• 대한조선학회논문집
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• 제35권4호
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• pp.76-86
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• 1998

본 연구에서는 보강재와 구조부재의 내부손실이 진동에너지 흐름에 미치는 영향을 파악하기 위하여 assumed mode method와 모드해석기법을 이용하여 점 가진된 평판과 보강판에 대한 진동인텐시티 해석을 수행하였다. 이때, 중첩모드수에 따른 진동인텐시티 해석 결과의 수렴성과 기진원으로부터 입력되는 파워를 진동인텐시티로 추정할 경우의 정확도에 대해서도 검토하였다. 일련의 수치해석 결과로부터 중첩모드수가 충분할 경우 진동인텐시티를 이용하여 추정한 기진원의 입력파워는 5%이내의 오차를 나타내고, 면외 기진력을 받는 판 구조물의 진동에너지는 전단력 성분에 의해서 지배적으로 전달됨을 확인하였다. 아울러, 구조부재의 내부손실 효과와 보강재의 진동에너지 흐름 차단 효과는 저차 공진주파수에서는 작고, 고차 공진주파수 및 비공진 주파수 영역에서 큼을 확인하였다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.240-244
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• 2017

가스터빈 엔진의 구성품 개발단계에서 블레이드의 Aeromechanics 시험은 블레이드 진동설계와 구조 안정성 검증 프로세스 사이에서 중요한 연결 고리를 제공한다. 이 전제에 근거하여 본 연구에서는 NSMS(Non-Intrusive Stress Measuring Systems)를 축류 압축기 구성품 시험리그에 적용하여 Tip Timing 센서가 장착된 단에서 모든 블레이드의 정적/동적 변위를 시험적으로 측정하였다. 진동 특성 분석을 통해 블레이드 고주기 손상을 유발할 수 있는 피로임계위치(Fatigue Critical Location)에서의 진동 응력을 평가하였으며, 공력가진에 의한 비동기 진동응답 및 개별 블레이드 Mistuning 패턴을 제시하였다.

• 조명전기설비학회논문지
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• 제22권12호
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• pp.101-109
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• 2008

유도전동기는 회전에 필요한 자계를 유지하기 위해 무효전력을 필요로 한다. 만일 전원측을 대신하여 부하측에서 무효전력이 제공될 경우 역률은 향상될 것이다. 유도전동기의 역률은 대개 낮으므로 커패시터로 보상이 필요하다. 내선규정에서 유도전동기의 역률 보상 커패시터의 용량은 출력에 따라 추천된 값의 설치를 권고하고 있다. 그러나 유도전동기는 같은 출력에서도 회전수에 따라 특성이 달라지므로 역률이 일정하지 않아 용량에 따라 일정한 커패시터의 적용은 부적합하다. 그래서 본 논문에서는 같은 출력조건에서 속도에 따라 기존에 제시된 값과 비교한 결과 역률 보상 커패시터의 용량이 약간 높게 설정되어야 함을 확인하였다.

• 조명전기설비학회논문지
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• 제29권11호
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• pp.59-65
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• 2015

By harnessing the thermal hysteresis behavior of vanadium dioxide($VO_2$), we demonstrated multi-resistance states in a two-terminal electronic device based on a $VO_2$ thin film by using a 966nm infrared laser diode as an excitation light source for resistance modulation. Before stimulating the device using 966nm laser pulses, the thermal hysteresis behavior of the device resistance was measured by using a temperature chamber. After that, the $VO_2$ device was thermally biased at ${\sim}71.6^{\circ}C$ so that its temperature fell into the thermal hysteresis region of the device resistance. Six multi-states of the device resistance could be obtained in the fabricated $VO_2$ device by five successive laser pulses with equal 10ms duration and increasing power. Each resistance states were maintained while the temperature bias was applied. And, the resistance fluctuation level was within 2.2% of the stabilized resistance and decreased down to less than 0.9% of the stabilized resistance 5s after the illumination.

• 한국산학기술학회논문지
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• 제7권6호
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• pp.1175-1179
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• 2006

유성음원과 무성음원을 사용하는 음성부호화 방식에 있어서, 프레임 안에 모음과 무성자음이 있는 경우에 음성 파형에 일그러짐이 나타난다. 본 논문에서는 LMS를 적용한 새로운 TSIUVC 근사합성법을 제시하였다. 실험결과, LMS를 적용하여 양호한 TSRIVC 근사합성 파형을 얻을 수 있었으며, 오차신호가 일그러짐이 적은 근사합성 파형에 중요한 역할을 한다는 것을 알 수 있었다. 이 방법은 음성합성, 음성분석, 새로운 Voiced/Silence/TSIUVC의 음성부호화 방식에 활용할 수 있을 것으로 기대된다.

• 한국소음진동공학회논문집
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• 제22권6호
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• pp.550-555
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• 2012

Among the various elements affecting a customer's evaluation of automobile quality, buzz, squeak and rattle(BSR) have been considered to be major factors. In most vehicle manufacturers, the BSR problems are solved by find-fix method with the vehicle road test, mainly due to various excitation sources, complex generation mechanism and subjective response. To systematically tackle the BSR problems in early stage of the vehicle development cycle, these difficulties should be resolved. The aim of the present paper is to characterize the sound quality property of BSR noise that can be used to assess the subjective responses to BSR. The four sound metrics from Zwicker's sound quality parameter are computed for the signals recorded for eight BSR noise source regions localized by using the acoustic-field visualized results. Then, the jury test of BSR noise are performed. On the basis of the computed sound metrics and jury test result is evaluated to represent the harshness of BSR noise. It is expected that the developed BSR measuring system and sound quality properties can be used to reduce the automotive interior BSR noise in terms of subjective levels as well as objective levels.

• 비파괴검사학회지
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• 제34권6호
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• pp.419-427
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• 2014

Nonlinear features of ultrasonic waves are more sensitive to the presence of a fatigue crack than their linear counterparts are. For this reason, the use of nonlinear ultrasonic techniques to detect a fatigue crack at its early stage has been widely investigated. Of the different proposed techniques, laser nonlinear wave modulation spectroscopy (LNWMS) is unique because a pulse laser is used to exert a single broadband input and a noncontact measurement can be performed. Broadband excitation causes a nonlinear source to exhibit modulation at multiple spectral peaks owing to interactions among various input frequency components. A feature called maximum sideband peak count difference (MSPCD), which is extracted from the spectral plot, measures the degree of crack-induced material nonlinearity. First, the ratios of spectral peaks whose amplitudes are above a moving threshold to the total number of peaks are computed for spectral signals obtained from the pristine and the current state of a target structure. Then, the difference of these ratios are computed as a function of the moving threshold. Finally, the MSPCD is defined as the maximum difference between these ratios. The basic premise is that the MSPCD will increase as the nonlinearity of the material increases. This technique has been used successfully for localizing fatigue cracks in metallic plates.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.620-628
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• 2005

Spatial control of sound is essential to deliver better sound to the listener's position in space. As it can be experienced in many listening environments, the quality of sound can not be manifested over every position in a hall. This motivates us to control sound in a region we select. The primary focus of the developed method has to do with the brightness and contrast of acoustic image in space. In particular, the acoustic brightness control seeks a way to increase loudness of sound over a chosen area, and the contrast control aims to enhance loudness difference between two neighboring regions. This enables us to make two different kinds of zone - the zone of quiet and the zone of loud sound - at the same time. The other perspective of this study is on the direction of sound. It is shown that we can control the direction of perceived sound source by focusing acoustic energy in wavenumber domain. To begin with, the proposed approaches are formulated for pure-tone case. Then the control methods are extended to a more general case, where the excitation signal has broadband spectrum. In order to control the broadband signal in time domain, an inverse filter design problem is defined and solved in frequency domain. Numerical and experimental results obtained in various conditions certainly validate that the acoustic brightness, acoustic contrast, direction of wave front can be manipulated for some finite region in space and time.

• 한국소음진동공학회논문집
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• 제20권3호
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• pp.263-271
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• 2010

A reaction wheel is commonly used, as an important actuator, to control the attitude of a satellite. Operation of the reaction wheel plays a role of an excitation source to loading equipment inside the satellite. As requirements for environmental vibration to manifest the performance of precision equipment are getting more stringent, the research for analysis or reduction of unwanted action force in high frequency range when operating the reaction wheel is necessary. In this paper, the procedure to extract input forces and damping of a rotor system of reaction wheel is suggested. The analysis for measured action forces of reaction wheel is accomplished and important higher harmonics of action forces are determined. The input forces and damping of the rotor system are, then, extracted by curve-fitting and a particular solution for input force.

• 한국소음진동공학회논문집
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• 제18권1호
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• pp.26-34
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• 2008

This paper summarizes a design procedure of radiated noise from engine blocks of marine engines. This air-borne noise is one of the significant noise contributors including the aeroacoustic noise due to intake and exhaust and the re-radiation due to structure-borne noise. Excitation forces by engine operations are evaluated taking into account the power generation mechanism from the burning process to the subsequence motion of internal parts; piston, connecting rod, and crank shaft. The acoustic transfer vector method is incorporated to effectively simulate the radiated noise field under the various operation conditions. A contribution analysis for the various excitations to the radiated noise is conducted. It is found that the firing pressure is the main source of the radiated noise, and so the structure of the cylinder can be modified to significantly reduce the radiated noise from the engine block.