Thomas K. Dempsey

A design tool for estimating passenger ride discomfort within complex ride environments

A series of experimental studies utilizing approximately 2200 test subjects has led to the development of a general empirical model for the prediction of passenger ride discomfort in the presence of complex noise and vibration inputs. The ranges of vibration and noise stimuli used to derive the model included the amplitudes and frequencies that are known to most influence passenger comfort. The ride quality model accounts for the effects of combined axis vibrations (up to three axes simultaneously) and includes corrections for the effect of vibration duration and interior noise. Output of the model consists of an estimate of the passenger discomfort produced by a given noise and/or vibration environment. The discomfort estimate is measured along a continuous scale that spans the range from below discomfort threshold to values of discomfort that are far above discomfort threshold.

Development of noise and vibration ride comfort criteria

A laboratory investigation was directed at the development of criteria for the prediction of ride quality in a noise-vibration environment. The stimuli for the study consisted of octave bands of noise centered at 500 and 2000 Hz and vertical floor vibrations composed of either 5 Hz sinusoidal vibration, or random vibrations centered at 5 Hz and with a 5 Hz bandwidth. The noise stimuli were presented at A-weighted sound pressure levels ranging from ambient to 95 dB and the vibration and acceleration levels ranging from 0.02--0.13 grms. Results indicated that the total subjective discomfort response could be divided into two subjective components. One component consisted of subjective discomfort to vibration and was found to be a linear function of vibration acceleration level. The other component consisted of discomfort due to noise which varied logarithmically with noise level (power relationship). However, the magnitude of the noise discomfort component was dependent upon the level of vibration present in the combined environment. Based on the experimental results, a model of subjective discomfort that accounted for the interdependence of noise and vibration was developed. The model was then used to develop a set of criteria (constant discomfort) curves that illustrate the basic design tradeoffs available between noise and vibration.

Ride quality meter

The invention is a ride quality meter that automatically transforms vibration and noise measurements into a single number index of passenger discomfort. The noise measurements are converted into a noise discomfort value. The vibrations are converted into single axis discomfort values which are then converted into a combined axis discomfort value. The combined axis discomfort value is corrected for time duration and then summed with the noise discomfort value to obtain a total discomfort value.

Vibration ride comfort criteria

This paper presents results obtained from a test program being conducted at Langley Research Center to develop an empirical model for predicting passenger comfort responses to multiaxis vibrations. The specific results contained in this paper are restricted to a description and understanding of human response to complex vertical axis vibrations. The approach to multifrequency vibration includes a separate consideration of the discomfort associated with each frequency component or band of the total spectrum, and a subsequent empirical weighting of the discomfort components of these frequency bands when in various random combinations. Mathematically, this may be represented as: DISC TOTAL = DISC MAX + F ( ∑ DISC - DISC MAX ) The discomfort (DISC) represents the subjective discomfort associated with the acceleration level of a particular frequency band. The F value, or masking factor specifies the fashion in which the discomfort of different frequency bands are added together. Fundamental to this approach is a detailed understanding of human response to discrete frequency inputs. A study has been recently completed that included 186 subjects, exposed to frequencies of 1 to 30 Hz, and ranging in acceleration level from 0.05 to 0.50 peak g. The F value was derived in a second set of tests that systematically explored the passenger discomfort response as a function of various random spectra. The results are in the form of equal discomfort curves that specify the discomfort associated with discrete frequencies between 1 and 30 Hz, of varying acceleration levels. These results, in addition to being necessary for the above equation, provide detailed information of the human discomfort response to increases of acceleration level, for each frequency investigated. More importantly, the results provide a method for adding the discomfort associated with separate frequencies for a total typification of the discomfort of a random spectrum of vibration.

Noise and vibration ride comfort criteria

A program is underway at Langley Research Center to develop a comprehensive ride quality model based upon the various physical and psychological factors that most affect passenger ride comfort. Two of the most important factors, namely vibration and noise, were studied in a previous investigation in which the relative contribution of each factor to overall passenger discomfort was determined. This earlier study utilized a category scale to elicit responses from subjects exposed to combined sinusoidal vibration and octave band noises. The present study is an extension of this work and used a magnitude estimation procedure to obtain subjective responses to combined noise and vibration where the vibration stimuli now included random vibrations. The specific purposes of this paper are to (1) determine the absolute contribution of noise and vibration to passenger discomfort in terms of the discomfort units associated with the ride quality model, and (2) determine if passenger discomfort responses to combined n...

Effect of whole-body vibration in combined axes and with noise on subjective evaluation of ride quality

The effects on ratings of ride quality of discomfort produced by complex vibration and noise stimuli were investigated. The initial study examined effects of simultaneous vibration in the vertical and lateral axes in a simulated passenger aircraft. The second study examined the effects of simultaneously presented vertical vibration and noise stimuli. In both studies the components of complex stimuli were found to combine their effects at low levels of stimulation but to act separately at higher levels.

Passenger ride quality within a noise and vibration environment

The subjective response to noise and vibration stimuli was studied in a ride quality simulator to determine the importance of these two stimuli (or their interaction) in the prediction of passenger ride quality. Subjects used category scales to rate noise comfort, vibration comfort, noise and vibration comfort, and overall comfort in an effort to evaluate parametric arrangements of noise and vibration. The noise stimuli were composed of octave frequency bands centered at 125, 250, 1000, and 2000 Hz, each presented at 70, 75, 80, and 85 dBA. The vertical vibration stimuli were 5‐Hz‐bandwidth random vibrations centered at 3, 5, 7, and 9 Hz, each presented at 0.03, 0.06, 0.09, and 0.12g rms. Analyses were directed at (1) a determination of the subjects ability to separate noise and vibration as contributors to discomfort, (2) an assessment of the physical measures of noise and vibration (and certain demographic factors) that optimize ride quality prediction in this type of multifactor environment, (3) an ev...

Resident annoyance response to aircraft noise events

A study of the annoyance response of airport community residents to the noise of aircraft takeoff and landing operations was conducted in Salt Lake City, Utah in the fall of 1980. The objective of the study was to develop a single‐event, dose‐response relationship for aircraft noise and determine the dependence of the relationship on variables such as aircraft type, time of day, and ambient noise level. The test at each home involved measuring indoor and outdoor noise for each flyover while simultaneously obtaining annoyance reactions from the residents. These tests were conducted at three different times of the day (morning, afternoon, and evening) to provide information on time‐of‐day weightings for noise metrics. A total of 101 residents (61 male and 40 female) completed the tests. Outdoor measured A‐weighted sound pressure level of the aircraft noise provided the single most accurate prediction of resident annoyance. However, increased accuracy was found by accounting for outdoor ambient noise and house attenuation. Annoyance response prediction was independent of aircraft type. Finally, time‐of‐day weightings derived from the results of the study, were smaller (≈6 dB) and shifted to the evening period as compared to the standard 10‐dB nightime penalty.

Effect of tactile vibration on annoyance to synthesized propfan noise

A research program at NASA‐Langley Research Center is being conducted to provide design information that maximizes passenger comfort for proposed propfan aircraft. Particular emphasis in this study is being placed on predicting noise and vibration environments and the resultant passenger acceptability. Previous ride quality research of this program has indicated that vibrations of sufficient intensity to produce whole body movements (at frequencies less than 30 Hz) cause passenger discomfort and annoyance. Within this complex interior environment, this type of vibration interacts additively with noise to produce discomfort. However, recent questions have arisen concerning the effect of high frequency tactile vibration (i.e., greater than 30 Hz) on passenger reactions. The current study addressed this question through obtaining passenger reactions to a wide range of noise and tactile vibration environments. The investigation was conducted in the passenger ride quality simulator located at the NASA‐LaRC usi...

Synthesized propfan interior noise

Recent fuel‐conservation measures have led to increased interest in propeller‐driven aircraft for commuter as well as long‐haul applications. The increased fuel efficiency of these vehicles could be offset, however, if passenger acceptance necessitates increased aircraft weight for purposes of noise reduction. Thus, a laboratory investigation was conducted to describe passenger acceptance criteria for the interior noise environment of these vehicles, and as a corollary, to assess the validity of various noise descriptors or metrics for quantifying the interior noise environment. The investigation was conducted in the passenger ride‐quality simulator located at the NASA‐Langley Research Center. The tests involved a total of 96 subjects which evaluated synthesized propeller noises using a nine‐point discomfort category scale. The sounds consisted of a turbulent boundary‐layer noise with a factorial combination of blade passage frequencies (50, 80, 100, 125, and 200 Hz), harmonic rolloffs (0 and 10 dB harmon...