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A Comparison of Petri Net and System Dynamics Approaches for Modelling Dynamic Feedback Systems (2014)

Duggan, James

A Comparison of Petri Net and System Dynamics Approaches for Modelling Dynamic Feedback Systems (2014)

Duggan, James

Abstract:

Petri nets are a valuable tool that can be used to simulate workflow systems. They are based on a state-transition approach, and in common with discrete event simulation, events can be scheduled to fire at different time intervals. This is in contrast to the stock and flow approach of System Dynamics, where workflows are aggregated and state transitions modelled continuously through sets of integral equations. This paper continues a theme explored at the Boston 2005 conference, where a paper was presented that identified a common simulation problem, and presented solutions using both discrete event simulation and system dynamics. The benefit of this approach is that it can provide modellers from different methodological worldviews insights into how common problems may be addressed. The problem approached here is a one-actor model of the Beer Game. Two models are developed, detailed experimentation is performed, and overall results and conclusions presented.

http://hdl.handle.net/10379/4040

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A System Dynamics View of the Acute Bed Blockage Problem in the Irish Healthcare System (2015)

Abo-Hamad, Waleed; Rashwan, Wael; Arisha, Amr

A System Dynamics View of the Acute Bed Blockage Problem in the Irish Healthcare System (2015)

Abo-Hamad, Waleed; Rashwan, Wael; Arisha, Amr

Abstract:

Global population ageing is creating immense pressures on hospitals and other healthcare services, compromising their abilities to meet the growing demand from elderly patients. Current demand–supply gaps result in prolonged waiting times in emergency departments (EDs), and several studies have focused on improving ED performance. However, the overcrowding in EDs generally stems from delayed patient flows to inpatient wards – which are congested with inpatients waiting for beds in post-acute facilities. This problem of bed blocking in acute hospitals causes substantial cost burdens on hospitals. This study presents a system dynamics methodology to model the dynamic flow of elderly patients in the Irish healthcare system aimed at gaining a better understanding of the dynamic complexity caused by the system's various parameters. The model evaluates the stock and flow interventions that Irish healthcare executives have proposed to address the problem of delayed discharges, and ult...

https://arrow.dit.ie/buschmanart/30

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An Empirical Estimation of Statistical Inferences for System Dynamics Model Parameters (2014)

Mesabbah, Mohammed; Rashwan, Wael; Arisha, Amr

An Empirical Estimation of Statistical Inferences for System Dynamics Model Parameters (2014)

Mesabbah, Mohammed; Rashwan, Wael; Arisha, Amr

Abstract:

For system dynamics simulation (SD) models, an estimation of statistical distributions for uncertain parameters is crucial. These distributions could be used for testing models sensitivity, quality of policies, and/or estimating confidence intervals for these parameters. Assumptions related to normality, independence and constant variation are often misapplied in dynamic simulation. Bootstrapping holds a considerable theoretical advantage when used with non-Gaussian data for estimating empirical distributions for unknown parameters. Although it is a widely acceptable approach, it has had only limited use in system dynamics applications. This paper introduces an application of Direct Residual Bootstrapping (DRBS) for statistical inference in system dynamic model. DRBS has been applied successfully to ‘The Irish Elderly Patient Delayed Discharge’ dynamic model to estimate empirical distribution for some unknown parameters with a minimal computation effort. The computational results sh...

https://arrow.dit.ie/buschmarcon/128

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An introduction to system dynamics (2017)

Duggan, James

An introduction to system dynamics (2017)

Duggan, James

Abstract:

This chapter presents the important concepts underlying the system dynamics modeling method. Following an initial definition of the term model, a summary of a successful system dynamics intervention is described. The key concepts of system dynamics stocks and flows are explained. The process for simulating stock and flow models integral calculus is described, with an example of a company s customer base used to illustrate how stocks change, through their flows, over time. A summary of dimensional analysis for stock and flow equations is provided before the second feature of system dynamics modeling feedback is presented. The chapter concludes by summarizing the system dynamics meth-odology, which is a five-stage iterative process that guides model design, devel-opment, test and policy design.
Peer reviewed
2017-06-15

http://hdl.handle.net/10379/6375

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Analytical and Computational Methods for Analyzing Feedback Structure in System Dynamics Models (2013)

Huang, Jinjing

Analytical and Computational Methods for Analyzing Feedback Structure in System Dynamics Models (2013)

Huang, Jinjing

Abstract:

The system dynamics approach is based on the observation that dynamic behaviour arises as a result of endogenous interactions, particularly the interplay of various feedback loops. There are many open questions relating to the relationship between system structure and its behavior, and there are opportunities to add to the range of formal mathematical methodologies which can identify dominant feedback structures that give rise to the system behavior. The objective of this thesis is to propose methodologies that can identify the structural origins of complex behavior, and investigate their application in system dynamics models. Our contributions to the field are: First, we have found a drawback of a widely adopted loop selection algorithm named SILS which is required by the eigenvalue elasticity analysis to identify dominant loops. We propose a specific algorithm is to address this problem, and demonstrate its applicability through an individual-oriented example. Second, with an inc...

http://hdl.handle.net/10379/3466

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Co-evolutionary analysis: a policy exploration method for system dynamics models (2013)

Hongliang, Liu; Howley, Enda; Duggan, James

Co-evolutionary analysis: a policy exploration method for system dynamics models (2013)

Hongliang, Liu; Howley, Enda; Duggan, James

Abstract:

Journal article
In system dynamics (SD), complex nonlinear systems can generate a wide range of possible behaviours that frequently require search and optimization algorithms in order to explore optimal policies. Within the SD literature, the conventional approach to optimization is the formulation of a single objective function, with a targeted parameter list, and the entire model is simulated repeatedly in order to arrive at optimum values. However, many sector-based SD models contain heuristics of intended rationality, and a desired outcome for modellers to be able to explore the policy implications of locally rational behaviours. This can now be achieved through a method known as coevolution, which allows modellers to divide an unsolved problem into constituent parts, where each part can be solved with respect to its own fitness function. In this paper, we specify a solution for evolving locally rational strategies across a multi-sector SD structure. Using the beer distribut...

http://hdl.handle.net/10379/3932

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Increasing Value Generation Using a Hierarchical Simulation-Based SCOR Framework (2012)

Crowe, John; Arisha, Amr

Increasing Value Generation Using a Hierarchical Simulation-Based SCOR Framework (2012)

Crowe, John; Arisha, Amr

Abstract:

We are part of extraordinary times, global recession coupled with increased competition; high costs and decreasing demand have changed the dynamics of supply chain management (SCM). In response, many organizations have fast-tracked changes to corporate-level strategies to reduce costs and maintain profit margins and have not considered the long-term impact these decisions have on more operational-level SCM activities. This has resulted in a renewed focus on customer value and the economic and behavioral systems of the supply chain, or more accurately, the value chain. The Supply Chain Operations Reference (SCOR) model increases the integration organizations have within their supply chains and increases alignment between different hierarchical strategies. Simulation techniques, in particular discrete-event simulation (DES) and system dynamics (SD) are proven techniques in improving SCM corporate and operational decision making processes. This paper presents a framework that integrate...

https://arrow.dit.ie/buschmancon/28

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Nature Inspired Computational Optimisation Methods for System Dynamics (2012)

Liu, Hongliang

Nature Inspired Computational Optimisation Methods for System Dynamics (2012)

Liu, Hongliang

Abstract:

This thesis aims to provide the state of the art "nature-inspired computing" (NIC) approaches and investigate their applications in system dynamics (SD) models. Specifically, we will focus on particle swarm optimisation (PSO), genetic algorithms (GAs) and cooperative coevolutionary approaches (CCEAs), and their application in the beer distribution game (BDG). Three pieces of work have been conducted in this thesis. Firstly, we focus on improving the performance of PSO. PSO is an intelligent random search algorithm, and the key to its success is to effectively balance between the exploration and the exploitation of the solution space. This thesis presents a new dynamic topology called "gradually increasing directed neighbourhoods (GIDN)". Each particle begins with a small number of connections and there are many small isolated swarms that improve the exploration ability. At each iteration, we gradually add a number of new connections between particles which improv...

http://hdl.handle.net/10379/3030

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Service networks performance analytics: a literature review (2011)

Carroll, Noel; Wang, Yan

Service networks performance analytics: a literature review (2011)

Carroll, Noel; Wang, Yan

Abstract:

The success of developing service networks rely on obtaining a correct understanding of the end-to-end business processes. However, there are major concerns as to the lack of research efforts to examine methods to successfully manage the complexity of service networks. The insufficient communication efforts between business and technical experts results in a dissatisfactory service delivery and the inability to predict and measure the service network performance. This literature survey is initiated with purpose of finding a novel way to represent business processes in service networks and analyses the process performance. Specifically, we discuss the need to conceive tools and techniques to manage the complexity of service networks without jeopardising the performance of service networks and provide an overview of current simulation-based modelling approaches and optimising business processes.

http://hdl.handle.net/10344/1706

Marked Mark

Using multiple objective optimisation to generate policy insights for system dynamics models. (2013)

Duggan, James

Using multiple objective optimisation to generate policy insights for system dynamics models. (2013)

Duggan, James

Abstract:

Conference paper
Multiple objective optimisation (MOO) is an optimisation approach that has been widely used to solve optimisation problems with more than one objective function. The benefit of this approach is that it generates a set of non-dominated solutions which a policy maker can explore and evaluate before making a final optimal selection. This paper demonstrates that MOO can be used to assist policy makers explore a richer set of alternatives when deciding on a range of values for key parameters in their system dynamics model. In order to demonstrate the approach, a well-known case study "The Domestic Manufacturing Company" is used, and a stock and flow model and a multiple objective optimiser are designed and coded. The results show that valid solutions are generated, and that each of these solutions can be examined independently - and hence give greater insight into the problem at hand - before a decision is made as to the most appropriate solution.

http://hdl.handle.net/10379/3931

Displaying Results 1 - 10 of 10 on page 1 of 1