• 한국가시화정보학회지
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• 제11권1호
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• pp.41-47
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• 2013

Turbulence properties of a cylinder wake (d=10 mm) have been investigated with a new volume PTV algorithm. The measurement system consists of two-high-cameras(1 $k{\times}1$ k), a Nd-Yag laser and a host computer. A fitness function representing three-dimensional coherency has been adopted to sort out spurious vectors. A hybrid fitness function representing the relations between the fitness and the three-dimensional shortest distances constructed by the two collinears of the two cameras has been also adopted. The constructed algorithm has been employed for the measurements of the cylinder wakes. The Reynolds numbers tested in this paper are 360, 540, 720, 900, 1080 and 1260. More than 10,000 instantaneous 3D vectors have been obtained by the constructed system. The volumetric distributions of the turbulence intensities (for u', v', w') indicate that clearly different patterns for all Reynolds numbers and imply that a regular pattern (like a similarity rule) for the turbulent properties exists.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2006년도 춘계학술대회 논문집
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• pp.239-240
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• 2006

For longer than picosecond pulses, bulk damage inside defect-free dielectrics involves the heating and multiplication of spurious electrons by the incident laser beam and transfer of this energy to the lattice. The situation is quite different for femtosecond pulses which are shorter than the time scale for electron energy transfer to the lattice. Damage caused by these pulses is produced with smaller statistical uncertainty and is controllable on a microscopic scale. These properties can be exploited to produce laser devices such as arrays of damage dots for all optical memories with high data storage density or arrays of parallel grooves to form transmission gratings. In this work, we observed characteristic of the femtosecond laser machining in BK7 and fused silica.

• 한국유체기계학회 논문집
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• 제13권4호
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• pp.31-36
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• 2010

Free energy based lattice Boltzmann method (LBM) has been used to simulate the rising bubble flows with large density ratio. LBM with compact discretization is able to reduce the spurious current of the static bubble test and be satisfied with the Laplace law. The terminal rise velocity and shape of the bubbles are dependent on Eotvos number, Morton number and Reynolds number. For single bubble flows, simulations are executed for various Eotvos number, Morton number and Reynolds number, and the results are agreed well with the experiments. For multiple bubbles, the bubble flow characteristics are related by the vortex pattern of the leading bubble. The coalescence of the bubbles are simulated successfully and the subsequent results are presented. The present method is validated for static, dynamic bubble test cases and compared to the numerical, experimental results.

• 대한기계학회논문집A
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• 제20권12호
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• pp.3792-3803
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• 1996

Since the skew beam element has two curvatures which are a curvature and a torsion, spatial behavior of curved beam which cannot be included in one plane can be anlayzed by emploting the skew beam element. The $C^{0}$-continuous skew beam element shows the stiffness locking phenomenon when full integration is employed. The locking phenomenpn is characterized by two typical phenomena ; one is the much smaller displacement thant the exact one and theother is the undelation phenomenon is stress distribution. In this paper, we examine how unmatched coefficient in the constrained energy brings about the locking by Reduced Minimization theory. We perform the numerical ones. These comparisons show that uniformly full integration(UFI), which employs full integration for the constrained energy, entails the locking phenomenon. But the use of uniformly reduced integration(URI) of selectively reduced integration(SRI), which employs reduced integration for constrained energy, does not produce the significant errors of displacements of the undulation phenomenon in stress distribution since they do not entails the locking, Additionally, the error due to the approximated parameters for describing the geometry of skew beam is examined.d.

• IEIE Transactions on Smart Processing and Computing
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• 제4권3호
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• pp.189-193
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• 2015

This paper provides the design techniques of a successive approximation register (SAR) type 12b analog-to-digital converter (ADC) for distributed maximum power point tracking (DMPPT) control in a photovoltaic system. Both a top-plate sampling technique and a $V_{CM}$-based switching technique are applied to the 12b capacitor digital-to-analog converter (CDAC). With these techniques, we can implement a 12b SAR ADC with a 10b capacitor array digital-to-analog converter (DAC). To enhance the accuracy of the ADC, a single-to-differential converted DAC is exploited with the dual sampling technique during top-plate sampling. Simulation results show that the proposed ADC can achieve a signal-to-noise plus distortion ratio (SNDR) of 70.8dB, a spurious free dynamic range (SFDR) of 83.3dB and an effective number of bits (ENOB) of 11.5b with bipolar CMOS LDMOD (BCDMOS) $0.35{\mu}m$ technology. Total power consumption is 115uW under a supply voltage of 3.3V at a sampling frequency of 1.25MHz. And the figure of merit (FoM) is 32.68fJ/conversion-step.

• 대한토목학회논문집
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• 제12권1호
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• pp.43-50
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• 1992

본(本) 연구의 목적(目的)은 평면응력/변형과 축대칭 및 쉘문제를 포함하는 다양한 응용문제에서 계층적(階層的) 성질을 갖는 적분형 르장드르 형상함수에 의한 P-version 모델의 통용성(通用性)을 확인하는 것이다. 현대 유한요소 해석에서 정확도를 확보하지 못하는 가장 큰 이유는 비(非)압축성 재료와 망목(網目)설계시 요소의 형상비(形狀比), 사다리꼴 요소에서 변(邊)의 감소비(減少比)와 평행사변형 요소의 왜곡도(歪曲度) 등을 갖는 불규칙 형상에서 나타나는 가상메카니즘과 Locking 현상이다. 조건수(條件數)와 에너지 노름이 계산오차, 수렴성 및 알고리즘의 효율성을 검증하는데 사용되었으며 해석결과는 NASTRAN과 SAP90 및 Cheung이 제안한 Hybrid 요소와 비교되었다. NASTRAN을 제외한 SAP90 및 P-version 프로그램은 16 Bit 소형컴퓨터에 의해 실행되었다.

• 대한전기학회논문지:시스템및제어부문D
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• 제49권6호
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• pp.330-333
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• 2000

In this paper, a new pitch estimation method is proposed using the Robinson cochlear model. This estimation method is useful in noisy environments and especially very efficient under cochannel in which two speaker voices exist at the same time. For the one speaker speech, the pitch can be extracted from just the neurogram of the Robinson cochlear model. In this case, as the estimation is performed in time domain, the exact pitch period can be detected though the pitch period is various. But in noisy and cochannel cases, the neurogram has many spurious peaks, so we use the autocorrelators in the neurogram to manifest the period. It the autocorrelators are used for the all delays, the large amount of calculations is necessary. Due to this defect, we propose that the autocorrelators are used for the part of the delays on which energy is concentrated. First of all, the proposed algorithm is applied to the one speaker speech, and later to the cochannel speech. And then the results are compared with the autocorrelation pitch detection method.

• JSTS:Journal of Semiconductor Technology and Science
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• 제3권4호
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• pp.211-216
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• 2003

This work describes a 3 V 12b 100 MS/s CMOS digital-to-analog converter (DAC) for high-speed communication system applications. The proposed DAC is composed of a unit current-cell matrix for 8 MSBs and a binary-weighted array for 4 LSBs, trading-off linearity, power consumption, chip area, and glitch energy with this process. The low-glitch switch driving circuits are employed to improve linearity and dynamic performance. Current sources of the DAC are laid out separately from the current-cell switch matrix core block to reduce transient noise coupling. The prototype DAC is implemented in a 0.35 um n-well single-poly quad-metal CMOS technology and the measured DNL and INL are within ${\pm}0.75$ LSB and ${\pm}1.73$ LSB at 12b, respectively. The spurious-free dynamic range (SFDR) is 64 dB at 100 MS/s with a 10 MHz input sinewave. The DAC dissipates 91 mW at 3 V and occupies the active die area of $2.2{\;}mm{\;}{\times}{\;}2.0{\;}mm$

• 한국전산구조공학회논문집
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• 제13권2호
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• pp.209-220
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• 2000

보강된 판 및 쉘구조의 기하학적 비선형해석을 수행하기 위하여, total lagrangian formulation에 근거한 증분 평형방정식을 적용하고, 강도행렬 산정시 회전각의 2차항을 포함시켜 기하학적 비선형 해석시 해의 수렴성을 향상시켰으며, 보강된 쉘 구조의 해석시 보강재를 쉘 요소로 모델링하고 주부재와 보강재의 연결점에서 일반적인 변환관계를 이용하였다. 등매개 쉘 유한요소의 단점인 locking 현상을 극복하기 위하여 가정 변형률장을 적용하여 감차적분 또는 선택적분시 나타날 수 있는 제로 에너지 모드를 제거하였다. 수치해석 예제를 통하여 가정 변형률장에 근거한 쉘유한요소에 대한 효율성 및 적용성을 확인하였다.

• 대한토목학회논문집
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• 제7권4호
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• pp.83-90
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• 1987

본 연구에서는 Mindlin 평판요소의 개선을 위하여 사용되고 있는 감차적분방법과 비적합 변위형의 추가방법에 대한 재검토가 이루어졌으며, 이 두방법을 혼합 사용하여 개발한 새로운 평판유한요소가 제시되었다. 요소는 2차 Mindlin 평판이론에 의하여 수식화되었다. 개발된 평판요소를 이용하여 구한 수치해석 결과는 이론치에 매우 빨리 수렴하여, 요소의 찌그러짐(distortion)에 관계없이 신뢰성 있는 결과를 보여주었다. 또한 개발된 요소들은 강체운동(rigid body motion)에 필요한 최소의 zero eigenvalue를 가지며, 두꺼운 평판은 물론 아주 얇은 평판의 해석에서도 항상 좋은 결과를 보여주었다.