Multi-Rotor UAV Noise Control Through Rotor Phase and Speed Spreading
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Solution Overview
Problem
Unmanned aerial vehicles (UAVs) generate tonal noise that can be perceived as a nuisance in populated areas, and existing noise control methods are inadequate in effectively spreading or reducing this noise to minimize annoyance.
Innovation Solution
The UAV system employs a control system to modulate the rotation rates and phase delays of rotor units, spectrally spreading the tonal noise by varying the physical geometries of bladed rotors and dynamically adjusting the rotation rates and phase delays of rotor units, either individually or in groups, to disperse the noise frequencies and amplitudes over time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the UAV operates in populated areas, then the utility and accessibility of the UAV is improved, but the tonal noise generated by the rotors increases the nuisance and reduces acceptability
Solution Approach 1:
The patent divides the rotor system into multiple independently controllable rotor units, each capable of operating at different rotation rates. This segmentation allows the noise frequencies from individual rotors to be distributed across a broader spectrum, reducing the concentration of tonal noise at any single frequency and thereby reducing overall noise nuisance in populated areas.
Solution Approach 2:
The control system dynamically adjusts the rotation rates of individual rotor units in real-time based on operational conditions and noise considerations. By varying rotation rates dynamically rather than maintaining a fixed speed, the system prevents the generation of consistent tonal frequencies, thereby reducing noise nuisance while maintaining flight performance.
2Stability of the object's composition
If the rotation rates of all rotor units are kept equal for stable flight, then the flight stability is maintained, but the tonal noise frequencies remain concentrated and annoying
Solution Approach 1:
The patent applies different rotation rates to different rotor units based on their local positions and noise characteristics. Rather than treating all rotors uniformly, the system tailors the rotation rate of each rotor unit to optimize both local noise reduction and overall flight stability, allowing concentrated tonal frequencies to be dispersed while maintaining compositional stability.
Solution Approach 2:
The control system changes the operational parameters (rotation rates) of individual rotor units away from a uniform state. By introducing controlled variations in rotation rates among rotor units, the system transforms the noise frequency distribution from concentrated to dispersed, reducing tonal noise annoyance while maintaining flight stability through compensatory control.
3Object-generated harmful factors
If the rotor units operate at different rotation rates to spread noise frequencies, then the tonal noise annoyance is reduced, but the control system complexity increases
Solution Approach 1:
The control system implements periodic modulation of rotor rotation rates using predetermined patterns. This periodic action allows the complex task of noise frequency spreading to be achieved through systematic, repeating sequences rather than continuous complex calculations, thereby reducing tonal noise annoyance while managing control system complexity through pattern-based control.
Solution Approach 2:
The control system uses lookup tables and predetermined control patterns that can be copied and applied across different rotor units. Rather than requiring complex real-time optimization for each rotor, the system employs pre-computed control strategies that simplify the control architecture while still achieving effective noise frequency dispersion.
Data Source
Figure 1
Figure 2A~2B
Figure 2C~2D
AI summary
A technique of controlling tonal noises produced by an unmanned aerial vehicle (UAV) includes generating thrust with a plurality of rotor units mounted to the UAV to propel the UAV into flight. Each of the rotor units includes a bladed rotor. A rotation rate or a phase delay of at least one of the rotor units is adjusted relative to another of the rotor units. The adjustment causes a spread in the tonal noises generated by the rotor units.