• 한국음향학회지
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• 제26권6호
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• pp.301-305
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• 2007

본 연구에서 관심을 갖는 수중환경에서의 천이소음도 가청주파수 대역임에 착안하여 이동통신 시스템의 표준 음성부호화기인 EVRC의 전처리단을 이용하여 배경잡음 구간을 판별하고 이를 바탕으로 수중 천이신호를 탐지하는 알고리즘을 제안하였다. EVRC 전처리 모듈에 프레임 단위의 입력신호가 들어가면 모듈로부터 잡음 구간을 결정하는 플래그, 각 채널의 에너지, 잡음이 제거된 신호, 입력신호의 에너지, 배경잡음의 에너지, 잡음이 제거된 신호의 에너지에 해당하는 파라미터 값을 얻게 된다. 잡음이 제거된 신호의 에너지를 배경잡음의 에너지로 정규화하고 이를 문턱값과 비교함으로써 천이신호를 검출할 수 있다. 또한 문턱 값은 잡음 구간에서 구한 이전 값을 이용해서 갱신된다. 실험결과를 통해 제안한 알고리즘이 백색 또는 유색잡음 하에서도 4% 미만의 오차를 보여주는 것을 검증한다.

• 한국음향학회지
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• 제31권8호
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• pp.532-541
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• 2012

수중 과도 신호는 주변 소음과는 구별된다. 과도 신호는 음향학적 특색에 따라 특징들이 다양하기 때문에 데이터베이스화가 요구된다. 이에 본 논문에서는 해양에서 국지적이고 일시적으로 존재하는 과도 신호를 추출하기위해 사운드 마스크 필터링 방법을 활용하였다. 표준 신호를 선택하여 원 음원과의 상호상관관계를 구하였다. 상호상관신호의 포락선에서 최대우도법에 의해 결정된 역치를 사용하여 과도 신호를 위한 사운드 마스크 필터를 구하였다. 사운드 마스크 필터를 활용하여, 수중 소음원에서 바다메기의 과도 신호를 추출하였다. 유사하게, 원 음원에 인위적으로 인공 신호를 추가한 신호에서 동일한 방식으로 바다메기와 인공 신호를 과도 신호로서 추출하였다. 또한 표준신호에 따라서 다르게 추출된 과도신호의 비교를 통해 표준신호 선택의 중요함을 제시하였다. 본 논문에서 제안된 사운드 마스크 필터링 방법은 해양 주변 소음원에서 과도 신호의 데이터베이스 구축에 활용될 수 있고, 특히, 임의의 신호에서 원하는 신호를 추출하는 데에 활용 가능성이 있다.

• 한국소음진동공학회논문집
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• 제17권8호
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• pp.726-735
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• 2007

Inside the factory buildings of aprecision industry (which produces semiconductors or TFT-LCD), thousands of vibration-sensitive precision equipments operate in the clean rooms. Various utility equipments that are installed around them for proper operation cause various sources of noise and of vibration to exist inside the clean rooms and thus deteriorate the noise and the vibration environment within. In this study, we check if the existing transient vibration phenomenon is caused by the vibrations that arise from operating the utility installed near these equipments; compare and evaluate the vibration criteria of precision equipments regarding the transient vibration phenomenon; and check the efficiency of these criteria.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.963-963
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• 2008

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 춘계학술대회논문집
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• pp.387-392
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• 2007

Turbomachinery such as turbines, pumps and compressors, which are installed in transportation systems such as warships, submarines and space vehicles, etc., often perform crucial missions and are exposed to potential dangerous impact environments such as base-transferred shock forces. To protect turbomachinery from excessive shock forces, it may be needed to accurately analyze transient responses of rotors, considering the dynamics of mount designs to be applied with. In this study a generalized FE transient response analysis model, introducing relative displacements, is firstly proposed to accurately predict transient responses of a flexible rotor-bearing system with mount systems to base-transferred shock forces. In the transient analyses the state-space Newmark method of a direct time integration scheme is utilized, which is based on the average velocity concept. Results show that for the identical mount systems considered, the proposed FE-based detailed flexible rotor model yields more reduced transient vibration responses to the same shocks than a conventional simple model or a Jeffcott rotor. Hence, in order to design a rotor-bearing system with a more compact light-weighted mount system, preparing against any potential excessive shock, the proposed FE transient response analysis model herein is recommended.

• 한국소음진동공학회논문집
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• 제17권12호
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• pp.1208-1216
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• 2007

Turbomachinery such as turbines, pumps and compressors, which are installed in transportation systems, including aircrafts, ships, and space vehicles, etc., often perform crucial missions and are exposed to potential dangerous impact environments such as base-transferred shock forces. To protect turbomachinery from excessive shock forces, it may be needed to accurately analyze transient responses of their rotors, considering the dynamics of mount designs to be applied. In this study a generalized FE transient response analysis model, introducing relative displacements, is proposed to accurately predict transient responses of a flexible rotor-bearing system with mount systems to base-transferred shock forces. In the transient analyses the state-space Newmark method of a direct time integration scheme is utilized, which is based on the average velocity concept. Results show that for the identical mount systems considered, the proposed FE-based detailed flexible rotor model yields more reduced transient vibration responses to the same shocks than a conventional simple model, obtained by treating a rotor as concentrated lumped mass, equivalent spring and a damper or Jeffcott rotor model. Hence, in order to design a rotor-bearing system with a more compact light-weighted mount system, preparing against any potential excessive shock, the proposed FE transient response analysis model herein is recommended.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문집
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• pp.44-50
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• 2002

Theoretical analysis on the transient torsional vibration was started from early 1960's for high power synchronous motor application. As for marine engineering, simulation and measuring techniques of transient torsional vibration have been steadily studied by manufacturer of flexible coupling and designer of four stroke marine diesel engine. In this paper, the simulation method of transient torsional vibration for four stroke marine diesel engine application using Newmark method is introduced.

• 한국음향학회지
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• 제22권8호
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• pp.670-679
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• 2003

본 논문에서는 수중 천이신호 탐지를 위하여 시간주파수 영역에서 신호분석이 가능한 웨이브렛을 적용하였다. 낮은 신호대 잡음비를 가지는 관측신호로부터 천이신호를 탐지하기 위하여 고차통계 기법과 웨이브렛을 사용하였으며, 웨이브렛을 이용하여 신호를 주파수 영역에서 분해한 다음 고차통계 기법을 이용하여 분해된 웨이브렛 계수들의 정규분포 특성을 측정하였다. 제안한 방법으로 천이신호를 탐지할 경우 낮은 신호대 잡음비를 가지는 관측 신호로부터 천이신호를 잘 탐지할 수 있었다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 춘계학술대회논문집
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• pp.669-674
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• 2004

In this study, the analytical method to evaluate the response of rotor-bearing system subjected to base excitation was presented. The equations of motion contain speed dependent gyroscopic terms, base rotation dependent parametric terms and several forcing function terms which depend on linear accelerations, rotational accelerations and a combination of linear and rotational combination. The study of rotor-bearing system excited by its base motion is not only able to predict the rotational performance, but provides the fundamental data for vibration isolation. In order to illustrate transient response, transient response analysis of a practical application sample were performed. The transient response was carried out for the given base excitation by using the state-space Newmark method that incorporates the average velocity concept.

• 한국해양공학회지
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• 제26권4호
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• pp.57-63
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• 2012

In this paper, a Bayesian classifier based on PCA (principle component analysis) is proposed to classify underwater transient signals using $16^{th}$ order LPC (linear predictive coding) coefficients as feature vector. The proposed classifier is composed of two steps. The mechanical signals were separated from biological signals in the first step, and then each type of the mechanical signal was recognized in the second step. Three biological transient signals and two mechanical signals were used to conduct experiments. The classification ratios for the feature vectors of biological signals and mechanical signals were 94.75% and 97.23%, respectively, when all 16 order LPC vector were used. In order to determine the effect of underwater noise on the classification performance, underwater ambient noise was added to the test signals and the classification ratio according to SNR (signal-to-noise ratio) was compared by changing dimension of feature vector using PCA. The classification ratios of the biological and mechanical signals under ocean ambient noise at 10dB SNR, were 0.51% and 100% respectively. However, the ratios were changed to 53.07% and 83.14% when the dimension of feature vector was converted to three by applying PCA. For correct, classification, it is required SNR over 10 dB for three dimension feature vector and over 30dB SNR for seven dimension feature vector under ocean ambient noise environment.