Q2. Why was high pass filtering proposed for the problem of vibration noise?
For the problem of vibration noise, high pass filtering was proposed due to the wide band signal generated by impacts which usually have much higher impact frequencies than operational vibration noise.
Q3. What was the purpose of the vibration noise generator?
To generate vibration noise, 8 vibration motors (consisting of 3V coin motors attached to LM8UU linear bearings) were bonded on the top side of both flat and curved plates generating noise.
Q4. What is the effect of increased height on the waveform?
Increased height (F7) gives higher kinetic energy and causes the amplitude of the signalto increase relative to the baseline case (F1) while the waveform does not change[23,25].
Q5. What is the effect of angle impact on the waveform?
Angled impact (F5) also lowers the general amplitude and introduces slight phase shift in the later parts of the wave without much alteration to the waveform.
Q6. What is the purpose of this work?
The aim of this work is to propose an impact localization methodology based onANN which is applicable for composite structures under operational and environmental conditions without the need for an impossibly large training data set.
Q7. What are the two groups of passive sensing methods?
The second group of impact location passive sensing methods are the data drivenmethods which utilize an initial reference set of wave features from known impacts to train an algorithm to map the said features to the impact location[
Q8. What is the first technique developed for determining the location of an impact?
One of the first techniques developed is the triangulation based methods where the impact location is determined using the linear relation between Time of Arrival (TOA) of the wave and the relative distance travelled to each sensor [3,14–18].
Q9. What is the effect of vibration filtering on the accuracy of ANNs?
It can be seen that the effect of geometry on accuracy is relatively small for NSET ANNs whilst for NT ANNs the accuracy is higher for curved plates.
Q10. What is the effect of vibration on aircraft parts?
In general, the probable impacts on aircraft parts, excite a wide band frequency response (above 10 kHz [34,35]) which is usually higher than operational vibration levels (under 2kHz as stated by RCTA DO-160C [32]).
Q11. What did not affect the accuracy of NSET ANNs?
Vibration filtering, number of sensors and difference in plate geometry (curvature) did not significantly affect the accuracy of NSET ANNs.
Q12. What is the effect of the impact condition on the signal?
From the gathered experimental data, it was observed that variation in impact condition (mass, angle, energy, temperature) has a significant effect on impact response signals.
Q13. How many gr were used to create the impactor?
The impactor head used was a 20 mm diameter round steel head and the impactor mass used was 100 gr (original) and 200 gr (increased by adding extra weight attachments to the impactor).
Q14. What are the main reasons for the use of composites in aircraft?
Whilst these types of impacts result in easily detectable damage (dents) on an aluminium airframe, they can generate visually undetectable damage in composite structures which may result in eventual failure if left undetected[3,4].
Q15. What are the two main types of impact location passive sensing methods?
The database reference methods match the features of an impact wave to a database of previously known impact wave features measured at different impact locations/points.
Q16. What are the challenges before SHM can be sought as a maintenance tool on an aircraft?
there still remains certain challenges before SHM can be sought as a maintenance tool on board of an aircraft such as survivability of sensors, wires, connectors [10,11] under operational conditions and the reliability of the diagnostics [12,13].