• Wind and Structures
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• 제25권1호
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• pp.1-24
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• 2017

This paper presents a 1:25 multi-freedom aero-elastic model for a high lighting pole at the Zhoushan stadium. To validate the similarity characteristics of the model, a free vibration test was performed before the formal test. Beat phenomenon was found and eliminated by synthesis of vibration in the X and Y directions, and the damping ratio of the model was identified by the free decay method. The dynamic characteristics of the model were examined and compared with the real structure; the similarity results were favorable. From the test results, the major along-wind dynamic response was the first vibration component. The along-wind wind vibration coefficient was calculated by the China code and Eurocode. When the peak factor equaled 3.5, the coefficient calculated by the China code was close to the experimental result while Eurocode had a slight overestimation of the coefficient. The wind vibration coefficient during typhoon flow was analyzed, and a magnification factor was suggested in typhoon-prone areas. By analyzing the power spectrum of the dynamic cross-wind base shear force, it was found that a second-order vortex-excited resonance existed. The cross-wind response in the test was smaller than Eurocode estimation. The aerodynamic damping ratio was calculated by random decrement technique and the results showed that aerodynamic damping ratios were mostly positive at the design wind speed, which means that the wind-induced galloping phenomenon is predicted not to occur at design wind speeds.

• Wind and Structures
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• 제18권6호
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• pp.693-715
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• 2014

Stochastic processes are used to represent phenomena in many diverse fields. Numerical simulation method is widely applied for the solution to stochastic problems of complex structures when alternative analytical methods are not applicable. In some practical applications the stochastic processes show non-Gaussian properties. When the stochastic processes deviate significantly from Gaussian, techniques for their accurate simulation must be available. The various existing simulation methods of non-Gaussian stochastic processes generally can only simulate super-Gaussian stochastic processes with the high-peak characteristics. And these methodologies are usually complicated and time consuming, not sufficiently intuitive. By revealing the inherent coupling effect of the phase and amplitude part of discrete Fourier representation of random time series on the non-Gaussian features (such as skewness and kurtosis) through theoretical analysis and simulation experiments, this paper presents a novel approach for the simulation of non-Gaussian stochastic processes with the prescribed amplitude probability density function (PDF) and power spectral density (PSD) by amplitude modulation and phase reconstruction. As compared to previous spectral representation method using phase modulation to obtain a non-Gaussian amplitude distribution, this non-Gaussian phase reconstruction strategy is more straightforward and efficient, capable of simulating both super-Gaussian and sub-Gaussian stochastic processes. Another attractive feature of the method is that the whole process can be implemented efficiently using the Fast Fourier Transform. Cases studies demonstrate the efficiency and accuracy of the proposed algorithm.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2009년도 제33회 추계학술대회논문집
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• pp.231-235
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• 2009

본 연구의 목적은 실제로 서인천 발전본부에서 운용하고 있는 GE 7FA+e DLN 2.6 가스터빈 연소기의 연소특성과 배기배출물에 대한 제어 연구를 소개하고 모형 가스터빈 연소기의 연소동특성 및 연소불안정 현상을 확인하고자 한다. 모형 연료노즐은 실제의 1/3 크기로 상사하여 제작되었고, 실제 노즐과 동일한 각도의 2단 스월러(swirl vane)를 가지고 있다. Plenum과 연소기의 형상은 실 가스터빈과 유사한 음향학적 특성을 가질 수 있도록 설계되었고 실험은 공기온도, 노즐출구 속도, 당량비, 연소실 길이를 변수로 이루어졌으며, 그 결과 연소실의 연소불안정 mode는 각각의 실험 변수에 따라서 연소실의 공진주파수의 영향, 연소온도와 공기-연료 혼합기 분포에 의해서 mode가 전이되는 현상을 확인하였다.

• 전자공학회논문지
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• 제50권7호
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• pp.149-156
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• 2013

본 논문에서는 bump 회로를 이용한 하드웨어 기반의 윤곽선 검출 회로를 제안한다. 하나의 픽셀은 빛을 전기적인 신호로 변환하는 active pixel sensor (APS)와 주변 픽셀의 밝기 차이를 비교하는 bump회로로 구성된다. 제안하는 회로는 $64{\times}64$의 이미지를 대상으로하며, 각 열(column)마다 비교기를 공유한다. 비교기는 외부에서 인가되는 기준전압을 통해 최종적으로 대상픽셀의 윤곽선 여부를 판별한다. 또한 기존의 4개 혹은 그 이상의 픽셀 데이터를 비교하는 윤곽선 검출 알고리즘을 상대적으로 간소화하여 대상픽셀을 포함하여 3개의 픽셀만으로 윤곽선 검출을 가능토록 제안하였다. 따라서 하나의 픽셀에 비교적 적은 수의 트랜지스터로 구성하였다. 따라서 제한적인 픽셀 크기에서 fill factor를 충분히 확보함으로써 수용 가능한 조도의 범위를 확장하였고, 기준전압을 외부에서 입력 받기 때문에 윤곽선 레벨을 조절 할 수 있다. Bump 회로기반의 윤곽선 검출 회로는 0.18um CMOS 공정에서 설계되었으며, 1.8V의 공급전압에서 픽셀 당 0.9uW의 전력 소모율, 34%의 fill factor을 갖는다. 이는 기존회로대비 전력 소모율을 90% 개선하였고, 기존 회로에 비하여 면적은 약 18.7%, fill factor는 약 16%를 더 확보하였다.

• Corrosion Science and Technology
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• 제14권1호
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• pp.19-24
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• 2015

지금까지 마그네타이트 전극의 제조 방법과 전기화학적 특성에 대해 살펴보았다. 마그네타이트 전극을 제조하는 방법은 프레스법, 페이스트법, 전기도금법 등이 있으며, 이들의 전기화학 특성은 다음과 같이 정리할 수 있다. 1. Cycle voltammetry 실험을 통하여 애노딕, 캐소딕 분극 방향으로 각각 2개의 peak가 관찰되고, 이것은 $Fe_3O_4$가 $Fe(OH)_2$, FeO 등의 중간 산화물 형태를 거쳐 $Fe^{2+}$로 용해되는 반응들이다. 2. 산성 및 중성 용액에서는 마그네타이트의 환원적 용해가, 염기성 용액에서는 헤마타이트로의 산화 반응이 나타난다. 3. 전기화학 실험 결과와 마그네타이트 용해도를 관련시키기 위해서는 마그네타이트 용해가 일어나는 전위에서 실험 후, 용액에서 $Fe^{2+}$, $Fe^{3+}$ 이온들에 대한 분석이 필요하다.

• Nuclear Engineering and Technology
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• 제52권3호
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• pp.508-519
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• 2020

During transients or accidents, the reactor core is uncovered, and droplets entrained above the quench front collides with the uncovered fuel rod surface. Droplet impact cooling can reduce the peak cladding temperature. Besides zirconium-based cladding, versatile accidental tolerant fuel (ATF) claddings, including FeCrAl, have been proposed to increase the accident coping time. In order to investigate the effect of surface properties on droplet impact cooling of cladding surfaces, the droplet impact phenomena are photographed on the FeCrAl and zircaloy-4 (Zr-4) surfaces under different conditions. On the oxidized FeCrAl surface, the Leidenfrost phenomenon is not observed even when the surface temperature is as high as 550 ℃ with We > 30. Comparison of the impact behaviors observed on different materials shows that nucleate and transition boiling is more intensive on surfaces with larger thermal conductivity. The Leidenfrost point temperature (LPT) decreases with the solid thermal effusivity (${\sqrt{k{\rho}C_p}}$). However, the CHF temperature is relatively insensitive to the surface oxidation and Weber number. Droplet spreading diameter is analyzed quantitatively in the film boiling stage. Based on the energy balance a correlation is proposed for droplet maximum spreading factor. A mechanistic model is also developed for the LPT based on homogeneous nucleation theory.

• 한국의학물리학회지:의학물리
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• 제30권4호
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• pp.112-119
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• 2019

Purpose: The advantages of ocular proton therapy are that it spares the optic nerve and delivers the minimal dose to normal surrounding tissues. In this study, it developed a solid eye phantom that enabled us to perform quality assurance (QA) to verify the dose and beam range for passive single scattering proton therapy using a single phantom. For this purpose, a new solid eye phantom with a polymethyl-methacrylate (PMMA) wedge was developed using film dosimetry and an ionization chamber. Methods: The typical beam shape used for eye treatment is approximately 3 cm in diameter and the beam range is below 5 cm. Since proton therapy has a problem with beam range uncertainty due to differences in the stopping power of normal tissue, bone, air, etc, the beam range should be confirmed before treatment. A film can be placed on the slope of the phantom to evaluate the Spread-out Bragg Peak based on the water equivalent thickness value of PMMA on the film. In addition, an ionization chamber (Pin-point, PTW 31014) can be inserted into a hole in the phantom to measure the absolute dose. Results: The eye phantom was used for independent patient-specific QA. The differences in the output and beam range between the measurement and the planned treatment were less than 1.5% and 0.1 cm, respectively. Conclusions: An eye phantom was developed and the performance was successfully validated. The phantom can be employed to verify the output and beam range for ocular proton therapy.

• Journal of Radiation Protection and Research
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• 제41권2호
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• pp.81-86
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• 2016

Background: For positron emission tomography (PET) application, cadmium zinc telluride (CZT) has been investigated by several institutes to replace detectors from a conventional system using photomultipliers or Silicon-photomultipliers (SiPMs). The spatial and energy resolution in using CZT can be superior to current scintillator-based state-of-the-art PET detectors. CZT has been under development for several years at the Korea Atomic Energy Research Institute (KAERI) to provide a high performance gamma ray detection, which needs a single crystallinity, a good uniformity, a high stopping power, and a wide band gap. Materials and Methods: Before applying our own grown CZT detectors in the prototype PET system, we investigated preliminary research with a developed discrete type data acquisition (DAQ) system for coincident events at 128 anode pixels and two common cathodes of two CZT detectors from Redlen. Each detector has a $19.4{\times}19.4{\times}6mm^3$ volume size with a 2.2 mm anode pixel pitch. Discrete amplifiers consist of a preamplifier with a gain of $8mV{\cdot}fC^{-1}$ and noise of 55 equivalent noise charge (ENC), a $CR-RC^4$ shaping amplifier with a $5{\mu}s$ peak time, and an analog-to-digital converter (ADC) driver. The DAQ system has 65 mega-sample per second flash ADC, a self and external trigger, and a USB 3.0 interface. Results and Discussion: Characteristics such as the current-to-voltage curve, energy resolution, and electron mobility life-time products for CZT detectors are investigated. In addition, preliminary results of gamma ray imaging using 511 keV of a $^{22}Na$ gamma ray source were obtained. Conclusion: In this study, the DAQ system with a CZT radiation sensor was successfully developed and a PET image was acquired by two sets of the developed DAQ system.

• 한국전문물리치료학회지
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• 제24권4호
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• pp.54-59
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• 2017

Background: Light touch cue is a sensory input that could potentially help in the control of posture. The immediate stimulatory effect of light touch cues using a cane during gait is associated with postural stability. This strategy can help post-stroke individuals regain their ability to perform the sit-to-stand (STS) transfer safely. Objects: The effects of light grip on postural control during the STS transfer in post-stroke subjects were investigated. Methods: Eleven participants (6 men, 5 women) with hemiplegia due to stroke were recruited in the study. The subjects with hemiparesis performed STS transfer in three randomly assigned conditions (1) without a cane (2) light grip with a cane (3) strong grip with a cane. Results: The difference in weight-bearing distribution between the left and right feet, when the subjects were instructed to stand up, was $52.73{\pm}2.13%$ without a cane, $42.75{\pm}3.26%$ with a strong grip, and $43.00{\pm}2.55%$ with a light grip (p<.05). The rate of rise in force indicates the peak power provided by subjects during their STS transfers. The rate of rise in force was statistically significantly lower without a cane than that with a light grip or a strong grip (p<.05). The subjects' centers of pressure sway on the mediolateral side during STS transfers statistically significantly declined with a light grip or a strong grip when compared to those without a cane (p<.05). Conclusion: When the subjects with hemiparesis used a cane during STS transfers, their duration, center of pressure sway, and difference in weight-bearing distribution were all reduced. The subjects also exhibited similar results during STS transfers with a cane gripped lightly. This result may provide guidelines for the use of assistive devices when patients with hemiparesis practice STS transfers in clinical settings.

• 한국항해항만학회지
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• 제29권8호
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• pp.755-761
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• 2005

본 논문에서는 OFDM 방식의 문제점으로 지적되고 있는 송신단에서의 PAR 특성을 고려하여 고속 적응형 PTS 기법과 SLM 기법을 결합한 SLM-PTS 결합기법을 제안하였다. 또한, PAR 저감기법을 적용한 시스템을 평가하기 위하여 ETD-Turbo 부호를 사용한 COFDM 시스템을 구성한 후 성능을 평가하였다. 분석 결과 제안된 SLM-PTS 기법이 연산량을 경감시키며 전반적으로 우수한 PAR 저감성능을 보임을 알 수 있었다. 특히 Combine 3의 경우 10-5 BER을 기준으로 약 $3.7\~3.9\;dB$ 정토의 개선된 PAR 성능을 보였다. 또한, 터보부호를 사용한 경우 전반적으로 우수한 PAR 성능을 보임을 알 수 있었고, ETD-Turbo 부호를 적응한 경우 추가적으로 약 0.5 dB 정도의 성능 개선효과가 있음을 알 수 있었다.