• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.98-98
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• 2019

중력류 또는 밀도류는 주변 유체에 비해 상대적으로 밀도가 큰 유체가 밀도차에 의한 추진력으로 흐르는 것이다. 중력류의 수치모델링에는 두 가지 어려움이 있다. 즉, 적합한 지배방정식을 구성하여 적용하는 것 그리고 난류의 영향을 합리적으로 반영하는 것이다. 기존 중력류 해석을 위한 지배방정식들은 유체의 연속방정식과 운동량 방정식 그리고 밀도 또는 농도의 이송방정식을 조합하여 구성된다. 이들 지배방정식을 이용한 연구들은 대부분 두 유체 사이의 밀도차가 충분히 작아서 밀도 변동(variations)의 영향은 오로지 부력항에서만 유지된다는 Boussinesq 근사에 근거를 둔다. 그리고 이송방정식에서 밀도 또는 농도의 확산계수을 점성계수의 함수로 표현하기 위해서 Schmidt 수를 이용한다. 수치모델링에서 Schimdt 수는 상수값을 적용하지만, 이 값은 밀도의 연직방향 경사에 근거한 부력빈도(buoyancy frequency)와 난류량의 따라 큰 차이를 보이는 것으로 알려져있다. 한편, 표준 통계학적 난류모델과 벽함수를 적용한 수치모델링은 초기 중력에 의해서 무너지는(slumping) 단계를 넘어 관성력으로 추진되는 단계와 점성 효과가 지배적인 단계에서는 정확도에 현저히 낮아지기 때문에 대부분 큰와모의(large-eddy simulation, LES) 또는 DNS(direct numerical simulation)수준의 고해상도(high-resolution) 해석기법을 적용하여 공학적인 문제에 적용하는 데는 한계가 있다. 이 연구에서는 Boussinesq 근사와 Schmidt 수를 사용하지 않으며, LES 보다 적용이 용이한 DES (detached-eddy simulation)기법을 조합한 다상흐름 수치모델을 적용하여 중력류를 해석을 시도하였다. 수치해석결과를 실험값과 함께 기존 수치모델링 기법으로 구한 수치해와 비교분석하여 이 연구에서 개발 및 적용된 수치모델링 기법의 적용성을 평가한다.

• Journal of Korean Society for Geospatial Information Science
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• v.18 no.1
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• pp.89-97
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• 2010

The ship-borne gravity data is essential to construct geoid in Korea surrounding ocean area. The altimeter data was used in previous study, however, the ship-borne gravity data could be used due to more ship-borne data was collected by improvement of instrument, positioning system. Therefore, the study on verification of precision of ship-borne gravity data and practical usage analysis is needed. In this study, free-air anomaly having 16.47mGal and 18.86mGal as mean and standard deviation was obtained after consistent processing such as Eotvos correction, Kalman Filter, Cross-over adjustment etc. The calculated free-air anomaly was compared to DNSC08 altimeter data and the difference was computed having -0.88mGal and 9.46mGal of mean and standard deviation. The reason causing those differences are owing to spatial limits of data acquisition and effects of ocean topography. To use ship-borne gravity data for precision geoid development, the efforts to overcome the limits of data collection and study for data combination should be proceeded.

• ICROS
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• v.16 no.3
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• pp.40-45
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• 2010

물체의 운동을 측정하기 위하여 관성 센서(inertial sensor)에 대한 배경 지식이 없는 사용자가 가속도계(accelerometer)를 사용하고자 할 경우 센서의 이름이 주는 혼동에 의하여 물체의 운동 가속도(acceleration)를 쉽게 얻어낼 수 있으리라 기대하게 된다. 반면, 가속도계가 실제 측정하여 주는 값은 비력 가속도(acceleration due to specific force)에 해당되므로 적절한 처리를 부가하지 않으면 기대한 바와 같이 물체의 운동 가속도를 얻을 수 없다. 가속도계의 측정값으로부터 운동 가속도를 추출하기 위해서는 중력장 가속도 (gravitational acceleration), 중력 가속도 (acceleration due to gravity), 비력 가속도, 그리고 운동 가속도 사이의 관계를 명확하게 구분 이해할 필요가 있다. 본 고에서는 앞선 고들에서 다룬(막대) 벡터, 좌표값, 좌표계, 좌표변환행렬, 그리고 코리올리 효과 등의 개념을 확장하여 다양한 개념의 가속도들을 구분 설명하였다.

• Geophysics and Geophysical Exploration
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• v.14 no.1
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• pp.88-97
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• 2011

We present a method for modelling the terrain response of gravity gradiometry surveys utilising an adaptive quadtree mesh discretization. The data- and terrain-dependent method is tailored to provide rapid and accurate terrain corrections for draped and barometric airborne surveys. The surface used in the modelling of the terrain effect for each datum is discretized automatically to the largest cell size that will yield the desired accuracy, resulting in much faster modelling than full-resolution calculations. The largest cell sizes within the model occur in areas of minimal terrain variation and at large distances away from the datum location. We show synthetic and field examples for proof of concept. In the presented field example, the adaptive quadtree method reduces the computational cost by performing 351 times fewer calculations than the full model would require while retaining an accuracy of one E$\"{o}$tv$\"{o}$s for the gradient data. The method is also used for the terrain correction of the gravity field and performed 310 times faster compared with a calculation of the full digital elevation model.

• Journal of the Korean earth science society
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• v.31 no.1
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• pp.1-7
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• 2010

Many studies have successfully developed a number of terrain correction programs in gravity data. Furthermore, terrain data that is a basic data for terrain correction has widely been provided through internet. We have also developed our own precise gravity terrain correction program. The currently existing gravity terrain correction programs have been developed for regional scale gravity survey, thus a more precise gravity terrain correction program needs to be developed to correct terrain effect. This precise gravity terrain program can be applied on small size geologic targets, such as small scale underground resources or underground cavities. The multiquadric equation has been applied to create a mathematical terrain surface from basic terrain data. Users of this terrain correction program can put additional terrain data to make more precise terrain correction. In addition, height differences between terrain and base of gravity meter can be corrected in this program.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.26 no.5
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• pp.519-527
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• 2008

The basic elements in precise geoid determination are the gravity and topographic data with reliable quality and distribution. In this study, the effect of the gravity and topographic data on the precision of the geoid are analyzed through simulations in which the quality and distribution of the data are artificially controlled. It was found that the distribution of the topographic data has more effect on the precision of geoid than the quality of the it. This leads to the conclusion that the SRTM (Shuttle Radar Topography Mission) DTM (Digital Terrain Model) with resolution of 90m is qualified as a topographic data in geoid determination. In the experiments with gravity data, on the other hand, the aliasing effect caused by the low data density caused large errors in geoid. It was found that the more gravity data especially in north-eastern mountainous area is needed for precise geoid determination in Korea.

• 한국지구물리탐사학회:학술대회논문집
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• 2005.05a
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• pp.255-260
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• 2005

A Gravity characteristic of Svalbard archipelago in Arctic was studied by using ArcGP data. There are situated the Dasan science station. After bouguer correction, an edge effect of free-air anomaly, which is similar to topography, are not shown at passive continent margin, and after terrain correction with GTOPO30 data, gravity anomaly increases from continent to marine. that is deep connected with rise of Moho discontinuity. The correlation of topography and free-air anomaly shows that the isostasy of continent attains a little less than marine. After filtering, the residual anomaly are shown high and low anomalies related to fracture zone in continent and base depression or thick sedimentary layer in continental slope, marine.

• 한국지구물리탐사학회:학술대회논문집
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• 2005.05a
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• pp.181-186
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• 2005

Gravity method produces subsurface density distribution, which is direct information of soundness of basement. Therefore, microgravity is one of the most effective method for detections of limestone cavities, abandoned mine-shafts and other tunnels, The paper show the effectiveness of microgravity by three different field cases.

• Journal of Astronomy and Space Sciences
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• v.7 no.1
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• pp.37-45
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• 1990

It was investigated that the effect of zonal harmonics to transfer orbit. Since parking orbit is located at low altitude, the zonal harmonics affects transfer orbit relatively high sense. So under the zonal harmonics, eccentricity and semi-major-axis which were related orbit altitude at the first hand, were investigated. As a result the zonal harmonics increases the altitude of apogee of transfer orbit. So if the zonal harmonics is considered in orbit transfer the fuel can be saved a little.

• Journal of the Korean earth science society
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• v.26 no.7
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• pp.691-697
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• 2005

Recently, the development of accurate gravity-meter and GPS make it possible to obtain high resolution gravity data. Though gravity data interpretation like modeling and inversion has significantly improved, gravity data processing itself has improved very little. Conventional gravity data processing removes gravity effects due to mass and height difference between base and measurement level. But, it would be a biased density model when some or whole part of anomalous bodies exist above the base level. We attempted to make a multiquadric surface of the survey area from topography with DEM (Digital Elevation Map) data. Then we constituted rectangular blocks which reflect real topography of the survey area by the multiquadric surface. Thus, we were able to carry out 3-D inversions which include information of topography. We named this technique, 3-D Gravity Terrain Inversion (3DGTI). The model test showed that the inversion model from 3DGTI made better results than conventional methods. Furthermore, the 3-dimensional model from the 3DGTI method could maintain topography and as a result, it showed more realistic geologic model. This method was also applied on real field data in Masan-Changwon area. Granitic intrusion is an important geologic characteristic in this area. This method showed more critical geological boundaries than other conventional methods. Therefore, we concluded that in the case of various rocks and rugged terrain, this new method will make better model than convention ones.