Supply chains providing high-value parts to the Government have been plagued by both shortages and excess inventory. In many of these supply chains, a computerized government process calculates recommended orders for both new and overhaul parts. A research effort was undertaken to understand the mathematics of this process and its impact on supply chain performance. A system dynamics model of the supply chain was developed that incorporates the equations of the requirements determination process. The model revealed that the process worked appropriately for constant demand and responded well to a ramp-up in demand. It was found, however, that in the face of varying demands substantial bullwhip was produced in the supply chain. Moreover, it was shown that the ordering process is extremely sensitive to common data errors such as the production lead-time and that production constraints, not included in the ordering algorithms, created deep and prolonged shortages. On going research is developing improvements to the formulation of the ordering process and developing supply chain strategies for the next five years under differing demand scenarios.
This paper describes an application of the Vee Model of Systems Engineering in developing a System Dynamics model of dryland salinity in the Murray Darling Basin. A modular approach was adopted. Simple modules of salt affected land were developed using Powersim Studio following decomposition, definition, integration and verification processes. Individual modules were verified, integrated and provided with options for policy testing. The use of Vee Model provides a structured way for developing computer simulation model with a top-down approach for requirements elicitation and ensures that the computer model meets requirements and limitations elicited through qualitative System Dynamics and defined at the start of the modelling exercise. It also provides rigorous verification processes. The results of this research provide an avenue for further exploration of the synergistic use of the two approaches to improve model quality.
A number of papers have been published describing various pedagogic techniques for the dissemination of the System Dynamics (SD) approach at various Education institutions and academic levels ranging from schools (K-12 in the US) to higher education. This paper builds on previous papers by this author that provided a partial catalogue and classification of this work in order to highlight potential areas of research in this field of study and to identify system archetypes at different hierarchical levels and discover new ones. This paper therefore presents taxonomy of System Dynamics Pedagogic Techniques. This paper builds on the earlier taxonomy by widening the scope of the survey of SD Pedagogic Techniques. The findings from these investigations are briefly described. The taxonomy classifies the completed investigations into specific areas of concern and hierarchical levels.
A number of papers have been published describing various System Dynamics (SD) models of various Education institutions and issues, on topics including the role of SD in Corporate Governance, Planning, Resourcing & Budgeting, Teaching Quality, Teaching Practice, Microworlds and Enrolment Demand. This paper builds on previous papers by this author that provided a partial catalogue and classification of this work in order to highlight potential areas of research in this field of study and to identify system archetypes at different hierarchical levels and discover new ones. This paper therefore presents taxonomy of System Dynamics Models in Education. This paper builds on the earlier taxonomy by widening the scope of the survey of completed SD investigations in educational management. The findings from these investigations are briefly described. The taxonomy classifies the completed investigations into seven specific areas of concern and five hierarchical levels.
A model of the repair operations of the voice telecommunications network is used to study labor management strategies under a disaster scenario where the workforce is overwhelmed. The model incorporates overtime and fatigue functions and optimizes the deployment of the workforce based on the cost of the recovery and the time it takes to recover. The analysis shows that the current practices employed in workforce management in a disaster scenario are not optimal and more strategic deployment of that workforce is beneficial.
Presently in Iran, gas-driven power stations and combined-cycle power stations compete as they share a common budget allocated by the government for their establishment. With the government offering gas at subsidized rates, the cost price of electricity production at gas-driven power stations is comparatively lower, thereby enhancing their attractiveness for the investor. Therefore, despite their decreased efficiency, the establishment of such power stations is on the increase which in turn imposes additional costs for the government. On the other hand, it would be in the best interest of the government to help increase investment in combined cycle power stations which are far superior in terms of efficiency, and which, in the long run, would be profitable. In this paper we present a model and suggest policies for the government through which a decrease in energy intensity can be achieved without incurring additional costs for the government. We suggest practical ways to optimize existing methods of power production by diverting subsidies offered by the government.
Planning and managing large-scale projects is non-trivial, as evidenced by the large number of projects that exceed budget and schedule targets. In many cases, rework is a key factor in project delays. Accurate rework prediction is challenging even when the tasks responsible for rework can be identified, the likely project impact is difficult to determine. The work described in this paper examines how Dependency Structure Matrix (DSM) techniques can be leveraged to support and improve System Dynamics applications. It demonstrates how the DSM can be used to identify tasks that are likely to drive rework within a project and exploits System Dynamics to quantify the associated financial and schedule downsides. Using the context of current oil and gas projects, the challenges of managing dependencies between multidiscipline teams working to identify, evaluate, and select a development concept are examined. An overview of DSM fundamentals and approaches used to help with the management of these dependencies is presented. Next a discussion of how System Dynamics can both benefit from DSM analysis and resolve known limitations are considered. The natural integration of DSM and System Dynamics for management of project dependencies is summarized and used as a basis for suggesting new research agendas.
This paper develops a model of economic growth when emissions are generated as a byproduct of the production process. The production of goods yields income that can be used either for consumption or investment. The production of goods also induces an undesired byproduct emissions. The emissions accumulate to a stock of pollutants which in turn impairs the economy. The consumption of good, in contrast, leads to an improvement of societal well-being. The positive impact of consumption utility and the negative impact of pollution are measured by a welfare function. In this setup of the problem there are two basic intertemporal control problems to solve: First, the society has to decide how much to consume today and how much tomorrow. Second, it has to decide how much of GDP should be invested in pollution abatement over time. The SD model developed in this paper allows simulating the consequences of policy choices and searching for optimal policy strategies. Several simulation scenarios demonstrate the scope of the modeling approach.
The performance of laymen on tasks testing for knowledge of basic dynamics, such as the bathtub tasks, is consistently weak. There are some reports of beneficial effects of introductory courses in system dynamics or a strong mathematical background. This study investigates the effects of a system dynamics background beyond the introductory level, and strong mathematical background including courses in differential equations and control theory, on the strategies applied to, as well as performance in, the rabbits-and-foxes task. The task objective is to establish equilibrium in a predator-and-prey system. These well-educated participants performed no better than social science students. The strategies applied differed however, and the dynamic systems educated participants did not demonstrate as much misconceptions about the system as social science students have been found to do. The weak performance raises the question if there are better ways to develop a mature concept of equilibrium.