• Wind and Structures
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• 제5권2_3_4호
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• pp.209-226
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• 2002

When predicting unsteady flow and pressure fields around a structure in a turbulent boundary layer by Large Eddy Simulation (LES), velocity fluctuations of turbulence (inflow turbulence), which reproduce statistical characteristics of the turbulent boundary layer, must be given at the inflow boundary. However, research has just started on development of a method for generating inflow turbulence that satisfies the prescribed turbulence statistics, and many issues still remain to be resolved. In our previous study, we proposed a method for generating inflow turbulence and confirmed its applicability by LES of an isotropic turbulence. In this study, the generation method was applied to a turbulent boundary layer developed over a flat plate, and the reproducibility of turbulence statistics predicted by LES computation was examined. Statistical characteristics of a turbulent boundary layer developed over a flat plate were investigated by a wind tunnel test for modeling the cross-spectral density matrix for use as targets of inflow turbulence generation for LES computation. Furthermore, we investigated how the degree of correspondence of the cross-spectral density matrix of the generated inflow turbulence with the target cross-spectral density matrix estimated by the wind tunnel test influenced the LES results for the turbulent boundary layer. The results of this study confirmed that the reproduction of cross-spectra of the normal components of the inflow turbulence generation is very important in reproducing power spectra, spatial correlation and turbulence statistics of wind velocity in LES.

• International Journal of Concrete Structures and Materials
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• 제10권1호
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• pp.87-97
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• 2016

In this study, a quantitative review was performed on the mechanical performance, permeation resistance of concrete, and durability of surface-modified coarse aggregates (SMCA) produced using low-quality recycled coarse aggregates, the surface of which was modified using a fine inorganic powder. The shear bond strength was first measured experimentally and the interface between the SMCA and the cement matrix was observed with field-emission scanning electron microscopy. The results showed that a reinforcement of the interfacial transition zone (ITZ), a weak part of the concrete, by coating the surface of the original coarse aggregate with surface-modification material, can help suppress the occurrence of microcracks and improve the mechanical performance of the aggregate. Also, the use of low-quality recycled coarse aggregates, the surfaces of which were modified using inorganic materials, resulted in improved strength, permeability, and durability of concrete. These results are thought to be due to the enhanced adhesion between the recycled coarse aggregates and the cement matrix, which resulted from the improved ITZ in the interface between a coarse aggregate and the cement matrix.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권12호
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• pp.5073-5086
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• 2015

The rock fracture detection by image analysis is significant for fracture measurement and assessment engineering. The paper proposes a novel image segmentation algorithm for the centerline tracing of a rock fracture based on Hessian Matrix at Multi-scales and Steger algorithm. A traditional fracture detection method, which does edge detection first, then makes image binarization, and finally performs noise removal and fracture gap linking, is difficult for images of rough rock surfaces. To overcome the problem, the new algorithm extracts the centerlines directly from a gray level image. It includes three steps: (1) Hessian Matrix and Frangi filter are adopted to enhance the curvilinear structures, then after image binarization, the spurious-fractures and noise are removed by synthesizing the area, circularity and rectangularity; (2) On the binary image, Steger algorithm is used to detect fracture centerline points, then the centerline points or segments are linked according to the gap distance and the angle differences; and (3) Based on the above centerline detection roughly, the centerline points are searched in the original image in a local window along the direction perpendicular to the normal of the centerline, then these points are linked. A number of rock fracture images have been tested, and the testing results show that compared to other traditional algorithms, the proposed algorithm can extract rock fracture centerlines accurately.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.476-476
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• 2011

Introduction of CNTs into a metal matrix has been considered to improve the mechanical properties of the metal matrix. However, the binding energy between metals and pristine CNTs wall is known to be so small that the interfacial slip between CNTs and the matrix occurs at a relatively low external stress. The interfacial strength between CNT and metal matrix is thus one of the key factors for successful development of the CNT/metal composites. Defective or functionalized CNT has been considered to enhance the interfacial strength of nanocomposites. In the present work, we design the various realistic hybrid structures of the single wall CNT/Cu complexes and characterize the interaction between single wall CNTs and Cu nano-particle and Cu13 cluster using first principle calculations. The characteristics of functionalized CNTs with various surface functional groups, such as -COOH, -OH, and -O interacting with Cu are investigated. We found that the binding energy can be enhanced by the surface functional group including oxygen since the oxygen atom can mediate and reinforce the interaction between carbon and Cu. These results strongly support the recent experimental work which suggested the oxygen on the interface playing an important role in the excellent mechanical properties of the CNT/Cu composite.

• 한국주조공학회지
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• 제19권1호
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• pp.77-83
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• 1999

Strip casting process, a new casting technology which makes thin strip of $0.5{\sim}5\;mm$ thickness directly from molten metal, has been dramatically developed for past 10 years and faced commercialization in the case of STS304 strip. In this study, ductile cast iron strip which is 1.1 mm thick and 100 mm wide is manufactured by the twin roll strip caster. Graphite and matrix structure of the strip can be controlled through heat treatments and the mechanical properties are examined. The microstructure of the as-cast strip consists of cementite and pearlite. Especially the equiaxed crystal zone of pearlite exists in the center region of the thickness due to the characteristics of the strip casting process. Matrix structure can be transformed into fully ferrite or ferrite/pearlite mixed structures by the different graphitization heat treatments. The heat-treated strip with ferrite/pearlite matrix structure showed higher hardness and tensile strength than that with full ferrite matrix structure.

• Smart Structures and Systems
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• 제7권3호
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• pp.213-222
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• 2011

The native extracellular matrix (ECM) consists of an integrated fibrous protein network and proteoglycan-based ground (hydrogel) substance. We designed a novel electrospinning technique to engineer a three dimensional fiber-hydrogel composite that mimics the native ECM structure, is injectable, and has practical macroscale dimensions for clinically relevant tissue defects. In a model system of articular cartilage tissue engineering, the fiber-hydrogel composites enhanced the biological response of adult stem cells, with dynamic mechanical stimulation resulting in near native levels of extracellular matrix. This technology platform was expanded through structural and biochemical modification of the fibers including hydrophilic fibers containing chondroitin sulfate, a significant component of endogenous tissues, and hydrophobic fibers containing ECM microparticles.

• Smart Structures and Systems
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• 제17권6호
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• pp.1017-1030
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• 2016

This study focuses on the system identification of reinforced concrete bridges using vector autoregressive model (VAR). First, the time series output response from a bridge establishes the autoregressive (AR) models. AR models are one of the most accurate methods for stationary time series. Burg's algorithm estimates the autoregressive coefficients (ARCs) at p-lag by reducing the sum of the forward and the backward errors. The computed ARCs are assembled in the state system matrix and the eigen-system realization algorithm (ERA) computes: the eigenvector matrix that contains the vectors of the mode shapes, and the eigenvalue matrix that contains the associated natural frequencies. By taking advantage of the characteristic of the AR model with ERA (ARMERA), civil engineering can address problems related to damage detection. Operational modal analysis using ARMERA is applied to three experiments. One experiment is coupled with an artificial neural network algorithm and it can detect damage locations and extension. The neural network uses a specific number of ARCs as input and multiple submatrix scaling factors of the structural stiffness matrix as output to represent the damage.

• Steel and Composite Structures
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• 제39권5호
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• pp.543-564
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• 2021

In this study free vibration analysis of a cracked Goland composite wing is investigated. The wing is modelled as a cantilevered beam based on Euler- Bernoulli equations. Also, composite material is modelled based on lamina fiber-reinforced. Edge crack is modelled by additional boundary conditions and local flexibility matrix in crack location, Castigliano's theorem and energy release rate formulation. Governing differential equations are extracted by Hamilton's principle. Using the separation of variables method, general solution in the normalized form for bending and torsion deflection is achieved then expressions for the cross-sectional rotation, the bending moment, the shear force and the torsional moment for the cantilevered beam are obtained. The cracked beam is modelled by separation of beam into two interconnected intact beams. Free vibration analysis of the beam is performed by applying boundary conditions at the fixed end, the free end, continuity conditions in the crack location of the beam and dynamic stiffness matrix determinant. Also, the effects of various parameters such as length and location of crack and fiber angle on natural frequencies and mode shapes are studied. Modal analysis results illustrate that natural frequencies and mode shapes are affected by depth and location of edge crack and coupling parameter.

• 마이크로전자및패키징학회지
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• 제29권1호
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• pp.67-70
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• 2022

본 연구는 최근 유행하고 있는 코로나 바이러스(SARS-CoV-2) UV 살균을 위한 1차원 광자 준결정 구조 개념의 광학 필터를 설계하고 시뮬레이션 하였다. 시뮬레이터는 수치해석 프로그램으로 사용되는 MATLAB 프로그램과 직접 코딩한 연산수식을 사용하였다. 비주기(복합구조) 다중층 구조 모델을 설계한 후, 특성 계산을 위하여 다중층 구조 모델의 물성치를 천이 행렬법(TMM, Transfer Matrix Method)으로 설정하였다. 설계된 복합 다중층 구조의 MATLAB을 활용한 전산모사법을 통하여 얻은 행렬값으로부터 반사도와 투과도를 계산하였다. 이 연구의 결과로 인체에 무해하면서 코로나 바이러스 UV 살균이 가능한 253.7 nm 파장만을 투과하는 광학 필터의 제작 및 응용 가능성을 증명하였다.

• 한국산림과학회지
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• 제88권3호
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• pp.342-351
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• 1999

도시화에 의해 고립된 임지인 인왕산에 발달하고 있는 산림식생이 식물사회학적 방법으로 해석되고 그것의 공간적 분포가 정밀하게 지도화되었다. 정밀식생도상의 patch의 수와 크기를 이용하여 인왕산의 경관구조 특성이 검토되었다. 인왕산지역의 산림식생단위는 10개 군락, 10개군 그리고 8개소군으로 구분되었으며, 경관요소유형은 이차림요소, 유적군락요소, 인공림요소 그리고 도시화지역을 비롯한 기타요소로 구분되었다. 소나무군락과 아까시나무군락이 각각 기질(matrix)을 형성하고 있었으며, 그와 같은 기질내에서 소면적의 일부 이차림, 유적군락 그리고 기타 인공림들이 소규모 patch로 분포하고 있었다. 단위면적당 patch의 수는 이차림요소가 인공림요소보다 많았으며, patch의 크기는 그 반대의 경향이었다. 경관요소유형별 유관속식물의 종풍부성은 patch의 크기와 양의 관련이 있는 것으로 판단되었다. 경관생태학적 검토결과, patch의 분화는 군락수준에서는 인위적 간섭이, 군이나 소군 등 하위군락수준에서는 자연적인 천이과정이 주로 관계하고 있는 것으로 생각되었다.