• 한국전기전자재료학회논문지
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• 제27권3호
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• pp.172-177
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• 2014

Industrial, medical, environment and agriculture application of pulse power technology have been developing rapidly in many field. In order to make use in the form of pulses is applied to the pulse forming technique. At this time, spark gap is generally used for the pulse forming. Spark gap may be possible to simulate the shape of the electrode, to know the uniform or non-uniform electric field of the electrode structure. Further, it can be determined using Paschen's law applied pressure of the insulating gas in accordance with the voltage which is created using the value of the electric field. In this paper, we tried to found using a formula and the simulation process to determine the pressure. The value of the electric field is different according to the shape of the electrode. So, the range of pressure applied also varies. In order to withstand the 100 kV with a gap of 5 mm, the nitrogen gas must be applied to about 7 bar in the electrode structure. On the other hand, in the same conditions, Sulfur hexafluoride gas must be applied to about 2 bar. Consequently, the Sulfur hexafluoride gas has a higher insulation properties than nitrogen gas may be applied to low pressure at the same conditions.

• 지능정보연구
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• 제17권4호
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• pp.227-240
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• 2011

특허의 중요성이 커짐에 따라 특허분석의 중요성 또한 점점 커지고 있다. 특허분석은 네트워크 기반 방법과 키워드 기반 방법으로 나눠지는데 네트워크 기반은 특허 내부에 존재하는 세부 기술정보에 대한 분석이 불가능하다는 단점이 있고 키워드 기반은 기술정보간의 상호관계를 규명하지 못한다는 단점이 있다. 기존에 제시된 네트워크 기반 특허 분석과 키워드 기반 분석의 한계를 극복하기 위해서 두 방법을 혼합한 방법으로서 본 연구에서는 특허 키워드 네트워크 기반 분석 방법론을 제시하였다. 본 연구에서는 LED 분야의 특허들을 대상으로 텍스트 마이닝을 통해 중요한 기술정보를 추출한 다음, 키워드 네트워크를 구축하고, 이를 대상으로 커뮤니티 네트워크 분석을 수행하였다. 분석 결과는 다음과 같다. 첫째, 특허 키워드 네트워크는 매우 낮은 밀도와 매우 높은 클러스터링 지수를 나타내었다. 밀도가 높다는 것은 LED 분야내 특허 키워드 네트워크 내 노드(키워드)들이 산발적으로 연결되어 있다는 것을 의미하며, 클러스터링 지수가 높다는 것은 해당 키워드 네트워크 내 노드, 즉 키워드들이 각각의 커뮤니티로 매우 긴밀하게 연결되어 있음을 나타낸다. 둘째, 특허 키워드 네트워크도 다른 지식네트워크와 마찬가지로 명확한 멱함수 분포를 따른다는 사실을 알 수 있었다. 이는 기존에 활발히 연구, 활용되어 많은 연결고리를 갖고 있는 특허개념(키워드)수록 지속적으로 다른 연구자들에 의해 선택되고 이 키워드를 바탕으로 새로운 키워드들이 연결되어서 이들 키워드간의 조합으로 새로운 기술이 발명된다는 것이다. 셋째, 특허가 개발될 때 특정 분야에 유입된 키워드 중 새로운 링크가 생긴 키워드의 대부분이 기존에 연결되어 있던 커뮤니티 내의 키워드들과 결합되어 새로운 특허 개념을 구성한다는 사실을 발견하였다. 이러한 사실은 단기(4년) 장기(10년) 두 기간 모두 동일하게 나타났다. 나아가 본 연구에서 제시한 방법론을 통해 도출된 특허 키워드 조합 정보를 활용하면 미래에 어떤 개념들이 합쳐져서 새로운 특허 단위로 만들어 질지 가늠해볼 수 있고, 새로운 특허를 개발할 때 참고할 수 있는 유용한 정보로 활용할 수 있다.

• 한국산업융합학회 논문집
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• 제20권4호
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• pp.257-263
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• 2017

The following thesis researched into the characteristics of electrolytic ion water with different levels of electrical conductivity by adding NaCl into tap water which is for experimental use in multi-layered electrolytic ion water generator. Electrolytic ion water is generated by underwater electrolysis and the electrolysis generator has a simple structure, is easy to control and is highly utilized in industries. Electrolytic ion water is useful in many areas since it has a superior sterilizing power, has no possibility of secondary pollution itself as water and removes active oxygen. In the experiment, we used tap water with NaCl excluded and water with three different levels of electrical conductivity by changing NaCl concentration levels into three levels. The features of current and voltage in electrolytic ion water represented a form of quadric instead of the linear characteristic following ohm's law. As well, as the electric conductivity of water and applied voltage increased, we were able to generate much stronger acid water and alkali water.

• Advances in aircraft and spacecraft science
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• 제5권1호
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• pp.141-164
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• 2018

In this paper, the thermal effect on buckling and free vibration characteristics of functionally graded (FG) size-dependent Timoshenko nanobeams subjected to an in-plane thermal loading are investigated by presenting a Navier type solution for the first time. Material properties of FG nanobeam are supposed to vary continuously along the thickness according to the power-law form and the material properties are assumed to be temperature-dependent. The small scale effect is taken into consideration based on nonlocal elasticity theory of Eringen. The nonlocal equations of motion are derived based on Timoshenko beam theory through Hamilton's principle and they are solved applying analytical solution. According to the numerical results, it is revealed that the proposed modeling can provide accurate frequency results of the FG nanobeams as compared to some cases in the literature. The detailed mathematical derivations are presented and numerical investigations are performed while the emphasis is placed on investigating the effect of the several parameters such as thermal effect, material distribution profile, small scale effects, aspect ratio and mode number on the critical buckling temperature and normalized natural frequencies of the temperature-dependent FG nanobeams in detail. It is explicitly shown that the thermal buckling and vibration behaviour of a FG nanobeams is significantly influenced by these effects. Numerical results are presented to serve as benchmarks for future analyses of FG nanobeams.

• 대한기계학회논문집
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• 제15권1호
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• pp.299-307
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• 1991

본 연구에서는 근사수평 반류 성층유동에서의 계면마찰계수에 관한 일반화된 실험식을 개발하고자 한다. 이 실험식은 본 저자가 발표한 포화수-수증기와 물-공기 의 실험자료를 기초로 개발되며 공학적인 응용을 위하여 기액상레이놀즈 수와 유체의 물성치를 포함하는 거시적인 유동변수로 표현된다. 또 동일한 계면 마찰계숭에 대한 Nikuradse의 표면조도와 계면의 특성치로 표현되는 무차원 계면 유효조도와의 상관관 계를 구명하고 포화수-수증기와 물-공기의 2상유동에 공통적으로 적용할 수 있는 무차 원 계면유효조도와의 상관관계를 구명하고 포화수-수증기와 물-공기의 2상유동에 공통 적으로 적용할 수 있는 무차원 계면유효조도를 제안할 예정이다. 마지막으로 본 연 구에서 개발한 실험식과 기존 실험식을 비교 검토하고자 한다.

• Wind and Structures
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• 제26권4호
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• pp.205-214
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• 2018

In this paper, the thermo-mechanical buckling characteristics of functionally graded (FG) size-dependent Timoshenko nanobeams subjected to an in-plane thermal loading are investigated by presenting a Navier type solution for the first time. Material properties of FG nanobeam are supposed to vary continuously along the thickness according to the power-law form and the material properties are assumed to be temperature-dependent. The small scale effect is taken into consideration based on nonlocal elasticity theory of Eringen. The nonlocal governing equations are derived based on Timoshenko beam theory through Hamilton's principle and they are solved applying analytical solution. According to the numerical results, it is revealed that the proposed modeling can provide accurate critical buckling temperature results of the FG nanobeams as compared to some cases in the literature. The detailed mathematical derivations are presented and numerical investigations are performed while the emphasis is placed on investigating the effect of the several parameters such as material distribution profile, small scale effects and aspect ratio on the critical buckling temperature of the FG nanobeams in detail. It is explicitly shown that the thermal buckling of a FG nanobeams is significantly influenced by these effects. Numerical results are presented to serve as benchmarks for future analyses of FG nanobeams.

• Advances in materials Research
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• 제5권4호
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• pp.245-261
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• 2016

Thermo-mechanical buckling problem of functionally graded (FG) nanoplates supported by Pasternak elastic foundation subjected to linearly/non-linearly varying loadings is analyzed via the nonlocal elasticity theory. Two opposite edges of the nanoplate are subjected to the linear and nonlinear varying normal stresses. Elastic properties of nanoplate change in spatial coordinate based on a power-law form. Eringen's nonlocal elasticity theory is exploited to describe the size dependency of nanoplate. The equations of motion for an embedded FG nanoplate are derived by using Hamilton principle and Eringen's nonlocal elasticity theory. Navier's method is presented to explore the influences of elastic foundation parameters, various thermal environments, small scale parameter, material composition and the plate geometrical parameters on buckling characteristics of the FG nanoplate. According to the numerical results, it is revealed that the proposed modeling can provide accurate results of the FG nanoplates as compared some cases in the literature. Numerical examples show that the buckling characteristics of the FG nanoplate are related to the material composition, temperature distribution, elastic foundation parameters, nonlocality effects and the different loading conditions.

• Structural Engineering and Mechanics
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• 제17권3_4호
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• pp.393-408
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• 2004

There exists a clear need to monitor the performance of civil structures over their operational lives. Current commercial monitoring systems suffer from various technological and economic limitations that prevent their widespread adoption. The wires used to route measurements from system sensors to the centralized data server represent one of the greatest limitations since they are physically vulnerable and expensive from an installation and maintenance standpoint. In lieu of cables, the introduction of low-cost wireless communications is proposed. The result is the design of a prototype wireless sensing unit that can serve as the fundamental building block of wireless modular monitoring systems (WiMMS). An additional feature of the wireless sensing unit is the incorporation of computational power in the form of state-of-art microcontrollers. The prototype unit is validated with a series of laboratory and field tests. The Alamosa Canyon Bridge is employed to serve as a full-scale benchmark structure to validate the performance of the wireless sensing unit in the field. A traditional cable-based monitoring system is installed in parallel with the wireless sensing units for performance comparison.

• Steel and Composite Structures
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• 제13권1호
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• pp.91-107
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• 2012

In this research, mechanical buckling of hybrid functionally graded plates is considered using a new four variable refined plate theory. Unlike any other theory, the number of unknown functions involved is only four, as against five in case of other shear deformation theories. The theory presented is variationally consistent, does not require shear correction factor, and gives rise to transverse shear stress variation such that the transverse shear stresses vary parabolically across the thickness satisfying shear stress free surface conditions. The plate properties are assumed to be varied through the thickness following a simple power law distribution in terms of volume fraction of material constituents. Governing equations are derived from the principle of minimum total potential energy. The closed-form solution of a simply supported rectangular plate subjected to in-plane loading has been obtained by using the Navier method. The effectiveness of the theories is brought out through illustrative examples.

• Interaction and multiscale mechanics
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• 제2권4호
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• pp.375-396
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• 2009

In the present work, the elasto-viscoplastic behavior, interactions between grains, and the texture evolution in polycrystalline materials subjected to finite deformations are modeled using a multiscale analysis procedure within a finite element framework. Computational homogenization is used to relate the grain (meso) scale to the macroscale. Specifically, a polycrystal is modeled by a material representative volume element (RVE) consisting of an aggregate of grains, and a periodic distribution of such unit cells is considered to describe material behavior locally on the macroscale. The elastic behavior is defined by a hyperelastic potential, and the viscoplastic response is modeled by a simple power law complemented by a work hardening equation. The finite element framework is based on a Lagrangian formulation, where a kinematic split of the deformation gradient into volume preserving and volumetric parts together with a three-field form of the Hu-Washizu variational principle is adopted to create a stable finite element method. Examples involving simple deformations of an aluminum alloy are modeled to predict inhomogeneous fields on the grain scale, and the macroscopic effective stress-strain curve and texture evolution are compared to those obtained using both upper and lower bound models.