Soft with a hard centre: discrete-event simulation in facilitation

Discrete event simulation is normally described as a ‘hard’ OR technique. This may not, however, always be the case. An example of a simulation of a user support helpline is described which, it is argued, has many of the traits of a ‘soft’ OR intervention. In particular, the study involved a facilitated discussion around a simulation model about possible improvements to a problem situation. The nature of the intervention is considered from both a methodological and paradigmatic perspective, and conclusions are drawn about where the intervention lies on a ‘hard’ to ‘soft’ continuum. It is argued that ‘soft’ issues need to be subsumed into the prescribed methodology for discrete-event simulation.     

基地化保障模式下飞机四站装备需求确定研究

基地化保障模式对飞机保障资源需求的影响是制约其发展的重要问题.基于离散事件仿真(DES)方法建立了航空兵场站四站保障过程的数学模型,考虑了四站装备自身故障的影响,并在所建模型的基础上提出运用离散系统仿真软件ARENA对四站保障过程进行仿真.仿真结果表明,与现行的航空兵场站单机种保障策略相比,基地化保障模式能够减少各个机种通用的四站装备数量需求,而单个机种特有的四站装备需求不变.     

Evaluating the quality of online optimization algorithms by discrete event simulation

A key feature of dynamic problems which offer degrees of freedom to the decision maker is the necessity for a goal-oriented decision making routine which is employed every time the logic of the system requires a decision. In this paper, we look at optimization procedures which appear as subroutines in dynamic problems and show how discrete event simulation can be used to assess the quality of algorithms: after establishing a general link between online optimization and discrete event systems, we address performance measurement in dynamic settings and derive a corresponding tool kit. We then analyze several control strategies using the methodologies discussed previously in two real world examples of discrete event simulation models: a manual order picking system and a pickup and delivery service.     

WASAN: The development of a facilitated methodology for structuring a waste minimisation problem

This paper contributes a new methodology called Waste And Source-matter ANalyses (WASAN) which supports a group in building agreeable actions for safely minimising avoidable waste. WASAN integrates influences from the Operational Research (OR) methodologies/philosophies of Problem Structuring Methods, Systems Thinking, simulation modelling and sensitivity analysis as well as industry approaches of Waste Management Hierarchy, Hazard Operability (HAZOP) Studies and As Low As Reasonably Practicable (ALARP). The paper shows how these influences are compiled into facilitative structures that support managers in developing recommendations on how to reduce avoidable waste production. WASAN is being designed as Health and Safety Executive Guidance on what constitutes good decision making practice for the companies that manage nuclear sites. In this paper we report and reflect on its use in two soft OR/problem structuring workshops conducted on radioactive waste in the nuclear industry.     

The Use of Soft Systems Methodology in the Development of a Simulation of Out-patient Services at Watford General Hospital

The effective and efficient provision of out-patient services may be assisted by the appropriate use of discrete event simulation. Resource use must be carefully monitored and suitable control actions must be taken, if service level and quality are to be maintained, whilst keeping cost increases to a minimum. In itself, simulation provides no means by which system activities may be identified. The use of soft systems methodology as a tool to aid in activity identification for simulation modelling is being explored. The investigation focuses on the effects the participative nature of soft systems methodology has on the acceptability of a simulation model. This case study forms part of a research objective of developing a generic approach to link soft systems methodology and simulation. Its aim is to provide analysts and managers with a process which may assist in planning strategies for health care.     

How do we know who to include in collaborative research? Toward a method for the identification of experts

Collaborative research, defined as research involving actors participating in the problem situation under study, has an important role in operational research, strategic management and systems thinking. In a recent study, we found that a strong organizational focus incorporated into many soft operational research (OR) approaches is inadequate for studying societal problem situations, which are fragmented and have no clear boundary. Specifically, we failed to find a process of identifying individuals that is capable of representing the perspectives of actors and sufficient for research into societal problem situations. We found no clear terminology accounting for ontological differences between actors, individuals representing them and conceptual representations of acting entities. In response to this gap in the literature, we propose terminology that differentiates among actors (individuals or collective entities in the real world), experts (individuals capable of representing the perspective of an actor) and agents (ideal-typical representations of actors). Based on this terminology, we propose an iterative method to guide the assembly of an expert group to undertake collaborative research into societal problem situations. To demonstrate the application of our method, we present selected insights from our study in an electronic supplement.     

Widening requirements capture with soft methods: an investigation of hybrid M&S studies in health care

A simulation study consists of several stages: problem formulation, model implementation, verification and validation, experimentation and output data analysis. The application of multiple techniques in the model implementation stage is referred to as hybrid simulation, which we distinguish in this paper from a hybrid M&S study, the latter referring to studies that apply methods and techniques from disciplines like Operations Research (OR), Systems Engineering and Computer Science to one or more stages of a simulation study. Our paper focuses on the contribution of soft OR methods in the problem formulation stage of a simulation study (and by extension a hybrid M&S study). Soft Systems Methodology (SSM) has, arguably, been the most widely used qualitative approach for eliciting system requirements. In this paper, we present Qualitative System Dynamics (QSD), a soft systems method, as having potential use in the problem formulation stage of a healthcare M&S study. The contribution of this paper is thus twofold: (1) a review of the literature in SSM for healthcare operations management and (2) an examination of QSD as an additional soft OR method, complementing (rather than supplanting) existing approaches, which can further aid the understanding of the system in the problem formulation/conceptual modelling stage of a hybrid M&S study.     

The Role of Discrete Event Simulation Techniques in Finite Capacity Scheduling

Discrete event simulation is becoming an established tool in finite capacity scheduling. However, recent work on scheduling systems has concentrated on the development of different modelling approaches and tools, without proper examination of how they can be used to meet business objectives. This paper examines the role of scheduling in improving business performance and suggests possible considerations in the development and implementation of a finite capacity scheduler. It reviews the advantages and limitations of discrete event simulation as a modelling technique for scheduling, and argues the need for further research to develop more versatile tools. A simulation-based scheduling system incorporating bottleneck planning principles to maintain throughput with low inventory is described, as are the experiences gained during its implementation in a medium-sized press shop.     

Simulation for business process re-engineering: case study of a database management system

This paper describes the use of discrete event simulation in the resource, throughput and content analysis and improvement of a business process in the Iranian Information and Documentation Centre (IRANDOC). The process was initially mapped using Data Flow Diagrams (DFD), and the objectives of the study for a range of users were captured using the Delphi method. The time taken for the tasks in the process were estimated by work study, and the simulation was developed in ServiceModel?. The simulation was valuable in understanding why the current systems were not performing satisfactorily and led to a number of proposals for improvement. This mixed use of hard (simulation) and soft (Delphi) methods proved a fruitful way to gain process improvements and could be employed in other organisations.     

A methodology for supporting strategy implementation based on the VSM: A case study in a Latin-American multi-national

Soft OR tools have increasingly been used to support the strategic development of companies at operational and managerial levels. However, we still lack OR applications that can be useful in dealing with the “implementation gap”, understood as the scarcity of resources available to organizations seeking to align their existing processes and structures with a new strategy. In this paper we contribute to filling that gap, describing an action research case study where we supported strategy implementation in a Latin American multinational corporation through a soft OR methodology. We enhanced the ‘Methodology to support organizational self-transformation’, inspired by the Viable System Model, with substantive improvements in data collection and analyses. Those adjustments became necessary to facilitate second order learning and agreements on required structural changes among a large number of participants. This case study contributes to the soft OR and strategy literature with insights about the promise and constraints of this soft OR methodology to collectively structure complex decisions that support organizational redesign and strategy implementation.     

考虑协同信息的人员与岗位双边匹配决策方法

针对考虑协同信息的人员与岗位双边匹配问题,提出一种决策分析方法。首先,给出了考虑协同信息的人员与岗位双边匹配问题描述;其次,依据人员和岗位给出的多指标评价信息,计算了人员对岗位的满意度、岗位对人员的个体技能满意度及人员之间的工作协同度;在此基础上,建立了以人员对岗位满意度最大、岗位对人员个体技能满意度最大和人员之间协同度最大为目标的多目标优化模型,该模型是一个具有多目标的0-1型二次整数规划问题,也是一个NP-hard问题,为了求解该多目标优化模型,设计了一个多目标离散差分进化算法;最后,通过一个实例验证了所提方法的可行性和有效性。     

Planning for disaster: developing a multi-agency counselling service

Multi-agency planning is becoming increasingly important to organisations, especially those concerned with delivering services for the benefit of the community. This paper describes how a modified version of the methods from soft systems methodology (SSM), chosen through methodological reflections informed by critical systems thinking, was used to support the planning of a multi-agency counselling service that could be activated in the event of a disaster. Representatives of nineteen agencies were involved in this exercise, working together in six, one-day workshops. Feedback from participants, using four evaluation criteria (derived from the principles of SSM and the stated priorities of workshop participants), suggests that the methods of SSM, modified as described, show a great deal of promise as a support to multi-agency planning.     

Hospital preparedness during epidemics using simulation: the case of COVID-19

Central European Journal of Operations Research - This paper presents a discrete event simulation model to support decision-making for the short-term planning of hospital resource needs, especially...     

Linguistic fuzzy consensus model for collaborative development of fuzzy cognitive maps: a case study in software development risks

Fuzzy cognitive maps (FCMs) have been widely used in several domains for information processing, such as, data fusion, decision making. Although several methods to automatically learn FCMs are recognized from the scientific literature, the most used approach to build an FCM relies on a collaborative task involving single person or, more suitably, group of experts. Collaborative development increases reliability and robustness of the resulting FCM, but rises some problems in terms of group decision making to aggregate different perspectives of the problem representation. This paper proposes to support collaborative development of FCMs introducing knowledge engineering process that relies on Linguistic Fuzzy Consensus Model. In the proposed approach, each expert builds the own version of the FCM. When all different versions are available, a Group Decision Making process is activated in order to reach the consensus on conflictual modeling opinions. The result is a unique final version of the FCM that is not a simple aggregation of the versions provided by the experts but is the result of a well-suited mathematical model. In addition, this work adopts consensus model with incomplete preference relations scheme to address knowledge harmonization issues. Finally, advantages and the limitations of the proposed framework are argued.     

A hybrid analysis approach for finite-capacity queues with general inputs and phase type service

A new analysis method for queueing systems with general input stream and phase type service time distributions is introduced. The approach combines discrete event simulation and numerical analysis of continuous time Markov chains. Simulation is used to represent the arrival process, whereas the service process is analyzed with numerical techniques. In this way the state of the system is characterized by a probability vector rather than by a single state. The use of a distribution vector reduces the variance of result estimators such that the width of confidence intervals is often reduced compared to discrete event simulation. This, in particular, holds for measures based on rare events or states with a small probability. The analysis approach can be applied for a wide variety of result measures including stationary, transient and accumulated measures. This revised version was published online in June 2006 with corrections to the Cover Date.     

An interactive visual simulation system for industrial management

This paper describes a discrete event interactive simulation system which allows a user to watch the progress of a simulation model on a visual display terminal. The user may interact with the model in a flexible manner, in order to explore the consequence of alternative decisions or strategies. Output from the simulation may be directed, in an animated form, to a refresh display computer graphics screen, a black and white visual display unit or an intelligent colour visual display divice. The interactive system has been specifically designed to assist in decision making processes associated with industrial management problem situations.     

The trapezoidal fuzzy soft set and its application in MCDM

Soft set theory is a newly emerging mathematical tool to deal with uncertain problems. Since the trapezoidal fuzzy number, as a vital concept of fuzzy set, can express linguistic assessments by transforming them into numerical variables objectively, this paper aims to extend classical soft sets to trapezoidal fuzzy soft sets based on trapezoidal fuzzy numbers. Then, some operations on a trapezoidal fuzzy soft set are defined, such as complement operation, “AND” operation, and “OR” operation. Finally, a Multiple Criterion Decision-Making (MCDM) problem under a fuzzy environment is analyzed by trapezoidal fuzzy soft sets with the demonstration of a numerical example. This paper also uses traditional fuzzy soft sets to deal with the MCDM problem. The result shows that the method provided by this paper outperforms the traditional one.     

Dynamic transport scheduling under multiple resource constraints

This paper presents a heuristic for the dynamic vehicle scheduling problem with multiple resource capacity constraints. In the envisaged application, an automated transport system using Automated Guided Vehicles, bottleneck resources are (1) vehicles, (2) docks for loading/unloading, (3) vehicle parking places, and (4) load storage space. This problem is hard, because interrelated activities (loading, transportation, unloading) at several geographical locations have to be scheduled under multiple resource constraints, where the bottleneck resource varies over time. Besides, the method should be suitable for real-time planning. We developed a dedicated serial scheduling method and analyzed its dynamic behavior using discrete event simulation. We found that our method is very well able to find good vehicle schedules satisfying all resource constraints. For comparison, we used a simple approach where we left out the resource constraints and extended the processing times by statistically estimated waiting times to account for finite capacities. We found that our newly designed method finds better schedules in terms of service levels.     

Variance reduction for Markov chain processes using state space evaluation for control variates

We develop a method for reducing variance in Monte Carlo simulation of Markov chain processes based on extracting accurate control variates from state space evaluation functions. An example is given in the form of a simple combat model, where the net variance reduction (adjusted for additional calculation) is larger than a factor of 80. We also indicate how our algorithm may be applied to discrete event simulations and system dynamic models with discrete random events.     

Modeling and analysis of a Canadian Forces Geomatics division workflow

This paper addresses workflow issues of a Geomatics division in the Canadian Forces. This division is dedicated to the production of Geomatics Information under the US National Geospatial-Intelligence Agency’s Foundation Based Operations concept. This paper outlines a methodology for modeling and analyzing the workflow of the Canadian Forces Geomatics division. A discrete event simulation model is developed and applied to measure the performance of the workflow system for developing Geomatics products. A hybrid queueing network/optimization model is also developed to support the simulation model. The objective of the queueing network/optimization formulation is to provide the optimal configuration of the Geomatics division. The paper successfully addresses a complex workflow problem in the context of real world system and provides insights into the performance of the Canadian Forces Geomatics processing.