System modeling and simulation is a complex technological activity, which methodological and conceptual analysis could suggest some new and interesting perspectives about the philosophical subject of the relationships between knowledge and reality.Of the three kinds of knowledge involved in the system dynamics model building process (mental models, reference modes and operational knowledge), mental models look like specially important, because they let us to express the ideas we have about the internal interactions we find in a real system and that produce a known behavior. From this mental model, we build the formal model, the system dynamics model.But, after that, it is very difficult to find out formal restrictions that let us to select a single model, because a behavior can be generated by different structures ( Searle 1980,1984; Zeigler 1976,1984). The internal realism of Hilary Putnam (Putnam 1981,1983,1987) allows us to understand why there is not an unique model able to pick up every single aspect of a real system and to clarify the interactive character of the modeling process and the important role that mental models, as a kind of knowledge, play.
In this paper we present a program package which combines System Dynamics Simulation with programs for Interactive Multicriteria Optimization (IMO)The program package incorporates conventional well tested routines for nonlinear optimization, that do not require previous computations of derivatives, and methods to optimize a set of objective functions by progressive articulation of the user preferences between different criteria.To facilitate the user interaction, a special purpose man-machine interface have been included in the package. By means of this interface, the user can impose the required preferences structure by only expressing, in a linguistic way, his/her opinion about each objective in the current solution of the Interactive Multicriteria Optimization algorithm.The program package can be used to optimize a set of objective functions both in problems concerning the estimation of model parameters from historical data, and problems related with the search of optimal policies.The man-machine interface and optimization programs have been written in C and linked with the DYNAMO continuous systems simulation language to configurate the program package. The package can be used in IBM PC (or compatible) with a hard disk.
This report is based on results of the TERC Modeling Project funded by the National Science Foundation grant MDR-8550373. Any options, findings, or recommendations expressed herein are those of the authors and do not necessarily reflect the views of the Foundation.We gratefully acknowledge the support of Apple Computer, Inc.Apple, Macintosh are trademarks of Apple Computer, Inc.Stella is a trademark of High Performance Systems, Inc.Excel is a trademark of Microsoft, Inc.
We have investigated the complex dynamic phenomena, which arise when the economic long wave model is perturbed by a sinusoidal variation in the orders for capital to the goods sector. The modulation represents a coupling to more short term oscillatory modes in the macroeconomic system. As the period of the external forcing is changed, a devil’s staircase of frequency -locked oscillations develops. For higher amplitudes of the perturbing signal, period-doubling bifurcations, simultaneously existing periodic solutions and deterministic chaos can be observed. The distribution of modes is determined as a function of the frequency and amplitude of the external signal. The phase diagram reveals characteristic bumps on the Arnol’d tongues, where they approach each other. The Lyapunov exponents are calculated, and the influence of noise is discussed in terms of the lock-in time for the periodic solutions.
Over the past thirty years the black rhinoceros (Diceris bicornis) population in Africa has declined from about 30,000 to less than 3,000. In contrast the South African population has increased four-fold to 600 over the same period. The recently developed national conservation strategy for black rhino has as it main goal the increase of the current population to at least 2,000 in as short a period as possible. To achieve this, the growth rate of the population as a whole will have to be maximized. This involves removing animals from areas where the population is approaching the ecological carrying capacity and establishing new viable populations in other suitable reserves.A model, incorporating what is known about the population biology of black rhino, was developed to give guidance to managers on the most appropriate harvesting strategy to adopt for their populations; in particular, to determine the rate of removals and the age and sex of individuals to be removed to attain a 2,000 strong Southern African population as soon as possible.
This paper attempts to highlight how system dynamics methodology is useful in modeling and testing the dynamics involved in group interaction process to explain its behavior over time. Out of the prominent group models, Gladstein’s model of groups in context is taken as reference model. The SD model of group structure which is a system component consists of six modules; roles, goal clarity, specific work norms, task control, size and formal leadership. This paper deals in detail, the module of formal leadership, and studies how the interrelations and interdependence influence the system behavior.
This paper describes a System Dynamic approach to the study of the relationship between people participation in Agricultural Land Reform Cooperative performance and the economic performance over time. Two Cooperatives are examined- “successful” and “non-successful” -and policy changes are discussed in terms of the performance of these two Cooperatives.
This paper reports on the annual summer training program of children’s creative development conducted since 1986. The training targets per program are between 80-100 children aged between 9-14 years coming from various urban and rural parts of Thailand to join the 8-10 day program for moral and technical development. The program is planned and coordinated by the author with considerable inputs from Buddha’s teaching in self-reliance: the potential of human being prevent their defilement; and from people who expertise in architecture and technology. The method approached for explaining human performance in nature, is a simulation game designed by the author with the help of her colleague in computers. The model concept is derived from a system dynamics method as a tool for dissemination of the law of cause-effect action in Buddhism. The children evaluated joyfully and rapidly understand the mechanism of mind in decision making whether to conduct good or bad actions according to the Buddha’s principle by playing and thinking themselves with this simulation game in a better way than they do in the traditional method of lectures by monks or teachers. The game simulates the interaction relationship between a human’s performance and his life expectancy. Later the workshop practice of the electronic application is approached for systematic problem-solving about peoples’ needs in terms of technological development in relation to promotion of moral values.
In this paper, first of all, a qualitative analysis is done on a general infections disease SD model, and a new epidemic threshold value and an epidemic scale forecasting formula are proposed. Then in consideration of the properties of type-A hepatitis and its eruptive spread SD model is put forward. A lot of work in various aspects is done, for example: the problem to simulate the type-A hepatitis incubation period is solved practically; the simulation results fitted in with the reality are achieved; through simulation analysis and qualitative analysis, the reason for that the predicted 2nd peak of this spread didn’t appear is found out; the short-term and long-term prospects of Shanghai type-A hepatitis situation are brought forward; especially, hypotheses about the mechanisms of the periodic epidemic and the eruptive spread of type-A hepatitis are put forward. These results are imbued with guiding significance for prevention and control of the type-A hepatitis and other infectious diseases.
An integrated system dynamics policy model was developed for a state level economic activity, population, energy demand, supply, and price with realistic feedback mechanisms. Environmental impacts and influences on technical and economic efficiency were also modeled. The model and its use to perform a joint analysis of several interacting policies, including electric and gas utility least cost planning and the construction of an interstate natural gas pipeline are described. A number of interesting results from a variety of perspectives are presented. These include an evaluation of the economic development; air quality and energy efficiency impacts of the pipeline proposal; their sensitivity to fuel prices; and some novel observed feedback relationships between energy price and air quality. The lessons learned in model development, implementation and utilization in both policy and regulatory arenas are discussed. The benefits of fully integrating economic and environmental impacts for policy modeling are evaluated.