• 분석과학
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• 제19권6호
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• pp.490-497
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• 2006

액화 천연가스(LNG) 공정 분석 결과의 불확도 요인을 평가하였다. 평가된 불확도 요인은 측정 반복성, 사용된 GC의 비 직선성, 사용된 표준가스의 불확도, 시료 채취 방법에 따른 농도 변화 그리고 교정 후의 기기 변동이었으며, 이 중에서 중요한 불확도 요인은 사용된 GC의 비 직선성, 사용된 표준가스의 불확도 그리고 교정 후의 기기 변동이었다. 주요 성분인 메탄 및 에탄의 경우, 각각 $90.0{\pm}0.9%mol/mol$(확장불확도, 95% 신뢰 수준) 및 $6.26{\pm}0.08%mol/mol$(확장불확도, 95% 신뢰 수준)이었다. 가스 성분원소별로 각 불확도 요소의 기여 정도는 차이가 있었고, 메탄 분석의 경우 사용된 GC의 비 직선성의 상대 표준불확도가 0.28%, 사용된 표준가스의 상대 표준불확도가 0.25%, 그리고 교정 후의 기기 변동에 의한 상대 표준불확도가 0.24%이었다.

• Earthquakes and Structures
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• 제7권5호
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• pp.647-665
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• 2014

Squat reinforced concrete walls require enough shear strength in order to promote flexural yielding, which creates the need for designers of an accurate method for strength prediction. In many cases, especially for existing buildings, strength estimates might be insufficient when more accurate analyses are needed, such as pushover analysis. In this case, estimates of load versus displacement are required for building modeling. A model is developed that predicts the shear load versus shear deformation of squat reinforced concrete walls by means of a panel formulation. In order to provide a simple, design-oriented tool, the formulation considers the wall as a single element, which presents an average strain and stress field for the entire wall. Simple material constitutive laws for concrete and steel are used. The developed models can be divided into two categories: (i) rotating-angle and (ii) fixed-angle models. In the first case, the principal stress/strain direction rotates for each drift increment. This situation is addressed by prescribing the average normal strain of the panel. The formation of a crack, which can be interpreted as a fixed principal strain direction is imposed on the second formulation via calibration of the principal stress/strain direction obtained from the rotating-angle model at a cracking stage. Two alternatives are selected for the cracking point: fcr and 0.5fcr (post-peak). In terms of shear capacity, the model results are compared with an experimental database indicating that the fixed-angle models yield good results. The overall response (load-displacement) is also reasonable well predicted for specimens with diagonal compression failure.

• Earthquakes and Structures
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• 제7권3호
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• pp.365-384
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• 2014

The intensity of a ground motion can be measured by a number of parameters, some of which might exhibit robust correlations with the damage of structures subjected to that motion. In this study, 204 near-fault pulse-type records are selected and their seismic parameters are determined. Time history and damage analyses of a tested 3-storey reinforced concrete frame representing for low-rise reinforced concrete buildings subjected to those earthquake motions are performed after calibration and comparison with the available experimental results. The aim of this paper is to determine amongst several available seismic parameters, the ones that have strong correlations with the structural damage measured by a damage index and the maximum inter-story drift. The results show that Velocity Spectrum Intensity is the leading parameter demonstrating the best correlation, followed by Housner Intensity, Spectral Acceleration and Spectral Displacement. These seismic parameters are recommended as reliable parameters of near-fault pulse-type motions related to damage potential of low-rise reinforced concrete structures. The results also reaffirm that the conventional and widely used parameter of Peak Ground Acceleration does not exhibit a good correlation with the structural damage.

• Nuclear Engineering and Technology
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• 제55권7호
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• pp.2432-2437
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• 2023

Methodology for suppressing or recovering the distorted spectra, which may occur due to mutual non-uniformity and nonlinear response when a multi-detector is simultaneously operated for gamma spectroscopy, is presented with respect to its applicability to stabilization of spectra having the non-identical feature using modified full spectrum reallocation method. The modified full-spectrum reallocation method is extended to provide multiple coefficients that describe the gain drift for multi-division of the spectrum and they were incorporated into an optimization process utilizing a random sampling algorithm. Significant performance improvements were observed with the use of multiple coefficients for solving partial peak dislocation. In this study, our achievements to confirm the stabilization of spectrum having differences in moments and modify the full spectrum reallocation method provide the feasibility of the method and ways to minimize the implication of the non-linear responses normally associated with inherent characteristics of the detector system. We believe that this study will not only simplify the calibration process by using an identical response curve but will also contribute to simplifying data pre-processing for various studies as all spectra can be stabilized with identical channel widths and numbers.

• 재활복지공학회논문지
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• 제9권2호
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• pp.161-168
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• 2015

본 논문은 자체 개발한 관성측정장치의 가속도, 각속도, 지자기계 데이터를 이용하여 보행거리를 측정하는 시스템 개발에 관한 것이다. 관성센서들의 오프셋 및 이득 오차를 최소화하기 위하여 9축의 자유도를 갖는 지그를 제작하였으며, 이를 이용하여 캘리브레이션을 수행하였다. 보행거리의 정확한 측정을 위하여, 기울기 하강법을 이용하여 가속도계의 중력성분 제거 및 보행패턴 분석을 통한 드리프트 성분을 제거하였다. 최종적으로 보정된 가속도 데이터의 이중적분을 통하여 보행거리를 측정하였다. 시스템의 성능 평가를 위하여, 실내 직선 10m 직선 보행에 대하여 캘리브레이션 전, 후 오차 개선 비율를 비교하였으며, 간단한 보행에 대해 Vicon과의 비교 실험을 수행하였다. 직선 보행에 대해서는 x, y, z축 각각에 대하여 $31.4{\pm}14.38%$(mean${\pm}$S.D.), $78.64{\pm}10.84%$ 및 $69.71{\pm}26.25%$ 개선이 되었음을 확인하였으며, Vicon과의 비교 실험 결과 x, y, z축 각각에 대하여 0.1m, 0.16m, 0.12m의 오차를 얻을 수 있었다.

• 한국시뮬레이션학회논문지
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• 제18권3호
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• pp.103-112
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• 2009

원자력발전소에서 센서의 주기적 교정은 안전운전을 위해 꼭 필요하다. 그러나 실제 드리프트가 발생하여 교정을 요하는 센서는 약 2% 미만이다. 또한, 센서의 작동 상태를 매 핵연료 주기마다 수행하는 것은 고장 혹은 드리프트가 발생한 센서를 최대 18개월까지 감지하지 못한 채 운전할 위험이 있다. 원전의 안전운전 및 불필요한 교정을 줄이기 위해 센서의 상시 교정 감시가 필요하다. 이를 위해 주성분 분석과 Support Vector Regression(SVR)을 이용한 PCSVR 알고리즘을 개발하였고, 고리원전 3호기의 출력증발 데이터를 이용하여 검증하였다. 주성분분석은 선형변환을 통한 입력공간의 축소 및 노이즈 제거 효과를 나타내며, AASVR은 해석학적 및 기계학적 모델로 모델링하기 힘든 복잡계를 쉽게 나타낼 수 있는 장점이 있다. SVR의 세가지 파라미터는 반응표면분석법에 의해 최적화하였다. 센서의 고장탐지를 위해 모델 출력의 잔차를 슈하르트 관리도, EWMA, CUSUM 및 일반화우도비검정(GLRT)을 통해 그 결과를 비교하였다. 미세한 드리프트에 대해 CUSUM과 GLRT가 우수한 결과를 보였다. 개발된 알고리즘은 수출형 원전 APR1000 설계시 적용가능 할 것으로 판단된다.

• 한국정밀공학회지
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• 제24권9호
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• pp.68-75
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• 2007

The pitch and orthogonality of two-dimensional (2D) gratings have been measured by using a metrological atomic force microscope (MAFM) and measurement uncertainty has been analyzed. Gratings are typical standard artifacts for the calibration of precision microscopes. Since the magnification and orthogonality in two perpendicular axes of microscopes can be calibrated simultaneously using 2D gratings, it is important to certify the pitch and orthogonality of 2D gratings accurately for nano-metrology using precision microscopes. In the measurement of 2D gratings, the MAFM can be used effectively for its nanometric resolution and uncertainty, but a new measurement scheme was required to overcome some limitations of current MAFM such as nonnegligible thermal drift and slow scan speed. Two kinds of 2D gratings, each with the nominal pitch of 300 nm and 1000 nm, were measured using line scans for the pitch measurement of each direction. The expanded uncertainties (k = 2) of measured pitch values were less than 0.2 nm and 0.4 nm for each specimen, and those of measured orthogonality were less than 0.09 degree and 0.05 degree respectively. The experimental results measured using the MAFM and optical diffractometer were coincident with each other within the expanded uncertainty of the MAFM. As a future work, we also proposed another scheme for the measurements of 2D gratings to increase the accuracy of calculated peak positions.

• Smart Structures and Systems
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• 제25권2호
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• pp.135-153
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• 2020

There has been a sustained interest towards the non-contact structural displacement measurement by means of videogrammetric technique. On the way forward, one of the major concerns is the spurious image drift induced by temperature variation. This study therefore carries out an investigation into the temperature effect of videogrammetric technique, focusing on the exploration of the mechanism behind the temperature effect and the elimination of the temperature-caused measurement error. 2D videogrammetric measurement tests under monotonic or cyclic temperature variation are first performed. Features of measurement error and the casual relationship between temperature variation and measurement error are then studied. The variation of the temperature of digital camera is identified as the main cause of measurement error. An excellent linear relationship between them is revealed. After that, camera parameters are extracted from the mapping between world coordinates and pixels coordinates of the calibration targets. The coordinates of principle point and focal lengths show variations well correlated with temperature variation. The measurement error is thought to be an outcome mainly attributed to the variation of the coordinates of principle point. An approach for eliminating temperature-caused measurement error is finally proposed. Correlation models between camera parameters and temperature are formulated. Thereby, camera parameters under different temperature conditions can be predicted and the camera projective matrix can be updated accordingly. By reconstructing the world coordinates with the updated camera projective matrix, the temperature-caused measurement error is eliminated. A satisfactory performance has been achieved by the proposed approach in eliminating the temperature-caused measurement error.

• Steel and Composite Structures
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• 제23권5호
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• pp.571-583
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• 2017

A kind of accordion-web RBS connection, "Tubular Web RBS (TW-RBS)" connection is proposed in this research. TW-RBS is made by replacing a part of web with a tube at the desirable location of the beam plastic hinge. This paper presents first a numerical study under cyclic load using ABAQUS finite element software. A test specimen is used for calibration and comparison of numerical results. Obtained results indicated that TW-RBS would reduce contribution of the beam web to the whole moment strength and creates a ductile fuse far from components of the beam-to-column connection. Besides, TW-RBS connection can increase story drift capacity up to 9% in the case of shallow beams which is much more than those stipulated by the current seismic codes. Furthermore, the tubular web like corrugated sheet can improve both the out-of-plane stiffness of the beam longitudinal axis and the flange stability condition due to the smaller width to thickness ratio of the beam flange in the plastic hinge region. Thus, the tubular web in the plastic hinge region improves lateral-torsional buckling stability of the beam as just local buckling of the beam flange at the center of the reduced section was observed during the tests. Also change of direction of strain in arc shape of the tubular web section is smaller than the accordion webs with sharp corners therefore the tubular web provides a better condition in terms of low-cycle fatigue than other accordion web with sharp corners.

• Journal of Biosystems Engineering
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• 제41권2호
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• pp.75-84
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• 2016

Purpose: In-situ water quality monitoring based on ion-selective electrodes (ISEs) is a promising technique because ISEs can be used directly in the medium to be tested, have a compact size, and are inexpensive. However, signal drift can be a major concern with on-line management systems because continuous immersion of the ISEs in water causes electrode degradation, affecting the stability, repeatability, and selectivity over time. In this study, a computer-based nitrate monitoring system including automatic electrode rinsing and calibration was developed to measure the nitrate concentration in water samples in real-time. Methods: The capabilities of two different types of poly(vinyl chloride) membrane-based ISEs, an electrode with a liquid filling and a carbon paste-based solid state electrode, were used in the monitoring system and evaluated on their sensitivities, selectivities, and durabilities. A feasibility test for the continuous detection of nitrate ions in water using the developed system was conducted using water samples obtained from various water sources. Results: Both prepared ISEs were capable of detecting low concentrations of nitrate in solution, i.e., 0.7 mg/L $NO_3-N$. Furthermore, the electrodes have the same order of selectivity for nitrate: $NO_3{^-}{\gg}HCO_3{^-}$ > $Cl^-$ > $H_2PO_4{^-}$ > $SO{_4}^{2-}$, and maintain their sensitivity by > 40 mV/decade over a period of 90 days. Conclusions: The use of an automated ISE-based nitrate measurement system that includes automatic electrode rinsing and two-point normalization proved to be feasible in measuring $NO_3-N$ in water samples obtained from different water sources. A one-to-one relationship between the levels of $NO_3-N$ measured with the ISEs and standard analytical instruments was obtained.