Search NASA⌕ Search

Engineering topics

Stephen A Rizzi

Publications and source records attributed to Stephen A Rizzi.

At least 19 records

Toward a Psychoacoustic Annoyance Model for Urban Air Mobility Vehicle Noise

A psychoacoustic test was performed to obtain annoyance responses to noise from a quadrotor Urban Air Mobility (UAM) vehicle to aid in the development of a model of annoyance to UAM vehicle noise. Previous analysis of that test concluded that a psychoacoustic annoyance (PA) model, including the effects of loudness, sharpness, fluctuation strength and roughness, correlated well with the collected annoyance responses. This motivated the assessment of other PA models available in the literature, as well as the development of a new PA model based on the previously collected annoyance responses to UAM noise. To build the PA model for UAM noise, annoyance ratings to individual sounds and annoyance comparisons between pairs of sounds are first combined into a latent annoyance scale that has a correlation coefficient of 0.98 with the raw responses and that is based on just-noticeable-differences (JNDs) in annoyance. Examples for two sounds that differ in annoyance by 1 JND show when there is 75% agreement about which sound is more annoying. This latent annoyance (JND) scale also gives insight into the interplay of various perceptual components, such as overall loudness, temporal effects and spectral effects. The proposed PA model for UAM noise is fit to the latent annoyance scale, includes the sound quality effects mentioned above, as well as a term for tonality, and offers a step forward in the prediction of annoyance to UAM vehicle noise.

Urban Air Mobility↗

Perceptual Evaluation of Sound Exposure Level in Annoyance Ratings to Helicopter Noise

A psychoacoustic test was performed to assess the effectiveness of Sound Exposure Level (SEL) for indicating changes in annoyance to helicopter noise. SEL was evaluated for flyover auralizations of optimized rotor designs and for flyover recordings of different helicopters and maneuvers. The test used paired comparisons of flyovers within 10 dB of the maximum A-weighted sound pressure level. For stimuli of equal SEL, annoyance responses showed whether or not SEL is a good indicator of annoyance. While this work does not seek to determine specific attributes contributing to annoyance that are not included in SEL, the magnitude of this offset is of primary interest. Specifically, annoyance responses to relative differences in SEL allowed the calculation of an Equal Annoyance Point. Reductions in SEL lead to reductions in annoyance as expected, but for certain cases, SEL can fail to capture perceptually significant features such as audible differences due to changes in tail rotor design or unsteadiness in the sound of the helicopter.

Sound Exposure Level↗

Urban Air Mobility Noise: Current Practice, Gaps, and Recommendations

In 2018, NASA formed an Urban Air Mobility Noise Working Group to assemble noise experts from industry, universities and government agencies to identify, discuss, and address urban air mobility (UAM) noise issues. This paper presents a set of high-level goals intended to address barriers associated with UAM noise that may hamper their entry into service. It summarizes the current practice, identifies gaps in the current practice, and makes recommendations to address the gaps to achieve the high-level goals in four areas of interest: Tools and Technologies, Ground and Flight Testing, Human Response and Metrics, and Regulation and Policy.

urban air mobility↗

Urban Air Mobility Generation 1 Acoustic Database

An acoustic database has been generated in support of the NASA Revolutionary Vertical Lift Technology (RVLT) project, Technical Challenge (TC) TC.UAM.Noise.1, entitled “Urban Air Mobility Operational Fleet Noise Assessment.” As part of that TC, a periodic (approximately annual) development of an acoustic database will be performed based on the latest available information. The release of the first such database, namely, the “Gen 1 database for fleet noise assessments,” developed in support of RVLT milestone RVLT.23.02.L350, is the subject of this document.

urban air mobility↗

Sound Quality Metric Indicators of Rotorcraft Noise Annoyance Using Multilevel Regression Analysis

Although every helicopter in operation has to go through a noise certification process, annoyance due to helicopters still persists within various communities. This implies that certification metrics do not capture the full range of human response and that predicted reactions could be supplemented with other information, which could be acoustic or non-acoustic in nature. The rotorcraft sound quality metric (RoQM) psychoacoustic experiment was designed to determine the relative importance of sound quality metrics (SQMs), such as sharpness, tonality, loudness, fluctuation strength and impulsiveness, on human annoyance to rotorcraft sounds. Starting from a baseline helicopter recording, SQMs were varied synthetically and presented to subjects who responded with an annoyance rating. The RoQM test took place in 2017 at the NASA Langley Research Center in the Exterior Effects Room. A total of 105 sounds were played to 40 subjects. The relationship between helicopter noise sound quality and annoyance is modeled using multilevel regression in this work, which takes into account the variability of responses across subjects. Previous analyses did not consider such a grouping of the data.

Matthew Boucher↗

Noise Reduction Potential of Phase Control for Distributed Propulsion Vehicles

Phase control is a noise reduction technique leveraging destructive interference of the coherent acoustic source field between a system of propellers rotating at equivalent rates. Carefully selecting the relative azimuthal blade positions (phase), the overall directivity of the blade passage frequency noise can be modified, potentially steering these tonal components away from sensitive areas. A modeling technique is described and validated using measurements of a dual-rotor system. The sensitivity of noise reduction through phase control is studied in a typical parameter space, i.e., dependence on rotation rate, number of propellers, spacing and layout, and rotation direction. Additionally, estimates of how realistic conditions, e.g., error in the phase controller, degrade potential benefits are described based on the generalized coherence of the system. From this, it is observed that the deviation from the nominal rotation rate should not exceed approximately 0.5% to achieve a 6 dB decrease at the blade passage frequency.

Kyle A Pascioni↗

TPSAS-NF1676L-19524-DND

Distributed propulsion is being proposed as an approach to achieve greater aircraft efficiency. An added benefit which might be realized with a distributed propulsion configuration is a reduction in radiated sound power. A reduction in radiated sound power could relieve concerns related to an increase in community noise that would accompany the adaptation of a fleet of many small aircraft fielded to meet increased travel demand. However, a reduction in radiated sound power does not necessarily translate into community acceptance of the new noise signature. Some characteristics of distributed propulsion configurations can create aural effects that people would find more annoying even though the sound is at a lower power level. To understand the community response to the new class of noise that a distributed propulsion system would present requires the prediction, synthesis and auralization of the noise in a controlled environment. Representative members of the community can then be exposed to the noise and queried for their reaction. These are the types of tests performed in NASA Langley’s Exterior Effects Room. This report summarizes preliminary results obtained using isolated propeller predictions. The sound pressure level of a single ‘large’ propeller is compared to that of two ‘smaller’ propellers of equivalent total thrust. The aural effects of different implementations of the two propellers are also considered. The different implementations include rotation direction and blade passage frequency separation.

Stephen A Rizzi↗

TPSAS-NF1676L-19003-DND

Distributed propulsion is being proposed as an approach to achieve greater aircraft efficiency. An added benefit which might be realized with a distributed propulsion configuration is a reduction in radiated sound power. A reduction in radiated sound power could relieve concerns related to an increase in community noise that would accompany the adaptation of a fleet of many small aircraft fielded to meet increased travel demand. However, a reduction in radiated sound power does not necessarily translate into community acceptance of the new noise signature. Some characteristics of distributed propulsion configurations can create aural effects that people would find more annoying even though the sound is at a lower power level. To understand the community response to the new class of noise that a distributed propulsion system would present requires the prediction, synthesis and auralization of the noise in a controlled environment. Representative members of the community can then be exposed to the noise and queried for their reaction. These are the types of tests performed in NASA Langley’s Exterior Effects Room. This report summarizes preliminary results obtained using isolated propeller predictions. The sound pressure level of a single ‘large’ propeller is compared to that of two ‘smaller’ propellers of equivalent total thrust. The aural effects of different implementations of the two propellers are also considered. The different implementations include rotation direction and blade passage frequency separation.

Daniel L Palumbo↗

TPSAS-NF1676L-35855-DND

UAM Noise Exploratory Meeting (April ’18): there is positive interest in forming a focused working group to define and address noise goals for UAM vehicles. Participants should include stakeholders across industry, government agencies, academia, and community groups; focus efforts on reducing or eliminating the barriers associated with community noise. Key topics of interest include: Tools & Technologies Ground & Flight Testing Human Response & Metrics Regulation & Community Outreach

Stephen A Rizzi↗

A Synthesis Plug-in for Steady and Unsteady Loading and Thickness Noise Auralization

This paper describes the development and architecture of a plugin for the NASA Auralization Framework that synthesizes rotor sound pressures sample by sample for simulated propagation to auralize rotorcraft flyovers. The main component of the plugin is a preprocessor that synthesizes sound pressures before propagation methods are called. Rotor blade loadings, motion, and geometry data from various tools serve as input to the plugin. Farassat formulation 1A, a solution to the Ffowcs Williams-Hawkings equation, is used for the sound pressure calculations. Use of the plugin is demonstrated with two examples of steady periodic sound synthesis, but the synthesis method and preprocessor architecture described in this paper are also applicable to unsteady periodic and aperiodic sound syntheses.

Siddhartha Krishnamurthy↗

A Comparison of Aircraft Flyover Auralizations by the Aircraft Noise Simulation Working Group

The Aircraft Noise Simulation Working Group (ANSWr), comprised of NASA, DLR, and ONERA, recently completed an analysis campaign to compare aircraft noise simulation tools, establish guidelines for noise prediction, and launch activities to assess uncertainties associated with the simulation. The campaign included the analyses of two DLR conceptual aircraft, a reference tube-and-wing aircraft, and a low noise aircraft with engines mounted above the fuselage-wing-junction. While the total predicted noise for each of the concepts compared favorably among analyses at the peak level, significant differences were noted at the component level. This paper aims to further that effort by auralizing aircraft flyover noise associated with those predictions. Comparisons are made among the NASA, DLR/Empa, and ONERA generated sounds to determine how differences between the system noise prediction and auralization methods result in changes to the auralized sound.

Stephen A Rizzi↗

Urban Air Mobility Noise: Current Practice, Gaps, and Recommendations

AN Air Mobility (UAM) is an opportunity for aviation to improve transportation systems across the world. Representative UAM vehicle attributes include electrical vertical takeoff and landing (eVTOL) vehicles that can accommodate up to 6 passengers (or equivalent cargo), are possibly autonomous, perform missions of up to 100 nautical miles at altitudes up to 3000 ft. above ground level, have flight speeds up to 200 knots, and weigh between 800 and 8000 pounds. Along with the many anticipated benefits, there will be noise issues that need to be addressed. In 2018, NASA formed an Urban Air Mobility Noise Working Group (UNWG) to assemble noise experts from industry, universities and government agencies to identify, discuss, and address UAM noise issues. This oral presentation summarizes technology gaps and goals associated with four areas of interest: Tools & Technologies, Ground & Flight Testing, Human Response & Metrics, and Regulation & Policy, and is drawn from a draft white paper [1] by the same title. Tools & Technologies include noise prediction tools and noise reduction technologies that have been developed for conventional rotorcraft and fixed-wing vehicles that may be applicable or need to be modified for UAM. Prediction tools need to be able to account for variable speed rotors and other temporal variation effects that impact community noise. A reprioritization of noise sources needs to be done since UAM vehicles include multiple rotors/propellers, often in proximity to one another and/or the airframe, with dynamic transition, and new noise sources such as electric motors or hybrid-electric propulsion. Scattering and propagation methods need to be developed that include the vehicle components and surfaces near a receiver such as buildings and vertiports. Validation databases are needed to quantify prediction uncertainties. Prediction tools used to evaluate community noise will need source models appropriate for a wide range of UAM vehicles. Existing noise reduction technologies need to be evaluated and new noise reduction technologies should be developed in anticipation of future noise requirements. Although the prediction and treatment of interior cabin noise is a secondary goal, it is recognized that new tools and methods may be needed due to the uniqueness of the vehicle design and the presence of both acoustic and structure-borne loads. Ground & Flight Testing has been a critical part of validating noise reduction technologies and verifying that an air vehicle is ready for certification. UAM vehicles introduce new challenges for test procedures such as different source noise directivity, unsteady sources due to maneuvers, and a variety of takeoff and approach trajectories. The operating environment will be more complex than current aircraft with the introduction of vertiports in populated areas with “urban canyons” making reflections an important part of noise prediction and annoyance. It is expected that new test procedures and measurement methods will be necessary. Consideration will need to be given for both piloted and autonomous operations. Human Response & Metrics may be very different for UAM noise compared to current experience with airport noise. Current metrics used to certify rotorcraft and fixed-wing aircraft may not be as useful for evaluating UAM noise. Operations at lower altitudes may influence annoyance. Psychoacoustic and community testing will be needed to quantify annoyance and assess appropriate metrics. In addition to conventional noise level metrics, considerations such as audibility and temporal variation of the sound may be required. Differences between indoor or outdoor exposure will have an impact with dependence on urban and residential flight paths. Aircraft noise is currently regulated at a national level and typically involves partnerships with the industry to establish regulations. Regulators realize that current policies and procedures may not be appropriate for some of the emerging air vehicles and new procedures may be needed to address UAM noise. Development of new policies and procedures are needed so that local communities do not hastily attempt to establish their own restrictions that will both limit growth of the market and create an inconsistent and confusing regulatory environment. To expedite this development, it is crucial early measurement data are shared through partnership arrangements to support both noise certification and noise modeling/noise assessment. At the same time, an effective engagement strategy should be developed to address local community noise issues associated with UAM vehicles and flight operations as they arise.

urban air mobility↗

A Perceptual Evaluation of the Efficacy of Sound Exposure Level in the Rating of Annoyance to Helicopter Noise

A psychoacoustic test was performed that aimed to test how well Sound Exposure Level (LAE) is at indicating changes in annoyance to helicopter noise for simple changes in design as well as for realistic changes found from flight tests. In particular, LAE was evaluated for auralizations of optimized designs of rotor geometries when compared to a baseline design and for recordings that compare different helicopters and maneuvers. Paired comparisons consisted of the 10dBA-down portion of flyovers, which is the same portion used to calculate LAE. When played at the same LAE, annoyance responses showed in which cases LAE is a good indicator as well as when other aspects not included in the calculation of LAE may be important. Annoyance responses for relative differences in LAE allowed the calculation of an Equal Annoyance Point, giving further insight to the performance of LAE. Confidence intervals calculated with Monte Carlo simulations showed when responses are statistically different from the equal LAE comparison and also gave an indication of the necessary reduction for designers to be confident that a low noise design is impactful or that a difference in rotorcraft or maneuver is perceptually favorable.

Matthew Alban Boucher↗