• 한국해안·해양공학회논문집
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• 제26권2호
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• pp.103-111
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• 2014

크기가 작은 다수의 부이들이 원형으로 배열되어 있을 때 부이를 통한 추출 파워를 포텐셜이론 통하여 살펴보았다. 부이의 크기와 배열 간격이 수심과 파장 그리고 설치면적의 반경에 비하여 작다는 가정 아래에서 다수부이로 채워진 수면에서의 경계조건식을 유도하고 이를 포함한 경계치문제를 고유함수전개법을 이용하여 해석하였다. 추출 파워와 입사파 에너지의 비인 취득 폭을 packing ratio, 배열 반경, 그리고 PTO 감쇠계수를 바꿔가면서 살펴보았다. 또한 다수의 소형 부이를 원형 배열하였을 때 추출된 파력이 같은 잠긴 체적을 갖는 대형 단일 부이보다 효율적임을 계산을 통하여 밝혔다.

• 한국안전학회지
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• 제33권5호
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• pp.1-8
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• 2018

A fuel cell is an energy conversion device that converts a chemical energy directly into an electrical energy and has higher energy efficiency than an internal combustion engine, but solid oxide fuel cell (SOFC) consisting of brittle ceramic material remains as a major issue regarding the mechanical properties as the crack formation and propagation. In this study, the stress distribution and crack behavior around the crack tip were evaluated, due to investigated the effects of the surface crack at the operating condition of high temperature. As a result, the difference of the generated stress was insignificant at operating conditions of high temperature according to the surface crack length changes. This is because, the high stiffness interconnect has a closed structure to suppress cell deformation about thermal expansion. The stress intensity factor ratio $K_{II}/K_I$ increased as the crack depth increased, at that time the effect of $K_{II}$ is larger than that of $K_I$. Also the maximum stress intensity factor increased as the crack depth increased, but the location of crack was generated at the electrolyte/anode interface, not at the crack tip.

• 한국식품영양학회지
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• 제6권3호
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• pp.178-188
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• 1993

This research was attempted to investigate changes in physicochemical properties of rice extrudate with added ginger powder extruded by single screw extruder. Graphic three dimensional analysis on response surface regression was used to evaluate effects of extrusion variables on quality factors of the extrudate according to two independent variables, ginger consent 0∼12%, moisture content 14∼26%. The summarized results are as follows : 1) Regarding proximate composition of rice extrudate with added ginger powder, as ginger powder content of raw material Increased, crude tat, crude protein, crude ash and crude fiber increased, while soluble nitrogen free extract decreased. 2) Graphic three dimensional analysis on response surface regression was conducted for each dependent variable which revealed statistically significant relationship with independent variables, 0∼120A ginger and 14∼26% moisture content. Expansion ratio had a critical point as moisture content changed. As ginger and moisture content Increased, bulk density, break strength and water absorption Index Increased, while water solubility Index decreased. The predicted maximum degree of gelatinization in 6.15% ginger and 15.56% moisture content is 88.27%, and lightness decreased as ginger content Increased. According to the microstructure for the cross section of extrudate obsorbed with image analyzer, air cell number and perimeter revealed saddle point, meanwhile total area and fractarea of air cell had critical points as moisture content changed. In view of the results, quality of rice extrudate with added ginger powder was optimum when rice flour was fed to the extruder with 2∼7% singer powder and 15∼20% moisture content.

• 한국식품영양과학회지
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• 제28권2호
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• pp.429-437
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• 1999

A mathematical model was established for estimating changes in pressure and volume of permeable kimchi packages. The model comprises the CO2 gas production from kimchi and permeation of O2, CO2 and N2 through the permeable film or sheet. Using the developed model, the effects of various packaging variables on the pressure and volume changes were analyzed for rigid and flexible packag es of kimchi(3% salt content) at 15oC, and then effect of storage temperature was also looked into. In case of rigid pack of 400g, using the plastic sheet of high CO2 permeability and initial vacuumizing can help to relieve the problem of pressure build up. The lower fill weight can further reduce the pressure, but will result in higher packaging cost. For the flexible package of 3 kg, highly permeable films such as low density polyethylene(LDPE) and polypropylene can reduce the volume expansion. Higher ratio of CO2 permeability to O2 and N2 permeabilities are effective in reducing the volume expansion. Increased surface area cannot contribute to reduction of volume expansion for highly permeable flexible packages of kimchi. For the impermeable packages, pressure and volume at over ripening stage (acidity 1.0%) increase with decreased temperature, while those at optimum ripening stage(acidity 0.6%) change little with temperature. Pressure of permeable rigid LDPE package increases with tem perature at any ripening stage, and temperature affects the volume of flexible LDPE package very slightly. Experimental verification of the present results and package design with economical consid eration are needed as a next step for practical application.

• 지능정보연구
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• 제24권2호
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• pp.171-193
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• 2018

본 연구는 시멘틱 웹의 실질적 구현체인 LOD 클라우드에서 연결정책을 활용함으로써 LOD들간 연결을 효과적으로 제공하고 LOD의 변경된 내용을 검색결과에 빠짐없이 반영할 수 있는 방안을 제시한다. 현재 LOD 클라우드에서는 개체간 연결은 를 이용하여 개체들이 동일함을 명시적으로 기술하는 방식으로 이루어져 있다. 하지만, 이러한 명시적 연결방식은 LOD 클라우드 규모의 방대함에도 불구하고 개체간 동일성을 개체단위에서 파악하여야 하는 어려움이 있으며 주기적으로 LOD에 추가하여야 함에 따라 검색 시 개체들이 누락되는 한계가 있다. 이를 극복하기 위하여 본 연구에서는 명시적 연결을 생성하는 대신 LOD별로 연결하고자 하는 LOD와의 연결정책을 수립하여 LOD와 함께 공개하는 방식을 제안한다. 연결정책을 활용함으로써 연결하여야 할 동일개체를 검색시점에서 파악할 수 있으므로 추가되었던 개체들을 누락됨 없이 검색결과에 포함시킬 수 있고 LOD 클라우드에서의 연결성도 효과적으로 확충할 수 있다. 확충된 연결성은 정보의 지능적 처리의 선행과정인 지식확장의 근간이 된다. 연결정책은 연결하고자 하는 소스와 타겟 LOD의 주어 개체들간의 동일성을 평가하는데 도움이 되는 술어 쌍을 명세하는 방식으로 수립하며 검색 시 이러한 술어쌍에 대응하는 RDF 트리플을 검색하고 이들의 목적어들이 충분히 동일한 것인가를 평가하여 주어개체들의 동일수준을 판단한다. 본 연구에서는 이러한 연결정책을 이용하여 여러 LOD들을 심층적으로 검색하는 시스템을 구현하였다. 검색과정에서는 기존 명시적 연결들도 함께 활용하도록 구현하였다. 검색시스템에 대한 실험은 DBpedia의 주요 LOD들을 대상으로 진행하였다. 실험결과 연결대상 개체들의 목적어들이 0.8 ~ 0.9의 유사수준을 가지는 경우 적정한 확장성을 가지고 충분히 신뢰적인 개체들을 적절하게 포함하는 것으로 확인하였다. 또한, 개체들은 8개 이상의 동일연결을 제공하여야 검색결과가 신뢰적으로 활용될 수 있을 것으로 파악되었다.

• 한국해양공학회지
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• 제28권5호
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• pp.474-483
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• 2014

The majority of existing WECs (wave energy converters) are designed to achieve maximum power at a resonance condition. In the case of a single WEC, its size must be large enough for tuning, and it has high efficiency only within a limited frequency band. Recently, wave power extraction by deploying many small buoys in a compact array has been studied under the assumption that the buoy's size and separation distance are much smaller than the water depth, wave length, and size of the array. A boundary value problem involving the macro-scale boundary condition on the mean surface covered by an infinite strip of buoys is solved using the eigenfunction expansion method. The energy extraction efficiency (${\varepsilon}=1-R^2_f-T^2_r$), where $R_f$ and $T_r$ are the reflection and transmission coefficients for a strip array of buoys, is assessed for various combinations of packing ratio, strip width, and PTO damping coefficient.

• 소성∙가공
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• 제19권8호
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• pp.494-501
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• 2010

The main objective of this study is to examine the sensitivity of calibration curves of FEA of ring compression test to frictional shear factor. Ring compression test has been investigated by measuring dimensional changes at different positions of ring specimen and they include the changes in internal diameter at the middle and top section of the specimen, outer diameter at the middle and top section, surface expansion at the top surface, respectively. Initial ring geometries employed in analysis maintain a fixed ratio of 6 : 3 : 2, i.e. outer diameter : inner diameter : thickness of the ring specimen, which is generally known as 'standard' specimen. A rigid plastic material for different work-hardening characteristics has been modeled for simulations using rigid-plastic finite element code. Analyses have been performed within a definite range of friction as well as over whole range of friction to show different sensitivities to the interfacial friction for different ranges of friction. The results of investigation in this study have been summarized in terms of a dimensionless gradient. It has been known from the results that the dimensional changes at different positions of ring specimen show different linearity and sensitivity to the frictional condition on the contact surface.

• Structural Engineering and Mechanics
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• 제62권5호
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• pp.587-593
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• 2017

The objective of this analytical study is to calculate the elasto-plastic stresses of Functionally Graded (FG) hyperbolic disc subjected to uniform temperature. The material properties (elastic modulus, thermal expansion coefficient and yield strength) and the geometry (thickness) of the disc are assumed to vary radially with a power law function, but Poisson's ratio does not vary. FG disc material is assumed to be non-work hardening. Radial and tangential stresses are obtained for various thickness profile, temperature and material properties. The results indicate that thickness profile and volume fractions of constituent materials play very important role on the thermal stresses of the FG hyperbolic discs. It is seen that thermal stresses in a disc with variable thickness are lower than those with constant thickness at the same temperature. As a result of this, variations in the thickness profile increase the operation temperature. Moreover, thickness variation in the discs provides a significant weight reduction. A disc with lower rigidity at the inner surface according to the outer surface should be selected to obtain almost homogenous stress distribution and to increase resistance to temperature. So, discs, which have more rigid region at the outer surface, are more useful in terms of resistance to temperature.

• Computers and Concrete
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• 제32권5호
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• pp.475-486
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• 2023

Nondestructive evaluation (NDE) is an important task of civil engineering structure monitoring and inspection, but minor damage such as small cracks in local structure is difficult to observe. If cracks continued expansion may cause partial or even overall damage to the structure. Therefore, monitoring and detecting the structure in the early stage of crack propagation is important. The crack detection technology based on machine vision has been widely studied, but there are still some problems such as bad recognition effect for small cracks. In this paper, we proposed a deep learning method based on sweep signals to evaluate concrete surface crack with a width less than 1 mm. Two convolutional neural networks (CNNs) are used to analyze the one-dimensional (1D) frequency sweep signal and the two-dimensional (2D) time-frequency image, respectively, and the probability value of average damage (ADPV) is proposed to evaluate the minor damage of structural. Finally, we use the standard deviation of energy ratio change (ERVSD) and infrared thermography (IRT) to compare with ADPV to verify the effectiveness of the method proposed in this paper. The experiment results show that the method proposed in this paper can effectively predict whether the concrete surface is damaged and the severity of damage.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2018년도 춘계학술대회 논문집
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• pp.140-140
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• 2018

The 3D interconnect technologies have been appeared, as the density of Integrated Circuit (IC) devices increases. Through Silicon Via (TSV) process is an important technology in the 3D interconnect technologies. And the process is used to form a vertically electrical connection through silicon dies. This TSV process has some advantages that short length of interconnection, high interconnection density, low electrical resistance, and low power consumption. Because of these advantages, TSVs could improve the device performance higher. The fabrication process of TSV has several steps such as TSV etching, insulator deposition, seed layer deposition, metallization, planarization, and assembly. Among them, TSV metallization (i.e. TSV filling) was core process in the fabrication process of TSV because TSV metallization determines the performance and reliability of the TSV interconnect. TSVs were commonly filled with metals by using the simple electrochemical deposition method. However, since the aspect ratio of TSVs was become a higher, it was easy to occur voids and copper filling of TSVs became more difficult. Using some additives like an accelerator, suppressor and leveler for the void-free filling of TSVs, deposition rate of bottom could be fast whereas deposition of side walls could be inhibited. The suppressor was adsorbed surface of via easily because of its higher molecular weight than the accelerator. However, for high aspect ratio TSV fillers, the growth of the top of via can be accelerated because the suppressor is replaced by an accelerator. The substitution of the accelerator and the suppressor caused the side wall growth and defect generation. The suppressor was used as Single additive electrodeposition of TSV to overcome the constraints. At the electrochemical deposition of high aspect ratio of TSVs, the suppressor as single additive could effectively suppress the growth of the top surface and the void-free bottom-up filling became possible. Generally, copper was used to fill TSVs since its low resistivity could reduce the RC delay of the interconnection. However, because of the large Coefficients of Thermal Expansion (CTE) mismatch between silicon and copper, stress was induced to the silicon around the TSVs at the annealing process. The Keep Out Zone (KOZ), the stressed area in the silicon, could affect carrier mobility and could cause degradation of the device performance. Cobalt can be used as an alternative material because the CTE of cobalt was lower than that of copper. Therefore, using cobalt could reduce KOZ and improve device performance. In this study, high-aspect ratio TSVs were filled with cobalt using the electrochemical deposition. And the filling performance was enhanced by using the suppressor as single additive. Electrochemical analysis explains the effect of suppressor in the cobalt filling bath and the effect of filling behavior at condition such as current type was investigated.