• Convergence Security Journal
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• v.18 no.2
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• pp.41-47
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• 2018

Theorists of war have often used Clausewitz's trinity theory as a framework for analyzing war strategies and histories. Heretofore, studies on cyber warfare have focused primarily on laws, policies, structuring organizations, manpower, and training pertaining to preparing the cyberspace for war. Currently, studies highlighting the comparative characteristics of war in cyberspace, how it differs from conventional warfare, and analytical frameworks for understanding war in cyberspace are rare. Using Clausewitz's trinity theory, this paper interprets the essence of war from the perspectives of (1) Intellect, (2) Bravery, and (3) Passion, to propose an analytical model for understanding war in cyberspace, one that factors in the intrinsic qualities and characteristics of cyberspace under spatial and temporal constraints. Furthermore, this paper applies the aforementioned analytical model to the Iraq War and concludes with a theoretical illustration that cyber warfare played a significant role in winning the war.

• Journal of the Korea Concrete Institute
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• v.14 no.3
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• pp.382-391
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• 2002

This study is devoted to the problems of thermal and shrinkage stresses in order to avoid cracking at early ages. The early-age damage induced by volume change has great influence on the long-term structural performance of the concrete structures such as its durability and serviceability To solve this complex problem, the computer programs for analysis of thermal and shrinkage stresses were developed. In these procedures, numerous material models are needed and the realistic numerical models have been developed and validated by comparison with relevant experimental results in order to solve practical problems. A framework has been established for formulation of material models and analysis with 3-D finite element method. After the analysis of the temperature, moisture and degree of hydration field in hardening concrete structure, the stress development is determined by incremental structural formulation derived from the principle of virtual work. In this study, the stress development is related to thermal and shrinkage deformation, and resulting stress relaxation due to the effect of early-age creep. From the experimental and numerical results it is found that the early-age creep p)ays important role in evaluating the accurate stress state. The developed analysis program can be efficiently utilized as a useful tool to evaluate the thermal and shrinkage stresses and to find measures for avoiding detrimental cracking of concrete structures at early ages.

• Tunnel and Underground Space
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• v.32 no.5
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• pp.312-326
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• 2022

The generalized Hoek-Brown (GHB) criterion, which is recognized as one of the standard failure conditions for rock mass, is specialized for rock engineering applications and covers a wide range of rock mass conditions. Accordingly, many research efforts have been devoted to the incorporation of this criterion into the stability analysis of rock structures. In this study, the slip-line analysis method, which is a kind of elastoplastic analysis method, is combined with the GHB failure criterion to derive analytical equations that can easily calculate the plastic radius and stress distribution in the vicinity of the circular tunnel. In the process of derivation of related formulas, it is assumed that the behavior of rock mass after failure is perfectly plastic and the in-situ stress condition is hydrostatic. In the formulation, it is revealed that the plastic radius can be calculated analytically using the two respective tangential friction angles corresponding to the stress conditions at tunnel wall and elastic-plastic boundary. It is also shown that the plastic radius and stress distribution calculated using the derived analytical equations coincide with the results of Lee & Pietruszczak's numerical method published in 2008. In the latter part of this paper, the influence of the quality of the rock mass on the size of the plastic zone, the stress distribution, and the change of the tangential friction angle was investigated using the derived analytical equations.

• Journal of the Korean GEO-environmental Society
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• v.24 no.1
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• pp.5-14
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• 2023

In this study, the load transfer characteristics of the base and skin of drilled shafts were analyzed and the load sharing ratio was calculated by performing a load transfer large-scale model test and three-dimensional numerical analysis considering the similarity of drilled shafts, which is the design target. From the linear behavior of drilled shafts shown in the large-scale model test and 3D numerical analysis results, the skin load transition curve for the design conditions of this study was proposed by Baquelin et al., and the base load transition curve was proposed by Baquelin et al. For the horizontal load transition curve, the formula proposed by Reese et al. was confirmed to be appropriate. The test value was slightly larger than the numerical analysis value for the axial load at the rock socketing, but the load sharing ratio at the rock socketing increased, on average, about 27.8% as the vertical load increased. The analysis value of the vertical settlement of the pile head under the vertical load was evaluated to be slightly smaller than the test value, and the maximum vertical settlement of the pile head in the model test and analysis maximum vertical load was 10.6 mm in the test value and 10.0 mm in the analysis value, and the maximum vertical settlement value at the base of the pile was found to be a test value of 2.0 mm and an analysis value of 1.9 mm. The horizontal displacement at the head of the column (ground surface) and the head of the pile during the horizontal load was found to agree relatively well with the test value and the analysis value. As a result of the model soil test, the horizontal load measured at the maximum horizontal displacement of 38.0 mm was evaluated to be 24,713 kN, and the horizontal load in the numerical analysis was evaluated to be 26,073 kN.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.39 no.2
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• pp.317-325
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• 2019

A suction caisson has been widely used for anchor and foundation of offshore structures due to its broad application, simple installation, and rapid construction. In design of suction caisson foundation, the bearing capacity and the stability of soil are mainly dealt with and analysis methods for them are presented in design codes related to the foundation. On the other hand, the method for structural safety analysis of the suction caisson is not generalized, in particular for load modeling of the caisson under suction. Consequently, there are difficulties in design of the caisson cross section. For this reason, this study analyzed the magnitude and distribution of pore water pressure on inner and outer surface of the caisson using theoretical and numerical seepage analyse, and an approach to reasonably estimate the load applied to the structural analysis of the caisson was presented. Furthermore, effects of penetration depth, anisotropy of permeability, and suction pressure on the pore water pressure were analyzed.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.389-389
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• 2021

불투수면의 증가는 유량변화 및 지하수위와 기저유출의 감소로 이어질 수 있으며 기저유량의 감소는 건기 시 하천의 유량공급까지 영향을 줄 수 있다. 이런 이유로 기저유량에 대한 정확한 분석 및 검증은 반드시 필요하지만 지표수-지하수를 고려한 통합적 해석의 어려움과 기저유출 분석에 대한 불확실성 및 기술적 한계로 분석이 어려운 실정이다. 따라서 본 연구에서는 SWAT 해석을 통해 획득한 모의유량과 관측유량을 비교하여 R²값을 계산하였으며 SWAT-CUP을 이용하여 검보정을 실시한 후 기저유출량을 정량적으로 산정하고 비교하였다. 연구지역 모의기간은 실측 유량자료가 있는 4개년을 대상으로 모의 하였으며 SWAT-CUP을 이용한 검보정 시 모의 횟수는 연구자에 따라 다양한 기준을 제시하고 있지만 모의 시간 대비 최대 효율인 1,000회 수행하였다. 또한 관측유량에 대하여 SPE(Swat Parameter Estimator) 알고리즘으로 모의유량을 최적화하였다. 실측유량과 모의유량을 비교한 결과 SWAT 분석에 의한 R²값보다 SWAT-CUP을 이용하여 검보정을 수행한 R²값이 높게 나타나 검보정 효과를 확인하였다. 또한 검보정 전후에 대한 기저유량을 비교하기 위하여 SWAT Output Data를 이용하여 유역에 대한 지표수유출, 중간유출, 지하수유출 등을 추출하였다. 추출한 단위면적당 데이터를 단위환산을 통해 유출량으로 산정하였으며 검보전 전과 데이터를 비교하였다. 지표수-지하수를 고려한 통합적 해석의 어려움과 실측치의 부족, 분석에 대한 불확실성 등으로 기저유량에 대한 해석은 어렵지만 SWAT-CUP을 이용하여 검보정 및 불확실성 개선이 수행되면 좀더 정확한 유량을 계산할 수 있으며 이는 향후 연구지역 지표수-지하수 연계해석을 위한 기초자료로 활용될 수 있을 것으로 판단된다.

• Journal of Biosystems Engineering
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• v.10 no.1
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• pp.24-38
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• 1985

경사진 밀폐 공간에서 마주 보는 두 벽면의 온도 차로 인하여 발생되는 자연 대류 현상은 여러 공학 분야에서 볼 수 있는 중요한 열전달 현상으로서, 최근 들어 평판형 태양열 집열기를 설계하려는 사람들에게 많은 관심의 대상이 되고 있다. 평판형 태양열 집열기의 경우 덮개판으로 부터의 대류 열손실을 감소시킴으로서 집열 효율을 높일 수 있을 뿐만 아니라 사용목적에 따라 소형 집열기를 제작할 수 있어 경제적으로 유리하게 될 것이다. 밀폐된 공간에서 최초에 정지 상태에 있는 얇은 유체층을 하부에서 가열시켜 주면 열팽창 현상이 일어나고, 이것에 의한 부력이 점도나 열전도도 등의 안정화 요인을 극복할 수 있을 정도로 커지면 System이 불안정하게 되어 자연 대류 현상이 수반되며 이 때문에 열전달율이 급격히 증가하게 된다. 이러한 현상의 지배 방정식은 연립 비선형 편미분 방정식으로 특수한 경계 조건외에는 일반적으로 해석적 해를 구하기가 어렵기 때문에 실험적 연구가 많이 실시되어 왔고 이들 결과의 대부분은 전반적인 열전달 특성치만을 구하는데 집중되어 왔다. 본 연구에서는 수치 해석법의 하나인 유한 차분법을 도입하여 이차원으로 가정한 경사진 평판형 밀폐 공간에서의 자연 대류 현상의 지배 방정식을 유한 차분화시켜, $$2.74{\times}10^3\leq_-Gr\leq_-2.0{\times}10^6$$, Pr=0.73, $$15^{\circ}\leq_-a\leq_-150^{\circ}$$, 종횡비는 1, 2, 3, 5, 9에 대하여 정상 상태에서의 해를 구하면서 수치적으로 실험하였다. 본 연구에서 얻어진 결론을 요약하면 다음과 같다. (1) 해석적으로 구하기 어려운 경사진 밀폐 공간에서 자연대류현상의 지배 방정식을 유한 차분법으로 해결할 수 있으며, 대류항과 확산항을 따로 고려한 유한차분법이 효과적임을 확인하였다. (2) 저온과 고온 벽면에서의 온도를 각각 균일하게 놓고 단변으로 이루어진 벽면은 완전히 절연되어 있는 경우에 대하여 수치해를 구한결과, 이전의 해석적 및 실험적 결과와 일치하였으며, 시간의 경과에 따른 온도 및 유선의 변화를 현상학적으로 관찰할 수 있었다. (3) 평균 열전달 계수에 미치는 경사각의 효과를 살펴본 결과 종횡비가 1 인 경우 경사각이 $45^{\circ}$에서, 종횡비가 2, 3, 5, 9인 경우 경사각이 $60^{\circ}$에서 각각 평균 열전달 계수 최대치가 나타났다. (4) Ra수(Rayleigh number) 가 증가될수록, 경사각에 상관없이 평균 열전달 계수도 증가되었다. 한편 Ra수 및 경사각의 변화에 따라 종횡비가 증가될수록 평균 열전달 계수는 경사각이 $90^{\circ}$인 경우를 제외하고는 감소됨을 볼 수 있었다. 경사각이 $90^{\circ}$인 경우, 평균 열전달 계수는 종횡비가 2 인 곳에서 최대치를 얻을 수 있었으며, 종횡비가 계속 증가될수록 평균 열전달 계수는 점차 감소되어짐을 볼 수 있었다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.6
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• pp.349-357
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• 2019

Finite element method (FEM) is utilized in the development of products to realistically analyze and predict the mechanical behavior of materials in various fields. However, the approach based on the numerical analysis of glass fiber reinforced plastic (GFRP) composites, for which the fiber orientation and strain rate affect the mechanical properties, has proven to be challenging. The purpose of this study is to define and evaluate the mechanical properties of glass fiber reinforced plastic composites using the numerical analysis models of Digimat, a linear, nonlinear multi-scale modeling program for various composite materials such as polymers, rubber, metal, etc. In addition, the aim is to predict the behavior of realistic polymeric composites. In this regard, the tensile properties according to the fiber orientation and strain rate of polybutylene terephthalate (PBT) with short fiber weight fractions of 30wt% among various polymers were investigated using references. Information on the fiber orientation was calculated based on injection analysis using Moldflow software, and was utilized in the finite element model for tensile specimens via a mapping process. LS-Dyna, an explicit commercial finite element code, was used for coupled analysis using Digimat to study the tensile properties of composites according to the fiber orientation and strain rate of glass fibers. In addition, the drawbacks and advantages of LS-DYNA's various anisotropic material models were compared and evaluated for the analysis of glass fiber reinforced plastic composites.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.2
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• pp.620-626
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• 2016

Estimating the nonlinear seismic response of structure in earthquake engineering is important. Nonlinear static analysis is a typical method, and a variety of methods and techniques for estimating the stiffness of structural system at a certain analysis stage have been introduced and used in numerical structural analysis. On the other hand, such methods have many difficulties in practical usage because they use time-consuming iterative methods or simplified algorithms for calculating the structural stiffness at specific points in the time of nonlinear static analysis. For this reason, this study suggests an accurate and effective method for estimating the stiffness of a structure in nonlinear static analysis. For this goal, existing theories of an incremental step-by-step solution was investigated first. Subsequently, an algorithm available for calculating the precise stiffness of a structural system, each element of which has a bilinear material model, was developed based on the investigated methods. Finally, a computer program, sNs, was developed with the algorithm used.

• Journal of the Korean Recycled Construction Resources Institute
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• v.3 no.4
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• pp.301-306
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• 2015

For the purpose of developing high performance marine concrete with improved crack resistance and durability, this analytical study aimed to estimate strength, hydration heat characteristics, and chloride attack resistance of concrete with mineral admixture. Ground granulated furnace slag and fly ash were considered for mineral admixture. The replacement of ground granulated furnace slag and fly ash considered in the analysis was in the range of 0~70% and 0~40 %, respectively. The analysis results indicated that both ground granulated furnace slag and fly ash decreased compressive strength, and the effect of adding ground granulated furnace slag on mitigation of hydration heat was limited whereas fly ash had an noticeable influence on it. It was also found that the replacement with ground granulated furnace slag enhanced the chloride attack resistance but fly ash deteriorated the resistance. From the analytical studies, It could be expected that a ternary blended cement composition with proper amount of ground granulated furnace slag and fly ash might be effective to control crack resistance as well as chloride attack resistance of marine concrete.