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- Type:
- Document
- Fecha de Creacion:
- 1984
- Collection:
- System Dynamic Society Records
- Collecting Area:
- University Archives
- Collection ID:
- ua435
- Parent Record(s):
- dcf80aca09fd0af264c0472357441115, 23d738ba88f8333bc39725f9cb5bd0b8, and 6e5cbea1fd05527880f389afd8fb85d1
- Descripción:
- There is a conspicuous gap in the literature about feedback and circular causality between intuitive statements about shifts in loop dominance and precise statements about how to define and detect such important nonlinear phenomena. This paper provides a consistent, rigorous, and useful set of definitions of loop polarities, dominant polarity, shift in dominant polarity, and shift in loop dominance, and illustrates their application in a range of system dynamics models. Consistent with the usual intuitive definitions, the polarity of a first-order feedback loop involving a level x and a single inflow ẋ is defined to be the sign dẋ/dx. Loop polarity is shown to depend upon the sign of parameters not usually considered part of the loop itself. This expression of loop polarity is then applied to multi-loop first-order systems to define the polarity of such systems. All positive loops with gain less than one, such as economic multipliers, are shown to be multi-loop systems with dominant negative polarity. The shifts in loop dominance that occur in nonlinear systems arise naturally as changes in the sign of the dominant polarity. Examples applying the notion of dominant polarity reveal a useful geometric characterization of shifts in loop dominance in nonlinear first-order systems. The concepts developed in the paper are then applied to simple higher-order nonlinear feedback systems. The final application to a bifurcating system suggests that all bifurcations in continuous systems can be understood as consequences of shifts in loop dominance at equilibrium points.
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- Type:
- Document
- Fecha de Creacion:
- 1984
- Collection:
- System Dynamic Society Records
- Collecting Area:
- University Archives
- Collection ID:
- ua435
- Parent Record(s):
- dcf80aca09fd0af264c0472357441115, 23d738ba88f8333bc39725f9cb5bd0b8, and 6e5cbea1fd05527880f389afd8fb85d1
- Descripción:
- This paper presents a total stability analysis of a simplified Kondratieff-wave model. The purpose is to show how such an analysis can be carried out and to illustrate the kind of information one obtains. For normal parameter values the Kondratieff wave model has a single unstable equilibrium point. Combined with non-linear constraints in the model's table-functions, this instability creates a characteristic limit cycle behavior. For other parameter values, however, the model is stable and generates damped oscillations instead of the limit cycle. For yet other combinations of parameters, the non-linear constraints yield to the instability, and sustained exponential growth or total collapse result. By means of linear stability analysis we first determine the conditions for the transition between a stable and an unstable equilibrium to take place. This transition is known as a Hopf-bifurcation. Using global analysis we outline the phase-portrait of a fully developed limit cycle. By the same method, we examine the conditions under which the non-linear functions fail to contain the system so that exponential run-away or collapse occur. A DYNAMO-program is then developed which calculates the Lyapunov exponents of the system during a simulation, and we discuss how these exponents can be used as a measure of the divergence or convergence of nearby trajectories. Finally, we illustrate how subsequent period doublings and chaotic behaviour can occur if the model is driven exogenously by a weak sine-wave, representing for instance the short term business cycle.
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- Type:
- Document
- Fecha de Creacion:
- 1984
- Collection:
- System Dynamic Society Records
- Collecting Area:
- University Archives
- Collection ID:
- ua435
- Parent Record(s):
- dcf80aca09fd0af264c0472357441115, 23d738ba88f8333bc39725f9cb5bd0b8, and 6e5cbea1fd05527880f389afd8fb85d1
- Descripción:
- During the summer of 1982 the author made predictions of wood pulp prices for the period 1982 to 1986. The predictions were part of a decision on whether to sell a large pulping plant in Norway. This paper presents the predictions and the basis on which they were made. Next, the predictions are compared with actual data for the period 1982 to 1984.
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- Type:
- Document
- Fecha de Creacion:
- 1984
- Collection:
- System Dynamic Society Records
- Collecting Area:
- University Archives
- Collection ID:
- ua435
- Parent Record(s):
- dcf80aca09fd0af264c0472357441115, 23d738ba88f8333bc39725f9cb5bd0b8, and 6e5cbea1fd05527880f389afd8fb85d1
- Descripción:
- A dynamic simulation model of the Indian economy has been developed which captures the important linkages between economic growth and the development of various forms of energy. Non-commercial forms of energy which supplied the bulk of total energy requirements of the economy so far have clearly reached their saturation limits. Capital costs for coal and petroleum increase with resource depletion. The cost of hydroelectricity increases as the cheaper and more accessible resources are exhausted. The costs of renewable energy sources such as solar, wind and biomass decrease with cumulative production due to technical progress. Such sources of energy become more important sources in the future though their current share of the total energy production is negligible. The thesis examines the dynamics of the transition to the new era as well as responses of the economy to energy shocks such as steep increases in international oil prices. It investigates the possibility of an interim crisis if the domestic energy industry is slow to develop or if the response of energy demand to rising energy prices is sluggish. Such a difficult transition may be marked by persistent import dependence, high energy prices and high outlays in the energy sectors that reduce the resources available to the non-energy sectors for consumption and growth. An aggregate production function utilizing capital, labour and energy as factor inputs has been utilized for the economy along with a neo-classical formulation for consumption and saving in the economy. The model generates the energy demand of the economy endogenously and incorporates the adaptation of energy intensity to rising real energy prices through more efficient new capital equipment as well as retrofits of inefficient equipment. The model has been calibrated using Indian data. Where parameters or assumptions are based on uncertain facts, sensitivity tests have been carried out. The effect of government policies such as taxation of energy or emphasis on conservation have been investigated.
-
- Type:
- Document
- Fecha de Creacion:
- 1984
- Collection:
- System Dynamic Society Records
- Collecting Area:
- University Archives
- Collection ID:
- ua435
- Parent Record(s):
- dcf80aca09fd0af264c0472357441115, 23d738ba88f8333bc39725f9cb5bd0b8, and 6e5cbea1fd05527880f389afd8fb85d1
- Descripción:
- The emergence of powerful personal computers and CAD/CAM machines offers a new opportunity for DYNAMO. Although users are generally satisfies with the language, a survey shows they want expanded simulation capabilities including single simulations, eigenvalue analysis, sensitivity analysis, and the optimization by multiple simulation and hill climbing. Novices want easier access to models and simulation. The modular version of DYNAMO now in development will meet these goals. It will break DYNAMO’s normal functions into separate programs that users can reassemble in different ways. For example, one compiler will translate both conventional models and games. The simulation controller will work with a regular rerun, a game, or a sensitivity analysis package. The report generator will display output from any of these packages. These modules will communicate through standard data files, which users can also access for other purposes such as statistical analysis.
-
- Type:
- Document
- Fecha de Creacion:
- 1984
- Collection:
- System Dynamic Society Records
- Collecting Area:
- University Archives
- Collection ID:
- ua435
- Parent Record(s):
- dcf80aca09fd0af264c0472357441115, 23d738ba88f8333bc39725f9cb5bd0b8, and 6e5cbea1fd05527880f389afd8fb85d1
- Descripción:
- A division of a large textile company was chosen as the focus of a system dynamics study to determine how management would respond to any capacity adjustment problem. The company produces fabrics for household as well as industrial uses and the annual sales of the company are several billion dollars. The division under study produces yarn and piece dyed draperies, mattress tickings, and upholstery fabrics. The four major manufacturing processes in the division are spinning, yarn preparation, fabric formation and fabric dyeing and finishing. Although not aimed at any particular perceived problems, the study was undertaken with two purposes, firstly to develop a system dynamics model that would describe the performance of the division and secondly to use the mode to investigate the effects of demand changes on various capacity adjustment policies practiced in the division. The study includes interactions among a large number of factors in forecasting and inventory control, raw material supplies, employment, and production capacity. These factors related to some ten points and four processes of the division. Data and other information have been collected by questionnaires and interviews with management. The model has been tested for its validity in representing the actual operations. The model is now being used in testing some of the policies in response to change in customer order rate.
-
- Type:
- Document
- Fecha de Creacion:
- 1984
- Collection:
- System Dynamic Society Records
- Collecting Area:
- University Archives
- Collection ID:
- ua435
- Parent Record(s):
- dcf80aca09fd0af264c0472357441115, 23d738ba88f8333bc39725f9cb5bd0b8, and 6e5cbea1fd05527880f389afd8fb85d1
- Descripción:
- A static and a dynamic model of the oil market are compared. Three major differences appear in forecasts. The dynamic model fluctuates around the static mode equilibrium price. The dynamic model shows greater uncertainty in trend development. The dynamic model forecast overshoots the cost level of synthetic oil.
-
- Type:
- Document
- Fecha de Creacion:
- 1984
- Collection:
- System Dynamic Society Records
- Collecting Area:
- University Archives
- Collection ID:
- ua435
- Parent Record(s):
- dcf80aca09fd0af264c0472357441115, 23d738ba88f8333bc39725f9cb5bd0b8, and 6e5cbea1fd05527880f389afd8fb85d1
- Descripción:
- How should a causal loop diagram be drawn to explain structure as clearly as possible? Two basic rules are formulated: Feedback-loops should be drawn with loop-form, and influence should be unidirectional through each variable. An example shows that application of the two rules leads to enhanced clarity. Artistic derivations from the two rules can be used to produce memorable figures. Current practice in causal loops diagramming indicates a potential for improvements.
-
- Type:
- Document
- Fecha de Creacion:
- 1984
- Collection:
- System Dynamic Society Records
- Collecting Area:
- University Archives
- Collection ID:
- ua435
- Parent Record(s):
- dcf80aca09fd0af264c0472357441115, 23d738ba88f8333bc39725f9cb5bd0b8, and 6e5cbea1fd05527880f389afd8fb85d1
- Descripción:
- This paper presents a flexible, model-based approach to strategic program design--the process of putting together consistent business programs and policies to support new strategic initiatives. The new approach combines ideas from administrative theory and feedback theory. Administrative theory reveals the organizational and diffusion processes that connect business programs and customers. Feedback theory reveals patterns (feedback loops) in the connections between programs and policies of a business and its market. This conceptual framework is applied to strategic program design in a two-phase analysis which is much more flexible than traditional system dynamics business modeling. Phase 1 is a descriptive analysis that explores business-market structure in terms of organizational and diffusion processes, showing where conflicts of responsibility, confused incentives, misinformation, and administrative inertia may degrade business performance. Phase 2 uses simulation modeling and the descriptive information from phase 1 to debate policy options and program design. The style of analysis is illustrated with business cases and applications projects.
-
- Type:
- Document
- Fecha de Creacion:
- 1984
- Collection:
- System Dynamic Society Records
- Collecting Area:
- University Archives
- Collection ID:
- ua435
- Parent Record(s):
- dcf80aca09fd0af264c0472357441115, 23d738ba88f8333bc39725f9cb5bd0b8, and 6e5cbea1fd05527880f389afd8fb85d1
- Descripción:
- The simple two-sector Kondratieff model developed by John Sterman has contributed significantly to our understanding of some of the basic mechanisms underlying the economic long wave. The dynamic hypothesis of this model is that the positive feed-back associated with the so-called self-ordering of capital reinforces and prolongs the characteristic expansions and contractions of the capital sector as it adjusts its capacity to the required production. It is assumed that this feed-back can be strong enough to produce a self-sustained oscillation (a limit cycle) with a period which is about twice as long as usual capital lifetimes. Concentrating on the ordering and production of capital, the Sterman model only depicts a relatively small fraction of our economic system. At least in its original version, the model doesn't deal with several of the basic phenomena involved in the verbal description of the economic long wave, as it is usually presented. There is no account of variations in employment, buying power or political attitudes, for instance, and changes in the rate of innovations are also outside the model boundary. We do not think that one can presently develop a complete and satisfactory model of the economic long wave. We have therefore adopted an alternative starting point by assuming that the alternating phases of economic expansion and stagnation arrise from the succession of technical-economic cultures each characterized by its own infrastructure, leading industrial sectors, typical production methods and main products. Even the geographical location of the dominant political-economic center may shift from wave to wave. This is Mensch's process of metamorphosis. Where the Sterman approach emphasizes the cyclic character of the wave, our model is meant to describe the qualitative changes through which one set of technologies replaces the next. In our model, the economic system has no equilibrium point to oscillate around. As long as technology develops and new discoveries are made, the potential for economic activity continues to grow. A purpose of the model is therefore to show how randomly distributed discoveries can be bunched into waves of innovations with a relatively well defined period.
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