bondgraph

A python library for creating bond graphs of physical systems and generating differential equations.

It heavily relies on sympy for manipulation and simplification of equations symbolically.

Installation

Install via pip:

pip install bondgraph

To install with extra dependencies for visualization using graphviz:

pip install bondgraph[visualization]

Usage

Create a BondGraph object and add Bond objects connecting various elements:

# This example generates the following simple bond graph:
#
# Se ---> 1 ---> I
#         |
#         v
#         R

from bondgraph.core import Bond, BondGraph
from bondgraph.junctions import JunctionEqualFlow
from bondgraph.elements import Element_R, Element_I, Source_effort
from sympy import Symbol

force = Source_effort("force", Symbol("F"))
friction = Element_R("friction", Symbol("k_f"))
inertia = Element_I("inertia", Symbol("m"), Symbol("p"))
mass_object = JunctionEqualFlow("mass_object")

graph = BondGraph()
graph.add(Bond(force, mass_object))
graph.add(Bond(mass_object, friction))
graph.add(Bond(mass_object, inertia))

state_equations = graph.get_state_equations()

# Print the dictionary of state variables and the right hand side of their state equations:
print(state_equations)
# {p: F - k_f*p/m}

# If using the optional visualization features, generate and display a graphviz graph:
from bondgraph.visualization import gen_graphviz

output_graph = gen_graphviz(graph)
output.view()

Limitations

• Algebraic loops are not handled at all and will result in failure to generate equations.
• Non-integrating (differential) causality for C or I elements is not currently possible.