in one way or another during the period of optimization. Different modes of inspection of both pure and mixed strategies are analyzed. The objective functions are set forth and solved by both a differentiation method and a dynamic programming approach.     

A characteristic line based method to build finite-dimensional medoels of heat exchangers

surface heat exchngers are typical simulated with simplified models obtained through segmentation of the heat exchanging fluid path in a number of consecutive lumps In order to aviod major drawbacks of this approach, which may be very misleading for control design purpose, we propose a method, based on the intergration of the PDE system by the method of characteristic lines, for the construction of numerical heat exchangers models. It can be proved that the time response of such new models is indeed rid of parasitic oscillation and suitable for the understanding of complex dynamic phenomena occurring and suitable for the understanding of complex dynamic phenomena occurring in long residence time heat exchangers, both with one- and two- phase flow. In this paper, particular attention is paid to the problem of generating finite dimensional dynamic system by application of the characteristic lines method and computing the frequency responce of such models. Actually, since the characteristic lines method is not naturally is not straightforward to define Finally, the accuracy of CL models is compared with classical models of comparable complexity, with special reference to real application cases, taken from the power generation field.     

A System Dynamics Model of Submarine Operations and Maintenance Schedules

The extent to which a proposed military force will achieve operational objectives is a prime concern of defence planners. This paper discusses the problem in the context of the exercise of sea power in distant waters and shows that a model of the whole problem would require a feedback analysis, for which an appropriate approach would be system dynamics. Such models have, in general, been continuous, but ships are discrete objects. The paper therefore addresses the construction of discrete system dynamics models as the basis for a model of the whole problem. Two models of a submarine force are presented. The first deals with the construction and major refit programmes, to evaluate the periods of fleet service availability achievable from a submarine force of a given size. The second examines unit usage during periods of fleet service.     

Defence operational analysis using system dynamics

This paper reflects on experiences gained in applying system dynamics as a modelling methodology to create a feedback perspective of army defence situations. The ideas of the approach are outlined, and a case study model presented to demonstrate the type of insight which can be generated by the method. This example is further used to make a comparison between system dynamics and other methods of defence operational analysis.     

Team-based reconstruction for expanding organisational ability

Organisations can be interpreted as a collection of actors who produce value for clients. In order for organisations to stay competitive there is a need for organisations to continuously develop their ability. An organisation's ability is determined by its ability to effectively apply existing knowledge to create new knowledge and to take action that forms the basis for achieving competitive advantage from knowledge-based assets. One means for developing the organisational ability is to establish a mutually accepted understanding of the context in which the actors are acting. One important part of the organisation's knowledge creation processes is to facilitate the sharing of personal knowledge. A condition for developing the organisational ability is to expand the amount of shared knowledge to an appropriate level. One type of knowledge that needs to be shared among different actors within the organisation is the knowledge about how and in which order actions are performed (contextual knowledge) in order to satisfy client needs. In this paper an approach for team-based reconstruction, used for moving from personal to shared contextual knowledge, is presented. The approach bears on the foundation of theories about knowledge management for understanding the process of externalisation and theories about language action for understanding organisations. Experiences from three case studies are presented. Team-based reconstruction can be used for (1) moving from personal knowledge to shared contextual knowledge in an efficient way, (2) arriving at a foundation for efficient organisational coordination, (3) arriving at a base for development work, and (4) organisational learning.     

A clone-based graphical modeler and mathematical model generator for optimal production planning in process industries

This paper outlines a visually interactive graphical modeling approach for process type production systems, with hidden generation of complex optimization models for production planning. The proposed system lets the users build a graphical model of the production system with one-to-one clones of its production units through its interactive visual interface, accepts production-specific data for its components, and finally, internally generates and solves its mathematical programming model without any interaction from the user. This “clone-based” modeling approach allows the continued use of optimization models with minimal mathematical programming understanding, as generation of mathematical model by clones is hidden and automatic, therefore maintenance-free: Updating graphical production system models is enough for renewing internal optimization models. The concept is demonstrated in this paper with a linear programming prototype developed for a petroleum refinery.     

A comparison of ratios and fractions and their roles as tools in proportional reasoning

In an attempt to develop our shared understanding of the relationship between ratios and fractions, we began a phenomenological study to gather evidence from teachers and textbooks and to collect evidence from our own experiences. In this article, we present five possible models for this relationship and a summary of evidence to support each. We also present the model that we developed to represent our shared understanding and provide the results of a study for which we have used our model to help us analyze students’ uses of ratios and fractions in their solutions to proportion-related problems.     

Simultaneous engineering approach to an integrated design and process planning

To support integration of design and process planning, a reference model has been developed. This reference model represents the basis for a new methodology for integrated design and process planning which enables a Simultaneous Engineering approach in the early stages of product development. The reference model consists of four partial models. These are the activity model, the information model, the technical system model and the model of integrating methods. Using these models, the methodology enables a concurrent processing of design and process planning activities with regard to different components of a product. Furthermore, the methodology covers planning methods as well as execution methods, to support early transmission of information to downstream activities and a feedback of information to upstream activities within the process chain of design and process planning.     

Developing a risk-assesment methodology in the U.K.defence industry

As a leading defence equipment company, the Dynamics Divisionof British Aerospace Defence Company (BAeDef(DD)) has experiencedthe worst effects of post-Coldwar defence cuts, a global recession,and a determination by the U.K. Government to achieve greatervalue for money in defence procurement. The major tenet of thisnew approach to defence prwurement was 'eyes on, hands off',promoting a shift of the management of project risks from theMinistry of Defence (MOD) to industry. Initial industry reactionwas sceptical but bxame increasingly compliant as tenderingrequirements included visibility of contractors' risk assessment.This paper describes the risk-assessment methodology createdby BAeDef(DD) to meet these changed conditions. The human and organizational aspects of these developments onrisk have helped create a pro-active risk-management cultureat BAeDef(DD). Continuous assessment of project risks providesthe impetus for wider thinking beyond risk-taking or risk-aversionpreferences, leading to greater realism in planning. Decisionsto implement risk resolution measures require competence incost-benefit analysis. The conditions to foster this new behaviourare better-informed senior management, with the rejection ofbad news eliminated at all levels, and the laying of a pathto becoming a learning company.     

Compound negative binomial shared frailty models for bivariate survival data

In this paper, we introduce a new shared frailty model called the compound negative binomial shared frailty model with three different baseline distributions namely, Weibull, generalized exponential and exponential power distribution. To estimate the parameters involved in these models we adopt Markov Chain Monte Carlo (MCMC) approach. Also we apply these three models to a real life bivariate survival data set of McGrilchrist and Aisbett (1991) related to kidney infection and suggest a better model for the data.     

Validation of the mission-based approach to representing command and control in simulation models of conflict

There is a need to represent military command and control in closed-form simulation models of conflict, in order to compare investment in such capability with alternative defence investments. This paper considers such representation of military command and control in the context of embodied cognitive science. This means that we represent such processes in terms of both decision-making and resultant behaviour. Previous work leads to the view that such a representation can be captured by a combination of deliberate (top down) planning and rapid (bottom up) planning. We have developed an approach on these lines as a way of representing human decision-making and behaviour in conflict. Here we show, by comparing simulation model results with real conflict situations, that our approach yields emergent force behaviour which is valid and representative. This thus increases our confidence that our representation of command and control in such simulation models is sufficient for our requirements.     

Representing the command and control process in simulation models of conflict

Command and Control is the process by which military personnel in war command their forces to take account of military aims and objectives. Across NATO, there is a growing realisation that the proper representation of Command and Control (C2) in models of conflict is very important. Since it essentially concerns itself with the representation of human decision-making, this is recognised as one of the most difficult areas for defence analysis. One approach to this problem is through the use of large rule-based expert systems. The work reported here lays out an alternative approach founded on the use of Bayesian inference and transitions between different mission ‘states’, leading to what we call the the mission based approach to Command and Control. These ideas are already being incorporated into the next generation of simulation models currently under development which range across the land/air, maritime and peacekeeping areas of application.     

An integrated algebraic approach to conflict resolution with three-level preference

An integrated algebraic approach is developed to calculate stabilities in multiple decision maker graph models with three levels of preference. The algebraic approach establishes an integrated paradigm for stability analysis and status quo analysis under different preference structures, such as two-level preference and three-level preference. Difficulties in coding algorithms to analyze stabilities, rooted in their logical representation, led to the development of matrix representations of preference and explicit matrix calculations to determine stabilities. Here, the algebraic approach is used to represent graph models with three levels of preference and to conduct stability analysis for such models. The algebraic approach facilitates the development of new stability concepts and algorithms to calculate them, and reveals an inherent link between status quo analysis and traditional stability analysis. Hence, it will facilitate the design of an integrated decision support system for the graph model for conflict resolution.     

Interpretation by Implementation for Understanding a Multiagent Organization

This paper stresses the importance of focusing on the modeling process of computational models for precisely understanding a complex organization and for solving given problems in the organization. Based on our claim, we proposes a method of interpretation by implementation (IbI), which explores factors that drastically change simulation results through an investigation on the modeling process of computational models. A careful investigation on the capabilities of the IbI approach, which comprises the three methods of (a) breakdown and representation, (b) assumption or premise modification, and (c) layer change investigation, derives the following conclusions: (1) the IbI approach has the potential of finding underlying factors that determine the characteristics of an organization; (2) the IbI approach can specify points of attention at necessary levels when analyzing an organization; and (3) the IbI approach has suchadvantages as wide applicability, the effective use of employed models, and KISS principle support.     

A robust disaster preparedness model for effective and fair disaster response

Humanitarian network design decisions belonging to the preparedness stage of disaster management life-cycle are of critical importance since they set the frame for all further post-disaster operations. Having an adequate number of strategically located storage and distribution centers for critical supplies is the key that enables effectiveness, efficiency and fairness when responding to a disaster situation. The preparedness model proposed in this study selects locations and inventory levels of these facilities such that the right mix of relief items can be supplied at the right time. Our mixed integer linear model aims to find a robust relief network design that satisfies the demand for all given disaster scenarios, and to help achieve a better response during the response stage when the relief items are distributed. The assumptions and the parameters used in the model are justified by authorities of humanitarian organizations. We propose a logic-based Benders decomposition approach to solve this problem to optimality. Although the problem is NP-hard, our numerical studies demonstrate that it is possible to obtain optimal or very good solutions to problem instances with realistic sizes.     

Analytical approximations to predict performance measures of manufacturing systems with general distributions,job failures and parallel processing

Parallel processing is prevalent in many manufacturing and service systems (i.e. some components may have to wait for other components before the assembly can begin). It is also common to observe manufacturing systems that deal with multiple products, resources shared between different products, and circulation due to random part failures. An example of such a system configuration is observed at a facility equipped to assemble and test web servers. The primary objective of this research was to develop analytical approximations to predict performance measures of a system with the above characteristics and evaluate its accuracy. Manufacturing systems with general distributions, multiple products, job circulation due to failures, resource sharing, and a fork and join system (to model parallel processing of some assembly operations) were studied using the parametric decomposition approach. The different work centers (or stations) in the manufacturing system is modeled as a network of queues and the parametric decomposition approach is applied to decompose the network of queues into individual queues to estimate the performance measure of the system. Existing analytical formulations were modified and appropriate correction terms were added to the approximations to bridge the gap in the error between the analytical approximation and the simulation models. Random instances were generated and the flow times from the approximations and simulation models were compared. The experimental study conducted indicates that the analytical approximations along with the correction terms can serve as a good estimate for the flow times of the manufacturing systems with the above characteristics.     

社会经济管理系统和谐性模型的构建与分析

本文从非线性自然观的视野。引用与分析了社会经济系统功能模型与效应模型。构建了系统和谐状态模型与和谐状态可信度模型，形象地说明了企业系统的和谐既是一个随机不确定状态。又是企业和谐力量与不和谐力量相互抗争干涉的过程。依据协同学原理提出了企业系统和谐演进的机制，表明企业系统的和谐发展是子系统和谐协同的过程。即子系统竞争合作的过程。文中所构建的模型，从理论上清晰地说明了企业系统和谐有序运行的机理，为如何构建和谐企业。提供了建设性的思考。     

Research into Expert Systems to Aid Simulation Model Formulation

The widespread availability of inexpensive computing power and recent developments in machine intelligence now makes it possible to consider computer assistance in the formulation phase of a discrete-event simulation model. The goal is to speed up this process. With this in mind, a series of prototype expert systems (written in LISP and run on an APPLE II) have been produced. The first prototype system was built using the ‘MYCIN’ approach. In the second prototype system a more informal approach was used, and the resulting computer-aided system is a natural-language understanding system. This paper outlines the need for such research and discusses the system development by describing the two main models and explaining why the natural-language approach was adopted.     

企业技术创新能力评价新方法的研究

企业发展的核心竞争力是技术创新能力,公正客观的评价企业的技术创新能力十分必要,研究新型的企业技术创新能力评价方法对企业的成长和可持续发展有所帮助。本文较为全面的分析了企业技术创新能力的概念、内涵与特征,并对现有的评价方法进行了调研和对比分析。提出企业技术创新能力评价分析时应将企业持续创新能力和经济效益作为评价的重要内容,研究并构建了包括创新支撑和创新主体两个二级指标在内的新的企业技术创新能力评价指标体系,并对指标的重要性进行了划分,以期为企业评价技术创新能力提供参考。