• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년도 제30회 춘계학술대회논문집
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• pp.299-302
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• 2008

램제트 추진체의 성능연구를 위하여 램제트 전 영역, 즉 흡입구에서부터 연소실과 노즐까지 통합하여 연소수치해석을 수행하였다. 램제트가 작동 시작하여 비행체가 상승하는 가속모드(Acceleration mode)와 고고도에서의 순항모드(Cruise mode)를 설정 하였으며, 각 모드에 대하여 분사되는 연료의 당량비 변화를 고려하였다. 각 모드에서 추진체 전 영역의 압력 분포, 흡입구의 종말충격파의 위치, 연소실에서의 온도분포, 노즐출구에서의 연료분포를 분석하였다.

• Advances in aircraft and spacecraft science
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• 제3권1호
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• pp.95-112
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• 2016

This paper presents the free vibration analysis of damaged beams by means of 1D (beam) advanced finite element models. The present 1D formulation stems from the Carrera Unified Formulation (CUF), and it leads to a Component-Wise (CW) modelling. By means of the CUF, any order 2D and 1D structural models can be developed in a unified and hierarchical manner, and they provide extremely accurate results with very low computational costs. The computational cost reduction in terms of total amount of DOFs ranges from 10 to 100 times less than shell and solid models, respectively. The CW provides a detailed physical description of the real structure since each component can be modelled with its material characteristics, that is, no homogenization techniques are required. Furthermore, although 1D models are exploited, the problem unknown variables can be placed on the physical surfaces of the real 3D model. No artificial surfaces or lines have to be defined to build the structural model. Global and local damages are introduced by decreasing the stiffness properties of the material in the damaged regions. The results show that the proposed 1D models can deal with damaged structures as accurately as a shell or a solid model, but with far lower computational costs. Furthermore, it is shown how the presence of damages can lead to shell-like modal shapes and torsional/bending coupling.

• 콘크리트학회지
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• 제9권2호
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• pp.133-144
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• 1997

2차원 응력상태의 철근콘크리트 부재해석을 위하여 소성이론과 파괴모델의 통합방법을 연구하였다. 콘크리트의 대별되는 두 가지 거동특성인 다차원 압축상태의 강도증가와 인장균열파괴를 동시에 나타내기 위하여, 압축파괴와 인장균열의 다중파괴기준을 사용하는 소성이론을 근간으로 여러 실험결과를 반영하는 파괴모델을 적용한다. 압축파괴기준으로서 Drucker-Prager모델과 von Mises 모델을 비교 사용하며 인장균열거동에 대하여 회전균열소성모델과 고정균열소성모델을 비교한다. 이러한 압축파괴기준과 이장균열파괴기준의 설정에는 다차원 압축상태의 강도증가, 균열로 인한 인장과 압축응력도의 저하, 보강철근의 영향등을 나타내는 실험식과 파괴에너지개념을 사용한다. 이 재료모델을 비선형유한요소해석에 사용하여 기존의 실험결과와 비교한다. 재료모델의 압축파괴와 인장균열거동을 검증하기 우하여 콘크리트의 압축파괴 또는 철근의 인장항복에 의하여 거동이 대별되는 실험들과 비교한다.

• Structural Engineering and Mechanics
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• 제6권7호
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• pp.727-746
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• 1998

Finite element models and numerical results are presented for bending and natural vibration using the unified third-order plate theory developed in Part 1 of this paper. The unified third-order theory contains the classical, first-order, and other third-order plate theories as special cases. Analytical solutions are developed using the Navier and L$\acute{e}$vy solution procedures (see Part 1 of the paper). Displacement finite element models of the unified third-order theory are developed herein. The finite element models are based on $C^0$ interpolation of the inplane displacements and rotation functions and $C^1$ interpolation of the transverse deflection. Numerical results of bending and natural vibration are presented to evaluate the accuracy of various plate theories.

• 한국정보시스템학회지:정보시스템연구
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• 제16권1호
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• pp.111-133
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• 2007

The purpose of this study is to present a new function point estimation approach for the Object-Oriented information systems. In order to fulfill this purpose, we first review the literature on Function Point Analysis of IFPUG, Unified Modeling Language, and Unified Process. Then, we derive a method and rules for estimating Function Points based on Use Cases and Class Diagrams. To analyze the appropriateness of the proposed approach, we conduct the empirical testing. 143 use cases are collected from production, marketing, distribution, sales, and other areas from the Object-Oriented systems development projects. We compare our new approach with the existing methods that are usually used for traditional systems development projects. The results show that our proposed approach is more appropriate for the Object-Oriented environment.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2003년도 춘계전력전자학술대회 논문집(1)
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• pp.251-255
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• 2003

This paper proposes a novel UPQC(unified power quality conditioner) based on H-bridge modules, isolated through single-phase multi-winding transformers. The dynamic performance of proposed system was analyzed by simulation with EMTDC/PSCAD, assuming that the UPQC is connected with the 22.9kV distribution line. The proposed system can be directly connected to the transmission line without series injection transformers. It has flexibility in expanding the operation voltage by increasing the number of H-bridge modules and can compensate reactive power, harmonics, voltage sag and swell, voltage unbalance. The control strategy for the proposing UPQC was derived using the instantaneous power method. The proposing UPQC has the ultimate capability of improving power quality at the point of installation on power distribution systems and can be utilized for the future distribution system.

• 전기학회논문지
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• 제56권4호
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• pp.716-723
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• 2007

This paper suggests of a 3-phase 3-wire unified active power filter. The system is composed of a series active power filter and a parallel active power filter. The proposed series active power filter compensating unbalance source voltage and current harmonics of the parallel active power filter improves power factor. The proposed algorithm which improves for power factor and harmonic reduction are calculated by the performance function, and which compensates for the unbalanced source voltage is calculated based on the symmetrical component analysis. We composed a combined system of the series active power filter and parallel active power filter to confirm a validity of the proposed control methods. The effectiveness of the proposed algorithm is confirmed by the experiments.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권7호
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• pp.1569-1584
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• 2013

Ubiquitous interaction in a pervasive environment is the main attribute of smart spaces. Pervasive systems are weaving themselves in our daily life, making it possible to collect user information invisibly, in an unobtrusive manner by known and even unknown parties. Huge number of interactions between users and pervasive devices necessitate a comprehensive trust model which unifies different trust factors like context, recommendation, and history to calculate the trust level of each party precisely. Trusted computing enables effective solutions to verify the trustworthiness of computing platforms. In this paper, we elaborate Unified Trust Model (UTM) which calculates entity's trustworthiness based on history, recommendation, context and platform integrity measurement, and formally use these factors in trustworthiness calculation. We evaluate UTM behaviour by simulating in different scenario experiments using a Trust and Reputation Models Simulator for Wireless Sensor Networks. We show that UTM offers responsive behaviour and can be used effectively in the low interaction environments.

• 한국콘텐츠학회:학술대회논문집
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• 한국콘텐츠학회 2007년도 추계 종합학술대회 논문집
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• pp.607-610
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• 2007

시스템 개발방법론은 소프트웨어 생성을 위한 개발 단계를 정의하고, 활동, 산출물, 검증 절차, 각 단계의 완결 조건을 명시하는 체계적인 방법으로 정의할 수 있다. 정보시스템의 대형화, 복잡화, 분산화 추세에 따라서 표준화된 개발방법론에 대한 관심이 국내에서도 급속히 증가하고 있다. 정보기술의 발전에 따른 신기술의 계속적인 수용과 사용자 요구사항의 변화의 수용, 시스템 개발의 생산성과 품질의 보증을 위해서는 개발방법론과 개발도구의 활용이 필수적이다. 최근 많은 관심을 보이고 있는 마르미(Magic and Robust Methodology Integrated)와 RUP(Rational Unified Process)을 비교 분석하고자 한다.

• Journal of Communications and Networks
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• 제12권1호
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• pp.1-4
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• 2010

As a countermeasure to simple power attack, the unified point addition codes for the elliptic curve cryptosystem were introduced. However, some authors proposed a different kind of power attacks to the codes. This power attack uses the observation that some internal operations in the codes behave differently for addition and doubling. In this paper, we propose a new countermeasure against such an attack. The basic idea of the new countermeasure is that, if one of the input points of the codes is transformed to an equivalent point over the underlying finite field, then the code will behave in the same manner for addition and doubling. The new countermeasure is highly efficient in that it only requires 27(n-1)/3 extra ordinary integer subtractions (in average) for the whole n-bit scalar multiplication. The timing analysis of the proposed countermeasure is also presented to confirm its SPA resistance.