• The Journal of the Acoustical Society of Korea
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• 제20권4E호
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• pp.17-23
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• 2001

To develop the code of predicting flow-field and aeroacoustic noise by an electrical cable, a combined CFD-Acoustic analogy approach is selected. The two dimensional, unsteady and incompressible Reynolds-averaged Navier-Stokes solver with κ-ω and κ-ω SST turbulence modeling is used to calculate the near flow-field around an electric cable. Near-field results are then coupled with two-dimensional Curle's integral formulation based upon Lighthill's acoustic analogy with the assumption of acoustic compactness. To validate this code, numerical results are compared with experimental data for a circular cylinder. The simulation shows an overprediction on acoustic amplitudes, but overally speaking, the spectrum pattern of sound pressure agrees well with experiment within an acceptable amount of error. In addition, a few cross-sections of the cable were selected and tested with each other in terms of drag and radiated noise

• 대한기계학회논문집A
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• 제38권3호
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• pp.269-274
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• 2014

본 논문에서는 사보니우스형 풍력터빈의 저소음 설계에 관한 연구를 수행하였다. 선행연구를 통해 BPF 보다 높은 주파수를 기본주파수로 가지며 발생하는 하모닉 성분의 순음소음이 사보니우스형 풍력터빈의 주요한 소음임을 밝혔고, 이러한 하모닉 성분의 소음은 와류에 의한 것임을 확인하였다. 본 연구에서는 이러한 선행연구결과를 바탕으로, 사보니우스형 풍력터빈의 저소음 설계를 위해 이탈되는 와류에 위상차를 유도할 수 있는 터빈 날개 끝단을 도입하였다. CFD 기법 및 음향상사법을 적용한 복합 전산공력음향학 기법을 적용하여 제안한 저소음 사보니우스형 풍력터빈의 방사 소음을 수치적으로 예측하였고, 기존의 형상과 비교를 통해 소음 저감 효과를 확인하였다.

• 한국해양공학회지
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• 제12권2호통권28호
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• pp.22-32
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• 1998

Many of steel structures having little internal damping consist of stiffened plates. In case that viscoelastic materials are adhered to the stiffened plates for the reduction of structure-borne noise, their effects are varied by the adhered position and dynamic characteristics of the structures as well as their material properties and adhered amount. In this paper, sound reduction effects of viscoelastic materials partially adhered to the different positions of a stiffened steel plate have been investigated by the measurement of vibratory velocity and sound intensity. The results show that optimal adherent positions of viscoelastic materials to reduce sound radiation power are the loop areas of modes.

• 전력전자학회논문지
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• 제9권2호
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• pp.178-186
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• 2004

본 연구에서는 3상 RCD(Random Pulse Centered Displacement) PWM기법에 비하여 구현이 용이하고 스위칭 주파수의 정수배 스펙트럼의 광대역화와 선형화의 효과가 우수한, 2상 RCD-PWM을 제안하였으며, 그 파워 스펙트럼을 비교하고 있다 종전의 3상 RCD-PWM과 제안된 2상 RCD-PWM을 구현하기 위하여, 16비트 고성능 마이크로 컨트롤러 SAB-Cl67이 사용되었다 SAB-C167에 의하여 각 변조 구간에서의 듀티비를 구한 후, 선형 랜덤 발생기를 이용하여 균일한 확률 분포로 각 상의 펄스의 위치를 재배치하였다. 제안된 2상 RCD-PWM에 의한 모터전압과 전류 그리고 직류링크 전류의 파워 스펙트럼 및 모터의 가청 스위칭 소음 효과를 종전의 3상 RCD-PWM과 비교 검토하였다

• 오토저널
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• 제8권4호
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• pp.43-55
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• 1986

소음저감에 대한 연구에서 소음언을 규명하기 위해서 소음의 발생 메카니즘을 안다는 것은 중요 하다. 구조물의 진동과 이로 인해서 발생되는 방사음과의 관계는 상당히 복잡하기 때문에 본 연 구에서는 음향인텐시티의 측정을 위하여 간단한 방사 모델을 대해 연구하였다. 소음원 규명의 첫 단계로서 본 연구에서는 음압측정에 의한 소음평가에 대해 알아 보았다. 두 번째 단계로서 음향 인텐시티법을 이용하여 음향 방사 모우드 패턴을 결정하였으며 음향인텐시티법이 소음원 검출에 유효함을 입증하였다. 또한 본 연구에서는 방진재 부착에 따른 음의 방사특성을 예측하고 방 진재 부착위치를 결정할 수 있었다.

• 한국소음진동공학회논문집
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• 제26권4호
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• pp.428-435
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• 2016

In this paper, high-performance and low-noise centrifugal fan used to circulate cold air inside a household refrigerator is developed by reducing the vortex flow observed near the tip of fan hub. First, the performance of the existing centrifugal fan is investigated through the experiment using a fan tester and the characteristics of detailed flow field obtained from the CFD simulation are closely examined. The strong vortex flow is observed in the vicinity of the tip of fan hub. Based on this result, new design is devised to reduce this vortex flow. As a result, it is numerically and experimentaly found that the volume flow rate of the new fan increases and the radiated noise decreases in comparison with the existing fan at the same rotation speed.

• 설비공학논문집
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• 제3권2호
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• pp.103-113
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• 1991

This paper presents a method for estimating the noise source contribution of a pulse combustion burner in a multiple input system where the input sources may be coherent each other. By coherence function method, it is found that the biggest part of the noise source in the pulse combustion burner is generated by the part of the combustion chamber. This analysis is modeled as three input / single output system because the noise generating mechanism of the pulse combustion burner is very complicated. The coherence function method is proved to be useful tool for the identification of noise source. The overall levels of the radiated source pressure by coherence function method are compared with those measured and calculated by the frequency response function approach. The experimental results have shown a good agreement with the results calculated by the coherence function method when the input sources are coherent strongly each other. The estimation of shield effect by FRF method indicates that significant reduction can be achieved in sound radiation if only transmission path generated by the part of combustion chamber is acoustically shield.

• 한국소음진동공학회논문집
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• 제19권5호
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• pp.482-490
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• 2009

In this paper, the author proposes a new method for acoustic radiation optimum design to minimize noise from a vibrating panel-like structure using a collaborative population-based search method called the particle swarm optimization algorithm(PSOA). The PSOA is a parallel evolutionary computation technique initially developed by Kennedy and Eberhart. The acoustic radiation optimization method based on the PSOA consists of two processes. In the first process, the acoustic radiation analysis by an integrated p-version FEM/BEM, which was developed by using MATLAB, is performed to evaluate the exterior acoustic radiation field of the panel. The second process is to search the optimum design variables: 1) Shape of Bezier curves and 2) Shape and position of ribs, to minimize noise from the panel using the PSOA. The optimization method based on the PSOA is compared to that based on the steady state genetic algorithm(SSGA) in order to verify the effectiveness and validity of the optimal solution by PSOA. Finally, it is shown that the optimal designs of the panel obtained by using the PSOA can achieve effective reductions in radiated sound power.

• 한국군사과학기술학회지
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• 제7권1호
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• pp.24-33
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• 2004

Recently, ship acoustics takes more important role in acoustic stealth and classification of underwater targets. In this paper, a theoretical concept is proposed for M＆S-based test and evaluation of ship acoustics. The concept is based on two different approaches: on Top-Down method which emphasizes the survivability of the ship and on Bottom-Up method which considers acoustic characteristics of the ship-equipments. In order to improve the effectiveness of M＆S-based T＆E for ship acoustics, it is recommended in this paper to compromise the two approaches as adequate.

• 융복합기술연구소 논문집
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• 제9권1호
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• pp.21-24
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• 2019

This research presents an development of impact damper for reduction of vehicle vibration from road excitation. The structural vibrations are transferred through the vehicle body. The impact damper for reducing structural vibration from road excitation were designed and derived by using simplified numerical model. To analyze the characteristics of the impact damper, the vibration of simplified beam attached to impact damper was simulated. The damping ratios for different mass ratios of the impact dampers were calculated. The numerical results can be utilized to reduce the radiated noise from the electric vehicle.