Visual Interaction in Acoustic-Structural Analysis of Automobiles

1994 ◽  
Author(s):  
Vijoy Gaddipati ◽  
Judy M. Vance ◽  
Richard DeVries
Keyword(s):  
Structural Design ◽  
Sound Pressure ◽  
Low Frequency ◽  
Frequency Noise ◽  
Noise Levels ◽  
Passenger Compartment ◽  
Structural Vibrations ◽  
Design Variables ◽  
Design Changes ◽  
Graphical Technique

Abstract This paper describes a graphical technique used for investigating the effects of structural design changes on the sound pressure levels generated in an automobile compartment. Low frequency noise in the passenger compartment (in approximately the 20–85 Hz frequency range) is of primary interest, and particularly that noise which is generated by the structural vibrations of the wall panels and various other smaller parts of the compartment. A designer faced with reducing the noise levels at various frequencies typically has several hundred design variables as candidates for change. This paper describes a computer interface that facilitates understanding of the effect various design changes have on the noise levels. This interface allows the designer to investigate the design space to determine which variables hold the most promise for achieving the objectives of noise reduction and allows the designer to set targets or constraints, to a desired confidence level, using the sensitivity information of these design variables. The design targets set in this manner are then input to an optimization algorithm which solves for the optimized sound pressure level.

Aerodynamic noise from an asymmetric airfoil with perforated extension plates at the trailing edge

2020 ◽  
pp. 1475472X2097838
Author(s):  
CK Sumesh ◽  
TJS Jothi
Keyword(s):  
High Frequency ◽  
Sound Pressure ◽  
Pore Diameter ◽  
Low Frequency ◽  
Aerodynamic Noise ◽  
Frequency Noise ◽  
Low Frequency Noise ◽  
Trailing Edge ◽  
High Frequency Noise ◽  
Displacement Thickness

This paper investigates the noise emissions from NACA 6412 asymmetric airfoil with different perforated extension plates at the trailing edge. The length of the extension plate is 10 mm, and the pore diameters ( D) considered for the study are in the range of 0.689 to 1.665 mm. The experiments are carried out in the flow velocity ( U∞) range of 20 to 45 m/s, and geometric angles of attack ( αg) values of −10° to +10°. Perforated extensions have an overwhelming response in reducing the low frequency noise (<1.5 kHz), and a reduction of up to 6 dB is observed with an increase in the pore diameter. Contrastingly, the higher frequency noise (>4 kHz) is observed to increase with an increase in the pore diameter. The dominant reduction in the low frequency noise for perforated model airfoils is within the Strouhal number (based on the displacement thickness) of 0.11. The overall sound pressure levels of perforated model airfoils are observed to reduce by a maximum of 2 dB compared to the base airfoil. Finally, by varying the geometric angle of attack from −10° to +10°, the lower frequency noise is seen to increase, while the high frequency noise is observed to decrease.

Recurrence Plot Analysis of HRV for Exposure to Low-Frequency Noise

2014 ◽  
Vol 1044-1045 ◽  
pp. 1251-1257 ◽  
Author(s):  
Shih Tsung Chen ◽  
Chia Yi Chou ◽  
Li Ho Tseng
Keyword(s):  
Low Frequency ◽  
Cardiovascular Responses ◽  
Recurrence Plot ◽  
Frequency Noise ◽  
Cardiovascular Activity ◽  
Low Frequency Noise ◽  
Noise Levels ◽  
Noise Condition ◽  
Plot Analysis ◽  
Recurrence Plot Analysis

Previous studies have indicated that the chronic effects of exposure to low-frequency noise causes annoyance. However, during the past two decades, most studies have employed questionnaires to characterize the effects of noise on psychosomatic responses. This study investigated cardiovascular activity changes in exposure to low-frequency noise for various noise intensities by using recurrence plot analysis of heart rate variability (HRV) estimation. The authors hypothesized that distinct noise intensities affect cardiovascular activity, which would be reflected in the HRV and recurrence quantification analysis (RQA) parameters. The test intensities of noises were no noise, 70-dBC, 80-dBC, and 90-dBC. Each noise level was sustained for 5 min, and the electrocardiogram (ECG) was recorded simultaneously. The cardiovascular responses were evaluated using RQA of the beat-to-beat (RR) intervals obtained from ECG signals. The results showed that the mean RR interval variability and mean blood pressure did not substantially change relative to the noise levels. However, the length of the longest diagonal line (Lmax) of the RQA of the background noise (no noise) condition was significantly lower than the 70-dBC, 80-dBC, and 90-dBC noise levels. The laminarity showed significant changes in the noise levels of various intensities. In conclusion, the RQA-based measures appear to be an effective tool for exposure to low-frequency noise, even in short-term HRV time series.

scholarly journals Noise-silencing technology for upright venting pipe jet noise

2018 ◽  
Vol 10 (8) ◽  
pp. 168781401879481 ◽  
Author(s):  
Enbin Liu ◽  
Shanbi Peng ◽  
Tiaowei Yang
Keyword(s):  
Natural Gas ◽  
Sound Pressure Level ◽  
Sound Pressure ◽  
Low Frequency ◽  
Jet Noise ◽  
Pressure Level ◽  
Living Environment ◽  
Frequency Noise ◽  
Frequency Range ◽  
Expansion Chamber

When a natural gas transmission and distribution station performs a planned or emergency venting operation, the jet noise produced by the natural gas venting pipe can have an intensity as high as 110 dB, thereby severely affecting the production and living environment. Jet noise produced by venting pipes is a type of aerodynamic noise. This study investigates the mechanism that produces the jet noise and the radiative characteristics of jet noise using a computational fluid dynamics method that combines large eddy simulation with the Ffowcs Williams–Hawkings acoustic analogy theory. The analysis results show that the sound pressure level of jet noise is relatively high, with a maximum level of 115 dB in the low-frequency range (0–1000 Hz), and the sound pressure level is approximately the average level in the frequency range of 1000–4000 Hz. In addition, the maximum and average sound pressure levels of the noise at the same monitoring point both slightly decrease, and the frequency of the occurrence of a maximum sound pressure level decreases as the Mach number at the outlet of the venting pipe increases. An increase in the flow rate can result in a shift from low-frequency to high-frequency noise. Subsequently, this study includes a design of an expansion-chamber muffler that reduces the jet noise produced by venting pipes and an analysis of its effectiveness in reducing noise. The results show that the expansion-chamber muffler designed in this study can effectively reduce jet noise by 10–40 dB and, thus, achieve effective noise prevention and control.

scholarly journals Development of an on-site system for measuring the low-frequency noise and complainant’s responses

2018 ◽  
Vol 37 (2) ◽  
pp. 373-384
Author(s):  
Hiroshi Sato ◽  
Jongkwan Ryu ◽  
Kenji Kurakata
Keyword(s):  
Time Trends ◽  
Sound Pressure ◽  
Low Frequency ◽  
Dominant Frequency ◽  
Pressure Level ◽  
Frequency Noise ◽  
Low Frequency Noise ◽  
Measurement Results ◽  
Frequency Components ◽  
The Relationship

An on-site system for measuring low-frequency noise and complainant's responses to the low-frequency noise was developed to confirm whether the complainant suffer from the environmental noise with low-frequency components. The system suggests several methods to find the dominant frequency and major sound pressure level spectrum of the noise causing annoyance. This method can also yield a quantified relationship (correlation coefficient and percentage of response to the noise) between physical noise properties and the complainant’s responses. The advantage of this system is that it can easily find the relationship between the complainant’s response to the acoustic event of the houses and the physical characteristics of the low-frequency noise, such as the time trends and frequency characteristics. This paper describes the developed system and provides an example of the measurement results.

The Effect of Fluctuations on the Perception of Low Frequency Sound

2007 ◽  
Vol 26 (2) ◽  
pp. 81-89 ◽  
Author(s):  
A T Moorhouse ◽  
D C Waddington ◽  
M D Adams
Keyword(s):  
Laboratory Tests ◽  
Sound Pressure ◽  
Hearing Threshold ◽  
Low Frequency ◽  
Fast Response ◽  
Pressure Level ◽  
Rate Of Change ◽  
Frequency Noise ◽  
The Difference ◽  
Method Of Adjustment

Results of laboratory tests are presented in which 18 subjects, including some low frequency noise sufferers, were presented with low frequency sounds with varying degrees of fluctuation. Thresholds of acceptability were obtained for each sound and each subject, using the method of adjustment. These thresholds were then normalised to individual low frequency hearing threshold. It was found that sufferers tend to set thresholds of acceptability closer to their hearing threshold than other subject groups. Also, acceptability thresholds were set on average 5dB lower for fluctuating sounds. It is proposed that a sound should be considered fluctuating when the difference between L10 and L90 exceeds 5dB, and when the rate of change of the ‘Fast’ response sound pressure level exceeds 10dB/s

scholarly journals FACTORS AFFECTING VENTILATION, INDOOR-AIR QUALITY AND ACOUSTICAL QUALITY IN ‘GREEN’ AND NON-‘GREEN’ BUILDINGS: A PILOT STUDY

2011 ◽  
Vol 6 (3) ◽  
pp. 168-180 ◽  
Author(s):  
Alireza Khaleghi ◽  
Karen Bartlett ◽  
Murray Hodgson
Keyword(s):  
Mechanical Ventilation ◽  
Air Quality ◽  
Indoor Air Quality ◽  
Indoor Air ◽  
Natural Ventilation ◽  
Sound Pressure ◽  
Low Frequency ◽  
Green Buildings ◽  
Noise Levels ◽  
Ventilation Rates

This paper discusses a pilot project involving the direct monitoring of ventilation, indoor-air quality and the acoustical conditions in selected nominally ‘green’ and non-‘green’ buildings located on a university campus. The objectives were to measure parameters quantifying these three aspects of indoor environmental quality, determine the relationships between them and the building-design concepts, and evaluate the implications of the results for ventilation-system design, especially in ‘green’ buildings. Measurements were made in rooms, with and without acoustical treatment, in buildings with natural ventilation or mechanical (displacement and/or mixed-flow) ventilation systems. Measurements were made of ventilation rates (air changes per hour), indoor air quality (respirable-fibre, total-VOC and ultrafine-particulate concentrations), and the acoustical conditions (noise levels and reverberation times). Correlations between the environmental results, the building concept, the ventilation concept and the building window status were explored. In rooms with natural ventilation, low-frequency noise and total sound-pressure levels were lower; however, the rooms had higher ultrafine-particulate counts and lower ventilation rates. Rooms with mechanical ventilation had higher low-frequency and total sound-pressure levels, higher ventilation rates and fibre concentrations, but lower concentrations of ultrafine particulates. It was concluded that, in general, mechanical ventilation can provide better indoor air-quality, but that HVAC noise is an issue if the system is not properly designed. In ‘green’ buildings, noise levels were acceptable when the windows were closed, but increasing the ventilation rate by opening the windows resulted in higher noise levels. The results suggest that the acceptability of environmental factors in buildings depends on the degree of compliance of the design and its implementation with standards and design guidelines (i.e. for ventilation, air quality, thermal comfort, etc.), whether the original design concept is ‘green’ or non-‘green’.

Evaluation of Aerodynamic Infrasound Radiating From Upwind and Downwind HAWTs

2012 ◽  
Author(s):  
Adrian Sescu ◽  
Abdollah A. Afjeh
Keyword(s):  
Flow Field ◽  
Wind Turbine ◽  
Sound Pressure ◽  
Low Frequency ◽  
Pressure Level ◽  
Frequency Noise ◽  
Far Field ◽  
Acoustic Analogy ◽  
Horizontal Axis Wind Turbines ◽  
Tower Shadow

A Computational Fluid Dynamics tool is used to determine the detailed flow field developing around two-blade horizontal axis wind turbines (HAWT) in downwind and upwind configurations. The resulting flow field around the wind turbine is used to evaluate the low-frequency noise radiating to the far-field, using an acoustic analogy method. The influence of the variation of wind velocity and rotational speed of the rotor to the sound pressure level is analyzed. This paper shows that the tower shadow effect of a downwind configuration wind turbine generates higher aerodynamic infrasound when compared to a corresponding upwind configuration. For validation, a comparison between numerical results and experimental data consisting of sound pressure levels measured from a two-blade downwind configuration wind turbine is presented.

Efficiency of an ANC system in the tractor cabin under controlled engine workload

2020 ◽  
Vol 68 (5) ◽  
pp. 339-357
Author(s):  
Roberto Fanigliulo ◽  
Lindoro Del Duca ◽  
Laura Fornaciari ◽  
Renato Grilli ◽  
Roberto Tomasome ◽  
...  
Keyword(s):  
Sound Pressure ◽  
Noise Control ◽  
Active Noise Control ◽  
Low Frequency ◽  
Engine Performance ◽  
Noise Spectrum ◽  
Broadband Noise ◽  
Frequency Noise ◽  
Residual Noise ◽  
Agricultural Tractor

The noise at the driver seat of an agricultural tractor is produced mostly by the engine. Its characteristic broadband noise spectrum varies considerably with engine workload. The passive noise control techniques adopted in tractor cabins, based on the application of sound-absorbing and sound-proofing materials, are effective against medium-high frequencies noise components. The residual noise in sound-proof cabins is characterized by tonal emissions with low frequency components (< 500 Hz) but regarded as responsible for various disorders and diseases following long-term exposure. In addition to the "A" weighting filter adopted to evaluate occupational exposure to noise, other approaches are reported in the scientific literature considered more appropriate to evaluate low frequency noise (LFN), as well as studies testifying the effectiveness of active noise control (ANC) technologies in the low frequency range. In this article, the performance of an ANC system is evaluated in its ability to reduce noise levels inside the soundproof cabin of an agricultural tractor. To test this system, spectro-phonometric measurements of the equivalent linear sound pressure level were conducted under controlled and repeatable engine workloads, obtained by connecting the tractor to a dynamometric brake, while simultaneously acquiring the related engine performance curves. Altogether, three different couples of loudspeakers were tested. Frequency analysis in one-third octave band showed that the ANC system was mainly effective against LFN components (below 120 Hz) with peaks of reduction up to 20 dB. Then, on the basis of indications from previous studies, the data of linear sound pressure levels were processed applying the "A", "B", and "C" weighting filters, to show the different emphasis given to the effects of the system. Eventually, a point-by-point composition of the equivalent levels of sound pressure was drawn over the whole range of the engine, to highlight the conditions in which the ANC system was more effective.

scholarly journals Evidence of Cnidarians sensitivity to sound after exposure to low frequency noise underwater sources

2016 ◽  
Vol 6 (1) ◽  
Author(s):  
Marta Solé ◽  
Marc Lenoir ◽  
José Manuel Fontuño ◽  
Mercè Durfort ◽  
Mike van der Schaar ◽  
...  
Keyword(s):  
Fish Larvae ◽  
Low Frequency ◽  
Noise Pollution ◽  
Marine Species ◽  
Acoustic Trauma ◽  
Sensory Epithelium ◽  
Frequency Noise ◽  
Noise Levels ◽  
Sound Sources ◽  
The Impact

Abstract Jellyfishes represent a group of species that play an important role in oceans, particularly as a food source for different taxa and as a predator of fish larvae and planktonic prey. The massive introduction of artificial sound sources in the oceans has become a concern to science and society. While we are only beginning to understand that non-hearing specialists like cephalopods can be affected by anthropogenic noises and regulation is underway to measure European water noise levels, we still don’t know yet if the impact of sound may be extended to other lower level taxa of the food web. Here we exposed two species of Mediterranean Scyphozoan medusa, Cotylorhiza tuberculata and Rhizostoma pulmo to a sweep of low frequency sounds. Scanning electron microscopy (SEM) revealed injuries in the statocyst sensory epithelium of both species after exposure to sound, that are consistent with the manifestation of a massive acoustic trauma observed in other species. The presence of acoustic trauma in marine species that are not hearing specialists, like medusa, shows the magnitude of the problem of noise pollution and the complexity of the task to determine threshold values that would help building up regulation to prevent permanent damage of the ecosystems.

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