• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.66-66
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• 2021

2011년에 일본 도호쿠 지방 태평양 해역에서 규모 9.0의 지진이 발생하여 거대한 쓰나미가 일본 본토 해안을 침수시켰다. 이로 인해, 정확한 피해규모가 파악되기 어려울 정도로 막대한 인명과 재산피해를 입게 되었다. 센다이지역의 경우 쓰나미로 인해 해안에 위치한 약 3.8 평방킬로미터의 방풍림이 모두 전복되었고 일부는 유목이 되어 쓰나미와 함께 내륙으로 흘러들어가 곳곳에 퇴적되어 농지를 훼손하고 가옥에 피해를 주었다. 따라서, 본 연구는 유목의 발생과 흐름에 따른 거동을 수치적으로 분석하여, 폭우나 쓰나미와 같은 거대흐름과 산지와 방풍림 등에서 발생하는 유목의 발생과 거동과정을 예측하고, 흐름과 유목 거동에 따른 피해지역을 선별할 수 있는 방법을 구축하기 위한 초기단계로서, 이를 위해 유목의 발생과정의 역학적 모델링을 수치모듈에 적용하였고 이를 활용하여 수치모의를 수행하였다. 흐름분석을 위해 쓰인 모형은 홍수범람 모형인 Nays2D Flood 이며 천수방정식을 기본으로 한다. 쓰나미의 흐름은 해안가의 방풍림지역을 상류단 경계조건으로 하여 발생 당시 관측된 수심변화를 본 모형의 상류단 경계조건으로 입력하였다. 상류단 경계조건에서 쓰나미의 유속은 수심에 따른 파속으로 계산하였다. 본 연구에서는 또한 유목의 발생과 흐름거동을 기존에 개발된 입자법 기반의 유목동역학모형을 활용하여 수치적으로 모델링 하였다. 유목은 유연성이 없는 원주형 강체로 가정하였고 초기설정으로는, 방풍림지역에 30만개의 유목이 하상의 수직방향으로 배치되어있는 것으로 가정하였다. 여기서, 본 연구에서는 쓰나미가 발생하면 흐름에 따른 항력으로 인해 수직방향으로 배치된 유목이 부러지며, 흐름과 함께 흘러가는 현상을 모델링하였다. 본 연구는 폭우나 쓰나미와 같은 거대흐름으로 인해 발생할 수 있는 유송잡물과 유목의 거동을 예측분석하는 기초연구자료로 활용될 수 있으며, 더 나아가 유목의 발생과정까지 수치적으로 재현하는 모델링을 수행하였기 추후에, 산지와 하천에서 발생할 수 있는 유송잡물의 발생과 연행 과정을 보다 세부적으로 예측할 수 있는 기초방법론으로 쓰일 수 있을 것으로 판단된다.

• Journal of the Korean earth science society
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• v.33 no.4
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• pp.337-349
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• 2012

In this study, we classify the 1000 hPa geopotential height fields around the Korean peninsula through the Kmeans cluster analysis and investigate the occurrence characteristics of each cluster pattern. The 11 clusters are identified as the typical pressure patterns, applying the pattern correlation as a similarity among clusters and the criterion of cluster similarity 0.8, of which three pressure patterns are associated with the extension of Siberia air mass, other three with the latitudes of the longest symmetry axis of North Pacific highs, two with the trough largely under the air mass of Siberia or North Pacific, and the remaining three, the migratory high patterns generally occurring in spring and autumn, are disjointed according to the direction of the longest symmetry axis of highs. The occurrence rate of air masses affecting the Korean peninsula, estimated from the number of occurrence days of 11 pressure patterns, is 55.4% Siberian, 29.3% North Pacific, 12.8% Yangtze-River, 2.5% Okhotsk sea and 68.2% of all these is the continental air masses. The wintertime pressure patterns around the Korean peninsula are nearly contrary to those in summertime, each dominated by the highs extended from the stationary air masses over the Central Siberia and the North Pacific ocean. The migratory highs occur largely in spring and autumn while transferring from the wintertime patterns to summertime patterns, or vice versa. Recently, the occurrence frequency of the highs extended from the North Pacific is on the decrease and while the wintertime pressure patterns occur frequently in spring and autumn, the occurrence frequency of the pressure patterns with trough is on the increase and the migratory highs occur in nearly all seasons.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.6
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• pp.483-488
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• 2007

The aerodynamic characteristics of FAST(Future Air Speed Transit) combined the body with tandem wing flying over nonplanar ground surface are investigated by using a boundary element method. To validate the present method, results of the present analysis are compared with the experiment and other numerical results. The arrangement of the tandem wing is determined to secure sufficient aero-levitation force and the stability through the analysis of the aerodynamic characteristics of the FAST. The FAST has the maximum lift characteristics when the tandem wing with lower endplate is located at the front side and the rear side of the body. The stability of the FAST can be secured by using the flaperon of the tandem wing.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.38 no.2
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• pp.110-118
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• 2002

The element free Galerkin method has been suggested by Belyschko, etc. it is applied for linear elastic analysis of solid problems and its convergence characteristics and stability are shown according to the weight function, influence domain and scattered points. The various numerical examples are performed to check the efficiency of 1D EFG and 2D EFG program by changing factors. As a result it have the best results when it used the cubic spline weight function and the scaling parameter d$_{max}$=2. These programs were developed by mixed language programming method using Visual Basic and the C language. so it is fast and efficient. and visually shown the result.t.

• Journal of Korea Water Resources Association
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• v.38 no.7 s.156
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• pp.537-544
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• 2005

For the proper management of high pressurized gas storage caverns, analysis of groundwater flow field and inflow quantity according to the groundwater head, gas storage pressure and water curtain head should be performed. The finite element method has been widely used for the groundwater flow analysis surrounding underground storage cavern because it can reflect the exact shape of cavern. But the various simulations according to the change of design factors such as the width of water curtain, shape of cavern etc. are not easy when elements were set up. To overcome these limitations, two dimensional groundwater flow model is established based on the boundary element method which compute the unknown variable by using only the boundary shape and condition. For the exact computation of drainage rate into cavern, the model test is performed by using the exact solution and pre-developed finite element model. The test result shows that the model could be used as an alternative to finite element model when various flow simulations are needed to determine the optimizing cavern shape and arrangement of water curtain holes and so forth.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.6
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• pp.1259-1265
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• 2013

In wireless environment such as wireless LAN, proper location of wireless LAN AP allows us to take an effective coverage to provide good wireless communication service. To simulate wireless environment, FDTD formulation is introduced and Gaussian pulse injection in grid space is considered to be replaced wireless LAN AP. So structural effect corresponding to location of arbitrary obstacle must be considered, and its received gain is estimated. An obstacle in scattering field should be modeled to be conductor and concrete wall and its diffraction effect for some cross wall is evaluated between transmitter and receiver point.

• Proceeding of KASS Symposium
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• 2008.05a
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• pp.179-183
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• 2008

Methods of damage detection are used non-destructive test in concrete structures. These are using various sensors, but the most of damage detections are used a visual angle of human. Problems of crack damage detection are occurred to directions and boundary conditions of steel bars using accelerometer in concrete element. In this study, fundamental studies for estimation using 3 axial type of accelerometer and electric resistance property of thermocouple sensors are discussed estimation to effect of arranged steel bars and damage from low strength when they are oscillated elastic wave in concrete specimen.

• Journal of Korean Society of Steel Construction
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• v.11 no.2 s.39
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• pp.117-129
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• 1999

The objective of this study is to identify the advantages of composite materials and to investigate the behavior of the anisotropic symmetric laminated cylindrical shell structures. To analyze the anisotropic symmetric laminated cylindrical shell structures, the finite difference technique. that consists of forward, central and backward difference, is introduced. In this study, the degree of freedom consists of three displacements and, especially, two moments except twisting moment. It has the advantage of improving the accuracy for calculating the moments. All four edges are assumed to be simply supported. From the numerical results, it is proved that the finite difference technique can be used efficiently to analyze the anisotropic symmetric laminated cylindrical shells and gives a guide in deciding how to make use of the fiber angle the anisotropic symmetric laminated cylindrical shells.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1752-1761
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• 2000

This paper describes the far-field estimation using the near-field measurement data. Measurement in far-field region gives us the acoustical characteristics of the source but in general measurement is made in near-field such as acoustic water tank or anechoic chamber, so far-field acoustical characteristics of the source should be predicted from near-field data. In this case, the number of measurement points in the near field which relates to the accuracy of the predicted field and the amount of data processing, should be optimized. Existing papers say that measurement points is proportional to kL and depends on geometry and directivity of the source. But they do not give us any definite criterion for the required number of measurement points. Boundary Collocation Method which is one of the far-field prediction methods, is analyzed based on Helmholtz integral equation and Green function and it has been found that the number of measurement points is optimized as 0.54kL which is about one half of the existing results.

• Tunnel and Underground Space
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• v.14 no.3
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• pp.229-240
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• 2004

Coastal aquifers may serve as major sources fur freshwater. In many coastal aquifers, intrusion of seawater has become one of the major constraints imposed on groundwater utilization. The management of groundwater in coastal acquifers means making decision as to the pumping rate and the spatial distribution of wells. Several numerical techniques for flow and solute transport simulation can provide the means to achieve this goal. As a basic study to predict the intrusion of seawater in coastal phreatic aquifers, the coupled flow and solute transport analysis was conducted by use of the 3-D finite element code, SWICHA. In order to understand how the location and the shape of freshwater-seawater transition zone were affected by the boundary conditions and hydrogeologic variables, parametric study was carried out.