Executing Multiple State Machines

Overview

Simulating behaviors at the mission level often requires multiple state machines. In this section, you will create a state machine for the UAV's onboard computer and a simulation dashboard that allows you to view the execution of both the computer and power system's state machines at the same time. You will also use the simulation state history log to help debug your simulation.

This section covers the following concepts:

• State machines
• simulation dashboards
• simulation state history log

Figure A1: Multiple State Machines

Prerequisites

Prerequisite	Description
Behavior Execution Engine Installation	You must have installed Behavior Execution Engine.
Tutorial Project	You must start this section with the Behavior Execution Engine simulation project from the last section of the previous tutorial. If you did not complete that section, you can use the following project from the Behavior Execution Engine installation: \documentation\tutorialFiles\01\SimulationExecution.mdzip
Recommended Reading	Before completing this section, you may want to read the following help topics: State machines The simulation dashboard and simulation state history log file section of the Running Interactively topic

Instructions

Create a state machine for the computer

1. Open the project from the previous tutorial.
2. In the Containment Tree, right-click the Structure > Computer block and select Create Diagram (or press CtrlShiftD).
3. Select SysML State Machine Diagram and enter Computer State Machine as its name.
4. Select the state on the diagram and enter Standby as its name.
5. Click the Transition button () on the context toolbar. Then click anywhere on the canvas to add a new state.
6. Select the new state on the diagram and enter PoweringOn as its name.
7. Click the Transition button () on the context toolbar. Then click anywhere on the canvas to add a new state.
8. Select the new state on the diagram and enter PoweredOn as its name.

Figure B1: The computer state machine

Create a simulation dashboard

A simulation dashboard is useful for viewing all of the behaviors of your system simultaneously during a simulation.

1. Right-click the Simulation package and select Create Diagram (or press CtrlShiftD).
2. In the UML Diagrams category, select Object Diagram and enter Simulation Dashboard as its name. You may need to click the Expert button at the bottom of the Create Diagram dialog box in order to be able to select Object Diagram.
3. Drag the Structure > PowerSystem > PowerSystem State Machine > PowerSystem State Machine diagram onto the dashboard, and click the Show Diagram Overview Content button () to display the state machine.
4. Drag the Structure > Computer > Computer State Machine > Computer State Machine diagram onto the dashboard and click the Show Diagram Overview Content button () to display the state machine.
5. In the Simulation Dashboard, click anywhere on the unused canvas area and press CtrlQ to auto-format the state machine diagrams.

Figure B2: The simulation dashboard

Examine the simulation state history log

The simulation state history log records every state and transition that executes, making it a useful tool for debugging unexpected behavior in your simulation.

1. Execute the simulation and look in the resulting state history trace to observe that only the PowerSystem State Machine executes.
2. Select Ansys > Behavior Execution Engine > Open Log File Directory in File Explorer (or press CtrlAltShiftL).
3. Open simulation_trace.json in a text editor.
4. Search for Computer. You should get no results, confirming that the Computer State Machine did not run. Close the log file.

Add the computer to the root instance specifications

Recall from the Simulation Execution section of the previous tutorial that in order for a state machine to be executed, it must be specified in the subject slot of the simulation instance specification.

1. In the Containment Tree, double-click the Simulation > simulation instance specification and select Slots from the left pane of the specification window.
2. In the center pane, select the subject slot.
3. In the right pane, click the Add button ().
4. Select Simulation > uav.computer. Then click OK and then Close.
5. Execute the simulation again and look at the state history trace output to note that now both state machines show up.
6. Save your work before continuing.

Next Section >