• The Journal of the Acoustical Society of Korea
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• v.12 no.2
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• pp.28-36
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• 1993

임의의 형상을 갖는 진동체에 의한 방사 음장해석은 경계요소법에 의하여 이미 많은 해석이 시도되었다. 그러나, 진동체의 형상이 매우 복잡한 경우에는 겉표면의 요소수가 크게 증가할 뿐만 아니라 각 요소에서의 경계조건을 모두 알아내어야 하므로, 저주파에 국한된 해석일지라도 엄청난 시간과 노력이 필요하게 된다. 이러한 어려움을 극복하기 위하여 경계요소법을 사용하되, 복잡한 형상의 진동체를 둘러싸는 가상적인 표면을 매우 간단하게 설정한 후 그 표면상의 경계조건인 음압을 측정한다. 임의의 형상에 대한 파수 영역에서의 감쇠파의여파작업을 위하여 특이값 분리를 사용하였다. 특이값 분리에 의하여 음압분포를 측정위치에서 설정된 일반 좌표계에서의 고유모드로 분해한다. 각 고유모드의 원거리 음장의 기여도에 해당하는 각 특이벡터에 대한 특이값의 크기를 비교하여, 유한개의 고유모드만을 포함시킴으로써 원거리 음장을 예측한다. 몇 개의 예제를 통하여 해석적 방법의 기존의 경계요소법에 의한 결과를 본 연구 방법의 결과와 비교하여 잘 일치함을 확인하였다.

• Journal of Korea Multimedia Society
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• v.17 no.2
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• pp.143-151
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• 2014

In images degraded by bad weather, edges representing object boundaries become weak and faint. In this paper we present an image enhancement method, which increases image visibility by making edges as clear as possible. First, we choose edge candidate regions by finding local maxima and minima in an image intensity field, and then build a histogram using image intensities of pixels located at the two sides of candidate edges. Second, we decompose this histogram into multiple modes, which are determined by local minima in the histogram. Once modes are computed, we find modes connected by edges in the image intensity field and build link chains of connected modes. Finally we choose the longest link chain of modes and make the distances between every connected modes as large as possible. The darkest mode and the brightest mode should be within the image intensity range. This stretch makes edges clear and increases image visibility. Experiments show that the proposed method real-time enhances images degraded by bad weather as good as well known time-consuming methods.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.04a
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• pp.177-178
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• 2014

• Korean Journal of Optics and Photonics
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• v.17 no.4
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• pp.354-358
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• 2006

A silicon lens and an insulator of pyrex, components of a micro-electron column, should be assembled by aligning and stacking simultaneously. An optical alignment of a diffraction beam and a laser welding were employed for the assembly of a source lens and an Einzel lens with precision within $\pm$4% for the maximum aperture size. The experimental condition for optical alignment and laser welding are explained. Anodic bonding was used to assist in stacking lenses. A micro-electron column of smaller apertures assembled with precise alignment and fabrication was tested with a current image of a Cu grid of 9$\mu$m in linewidth, and showed a higher resolution in acceleration mode.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.15 no.4
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• pp.23-29
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• 2016

Rotary machine is major equipment in industry. The rotary machine is applied for a machine tool, ship, vehicle, power plant, and so on. But a spindle fault increase product's expense and decrease quality of a workpiece in machine tool. A turbine in power plant is directly connected to human safety. National crisis could be happened by stopping of rotary machine in nuclear plant. Therefore, it is very important to know rotary machine condition in industry field. This study mentioned fault diagnosis algorithm with statistical parameter and empirical mode decomposition. Vibration locations can be found by analyze kurtosis of data from triaxial axis. Support vector of data determine threshold using hyperplane with fault location. Empirical mode decomposition is used to find fault caused by intrinsic mode. This paper suggested algorithm to find direction and causes from generated fault.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.305-305
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• 2011

표면 플라즈몬 공진(SPR) 현상을 이용한 광섬유 센서는 SPR 센서의 우수한 표면 민감도, 비표지 검출능 등의 특징은 유지하면서 측정시스템이 단순해지고 저렴하게 제작이 가능하며 원거리 검출에 유리하다는 장점으로 많은 연구가 진행되고 있다. 최근 스택 제어가 용이하고 민감도 또한 우수하다는 이유로 측면 연마형 센서 구조를 적용한 연구가 많이 이루어지고 있다. 본 연구에서는 기존 Kretchman형태의 SPR 센서의 분해능 향상을 위해 사용된 광도파로 구조를 측면 연마형 광파이버에 적용시켰다. 금속 층 / 유전체 층 / 금속 층으로 구성되어 있는 광도파로 구조와 Au 단일 층을 사용한 기존 구조에 대한 이론 전사모사를 진행하고 실물 소자를 제작하여 특성을 평가하였다. WCSPR 센서에서는 두 개의 반사율 dips이 나타난다. 하나는 단파장영역에서 나타나는 폭이 작은 형태이며 또 다른 하나는 장파장영역에서 나타나는 폭이 넓은 형태이다. 단파장에서의 dip은 입사각에 크게 영향을 받지 않기 때문에 Wavelength interrogation mode을 이용하는 광섬유 SPR센서에 적용할 경우 분해능이 향상될 것 이다. WCSPR 센서는 도파로의 유전체층에서 진행되는 모드를 이용하면 Self-referencing을 할 수 있다, 또한 유전체 층의 두께를 변화 시켜 중심파장의 위치를 조절할 수 있는 특징을 갖고 있다. 결과적으로 광도파로 구조를 광파이버에 적용시켜 기존 Au 단일 층 구조의 SPR 센서에 비해 좀 더 정확하고 광범위한 감지를 할 수 있다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.59-60
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• 2017

Combustion instability of gas turbine is performed by adopting dynamic mode decomposition (DMD). The unstable frequencies are calculated and compared with FFT results. The damping coefficient derived from the DMD technique and FFT results were compared and analyzed. OH radical is measured by experimental work and fluctuation field is extracted and FTF was calculated at various points with DMD. The gains of FTF are changed depending on the extraction position of the heat release fluctuation field.

• Journal of Radiation Protection and Research
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• v.37 no.1
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• pp.16-24
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• 2012

In the present study, a gamma-ray detector and associated signal processing circuit was developed for a side-absorber of a dual-mode Compton camera. The gamma-ray detector was made by optically coupling a CsI(Tl) scintillation crystal to a silicon photodiode. The developed signal processing circuit consists of two parts, i.e., the slow part for energy measurement and the fast part for timing measurement. In the fast part, there are three components: (1) fast shaper, (2) leading-edge discriminator, and (3) TTL-to-NIM logic converter. AC coupling configuration between the detector and front-end electronics (FEE) was used. Because the noise properties of FEE can significantly affect the overall performance of the detection system, some design criteria were presented. The performance of the developed system was evaluated in terms of energy and timing resolutions. The evaluated energy resolution was 12.0% and 15.6% FWHM for 662 and 511 keV peaks, respectively. The evaluated timing resolution was 59.0 ns. In the conclusion, the methods to improve the performance were discussed because the developed gamma-ray detection system showed the performance that could be applicable but not satisfactory in Compton camera application.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.2
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• pp.183-192
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• 2009

SAR(Synthetic Aperture Radar) is an all-weather imaging radar and is widely used in military and civil application. Especially high-resolution SAR images are very important in military purpose because it can be used at target recognition application. LIG Nex1 developed a SAR system called NexSAR with bandwidth of 600 MHz and resolution of 30 cm to obtain technologies required for high-resolution SAR. To achieve 600 MHz bandwidth of waveform generator, two DDSs are used and its output signals are SSB modulated. And deramp technique is used to reduce the sampling rate of ADC at high resolution mode. NexSAR has stripmap and spotlight modes and its functionality and performances are evaluated through ground and flight tests.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.31 no.6
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• pp.309-314
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• 2018

The wind load and structural characteristics of a twin building are more complex than those of conventional high-rise buildings. The pressure load due to wind on a twin building was therefore measured via wind tunnel experiments to analyze such characteristics. The wind pressure pattern was then deduced from measured data using proper orthogonal decomposition. Channeling and vortex shedding were observed in the first and second modes, respectively. The along-wind loads on the two buildings featured a positive correlation and the cross-wind loads featured no correlation. Such a correlation affected the wind-induced displacement. The structural member connecting the two buildings had an insignificant effect on the positive correlation, but it notably reduced the wind-induced displacement with a negative correlation.