• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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• pp.1865-1870
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• 2000

Sound propagation along the surface of the ground can be affected by the roughness of the ground surface and the direction of the wind. Noise Source parameter and ground factor are estimated using the measured results of two points under particular environmental condition, and the noise level of arbitrary points under the same environmental condition can be estimated. The results can be used for the prediction of the noise level from a source above a plain and homogeneous ground surface with no obstacles nearby. Upward and downward conditions are also addressed in addition to ground effect. The proposed method can be utilized to estimate the noise level of specific noise environment and its validity was confirmed with the results of actual field measurement.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2010년도 춘계학술대회 논문집
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• pp.74-75
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• 2010

Inflow broadband noise is generated when turbulence in the rotor wakes impinges on the downstream stator vanes. In this paper a three-dimensional model is developed to investigate the broadband noise due to turbulence-cascade interaction. In the newly-developed model, we consider the effects of incident turbulent gust component in span-wise direction on the inflow broadband noise. The quasi-three-dimensional theory is deduced based on the tonal analytic theory of Smith (1972) and two-dimensional broadband noise generalization by Cheong et al. (2006; 2009). Extending the modified LINSUB code, quasi-three-dimensional computational results are presented. Finally, we compare these computational results with time-domain results to validate the theory.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.421-426
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• 2005

For the air-conditioner, refrigerant induced noise and vibration should be the problem when it reduced airflow rate in order to reduce the noise at low mode. With the test, it could be verified that one of the main reason for refrigerant induced noise were the velocity and flowing induced force of the refrigerant at the inlet of evaporator. So in order to reduce this velocity with same mass flow rate of refrigerant, quality at the evaporator inlet should be minimized. And in order to reduce flowing induced force of the refrigerant, flowing direction change should be eliminated. So in this paper, it would like to review the characteristics of refrigerating cycle at first and find how the quality and flowing induced force can be minimized.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.140-143
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• 2008

Experiments are performed to consider the ground effects on unsteady loading and acoustic generation. Partially inclined plate is used to maximize the unsteadiness of the rotor. Indirect method to recognize the unsteady effect is used by measuring the noise in the normal direction from the rotor plane. The experiment is conducted with a square plate of about $9m^2$ and one half of the plate is placed parallel with the rotor plane and the other half is inclined. The height of the plate and the angle of the inclined plate can be changed. Helicopter noise is also measured at the 4 different positions to study the directivity of the rotor noise. The distance between microphone and rotor hub is 1.3m. Tonal noise and broad band noise are measured and analyzed. Thickness noise, steady loading noise and unsteady loading noise are investigated from the rotor noise measurement.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 추계학술대회논문집
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• pp.269-274
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• 2004

The aims of this study were to Investigate the floor impact noise isolation performance of floating floor with isolation materials and propose the improvement direction of floor impact noise measurement method and evaluation classes using impact ball. Reduction of light-weight impact sound pressure level can be achieved by the finishing materials, such as vinyl finishing material and wooden flooring with isolation materials. Floor impact noise Isolation material which satisfy the properties of the floor impact noise isolation materials cause resonance in the low frequency band and worsen heavy-weight impact sound pressure level. Heavy-weight impact sound level can be reduced by using noise reduction flooring, ceiling and increase of slab thickness. Strong impact force in low frequency bang below 63Hz of bang machine is not similar to human impact source and causes some problem in evaluating heavy-weight impact noise but heavy-weight impact noise measurement and evolution using impact ball which is very similar to human impact is more reliable than bang machine. Correction value on the background noise and sensitivity of residents should be considered on the floor impact noise evaluation classes.

• 소음진동
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• 제8권6호
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• pp.1015-1022
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• 1998

This paper addresses the results of an experimental and analytical research of a helical coil spring subjected to dynamic behavior using space curve vector after considering elongation rate. Vibrations in helical coil spring can be divided into 3 modes such as vibrations of coil spring center axis' vertical direction. axis' horizontal direction, direction about center axis. However. these 3 modes are dependent one another and are characterized as coupled. The dependency was proved through both theoretically and experimentally analyzing the results of dynamic characteristics of coil spring center axis' vertical direction vibration by transfer matrix method using the governing equation of static equilibrium. Also this paper shows that pitch angle and active coils in coil spring affect the dynamic spring characteristics of the above 3 modes and are especially sensitive to the mode for vibration of axis' horizontal direction which most affects especially on dynamo stability of helical coil spring.

• 소음진동
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• 제5권2호
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• pp.247-256
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• 1995

In this paper, double exposure holographic interferometry using ruby pulse laser is formed in order to investigate the propagation of transient waves. The vibration characteristics according to the change of impact load direction, i.e., impacted in the shear direction and in the normal direction are analyzed. It was observed that the macroscopic trends of transient wave generation and propagation in the assembly of precipitator plates were almost similar regardless of the change of impact load direction. But the propagation and mixing of transient wave was advanced relatively slowly when impacted in the normal direction.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 춘계학술대회논문집
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• pp.209-212
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• 2005

Recently, since structures have become extremely airtight with the development of high-rise apartments, mixed use residential and commercial buildings and offices, large capacity range hoods have become commonly implemented. However, the high noise level caused by this range hood system made of thin plate is the cause of increased complaints among users. In this study, the level of noise emitted from this type of range hood was measured by height at the user's location in the kitchen. It was confirmed that a great deal of noise was emitted in the downward direction of the hood. In order to minimize the noise emitted from this type of range hood, a new type of fan was manufactured. This was done by changing only the material and shape of the fan, since it was determined to be the primary source of noise emission. Then a comparison and evaluation were carried out regarding the noise characteristics between the new type of fan and the existing type of fan. As a result, it was confirmed that the noise from the new fan was reduced by more than 2 dB compared to the existing fan without noise interference at the discharge end.

• 한국항공우주학회지
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• 제33권2호
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• pp.39-45
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• 2005

본 연구에서는 현재 일반 프로펠러 항공기에 사용 중인 둥근 팁 형상을 갖는 Hartzell 사 제작 프로펠러에 대해서 두께소음과 하중소음에 대한 예측을 시도하였다. 음향장 해석에 앞서서 프로펠러 표면상에 존재하는 압력분포는 자유후류 패널 방법과 비정상 베르누이 방정식을 이용하여 구하였다. 음향장 해석을 위해서는 FW-H의 음향상사 법칙을 적용하였다. 주어진 프로펠러 형상과 운전 조건에 대한 소음 예측으로부터 두께소음은 프로펠러 회전면을 기준으로 전방과 후방이 서로 비슷한 면대칭 분포를 갖는 반면에, 하중소음은 프로펠러 후방의 소음이 전방에 비해서 더 크게 나오는 결과를 보여주었다. 일반적인 운전조건에서는 전반적으로 하중소음이 두께소음보다 지배적인 결과를 보여주었다.

• Corrosion Science and Technology
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• 제3권3호
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• pp.102-106
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• 2004

Al foil used was 99.9 and 99.99 %. Test solution used was NaCl solution. The noise was determined using controlled potential electrolysis at -200 and -700 mV vs. NHE. The current fluctuation was caused by breakdown and repaired process of aluminum oxide film. The current fluctuation value of noise was proportion to degree of growth. The number of noise was proportion to the number of pit. The examining of current flutulation value and number of noise could be evaluated corrosion. A 99.99 % Al foil was the mostly crystal of {100} plane, and showed three-dimensional, as azimuth pit with along the direction of this place piled up. A 99.9 % Al foil was polycrystal, and in order of (311) >(222) >(200) >(111) plane. The azimuth pit did not occurred as the dissolution was occurred from each plane.