• Title/Summary/Keyword: Spatial Grid

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Influence of TVD Schemes on the Spatial Accuracy of Turbulent Flows Around a Hull When Using Structured and Unstructured Grids (정렬 및 비정렬 격자를 이용한 선체 주위 유동에서 TVD 기법이 공간 정확도에 미치는 영향)

  • Sim, Min Gyeoung;Lee, Sang Bong
    • Journal of the Society of Naval Architects of Korea
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    • v.58 no.3
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    • pp.182-190
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    • 2021
  • Computational simulations of turbulent flows around a model ship have been performed to investigate an influence of TVD schemes on the accuracy of advective terms associated with ship resistances. Several TVD schemes including upwind, second-order upwind, vanLeer, and QUICK as well as a nonTVD linear scheme were studied by examining temporal and spatial characteristics of accuracy transition in adjacent cells to the hull. Even though vanLeer scheme was the most accurate among TVD schemes in both structured and unstructured grid systems, the ratio of accuracy switch from 2nd order to 1st order in vanLeer scheme was considerable compared with the 2nd order linear scheme. Also, the accuracy transition was observed to be overally scattered in the unstructured grid while the accuracy transition in the structured grid appeared relatively clustered. It concluded that TVD schemes had to be carefully used in computational simulations of turbulent flows around a model ship due to the loss of accuracy despite its attraction of numerical stability.

Flow solutions around rectangular cylinders: The question of spatial discretization

  • Corsini, Roberto;Angeli, Diego;Stalio, Enrico;Chibbaro, Sergio;Cimarelli, Andrea
    • Wind and Structures
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    • v.34 no.1
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    • pp.151-159
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    • 2022
  • The aerodynamics of blunt bodies with separation at the sharp corner of the leading edge and reattachment on the body side are particularly important in civil engineering applications. In recent years, a number of experimental and numerical studies have become available on the aerodynamics of a rectangular cylinder with chord-to-thickness ratio equal to 5 (BARC). Despite the interest in the topic, a widely accepted set of guidelines for grid generation about these blunt bodies is still missing. In this work a new, well resolved Direct Numerical Simulation (DNS) around the BARC body at Re=3000 is presented and its results compared to previous DNSs of the same case but with different numerical approaches and mesh. Despite the simulations use different numerical approaches, mesh and domain dimensions, the main discrepancies are ascribed to the different grid spacings employed. While a more rigorous analysis is envisaged, where the order of accuracy of the schemes are kept the same while grid spacings are varied alternately along each spatial direction, this represents a first attempt in the study of the influence of spatial resolution in the Direct Numerical Simulation of flows around elongated rectangular cylinders with sharp corners.

A Study of Optimal Mesh Interface Region Generation to Improve Spatial and Temporal Accuracy (공간 및 시간 정확도 향상을 위한 최적의 삽간영역 구성에 관한 연구)

  • Cho Kum Won
    • Journal of computational fluids engineering
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    • v.8 no.3
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    • pp.41-49
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    • 2003
  • The spatial accuracy becomes first-order when second-order conservation schemes including the non-conservative interpolation in general Chimera method are used. To ensure the solution accuracy, the discontinuities must be located away from the overlapped regions, and the length of overlapped region also must be proportional to the grid spacing. In this paper, a proposed method, cut-paste algorithm, is used to satisfy above constraints. The cut-paste algorithm can generate the optimal mesh inteface region automatically, To validate the spatial and temporal accuracy due to the non-conservative interpolation, inviscid and viscous problems are tested.

Spatial Selectivity Estimation for Intersection region Information Using Cumulative Density Histogram

  • Kim byung Cheol;Moon Kyung Do;Ryu Keun Ho
    • Proceedings of the KSRS Conference
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    • 2004.10a
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    • pp.721-725
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    • 2004
  • Multiple-count problem is occurred when rectangle objects span across several buckets. The Cumulative Density (CD) histogram is a technique which solves multiple-count problem by keeping four sub-histograms corresponding to the four points of rectangle. Although it provides exact results with constant response time, there is still a considerable issue. Since it is based on a query window which aligns with a given grid, a number of errors may be occurred when it is applied to real applications. In this paper, we proposed selectivity estimation techniques using the generalized cumulative density histogram based on two probabilistic models: (1) probabilistic model which considers the query window area ratio, (2) probabilistic model which considers intersection area between a given grid and objects. In order to evaluate the proposed methods, we experimented with real dataset and experimental results showed that the proposed technique was superior to the existing selectivity estimation techniques. The proposed techniques can be used to accurately quantify the selectivity of the spatial range query on rectangle objects.

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Study of Spatial and Temporal Accuracy Estimation Related with Mesh Interafce Region on Overlapped Grids (중첩격자계에서 교차영역 구성에 따른 시간/공간 정확도에 관한 연구)

  • Cho K. W.;Kwon J. H.;Lee S.
    • 한국전산유체공학회:학술대회논문집
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    • 1999.11a
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    • pp.95-107
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    • 1999
  • The spatial error due to the non-conservative interpolation become first-order when second-order conservative schemes are used, discontinuities are located away from the overlapped regions, and if the length of the overlapped region is not proportional to the grid spacing. Therefore, the solution accuracy is ensured if two domains overlap each other with a fixed grid point and the interpolation is occurred in smooth flow regions. To validate the spatial and temporal accuracy due to the non-conservative interpolation, inviscid and viscous problems are tested.

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Performance Evaluation of Spatial Clustering Method using Regular Grid (균등 격자를 이용한 공간 클러스터링 기법의 성능 평가)

  • 문상호
    • Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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    • 2003.10a
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    • pp.468-471
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    • 2003
  • In this paper, experimental tests are performed to evaluate the efficiency of spatial clustering method using regular grid that is proposed in our recent research. In details, we estimate the execution time for finding clusters varying spatial objects on sample data sets with various distributions and perform experimental tests varying threshold value on a data set. We also compare the running time of cluster generating algorithm with that of cluster merging algorithm per each test.

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A Novel Air Indexing Scheme for Window Query in Non-Flat Wireless Spatial Data Broadcast

  • Im, Seok-Jin;Youn, Hee-Yong;Choi, Jin-Tak;Ouyang, Jinsong
    • Journal of Communications and Networks
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    • v.13 no.4
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    • pp.400-407
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    • 2011
  • Various air indexing and data scheduling schemes for wireless broadcast of spatial data have been developed for energy efficient query processing. The existing schemes are not effective when the clients' data access patterns are skewed to some items. It is because the schemes are based on flat broadcast that does not take the popularity of the data items into consideration. In this paper, thus, we propose a data scheduling scheme letting the popular items appear more frequently on the channel, and grid-based distributed index for non-flat broadcast (GDIN) for window query processing. The proposed GDIN allows quick and energy efficient processing of window query, matching the clients' linear channel access pattern and letting the clients access only the queried data items. The simulation results show that the proposed GDIN significantly outperforms the existing schemes in terms of access time, tuning time, and energy efficiency.

Design of Spatial Clustering Method for Spatial Objects with Polygonometry (다각형 객체를 지원하는 공간 클러스터링 기법의 설계)

  • 황지완;문상호
    • Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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    • 2004.05b
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    • pp.374-377
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    • 2004
  • Existing Clustering Methods for spatial data mining process only point objects, not objects with polygonometry such as lines and areas. It is because that distance computation between objects with polygonomery for clustering is more complex than point objects. To solve this problem, we design a clustering method based on regular grid cell structures. In details, it refutes cost and time for distance computation using cell relationships in grid cell structures.

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An Enhanced Density and Grid based Spatial Clustering Algorithm for Large Spatial Database (대용량 공간데이터베이스를 위한 확장된 밀도-격자 기반의 공간 클러스터링 알고리즘)

  • Gao, Song;Kim, Ho-Seok;Xia, Ying;Kim, Gyoung-Bae;Bae, Hae-Young
    • The KIPS Transactions:PartD
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    • v.13D no.5 s.108
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    • pp.633-640
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    • 2006
  • Spatial clustering, which groups similar objects based on their distance, connectivity, or their relative density in space, is an important component of spatial data mining. Density-based and grid-based clustering are two main clustering approaches. The former is famous for its capability of discovering clusters of various shapes and eliminating noises, while the latter is well known for its high speed. Clustering large data sets has always been a serious challenge for clustering algorithms, because huge data set would make the clustering process extremely costly. In this paper, we propose an enhanced Density-Grid based Clustering algorithm for Large spatial database by setting a default number of intervals and removing the outliers effectively with the help of a proper measurement to identify areas of high density in the input data space. We use a density threshold DT to recognize dense cells before neighbor dense cells are combined to form clusters. When proposed algorithm is performed on large dataset, a proper granularity of each dimension in data space and a density threshold for recognizing dense areas can improve the performance of this algorithm. We combine grid-based and density-based methods together to not only increase the efficiency but also find clusters with arbitrary shape. Synthetic datasets are used for experimental evaluation which shows that proposed method has high performance and accuracy in the experiments.

Development of GRld-eased Soil MOsture Routing Model (GRISMORM) Applied to Bocheongchun Watershed (격자기반의 토양수분추적표형 개발 : 보청천 유역 사례연구)

  • 김성준;채효석
    • Spatial Information Research
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    • v.7 no.1
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    • pp.39-48
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    • 1999
  • A GRId-based Soil MOsture Routing Model(GRISMORM) which predicts temporal variation and spatial distribution of water balance on a daily time step for each grid element of the watershed was developed. The model was programmed by C-language which aims for high flexibility to any kind of GIS softwares. The model uses ASCII-formatted map data supported by the irregular gridded map of the GRASS(Geographic Resources Analysis Support System)-GIS and generates daily or monthly spatial distribution map of water balance components within the watershed. The model was applied to Ipyunggyo watershed(75.6$km^2$) ; the part of Bocheongchun watershed. Predicted streamflows resulting from two years(95 and 96) daily data were compared with those observed at the watershed outlet. The results of temporal variation and spatial distribution of soil moisture are also presented by using GRASS.

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