• 지질공학
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• 제31권3호
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• pp.283-293
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• 2021

고해상 드론 기반의 지형 정보와 중력장 데이터를 이용하여 다짐지반의 모양과 균질성을 분석하였다. 지형과 수문 모형에서 계산된 지형요소 중 곡률은 다짐과정에서 발생한 지형의 변화를 효과적으로 보여 주었으며 이를 통해 불균질 다짐 영역을 확인할 수 있다. 지형 정보의 적정 해상도는 10 cm 정도였다. 성토지반의 공간적인 밀도변화를 분석하기 위해 중력장 해석을 수행하였으며 완전 부게이상의 변화로부터 불균질 다짐 영역과 지하 밀도구조 모델링을 통해 다짐도 차이에 의한 불균질 영역을 파악하였다. 연구결과로부터 지형요소와 중력장 해석법은 다짐된 지반의 균질성을 평가법이 될 수 있을 것으로 판단된다.

• Structural Engineering and Mechanics
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• 제74권3호
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• pp.425-434
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• 2020

The present paper is concerned at investigating the effect of hydrostatic initial stress, gravity and magnetic field in fiber-reinforced thermoelastic solid, with variable thermal conductivity. The formulation of the problem applied in the context of the three-phase-lag model, Green-Naghdi theory with energy dissipation, as well as coupled theory. The exact expressions of the considered variables by using state-space approaches are obtained. Comparisons are performed in the absence and presence of the magnetic field as well as gravity. Also, a comparison was made in the three theories in the absence and presence of variable thermal conductivity as well as hydrostatic initial stress. The study finds applications in composite engineering, geology, seismology, control system and acoustics, exploration of valuable materials beneath the earth's surface.

• Geomechanics and Engineering
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• 제37권6호
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• pp.591-597
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• 2024

The purpose of this paper is to depict the effect of gravity on a nonlocal thermoelastic medium with initial stress. The Lord-Shulman and Green-Lindsay theories with fractional derivative order serve as the foundation for the formulation of the fundamental equations for the problem. To address the problem and acquire the exact expressions of physical fields, appropriate non-dimensional variables and normal mode analysis are used. MATLAB software is used for numerical calculations. The projected outcomes in the presence and absence of the gravitational field, along with a nonlocal parameter, are compared. Additional comparisons are made for various fractional derivative order values. It is evident that the variation of physical variables is significantly influenced by the fractional derivative order, nonlocal parameter and gravity field.

• 지구물리와물리탐사
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• 제23권1호
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• pp.50-54
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• 2020

이 논문에서는 축 방향 대칭성을 가지는 원통형 이상체 대한 자력 반응식을 유도하였다. 일정한 방향으로 자화된 이상체가 생성시키는 자력장은 일정한 밀도를 가지는 이상체에 의한 중력 변화율 텐서로부터 변환 가능한 포아송(Poisson) 관계식을 이용하여 기존에 이미 유도된 원통형에 의한 중력 변화율 텐서로부터 3성분 자력 벡터를 유도하였다. 축 방향 대칭성을 이용하여 중력 변화율 텐서를 원통 좌표계에서 유도하였고 이를 직교 좌표계로 변환한 후 이상체의 자화 방향과 결합하여 3성분 자력 벡터를 유도하였다.

• Structural Engineering and Mechanics
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• 제76권5호
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• pp.579-590
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• 2020

This paper's objective is to investigate the effect of gravity on a micropolar thermoelastic medium with voids. The problem is assessed according to the three-phase-lag model. An analysis of the resulting non-dimensional displacement, temperature variation, and internal stress of the study material is carried out and presented graphically. The non-dimensional displacement, temperature, micro-rotation, the change in the volume fraction field and stress of the material are obtained and illustrated graphically. Comparisons are made with the results predicted by different theories for different values of gravity, the phase-lag of the heat flux and the phase-lag of the temperature gradient. The numerical results reveal that gravity and relaxation times have a significant influence on the distribution of the field quantities. Some notable insights of interest are deduced from the investigation.

• 한국항공우주학회지
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• 제31권8호
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• pp.58-68
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• 2003

정밀한 지구중력장 측정은 지구역학적인 현상을 이해하는데 매우 중요한 역할을 한다. 지구중력장 측정 목적에 관하여 간략히 언급한 뒤, 중력장 측정 전용위성을 이용한 측정 기법에 관해 고찰하였다. 최근에 발사된 NASA/DLR의 중력장 측정 전용위성인 Gravity Recovery and Climate Experiment (GRACE)의 개요 및 주요 관측기기들을 소개하였다. 두 개의 저궤도 위성으로 구성된 이 사업의 성능분석을 위한 시뮬레이션 기법과 관측기 모델링 방법 등을 소개하였다. 시뮬레이션 결과 GRACE를 이용하여 지구중력장 정확도를 상당히 향상시킬 수 있을 것으로 예상된다.

• Geomechanics and Engineering
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• 제31권2호
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• pp.159-166
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• 2022

The model of two-dimensional plane waves is analyzed in a micropolar-thermoelastic solid with microtemperatures in the context of the three-phase-lag model, dual-phase-lag model, and the Green-Naghdi theory of type III. Harmonic wave analysis is used to hold the solution to the problem. Numerical results of the physical fields are visualized to show the effects of the gravity field, magnetic field, and viscosity. The expression for the field variables is obtained generally and represented graphically for a particular medium.

• 한국측량학회지
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• 제27권1호
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• pp.713-722
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• 2009

중력측량은 지구중력장 결정, 지각의 수직운동, 지오이드면의 변화, 해수면변화, 기후변화 등 측지학적, 지구동력학적 연구의 기초이다. 국토지리정보원에서는 최근 들어 FG-5 절대중력계를 도입하여 절대중력 기준망의 구축을 위한 틀을 마련하였고 다차원 다기능 기준점인 통합기준점을 전국에 약 1,200점을 설치하여 상대중력측량을 실시함으로써 한국의 고정밀 지오이드모델의 개발에 큰 기여를 할 것으로 판단된다. 본 연구에서는 상대중력측량의 기본적인 이론 및 방법을 상세하게 설명하였고, 최신 상대중력계 Scintrex CG-5를 이용하여 총 21점에 대한 상대중력측량을 수행하였으며, 자유망조정 및 무게제한 망조정 방법을 이용하여 중력성과를 계산 및 비교 분석하였다. 결과, 두 가지 방법 모두 높은 정밀도의 중력성과 계산이 가능하지만 자유망조정이 무게제한 망조정 방법에 비해 상대적인 우위를 보여주는 것으로 나타났다.

• 한국측량학회지
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• 제38권2호
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• pp.153-163
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• 2020

After launching the GOCE (Gravity Field and Steady-State Ocean Circulation Explorer) which obtains high-frequency gravity signal using a gravity gradiometer, many research institutes are concentrating on the development of GGM (Global Geopotential Model) based on GOCE data and evaluating its precision. The precision of some GGMs was also evaluated in Korea. However, some studies dealt with GGMs constructed based on initial GOCE data or others applied a part of GNSS (Global Navigation Satellite System) / Leveling data on UCPs (Unified Control Points) for the precision evaluation. Now, GGMs which have a higher degree than EGM2008 (Earth Gravitational Model 2008) are available and UCPs were fully established at the end of 2019. Thus, EIGEN-6C4 (European Improved Gravity Field of the Earth by New techniques - 6C4), GECO (GOCE and EGM2008 Combined model), XGM2016 (Experimental Gravity Field Model 2016), SGG-UGM-1, XGM2019e_2159 were collected with EGM2008, and their precisions were assessed based on the GNSS/Leveling data on UCPs. Among GGMs, it was found that XGM2019e_2159 showed the minimum difference compared to a total of 5,313 points of GNSS/Leveling data. It is about a 1.5cm and 0.6cm level of improvement compare to EGM2008 and EIGEN-6C4. Especially, the local biases in the northern part of Gyeonggi-do, Jeju island shown in the EGM2008 was removed, so that both mean and standard deviation of the difference of XGM2019e_2159 to the GNSS/Leveling are homogeneous regardless of region (mountainous or plain area). NGA (National Geospatial-Intelligence Agency) is currently in progress in developing EGM2020 and XGM2019e_2159 is the experimentally published model of EGM2020. Therefore, it is expected that the improved GGM will be available shortly so that it is necessary to verify the precision of new GGMs consistently.

• 대한조선학회논문집
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• 제51권5호
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• pp.435-449
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• 2014

The effects of the gravity field and the free surface on the cavity shape and the drag are investigated through a numerical analysis for the steady supercavitating flow past a simple two-dimensional body underneath the free surface. The continuity and the RANS equations are numerically solved for an incompressible fluid using a $k-{\epsilon}$ turbulence model and a mixture fluid model has been applied for calculating the multiphase flow of air, water and vapor using the method of volume of fluid and the Schnerr-Sauer cavitation model. Numerical solutions have been obtained for the supercavitating flow about a two-dimensional $30^{\circ}$ wedge in wide range of depths of submergence and inflow velocities. The results are presented for the cavity shape, especially the length and the width, and the drag of the wedge in comparison with those of the case for the infinite fluid flow neglecting the gravity and the free surface. The influences of the gravity field and the free surface on the aforementioned quantities are discussed. The length and the width of the supercavity are reduced and the centerline of the cavity rises toward the free surface due to the effects of the gravity field and the free surface. The drag coefficient of the wedge, however, is about the same except for shallow depths of submergence. As the supercavitating wedge is approaching very close to the free surface, it is found the length and the width of a cavity are shorten even though the cavitation number is reduced. Also the present result suggests that, under the influence of the gravity field and the free surface, the length of the supercavity for a certain cavitation number varies and moreover is proportional to the inverse of the submergence depth Froude number.