Rotorcraft flyover noise has long been a field of study for researchers. This is because for many people, the sounds produced by these vehicles are found to be extremely annoying. The focus of this thesis is to recreate the time-varying rotorcraft noise at the source for a single emission angle. Then, through interpolation between emission angles, produce a simulated flyover at the source that can then be propagated to a receiver. This will allow for the creation of a simulated flyover without the need of having to use a physical aircraft, or pre-existing data from some type of data collection means, such as a microphone array. The current methods are limited to a predefined length of data in order to synthesize signals. It has been documented that synthesizing flyover noise, from direct use of physical flyover recordings through an empirical approach, yields a high fidelity signal, as long as both unmodulated and modulated components are present. In order to extend these signals indefinitely, models for the amplitude and phase modulation must be developed. A band-limited random process will be explored for both the amplitude and phase modulations. An overlap-add technique, as well as a randomization technique and a modified phase modulation signal, defined as the "residual", will also be attempted in order to model the phase modulation. The results from this work have successfully found a means in which to produce a viable model of the amplitude modulation. Further investigation is still required in order to produce a model of the phase modulation which results in a high-fidelity model that can be extended indefinitely. / Master of Science / Helicopter noise has long been a field of study for researchers. This is because for many people, the sounds produced by these vehicles are found to be extremely annoying. The focus of this thesis is to recreate the sounds heard by an observer as a helicopter flies overhead. This will allow for the creation of a simulated flyover without the need of having to use a physical aircraft, or pre-existing data from some type of data collection means. The current methods used to produce helicopter flyovers are limited to a predefined length of data in order to create sounds an individual may hear on the ground. It has been documented that creating flyover noise, from direct use of physical flyover recordings, yields a high fidelity signal, as long as all components are present when recreating the new sound. In order to extend these signals indefinitely, models must be developed in order to model the key components heard as a helicopter passes over an observer. The results from this work have successfully found a means in which to produce a viable model for certain components of the original flyover. Further investigation is still required in order to produce a high-fidelity model that can be extended indefinitely with all the necessary components included. This research is part of a broader effort to study the effects flyovers have on the population in terms of annoyance and detection. The work done here will help to aid further models used to determine what individuals find annoying with regard to helicopters and the noises they produce.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/78188 |
| Date | 13 June 2017 |
| Creators | Pera, Nicholas Matthew |
| Contributors | Aerospace and Ocean Engineering, Fuller, Christopher R., Lowe, K. Todd, Philen, Michael K., Rizzi, Stephen A. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf, application/x-zip-compressed |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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