Bond graphs of open systems: a water rocket example

A model of a small-scale water rocket is developed as an example of open-system modelling by both a bond graph approach and a more classical method. In addition to the formulation and bond graph development, a goal of the research is to determine the benefits of the bond graph approach into affording an insight into the system dynamics. Both modelling approaches yield equivalent differential equations, as they should, while the bond graph approach yields significantly more insight into the system dynamics. If a modelling goal is to simply find the system equations and predict behaviour, the classical approach may be more expeditious. If insight and ease of model modification are desired, the bond graph technique is probably the better choice.