In addition to the features shown in the two previous parts of this blog series, Model-Based Engineering (MBE) must meet two more requirements:
- Architecture modeling must capture the interconnections between system parts, and
- Architecture modeling must support simulation with the appropriate software tools.
In the third part of this series, we will look at how these might be implemented in our washing machine model.
The Washing Machine – Internal Connections
Our washing machine has multiple sets of critical connections: fluid, electrical and mechanical. In SysML, these connections can be represented in Internal Block Diagrams, which show how the parts of the system are connected.
Figure 1 SysML Internal Block Diagram, power connections
Figure 1 shows the main power connections in our simplified washing machine model. The main power input into the system is shown on the lower left, entering the Circuit Breaker subsystem, which redistributes it to Control_Power and Motor_Power outputs and ultimately to the components that require power, such as the tub agitator and spin motors.
Figure 2 SysML Internal Block Diagram, water connections
Figure 2 shows a combination of fluid flows and the electrical signals that monitor and control them. The characteristics of these flows are captured by the port types that are connected. For example, the ports typed by Water_Flow are characterized by three parameters: flow rate (GPM, gallons-per-minute), temperature (°F) and pressure (psi).
Note that while the system parts have been somewhat arbitrarily categorized into mechanical, hydraulic and electrical subsystems, the connections in these diagrams can cross between subsystems.
Connections to Simulation
While SysML has some capability for quantitative analysis through parametrics, complex simulations will continue to be performed with software tools designed for the purpose, such as Simulink or Modelica. The challenge is maintaining consistency between the modeling and simulation tools as the system evolves.
Syndeia addresses this challenge, providing the ability to generate, compare and synchronize such models across tool boundaries. In this example, Syndeia has taken the multilevel connectivity information represented in the SysML diagrams in Figures 1 and 2 and used them to generate equivalent models in Simulink (The MathWorks, Inc.).
Figure 3 Simulink top-level structure, Washing Machine system
Figure 4 Simulink structure, Electrical Subsystem
Figure 3 shows the top-level Simulink structure, the three main subsystems with the connections between them. Figure 4 shows the internal structure of one of those subsystems. What is carried over from SysML to Simulink are blocks, connectors and ports. The resulting Simulink model is a starting point for the Simulink specialist to build MATLAB code into the blocks that result in an executable model. Because Syndeia maintains a set of persistent connections between the models, changes to the block/connector/port structure on either side can be identified and updated (bidirectionally) as system development proceeds.
In the first three parts of this series, we created connections between SysML, PLM, requirements and simulation models. The resulting network becomes an important asset in its own right, representing a high-level map of system data that can support traceability and navigation across the Total System Model (TSM). In Parts 4 and 5, we will look at visualizing and querying the TSM with Syndeia.