• 한국지반공학회논문집
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• 제36권7호
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• pp.5-14
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• 2020

간사이 공항은 1994년 9월에 개항하였다. 제 1기섬 완공 후 26년이 지났지만 여전히 장기침하가 진행되고 있다. 이 침하는 Pleistocene층에서 발생하고 있다. 계속적으로 변하는 수평방향으로의 지층두께 및 세립분의 함유량이 달라 Pleistocene 모래층의 투수성을 결정하는 것이 쉽지 않기 때문이다. 또한 인접한 제 2기섬의 건설에 따른 지반의 상호거동을 예측에 대한 어려움도 존재한다. 이 문제를 해결하기 위해서, 인접한 두 매립 섬의 건설에 따른 교차하는 Pleistocene 지반의 상호거동을 포함한 장기변형을 평가하기 위해 탄점소성을 고려한 2차원 유한요소해석이 수행되었다. 일반적으로 2차원해석은 한 개의 단면이 전체 단면을 대표할 수 있을 때 사용이 가능하다. 하지만 간사이공항은 매립에 의한 인공섬으로서 2차원 해석으로는 섬의 코너(corner) 부분의 응력 변형문제에 적용할 수 없으며, 물리탐사를 통한 실제 하부지반의 구조도 불균질하며 그 두께 또한 일정하지 않아 2차원해석만으로는 한계가 있다. 즉, 3차원 해석이 강력히 요구된다. 이러한 요구에 의해 본 저자는 탄점소성 해석이 가능한 기존의 2차원 프로그램을 3차원으로 확장하였으며, 1차원 압밀해석해을 통해서 개발한 3차원 프로그램의 검증(verification)을 완료하였다. 본 논문은 검증을 마친, 개발한 3차원 프로그램의 유효성을 입증하기 위해서, 2차원 프로그램을 이용한 기존의 연구와 동일한 해석조건으로 해석을 수행하여, 해석결과를 2차원 결과와 실제 계측값과 비교함으로서 개발한 3차원 수치해석프로그램의 유효성을 입증(demonstration)하였다.

• 농업과학연구
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• 제37권1호
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• pp.27-35
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• 2010

A study examined visitors' satisfaction to urban arboretum in Daejeon metropolitan city, and analyzed utilization status. Also, the study was based on POE. POE is a last phase in the environmental planning and design process that follows the sequence of planning, programing, design construction, and use of a project. Urban arboretum contribute to improvement in the quality of living by providing urban citizens with places for refreshment, natural have important values on urban environment and to promote the quality of life for urbanite. So, the study aims to present data on the human activities responding to the physical environment of 'the Daejeon Hanbat Arboretum' by evaluating visitor's behavior and activity, visiting motivations, preference patterns, and the degree of visitor's satisfaction. This study is conducted by multi-method such as interviews and questionnaires surveys. On-site questionnaire surveys were conducted in the Hanbat arboretum on October 25-31 of 2009. Total of 265 questionnaires were analyzed for this study. The analysis of data was used SPSS 18.0 statistical analysis program. Data from visitors was analyzed by descriptive statistics, frequency analysis, multiple response analysis, and Anova. Then, the outcome will be compared and evaluated to install urban arboretum that reflect the desires of users in the future.

• 한국화재소방학회논문지
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• 제33권4호
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• pp.50-58
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• 2019

구획실 내 가연물들의 화재거동에 대한 B-RISK의 예측성능을 Fire dynamics simulator (FDS)와 연계하여 검토하였다. 먼저 열발생률(Heat release rate, HRR)에 대한 B-RISK의 예측성능을 검토하기 위해 가연물 한 세트의 실험에서 측정된 HRR 값과 디자인 화재곡선을 B-RISK의 입력조건으로 사용하여 가연물 두 세트에 대한 HRR 곡선을 계산하고 실험에서 측정된 가연물 두 세트의 HRR 값과 비교하였다. B-RISK 결과와 실험결과를 비교하여 B-RISK가 화재성장률에 대한 예측은 어렵지만 최대 HRR 값과 총 열발생량에 대해서는 충분히 예측할 수 있음을 확인하였다. 그리고 B-RISK 계산을 통해 예측된 HRR 값을 FDS의 입력조건으로 사용하여 계산된 결과와 실험결과를 비교하여 B-RISK 계산을 통해 예측된 HRR 값의 화재거동에 대해 검토하였다. 실험에서 측정된 온도 및 화학종 농도 결과와 비교하여 화재성장구간에 대해 차이가 있는 것을 확인하였지만 예측된 HRR 값에서 Percentile이 약 70%인 HRR 값을 사용하더라도 충분히 전체적인 화재거동을 예측할 수 있음을 확인하였다.

• 한국추진공학회지
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• 제21권1호
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• pp.72-83
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• 2017

본 연구에서는 유도탄 사출관 내부의 수치모사를 통해 이상 유동에 대한 열 유체역학적 분석을 수행하였다. 고정된 해석영역에서 계산이 진행되었고 증발이 완료된 물을 냉각제로 사용하였다. 고온의 공기와 냉각제간의 상호작용 및 유동장을 해석하기 위해, Realizable $k-{\varepsilon}$ 난류 모델과 VOF (Volume Of Fluid) 모델을 선정하고 냉각제 유량에 따른 수치 해석을 진행하였다. 해석결과, 사출관 상부 압력은 냉각제 유량에 따라 비선형적으로 증가하였다. 그리고 내부에서의 유동 진행 과정과 온도분포, 냉각제분포가 밀접한 연관이 있음을 확인하였다. 사출관 하부의 초기 온도는 냉각제량의 증가에 비례하여 감소하지만, 특정시간 이후 경향이 역전되면서 오히려 온도의 상승을 유발하였다. 또한, 혼합가스의 순환유동에 의해 초기의 온도변화가 요동하는 경향도 확인되었다.

• Journal of the Optical Society of Korea
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• 제18권3호
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• pp.236-243
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• 2014

Surface profiling and film thickness measurement play an important role for inspection. White light interferometry is widely used for engineering surfaces profiling, but its applications are limited primarily to opaque surfaces with relatively simple optical reflection behavior. The conventional bucket algorithm had given inaccurate surface profiles because of the phase error that occurs when a thin-film exists on the top of the surface. Recently, reflectometry and white light scanning interferometry were combined to measure the film thickness and surface profile. These techniques, however, have found that many local minima exist, so it is necessary to make proper initial guesses to reach the global minimum quickly. In this paper we propose combing reflectometry and white light scanning interferometry to measure the thin-film thickness and surface profile. The key idea is to divide the measurement into two states; reflectometry mode and interferometry mode to obtain the thickness and profile separately. Interferogram modeling, which considers transparent thin-film, was proposed to determine parameters such as height and thickness. With the proposed method, the ambiguity in determining the thickness and the surface has been eliminated. Standard thickness specimens were measured using the proposed method. Multi-layered film measurement results were compared with AFM measurement results. The comparison showed that surface profile and thin-film thickness can be measured successfully through the proposed method.

• Steel and Composite Structures
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• 제38권5호
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• pp.477-496
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• 2021

The main objective of this paper is to study vibration of sandwich open cylindrical panel with damaged core and FG face sheets based on three-dimensional theory of elasticity. The structures are made of a damaged isotropic core and two external face sheets. These skins are strengthened at the nanoscale level by randomly oriented Carbon nanotubes (CNTs) and are reinforced at the microscale stage by oriented straight fibers. These reinforcing phases are included in a polymer matrix and a three-phase approach based on the Eshelby-Mori-Tanaka scheme and on the Halpin-Tsai approach, which is developed to compute the overall mechanical properties of the composite material. Three complicated equations of motion for the panel under consideration are semi-analytically solved by using 2-D differential quadrature method. Several parametric analyses are carried out to investigate the mechanical behavior of these multi-layered structures depending on the damage features, through-the-thickness distribution and boundary conditions. It is seen that for the large amount of power-law index "P", increasing this parameter does not have significant effect on the non-dimensional natural frequency parameters of the FG sandwich curved panel. Results indicate that by increasing the value of isotropic damage parameter "D" up to the unity (fully damaged core) the frequency would tend to become zero. One can dictate the fiber variation profile through the radial direction of the sandwich panel via the amount of "P", "b" and "c" parameters. It should be noticed that with increase of volume fraction of fibers, the frequency parameter of the panels does not increase necessarily, so by considering suitable amounts of power-law index "P" and the parameters "b" and "c", one can get dynamic characteristics similar or better than the isotropic limit case for laminated FG curved panels.

• 대한조선학회논문집
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• 제59권6호
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• pp.400-412
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• 2022

This paper provides the results of numerical and theoretical predictions of oil outflows from damaged single-hull and double-hull ships.Theoretical equations derived from the unsteady Bernoulli equation and a CFD method for multi-phase flow analysis were used to estimate the oil outflow rate from cargo tank. The predicted oil outflow rate from a single-hull cargo tank damaged due to grounding and collision accidents showed a good agreement with the available experimental results in both numerical and theoretical analyses. However, in the case of the double-hull conditions, the time variation of the amount of water and oil mixture inside the ballast tank predicted by the theoretical equation showed some different behavior from the numerical results. The reason was that the interaction of the oil flow with the water inflow in the ballast tank was not reflected in the theoretical equations. In the problems of the initial pressure condition in the cargo and ballast tanks, the oil outflow and water inflow were delayed at the pressure condition that the tanks were sealed. When the flow interaction between the oil and water in the ballast tank was less complicated, the theoretical and the numerical results showed a good agreement with each other.

• Steel and Composite Structures
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• 제44권1호
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• pp.65-79
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• 2022

The main goal of this paper is to study the vibration of damaged core laminated annular plates with FG face sheets based on a three-dimensional theory of elasticity. The structures are made of a damaged isotropic core and two external face sheets. These skins are strengthened at the nanoscale level by randomly oriented Carbon nanotubes (CNTs) and are reinforced at the microscale stage by oriented straight fibers. These reinforcing phases are included in a polymer matrix and a three-phase approach based on the Eshelby-Mori-Tanaka scheme and on the Halpin-Tsai approach, which is developed to compute the overall mechanical properties of the composite material. In this study the effect of microcracks on the vibrational characteristic of the sandwich plate is considered. In particular, the structures are made by an isotropic core that undergoes a progressive uniform damage, which is modeled as a decay of the mechanical properties expressed in terms of engineering constants. These defects are uniformly distributed and affect the central layer of the plates independently from the direction, this phenomenon is known as "isotropic damage" and it is fully described by a scalar parameter. Three complicated equations of motion for the sectorial plates under consideration are semi-analytically solved by using 2-D differential quadrature method. Using the 2-D differential quadrature method in the r- and z-directions, allows one to deal with sandwich annular plate with arbitrary thickness distribution of material properties and also to implement the effects of different boundary conditions of the structure efficiently and in an exact manner. The fast rate of convergence and accuracy of the method are investigated through the different solved examples. The sandwich annular plate is assumed to have any arbitrary boundary conditions at the circular edges including simply supported, clamped and, free. Several parametric analyses are carried out to investigate the mechanical behavior of these multi-layered structures depending on the damage features, through-the-thickness distribution, and boundary conditions.

• Elastomers and Composites
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• 제58권1호
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• pp.44-56
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• 2023

Additive manufacturing (AM) or three-dimensional (3D) printing of metals has been drawing significant attention due to its reliability, usefulness, and low cost with rapid prototyping. Among the various AM technologies, fused deposition modeling (FDM) or fused filament fabrication is receiving much interest because of its simple manufacturing processing, low material waste, and cost-effective equipment. FDM technology uses metal-filled polymer filaments for 3D printing, followed by debinding and sintering to fabricate complex metal parts. An efficient binder is essential for producing polymer filaments and the thermal post-processing of printed objects. This study involved an in-depth investigation of and a fabrication route for a novel multi-component binder system with steel alloy powder (45 vol.%) ranging from filament fabrication and 3D printing to debinding and sintering. The binder system consisted of polyvinyl pyrrolidone (PVP) as a binder and thermoplastic polyurethane (TPU) and polylactic acid (PLA) as a carrier. The PVP binder held the metal components tightly by maintaining their stoichiometry, and the TPU and PLA in the ratio of 9:1 provided flexibility, stiffness, and strength to the filament for 3D printing. The efficacy of the binder system was examined by fabricating 3D-printed cubic structures. The results revealed that the thermal debinding and sintering processes effectively removed the binder/carrier from the cubic structures, resulting in isotropic shrinkage of approximately 15.8% in all directions. The scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) patterns displayed the microstructure behavior, phase transition, and elemental composition of the 3D cubic structure.

• Steel and Composite Structures
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• 제45권2호
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• pp.205-218
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• 2022

Proper calculation of splitting tensile strength (STS) of concrete has been a crucial task, due to the wide use of concrete in the construction sector. Following many recent studies that have proposed various predictive models for this aim, this study suggests and tests the functionality of three hybrid models in predicting the STS from the characteristics of the mixture components including cement compressive strength, cement tensile strength, curing age, the maximum size of the crushed stone, stone powder content, sand fine modulus, water to binder ratio, and the ratio of sand. A multi-layer perceptron (MLP) neural network incorporates invasive weed optimization (IWO), cuttlefish optimization algorithm (CFOA), and electrostatic discharge algorithm (ESDA) which are among the newest optimization techniques. A dataset from the earlier literature is used for exploring and extrapolating the STS behavior. The results acquired from several accuracy criteria demonstrated a nice learning capability for all three hybrid models viz. IWO-MLP, CFOA-MLP, and ESDA-MLP. Also in the prediction phase, the prediction products were in a promising agreement (above 88%) with experimental results. However, a comparative look revealed the ESDA-MLP as the most accurate predictor. Considering mean absolute percentage error (MAPE) index, the error of ESDA-MLP was 9.05%, while the corresponding value for IWO-MLP and CFOA-MLP was 9.17 and 13.97%, respectively. Since the combination of MLP and ESDA can be an effective tool for optimizing the concrete mixture toward a desirable STS, the last part of this study is dedicated to extracting a predictive formula from this model.