• International Journal of Aeronautical and Space Sciences
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• 제4권2호
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• pp.17-25
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• 2003

Simple methods are developed to predict temperatures of a satellite box during launch stage. The box is mounted on outer surface of satellite and directly exposed to space thermal environment for the time period from fairing jettison to separation. These simple methods are to solve a 1st order ordinary differential equation (ODE) which is simplified from the governing equation after applying several assumptions. The existence of analytical solution for the 1st order ODE is determined depending on treatment of time-dependent molecular heating term. Even for the case that the analytical solution is not available due to the time dependent term, the 1st order ODE can be solved by relatively simple numerical techniques. The temperature difference between two different approaches (analytical and numerical solutions) is relatively small (Jess than $1^{\circ}C$ along the time line) when they are applied to STSAT-I launch scenario. The present methods can be generally used as tools to quickly check whether a satellite box is safe against space environment during the launch stage for the case that the detailed thermal analysis is not available.

• Structural Engineering and Mechanics
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• 제54권4호
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• pp.607-622
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• 2015

This paper presents a comparative study of analytical method and finite element method (FEM) for analysis of a continuous contact problem. The problem consists of two elastic layers loaded by means of a rigid circular punch and resting on semi-infinite plane. It is assumed that all surfaces are frictionless and only compressive normal tractions can be transmitted through the contact areas. Firstly, analytical solution of the problem is obtained by using theory of elasticity and integral transform techniques. Then, finite element model of the problem is constituted using ANSYS software and the two dimensional analysis of the problem is carried out. The contact stresses under rigid circular punch, the contact areas, normal stresses along the axis of symmetry are obtained for both solutions. The results show that contact stresses and the normal stresses obtained from finite element method (FEM) provide boundary conditions of the problem as well as analytical results. Also, the contact areas obtained from finite element method are very close to results obtained from analytical method; disagree by 0.03-1.61%. Finally, it can be said that there is a good agreement between two methods.

• Geomechanics and Engineering
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• 제13권6호
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• pp.1027-1044
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• 2017

Membrane penetration is the most important factor influencing the measurement of volume change for triaxial consolidated-drained shear test for coarse-grained soil. The effective pressure p, average particle size $d_{50}$, thickness $t_m$ and elastic modulus $E_m$ of membrane, contact area between membrane and soil $A_m$ as well as the initial void ratio e are the major factors influencing membrane penetration. According to the membrane deformation model given by Kramer and Sivaneswaran, an analytical solution of the membrane penetration considering the initial void ratio is deduced using the energy conservation law. The basic equations from theory of plates and shells and the elastic mechanics are employed during the derivation. To verify the presented solution, isotropic consolidation tests of a coarse-grained soil are performed by using the method of embedding different diameter of iron rods in the triaxial samples, and volume changes due to membrane penetration are obtained. The predictions from presented solution and previous analytical solutions are compared with the test results. It is found that the prediction from presented analytical solution agrees well with the test results.

• 인터넷정보학회논문지
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• 제15권3호
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• pp.91-100
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• 2014

IT 보안의 중요성으로 인해 IT 보안 솔루션의 성능 및 기업의 보안에 대한 투자는 꾸준히 증가하고 있지만, 보안 사고 발생으로 인한 기업의 금전적 손실 감소는 여전히 기대에 미치지 못하고 있는 상황이다. 보안 솔루션을 운영하고 있는 기업을 상대로 한 조사 결과에 따르면, 기업의 보안 솔루션에 대한 이해 부족과 잘못된 투자 전략이 기업의 투자 대비 보안 효율성 향상을 기대에 미치지 못하게 하는 주요한 원인으로 분석되었다. 본 논문에서는 기업의 보안 솔루션에 대한 잘못된 투자로 인한 투자 대비 보안 효율성 저하 문제를 해결하기 위한 보안 투자 결정 모델을 제안한다. 구체적으로는, IT 자산의 취약성 이용 공격으로 인한 조직의 피해 발생 이전에 보안 사고 예방이 가능한 사전 보안 솔루션(Proactive Security Solutions, PSSs)과 조직의 피해 발생 이후에 보안 사고를 조사 및 분석할 수 있는 사후 보안 솔루션 (Reactive Security Solutions, PSSs)에 대한 기업의 투자 방법론을 결정하기 위한 포괄적인 수학적 모델을 제안한다. 또한, 제안된 분석 모델을 사용하여 보안 솔루션의 다양한 매개 변수 영향력 아래에서 조직의 IT 보안 투자 예상 순 이익(expected net benefit)을 극대화하기 위한 최적의 방안을 모색한다.

• 물과 미래
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• 제28권6호
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• pp.159-168
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• 1995

본 논문에서는 2차원 경계요소법 수치모형을 이용하여 급경사에서 고립파의 처오름과 진행과정을 연구하였다. 먼저 수치모형을 상대적으로 완만한 경사에 적용하여 처오름 높이를 산정하여 기존의 수리모형실험의 결과, 수치해 및 해석해 등과 비교하여 수치모형의 정확도를 검증하였다. 경계요소법에 의한 수치해는 전체적으로 기존의 자료 등과 잘 일치하였다. 다음에 수치모형을 급경사 지형에 적용하여 처오름 높이를 산정한다. 경계요소법은 완경사 뿐만 아니라 급경사에서도 고립파의 최대 처오름 높이 산정에 매우 효율적이며, 경계요소법에 의한 결과는 인공수로의 제방 또는 방파제의 설계에 이용될 수 있을 것이다. 마지막으로, 급경사에서의 고립파의 파고를 계산하여 Green의 법칙에 의한 결과와 비교하였다.

• 대한토목학회논문집
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• 제40권6호
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• pp.555-561
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• 2020

본 연구에서는 상, 하부 2개의 대수층이 연결된 누수대수층에 대해 상부 1층 지하수 양수로 인한 하천수 감소량을 산정하기 위해 개발된 Hunt 해석해의 적용성을 평가하였다. 두 대수층의 투수량계수 및 저류계수, 층간 누수계수, 하천-관정 이격거리, 하상의 수리전도도, 하폭 등 다양한 수리특성치 크기 조합에 따라 양수 후 5년 평균 하천수 감소량을 해석해로 산정하고, 범용적으로 사용되고 있는 MODFLOW 지하수유동모형으로 정교하게 모의된 수치해와의 비교를 통해 하폭을 점으로 간주하여 유도한 해석해 적용 결과가 정확한지를 평가하였다. 그 결과 하천-관정 이격거리가 하폭 이상되거나, 하천고갈인자(Stream Depletion Factor)가 약 3,000일 이어야 해석해로 산정한 하천수 감소비의 오차를 0.05 아래로 줄일 수 있는 것으로 분석되었다. 또한 하상수리전도성이 1 m/d 보다 작거나, 하부대수층의 수리확산계수가 100 ㎡/d 보다 작거나, 상부와 하부대수층의 수리확산계수비가 5 이상, 층간 누수계수가 0.0004 m/d 보다 작을 때 해석해가 수치해에 비해 전반적으로 과다하게 산정되는 것으로 분석되었다.

• Ocean Systems Engineering
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• 제4권4호
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• pp.293-308
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• 2014

Unlike the traditional displacement type vessels, the high speed planing crafts are supported by the lift forces which are highly non-linear. This non-linear phenomenon causes their motions in an irregular seaway to be non-Gaussian. In general, it may not be possible to express the probability distribution of such processes by an analytical formula. Also the process might not be stationary or ergodic in which case the statistical behavior of the motion to be constantly changing with time. Therefore the extreme values of such a process can no longer be calculated using the analytical formulae applicable to Gaussian processes. Since closed form analytical solutions do not exist, recourse is taken to fitting a distribution to the data and estimating the statistical properties of the process from this fitted probability distribution. The peaks over threshold analysis and fitting of the Generalized Pareto Distribution are explored in this paper as an alternative to Weibull, Generalized Gamma and Rayleigh distributions in predicting the short term extreme value of a random process.

• Journal of applied mathematics & informatics
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• 제31권1_2호
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• pp.165-177
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• 2013

In this paper, we apply Homotopy perturbation transform method (HPTM) for solving singular fourth order parabolic partial differential equations with variable coefficients. This method is the combination of the Laplace transform method and Homotopy perturbation method. The nonlinear terms can be easily handled by the use of He's polynomials. The aim of using the Laplace transform is to overcome the deficiency that is mainly caused by unsatisfied conditions in other semi-analytical methods such as Homotopy perturbation method (HPM), Variational iteration method (VIM) and Adomain Decomposition method (ADM). The proposed scheme finds the solutions without any discretization or restrictive assumptions and avoids the round-off errors. The comparison shows a precise agreement between the results and introduces this method as an applicable one which it needs fewer computations and is much easier and more convenient than others, so it can be widely used in engineering too.

• Structural Engineering and Mechanics
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• 제48권4호
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• pp.519-545
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• 2013

An outline of the Timoshenko beam theory is presented. Two differential equations of motion in terms of deflection and rotation are comprised into single equation with deflection and analytical solutions of natural vibrations for different boundary conditions are given. Double frequency phenomenon for simply supported beam is investigated. The Timoshenko beam theory is modified by decomposition of total deflection into pure bending deflection and shear deflection, and total rotation into bending rotation and axial shear angle. The governing equations are condensed into two independent equations of motion, one for flexural and another for axial shear vibrations. Flexural vibrations of a simply supported, clamped and free beam are analysed by both theories and the same natural frequencies are obtained. That fact is proved in an analytical way. Axial shear vibrations are analogous to stretching vibrations on an axial elastic support, resulting in an additional response spectrum, as a novelty. Relationship between parameters in beam response functions of all type of vibrations is analysed.

• Journal of Information Processing Systems
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• 제14권2호
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• pp.455-468
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• 2018

The concepts of graph theory are applied to model and analyze dynamics of computer networks, biochemical networks and, semantics of social networks. The analysis of dynamics of complex networks is important in order to determine the stability and performance of networked systems. The analysis of non-stationary and nonlinear complex networks requires the applications of ordinary differential equations (ODE). However, the process of resolving input excitation to the dynamic non-stationary networks is difficult without involving external functions. This paper proposes an analytical formulation for generating solutions of nonlinear network ODE systems with functional decomposition. Furthermore, the input excitations are analytically resolved in linearized dynamic networks. The stability condition of dynamic networks is determined. The proposed analytical framework is generalized in nature and does not require any domain or range constraints.