Defining Ports and Flows

The diagrams in the topics of this section show how items that flow can be modeled, using Ports, Flows and Flow Specification on Block Definition, Internal Block and Parametric diagrams. Most physical systems will have items that flow, which can be an important part of how the system works. We could consider a number of examples, including:

• A desalination plant - where both salt and fresh water and power flow through the system
• A production line where assemblies, parts, power and robot control instructions flow through the system
• An urban transport system where trains, trams, buses, ferries and passengers flow through the system
• An aircraft where fuel, air, control signals, hydraulic fluid, passenger, flight attendants flow through the system

The diagrams start by defining a Controller Area Network (CAN) bus architecture and show how a number of flow specifications can be used to define the way that items flow between parts of the Power Subsystem. The flow of fuel is modeled using a Block Definition diagram that exhibits Flow Ports (deprecated in SysML version 1.5) that show the logical 'conduit' allowing fuel to flow from the Fuel Assembly and the Internal Combustion Engine. Internal Block diagrams take this further, and finally a Parametric diagram is used to show how a mathematical equation for fuel flow rate, defined in a Constraint, can be used to model the equation. Simulated plots are then visualized using Enterprise Architect's simulation capabilities.