检索结果-南通市图书馆

Numerical simulation of wind-driven circulation and pollutant transport in Taihu Lake based on a quadtree grid

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Water Science and Engineering 2019年第2期12卷 108-114页

作者： Xiao-dong Liu Ling-qi Li Peng Wang Zu-lin Hua Li Gu Yuan-yuan Zhou Lu-ying Chen Key Laboratory of Integrated Regulation and Resource Development on Shallow Lakes of Ministry of Education Nanjing 210098China College of Environment Hohai UniversityNanjing 210098China

In this study,a two-dimensional flow-pollutant coupled model was developed based on a quadtree grid.This model was established to allow the accurate simulation of wind-driven flow in a large-scale shallow lake with irregular natural boundaries when focusing on important smallscale localized flow features.The quadtree grid was created by domain decomposition.The governing equations were solved using the finite volume method,and the normal fluxes of mass,momentum,and pollutants across the interface between cells were computed by means of a Godunov-type Osher scheme.The model was employed to simulate wind-driven flow in a circular basin with non-uniform depth.The computed values were in agreement with analytical data.The results indicate that the quadtree grid has fine local resolution and high efficiency,and is convenient for local refinement.It is clear that the quadtree grid model is effective when applied to complex flow domains.Finally,the model was used to calculate the flow field and concentration field of Taihu Lake,demonstrating its ability to predict the flow and concentration fields in an actual water area with complex geometry.

关键词： Numerical simulation Wind-driven circulation Pollutant transport quadtree grid Shallow-flow hydrodynamics Taihu Lake

Solution of N-S equations based on the quadtree cut cell method

在线全文

学校读者我要写书评

暂无评论

Science China(Physics,Mechanics & Astronomy) 2009年第6期52卷 877-884页

作者： KASE Kiwamu Volume CAD Modeling Team RIKEN Institute

With the characteristic of the quadtree data structure, a new mesh generation method, which adopts square meshes to decompose a background domain and a cut cell approach to express arbitrary boundaries, is proposed to keep the grids generated with a good orthogonality easily. The solution of N-S equations via finite volume method for this kind of unstructured meshes is derived. The mesh generator and N-S solver are implemented to study two benchmark cases, i.e. a lid driven flow within an inclined square and a natural convection heat transfer flow in a square duct with an inner hot circular face. The simulation results are in agreement with the benchmark values, verifying that the present methodology is valid and will be a strong tool for two-dimensional flow and heat transfer simulations, especially in the case of complex boundaries.

关键词： quadtree cut cell N-S equations finite volume method

Loose architecture of multi-level massive geospatial data based on virtual quadtree

在线全文

学校读者我要写书评

暂无评论

Science China(Technological Sciences) 2008年第S1期51卷 114-123页

作者： YANG ChongJun,WU Sheng,REN YingChao,FU Li,ZHANG FuQing,WANG Gang,TAN Jian,LIU DongLin,MA ChaoJi & LIANG Li State Key Laboratory of Remote Sensing Science,Jointly Sponsored by the Institute of Remote Sensing Applications of Chinese Academy of Sciences and Beijing Normal University,Beijing 100101,China State Key Laboratory of Remote Sensing Science Jointly Sponsored by the Institute of Remote Sensing Applications of Chinese Academy of Sciences and Beijing Normal University Beijing China

This paper proposed a virtual quadtree (VQT) based loose architecture of multi-level massive geospatial data for integrating massive geospatial data dispersed in the departments of different hierarchies in the same sector into a unified GIS (Geographic Information System) platform. By virtualizing the nodes of the quad-tree,the VQT separates the structure of data organization from data storage,and screens the difference between the data storage in local computer and in the re-mote computers in network environment. And by mounting,VQT easily integrates the data from the remote computers into the local VQT so as to implement seam-less integration of distributed multi-level massive geospatial data. Based on that mode,the paper built an application system with geospatial data over 1200 GB distributed in 12 servers deployed in 12 cities. The experiment showed that all data can be seamlessly rapidly traveled and performed zooming in and zooming out smoothly.

关键词： massive geospatial data virtual quadtree loose architecture

Image　Coding　Using　Wavelet　Transform　and　EntropyConstrained　Vector　Quantization　with　quadtree　Structure　Vectors

在线全文

学校读者我要写书评

暂无评论

Journal of Southeast University(English Edition) 1996年第1期12卷 19-24页

作者：高西奇何振亚

This paper presents a new wavelet transform image coding method. On the basis of a hierarchical wavelet decomposition of images, entropy constrained vector quantization is employed to encode the wavelet coefficients... 详细信息

关键词： wavelet transform entropy constrained vector quantization quadtree structure vector image coding

Spatial Topology Rule Checking Algorithm of Linear Entity Based on quadtree

在线全文

学校读者我要写书评

暂无评论

Journal of Geographic Information System 2009年第1期1卷 1-4页

作者： Shunping ZHOU Shaohuai CHEN Bo WAN 不详

Spatial topology rule is the primary method to insure the consistency and validity of spatial topology relation in GIS software. Topology rule can be divided into three categories according to geographic entity’s geometric shape: point topology rule, line topology rule and polygon topology rule. At first, this paper summarizes the various linear geographic entities’ topological relations which have practical application, then designs a series of linear entity topology rules detailedly. Based on these rules, this paper proposes a topology rule checking algorithm using quadtree, which is designed on the basis of MAPGIS7.4 spatial data model. The algorithm has already been applied to MAPGIS platform and gained good effects.

关键词： linear entity topology rule rule check quadtree

Finite cell method compared to h-version finite element method for elasto-plastic problems

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Applied Mathematics and Mechanics(English Edition) 2014年第10期35卷 1239-1248页

作者： A.ABEDIAN J.PARVIZIAN A.DSTER E.RANK Department of Mechanical Engineering Daneshpajoohan Higher Education Institute Department of Mechanical Engineering Isfahan University of Technology Numerische Strukturanalyse mit Anwendungen in der Schiffstechnik (M-10) Technische Universitt Hamburg-Harburg Lehrstuhl fr Computation in Engineering Fakultt fr Bauingenieur-und Vermessungswesen Technische Universitt Mnchen

The finite cell method （FCM） combines the high-order finite element method （FEM） with the fictitious domain approach for the purpose of simple meshing. In the present study, the FCM is used to the Prandtl-Reuss flow theory of plasticity, and the results are compared with the h-version finite element method （h-FEM）. The numerical results show that the FCM is more efficient compared to the h-FEM for elasto-plastic problems, although the mesh does not conform to the boundary. It is also demonstrated that the FCM performs well for elasto-plastic loading and unloading.

关键词： finite cell method （FCM） h-version finite element method （h-FEM）,Prandtl-Reuss quadtree octree

Efficient dark channel based image dehazing using quadtrees

在线全文

学校读者我要写书评

暂无评论

Science China(Information Sciences) 2013年第9期56卷 231-239页

作者： DING Meng TONG RuoFeng College of Computer Science and Technology Zhejiang University TNList Department of Computer Science and Technology Tsinghua University

Using dark channel prior-a kind of statistics of the haze-free outdoor images-to remove haze from a single image input is simple and effective. However, due to the use of soft matting algorithm, the method suffers from massive consumption of both memory and time, which largely limits its scalability for large images. In this paper, we present a hierarchical approach to accelerate dark channel based image dehazing. The core of our approach is a novel, efficient scheme for solving the soft matting problem involved in image dehazing, using adaptively subdivided quadtrees built in image space. Acceleration is achieved by transforming the problem of solving a N-variable linear system required in soft matting, to a problem of solving a much smaller m-variable linear system, where N is the number of pixels and m is the number of the corners in the quadtree. Our approach significantly reduces both space and time cost while still maintains visual fidelity, and largely extends the practicability of dark channel based image dehazing to handle large images.

关键词： image dehazing quadtree soft matting

VGIS-COLLIDE:an effective collision detection algorithm for multiple objects in virtual geographic information system

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

International Journal of Digital Earth 2011年第1期4卷 65-77页

作者： Feixiong Luo Ershun Zhong Junlai Cheng Yuefeng Huang State Key Lab of Resources and Environmental Information System Institute of Geographic Sciences and Natural Resources ResearchChinese Academy of SciencesBeijingChina

Collision detection is an important component in simulation applications which are based on virtual geographic information system(VGIS).In this paper,an effective collision detection algorithm for multiple objects in VGIS,VGISCOLLIDE,is presented.The algorithm firstly integrates existing quadtree,which is the global hierarchical structure of VGIS,with axis-aligned bounding box of object to perform the broad-phase of collision detection.After that,exact collision detection between two objects which have passed the broad-phase of collision detection is performed.The algorithm makes no assumption about input primitives or object’s motion and is directly applicable to all triangulated models.It can be applicable to both rigid and deformable objects without preprocessing.The performance of the algorithm has been demonstrated in several environments consisting of a high number of objects with hundreds of thousands of triangles.

关键词： collision detection multiple objects quadtree VGIS

Improving Linked-Lists Using Tree Search Algorithms for Neighbor Finding in Variable-Resolution Smoothed Particle Hydrodynamics

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Communications in Computational Physics 2019年第6期26卷 57-86页

作者： Shahab Khorasanizade J.M.M.Sousa IDMEC Instituto Superior T́ecnicoUniversidade de LisboaAv.Rovisco Pais1049-001 LisboaPortugal

Improving linked-lists for neighbor finding with the use of tree search algorithms is proposed here,aiming to cope with highly non-uniform resolution simulations employing a meshless method.The new procedure,coined quadtree Cells Grid,has been implemented in Smoothed Particle Hydrodynamics(SPH).The SPH scheme employed is adaptive,thus allowing for particle refinement in desired regions of the flow.Owing to the wide range of coexisting particle mass levels,standard linked-list neighbor search algorithms become ineffective.Hence,an alternative is found based on the use of hierarchical data structures,using quadtrees(in 2D problems).The present algorithm exploits the advantages of both linked-lists and quadtree meth-ods with the goal of increasing computational efficiency,when dealing with highly non-uniform particle distributions.Test cases involving two distinct flow problems have demonstrated that the computational cost of the current adaptive neighbor finding algorithm scales linearly with the total number of particles,thus retrieving this characteristic of linkedlists in uniform grid search.Nevertheless,the memory usage increased as a result of the more complex data structure.

关键词： Smoothed particle hydrodynamics linked-list quadtree neighbor finding variable resolution