Jack D. Leatherwood

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.

Acoustic Testing of High-Temperature Panels

This paper summarizes recent thermoacoustic test activities at NASA Langley Research Center. The Langley Thermal Acoustic Fatigue Apparatus facility is described and results of two experiments to measure dynamic strain response of advanced structural panels at ambient and elevated temperatures are presented. The first study investigated techniques for measuring the dynamic strain of superalloy honeycomb thermal protection system panels subjected to combined thermal and acoustic loads. Results illustrating the linear response of these panels as a function of sound pressure level and temperature are presented. The second study was a joint NASA/ General Dynamics test of two flat and two blade-stiffened carbon-carbon panels. These panels were tested to failure at an acoustic excitation level of 160 dB. Failure times ranged from several minutes to about 3 h. The flat panels failed due to development of edge-cracks, and the blade-stiffened panels due to delamination. Results showed that the carbon-carbon panels tested at elevated temperatures had significantly longer fatigue life. Strain data from both types of panels were obtained, although difficulties were encountered in returning reliable strain measurements on the carbon-carbon panels.

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.

The development of interior noise and vibration criteria

The NASA Langley Research Center has completed a comprehensive research program that resulted in the development of a generalized model for estimating passenger discomfort response to combined noise and vibration. This model accounts for multiple frequency and multiple axes of vibration as well as the interactive effects of combined noise and vibration. The model has the unique capability of transforming individual components of a noise/vibration environment into subjective comfort units and then combining these comfort units to produce a total index of passenger discomfort and useful subindices that typify passenger comfort within the environment. This paper presents an overview of the model development including the methodology employed, major elements of the model, model applications, and a brief description of a commercially available portable ride comfort meter based directly upon the model algorithms. Also discussed are potential criteria formats that account for the interactive effects of noise and...

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...

Passenger discomfort response to combined noise and vibration

A comprehensive research program has been conducted by NASA Langley Research Center to develop a fundamental understanding of human discomfort response to combined noise and vibration typical of that experienced within air and surface transportation systems. Results of this research program produced an empirical model of passenger ride comfort for use in the prediction and/or assessment of passenger ride comfort. The model is based on subjective ratings from more than 3000 persons who were exposed to controlled combinations of noise and vibration in the passenger ride quality apparatus at Langley Research Center. This model has the unique capability of transforming individual elements of a vehicles noise and vibration environment into subjective units and then combining the subjective units to produce a single discomfort index typifying passenger acceptance of the environment. This paper discusses the approach and basic elements of the NASA ride comfort research program, describes the resultant model and its applications to real vehicles, and discusses a portable ride quality meter that is a direct hardware/software implementation of the NASA ride comfort model.