• Title/Summary/Keyword: Gravity Model

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Determination of Local Vortical in Celestial Navigation Systems (천측 항법 시스템의 수직 방향 결정)

  • Suk, Byong-Suk;Lyou, Joon
    • Journal of Institute of Control, Robotics and Systems
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    • v.13 no.1
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    • pp.72-78
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    • 2007
  • Determination of the local vertical is not trivial for a moving vehicle and in general will require corrections for the Earth geophysical deflection. The vehicle's local vertical can be estimated by INS integration with initial alignment in SDINS(Strap Down INS) system. In general, the INS has drift error and it cause the performance degradation. In order to compensate the drift error, GPS/INS augmented system is widely used. And in the event that GPS is denied or unavailable, celestial navigation using star tracker can be a backup navigation system especially for the military purpose. In this celestial navigation system, the vehicle's position determination can be achieved using more than two star trackers, and the accuracy of position highly depends on accuracy of local vertical direction. Modern tilt sensors or accelerometers are sensitive to the direction of gravity to arc second(or better) precision. The local gravity provides the direction orthogonal to the geoid and, appropriately corrected, toward the center of the Earth. In this paper the relationship between direction of center of the Earth and actual gravity direction caused by geophysical deflection was analyzed by using precision orbit simulation program embedded the JGM-3 geoid model. And the result was verified and evaluated with mathematical gravity vector model derived from gravitational potential of the Earth. And also for application purpose, the performance variation of pure INS navigation system was analyzed by applying precise gravity model.

A Study on Interpretation of Gravity Data on Two-Dimensional Geologic Structures by Iterative Nonlinear Inverse (반복적 비선형역산에 의한 2차원 지질구조의 중력자료 해석 연구)

  • Ko, Chin-Surk;Yang, Seung-Jin
    • Economic and Environmental Geology
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    • v.27 no.5
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    • pp.479-489
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    • 1994
  • In this paper, the iterative least-squares inversion method is used to determine shapes and density contrasts of 2-D structures from the gravity data. The 2-D structures are represented by their cross-sections of N-sided polygons with density contrasts which are constant or varying with depth. Gravity data are calculated by theoretical formulas for the above structure models. The data are considered as observed ones and used for inversions. The inversions are performed by the following processes: I) polygon's vertices and density contrast are initially assumed, 2) gravity are calculated for the assumed model and error between the true (observed) and calculated gravity are determined, 3) new vertices and density contrast are determined from the error by using the damped least-squares inversion method, and 4) final model is determined when the error is very small. Results of this study show that the shape and density contrast of each model are accurately determined when the density contrast is constant or vertical density gradient is known. In case where the density gradient is unknown, the inversion gives incorrect results. But the shape and density gradient of the model are determined when the surface density contrast is known.

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Model-independent test of gravity

  • L'Huillier, Benjamin
    • The Bulletin of The Korean Astronomical Society
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    • v.45 no.1
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    • pp.48.3-48.3
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    • 2020
  • Using redshift-space distortion, I reconstruct the growth history as a smooth function using model independent methods. Assuming general relativity, I obtain the expansion history independently of the dark energy model, and test it to the supernovae data. The results are consistent with general relativity as gravity and the cosmological constant as dark energy, although interestingly negative dark energy densities are not ruled out by the data at z~0.7 to 1.

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A Green House Gas Emission Estimation Based on Gravity Model and Its Elasticity (중력모형을 이용한 온실가스 배출량추정 및 탄력성분석)

  • Im, Yong-Taek
    • Journal of Korean Society of Transportation
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    • v.29 no.4
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    • pp.85-93
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    • 2011
  • Many policies, such as transit-oriented development, encouraged use of bicycle and pedestrian, reduction of green house gas (GHG) and etc., have been deployed to support transport sustainability. Although various studies regarding GHG were presented, no one has yet adequately explained the behavior of travelers. This paper proposes a GHG emission model by highlighting its sensitivity, elasticity with regard to such travel cost as travel time, travel fare, and GHG pricing, introduced to reduce the amount of GHG in transportation system. For better estimation of GHG, the proposed model adopts (1) a production-constrained gravity model and (2) the travel distance from the origin and the destination (OD). The gravity model has a merit that it considers travel pattern between OD pairs. The model was tested with an example, and the promising results confirmed its validation and applications.

Effect of gravity on a micropolar thermoelastic medium with voids under three-phase-lag model

  • Alharbi, Amnah M.;Othman, Mohamed I.A.;Al-Autabi, Al-Anoud M.Kh.
    • Structural Engineering and Mechanics
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    • v.76 no.5
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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.

Experimental study on high gravity dam strengthened with reinforcement for seismic resistance on shaking table

  • Wang, Mingming;Chen, Jianyun;Fan, Shuli;Lv, Shaolan
    • Structural Engineering and Mechanics
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    • v.51 no.4
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    • pp.663-683
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    • 2014
  • In order to study the dynamic failure mechanism and aseismic measure for high concrete gravity dam under earthquake, the comparative models experiment on the shaking table was conducted to investigate the dynamic damage response of concrete gravity dam with and without the presence of reinforcement and evaluate the effectiveness of the strengthening measure. A new model concrete was proposed and applied for maintaining similitude with the prototype. A kind of extra fine wires as a substitute for rebar was embedded in four-points bending specimens of the model concrete to make of reinforced model concrete. The simulation of reinforcement concrete of the weak zones of high dam by the reinforced model concrete meets the similitude requirements. A tank filled with water is mounted at the upstream of the dam models to simulate the reservoir. The Peak Ground Acceleration (PGA) that induces the first tensile crack at the head of dam is applied as the basic index for estimating the overload capacity of high concrete dams. For the two model dams with and without strengthening tested, vulnerable parts of them are the necks near the crests. The results also indicate that the reinforcement is beneficial for improving the seismic-resistant capacity of the gravity dam.

Gravity Measurement and Data Processing using Relative Gravimeter (상대중력계를 이용한 중력의 측정과 처리)

  • Kim, Cheol-Young;Kim, Gi-Won;Lee, Suk-Bae
    • Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
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    • 2009.04a
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    • pp.49-53
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    • 2009
  • In this study, point gravity was measured to achieve terrestrid gravity data and the gravity is important element in precise geoid modelling. Surveys the relative gravity of 56 stations on 1st level route. In addition, it calculates gravity values, analysis gravity survey results using tidal correction, drift correction, datum-free adjustment. These point gravity data could be contribute in development of precise geoid model.

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Case Study on Absolute Gravity Measurement using FG-5 (FG-5 절대중력계 사례조사 연구)

  • Lee, Young-Jin;Son, Soo-Ik;Lee, Myeong-Jun;Jung, Kwang-Ho
    • Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
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    • 2010.04a
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    • pp.197-199
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    • 2010
  • A gravity survey is a base of research earth gravity field determined, perception of the vertical motion, change of Geoid, sea-level changes, climate change etc. Recently, FG-5 was adopted in NGII. NGII has completed 4 points of absolute gravity survey and 1,400 points of relative gravity survey in 2009 to aim to observe 20 points of absolute gravity survey and 6,000 points of gravity control point by 2013. Using results of gravity survey, NGII will provide citizen with data for research about renewal of geoid model and geophysics. This study aims to go over examples of utilization of absolute gravimeter & method of utilization in korea.

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Lagrangian Particle Model for Dense Gas Dispersion (고밀도 가스 확산 예측을 위한 라그란지안 입자 모델)

  • Ko, S.;Lee, C.
    • Proceedings of the KSME Conference
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    • 2003.11a
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    • pp.899-904
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    • 2003
  • A new model for dense gas dispersion is formulated within the Lagrangian framework. In several accidental released situations, denser-than-air vapour clouds are formed which exhibit dispersion behavior markedly different from that observed for passive atmospheric pollutants. For relevant prediction of dense gas dispersion, the gravity and entrainment effects need to implemented. The model deals with negative buoyancy which is affected by gravity. Also, the model is subjected to entrainment. The mean downward motion of each particle was accounted for by considering the Langevin equation with buoyancy correction term.

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Study of geological structure in area of Hwasan caldera using geophysical method (지구물리학적 방법에 의한 화산 칼데라 지역의 지질구조 연구)

  • Kwon, Byung-Doo;Lee, Heui-Soon;Yang, Joon-Mo;Park, Gye-Soon;Eom, Joo-Young;Kim, Dong-Oh
    • 한국지구물리탐사학회:학술대회논문집
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    • 2007.06a
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    • pp.267-272
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    • 2007
  • Uiseong subbasin belonging to Kyungsang basin resulted from volcanic activity in the late Cretaceous. In this study, we carry out MT and gravity survey at the Hwasan caldera, which was formed of volcanic and abyssal rocks complex, then analyze and identify geological substructure. Potential survey such as gravity and magnetic survey has been mainly carried out in former studies, so depth information for understanding substructure was not enough. To complement a potential survey, we use MT method, which has high vertical resolution. Moreover we make a simple 2D model comparing with former study. The result of MT and gravity 2D modeling shows that this area is roughly composed of 3 layers; The bottom layer is a basement. In the second layer, intrusive rocks having high resistivity is placed along the ring faults and the sedimentary layer of low resistivity is inside caldera. The highest layer is alluvium. To comprehend the 3D structure of the Hwasan caldera, we perform 3D gravity inversion, and construct the 3D model from the result of 3D gravity inversion. MT responses are calculated by using the constructed 3D model and the 3D model of the Hwasan caldera's structure is suggested after comparing the calculated values with the observed values at MT line.

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