World3 in Modelica: System Dynamics Models

World3 in Modelica: Creating System Dynamics Models in the Modelica Framework

This paper and presentation by F. E. Cellier introduces a new release of the System-Dynamics library of Modelica and shows how it is being used by discussing a fairly large application code: Meadows’ World3 model.

Meadows’ only talked in Limits to Growth about the results obtained with the model. The model itself, originally coded in Dynamo, was described in a separate book.

Meadows’ World3 model has seen two major upgrades since its original inception, one in 1992, i.e. after 20 years, and the second in 2002, i.e., after 30 years. The World3 application code contained in SystemDynamics 2.0 implements the 2002 version of the World3 model. In the code, we offer not only the basic model, but also all 10 scenarios that Meadows and co-workers are talking about in Limits to Growth: The 30-Year Update.

Future Research

What future additions are in the works? In today’s world of dwindling fossil fuel reserves, it becomes important to track how much energy we are actually using. Whereas classical System Dynamics is designed to track material flows, it does not track energy flows. This is a major drawback of the methodology.

For this reason, a second version of the System Dynamics library has also been released as a sublibrary of BondLib, our bond graph library. In that version, all material flows are represented internally by bond graphs. A bond graph naturally tracks energy flows. Each energy flow, in that version of the library, is represented as the product of a specific enthalpy and a mass flow. Hence we can track material flows and energy flows simultaneously.

When I drive my car from home to work, I am not only spending energy in the form of the gas that my car consumes. Some energy was also spent in producing the car, and more energy will be spent in discarding it at the end of its lifecycle and in recovering those materials from it that can be recycled.

The accumulated energy that accounts for all of those indirect uses of energy is called emergy. The specific enthalpy can be used to encode in the model the specific emergy, i.e., the emergy per unit of mass.

I plan on porting examples of emergy modeling, as described in the publications by Howard Odum, over to the bond graph implementation of the System Dynamics library, but this work has not yet been completed.


Check out the full paper and presentation by Prof. Dr. François E. Cellier here.

Building a Green New House

In a short, funny, data-packed talk at TED U, Catherine Mohr walks through all the geeky decisions she made when building a green new house -- looking at real energy numbers, not hype. What choices matter most? Not the ones you think.



Catherine and Paul Mohr live in Silicon Valley with their daughter Natalie and cats Loki and Tia. In addition to building a green house, they both work on designing and building surgical robots at Intuitive Surgical.

Their 301 Monroe blog has entries about our house building process including:

• “Energy” for posts that are particularly concerned with energy calculations and energy savings
• “Sustainability” spans many subjects and includes many of the energy and water and strawbale posts, but also includes posts about sustainability of other materials

The Embodied energy calculations discussed in Catherine’s TED talk can be found on the Embodied Energy Blog post.

Environment, power, and society for the twenty-first century

"Get a rare, fresh, enlightening glimpse of the Big Picture of our environmental and energy problems - Highly recommended." -- Choice

Howard T. Odum possessed one of the most innovative minds of the twentieth century. He pioneered the fields of ecological engineering, ecological economics, and environmental accounting, working throughout his life to better understand the interrelationships of energy, environment, and society and their importance to the well-being of humanity and the planet.

Environment, Power and Society for the Twenty-First Century: The Hierarchy of Energy is a major modernization of Odum's classic work on the significance of power and its role in society, bringing his approach and insight to a whole new generation of students and scholars. For this edition Odum refines his original theories and introduces two new measures: emergy and transformity. These concepts can be used to evaluate and compare systems and their transformation and use of resources by accounting for all the energies and materials that flow in and out and expressing them in equivalent ability to do work. Natural energies such as solar radiation and the cycling of water, carbon, nitrogen, and oxygen are diagrammed in terms of energy and emergy flow. Through this method Odum reveals the similarities between human economic and social systems and the ecosystems of the natural world. In the process, we discover that our survival and prosperity are regulated as much by the laws of energetics as are systems of the physical and chemical world.


The Book Environment, Power and Society for the Twenty-First Century: The Hierarchy of Energy is available on Google Books with limited preview.

Climax and Descent (Chapter 13)

The growth of civilisation on the nonrenewable reserves of the earth is surging to a climax of information miracles, stormy economics, turbulent populations, concentrated wealth, and bewildering complexity. Although the future is always masked by the oscillations of smaller scale, the empower of society may be at climax in transition to times of receding energy. This last chapter uses principles of energy hierarchy and pulsing to anticipate the future, suggest adaptive policies, and seek a prosperous way down.

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By developing explanations and plans now for making descent prosperous, we can be ready when the shocks of change galvanize the attention of society. Some can have faith in the future from understanding energy principles. Other will find faith in religions that adapt the necessary commandments for once again fitting culture to the earth. The people of Easter Island disappeared, leaving only their monuments as an example to the world of what happens when culture cannot downsize to fit its environmental production.