• 소음진동
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• 제7권5호
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• pp.747-756
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• 1997

Wigner-Ville distribution which is a time-frequency analysis has a fatal drawback, when the signal has multiple components. This is the cross-talk and often causes a neagative value in the distribution. Wingner-Ville distriution is an expression of power, therefore the cross-talk must be avoided. Smoothing the Wigner-Ville distribution by convoluting it with a window, is most commonly used to reduce the cross-talk. There can be infinite number of distributions depending on the windows. But, the smoothing reduces resolution in time-frequency plane; this motives to design a more effective window in reducing cross-talk while remaining resolution. The domain in which the cross-talk and legitimate components can be easily distinguished, is the ambiguity function. In the ambiguity function domain, the legitimate components appear as linear lines passing through the orgine. But, the cross-talk is widely distributes in the ambiguity function plane. Based on the relative distributions of cross-talk and legitimate components, rotating window can be designed to minimize cross-talk. Applying the rotating window to the ambiguity function corresponds to smoothing the Wigner-Ville distribution. Therefore, the effects of rotating window is estimated in terms of the bias error due to smooting the Wigner-Ville distribution. By applying the rotating window, not only the Wigner-Ville distribution but also its properties are changed. The properties of the new distribution are checked, in order to complete analyzing the rotating window.

• 소음진동
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• 제7권2호
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• pp.319-329
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• 1997

Wigner-Ville distribution has been recognized as a useful tool and applied to various types of mechanical noise and vibration signals, but its limitation which mainly comes from the cross-talk has not been well addressed. The cross-talk takes place for a signal with multiple components, simply because the Wigner-Ville distribution is a bilinear transform. The cross-talk often causes a negative value in the distribution. This cannot be accepted for the Wigner- Ville distribution, because it is an expression of power. Smoothing the Wigner-Ville distribution by convoluting it wih a window, is most commonly used to reduce the cross-talk. There can be infinite number of distributions depending on the windows. In this paper, we attempted to develop a distribution which is the best or the optimal in reducing the cross-talk. This could be possible by employing the ambiguity function. For a general signal, however it is difficult to express the ambiguity function as a mathematically closed form. This requires an appropriate modeling to make such expression possible. We approximated the Wigner-Ville distribution as a sum of linear segments. In the ambiguity function domain, the legitimate components are reflected as linear lines passing through the origin. Every lines has its own length and slope. But, the cross-talk is widely distributed in the ambiguity function plane. Based on this realization, we proposed a two-dimensional window which is in fact 'rotating window', that can eliminate cross-talk component. The rotating window is examined numerically and is found to have a better performance in reducing the cross-talk than conventional windows, the Gaussian window.

• 한국소음진동공학회논문집
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• 제17권6호
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• pp.477-483
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• 2007

Major noise source in high speed rotating optical disk drives (CD and DVD-ROM) arises due to the high-speed airflow produced from the upper and lower surfaces on the rotating disk. The present paper deals with the experimental approach how to identify the noise source based on the fundamental principles of aeroacoustics and to propose a reduction method of the noise source. The CD-ROM device is composed of disk, window tray, motors at the bottom place and electronic circuit plate also located below the window plate. The window is cut in the tray to read the disk information using the optical device located below the tray and moving linearly from the center of the disk through the end of the disk. All components are possible noise generators. Experimental studies were carried out in the anechoic room with various design modifications, such as tray geometry, window size and hole location on tray, to identify the major aerodynamic noise source and significant reductions of the aerodynamic noise were obtained.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1998년도 춘계학술대회논문집; 용평리조트 타워콘도, 21-22 May 1998
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• pp.206-210
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• 1998

A study on dynamic characteristics of rotating disks in magneto optical disk drives is presented. Natural frequencies of rotating disks are investigated experimentally and numerically. The frequency response and critical speeds of the ASMO disk are discussed. The characteristics of airflow around the disk and their effects on disk vibrations are also investigated. It is found that the numerical calculation of the natural frequencies of rotating disks agrees well with the experimental results. The airflow around the disk in the cartridge affects the characteristics of the disk vibrations to reduce the modal frequencies of the disk. The experiment shows that negative vertical offsets of the disk in the cartridge possibly increase the vibration amplitudes. As being influenced by the geometry of the cartridge, the rotation of the disk causes an asymmetric airflow in the presence of window.

• 한국항공우주학회지
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• 제37권3호
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• pp.240-247
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• 2009

전자광학추적장치의 공력특성연구를 위한 풍동시험을 수행하였다. 특히 실제 EOTS 작동중 관측부의 회전을 위한 작동기의 충분한 파워 측정을 위한 공력토크 특성을 조사하였다. EOTS의 관측창의 영향을 조사하기 위해 반구와 실린더로 이루어진 단순 모형 실험결과와의 비교를 수행하였다. 단순모형과 EOTS모형의 표면 압력을 비교한 결과를 통해 관측창의 위치에 따라 급격한 압력계수의 변화와 회전 관측부의 토크 특성에 많은 영향을 미치는 것을 발견하였다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 추계학술대회논문집
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• pp.771-776
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• 2000

Major noise source in high speed rotating CD-Rom drives arises due to the high-speed airflow produced from the upper and lower surfaces on the rotating disk. The present paper deals with the experimental approach how to identify the noise source based on the fundamental principles of aeroacoustics and to propose a reduction method of the noise source. Experimental studies were carried out in the anechoic wind tunnel with various design modifications, such as tray geometry and window size, to identify and reduce the major aerodynamic noise source and significant reductions of the noise source were obtained.

• 한국공간구조학회지
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• 제14권3호
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• pp.11-16
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• 2014

• 에너지공학
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• 제24권4호
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• pp.63-70
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• 2015

창문에서의 틈은 열 손실 뿐만 아니라 차음 성능에도 중대한 결함으로 작용되며, 특히 인체에 유해한 미세먼지 유입 경로로도 작용된다. 이러한 틈을 제거하기위해 많은 시도들이 이루어지고 있으나, 창문의 고유 기능인 이동특성으로 인해 해결하기 어려운 난제로 인식되어왔다. 본 연구는 이를 해결하기위해 수평 회전 휠과 곡선 레일을 적용한 새로운 유형의 미서기 창문을 제작하고, KS 시험 기준에 따라 사용성, 내구성, 기밀성능, 등의 성능 시험을 하였다. 시험 결과, 개폐력은 2000 N 중량의 창문에서 30 N, 개폐 반복성 시험에서는 100,000 cycles, 기밀성 시험에서는 10 Pa에서 $0.00m^3/(m^2h)$의 성능을 보여주었다. 상기 시험 결과, 새로운 구동 방식을 지닌 본 연구에서의 창문은 기밀성과 경제적 측면에서 새로운 접근 방식을 제시하고 있다.

• 한국의학물리학회지:의학물리
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• 제23권4호
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• pp.229-233
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• 2012

광자선 출력측정시 업무 효율을 높이기 위한 소형 물팬톰(듀얼윈도우 팬톰)을 개발하였다. 이 팬톰은 고에너지 광자선의 출력측정뿐만아니라 선질지표의 결정에 적합하다. 이 팬톰은 두개의 창을 가지고 있으며 독립된 두 축에 의해 회전할 수 있도록 제작되어있다. 이 때 두 축은 전리함 이동 없이 조직팬톰선량비와 깊이선량율비를 결정하기 위한 것이다. 코발트조사기와 선형가속기의 고에너지 광자선을 이용하여 팬톰을 평가하였으며, 기준값과 비교할 때 Co-60의 경우 0.2% 그리고 가속기 x-선에 대해 1.4% 이내로 일치하였다. 이 팬톰은 발생 가능한 인적오차를 방지할 수 있기 때문에 일상의 출력측정에 매우 실용적이라고 본다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 하계학술대회 논문집 D
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• pp.2856-2858
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• 2000

This paper proposes a scan code method for obstacle avoidance of mobile robot. Obstacles detected in a circular window are converted to scan codes and then to the steering angle. The safe rotating radius is obtained by the scan code to avoid the collision between robot and obstacle and. the minimum distance for rotation is calculated. Effectiveness of the method is illustrated through simulations, and the results show that the proposed method can be efficiently implemented to an unknown environment.