Appendix: An Introduction to Bond Graph Modelling
2011
dissipation of energy (usually as heat), transient storage or transforming it to another useful form.With this brief explanation, the bond graph elements can be categorized as Sources (or Active elements), Passive elements, Converters, and Junctions. A.2.1 SourcesEnergy sources are devices that contain one sort of energy and, when connected to a system, the flow of energy is established.As stated earlier, any sort of energy has both flow and effort components.Sources in a bond graph are distinguished by their dictating component; in other words, an energy source can only dictate either flow or effort factors and cannot control the other factor.A flow source S f , therefore, is an energy source that has a specific flow level f à and, when connected to a system, energy will be passed to the system with a flow value of f à .The value of effort of the flow source will depend on the energy demand of the connected system.For an ideal source of flow, the flow level f à is independent of energy demand and always remains unchanged.An example of a flow source in mechanical systems is a large moving body with a constant speed (e.g. the Earth, a train, etc.) and in electrical systems the current source in electrical circuits is an example.An Effort source S e , is an energy source that has a specific effort level e à and, when connected to a system, energy will be passed to the system with effort value of e à .Again, the value of flow to the system depends on the energy demand of that system and cannot be controlled by the source.For ideal effort sources, the value e à will not be altered by the energy drain from the source.Examples of effort sources in mechanical and electrical systems are a force and a battery respectively.In bond graphs, simple arrows are used to indicate the direction of energy flow.The bond graph graphical symbols for the effort and flow sources are shown in Figure A.1.Energy sources are single-port elements since they transmit only one sort of energy to the systems.Appendix 10.