• Proceedings of the Korea Water Resources Association Conference
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• 2012.05a
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• pp.537-537
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• 2012

천수방정식의 수치모형은 하천의 유량예측, 홍수범람해석, 해일 모의 등에 널리 사용되고 있고, 그 결과는 수자원 관리, 재난 대책 등 정책적인 의사결정에 있어 유용한 자료로 활용되고 있다. 이처럼 천수방정식의 수치모형은 연구목적뿐만 아니라 실생활에 있어서도 큰 영향을 미치고 있으며, 이에 보다 정확하고 효율적인 수치모형의 구축이 수리/수자원/방재분야에서 중요한 영역이 되고 있다. 본 연구는 정확하고 안정적인 수치모의를 위해 천수방정식의 수치모형에 MLP(Multi dimensional Limiting Process)기법을 적용한 후 다차원 모의 시 MLP의 수치 진동 제어 성능을 검증하고자 하였다. MLP기법은 다차원에서 수치진동을 억제할 수 있도록 개발된 기법으로, 기존 TVD 제어자(limiter)과 MLP의 차이점은 기존 제어자들이 흐름이 발생하는 셀 경계면에서 재구성된 값이 Maximum Principle을 만족시키도록 제어자를 유도하는데 반해, MLP는 셀 절점에서 Maximum Principle을 만족시키도록 제어자를 유도한다는데 있다. MLP기법은 압축성 유체를 표현하는 2, 3차원 오일러 방정식에 적용되어 기존의 제어자들에 비해 안정적이며 정확한 수치모의를 가능하게 하는 것이 검증되었다. 하지만 천수방정식에 적용된 예는 없으며, 이에 본 연구는 천수방정식에 MLP를 적용하고 천수방정식 수치모형 검증에 주로 사용되는 수치모의를 통해 MLP의 수치 진동 제어 성능을 검증하였다. 모의 결과, MLP는 2차원 천수방정식에 있어서도 기존의 제어자들과 비교하여 수치진동을 보다 잘 제어하는 것으로 판단된다. MLP의 사용으로 인해 불연속면 근처에서 정확도가 향상되었고 수치진동이 발생하지 않아 보다 안정적인 모의가 가능하였다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.8
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• pp.1377-1383
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• 2008

Parameterization of a 3D triangular mesh is a fundamental problem in various applications of geometric modeling and computer graphics. There are two major paradigms in mesh parameterization: energy functional minimization and the convex combination approach. In general, the convex combination approach is wifely used because of simple concept and one-to-one mapping. However, the approach has some problems such as high distortion near the boundary and time complexity. Moreover, the stability of the linear system may not be preserved according to the geometric information of the mesh. In this paper, we present an extension of the convex combination approach based on the mean value coordinates, which resolves the drawbacks of the convex combination approach. This may be a more practical solution because it is able to generate a stable linear system in a short time.

• The Journal of Engineering Geology
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• v.19 no.2
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• pp.205-215
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• 2009

The conventional numerical models to analyze flow in subsurface porous media under the transient state usually generate numerical oscillation and unstability due to local flux domain for critical cases such as infiltration into initially dry soil during rainfall period. In this case, it is required refined mesh and small time step, but it decrease efficiency of computation. In this study, numerical unstability in discontinuity domain is removed by applying particle tracking algorithm to simulate unsteady subsurface flow with inflow boundary condition. Finally the hybrid LE FEM improving numerical stability is proposed. The hypothetical domains with unsteady uniform and nonuniform flow field were used to demonstrated algorithm verification. In comparison with analytic solution, we obtained reasonable results and conducted simulation of hypothetical 3-D recharge/pumping area. The proposed algorithm can simulate saturated/unsaturated porous media with more practical problems and will greatly contribute to accuracy and stability of numerical computation.

• Journal of the Mineralogical Society of Korea
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• v.15 no.3
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• pp.161-169
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• 2002

high pressure and temperature conditions. However, those results are not consistent with one another, and phase boundary between ilmenite and perovskite phases determined only from the quenching method may be not so reliable at all. Therefore, in-situ high pressure-temperature (hP-T) X-ray diffraction measurements were performed up to 19 GPa and $700^{\circ}C$ in a large volume press apparatus using synchrotron radiation. Experimental results show that perovskite phase is stable at pressures above 16 GPa, and transforms back to $LiNbO_3$phase near 15 CPa at room temperature, and that the perovskite-ilmenite transition is back and forth near 15 CPa at $500^{\circ}C$. LiNbO$_3$phase transforms to ilmenite at 13 CPa and $300^{\circ}C$ and at 10.8 CPa and $400^{\circ}C$, respectively. These data indicate that $LiNbO_3$phase may have a stability region in the hP-T phase diagram and that the perovskite-ilmenite phase boundary would be quite different from that previously reported.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.8
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• pp.728-733
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• 2008

Unsteady aerodynamic analysis of an air-pressure-levitated high-speed ground vehicle moving over the nonplanar ground surface are performed using the boundary-element method. The potential flow solution is included in a time-stepping loop and the wake is captured as part of the solution. When the vehicle moving inside the channel, the lift coefficient and the pitching moment coefficient of the vehicle are increased further because the air trapped by the channel increases the ground effect. In other words, the nonplanar ground surface such as the channel decreases further the longitudinal stability of the vehicle. On the other hand, there is little difference between the ground and the channel in the lateral stability of the vehicle because the lift increment due to the nonplanar ground surface such as the channel takes place on both sides of the wing with the same rate of increase.

• Journal of KIISE:Computer Systems and Theory
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• v.34 no.1
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• pp.28-37
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• 2007

This paper addresses a new surface reconstruction scheme for approximating the isosurface from a set of tomographic cross sectional images. Differently from the novel Marching cube algorithm, our method does not extract iso-density surface(isosurface) directly from the voxels but calculates the iso-density point(isopoint) first. After building the relatively coarse initial mesh by the Cell-boundary algorithm approximating the isosurface, it produces the final isosurface by iteratively shrinking and smoothing the initial mesh. Comparing with the Marching Cube algorithm, our method is robust and does not make any crack in resulting surface model. Furthermore, the proposed method surmounts the O(1)-adjacency limitation of MC in defining the isopoints by permitting the O(2) and O(3)-adjacent isopoints in surface reconstruction, and can produce more accurate isosurface. According to experiments, it is proved to be very robust and efficient for isosurface reconstruction from cross sectional images.

• Journal of the Korean Magnetics Society
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• v.26 no.3
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• pp.71-75
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• 2016

Monolayer $MoS_2$ is energetically most stable when it has a 1H phase, but 1H to 1T phase transition ($1H{\rightarrow}1T$) is easily realized by various ways. Even though magnetic moment is not observed during $1H{\rightarrow}1T$, $0.049{\mu}_B/MoS_2$ is obtained in local 1T phase; 75% 2H and 25% 1T phases are mixed in ($2{\times}2$) supercell. Most magnetic moment is originated from the 1T phase Mo atom in the supercell, while the magnetic moments of other atoms are negligible. As a result, magnetic/non-magnetic boundary is created in the monolayered $MoS_2$. Our result suggests that $MoS_2$ can be applied for spintronics such as a spin transistor.

• Journal of Korea Water Resources Association
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• v.31 no.4
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• pp.491-501
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• 1998

Numerical simulations were performed to analyse the flow pattern of the approach channel and to design the spillway guidewall for stable flow conditions. RMA-2, two dimensional finite element model which can easily represent complicated geometry was used, and model parameters were estimated from the observation data of hydraulic model test. Numerical experiments were made separately for the approach region and for the upstream region, and upstream boundary position of the hydraulic model beyond which the boundary effects are negligible was determined from the numerical results. For the stable flow condition in approach channel, alternative designs for guidewall were developed, and flow analysis for alternative designs was done through the numerical simulation. From the analysis of alternative design, we can see that the flow pattern in the approach channel is stable and the lateral stage difference disappears mostly before the spillway crest.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.16 no.1
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• pp.33-42
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• 2003

This paper deals with the FEM analysis of nonlinear sloshing of incompressible, invicid and irrotational flow in two dimensional rectangular tank. We use laplace equation based on potential theory as governing equation. For large amplitude sloshing motion, kinematic and dynamic free surface conditions derived from Bernoulli equation are applied. This problem is solved by FEM using 9-node elements. For the time integration and accurate velocity calculation, we introduce predictor-corrector time marching scheme and least square method. Also, numerical stability in tracking of free surface is obtained by direct calculation of free surface location to time variation. Numerical results of sloshing induced by harmonic excitations, while comparing with those of linear theory and references, prove the accuracy and stability. After verification of our program, we analyze sloshing response characteristics to the fluid height and the excitation amplitude.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.3
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• pp.102-113
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• 2017

A new index for the buckling strength of non-structured plates is proposed. The external work or the deformation energy caused by the external loads or the boundary displacement controled by a load parameter is calculated along an equilibrium path of the member under consideration. If the second variation of the energy with respect to the parameter loses its positiveness, it defined as the limit of the stability. In contrast to the current method given in codes where the stability limit is evaluated by using only representative internal forces, the evaluation of the stability limit is always consistent even with the change of the distribution of the internal forces on the boundary. If the elasticity is concerned, the result from this proposed approach becomes identical to that from the classical methods.