• Advances in aircraft and spacecraft science
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• v.9 no.4
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• pp.319-333
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• 2022

This work presents a numerical investigation of the aerodynamics and aero acoustics of the HVAB rotor in hover conditions. Two fully turbulent models are employed, the one-equation Spalart-Allmaras model and the two-equation k-ω SST model. Transition effects are investigated as well using the Langtry-Menter γ-Re θt transition transport model. The noise generation and propagation are being investigated using the Ffows-Williams Hawking model for far-field noise and the broadband model for near-field noise. Comparisons with other numerical solvers and with the PSP rotor test data are presented. The results are presented in terms of thrust and power coefficients, the figure of merit, surface pressure distribution, and Sound pressure level. Velocity, pressure, and vortex structures generated by the rotor are also shown in this work. In addition, this work investigates the contribution of different blade regions to the overall noise levels and emphasizes the importance of considering specific areas for future improvements.

• Journal of Korean society of Dental Hygiene
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• v.15 no.1
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• pp.11-17
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• 2015

Objectives: The purpose of the study is to investigate the relationship between noise awareness, hearing ability, and dental hygiene performance in dental hygienists. Methods: The subjects were 234 dental hygienists in Seoul, Gyeonggi-do, and Incheon. The questionnaire consisted of 3 questions of general characteristics of the subjects, 1 question of noise awareness, 3 questions of hearing ability, 5 questions of dental hygiene performance, 1 question of noise reduction necessity, and 2 questions of noise control. Noise awareness, dental hygiene performance, and noise reduction necessity were measured by Likert 5 scale. Cronbach's alpha was 0.825 in dental hygiene performance reliability. Results: There was a significant difference in noise recognition by age(p<0.01) and working career(p<0.05). Those who pumped up the higher TV volume accounted for 31.6% and 3.0% had hearing impairment in the regular health checkup. 3.4% of the respondents complained of hearing loss, ear fluid, and equilibrium problem diagnosed by the doctors. The relationship between the type of workplace environment and task performance showed a significant difference. Those who work in the dental hospitals had high score of 3.43, while those who work in dental clinics had 3.20(p<0.05). The increased level of noise recognition affected the task performance and it is necessary to reduce the noise level. More try must be focused on the noise exposure prevention. Conclusions: In order to reduce the problems due to noise and improve their quality of life, it is necessary to change the noise recognition in the work place.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.28 no.1
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• pp.100-107
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• 2018

Objectives: This study examines exposure to hazardous substances in the working environment caused by exposure to toxic substances produced in the aluminum die casting process in the automobile manufacturing industry. Materials and Methods: The exposure concentration levels, detection rates and time-trend of 15 hazardous factors in the aluminum die casting process over 10 years(from 2006 to 2016) were used as a database. Results: The study found that hazardous factors in the aluminum die casting process were mostly metals. The rate for detected samples was 70.6%(405 samples), and that for not detected samples was 29.4%. The noise for an eight-hour work shift showed a 49.7% exceedance rate for TLV-TWA. Average noise exposure was 89.0 dB. The maximum exposure level was 105.1 dB. Conclusion: The high numbers of no-detection rates for hazardous substance exposure shows that there is no need to do a work environment measurement. Therefore, alternatives are necessary for improving the efficiency and reliability of the work environment measurement. Moreover, to prevent noise damage, reducing noise sources from automation, shielding, or sound absorbents are necessary.

• Journal of Technologic Dentistry
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• v.36 no.2
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• pp.111-118
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• 2014

Purpose: Production of dental prosthesis by a dental technician causes a loud noise. Thus, we investigated stress of dental technicians due to a noise using a structured questionnaire. Methods: A survey was conducted on working dental technicians across the country from July 2013 to November 2013; among 200 sets of survey distributed, 166 were completed and returned, and excluding the 11 that deemed unsuitable, 155 sets were used for statistics. The program SPSS 19.0 was used to analyze the correlation among the collected data. Results: The stress of noise was found to be 2.83/5 points (2.93/5 for physical stress, 2.72/5 for emotional stress). Recognition of noise was found to be 2.71/5 points (3.39/5 for recognition of noise, 2.64/5 for accidents caused by noise, 2.29/5 for experiencing disability due to noise). For general items, the highest stress were shown for the following catogories: by gender, females (p=.008); by position, chief engineer (p=.033); by monthly pay, 2.51M-3.0M KRW (p=.023); by interior comfort, 'very unpleasant' was the highest recognized (p=.014). For the effect of time exposed to noise, its stress (p=.000) and recognition (p=.000) rose with increase of time. Conclusion: Dental technicians performs tasks in work environments exposed to extreme noise. This research attempts to re-emphasize the necessity for improving the work environment for noise and provide measures of blocking noise and precaution.

• Journal of the Korean GEO-environmental Society
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• v.13 no.12
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• pp.43-49
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• 2012

Noise measurements were performed by distance for major construction equipment. especially, For construction equipment that large width of variations is depending on the type of work, noise measurements were performed by the detail type of work. For a time of quiescent and construction, "A" compensation equivalent noise level (Leq) were measured. Most of the construction equipment and the characteristics of the point source appears to be similar in analyzed noise measurement results.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.8
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• pp.809-815
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• 2009

The previous work(Cheong et al., 2006) where the characteristics of acoustic emissions of wind turbines has been investigated according to the methods of power regulation, has showed that the acoustic power of wind turbine using the stall control for power regulation is more correlated with the wind speed than that using the pitch control. In this paper, basically extending this work, the noise generation characteristics of large modern upwind wind turbines are experimentally indentified according to the power regulation methods. To investigate the noise generation mechanisms, the distribution of noise sources in the rotor plane is measured by using the beam-forming measurement system(B&K 7768, 7752, WA0890) consisting of 48 microphones. The array results for the 660 kW wind turbine show that all noise is produced during the downward movement of the blades. This result show good agreement with the theoretical result using the empirical formula with the parameters: the convective amplification; trailing edge noise directivity; flow-speed dependence. This agreement implies that the trailing edge noise is dominant over the whole frequency range of the noise from the 660 kW wind turbine using the pitch control for power regulation.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.04a
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• pp.63-67
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• 2009

The previous work (Cheong et al., 2006) where the characteristics of acoustic emissions of wind turbines has been investigated according to the methods of power regulation, has showed that the acoustic power of wind turbine using the stall control for power regulation is more correlated with the wind speed than that using the pitch control. In this paper, basically extending this work, the noise generation characteristics of large modern upwind wind turbines are experimentally indentified according to the power regulation methods. To investigate the noise generation mechanisms, the distribution of noise sources in the rotor plane is measured by using the Beam-forming measurement system (B&K 7768, 7752, WA0890) consisting of 48 microphones. The array results for the 660 kW wind turbine show that all noise is produced during the downward movement of the blades. This result show good agreement with the theoretical result using the empirical formula with the parameters: the convective amplification; trailing edge noise directivity; flow-speed dependence. This agreement implies that the trailing edge noise is dominant over the whole frequency range of the noise from the 660 kW wind turbine using the pitch control for power regulation.

• Journal of the Korean Society of Safety
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• v.34 no.4
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• pp.95-102
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• 2019

The purpose of this study is to investigate the correlation between aluminum form work and noise-induced deafness by conducting special health examination on construction aluminum worker and noise measurement at the workplace. All the 11 aluminum form workers were diagnosed with noise-induced deafness after holding a special health examination. The workers have not had any previous history of noise-induced deafness which indicates that aluminum form work is related to noise-induced deafness disease. The impact noise of 120 dB(A)~125 dB(A), which exceeds the regulations of industrial safety and health act, was found during the dismantling rather than installation when noise measurement was made at the aluminum workplace. The aluminum form workers could permanently lose the hearing sense if they are exposed to this impact noise. This study is to suggest the method to prevent noise-induced deafness for aluminum form workers by firstly giving out hearing protection equipment at the construction site and secondly installing rubber mat, soundproof panel as well as changing the noise-lowering technique.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.30-37
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• 2009

In doing the foundation work in the downtown, the popular complaints by means of Noise and vibration have been became heavy burden. Therefore, the noise & vibration-free screw PHC pile method will contribute to the foundation work by removal of the popular complaints and improvement of the constructability. In this paper, the load bearing capacity and displacement characteristics of the noise & vibration-free screw PHC pile were analyzed. The noise & vibration-free screw PHC pile's behavior was better well than the existing PHC pile's one.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.04a
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• pp.643-648
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• 1997

Concern for noise problems of a commercial aircraft in community and cabin is increasing due to the more restrictive regulation and customer requirements. This paper introduces to the work packages of the aircraft noise engineer for the development of a commercial aircraft. First of all, the noise engineer establish the design requirement and objectives(DR&O). Then the design and analysis are performed to satisfy with the DR&O during the conceptual and preliminary design phase. And the test and evaluation(T&E) are carried out to verify the analysis results and to acquire the type certification.