• Structural Engineering and Mechanics
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• 제1권1호
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• pp.103-118
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• 1993

The near field is discretized into finite elements, and the far field into infinite elements. Closed form far-field solutions to three fundamental problems are used as the shape functions of the infinite elements. Such infinite elements are capable of transmitting all surface and body waves. An efficient scheme to integrate numerically the stiffness and mass matrices of these elements in presented. Results agree closely with those obtained by others.

• 전자공학회논문지A
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• 제32A권10호
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• pp.19-24
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• 1995

The majority of problems to which FDTD is being applied involve open structure which require the appropriate scheme to terminate the computational domain. In particular, for the propagation problem of the outgoing waves, a certain type of boundary condition needs to be applied on outer boundaries of the computational domain to generate no reflected waves. In this paper, a new simple technique is presented, which allows the reduced computation time and excellent absorbing characteristics for normal and oblique incident waves on outer boundaries. To illustrate the validity of this method, a numerical calculation for monopole antenna is carried out and the results are compared to measured data. The time-domain properties for circular patch antennas are investicated.

• International Journal of Naval Architecture and Ocean Engineering
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• 제3권1호
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• pp.105-110
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• 2011

Some research work on CFD computation of ship motions and added resistance in waves for a high speed trimaran is carried out in this paper. The governing equations, Reynolds Averaged Navier-Stokes and continuity equations are discretized by finite volume method. Volume of fluid method is adopted to deal with the nonlinear free surface. The incident waves are generated from the inflow boundary by prescribing a velocity profile resembling flexible flap wavemaker motions, and the outgoing waves are dissipated inside an artificial damping zone located at the rear part of the wave tank. In this paper, the computed results of ship motion and added resistance for a high speed trimaran are presented. The results of seakeeping experiment for the high speed trimaran carried out in CSSRC towing tank are also presented in this paper. Rather good agreements are shown between the computational and experimental results. The work in this paper provides a numerical tool for the study of seakeeping performance of high speed trimarans.

• 한국해양공학회지
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• 제23권3호
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• pp.6-13
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• 2009

Based on the boundary element method, the motion responses and transmission coefficients of a moored floating breakwater were investigated in oblique waves. To satisfy the outgoing radiation condition in the far field, the fluid domain was divided into inner and outer regions. The complete solution could be obtained by applying the matching conditions between the eigenfunction-based outer solution and BEM-based inner solution. Using the developed predictive tools, the wave exciting forces, added mass, damping coefficients, motion responses, and transmission coefficients were assessed for various combinations of breakwater configuration, wave heading, mooring cables properties, and wave characteristics. It was found that the transmission coefficient for a moored floating breakwater was closely dependent on the motion responses, which were greatly amplified at the resonant frequencies.

• Coupled systems mechanics
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• 제5권4호
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• pp.371-393
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• 2016

We propose a heat jet approach for a two-dimensional square lattice with nearest neighbouring harmonic interaction. First, we design a two-way matching boundary condition that linearly relates the displacement and velocity at atoms near the boundary, and a suitable input in terms of given incoming wave modes. Then a phonon representation for finite temperature lattice motion is adopted. The proposed approach is simple and compact. Numerical tests validate the effectiveness of the boundary condition in reflection suppression for outgoing waves. It maintains target temperature for the lattice, with expected kinetic energy distribution and heat flux. Moreover, its linear nature facilitates reliable finite temperature atomic simulations with a correct description for non-thermal motions.

• 대기
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• 제30권1호
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• pp.1-15
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• 2020

This study analyzed and compared development mechanisms leading to heat waves of 2016 and 2018 in Korea. The European Centre for Medium-Range Weather Forecasts Reanalysis Interim (ERA Interim) dataset and Automated Surface Observing System data are used for synoptic scale analysis. The synoptic conditions are investigated using geopotential height, temperature, equivalent potential temperature, thickness, potential vorticity, omega, outgoing longwave radiation, and blocking index, etc. Heat waves in South Korea occur in relation to Western North Pacific Subtropical High (WNPSH) pressure system which moves northwestward to East Asia during summer season. Especially in 2018, WNPSH intensified due to strong large-scale circulation associated with convective activities in the Philippine Sea, and moved farther north to Korea when compared to 2016. In addition, the Tibetan high near the tropopause settled over Northern China on top of WNPSH creating a very strong anticyclonic structure in the upper-level over the Korean Peninsula. Unlike 2018, WNPSH was weaker and centered over the East China Sea in 2016. Analysis of blocking indices show wide blocking phenomena over the North Pacific and the Eurasian continent during heat wave event in both years. The strong upper-level ridge which was positioned zonally near 60°N, made the WNPSH over the South Korea stagnant in both years. Analysis of heat wave intensity (HWI) and duration (HWD) show that HWI and HWD in 2018 was both strong leading to extreme high temperatures. In 2016 however, HWI was relatively weak compared to HWD. The longevity of HWD is attributed to atmosphere blocking in the surrounding Eurasian continent.

• 한국지진공학회논문집
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• 제19권1호
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• pp.37-43
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• 2015

This paper presents a detailed procedure for a nonlinear soil-structure interaction of a seismically isolated NPP(Nuclear Power Plant) structure using the boundary reaction method (BRM). The BRM offers a two-step method as follows: (1) the calculation of boundary reaction forces in the frequency domain on an interface of linear and nonlinear regions, (2) solving the wave radiation problem subjected to the boundary reaction forces in the time domain. For the purpose of calculating the boundary reaction forces at the base of the isolator, the KIESSI-3D program is employed in this study to solve soil-foundation interaction problem subjected to vertically incident seismic waves. Wave radiation analysis is also employed, in which the nonlinear structure and the linear soil region are modeled by finite elements and energy absorbing elements on the outer model boundary using a general purpose nonlinear FE program. In this study, the MIDAS/Civil program is employed for modeling the wave radiation problem. In order to absorb the outgoing elastic waves to the unbounded soil region, spring and viscous-damper elements are used at the outer FE boundary. The BRM technique utilizing KIESSI-3D and MIDAS/Civil programs is verified using a linear soil-structure analysis problem. Finally the method is applied to nonlinear seismic analysis of a base-isolated NPP structure. The results show that BRM can effectively be applied to nonlinear soil-structure interaction problems.

• 한국군사과학기술학회지
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• 제27권1호
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• pp.15-23
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• 2024

In order to avoid the high observability due to the cavity resonance or electromagnetic wave leakages from the bridge of a battleship or the cockpit of an aircraft, this paper presents a transparent conductive oxide coated structure to prevent the incoming/outgoing electromagnetic waves. Currently, most of the RCS reduction technologies were focused on radar absorbing material such as paints based on conductive or magnetic materials in the fuselage, and there is not much research on countermeasures for achieving the low observability of materials that required optical transparency in actual weapon systems. In this study, the transmission/reflection and absorption performance of the ITO coated structure according to the change of the surface resistance of the transparent conductor were analyzed. Finally, the relationship between the electromagnetic and optical characteristics was established through fabrication and measurement.

• 한국해양학회지:바다
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• 제3권1호
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• pp.9-15
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• 1998

기상청에서는 1996년 7월부터 1997년 2월까지 목포앞바다의 칠발도 인접 해역에 1시간 간격으로 해양기상을 관측할 수 있는 부이를 설치하고 자료를 얻었다. 이 자료로부터 이 해역의 1일 평균 해양-대기 열교환량을 산출하고, 해양기상 상태의 특성을 조사하였다. 현열속의 경우, 7월에 최소(평균 -5.5 $Wm^{-2}$)이고, 1월에 최대(평균 12.6 $Wm^{-2}$)를 나타내고 있는데 이는 여름철에 대기가 해양으로 열을 공급하고 겨울철에는 반대로 해양에서 대기로 열을 공급하지만 그 크기는 여름철이 겨울철에 비해 작다는 것을 의미한다. 잠열속의 경우 7월에 최소(평균 -4.6 $Wm^{-2}$)를 보이고, 최대값은 11월에 월 평균 86.5 $Wm^{-2}$이고 10월에 일평균 최대값이 250$Wm^{-2}$까지 나타났다. 잠열 속은 대기가 건조해지고 바람이 강해지는 가을철에 최대가 나타나서 겨울철까지 지속된다. 파랑분석에 의하면 바람이 강한 겨울철이 여름철에 비해 높은 파의 출현율이 많았다 파주기는 4~6초의 출현율이 가장 많았고, 파향은 계절풍의 영향으로 겨울에는 북 또는 북동방향에서 유입되는 파가 우세하고, 여름에는 남, 남서 또는 서쪽에서 유입되는 파가 비교적 자주 출현하였다.

• 한국전산구조공학회논문집
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• 제27권2호
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• pp.95-102
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• 2014

이 논문에서는 경계반력법을 이용한 비선형 지반-구조물 상호작용 해석을 위해 LS-DYNA나 MIDAS/Civil 등의 유한요소해석 프로그램과 연계하는 방법을 제시하였다. 경계반력법 적용시 유한요소프로그램에서 구조물과 지반은 선형 또는 비선형 유한요소를 이용하여 모델링하였다. 유한요소의 해석모델 외부의 무한영역으로 전달되는 탄성파를 최대한 흡수하기위해 유한요소 모델의 외측에 LS-DYNA의 경우에는 PML(Perfectly Matched Layer) 요소를, MIDAS/Civil의 경우에는 점성감쇠-스프링 요소를 적용하였다. 비선형 유한요소는 구조물영역에만 적용되는 것으로 가정하였다. 이 연구에서는 입사지진파에 의한 경계반력은 KIESSI-3D 프로그램을 이용하여 계산하였다. 선형 지반-구조물 상호작용 문제에 대해 일반적인 KIESSI-3D의 해석결과와 BRM해석결과를 비교하여 제시된 방법의 효율성을 제시하였다. 또한 수치적 비교를 통해 비선형 구조에 대해 보수적인 응답을 보이는 선형 SSI문제에 대하여 얻은 경계반력이 비선형 지반-구조물 상호작용해석에 효과적으로 적용 가능함을 알 수 있었다.