No description available.

No description available.

No description available.

No description available.

The major problem facing air transportation for the next decade is aircraft noise. The noise level due to the operation of large jet aircraft has created a very serious annoyance problem to the people living near of adjacent to jet airports. The noise problem has developed both for take-off and landing operations of these aircraft with take -off noise causing the greatest annoyance factor. A technique called Noise Exposure Forecast (NEF) has been developed to identify the annoyance factor of these noises to people and activities on the ground. With these NEF ratings or numbers, planners can better determine the type of buildings and activities to locate in the vicinity of airports. This paper presents a computer method for determining NEF areas or contours which eliminate the necessity of performing laborious hand calculations and iterations normally required to determine a given NEF locus about an airport. A land use compatibility table showing land use versus NEF numbers is given on page 3. A sample computer program is given on pages 21 through 25 of the appendix and a sample computer output page is given on page 26. The computer technique developed for this paper can be used for any airport.

Within the overarching area of airplane noise, landing gear noise has been proven to be a major contributor to airframe noise. Despite a large focus given to it by past research work, landing gear noise investigations have continuously failed to include landing lights, completely disregarding their potential for seriously altering the landing gear wake structure and overall noise signature. This thesis is one of the first studies to focus on the effect of landing light orientation on landing gear wake and landing gear noise. Pressure fluctuations in the wake of a simplified single light landing gear model are investigated experimentally for several freestream velocities and at various elevations of measurement plane. The effect of the distance between the light and the landing gear strut is also investigated. Three-dimensional flow is found in the wake at the center, or zero elevation, plane. This three-dimensionality is found to be much weaker at the highest elevation from the light, where the wake is found to be primarily two-dimensional. The nature of the transition region between the three-dimensional flow and two-dimensional flow is not investigated, but it is acknowledged that a transition region exists. Complex flow behaviour leading to a wake width larger than twice the size of the light-strut assembly width is found to be present at the zero elevation, and phase-locked PIV imaging is unable to capture any periodic motion within the wake at this elevation. In contrast, the wake at the highest elevation is found to resemble the flow in the wake of circular cylinders, and phase-locked PIV imaging at this elevation clearly captures an alternate vortex shedding scheme. Due to this difference in wake structures, the periodicity at the highest elevation is found to be stronger than that observed at the zero elevation. Changes in light-strut spacing are found to inversely affect the strength of the periodicity in the wake, as larger spacing is linked to greater influence of three-dimensionality, and therefore a weaker periodicity. Changes in light-strut spacing are also found to be inversely related to the oscillation frequency of the periodicity, with the cause for this relationship possibly explained by the wider wake at increased spacing. It is found that the oscillation frequency of periodicity in the single light landing gear wake is consistently in the Strouhal number range of St=0.16-0.18 for all light-strut spacing distances, freestream velocities, and elevations. The flow around the light-strut assembly is therefore characterized as modulated flow around a cylindrical strut because alternate vortex shedding is dominant except for a slight region where the light acts to generate three-dimensionality, and because the oscillation frequency is near that of vortex shedding from a circular cylinder, St=0.19. The wakes of the single light landing gear and two-light landing gear models are compared, but neither design can be supported as quieter than the other at this time due to the unknown amount of vertical radiation from the landing gear wakes. / Thesis / Master of Applied Science (MASc)

In this work, the potential for a smart foam actuator in controlling interior cabin noise due to a turbulent boundary layer excitation has been experimentally demonstrated. A smart foam actuator is a device comprised of sound absorbing foam with an embedded distributed piezoelectric layer (PVDF) designed to operate over a broad range of frequencies. The acoustic foam acts as a passive absorber and targets the high frequency content, while the PVDF serves as the active component and is used to overcome the limitations of the acoustic foam at low frequencies. The fuselage skin of an aircraft was represented by an experimental test panel in an anechoic box mounted to the side of a wind tunnel. The rig was used to simulate turbulent boundary layer noise transmission into and aircraft cabin. An active noise control (ANC) methodology was employed by covering the test panel with the smart foam actuators and driving them to generate a secondary sound field. This secondary sound field, when superimposed with the panel radiation, resulted in a reduction in overall sound in the anechoic box. An adaptive feedforward filtered-x Least-Mean-Squared (LMS) control algorithm was used to drive the smart foam actuators to reduce the sound pressure levels at an array of microphones. Accelerometers measured the response of the test panel and were used as the reference signal for the feedforward algorithm. A detailed summary of the smart foam actuator control performance is presented for two separate low speed wind tunnel facilities with speeds of Mach 0.1 and Mach 0.2 and a single high speed tunnel facility operating at Mach 0.8 and Mach 2.5. / Master of Science

When creating data-based models it is important to include the underlying physical characteristics and constraints of the data. If physical characteristics are not properly included in the model, results may be infeasible or physically impossible. Acoustic environments are better characterized by ensuring that models include the fundamental spatial, spectral, and temporal characteristics of noise sources, or how they change based on location, frequency, and time. When model data are limited, in availability or in reliability, additional care must be taken to ensure models predict feasible results. This dissertation focuses on physics-guided modeling of acoustic environments using limited data, taking into consideration spatial, spectral, and temporal characteristics of noise sources, specifically focused on wind noise and traffic noise. Wind noise contamination in spectral data can be significant, even when using a windscreen. By modeling spectral characteristics of temporally varying wind noise contamination, a method for automatically detecting and reducing wind noise was developed. Reducing non-acoustic wind noise contamination allows for better characterization of outdoor acoustic environments and is useful for accurately measuring other noise sources. Traffic noise varies spatially, spectrally, and temporally, and depends on traffic volume (the number of vehicles per unit time) and traffic class mix (e.g., the relative number of small vehicles compared to large trucks). Using the temporal variation found in reported traffic volume at thousands of locations, a model was developed to represent and predict the spatio-temporal variability of traffic volume nationwide. Further models were created to include dynamic changes in traffic class mix and to predict spectral source traffic noise. The resulting model for predicting source traffic noise is known as VROOM, the Vehicular Reduced-Order Observation-based Model. The physics-guided modeling techniques presented in this dissertation are intended for characterizing acoustic environments, which has applications for such diverse areas as human health and wellness, bioacoustics, wildlife conservation, urban and roadway planning, land development and conservation, noise ordinance legislation, homebuying, and more.

Through the use of multiple-input/single-output (MISO) modeling, the propagation paths of sound within a reciprocating refrigeration compressor have been investigated and ranked. By investigating the nature of sound propagation within reciprocating compressors, it is hoped that compressor manufacturers can effectively formulate strategies for compressor sound reduction. From experimental data of compressor far-field sound output, suspension spring forces, and internal pressure fluctuations, a MISO model has been developed. From this model, the importance of the suspension system to the compressor far-field sound spectrum has been identified. In the frequency range above 800 Hz, forces passing through the suspension system appear to be the dominant contributor to shell excitation and sound radiation. Based upon this finding, it is recommended that modified suspension systems be considered as an avenue for compressor sound reduction efforts in the future. / Master of Science

Two experiments were conducted to investigate Adaptive Noise Cancelling and Cepstrum echo removal post-processing techniques on acoustic data from a linear microphone array in an anechoic chamber. A point source speaker driven with white noise was used as the primary signal. The first experiment included a background speaker to provide interference noise at three different Signal-to-Noise Ratios to simulate noise propagating down a wind tunnel circuit. The second experiment contained only the primary source and the wedges were removed from the floor to simulate reflections found in a wind tunnel environment. The techniques were applicable to both signal microphone and array analysis. The Adaptive Noise Cancellation proved successful in its task of removing the background noise from the microphone signals at SNRs as low as -20 dB. The recovered signals were then used for array processing. A simulation reflection case was analyzed with the Cepstral technique. Accurate removal of the reflection effects was achieved in recovering both magnitude and phase of the direct signal. Experimental data resulted in Cepstral features that caused errors in phase accuracy. A simple phase correction procedure was proposed for this data, but in general it appears that the Cepstral technique is and would be not well suited for all experimental data. / Master of Science