Sherman A. Clevenson

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...

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 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...

Effect of helicopter noise spectra on annoyance of passengers

The annoyance of passengers to helicopter noise was investigated by exposing subjects to simulated helicopter noises in the NASA Passenger Ride Quality Apparatus. The passengers were subjected to the measured internal noise of the NASA Civil Helicopter Research Aircraft and to five filtered conditions of the noise, each at four noise levels. In addition, the subjects were given an incentive to identify a series of phonetically balanced (PB) words prior to recording their annoyance. Each subject experienced each condition at four levels ranging from 70 to 86 dBA. Removal of the gear‐clash or other predominant‐frequency components reduced the noise level and the annoyance ratings of the subjects. The annoyance was essentially the same for a given noise level with or without the gear‐clash or other predominant‐frequency components. For identical noise conditions, the annoyance was greater when the passenger‐subjects were attempting to identify PB words.

Effect of vibration duration on ride quality

An investigation was conducted to systematically examine the effects of vibration duration on passenger discomfort. A realistic laboratory simulator was used to expose subjects to random vertical vibrations. Variables included the time of exposure (15 s–1 h) and the amplitude of vibration (0.025–0.10 grms). The vibration had a white noise spectrum whose bandwidth was 0 to 10 Hz. Data indicate that for acceleration levels greater than threshold of discomfort (0.027 grms), a systematic decrease in discomfort (less annoyance) occurs as a function of increasing duration of vibration. The magnitude of the discomfort decrement is equivalent to 0.01 grms for each 1/2‐h of vibration and is independent of acceleration level. The results suggest that the vibration annoyance does not increase with longer exposure as indicated in the International Standard “Guide for the Evaluation of Human Exposure to Whole‐Body Vibration.” ISO 2631‐1974(E).