• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.941-945
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• 2006

In the development of electricity generating wind turbines for wind farm application, only two types have survived as the methods of power regulation; stall regulation and fun span pitch control. The sound measurement procedures of IEC 61400-11 are applied to field test and evaluation of noise emission from each of 1.5 MW and 660 kW wind turbine generators (WTG) utilizing the stall regulation and the pitch control for the power regulation, respectively. Apparent sound power level, wind speed dependence and third-octave band levels are evaluated for both of WTGs. It is found that while 1.5 MW WTG using the stall control is found to emit lower sound power than 660 kW one using the pitch control at low wind speed (below 8 m/s), sound power from the former becomes greater than that of the latter in the higher wind speed. Equivalent continuous sound pressure levels (ECSPL) of the stall control type of WTG vary more widely with wind speed than those of the pitch control type of WTG These characteristics are believed to be strongly dependent on the basic difference of the airflow around the blade between the stall regulation and the pitch control types of WTG. These characteristics according to the methods of power regulation lead to the very different noise emission characteristics of WTG depending on the seasons because the average wind speed in summer is lower than the critical velocity over which the airflow on the suction side of blade in the stall types of WT are separated. These results propose that, in view of environmental noise regulation, the developer of wind farm should give enough considerations to the choice of power regulation of their WTG based on the weather conditions of potential wind farm locations.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문초록집
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• pp.366.2-366
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• 2002

Unsteady flow characteristics and associated blade tonal noise of a cross-flow fan are predicted by a computational method. The incompressible Wavier-Stokes equations are time-accurately solved for obtaining the pressure fluctuations between the rotating blades and the stabilizer, and sound pressure is predicted using Curie's equation. The computed fan performance is favorably compared with experimental data, and also indicates that the performance is not significantly altered by the random pitch effect at ø〉0.4. (omitted)

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2000년도 추계 학술대회논문집
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• pp.141-148
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• 2000

The discrete noise of the cross-flow fan with uniform/random pitch blades is predicted by computational methods. With the time dependent surface pressure data obtained by solving the Wavier-Stokes equation, the acoustic pressure is calculated by the Ffowcs Williams-Hawkings equation. The positions of the blade noise source are identified through investigation of the acoustic pressure history induced by one blade, and it is confirmed that the dominant noise source is near the stabilizer. Since the acoustic pressure of the random pitch fan fluctuates according to blade passing, the dominant BPF noise for the uniform pitch fan is modified into some reduced discrete noises which have a 50Hz difference from BPF.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.340-343
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• 2006

As the needs of consumer on ride comforts increase and the reduction of road traffic noise tightened step by step, the power unit noise emitted by cars has been reduced. It has been found that tire noise dominates noise produced by the power-train when vehicles are driven at high speeds. Therefore, in these days, tire/pavement noise is concerned. Tire/pavement noise is affected by pavement type and vehicle???s transmission loss. Tire noise mechanism is produced by several mechanisms. The sound of tire can propagate either through the air or through the structure of vehicle. Pattern noise is the result of pressure variations through the air to the interior side of vehicle. Especially, on smooth asphalt the periodicity of tread design, pitch sequence is important factor, which have an influence on the reduction of tire noise.

• 한국항공우주학회지
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• 제40권3호
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• pp.201-208
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• 2012

본 논문에서는 정지비행 조건에서의 무향실 내 축소 로터 실험을 이용해 Lowson의 하중 소음식과 FW-H의 음향상사식으로 예측한 이산 주파수 소음(Discrete frequency noise)을 검증하였다. 소음 예측 기법의 방향성(Directivity) 검증은 전반적으로 실험결과와 유사하게 예측되었으며, 거리에 대한 검증의 경우 근거리(Near-field)에서는 FW-H식의 예측결과가, 원거리(Far-field)에서는 Lowson식의 예측결과가 실험결과와 더 유사한 것을 확인하였다. 피치 각(Collective pitch angle)에 대한 검증의 경우 낮은 피치각에서는 FW-H식의 예측결과가, 높은 피치각에서는 Lowson식의 예측결과가 실험결과와 더 유사한 것을 확인하였다.

• 핵의학기술
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• 제17권2호
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• pp.67-71
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• 2013

PET/CT검사에서 CT촬영조건의 변화는 영상의 화질 및 환자가 받는 피폭선량에 영향을 미친다. 본 연구는 CT 매개 변수 중 Pitch와 X-선관 회전시간 변화에 따른 선량대비 CT 영상의 질과 이로 인해 PET상에서 SUV에 미치는 영향을 비교 평가하고자 하였다. Discovery STe PET/CT 장비를 이용하여 영상을 획득하였다. QA Phantom과 AAPM Phantom을 이용한 CT 영상 획득 시 Pitch는 0.562, 0.938, 1.375, 1.75:1로 4단계, X-선관 회전시간은 0.5에서 1.0까지 0.1초씩 증가시켜 6단계로 나누어 총 24개 조합을 적용한 영상을 각각 획득하였다. PET 영상은 $^{18}F-FDG$ 5.3 kBq/mL가 채워진 1994 NEMA PET Phantom을 이용하여 프레임당 2분 30초의 방출영상을 획득하였다. 각 조합의 CT 영상에 관심영역을 설정하고 CT number의 표준편차를 측정하였다. 동일한 영상에서 DLP변화에 따른 영상잡음의 예측값을 계산하여 예측값 대비 실측값의 비율을 구해 선량대비 영상잡음 효과를 비교하는 척도로 사용하였다. AAPM Phantom 영상에서 1.0 mm까지 식별이 가능한 지 확인하였다. NEMA PET Phantom의 방출영상에 관심영 역을 설정하고 SUV를 비교 평가하였다. Pitch가 0.562, 0.938, 1.375, 1.75:1로 변화할 때 영상잡음 효과는 QA Phantom에서 1.00, 1.03, 1.01, 0.96, AAPM Phantom에서 1.00, 1.04, 1.02, 0.97로 측정되었다. 회전시간의 증가에 따른 경우 QA Phantom에서 0.99, 1.02, 1.00, 1.00, 0.99, 0.99이었고, AAPM Phantom에서 1.01, 1.01, 0.99, 1.01, 1.01, 1.01로 SPSS Ver. 18을 이용하여 상관관계를 분석한 결과 피어슨 상관계수는 -0.059로 나타났다. 공간분해능에 대한 평가는 24개의 조합 모두에서 1.0 mm까지 육안으로 구별이 가능하였다. SUV의 경우 평균 SUV는 모든 조합에서 1.1로 모두 동일한 값을 나타내었다. Pitch 변화에 따른 CT 영상 평가에서 1.75:1을 적용 시 선량대비 가장 적은 영상잡음 효과를 보이며 공간분해능과 SUV에는 영향을 미치지 않는다. 그러나 회전시간 변화가 영상에 미치는 영향에는 유의한 차이가 없음을 알 수 있다. 결과에서와 같이 각 장비에 따른 선량대비 영상잡음이 적은 Pitch를 사용하고 환자의 체격에 따른 적절한 X-선관 회전시간을 이용한다면 환자의 피폭선량을 줄이면서 최적의 화질을 얻을 수 있는 프로토콜을 구성하는데 도움이 될 것이라 사료된다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.803-808
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• 2006

This paper was a study about noise reduction through flow stabilization in duel using experimental method and numerical analysis at the same time. To determine the fan's type three kinds of fans(axial fan, centrifugal fan, and axial fan with centrifugal type) was examined to investigate the suitability for duct. As a result, under the equal number of rotation 2000 RPM, performance of an axial fan with centrifugal type was the most superior by 55dBA at 4.3CMM among other fans. After this, analyzed the results of the numerical analysis to find out the optimum design of pitch angle such as $0^{\circ},\;10^{\circ},\;15^{\circ}\;and\;20^{\circ}$. The intensity of turbulence was low when pitch angle was $15^{\circ}$ and air volume became peak by 5.08 CMM. It was observed that axis component of velocity increased gradually when pitch angle increased from $0^{\circ}\;to\;20^{\circ}$. Finally, designed the shapes of D/S(Down Stream) in duct that agreed inlet angle($\delta$) of stationary blades with pitch angle($\beta$) of axial fan with centrifugal type and derived flow to duct medial, and changed the shape of motor-mount to reduce occurance of unstable vortex in tip of impeller, and embodied noise reduction and improvement of air flow rate through flow stabilization.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 추계학술대회논문집
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• pp.661-665
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• 2006

This study investigates objective and subjective evaluations of refrigerator noise. To describe the fluctuations like a click, a rapid increase of sound level, a change of pitch, a transition into the stationary and ending phase, the psychoacoustical and autocorrelation function(ACF) parameters have been employed. First, subjective evaluation of the noisiness of 24 kinds of refrigerators was conducted. Then, the relationship between objective measures of the refrigerator noise on perceived noisiness was examined with multiple regression analyses. Sound Quality Indices using the psychoacoustical and ACF parameters were also developed. The important psychoacoustical parameters for evaluating noisiness are loudness and roughness of stationary phase. The relationship between the noisiness and the ACF parameters shows that sound energy ${\Phi}(0)$ and its fluctuations are important. Also, refrigerator sounds that had a fluctuation of pitch were rated as more annoying. The fluctuation of pitch is expressed by ${\tau}_1\;and\;{\Phi}_1$ defined by the delay time and the amplitude of the first peak of the ACF.

• 한국음향학회지
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• 제10권4호
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• pp.12-18
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• 1991

음성 신호처리 분야에서 기본주파수를 정확히 검출하는 것이 아주 중요하다. 주파수 영역에서 피치검출 방법의 문제점은 대체로 배경잡음이나 제 1 포먼트에 의하여 발생한다. 그러므로, 본 논문에서는 스펙트럼 AMDF 함수를 이용하여 잡음의 영향이나 제 1 포먼트의 영향을 줄이는 주파수영역 피치검출 앨고리즘을 제안하였다. 여러 가지 컴퓨터 시뮬레이션 결과 제안한 앨고리즘이 기본주파수 검출에 효과적으로 나타났다.

• 한국소음진동공학회논문집
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• 제16권8호
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• pp.864-871
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• 2006

In the development of electricity generating wind turbines for wind farm application, only two types have survived as the methods of power regulation; stall regulation and full span pitch control. The main purpose of this paper is to experimentally identify the characteristics of noise emission of wind turbines according to the power regulation types. The sound measurement procedures of IEC 61400-11 are applied to field test and evaluation of noise emission from each of 1.5 MW and 660 kW wind turbines (WT) utilizing the stall regulation and the pitch control for the power regulation, respectively. Apparent sound power level, wind speed dependence, third-octave band levels and tonality are evaluated for both of WTs. It is observed that equivalent continuous sound pressure levels (ECSPL) of the stall control type of WT continue to increase with increasing wind speed whereas those of the pitch control type of WT show less correlation with wind speed. These observed characteristics are believed to be due to the different airflow patterns around the blade between the stall regulation and the pitch control types of WT; the airflow on the suction side of blade in the stall types of WT are separated at the high wind speed. It is also found that the 1.5 MW WT using the stall control emits lower sound power than 660 kW one using the pitch control at wind speeds below 8m/s, whereas sound power of the former becomes higher than that of the latter in the wind speed over 8m/s. This wind-speed dependence of sound power leads to the very different noise omission characteristics of WTs depending on the seasons because the average wind speed in summer is lower than 8m/s whereas that in summer is higher. Based on these experimental observations, it is proposed that, in view of environmental noise regulation, the developer of wind farm should give enough considerations to the choice of power regulation of their WTG based on the weather conditions of potential wind farm locations.