• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 추계학술대회논문집
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• pp.554-558
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• 2004

In this paper, we introduce noise prediction program of HVAC system to assist low-noisy design of ship's cabin. The developed program calculates sound power levels at HVAC components considering primary and secondary noise generated by fan and duct element, duct element noise attenuation, and duct break-in noise based on the authentic empirical method suggested by NEBB and acoustic power balancing method. Sound pressure level at cabin with or without ceiling system is evaluated by the diffuse-field theory considering diffuser and duct break-out sound powers. Moreover, the program provides intuitive pre- and post-processors using modem GUI functions to help efficient modeling and evaluation of cabin and HVAC component noise. To validate the accuracy and convenience of the program, noise prediction for a HVAC system is demonstrated.

• 한국소음진동공학회논문집
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• 제26권2호
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• pp.141-147
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• 2016

Underwater cavitation is one of the most important issues because it causes not only vibration and erosion of submerged bodies but also significant flow noise problems. In this paper, flow noise due to cavitation flows around the NACA66 MOD hydrofoil is numerically investigated. The cavitation flow simulation is conducted using the Reynolds-Averaged Navier-Stokes equations based on finite difference methods. To capture the cavitation phenomena accurately and effectively, the homogeneous mixture model with the Merkle's cavitation model is applied. The predicted results are compared with available experimental data in terms of pressure coefficients and volume fraction, which confirms the validity of numerical results. Based on flow field analysis results, hydro-acoustic noise field due to the cavitation flow is predicted using the Ffowcs-Williams and Hawkings equation derived from the Lighthill's acoustic analogy. The typical lift dipole propagation patterns are identified.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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• pp.1476-1481
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• 2007

Numerical investigation on radiation characteristics of discrete frequency noise from asymmetry aero-intakes was carried out. The near-field predictions were obtained by solving the linearized Euler equations with computational aeroacoustic techniques consisting of high order finite difference scheme, non-reflecting boundary conditions, oversetgrid techniques. For the prediction of far-field directivity pattern, the Kirchhoff integral method was applied. By comparing the directivities of noise radiating from the scarf and the scoop aero-intakes with that from an axisymmetric aero-intake, it is shown that noise reduction at downward peak radiation angle can be achieved. The scattering of the radiating acoustic wave by background mean flow shifts the peak lobe radiation angle toward ground and increases the amplitude of the acoustic pressure compared with the cases without mean flow effect.

• Ocean Systems Engineering
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• 제13권2호
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• pp.147-172
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• 2023

This study investigates the influence of loading and inflow conditions on tidal turbine performance from a hydrodynamic and hydroacoustic point of view. A boundary element method is utilized for the former to investigate turbine performance at various loading conditions under zero/non-zero yaw inflow. The boundary element method is selected as it has been selected, tested, and validated to be computationally efficient and accurate for marine hydrodynamic problems. Once the hydrodynamic solutions are obtained, such as the time-dependent surface pressures and periodic motion of the turbine blade, they are taken as the known noise sources for the subsequence hydroacoustic analysis based on the Ffowcs Williams-Hawkings formulation given in a form proposed by Farassat. This formulation is coupled with the boundary element method to fully consider the three-dimensional shape of the turbine and the speed of sound in the acoustic analysis. For validations, a model turbine is taken from a reference paper, and the comparison between numerical predictions and experimental data reveals satisfactory agreement in hydrodynamic performance. Importantly, this study shows that the noise patterns and sound pressure levels at both the near- and far-field are affected by different loading conditions and sensitive to the inclination imposed in the incoming flow.

• 한국소음진동공학회논문집
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• 제13권2호
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• pp.83-91
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• 2003

Pantograph design Process must be considered in terms of stability of aerodynamics and reduction of aeroacoustics. Furthermore pantograph needs to be insensible to severe circumstance condition like typhoon, tunnel, a change of season. In this paper, robust design of panhead sections is conducted based on the Taguchi's design of experiment method. In the aeroacoustic noise analysis, an acoustic analogy using the Ffowcs Williams and Hawkings(FW-H) equation is used to calculate the flow induced sound pressure level in aeroacoustics. From the near-field CFD analysis data, the far-field noise is predicted at the positions of 25 m away from Pantograph. Based on aerodynamic(CFD) and aeroacoustic(FW-H) analysis data, the optimal sizing and Positioning of panhead elements are determined using robust design optimization method. Design parameters such as thickness, length and radius are controllable factors, while outdoor air temperature and atmospheric pressure are considered as uncontrollable factors in the context of Taguchi's approach. A number of CFD simulation and aeroacoustic analysis are performed based on orthogonal arrays. In this paper, two-step optimization method is used as a parameter design procedure. It is executed using signal to noise(S/N) ratio and analysis of means(ANOM) method. So Thus, an optimal level of design parameters Is extracted to minimize the disconnection ration between contact strips and catenary system, and reduce the far-field aeroacoustic noise.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 추계학술대회논문집 II
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• pp.1235-1241
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• 2001

Pantograph design process must be considered in terms of stability of aerodynamics and reduction of aeroacoustics. Furthermore Pantograph needs to be insensible to severe circumstance condition like typhoon, tunnel, a change of season. In this paper, robust design of panhead sections is conducted based on the Taguchi's design of experiment method. In the aeroacoustic noise analysis, an acoustic analogy using the Ffowcs Williams and Hawkings (FW-H) equation is used to calculate the flow induced sound pressure level. From the near-field CFD analysis data, the far-field noise is predicted at the positions of 25m away from panhead contact strips. Based on aerodynamic (CFD) and aeroacoustic (FW-H) analysis data, the optimal sizing and positioning ofpanhead elements are determined using robust design optimization method. Design parameters such as thickness, length and radius are controllable factors, while outdoor air temperature and atmospheric pressure are considered as uncontrollable factors in the context of Taguchi's approach. A number of CFD simulation and aeroacoustic analysis are performed based on orthogonal arrays. Using a parameter design procedure associated with signal-to-noise (SIN) ratio and sensitivity analysis, an optimal level of design parameters are extracted to minimize the disconnection ratio between contact strips and catenary system, and reduce the far-field aeroacoustic noise.

• 수산해양기술연구
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• 제22권4호
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• pp.75-82
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• 1986

음향집어에 관한 기초자료를 제공하기 위하여 정치망내의 수중환경소음과 방성음의 분포 및 집어효과를 실험, 분석하였고, 그 결과를 요약하면 다음과 같다. 1. 수중환경 소음 및 방성음의 중심주파수대는 각각 150Hz~400Hz, 400Hz~1000Hz이고, 음압준위는 원통, 헛통, 장등, 비탈그물의 순으로 , 비탈그물, 원통, 헛통, 장등의 순으로 각각 높았다. 양망작업중의 수중소음은 양망개시후 시간의 경과에 따라 음압준위가 높아지나 양망의 마무리 단계에서는 오히려 낮아졌다. 2. 본 실험에서 제작한 방성장치로서 정치망어포부내에 방성한 결과, 초기에는 어군이 방성기주변으로 모여드는 반응을 나타내었으나, 약 30분이 경과하면서 이러한 반응은 약화되었다. 그리고 방성시간과 휴지시간의 간격보다는 방성음압에 군락이 더 민감하였다. 3. 일본에서 제작된 음향집어기(Dainy 0-8)로 해상에서 방성시험을 하여 본 결과, 대체로 방성개시후 약 20분에 어군이 모여들고 방성을 멈추면 곧 흩어졌다. 유집된 어군은 선박교통소음의 환경을 많이 받는 것으로 나타났다. 정치망입구 근처의 장등에 음향집어기를 설치하여 방성하였을 경우와 방성하지 않았을 경우에 대한 어획량이 방성하지 않았을 때에 비하여 약 3~5배 많은 것으로 나타났다.

• 한국결정성장학회지
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• 제33권3호
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• pp.116-123
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• 2023

압전 HIFU 트랜스듀서는 바이오 의료분야에 적용되고 있는 새로운 기술로 발생한 초음파 에너지를 열로 변환하여 사용하는 디바이스이다. 최근 HIFU 디바이스는 7 MHz 이상의 고 작동 주파수를 갖는 디바이스를 개발하는 추세이다. 본 논문에서는 유한요소법을 이용해 10MHz 작동주파수를 갖는 HIFU 트랜스듀서에 의해 발생된 tissue에서의 음압 및 온도분포를 계산하고, 압력의 focusing 특성 등을 분석하였다. HIFU의 형상변수로는 압전소재 두께, 렌즈 형상, 물 높이, 필름의 두께 등을 고려하였다. 그 결과, 디바이스의 발생 음압은 렌즈의 H_L/R_L 비가 증가함에 따라 증가하다 일정한 값에 도달하는 경향을 보이고 있다. 그러나 디바이스의 focusing 면적은 렌즈의 H_L/R_L 비가 증가함에 급격하게 감소하는 특성을 보이고 있다. 최적 형상을 갖는 HIFU 디바이스의 경우, 최대 음압 및 온도는 각각 19 MPa 및 65도 정도로 분석되었다. 또한 축방향 및 이와 수직한 방향에서 -3 d B 초점 거리는 각각 2.3 mm 및 0.23 mm 정도인 것으로 나타났다

• International Journal of Automotive Technology
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• 제8권1호
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• pp.67-73
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• 2007

This study analyzes the interior noise that is generated during acceleration of a passenger car in terms of car body structure and panel contribution. According to the transfer method, interior noise is classified into structure-borne noise and air-borne noise. Structure-borne noise is generated when the engine's vibration energy, an excitation source, is transferred to the car body through the engine mount and the driving system and the panel of the car body vibrates. When structure-borne noise resonates in the acoustic cavity of the car interior, acute booming noise is generated. This study describes plans for improving the car body structure and the panel form through a cause analysis of frequency ranges where the sound pressure level of the rear seat relative to the front seat is high. To this end, an analysis of the correlation between body attachment stiffness and acoustic sensitivity as well as a panel sensitive component analysis were conducted through a structural sound field coupled analysis. Through this study, via research on improving the car body structure in terms of reducing rear seat noise, stable performance improvement and light weight design before the proto-car stage can be realized. Reduction of the development period and test car stage is also anticipated.

• 한국소음진동공학회논문집
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• 제20권11호
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• pp.1001-1008
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• 2010

The architectural, facility makes the housing environment more pleasant, while too much noise coming from machinery room is detrimental to the workers physically and mentally. Therefore, more sound insulation and sound proof policies are increasingly required. However, as the annoyance caused by facility noise is influenced by various human listening characteristics as well as physical characteristics such as sound pressure level, it requires subjective evaluation characteristics through acoustic-psychological approach. For this purpose, the facility noise in the machinery room was actually measured and analyzed in the field to understand physical characteristics, and the correlation between physical evaluation value and psychological response value through listening test. Further, this study aims at presenting the data to set the standards of 'Just noticeable difference' of the facility noise together with reasonable evaluation with psychological reaction, through the grading of facility noise using trend formula. In the result, 13 stages of physical properties were forecasted for each evaluation method, together with 'Just noticeable difference' using the grading of architectural facility noise.