This example shows how to use a combination of Simulink^{®}
Control Design™ and Simulink verification blocks, to assert that the linear system characteristics
satisfy one of the following bounds:

Phase margin greater than 60 degrees

Phase margin less than 60 degrees and the velocity less than or equal to 90% of the cruise velocity.

Open the Simulink model of an aircraft.

scdmultiplechecks

The aircraft model is based on a long-haul passenger aircraft flying at cruising altitude and speed. The aircraft starts with a full fuel load and follows a pre-specified 8-hour velocity profile. The model is a simplified version of a velocity control loop, which adjusts the fuel flow rate to control the aircraft velocity.

The model includes blocks to model:

Fuel consumption and resulting changes in aircraft mass

Nonlinear draft effects limiting aircraft velocity

Constants used in the model, such as the drag coefficient, are defined in the model workspace and initialized from a script.

The

`v <= 0.9*vCruise`

and`Assert that: PM >= 60 or if PM < 60 then v <= 0.9*vCruise`

blocks are Check Static Upper Bound and Assertion blocks, respectively, from the Simulink Model Verification library. In this example, you use these blocks with the Check Gain and Phase Margins block to design a complex logic for assertion.View the linearization input, output and settings in the

**Linearizations**tab of the Check Gain and Phase Margins block parameters dialog box.The model has already been configured with:

Linearization input and output for computing gain and phase margins

Settings to compute the linear system

The software linearizes the loop seen by the Velocity Controller block every 30 minutes of simulated time and computes the gain and phase margins.

Specify phase margin bounds in the

**Bounds**tab of the Check Gain and Phase Margins block.In this example, the linearization input and output include the summation block with negative feedback. Change the

**Feedback sign**, used to compute the margin, to`positive feedback`

.To view the phase margins to be computed later during simulation, specify

`Tabular`

in**Plot type**, and click**Show Plot**.Design assertion logic that causes the verification blocks to assert when the phase margin is greater than 60 degrees or if the phase margin is less than 60 degrees, the velocity is less than or equal to 90% the cruise velocity.

In the Check Gain and Phase Margins Block Parameters dialog box, in the

**Assertion**tab, select**Output assertion signal**, and click**Apply**.This action adds an output port

`z`

to the block.^{-1}Double-click the

`v <= 0.9*vCruise`

block, and specify the block parameters, as shown in the following figure. After setting the parameters, click**Apply**.These parameters configure the block to:

Check if the aircraft velocity exceeds the cruise velocity by 0.9 times

Add an output port to the block

Connect the Check Gain and Phase Margins,

`v <= 0.9*vCruise`

and`Assert that: PM >= 60 or if PM < 60 then v <= 0.9*vCruise`

blocks, as shown in the following figure.This connection causes the

`Assert that: PM >= 60 or if PM < 60 then v <= 0.9*vCruise`

block to assert and stop the simulation if the phase margin is less than 60 degrees and the velocity is greater than 90% of the cruise velocity.

Alternatively, you can type

`scdmultiplechecks_final`

at the MATLAB^{®}prompt to open a Simulink model already configured with these settings.Simulate the model.

During simulation:

The

`v <= 0.9*vCruise`

block asserts multiple times.The Check Gain and Phase Margins block asserts two times. You can view the phase margins that violate the bound in the plot window.

The

`Assert that: PM >= 60 or if PM < 60 then v <= 0.9*vCruise`

does not encounter the assertion condition. Therefore, the simulation does not stop.

Click the link at the bottom of the Simulink model to open the Diagnostic Viewer window.

When a block asserts, warnings appear in this window. You can view the details of the assertions by clicking the link in this window.