• 한국음향학회지
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• 제37권4호
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• pp.163-173
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• 2018

본 논문에서는 비행 중 비행체 표면에 작용하는 음향하중 예측을 수행하였다. 비행 중 음향하중은 비행체 표면의 압력 변동에 의해 발생한다. 기존의 비행 중 음향하중 예측방법은 반경험적 방법으로 이론과 실험 결과를 기반으로 도출한 경험식을 활용한다. 하지만 경험식의 입력 값으로 사용되는 비행체 주변 유동특성 및 경계층 파라미터를 매번 실험을 통해 얻는 것에는 한계가 있다. 따라서 본 논문에서는 전산유체해석(Computational Fluid Dynamics, CFD) 결과를 반경험적 방법과 혼합하는 하이브리드 방법을 이용하여 비행 중 비행체에 작용하는 음향하중을 예측하였다. Cone-cylinder-flare 형상 비행체에 대해 아음속, 천음속, 초음속, 최대동압도달(Maximum dynamic pressure, Max-q) 시점의 비행 환경에 대한 음향하중 예측을 수행하였다. 하이브리드 방법 적용 시 전산유체해석결과를 기반으로 한 경계층 끝단 영역 판단 방법에 대해 비교하였고 여러 연구자에 의해 제시된 경험식에 따른 음향하중 예측결과를 비교하였다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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• pp.1325-1328
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• 2007

When we visualize the sound field radiated from a spherical sound source, spherical acoustic holography is proper among acoustic holography methods. However, there are measurement errors due to sensor position mismatch, sensor mismatch, directivity of sensor, and background noise. These errors are amplified if one predicts the pressures close to the sources: backward prediction. The goal of this paper is to quantitatively examine the effects of the error due to sensor position mismatch on acoustic pressure estimation. This paper deals with the cases of which the measurement deviations are distributed irregularly on the hologram plane. In such cases, one can assume that the measurement is a sample of many measurement events, and the cause of the measurement error is white noise on the hologram plane. Then the bias and random error are derived mathematically. In the results, it is found that the random error is important in the backward prediction. The relationship between the random error amplification ratio and the measurement parameters is derived quantitatively in terms of their energies.

• 한국소음진동공학회논문집
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• 제12권9호
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• pp.694-701
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• 2002

In this paper, through the study on locations of structural transducers for active control of the radiated sound from the vibrating plate, the active structural acoustic control (ASAC) system is proposed. And, for the evaluation of the proposed location, the experiment of the active structural acoustic control is implemented using the multi-channel filtered-x LMS algorithm and an additional filter (Acoustic Prediction Filter) to estimate the radiated sound using the acceleration signals of the plate. The structural transducers are piezoceramic actuator (PZT) and accelerometer. PZT is used as an actuator to reduce the vibration and the radiated sound. To maximize the control performance, each PZT actuator is located at the position that has the largest control sensitivity of the plate bending moment in the direction of x and y coordinates and the optimal PZT location is validated experimentally. Also, to find the acoustic prediction filter accurately, two accelerometers are located at the positions that have the largest radiation efficiencies of the plate, and the proposed locations are validated by simulation using the Rayleigh integral. The multi-channel filtered-x LMS algorithm is introduced to control a complex 2-D structural vibration mode. Finding the locations of structural transducers for active structural acoustic control of the radiated sound, the active structural acoustic control (ASAC) system can be presented and validated by experiments using a real time control system.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 춘계학술대회논문집
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• pp.717-720
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• 2005

Acoustic loads generated by a rocket propulsion system cause severe random vibrations on payloads. In developing a new launch vehicle, a random vibration level must be specified before the detailed design of payloads or electronic equipments. This paper deals with prediction procedures of a random vibration level on payload section of KSLV-I. The prediction is based on statistical energy analysis. In order to verify the prediction methodology, test and analysis on a sub-scale payload section are performed. The predicted results subject to very high level of acoustic loads show a good agreement with the test results performed in the high intensity acoustic chamber. The predicted random vibration level on payload section of KSLV-I is also presented in this paper.

• 한국조명전기설비학회지:조명전기설비
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• 제8권2호
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• pp.77-84
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• 1994

이 논문에서는 저밀도 폴리에틸렌(이하 LDPE라 함)의 절연파괴 실험시 발생되는 전기적 트리진전시 발생되는 부분방전을 음향방출 측정법에 의해서 측정하였다. 부분방전 발생시 생기는 음향방출 펄스와 플스 진폭을 각 위상각별 시간별로 측정하였고, 왜도 즉 Skewness(이하 S라 함)개념을 도입하여 S값에 의한 LDPE 파괴예지가 가능함을 보였다. 또한 시료로서 인공보이드가 있는 시료와 보이드가 없는 시료를 사용하여 같은 전압 인가시 보이드가 있는 시료가 절연파괴로의 진전이 빠르게 진행됨을 알았다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.416-421
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• 2001

This paper presents the numerical prediction of sound generated by viscous flow past a circular cylinder. The two dimensional flow field is predicted using FEM based Reynolds-averaged Navier-Stokes solver, and the calculated unsteady fluid field values are utilized by an acoustic code that implements Ffowcs Willianms-Hawkings(FW-H) equation. The integration surface used in acoustic analysis is extended from the cylinder surface to permeable surfaces. The 2D based CFD calculations overpredict the acoustic amplitude, however, if adequate correlation length is used, the predicted acoustic amplitude agrees well with experiment. The predictions using extended integral surface in FW-H equation show results that contain the characteristics of quadrupole - volume integration - noise term, and do not vary seriously with the integral surface location.

• 한국소음진동공학회논문집
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• 제20권1호
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• pp.74-82
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• 2010

Power flow analysis(PFA) methods have shown many advantages in noise predictions and vibration analysis in medium-to-high frequency ranges. Applying the finite element technique to PFA has produced power flow finite element method(PFFEM) that can be effectively used for analysis of vibration of complicated structures. PFADS(power flow analysis design system) based on PFFEM as the vibration analysis program has been developed for vibration predictions and analysis of coupled structural systems. In this paper, to improve the function of vibro-acoustic coupled analysis in PFADS, the PFFEM has been extended for analysis of the interior noise problems in the vibro-acoustic fully coupled systems. The vibro-acoustic fully coupled PFFEM formulation based on energy coupled relations is extended to structural system model by using appropriate modifications to structural-structural, structural-acoustic and acoustic-acoustic joint matrices. It has been applied to prediction of the interior noise in two room model coupled with panels, and the PFFEM results are compared to those of statistical energy analysis(SEA).

• 소음진동
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• 제8권6호
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• pp.1023-1029
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• 1998

When one attempts to construct a hologram. one finds that there are many sources of measurement errors. These errors are even amplified if one predicts the pressures close to the sources. The pressure estimation errors depend on the following parameters: the measurement spacing on the hologram plane. the prediction spacing on the prediction plane. and the distance between the hologram and the prediction plane. This raper analyzes quantitatively the errors when these are distributed irregularly on the hologram plane The sensor mismatch and inaccurate measurement location. position mismatch. are mainly addressed. In these cases. one can assume that the measurement is a sample of many measurement events. The bias and random error are derived theoretically. Then the relationship between the random error amplification ratio and the parameters mentioned above is examined quantitatively in terms of energy.

• 한국기계가공학회지
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• 제11권2호
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• pp.34-39
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• 2012

In this study, the friction welding experiment was performed by using the design of experiment. And the signal data acquired by acoustic emission sensor were analyzed to predict the tensile strength of friction welding part at friction welding process for AZ31 magnesium alloy. A dimensionless coefficient($\phi_{AE}$), which consisted in the square of AE rms and variance, was defined as the characteristic of friction welding and the prediction equation was obtained by using linear regression. As the result of analysis, it was seen that the correlation between predicted and measured values became very close and on-line prediction of the ensile strength was possible in friction welding part.

• 한국유체기계학회 논문집
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• 제16권2호
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• pp.15-20
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• 2013

An aero-acoustic performance analysis method of regenerative blower is developed as one of the FANDAS codes. The aerodynamic performance of regenerative blower is predicted by using momentum exchange theory coupled with pressure loss and leakage flow models. Based on the performance prediction results, the noise level and spectrum of regenerative blower are predicted by discrete frequency and broadband noise models. The combination of the performance and the noise prediction methods gives aero-acoustic performance map and noise spectrum analysis results, which are well-agreed with the actual measurement results within a few percent relative error.