In order to study the acoustic characteristics of low-speed and slow speed drones, different drone models were selected in anechoic chambers and outdoor urban environments, and test states such as single engine hovering, multi aircraft hovering, wing variation, drone wings, and low altitude scanning were used to test the acoustic characteristics of drones. By analyzing the total sound pressure level, FFT, and noise distribution, the acoustic characteristics of weak slow targets were obtained. The results indicate that the acoustic characteristics of "weak yet slow" drones are related to the aerodynamic noise generated by engine speed and wing rotation. As the motor speed of low-speed and slow speed drones changes, their sound frequency characteristics and flight speed synchronously change. That is, as the motor speed increases, the frequency of the sound speed characteristics of low-speed and slow speed drones increases, and the flight speed accelerates. At the same time, due to the rotation of the wings, aerodynamic noise is generated in the air near the driven wings as the wing speed changes.
The level and theodolite are used in the calibrator of the current automobile headlamp tester to align the optical axis center, this method needs many people to cooperate with the operation, the low degree of automation is insufficient. To solve the problem, this paper presents an automatic alignment device and method for calibrator optical axis of vehicle headlamp tester, introduces the structure, composition and principle of the alignment device and the specific implementation methods and steps. The comparison of experimental data shows that the alignment device has the advantages of high automation, simple operation and high accuracy. It can replace the existing level and theodolite to ensure the alignment of the luminous optical axis center of calibrators for headlamp tester of motor vehicle and the geometric center of the illuminometer probe.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.