This paper describes transform approaches to control Vendor-Managed Inventory (VMI). The effect of different modelling techniques and their significance is examined. Modelling was achieved with the Simulink package using the equations developed by Disney and Towill for a VMI system model. Analysis of several types of delay representation were compared to illustrate how the results depend on their formulation. The effect of using a discrete model is to deepen the stock-out and increase the required order rate. Analysis of the stability of the different models are discussed and evaluated. It is shown that the continuous model with an exponential delay is always stable and with a fixed delay can be made stable. The requirement for the system is also computed for a discrete model with exponential delay. Reduced inventory stock-out and a smaller WIP peak are achieved with different order smoothing function. This has special significance for e-manufacture.
An interactive learning environment (ILE) appropriate for intermediate macroeconomics students has
been simplified for students in introductory college and high school courses. Without changing the
underlying model or the simulation options, the simplified instructional approach relies on feedback
loop diagramming more than stock-and-flow diagramming. Interactive Vensim causal loop diagrams
are embedded in a STELLA interface, using slide show and video software. In addition, students appear
to learn more as model-users if they engage in preliminary model-building activities using simple
word-and-arrow diagrams.
Diffusion models of radical technologies are often based on an epidemic structure developed on the Bass principles of generic external and internal communications. However, in most cases such processes involve more complex communication and decision mechanisms. The diffusion processes should account for interdependences with other innovations and also the substitution mechanisms with regard to the technology in place. Substitution must be understood with a much broader scope than the analytical view of the Fisher and Pry model. As many diffusion authors have acknowledged (but partially excluded from their models), diffusion is a social process with innovation moving through interpersonal networks. We propose a model that accounts for the dynamics of social factors in technological substitution. Based on the System Dynamics methodology, our model disaggregates most of the communication structure and individuals characteristics that are implicitly embedded in traditional diffusion models. Our discussion starts with the characteristics of radical technological innovations. We then proceed with the theoretical basis of our social aggregation approach by presenting Kellys personal constructs system theory, outlines of social psychology, decision making under uncertainty, and the interdependences between innovations characteristics and human behavior. We also make an attempt at considering both sides (consumers adoption / competitors imitation) of a substitutive diffusion. Brice Dattée's research is funded by the National Institute of Technology Management in Ireland.
This work captures and analyzes the fundamental dynamics of innovative industries with a System Dynamics model. We selectively reviewed the innovation literature, identified the dynamics to be modelled, formulated a conceptual model of these dynamics, and then developed the initial simulation model. By design the conceptual model is simple and generic. It is intended to apply to a broad range of products and services assembled and process-based, complex and simple, physical and digital, business and consumer, early stage and mature, 19th century and 21st century. That is what we mean by the fundamental dynamics of innovative industries. In many variations and combinations they can explain the evolution of most markets. The initial simulation model was developed from the conceptual model. It represents products based on two generations of technology. At this stage the simulation model does not represent a specific market or industry. It is quantified with hypothetical inputs, parameters, and cause/effect relationships. The simulation model recreates well-documented reference modes of market evolution. We currently are building the information base which will enable the initial model to be applied to the photography and display markets.
The, for economists well-known Goodwin model was one of the first models which tried to combine cyclical behavior and economic growth. The basis for this is the predator-prey model a basic structure for every System Dynamicists. The economic literature about the Goodwin model is enormous, but so far, it was mostly concentrate on the mathematical behavior or on some extensions that could be implemented. In addition, there are only two papers from R. Solow and D. Harvie about an econometrical verification of the model and none from a System Dynamics perspective. This article provides therefore two System Dynamics models of Goodwins theory and tests the enhanced one on the German economic situation and on the data provide by Harvie 2000. Additionally there are some suggested modifications of the Goodwin model, tested from different authors, which reveal surprising outcomes for the understanding of Goodwins theory.
In this paper, I will present relatively simple system dynamics models which capture some of the insights of a key critic of the U.S. policy for defending the country, Stephen Flynn. Flynn is especially concerned with the over-reaction to the attacks of September 11, 2001. He warns of the dangers of shutting down legitimate commerce and investing in overseas offensive measures as a knee-jerk reaction to the attacks. It is not that he is advocating a lax approach to security. Rather he is advocating a measured look at the implications of a draconian defense policy which may cause much more damage to our societal infrastructures than the attacks that triggered it. He also presents recommended solutions.
In the modern era, the advances in information technology have been dramatically shaping the ways people live as well as the ways organizations manage their businesses in their professional business domains. Implementing various kinds of information systems, such as Decision Support Systems, has been recognized as one of the most crucial tasks for organizations in order to continue to be competitive or even to survive. Although considerable effort has been devoted to improving the performance of information system implementations, organizations are still constantly suffering from the failures of information system implementations. In this study an extensive framework that depicts the context of information system implementation is developed. A system dynamics approach is used to investigate the dynamic nature of information system implementations. By using the proposed system dynamics model, we contend, executives and information system professionals of organizations can gain comprehensive insights into organizational behaviors and substantial policy-making implications regarding information system implementations.
The pattern of one-shot growth is most seen in software industry. The purpose of this paper is to understand the growth dynamics of a software house and to facilitate the software house to manage its growth. This paper models a major domestic ERP software house in Taiwan that is experiencing the one-shot growth process. Business type-level packages and high quality service is the companys secrets for its success. With a good reputation for high quality systems and services, the companys growth strategy is to expand the market it serves by developing new kinds of packages for more business types. However, how to balance the human resources requirements of R&D and ERP is rather difficult when long delays exist everywhere in a software house. With the system dynamics model built, this paper identifies the archetype of limits to growth hidden inside the software house and illustrates how the problem is worsened by the companys intuitive reactions.
A discussion, with panelists representing different perspectives, facilitated to encourage full participation by everyone present. The field of inquiry dubbed environmental dynamics (ED) includes a broad range of interests, many with differing views of the ecological world. These include, for example, purely ecological studies involving the interactions of organisms and their natural environment, technical studies of the effects of human activities on the environment and different methods employed to limit or counteract those effects, big picture analysis of the human-influenced world and the direction it is headed, plus many others. Popular topics often associated with ED include: environmental regulation, the ecocosm dilemma, the oil crisis, global warming, environmental limits [to growth], etc. The roundtable will explore the relationships among these different topics, emphasizing the role of system dynamics. The goals will be to establish common ground, to create useful distinctions, and to help organize the ED endeavor.