• Composites Research
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• 제35권4호
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• pp.269-276
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• 2022

본 연구에서는 층간분리의 위험이 없는 3차원 직조방식으로 복합재 보강패널을 제작하고 좌굴하중과 고유진동수 등의 기계적 특성을 연구하였다. 보강패널의 스트링거와 외피는 일체형으로 제작하였고 T800급 탄소섬유로 만들어진 프리폼에 수지(EP2400)를 충진시키는 방식을 적용하였다. 제작된 보강판에 대하여 압축시험과 고유진동수 측정 시험을 수행하였고 유한요소해석 결과와 비교하였다. 또한 3차원 직조 구조물의 성능을 상대적으로 비교하기 위해 일방향 프리프레그와 2차원 평직(fabric)으로 동일한 치수의 보강패널을 제작하여 시험과 해석을 수행하였다. 시험값을 기준으로 일방향 프리프레그와 2차원 평직으로 제작된 보강패널의 좌굴하중은 3차원 직조 패널의 좌굴하중 대비 각각 20%, -3%의 차이를 보였다. 본 연구로부터 3차원 직조방식으로 제작된 일체형 보강패널의 좌굴하중은 일방향 프리프레그 적층 보강판의 좌굴하중보다는 낮지만 2차원 평직 보강판넬보다는 미세하게 높은 수준의 값을 보임을 확인하였다.

• International Journal of Aeronautical and Space Sciences
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• 제14권4호
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• pp.310-323
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• 2013

In this paper, the aeroelastic static response of flexible wings with arbitrary cross-section geometry via a coupled CUF-XFLR5 approach is presented. Refined structural one-dimensional (1D) models, with a variable order of expansion for the displacement field, are developed on the basis of the Carrera Unified Formulation (CUF), taking into account cross-sectional deformability. A three-dimensional (3D) Panel Method is employed for the aerodynamic analysis, providing more accuracy with respect to the Vortex Lattice Method (VLM). A straight wing with an airfoil cross-section is modeled as a clamped beam, by means of the finite element method (FEM). Numerical results present the variation of wing aerodynamic parameters, and the equilibrium aeroelastic response is evaluated in terms of displacements and in-plane cross-section deformation. Aeroelastic coupled analyses are based on an iterative procedure, as well as a linear coupling approach for different free stream velocities. A convergent trend of displacements and aerodynamic coefficients is achieved as the structural model accuracy increases. Comparisons with 3D finite element solutions prove that an accurate description of the in-plane cross-section deformation is provided by the proposed 1D CUF model, through a significant reduction in computational cost.

• 한국화재소방학회논문지
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• 제31권6호
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• pp.74-82
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• 2017

유기단열재를 사용한 샌드위치패널(복합자재) 건축물 화재는 소화가 어려우며, 가연성 심재를 통한 빠른 화재 확산으로 화재 시 피해가 크다. 샌드위치패널은 양면이 불연재로 되어있고, 불연재 사이에 심재인 단열재로 이루어져 있다. 단열재는 유기단열재와 무기단열재가 사용되고 있으며, 유기단열재가 무기단열재에 비하여 약 80% 이상 사용되고 있다. 유기단열재는 무기단열재에 비하여 경제적인 장점이 있지만 화재에 취약하다는 단점을 가지고 있기 때문에 샌드위치패널 화재 시 일반화재에 비하여 피해가 크다. 가스유해성시험의 경우 복합자재의 심재 위험성을 측정하기 위해 패널에 지름 25 mm 크기 3개의 원형 천공을 하여 시험하지만 콘칼로리미터 시험은 샌드위치패널 형태 그대로 시험을 진행한다. 본 연구에서는 KS F ISO 5660-1 콘칼로리미터 시험에서 복합자재의 경우 불연재인 표면에 가열한 경우와 천공을 통한 심재 노출 시험 및 심재에 직접가열 시 발생하는 화재의 위험성을 측정하였다. 시험에 사용된 유기단열재는 일반 EPS와 난연 EPS를 사용하였으며, 시험체 구성은 샌드위치패널, 천공된 샌드위치 패널, 심재의 3가지 형태로 시험을 진행하였다. 본 연구의 목적은 콘칼로리미터 시험 시 복합자재 심재의 화재 위험성을 평가하는 방안을 제시하고자 하였다.

• 대한조선학회논문집
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• 제50권1호
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• pp.1-7
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• 2013

The high-skewed and/or composite propellers of current interests to reduce the ship vibration and to increase the acoustic performance are likely to be exposed to the unexpected structural problems. One typical example is that the added mass effect on the propellers working in the non-uniform wake field reduces the natural frequency of the propeller leading to the resonance with the low-frequency excitation of the external forces. To avoid this resonance problem during the design stage, the technique of fluid-structure interaction has been developed, but the higher-order effect of the blade geometry deformation is not yet considered in evaluating the added mass effects. In this paper the fluid boundary-value problem is formulated by the potential-based panel method in the inviscid fluid region with the velocity inflow due to the body deformation, and the structural response of the solid body under the hydrodynamic loading is solved by applying the finite element method which implements the 20-node iso-parametric element model. The fluid-structure problem is solved iteratively. A basic fluid-sturcture interaction study is performed with the simple rectangular plates of thin thickness with various planform submerged in the water of infinite extent. The computations show good correlation with the experimental results of Linholm, et al. (1965).

• 대한조선학회논문집
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• 제46권3호
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• pp.232-248
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• 2009

Numerical methodology to solve ship springing problem, which is basically fluid-structure interaction problem, was explored in this study. Solution of this hydroelasticity problem was sought by coupling higher order B-spline Rankine panel method and finite element method in time domain, each of which is introduced for fluid and structure domain respectively. Even though varieties of different combinations in terms of numerical scheme are possible and have been tried by many researchers to solve the problem, no systematic study regarding the characteristics of each scheme has been done so far. Here, extensive case studies have been done on the numerical schemes especially focusing on the iteration method, FE analysis of beam-like structure, handling of forward speed problem and so on. Two different iteration scheme, Newton style one and fixed point iteration, were tried in this study and results were compared between the two. For the solution of the FE-based equation of motion, direct integration and modal superposition method were compared with each other from the viewpoint of its efficiency and accuracy. Finally, calculation of second derivative of basis potential, which is difficult to obtain with accuracy within grid-based method like BEM was discussed.

• Steel and Composite Structures
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• 제31권3호
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• pp.261-276
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• 2019

The study investigates the free vibration of a nano-scale sandwich beam by an extended high order approach, which has not been reported in the existing literature. First-order shear deformation theory for steel skins and so-called high-order sandwich panel theory for the core are applied. Next, the modified couple stress theory is used for both skins and cores. The Hamilton principle is utilized for deriving equations and corresponding boundary conditions. First, in the study the three-mode shapes natural frequencies for various material parameters are investigated. Also, obtained results are evaluated for two types of stiff and soft cores and isotropic, homogenous steel skins. In the research since the governing equations and also the boundary conditions are nonhomogeneous, therefore some closed-form solutions are not applicable. So, to obtain natural frequencies, the boundary conditions are converted to initial conditions called the shooting method as the numerical one. This method is one of the most robust approaches to solve complex equations and boundary conditions. Moreover, three types of simply supported on both sides of the beam (S-S), simply on one side and clamp supported on the other one (S-C) and clamped supported on both sides (C-C) are scrutinized. The parametric study is followed to evaluate the effect of nano-size scale, geometrical configurations for skins, core and material property change for cores as well. Results show that natural frequencies increase by an increase in skins thickness and core Young modulus and a decrease in beam length, core thickness as well. Furthermore, differences between obtained frequencies for soft and stiff cores increase in higher mode shapes; while, the more differences are evaluated for the stiff one.

• 전기학회논문지
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• 제64권11호
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• pp.1587-1591
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• 2015

For a higher definition discharge cell, the method of high speed addressing is necessary. In order to modify the surface charges, the liquefied $TiO_2$ or MgO powder is added on MgO layer in front glass and on the phosphor in rear glass in micro barrier discharge. Both the electro-optical properties and the discharge time lag characteristics are measured from 4 inch. test panel, such as the discharge voltage, current, luminance, luminous efficacy and discharge time lag. As the results, the statistic time lag is improved by about 40 %.

• 한국콘텐츠학회논문지
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• 제15권8호
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• pp.366-374
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• 2015

본 연구는 공공부조를 지원받고 있는 대상자를 중심으로 자살생각에 영향을 미치는 요인이 무엇인지 살펴보았다. 이를 위하여 한국보건사회연구원과 서울대학교 사회복지연구소에서 조사한 한국복지패널(Korea Welfare Panel Study) 7차년도(2012년) 자료를 사용하였으며, 분석방법은 자살생각에 대한 영향의 정도를 파악하기 위해 이항 로짓모형을 이용한 회귀분석(binary logistic regression analysis)을 실시하였다. 분석 결과 중졸인 경우, 기혼인 경우, 자아존중감이 높을수록, 공공부조 만족도가 높을수록 자살생각을 할 가능성이 낮은 것으로 나타났다. 또한 우울이 있는 경우, 중년층인 경우 자살생각을 할 가능성이 높았다. 빈곤층에게 신체적, 심리적 요인만이 아닌 공공부조 만족도 역시 자살생각에 영향을 미칠 수 있다는 것을 증명하였다. 따라서 지원을 받는 대상자들의 만족도를 측정하는 것도 자살생각에 영향을 미치는 중요한 요인 중 하나일 수 있음을 시사한다.

• 산업경영시스템학회지
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• 제40권1호
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• pp.114-123
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• 2017

The global small and mid-sized display market is changing from thin film transistor-liquid crystal display to organic light emitting diode (OLED). Reflecting these market conditions, the domestic and overseas display panel industry is making great effort to innovate OLED technology and incease productivity. However, current OLED production technology has not been able to satisfy the quality requirement levels by customers, as the market demand for OLED is becoming more and more diversified. In addition, as OLED panel production technology levels to satisfy customers' requirement become higher, product quality problems are persistently generated in OLED deposition process. These problems not only decrease the production yield but also cause a second problem of deteriorating productivity. Based on these observations, in this study, we suggest TRIZ-based improvement of defects caused by glass pixel position deformation, which is one of quality deterioration problems in small and medium OLED deposition process. Specifically, we derive various factors affecting the glass pixel position shift by using cause and effect diagram and identify radical reasons by using XY-matrix. As a result, it is confirmed that glass heat distortion due to the high temperature of the OLED deposition process is the most influential factor in the glass pixel position shift. In order to solve the identified factors, we analyzed the cause and mechanism of glass thermal deformation. We suggest an efficient method to minimize glass thermal deformation by applying the improvement plan of facilities using contradiction matrix in TRIZ. We show that the suggested method can decrease the glass temperature change by about 23% through an experiment.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2002년도 International Meeting on Information Display
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• pp.552-555
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• 2002

In order to achieve higher performance and low cost a-Si TFT-LCD panel, new material architecture and its process integration for a-Si TFT array manufacturing method were developed. Material combination of low resistant dry-etchable metal and new pixel electrode under currently adopted 4 mask process made it possible to get more-simplified manufacturing method and better device performance for the a-Si TFT-LCD application. Proposed 4 mask process architecture with optimized wet etchants and dry etching process was applicable to various devices such as notebook, monitor and TV.