• 한국측량학회지
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• 제39권5호
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• pp.313-319
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• 2021

The national geodetic reference frame of Korea was adopted in 2003, which is referenced to ITRF (International Terrestrial Reference Frame) 2000 at the epoch of January 1, 2002. For precise positioning based on the satellites, it should be thoroughly maintained to the newest global reference frame. Other than plate tectonic motion, there are significant events or changes such as earthquakes, antenna replacement, PSD (Post-Seismic Deformation), seasonal variation etc. We processed three years of GNSS (Global Navigation Satellite System) data(60 NGII CORS stations, 51 IGS core stations) to produce daily solutions minimally constrained to ITRF. From the time series of daily solutions, the sites with unexpected discontinuity were identified to set up an event(mostly antenna replacement). The combined solution with minimum constraints was estimated along with the velocity, the offsets, and the periodic signals. The residuals show that the surrounding environment also affects the time series to a certain degree, thus it should be improved eventually. The transformation parameters to ITRF2014 were calculated with stability and consistency, which means the national geodetic reference frame is properly aligned to the global reference frame.

• 한국지구과학회지
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• 제40권4호
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• pp.353-381
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• 2019

The general world model for homogeneous and isotropic universe has been proposed. For this purpose, we introduce a global and fiducial system of reference (world reference frame) constructed on a (4+1)-dimensional space-time, and assume that the universe is spatially a 3-dimensional hypersurface embedded in the 4-dimensional space. The simultaneity for the entire universe has been specified by the global time coordinate. We define the line element as the separation between two neighboring events on the expanding universe that are distinct in space and time, as viewed in the world reference frame. The information that determines the kinematics of the geometry of the universe such as size and expansion rate has been included in the new metric. The Einstein's field equations with the new metric imply that closed, flat, and open universes are filled with positive, zero, and negative energy, respectively. The curvature of the universe is determined by the sign of mean energy density. We have demonstrated that the flat universe is empty and stationary, equivalent to the Minkowski space-time, and that the universe with positive energy density is always spatially closed and finite. In the closed universe, the proper time of a comoving observer does not elapse uniformly as judged in the world reference frame, in which both cosmic expansion and time-varying light speeds cannot exceed the limiting speed of the special relativity. We have also reconstructed cosmic evolution histories of the closed world models that are consistent with recent astronomical observations, and derived useful formulas such as energy-momentum relation of particles, redshift, total energy in the universe, cosmic distance and time scales, and so forth. The notable feature of the spatially closed universe is that the universe started from a non-singular point in the sense that physical quantities have finite values at the initial time as judged in the world reference frame. It has also been shown that the inflation with positive acceleration at the earliest epoch is improbable.

• 인지과학
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• 제22권1호
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• pp.19-38
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• 2011

사람이 공간에 대한 표현이나 추론을 기술할 때, 정량적 정보 표현과 관련 추론이 어렵거나 불가능 할 때 정성적 표현과 추론을 사용할 수 있다. 2차원 공간에 대한 많이 알려진 정성적 방법 중에 RCC(Region Connection Calculus)-8이 있다. 지역(region)을 공간에 대한 온톨로지 기본 개체로 하는 RCC-8은 위상학적 의미에서 두 개의 지역에 관해 connection 기반의 논리식 및 개념적 이웃과 변환을 나타낸 것으로 각 지역의 이동이나 크기 변화를 전제로 하고 있다. 그러나 현실 세계의 공간 표현과 추론에는 몇 가지 측면들이 더 고려되어야 한다. 본 논문에서는 중력장내에서 일어나는 물리적 화학적 작용에 의해 변화하는 동적인 물질세계의 정성적 공간 표현을 위해 RCC-8의 수정 확장된 방법을 제안한다. 2D의 정성적 공간 표현 및 추론에서 전역적 참조 프레임(global reference frame)의 필요성을 기술하고, 전역적 참조 프레임을 사용하여 동적 물질세계의 물리적 화학적 변화를 표현하고 추론하기 위한 QSR-14을 기술한다. QSR-14는 RCC-8에서 불가능한 상황을 표현할 수 있어 실제 세계의 정성적 공간 표현 및 변화에 더 적합하다고 판단된다. 몇 개의 예제를 통해 정성적 표현과 추론에 대한 QSR-14의 유용성을 보인다.

• 한국방송∙미디어공학회:학술대회논문집
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• 한국방송공학회 2011년도 추계학술대회
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• pp.288-291
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• 2011

Video stabilization is an important image enhancement widely used in surveillance system in order to improve recognition performance. Most previous methods calculate inter-frame homography to estimate global motion. These methods are relatively slow and suffer from significant depth variations or multiple moving object. In this paper, we propose a fast and practical approach for video stabilization that selects the most reliable key frame as a reference frame to a current frame. We use optical flow to estimate global motion within an adaptively selected region of interest in static camera environment. Optimal global motion is found by probabilistic voting in the space of optical flow. Experiments show that our method can perform real-time video stabilization validated by stabilized images and remarkable reduction of mean color difference between stabilized frames.

• Journal of Mechanical Science and Technology
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• 제17권1호
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• pp.77-84
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• 2003

Virtual work in multibody systems is frequently expressed as the inner product of the virtual displacement and the resultant force at the centroid. But provided that the resultant force is converted into the equipollent forces there is no restriction on where the analysis reference point is placed. There are basically three candidate points : the centroid, joint point and the instant global origin. The traditional fully recursive formulation uses the centroid, but the present work verifies that the instant global origin always shows better efficiency (e.g. 86% CPU time of the centroid for quarter car model) and joint point shows the efficiency between that of the centroid and the instant global origin. A discussion on how important it is to define the analysis reference point properly in a fully recursive formulation is also presented.

• Earthquakes and Structures
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• 제8권1호
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• pp.205-224
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• 2015

A new method for designing moment resisting concrete frames failing in a global mode is presented in this paper. Starting from the analysis of the typical collapse mechanisms of frames subjected to horizontal forces, the method is based on the application of the kinematic theorem of plastic collapse. The beam section properties are assumed to be known quantities, because they are designed to resist vertical loads. As a consequence, the unknowns of the design problem are the column sections. They are determined by means of design conditions expressing that the kinematically admissible multiplier of the horizontal forces corresponding to the global mechanism has to be the smallest among all kinematically admissible multipliers. In addition, the proposed design method includes the influence of second-order effects. In particular, second-order effects can play an important role in the seismic design and can be accounted for by means of the mechanism equilibrium curves of the analysed collapse mechanism. The practical application of the proposed methodology is herein presented with reference to the design of a multi-storey frame whose pattern of yielding is validated by means of push-over analysis.

• 해양환경안전학회지
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• 제1권2호
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• pp.39-52
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• 1995

There are numerous mapping, charting, geodetic systems and electronic digital products defined in various local geodetic datum. It becomes a straight forward requirement to simplify the complexity by referencing all the products to a common reference globally. WGS-84 is well known as a state-of-the-art global reference system based on the use of data, techniques and technology available within American Defence Mapping Agency(DMA). Its parameters can be translated into more accurate maps, charts and geodetic positioning compared to others previously. Since Global Positioning System(GPS/NAVSTAR), which is asssociated with World Geodetic System(WGS-84)in reference frame, has been widely used, the unified geodetic system has been required for GPS users in many fields.

• 한국측량학회지
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• 제27권3호
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• pp.303-310
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• 2009

지구기준계 실현을 위해 최적망 구성 알고리즘에 근거하여 선택된 142개의 IGS 관측소를 선정하고 7년간 GPS 자료를 처리하였다. 본 연구에서 결정된 기준좌표와 속도를 이용하여 본 연구의 지구기준좌표계와 ITRF2005와의 변환매개변수를 추정하였으며, 각각의 관측소에서의 좌표와 속도를 비교하였다. 산출한 변환매개변수는 최대 4.3mm 이내에 분포하였고, 좌표와 속도 차의 RMS(root mean square)는 수평성분이 6.7mm와 1.3mm/yr, 수직성분이 13.3mm와 2.4mm/yr로서 ITRF2005와 잘 일치하고 있다. 이러한 연구는 측지기준계 결정을 위한 자체기술개발에 의의를 가지며 판구조운동 연구와 같은 전지구 관측을 위한 연구에 활용될 수 있다. 향후 다양한 자료처리 전략 개발과 더불어 관측소의 개수와 관측기간을 확대함으로써 보다 향상된 지구기준좌표계가 결정될 것이다.

• 한국구조물진단유지관리공학회 논문집
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• 제18권1호
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• pp.174-182
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• 2014

건물의 풍진동을 모니터링 하기 위해, 두 개 (이동국과 기준국)의 global positioning system (GPS)에 기반한 종래의 real-time kinematic (RTK) 기법이 널리 적용되고 있다. 그러나 이는 기준국을 위한 공간을 확보하거나 유지 관리하는데 어려움을 겪을 수 있다. 한편, 최근에 하나의 이동국 만을 이용하여 구조물의 움직임을 계측할 수 있는 새로운 virtual reference station (VRS)-RTK 기법이 개발되었으며, 측량 분야에서 널리 사용되고 있다. 본 연구에서는 골조 구조물의 횡방향 구조 응답을 모니터링하기 위한 VRS-RTK 기법의 적용성을 평가하기 위해 단층 골조 모형 (1차 고유진동수 : 1 Hz)과 3층 골조 모형 (1차 고유진동수 : 0.85 Hz)의 자유진동 실험을 수행하였다. GPS에 의해 계측된 변위 및 가속도 응답의 신뢰성을 평가하기 위해, 레이져 변위계와 가속도계가 설치되었으며, 이들로부터 얻은 계측값을 GPS의 계측값과 비교하였다. 또한, 건물의 지속적인 모니터링을 위한 적절한 계측 샘플링 수를 파악하기 위해, 변위 응답에서의 오차가 각기 다른 GPS 샘플링 수 (5, 10, 20 Hz)에서 평가되었다. 실험 결과, GPS으로부터 얻은 변위 및 가속도 응답은 레이져 변위계와 가속계로부터 얻은 응답과 좋은 유사 관계를 가지는 것을 확인하였다. 그리고, GPS 샘플링 수가 증가할수록 변위 오차는 감소하였으며, 3층 실험체에 대해서는 20 Hz의 GPS 샘플링 수로 구조물의 전 모드 성분 (1, 2, 3차 모드)을 검출할 수 있었다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제6권4호
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• pp.1024-1040
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• 2014

The theoretical background and a numerical solution procedure for a time domain hydroelastic code are presented in this paper. The code combines a VOF-based free surface flow solver with a flexible body motion solver where the body linear elastic deformation is described by a modal superposition of dry mode shapes expressed in a local floating frame of reference. These mode shapes can be obtained from any finite element code. The floating frame undergoes a pseudo rigid-body motion which allows for a large rigid body translation and rotation and fully preserves the coupling with the local structural deformation. The formulation relies on the ability of the flow solver to provide the total fluid action on the body including e.g. the viscous forces, hydrostatic and hydrodynamic forces, slamming forces and the fluid damping. A numerical simulation of a flexible barge is provided and compared to experiments to show that the VOF-based flow solver has this ability and the code has the potential to predict the global hydroelastic responses accurately.