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  • Title/Summary/Keyword: 모멘트방정식

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MLFMA for Computation of TM Scattering from Near Resonant Object (유사 공진형 물체에 대한 TM 전자파의 산란계산을 위한 MLFMA방법)

  • ;W. C. Chew
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.9 no.6
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    • pp.735-745
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    • 1998
  • The method of moments has been widely used in the analysis of TM scattering problems. Recently, significant advances in the development of fast and efficient techniques for solving large problems have been reported. In such methods, iterative matrix solvers are preferred by virtue of their speed and low memory requirements. But for near resonant and strong multiple scattering problems, e.g., involving an aircraft engine inlet, a large number of iterations is required for convergence. In this paper, an efficient approximate inverse based preconditioner is used to reduce this number of iterations. By using the matrix partitioning method, the computational is used to reduce this number of iterations. By using the matrix partitioning method, the computational cost for obtaining the approximate inverse is reduced to O(N). We apply this preconditioner to an O(NlogN) algorithm, the multilevel fast multipole algorithm, for the aircraft engine inlet problem. The numerical results show the efficiency of this preconditioner.

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Geometrical Non-linear Analyses of Tapered Variable-Arc-Length Beam subjected to Combined Load (조합하중을 받는 변단면 변화곡선 보의 기하 비선형 수치해석)

  • Lee, Byoung-Koo;Oh, Sang-Jin;Lee, Tae-Eun
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.25 no.2
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    • pp.129-138
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    • 2012
  • This paper deals with geometrical non-linear analyses of the tapered variable-arc-length beam, subjected to the combined load with an end moment and a point load. The beam is supported by a hinged end and a frictionless sliding support so that the axial length of the deformed beam can be increased by its load. Cross sections of the beam whose flexural rigidities are functionally varied with the axial coordinate. The simultaneous differential equations governing the elastica of such beam are derived on the basis of the Bernoulli-Euler beam theory. These differential equations are numerically solved by the iteration technique for obtaining the elastica of the deformed beam. For validating theories developed herein, laboratory scaled experiments are conducted.

Numerical Simulation of Turbulent Flow around 2-D Airfoils in Ground Effect (CFD에 의한 2차원 지면 효과익 주위의 난류유동계산)

  • H.H. Chun;R.H. Chang;M.S. Shin
    • Journal of the Society of Naval Architects of Korea
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    • v.39 no.3
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    • pp.28-40
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    • 2002
  • Turbulent flows around two-dimensional wing sections in ground effect are analysed by incompressible RANS equations and a finite difference method. The Baldwin-Lomax algebraic turbulence model is used to simulate high Reynolds number flows. The main purpose of this study is to clarify the two-dimensional ground effect and its flow characteristics due to different ground boundary conditions, i.e., moving and fixed bottom boundary. As a first step, to validate the present numerical code, the computational result of Clark-Y(t/C 11.7%) is compared with published numerical results and experimental data. Then, NACA4412 section in ground effect is calculated for various ground clearances with two bottom boundary conditions. According to the computational results, the difference in the lift and moment simulated with the two bottom boundary conditions is negligible, but the drag force simulated by the fixed bottom is to some extent smaller than that by the moving bottom. Therefore, it can be concluded that the drag force measured in a wind tunnel with the fixed bottom could be smaller than that with the moving bottom.

Slope Stability Analysis Considering Reinforcing Effects of Geosynthetics (토목섬유의 보강효과를 고려한 사면안정해석)

  • Kim, Kyeong-Mo;Kim, Hong-Tack;Lee, Hyung-Kyu
    • Journal of the Korean GEO-environmental Society
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    • v.6 no.1
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    • pp.73-82
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    • 2005
  • Generally, to evaluate a slope stability of the geosynthetic reinforced soil slope, the modified version of limit equilibrium method can be used. In most cases, resisting effects of reinforcement are dealt with considering an increased shear strength on the potential slip surface. However, it is not clear that the methods satisfy all three equilibrium equations. In this study, the new slope stability analysis method in which not only reinforcing effects of geosynthetics can be considered but also all three equilibrium equation can be satisfied is proposed. A number of illustrative examples, including published load test of large-scale reinforced retaining wall and centrifuge model tests on the geotextile reinforced soil slopes, are also analyzed. As a result, it is shown that the newly suggested method produces a relatively accurate factor of safety.

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Analysis on Forces Acting on the Contact Lens Fitted on the Cornea (콘택트 렌즈에 작용하는 힘의 해석)

  • Kim, Dae-Soo
    • Journal of Korean Ophthalmic Optics Society
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    • v.7 no.2
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    • pp.1-11
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    • 2002
  • A mathematical model is proposed to analyze the force; acting on the hard contact lens fitted on the cornea. The model incorporates the nonlinear equations and their numerical solution program, based on the formulations of surface tension force arising from the capillary action in the tear-film layer between the lens and cornea. The model simulates how the adhesion between lens and cornea varies according to the base curves and diameters of the lenses. When the spherical lens is fitted on the spherical cornea it is to rotate downward due to the weight of lens itself until it reaches an equilibrium position along the cornea where the counter(upward) moment caused by net force between the upper and lower portion of the periphery of lens. It is found that both the adhesion and displacement of lens along the cornea, where the gravity of lens balances the capillary-induced upward force, increases rapidly as the base curve of lens increases, i.e., as the lens gets flatter, while the increase in the diameter of lenses has resulted in the less increase in the rotation and adhesion. With the base curve and diameters of lenses being remained constant the increase in surface tension of tear film yields the increase in the adhesion between the cornea and lens while the initial rotation of lens is inversely proportional to the surface tension of the tear film.

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Probability Distribution of Nonlinear Random Wave Heights Using Maximum Entropy Method (최대 엔트로피 방법을 이용한 비선형 불규칙 파고의 확률분포함수)

  • 안경모
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.10 no.4
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    • pp.204-210
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    • 1998
  • This paper presents the development of the probability density function applicable for wave heights (peak-to-trough excursions) in finite water depth including shallow water depth. The probability distribution applicable to wave heights of a non-Gaussian random process is derived based on the concept of the maximum entropy method. When wave heights are limited by breaking wave heights (or water depth) and only first and second moments of wave heights are given, the probability density function developed is closed form and expressed in terms of wave parameters such as Hm(mean wave height), Hrms(root-mean-square wave height), Hb(breaking wave height). When higher than third moment of wave heights are given, it is necessary to solve the system of nonlinear integral equations numerically using Newton-Raphson method to obtain the parameters of probability density function which is maximizing the entropy function. The probability density function thusly derived agrees very well with the histogram of wave heights in finite water depth obtained during storm. The probability density function of wave heights developed using maximum entropy method appears to be useful in estimating extreme values and statistical properties of wave heights for the design of coastal structures.

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Numerical Analysis of Ship Motions and Wave Loads Including Momentum Slamming (모멘텀 슬래밍을 고려한 선체 운동 및 파랑하중 해석)

  • Hwang, Ji-Hee;Park, In-Kyu;Koo, Weon-Cheol
    • Journal of the Society of Naval Architects of Korea
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    • v.49 no.2
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    • pp.109-115
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    • 2012
  • Slamming phenomenon may occur when a ship navigates a high sea region, where the response of ship can be expected as elastic behaviour and the resultant wave loads may increase. In this paper, numerical analysis of ship motions and wave loads including momentum slamming was performed using the strip theory with regular waves. In order to analyze the effect of slamming force on the global ship motions, time histories of each mode of displacement and forces were simulated by using Newmark-beta time integration scheme. The added mass and damping coefficients calculated by Lewis form method were compared with the results of given references. For verification of numerical results, the motion RAOs of a S175 containership were calculated as an example of application and time histories of respective displacement and vertical bending moment were compared with the results of ITTC workshop benchmark test.

Theoretical Curve of Classical Site Attenuation for Forced Resonant Type EMI Dipole Antennas (강제 공진형 EMI 다이폴 안테나에 대한 시험장 감쇠량 이론 곡선)

  • Ju Chang-Hyun;Park Eun-Jung;Kim Ki-Chai
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.16 no.6 s.97
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    • pp.571-579
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    • 2005
  • This paper presents the classical site attenuation characteristics of a forced resonant electromagnetic interference (EMI) dipole antenna for frequencies below 80 MHz. The coupled integral equations for unknown current distribution are solved by the Galerkin's method of moments with piecewise sinusoidal functions. The results show that the forced resonant type EMI dipole antenna for frequencies below 80 MHz can be used effectively for measuring the classical site attenuation of horizontal polarization. The theoretical site attenuation curves presented can be used as reference curves for evaluating the performance of an open area test site.

Efficient Analysis of Couplings through Periodically Arranged Slots in a Radial Line Slot Antenna (RLSA 설계를 위한 주기적으로 배열된 슬롯을 통한 결합의 효율적인 해석)

  • 이중원;김용훈;박종국;남상욱
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.12 no.6
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    • pp.931-939
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    • 2001
  • The slot coupling characteristics was analysed in a radial-line slot antenna for its design. The previously proposed waveguide model with a periodic boundary condition on its narrow walls and periodically arranged slots on its wide wall was used. The magnetic field integral equation and two dyadic Green\`s functions for respective regions was derived and the method of moments was used. To maximize the efficiency of numerical analysis and to extract singularities, two different kinds of basis functions, the entire domain basis function and the sub-domain one, are used. In addition, the Ewald sum technique for the rectangular waveguide and the Shanks transform for the half space were used to accelerate the computation of the slowly convergent potential Green\`s functions. Simulation results expressed the effects of the various design parameters on the slot coupling.

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Penetrated Electric Fields and Resonant Frequencies inside Metallic Enclosure with Aperture Exited by an External Dipole Source (개구를 갖는 함체의 외부 다이폴 파원에 의한 침투전계와 공진 주파수 특성)

  • 황보승;김기채
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.12 no.6
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    • pp.939-947
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    • 2001
  • This paper presents the penetrated electric fields and resonant frequencies inside a metallic enclosure with aperture excited by an external dipole source. In the theoretical analysis, integral equations for the current distribution and electric field distributions on the aperture are solved by applying Galerkin\`s method of moments. The results show that the electric fields inside metallic enclosure is maximum at the near the aperture and resonant frequencies are the same as calculated of the enclosure without aperture. To verify the theoretical analysis the electric field inside enclosure and resonant frequencies are compared with the experimental results.

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