MATLAB Examples

Assess the Damping Ratio of a Flutter Suppression System

Using a custom criteria script, verify that wing oscillations are damped in multiple altitude and airspeed conditions.

The Simulation and Model

The model uses Simscape™ to simulate a Benchmark Active Controls Technology (BACT) / Pitch and Plunge Apparatus (PAPA) setup. It uses Aerospace Blockset™ to simulate aerodynamic forces on the wing.

The test iterates over 16 combinations of Mach and Altitude. The test case uses custom criteria with Curve Fitting Toolbox™ to find the peaks of the wing pitch, and determine the damping ratio. If the damping ratio is not greater than zero, the assessment fails.

Running this test case requires

• Simscape Multibody™
• Aerospace Blockset™
• Curve Fitting Toolbox™

Open the model and the test file.

'sltestFlutterSuppressionSystemExample.slx'))
'sltestFlutterCriteriaTest.mldatx'))

Custom Criteria Script

The test case custom criteria uses this script to verify that the damping ratio is greater than zero.

% Get time and data for pitch
Time = test.sltest_simout.get('sigsOut').get('pitch').Values.Time(1:15000);
Data = test.sltest_simout.get('sigsOut').get('pitch').Values.Data(1:15000);
% Find peaks
[~, peakIds] = findpeaks(Data,'minpeakheight', 0.002, 'minpeakdistance', 50);
peakTime= Time(peakIds);
peakPos = Data(peakIds);
rn = peakPos(1)./peakPos(2:end);
L = 1:length(rn);
% Do curve fitting
fittedModel = exponentialFitAndPlot(L, rn);
delta = fittedModel.d;
% Find damping ratio
dRatio = delta/sqrt((2*pi)^2+delta^2);
% Make sure damping ratio is greater than 0
test.verifyGreaterThan(dRatio,0,'Damping ratio must be greater than 0');

Test Results

Running the test case returns two conditions in which the damping ratio is greater than zero.

results = sltest.testmanager.run
results =

ResultSet with properties:

Name: 'Results: 2018-Feb-10 17:03:48'
NumPassed: 14
NumFailed: 2
NumDisabled: 0
NumIncomplete: 0
NumTotal: 16
NumTestCaseResults: 0
NumTestSuiteResults: 0
NumTestFileResults: 1
Outcome: Failed
StartTime: '2018-Feb-10 17:03:48'
StopTime: '2018-Feb-10 17:06:16'
Duration: 148
CoverageResults: []
Release: ''

The wing pitch plots from iteration 12 and 13 show the difference between a positive damping ratio (iteration 12) and a negative damping ratio (iteration 13).

sltest.testmanager.close
close_system('sltestFlutterSuppressionSystemExample.slx',0)