• 한국전산유체공학회:학술대회논문집
• /
• 2009.04a
• /
• pp.116-120
• /
• 2009

A two-dimensional unsteady inviscid flow solver has been developed for the simulation of complex geometric configurations on adaptive Cartesian meshes. Embedded condition was used for boundary condition and a predictor-corrector explicit time marching scheme was used for time-accurate numerical simulation. The Cartesian mesh generator, which was previously developed for steady problem, was used grid generation for unsteady flow. The solver was based on ALE formulation for body motion. For diminishing the effects of cut-cells, the cell merging method was used. Using cell merging method, it was eliminated the CFL constraints. The conservation problem, which is caused cell-type variation around region swept by solid boundary, was also solved using cell merging method. The results are presented for 2D circular cylinder and missile launching problem.

• Journal of KIISE
• /
• v.43 no.12
• /
• pp.1428-1436
• /
• 2016

A multipath routing in wireless sensor networks (WSNs) provides advantage such as reliability improvement and load balancing by transmitting data through divided paths. For these reasons, existing multipath routing protocols divide path appropriately or create independent paths efficiently. However, when the sink node moves to avoid hotspot problem or satisfy the requirement of the applications, the existing protocols have to reconstruct multipath or exploit foot-print chaining mechanism. As a result, the existing protocols will shorten the lifetime of a network due to excessive energy consumption, and lose the advantage of multipath routing due to the merging of paths. To solve this problem, we propose a multipath creation and maintenance scheme to support the mobile sink node. The proposed protocol can be used to construct local grid structure with restricted area and exploit grid structure for constructing the multipath. The grid structure can also be extended depending on the movement of the sink node. In addition, the multipath can be partially reconstructed to prevent merging paths. Simulation results show that the proposed protocol is superior to the existing protocols in terms of energy efficiency and packet delivery ratio.

• Proceedings of the Korean Information Science Society Conference
• /
• 2001.10b
• /
• pp.535-537
• /
• 2001

3D MMORPG(Massive Multi-play Outline Role Playing Game) 게임은 넓은 3차원원지형을 실시간으로 표현되어야 하며, 많은 어려움이 따른다. 본 논문에서는 이러한 지형 처리를 위하여 메쉬나 버텍스, 혹은 폴리곤으로 사실적인 지형처리와 렌드링 속도 향상을 위하여 3차원 폴리곤을 동적으로 생성시키는 방법을 이용하려고 한다. 넓은 지형을 처리하기 위해서는 전체를 한번에 표현하기보다는 페이지 단위로 처리하기 위하여 격자화된 타일로 이루어진 맵으로 처리할 수 있다. Height field 처리 기법은 일정한 영역을 페이지 단위로 구분하고 처리할 수 있다. 옥트리를 이용하여 공간을 입체적인 컬링 방법으로 분할하고, 이를 세부 수준으로 나누어 처리하기 위해 CLOD(Continuous Level of Detail) 개념을 적용할 수 있다. 거리의 변화에 따라 지명을 표현하는 vertex들을 병합 또는 삭제함으로써 그 표현의 정도를 동적으로 달리 할 수 있는 CLOD를 이용하여 카메라의 위치와 방향에 따라 적절한 폴리곤을 생성해 낼 수 있다. 본 논문은 3 차원의 넓은 외부 지형을 실시간으로 처리할 경우 발생되는 그래픽 문제를 해결하기 위해 사용되는 방법 중에서 대표적인 방법을 통하여 효율적인 처리 기법을 제시하려 한다.

• Proceedings of the Korea Information Processing Society Conference
• /
• 2012.04a
• /
• pp.291-294
• /
• 2012

본 논문에서는 주어진 환경에 대한 정보가 충분하지 않은 상황에서 지능형 에이전트에게 요구되는 스스로의 위치를 파악하기 위해 로봇이 자신의 위치 추정과 동시에 주위 환경을 인식하여 주변 지도를 작성하는 방법을 제안한다. 이동 로봇의 위치를 추정하기 위해 센서 측정값을 통해 계산된 결과 값을 파티클 필터에 적용하며 로봇의 환경 지도 작성을 위해 점유 격자 지도 방법을 사용한다. 이 두 방법을 병합하여 동시적 위치 추정 및 지도 작성 문제에 적용하여 시스템을 설계 및 구현해보고 실험결과를 소개한다.

• Korean Journal of Crystallography
• /
• v.1 no.2
• /
• pp.99-104
• /
• 1990

The hetero-epitaxial growth of AmB v type onto-electronic material is attempted by means of the laser-induced chemical vapour deposition technique. The bimolecular gas phase reaction of trimethylgallium with ammonia on (001) alumina substrate for the epitaxy of gallium nitride is chosen as a model system. In this study, ArF exciter laser (193nm) is employed as a photon source. Marked difference is found in nucleation and in subsequent crystal incorporation between the doposits formed with and without the laser-irradiation. The surface coverage with isomorphically grown drystallites is pronounced upon "volume-excited" irradiation in comparison with the conventional thermal process. As to the crystal structure of the grown layers, the laser-induced deposits of GaN may be represented by either of the following two models: (001) plane of sapphire //y (001) plane of wurtzite-type GaN, OR (001) plane of sapphire//(001) plane of wurtzite-type-GaN (111) plane of twinned zinc blende-type GaN.

• Journal of the Korean earth science society
• /
• v.31 no.6
• /
• pp.555-562
• /
• 2010

Three-dimensional laser scanner was used to accurately measure any possible strain on a slope under pertaining stress with the time difference of 7 months. The laser scanner has the ability to measure the 3-D coordinate of a target point by calculating the travel time of laser beam between the laser device and the target point, and has been proved to be effective for analysis of the displacement of slopes or large construction. The scanning data measured with time difference were analyzed to find any strain by approaches of plane angle change, curvature variation, twist of frame, displacement of merging point, etc. From the analysis, some weak points showing heavily distorted shape were detected, which was used to design the reinforcement.

• The Journal of Korea Robotics Society
• /
• v.9 no.2
• /
• pp.104-110
• /
• 2014

Mapping is a fundamental element for robotic services. There are available many types of map data representation such as grid map, metric map, topology map, etc. As more robots are deployed for services, more chances of exchanging map data among the robots emerge and standardization of map data representation (MDR) becomes more valuable. Currently, activities in developing MDR standard are underway in IEEE Robotics and Automation Society. The MDR standard is for a common representation and encoding of the two-dimensional map data used for navigation by mobile robots. The standard focuses on interchange of map data among components and systems, particularly those that may be supplied by different vendors. This paper aims to introduce MDR standard and its application to map merging. We have applied the basic structure of the MDR standard to a grid map and Voronoi graph as a kind of topology map and performed map merging between two different maps. Simulation results show that the proposed MDR is suitable for map data exchange among robots.

• Journal of Korea Water Resources Association
• /
• v.52 no.10
• /
• pp.697-706
• /
• 2019

A multiphase flow modeling approach equipped with a hybrid turbulence modeling method is applied to compute the gravity currents in a rectangular channel. The present multiphase solver considers the dense fluid, the less-dense ambient fluid and the air above free surface as three phases with separate flow equations for each phase. The turbulent effect is simulated by the IDDES (improved delayed detach eddy simulation), a hybrid RANS/LES, approach which resolves the turbulent flow away from the wall in the LES mode and models the near wall flow in RANS mode on moderately fine computational meshes. The numerical results show that the present model can successfully reproduce the gravity currents in terms of the propagation speed of the current heads and the emergence of large-scale Kelvin-Helmholtz type interfacial billows and their three dimensional break down into smaller turbulent structures, even on the relatively coarse mesh for wall-modeled RANS computation with low-Reynolds number turbulence model. The present solutions reveal that the modeling approach can capture the large-scale three dimensional behaviors of gravity current head accompanied by the lobe-and-cleft instability at affordable computational resources, which is comparable to the LES results obtained on much fine meshes. It demonstrates that the multiphase modeling method using the hybrid turbulence model can be a promising engineering solver for predicting the physical behaviors of gravity currents in natural environmental configurations.

• Korean Journal of Remote Sensing
• /
• v.24 no.2
• /
• pp.141-152
• /
• 2008

The 3D building modeling is one of crucial components in constructing 3D geospatial information. The existing methods for 3D building modeling depend mainly on manual photogrammetric processes, which indeed take great amount of time and efforts. In recent years, many researches on 3D building modeling using aerial LiDAR data have been actively performed to aim at overcoming the limitations of existing 3D building modeling methods. Either techniques with interpolated grid data or data fusion with digital map and images have been investigated in most of existing researches on 3D building modeling with aerial LiDAR data. The paper proposed a method of 3D building modeling with LiDAR data only. Firstly, octree-based segmentation is applied recursively to LiDAR data classified as buildings in 3D space until there are no more LiDAR points to be segmented. Once octree-based segmentation is completed, each segmented patch is thereafter merged together based on its geometric spatial characteristics. Secondly, building model components are created with merged patches. Finally, a 3D building model is generated and composed with building model components. The experimental results with real LiDAR data showed that the proposed method was capable of modeling various types of 3D buildings.

• The Transactions of the Korea Information Processing Society
• /
• v.3 no.6
• /
• pp.1407-1417
• /
• 1996

In recent researches on thread partitioning algorithms break a thread at the long latency operation and merge threads to get the longer threads under the given constraints. Due to this limitation, even a program with little parallelism is partitioned into small-sized threads and context-swithings occur frequently. In the paper, we propose another method array localization about the array name, dependence distance(the difference of accessed element index from loop index), and the element usage that indicates whether element is used or defined. Using this information we can allocate array elements to the node where the corresponding loop activation is executed. By array localization, remote accesses to array elements can be replaced with local accesses to localized array elements. As a resuit,the boundaries of some threads are removed, programs can be partitioned into the larger threads and the number of context switchings reduced.