• 설비공학논문집
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• 제23권11호
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• pp.726-732
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• 2011

The aerodynamic and aeroacoustic performance of discharge grille of outdoor unit of air-conditioner was investigated in this study. Discharge grille is one of outdoor unit's important parts to affect the flow rate and Overall Sound Pressure Level(OSPL). New type of discharge grille was suggested based on the results of numerical simulation. To simulate the flow pattern near the propeller fan, commercial flow solver FLUENT was used. Sliding mesh method was used for rotating propeller fan and initial condition for unsteady model was calculated by Multiple Reference Frame(MRF) method. To minimize the interaction noise between fan blade wake and discharge grille, new discharge grille has radial rib which is aligned with trailing edge of fan blade. And inclined radial rib was adopted for reducing flow rate drop in discharge grille. The optimization of inclined angle of radial grille was performed experimentally.

• Journal of Mechanical Science and Technology
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• 제20권10호
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• pp.1653-1661
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• 2006

AC induction motors have been widely used for fan motor of the air conditioner indoor unit. Noise of these AC induction motors is usually caused by the coupling effects of structural and electrical systems. The rotating torque and the noise from AC induction motor were discussed in this paper,. First, the modification of motor was carried out in order to reduce the unbalance magneto motive force between main and sub winding. Second, structural modification based on normal mode analysis and modal testing was carried out so that the fan motor does not have the natural frequencies near the 2f-line frequency. Numerical modifications through these two processes were verified by experiments, which showed that the sound pressure level at 2f-line frequency of the modified system became about 25dB less than that of conventional one.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 추계학술대회 논문집
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• pp.327-327
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• 2007

This paper reports the simulation results of piezoelectric microspeakers due to structural changes(diaphragm materials, corrugation width and electrode shapes). When we compared the dependence of diaphragm material properties, the microspeaker with LTO(Low Temperature Oxide) diaphragm shows higher deflection than that of silicon nitride diaphragm, even though the resonant frequencies are almost same in both cases. In case of circular-electrode microspeaker, the deflection of diaphragm is about $16\;{\mu}m$ at 20 V, and it decreases as the corrugation width is decreased. However, the deflection of diaphragm with the square-electrode reveals almost twice times higher value at the same applied voltage than the circular one, and it increases as the corrugation depths are decreased from $30\;{\mu}m\;to\;10\;{\mu}m$. The first resonant frequency of microspeakers present about 1.8 kHz in circular-electrode and 1.2 kHz in square-electrode, respectively.

• 한국소음진동공학회논문집
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• 제24권1호
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• pp.62-68
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• 2014

Recently, MRI(magnetic resonance imager) scanner is continually used for medical diagnosis and many biomedical researches. When it operates, however, intense noise is generated. The SPL(sound pressure level) of the noise approaches 130 dB especially in 3 T(Tesla) MRI. Meanwhile, more than 3 T MRI scanners have been developed to get higher-resolution images, so louder noise is expected in the future. The intense noise makes patients feel nervous and uncomfortable. Moreover, it could possibly cause hearing loss to patient in extreme cases. For this reason, some active noise control systems have been researched. One of them used feedback Filtered-X LMS(FXLMS) algorithm which is able to control only narrowband noises and possible to diverge in severe case. In this paper, we determine the property of MRI noise. Using the property, we applied a method of open-loop and adaptive control for reducing MRI noise at target point inside bore. We verified performance of the method with computer simulation and preliminary experiment. The results demonstrate that the method can effectively reduce MRI noise at target point.

• 정보저장시스템학회논문집
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• 제2권1호
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• pp.50-55
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• 2006

As high performance and high speed have been accomplished by technology of optical disk drive. optical disk drives have gradually high percentage of the market share in market of storage devices. This technology helps to improve the quality of record/reproduction. However, simultaneously it causes various problems in the structural aspect and increases noise largely. Especially at high speed, dominant noise is more influenced by fluid noise than by structure-borne noise. The purpose of this study is that reduce the air-born noise in optical disk drive as it decreases a quantity of flow by using a micro muffler. The micro muffler is a miniaturized muffler. The muffler is used widely by solution to reduce air-borne noise which is generated by flow. According to frequency band of the noise source, it can be applied by muffler of various forms. In this study, we examined the acoustic characteristics of the micro muffler and applied it to reduction of the ODD noise. It could get an excellent noise reduction in high frequency band through the decrease of an inner flow. But it could not get a noise reduction in low frequency band.

• 한국음향학회지
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• 제26권3호
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• pp.115-122
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• 2007

본 연구에서는 마이크로스피커의 구조와 특성을 유닛과 덕트형 인클로저로 구성되어 있는 일종의 덕트형 스피커시스템처럼 취급할 수 있음을 처음으로 보여주었다. 후면기공의 면적이 증가할수록 스티프니스는 감소하고 컴플라이언스는 증가하였다. 그 결과로써, 후면기공의 면적이 증가할수록 공명진동수가 컴플라이언스의 제곱근에 비례하여 증가하였다. 후면기공의 면적이 감소함에 의하여 중저음 영역에서의 기준음압레벨이 지수함수적으로 감소하였다.

• 한국수산과학회지
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• 제10권4호
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• pp.227-235
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• 1977

1976년 8월 16일 (북위 $34^{\circ}27'30'$ 동경 $128^{\circ}23'15'$)과 1977넌 7월 28일(북위 $34^{\circ}47'$ 동경 $128^{\circ}53'$)에 관악산호의 선박소음이 r.p.m에 따라 항해시와 정선시 (기관의 공회전)의 소음압이 해중에 분포하는 것을 조사 연구한 결과를 요약하면 다음과 같다. 1. 기관의 r.p.m.과 음압관계 r.p.m.과 음압의 증가비는 100 : 1이었으며 r.p.m. 600에서 104dB로 peak를 이루었다. 2. 외현주변의 해중해압분포 A. 정선시의 기관소음압 100,102,103,104,104 dB일때 관측점 No.1에서 69,70,72,74,75 dB No.3은 No. 1에 비해 $2\~3\;dB$ 증가해 peak를 이루었고 No.5는 No.3에 비해 $10\~15\;dB$씩 감쇠되었다. 기관소음압이 최대 일때 관측점 $No.1\~No.5$에서의 음압이 투과된 백분율은 약 $78,79,80,73,70\%$였다. B. 항해시의 선박수중소음압 정선시와 같은 기관회전 조건하에서 No.2에서 69,72,75,77,78 dB로 peak를 이고 No. 1보다 $2\~3\;dB$씩 감쇠되었다. 기관 최고소음압에 대한 $No1.\~No.5$에서의 음압투과 백분율은 약 $78,81,79,77,71\%$ 였다. 3. 항해시와 정선시의 외현해중 음압 peak점에서의 음압을 비교하면 항해시가 1 dB 높았다. 4. 선박이 멀어질 때 0 m(관측점 통과시)에서 67 dB, 1,400 m에서 56 dB였다. 5. 선박이 가까워질 때 거리 0 m에서 72 dB, 1,400 m에서 57 dB로서 멀어 질때와 비교하면 0m에서 5 dB, 600 m에서 2 pB씩 증가한 도플러 효과가 일어남을 알 수 있다. 6. r.p.m.을 600으로 하여놓고 스크류를 돌리지 않고 기관만 공회전 시킬 때 수평거리 20 m인 곳의 No.7에서 수심 10 m마다 50 m까지의 음압은 68,75,62,59,55,51 dB였다.

• 한국추진공학회지
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• 제10권4호
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• pp.40-46
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• 2006

저궤도 위성 발사체에 적용 가능한 추력 30 tonf급의 연소기가 설계/제작되어 전반적인 연소 시험이 이루어졌다 터보 펌프식 개방형 사이클에 적용 가능한 재생냉각형으로 제작된 본 연소기는 초기 연소성능 및 기능 검증을 위해 내열재 방식의 연소실을 이용하여 연소 시험을 수행하였다. 설계 조건을 중심으로 넓은 작동 구간에서 본 연소기는 안정된 연소 특성을 보였다. 연소기의 물리적 손상 또한 발생하지 않았으며, 만족할 만한 기능적 특성을 나타내었다. 연소기의 성능은 연소 효율이 95%, 그리고 지상 비추력이 254초로 초기 설계 대비 초과 내지는 동등 수준의 결과를 보였다.

• 대한기계학회논문집B
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• 제40권5호
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• pp.321-327
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• 2016

본 연구에서는 고속 회전을 하는 진공청소기용 원심홴의 공력성능 향상을 위해 에어포일 임펠러(Airfoil Impeller)의 적용을 검토 및 연구하였다. 에어포일 최대두께 및 최대두께 위치에 따라 3종의 에어포일 임펠러를 제시하였고, 이때 C4 에어포일 두께분포를 이용하였다. 에어포일 임펠러의 성능 평가는 전산유체역학(Computational Fluid Dynamics) 해석과 흡입일률시험을 통해 수행되었다. 이를 통해 에어포일 형상 적용 시 기존 블레이드 형상에 비하여 임펠러 블레이드 압력면과 디퓨져 블레이드 압력면에서 발생하는 유동박리가 크게 줄어드는 것을 확인하였다. 그리고 이로 인해 기존 원심홴에 비하여 홴 효율이 약 3% 증가 및 비소음이 약 1.3dB(A) 감소되는 것을 확인하였다.

• Journal of Preventive Medicine and Public Health
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• 제19권1호
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• pp.100-122
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• 1986

Obtaining an available information on health concerns of parents of school-age children and furthermore developing the sound policy for the public on health education, this study was conducted during Nov.-Dec. 1985 in the four selected areas; Seoul, large, middle and small city, and farming and fishery villages for 3,337 parents of schoolchildren in Korea. In this study, parents complected a questionnaire containing 34 items related to health concerns(e.g. drinking alcohol, air pollution, cancer, etc. see Table 4 and Fig. 2). For each health items, respondents were asked to indicate a choice between three levels of concern; 'Very high concern,' 'Moderate concern,' 'Little concern', and 'No opinion'. An analysis of responses indicated that most of the top ten health concerns identified by parents as cancer, abortions among high school students, medical malpractice, water pollution, traffic accidents, air pollution, suicide of parents and homicide of offspring, heart disease, venereal diseases, and high blood pressure in that order. Those health problems about which respondents were least concerned were more closely related to the individual, such as drinking alcohol, smoking, tooth decay, gum disease, underweight, overweight. Of greater concern were more such as water pollution, abortions among high school students, air pollution, accidents, medical malpractice. For cancer, heart disease, high blood pressure, various accidents, environmental pollution, parents showed high concern, however, for health issues which contributed as causative influences such as lung cancer from smoking and liver cirrhosis and traffic accidents from drinking alcohol showed less concern. Relationship between parent's residential areas, educational level and sex distribution and health concern showed little difference, however, for these issues parents identified as relatively high concern. Most parents stowed more concern in sex-related of family-related health issues such as abortions among high school students, suicide of parents and homicide of offspring.