Bond graph modeling - Application to energy systems

This file should be read in conjunction with the fascicule "Bond graph modeling. Basic elements for energetics".

Industrial processes are governed by the mutual interaction of several phenomena of different natures, and involve technological components that apply laws from different disciplines. This is why their modeling requires a unified approach. The bond graph tool, with its multi-disciplinary vocation, is ideally suited to understanding such systems.

The dynamic behavior of this type of system is generally described by nonlinear differential equations. Their equation by classical methods and the deduction of state variables is complicated. Their modeling therefore requires a structured approach capable of highlighting the physical nature and location of state variables. State variables, in the sense of bond graphs, are variables associated with energy storage and directly deduced from the graphical model.

What's more, these systems are not static: the bond graph model is scalable, making it easy to refine the model simply by adding new elements (heat loss, inertia effect, etc.), without having to start all over again. To adapt the model, you simply need to add, for example, dissipative elementsR for heat transfer or hydraulic resistance phenomena, elementsC for fluid compressibility, for wall thermal capacities and for mass and volume storage, and elementsI for any inertia phenomena.

Finally, when modeling energy engineering processes, including chemical systems, the choice of power variables is not trivial, as the number of power variables is greater than the number of degrees of freedom. The bond graph energy approach and the use of generic power variables enable power variables to be selected according to the physical system to be modeled.

However, we must emphasize the limitations of the methodology, which is not applicable to systems with distributed parameters and to models described by discrete events. Finally, based on our teaching experience, we'd like to point out that the main difficulty in using this tool lies in the knowledge of physics, not in learning the language.

This text illustrates the theoretical concepts developed in the dossier. . It is devoted to applications for modeling single-energy and coupled-energy thermal systems (thermofluid process).