Simulink in barebones form not-well suited
for simulating networks/nodal systems
◦ 1) No sense of bi-directionality
◦ 2) No notion of ‘nodes’
◦ 3) Energy conservation has to be maintained via
algebraic constraint blocks in each sub-unit
Can be done….but very messy, difficult to
◦ Solve network state in one custom block
◦ Better understood on how to get the correct
◦ Not well-suited for ‘group’ approach
◦ Code interface to solver block could get messy fast
◦ Hard to expand to new sub-systems
◦ Use Simulink ‘Simscape’ Libraries
◦ Let Simulink do the book-keeping for energy
conservation, flows, network state, time etc
◦ Graphical components for building networks
◦ Built-in Hydraulic domain assumes constant temperature
◦ New thermo/hydraulic domain (and accompanying
components) have to be written/re-written
A simulink package to model physical
domains and networks
Based off of ‘Bond-Graph’ Theory
◦ Physical dynamic systems can be abstracted into
networks in which:
 1) There exists “Flow” variables
 2) There exists “Effort” variables
 3) Energy is conserved
How to write a domain that couples hydraulic
and thermal behavior?
◦ Learn the mechanics of ‘Simscape’ Language
(structure, syntax, etc)
◦ Test with a sample, energy conserving networks
How to modify that domain to accurately
model our system?
◦ Mass flow rate, pressure, enthalpy, momentum, etc.
◦ Build a source, flowing into a simple network of
Electro-Hydraulic Servo valve Example
2 ‘Effort’ (across) variables
◦ Temperature and Pressure drops
2 Corresponding ‘FLOW’ variables
Power = Flow*Effort
◦ Energy conserving variables noted
◦ Default values assigned (but are over-written in
each model)
At,p +
Bt,p Component Template
Constraints, not assignments!
Includes both domains, but not coupled
Units matter!!
Reference node
What are our effort variables and units?
What are our flow variables and units?
What are the governing network equations, in
nodal form?
What are the domain coupling
expressions/constraints between the two

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