### Coupled_Domains

```
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
expand

Approach
◦ Solve network state in one custom block

Pros
◦ Better understood on how to get the correct
solution

Cons
◦ Not well-suited for ‘group’ approach
◦ Code interface to solver block could get messy fast
◦ Hard to expand to new sub-systems

Approach

Pros
◦ Let Simulink do the book-keeping for energy
conservation, flows, network state, time etc
◦ Graphical components for building networks

Cons
◦ 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
pipes
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 +
qf
qt
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
domains?
```