• 한국전산구조공학회논문집
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• 제24권2호
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• pp.193-200
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• 2011

본 연구를 통해 superlite라 불리는 단열 파우더를 채용한 NO96 멤브레인 타입 LNG선 단열 화물창의 만선항해 시 LNG의 BOR(Boil-Off Rate) 예측모델을 제시하였다. LNGCC(LNG Cargo Containment)의 비정상상태 열전달 FEM모델은 만선항해 시 대기 및 해수 조건을 반영하고 복잡한 화물창 단열구조에 균질화 기법을 적용하여 구축하였다. BOR은 만선항해중 LNGCC 내부로 침입하는 총 열량을 이용하여 평가되었으며, 주요 변수에 따른 BOR의 변화는 파라메트릭 열전달해석을 통하여 분석하였다. 그리고 파라메트릭 BOR 특성해석 결과를 토대로 LNG선의 탱크 크기, 단열층의 두께 그리고 superlite의 열전도율을 함수로 하는 BOR 예측모델을 유도하였다. 비선형 과도 열전달해석을 통해 직접 구한 BOR과의 비교를 통해 유도한 예측모델은 최대 1% 이내의 상대오차를 나타내었다.

• 조명전기설비학회논문지
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• 제19권2호
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• pp.114-123
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• 2005

서보 설비를 위한 순차적 파라미터 자동 튜닝 알고리즘을 갖는 영구자석 동기전동기(Permanent Magnet Synchronous Motor: PMSM)의 비선형 속도 제어 기법이 제시된다. 비선형 제어 방식은 시스템 파라미터와 부하상태가 정확하게 일치하지 않는 경우 만족스러운 성능을 줄 수 일다. 최근에 향상된 속도 제어 성능을 위해 적응형 기법, 슬라이딩 모드 제어, 및 관측기에 기반 한 기법들이 제안되었다. 하지만, 이 방법들은 관성의 큰 변화, 속도의 빠른 과도 특성 및 샘플링 주기 증가와 같은 특정한 조건에서 더 이상 만족스러운 성능을 제공하지 않는다. 일반적으로, 속도 동특성에 영향을 주는 주요 파라미터를 동시에 추정하기는 쉽지 않다. 이를 해결하기 위해 설치 및 기동시 전동기 주요 파라미터를 시간 구간 별로 나누어 자동으로 추정하는 순차적 파라미터 튜닝 알고리즘이 제안된다. 제안된 방식이 DSP TMS320C31을 이용하여 구현되고 유용성이 시뮬레이션과 실험을 통해 입증된다.

• 한국콘텐츠학회논문지
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• 제15권2호
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• pp.499-506
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• 2015

마찰속도란 벽면 가까이의 흐름에서 벽면의 마찰 응력과 밀도로 정의되는 속도의 차원을 갖는 양이다. 또한 마찰속도는 바닥 흐름에서 전단력을 나타내는 수리학적 매개변수이다. 게다가 개수로 설계나 하천, 해안에서 유사 및 물질의 거동을 파악하는데 정확한 마찰속도의 산정이 매우 중요하며 주 흐름방향의 혼합계수를 결정하는데 필수적인 요소이다. 이러한 마찰속도를 산정하는 방법들은 하상경사를 이용하는 방법, 레이놀즈 응력분포를 이용하는 방법, 점성저층에서 평균유속의 선형법칙을 이용하는 방법, 벽 전단 응력의 직접적 측정방법 등이 있다. 본 연구에서는 기존 방법과 달리 확률통계 기법에 사용되는 엔트로피 개념에 접목하여 새로운 마찰속도공식을 제안하였고, 이를 검증하기 위해 Song의 실측 실험데이터를 이용하였다. 제안한 공식과 마찰속도 공식에 의해 산정된 마찰속도의 결정계수는 0.999-1.000로 잘 일치한 것으로 분석되었다.

• 대한토목학회논문집
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• 제34권6호
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• pp.1667-1676
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• 2014

강합성 바닥판은 두 방향의 휨 강성이 다르기 때문에 직교이방성의 성질을 가진다. 강합성 바닥판의 휨 강성비는 활하중 모멘트에 영향을 미친다. 비충전 강합성 바닥판의 휨 강성비는 메인 베아링 바 간격과 직접적인 관계를 가지고 있어 메인 베아링 바 간격과 형상비 영향이 고려된 하중분배 계수식에 대한 연구가 필요한 것으로 판단된다. 본 연구에서는 휨 강성비를 고려하는 AASHTO LRFD Bridge Design Specification에 의한 비충전 강합성 바닥판의 활하중 모멘트를 평가하고 비충전 강합성 바닥판의 하중분배 계수식을 제안하고자 한다.

• Tribology and Lubricants
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• 제31권2호
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• pp.35-41
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• 2015

A water-pump located in the cooling area of a car circulates cooling water. A particular bearing element, known as a water-pump bearing, installed in the rotating part carries the entire load. The failure of this water-pump bearing has a direct impact on the failure of the automobile engine, and so securing its reliability is crucial. Several researchers have examined the design principles of the water-pump bearing, but there are no reports on the life characteristic of the bearing yet. Herein, we report the construction of test equipment to reproduce the spalling of the roller contact, which is the main failure mode of the chosen water-pump bearing. We chose the radial load as an accelerated stress factor and validated the failure mode by monitoring the surface defects. We conducted the accelerated life test after determining the accelerated stress level through a combination of finite element analysis and a preliminary test. In the life tests, we used an accelerometer to perform failure diagnosis. In the last stage of this study, we present a statistical reliability analysis. Thus, we fully estimated the shape parameter of the water-pump bearing, accelerating level on the load , and the lifetime (MTTF and B₁₀ life) under real use conditions, and finally proposed an interval estimation value considering the uncertainty of the estimated value.

• 한국응용과학기술학회지
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• 제14권3호
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• pp.63-69
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• 1997

폴리올류 비이온성 계면활성제인 sucrose monolaurate, sucrose monomyristate, sucrose monopalmitate, sucrose monostearate 그리고 sucrose monooleate와 같은 5종의 sucrose monoester 유도체들을 선택하여 묽은 수용액내에서 임계미셀 농도와 미셀화 영역을 결정하는 방법으로서 컴퓨터 프로그래밍에 의한 표면장력 곡선의 최대화를 제안하였다. 임계미셀 농도와 미셀화 영역은 몇몇 실험치를 직접 프로그램에 대입함으로써 곡선의 최대화에 의해서 이론적으로 산정할 수 있다. 이론적으로 구한 임계미셀 농도값들은 실측치와 거의 일치함을 알 수 있다.

• Earthquakes and Structures
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• 제5권1호
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• pp.49-65
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• 2013

This article presents the statistical characteristics of elastic floor acceleration spectra that represent the peak response demand of non-structural components attached to a nonlinear supporting frame. For this purpose, a set of stiff and flexible general moment resisting frames with periods of 0.3-3.6 sec. are analyzed using forty-nine near-field strong ground motion records. Peak accelerations are derived for each single degree of freedom non-structural component, supported by the above mentioned frames, through a direct-integration time-history analysis. These accelerations are obtained by Floor Acceleration Response Spectrum (FARS) method. They are statistically analyzed in the next step to achieve a better understanding of their height-wise distributions. The factors that affect FARS values are found in the relevant state of the art. Here, they are summarized to evaluate the amplification and/or reduction of FARS values especially when the supporting structures undergo inelastic behavior. The properties of FARS values are studied in three regions: long-period, fundamental-period and short-period. Maximum elastic acceleration response of non-structural component, mounted on inelastic frames, depends on the following factors: inelasticity intensity and modal periods of supporting structure; natural period, damping ratio and location of non-structural component. The FARS values, corresponded to the modal periods of supporting structure, are strongly reduced beyond elastic domain. However, they could be amplified in the transferring period domain between the mentioned modal periods. In the next step, the amplification and/or reduction of FARS values, caused by inelastic behavior of supporting structure, are calculated. A parameter called the response acceleration reduction factor ($R_{acc}$), has been previously used for far-field earthquakes. The feasibility of extending this parameter for near-field motions is focused here, suggested repeatedly in the relevant sources. The nonlinearity of supporting structure is included in ($R_{acc}$) for better estimation of maximum non-structural component absolute acceleration demand, which is ordinarily neglected in the seismic design provisions.

• 한국재료학회지
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• 제29권5호
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• pp.328-335
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• 2019

Nb-doped $TiO_2$(NTO) coated NiCrAl alloy foam for hydrogen production is prepared using ultrasonic spray pyrolysis deposition(USPD) method. To optimize the size and distribution of NTO particles based on good physical and chemical stability, we synthesize particles by adjusting the weight ratio of the Nb precursor solution(5 wt%, 10 wt% and 15 wt%). The morphological, chemical bonding, and structural properties of the NTO coated NiCrAl alloy foam are investigated by X-ray diffraction(XRD), X-ray photo-electron spectroscopy(XPS), and Field-Emission Scanning Electron Microscopy(FESEM). As a result, the samples of controlled Nb weight ratio exhibit a common diffraction pattern at ${\sim}25.3^{\circ}$, corresponding to the(101) plane, and have chemical bonding(O-Nb=O) at 534 eV. The NTO particles with the optimum weight ratio of N (10 wt%) show a uniform distribution with a size of ~18.2-21.0 nm. In addition, they exhibit the highest corrosion resistance even in the electrochemical stability estimation. As a result, the introduction of NTO coated NiCrAl alloy foam by USPD improves the chemical stability of the NiCrAl alloy foam by protecting the direct electrochemical reaction between the foam and the electrolyte. Thus, the optimized NTO coating can be proposed for excellent protection of NiCrAl alloy foam for hydrocarbon-based steam methane reforming(SMR).

• 한국물환경학회지
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• 제27권4호
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• pp.405-412
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• 2011

Increased Non-permeable areas which have resulted from civilization reduce the volume of groundwater infiltration that is one of the important factors causing water shortage during a dry season. Thus, seeking the efficient method to analyze the volume of groundwater in accurate should be needed to solve water shortage problems. In this study, two different watersheds were selected and precipitation, soil group, and land use were surveyed in a particular year in order to figure out the accuracy of estimated infiltration recharge ratio compared to Web-based Hydrograph Analysis Tool (WHAT). The volume of groundwater was estimated considering Antecedent soil Moisture Condition (AMC) and Curve Number (CN) using Long Term Hydrologic Impact Assessment (L-THIA) model. The results of this study showed that in the case of Kyoung-an watershed, the volume of both infiltration and baseflow seperated from WHAT was 46.99% in 2006 and 33.68% in 2007 each and in Do-am watershed the volume of both infiltration and baseflow was 33.48% in 2004 and 23.65% in 2005 respectively. L-THIA requires only simple data (i.e., land uses, soils, and precipitation) to simulate the accurate volume of groundwater. Therefore, with convenient way of L-THIA, researchers can manage watershed more effectively than doing it with other models. L-THIA has limitations that it neglects the contributions of snowfall to precipitation. So, to estimate more accurate assessment of the long term hydrological impacts including groundwater with L-THIA, further researches about snowfall data in winter should be considered.

• Geomechanics and Engineering
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• 제24권4호
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• pp.323-335
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• 2021

This paper aims to estimate the range of the excavation damaged zone (EDZ) formation caused by the tunnel boring machine (TBM) advancement through dynamic three-dimensional large deformation finite element analysis. Large deformation analysis based on Coupled Eulerian-Lagrangian (CEL) analysis is used to accurately simulate the behavior during TBM excavation. The analysis model is verified based on numerous test results reported in the literature. The range of the formed EDZ will be suggested as a boundary under various conditions - different tunnel diameter, tunnel depth, and rock type. Moreover, evaluation of the integrity of the tunnel structure during excavation has been carried out. Based on the numerical results, the apparent boundary of the EDZ is shown to within the range of 0.7D (D: tunnel diameter) around the excavation surface. Through series of numerical computation, it is clear that for the rock of with higher rock mass rating (RMR) grade (close to 1st grade), the EDZ around the tunnel tends to increase. The size of the EDZ is found to be direct proportional to the tunnel diameter, whereas the depth of the tunnel is inversely proportional to the magnitude of the EDZ. However, the relationship between the formation of the EDZ and the stability of the tunnel was not found to be consistent. In case where the TBM excavation is carried out in hard rock or rock under high confinement (excavation under greater depth), large range of the EDZ may be formed, but less strain occurs along the excavation surface during excavation and is found to be more stable.