Simulation of braided river flow using a new cellular routing scheme     

R. Thomas  A. P. Nicholas 《Geomorphology》2002,43(3-4)

Results are presented from a numerical simulation of two-dimensional flow patterns in a braided river using a simple cellular routing scheme. The results of the routing scheme are compared with field measurements of discharge per unit width obtained within the study reach at low flow and, for higher flows, with the predictions of a more sophisticated hydraulic model that solves the two-dimensional shallow water form of the Navier–Stokes equations. An assessment is made of the sensitivity of the routing scheme to variations in the values of its main parameters, and appropriate values are determined based on the physical characteristics of the study site and available flow measurements. It is shown that despite the simple approach adopted by the cellular routing scheme to simulate processes of water redistribution, it is able to replicate accurately both the field data and the results of the more sophisticated hydraulic model. These results indicate that the routing scheme outlined here is able to overcome some of the limitations of previous simple cellular automata models and may be suitable for use in modelling bedload transport and channel change in complex fluvial environments. As such this research represents a small and ongoing contribution to the field of numerical simulation of braided river processes.  相似文献   

Cellular modelling as a tool for interpreting historic braided river evolution     

R. Thomas  A.P. Nicholas  T.A. Quine 《Geomorphology》2007,90(3-4):302

Results are presented from a new cellular model of braided river dynamics that simulates flow, sediment transport, morphological change and the effects of braidplain vegetation. This model is used to investigate the effect of changes in upstream sediment supply on braided river systems over simulation periods of 200 years. Modelled changes in channel morphology, associated with both aggradation and degradation, were seen to be consistent with those reported in the literature. In addition, simulation results allowed the identification of diagnostic characteristics of aggrading and degrading reaches, in the form of relationships between the age, extent and relative elevation of fluvial surfaces. Interpretation of spatial patterns of valley floor surface characteristics in the Avoca River, New Zealand, on the basis of these relationships, allowed the identification of channel reaches that appear to be experiencing either aggradation or degradation. These inferences are shown to be consistent with independent evidence of spatial patterns of sediment supply to the main valley floor, derived from aerial photographs and an existing sediment source inventory. These results illustrate the potential for using cellular models to develop an improved understanding of natural river behaviour.  相似文献   

Statistics of shallow convection on Mars based on large-eddy simulations. Part 1: shearless conditions     

Zbigniew Sorbjan 《Boundary-Layer Meteorology》2007,123(1):121-142

Results of large-eddy simulations of shallow, quasi-steady, shear-less convection in the Martian boundary layer are presented and discussed. In the considered three cases, turbulence is forced by the radiative flux divergence, prescribed as given functions of height, and the strength of the surface heat flux. It is constrained by the temperature inversion at the boundary-layer top. The resulting convective boundary layer exhibits horizontal cellular structures. The presence of radiative heating causes dimensionless statistics of turbulence to depend on the parameter F, defined in terms of the integrated radiative and turbulent heating rates in the boundary layer.  相似文献   

土地资源的动态监测和动态模拟研究   总被引：18，自引：3，他引：15  

崔伟宏  张显峰 《地球信息科学学报》2002,4(1):79-85

本文结合国家“九五”攻关项目 ,介绍了有关利用 3S技术进行县级土地资源动态监测的最新研究成果 ;将细胞自动机 (Cellular Automaton,CA )与 GIS系统集成 ,构建了基于 CA的土地利用演化模型.  相似文献   

运用细胞自动机模型模拟强震前地震活动时间演化过程     

李纲  刘杰  傅征祥  刘桂萍 《地震》2004,24(1):34-41

强震发生前震源及其周围地区可能会出现前震活动, 这种前震活动可以分为二种: 一种为连续型, 即前震的频度或震级随时间渐渐增大, 直至主震发生; 另一种为不连续型, 前震的频度和震级先增大后减小, 然后发震。 这种现象不但在破裂声发射试验中观测到, 也在中国大陆地区多次强震前被观测到。 文中基于细胞自动机模型, 引入时间-状态依从摩擦本构关系, 即把自组织非线性系统的普适特征与真实断层摩擦的具体特征结合起来, 研究了强震前短期前兆地震活动的时间演化过程的机理。 文中研究了模型中各参数对模拟事件时间过程的影响, 结果表明, 静摩擦强度在断层上的分布, 或是说静摩擦系数的离散程度直接影响强震前地震活动时间演化过程。  相似文献   

Modelling fluid flow through a single fracture with different contacts using cellular automata     

Peng-Zhi Pan  Xia-Ting FengDing-Ping Xu  Lin-Fang ShenJin-Bao Yang 《Computers and Geotechnics》2011

The representation of the surface of a rock fracture and a numerical method to simulate fluid flow in single fractures are the keys to understanding the hydraulic behaviour of rock fractures. In this paper, a cellular automaton (CA) approach is used to generate the single fracture structure, which is assumed to be composed of contacts and voids. We develop a CA evolution rule to produce a contact area, and randomly model a single rock fracture with different contact ratios to reflect natural fracture properties such as dead voids, islands and tortuous flow path. Then, based on the localisation theory of a CA, a numerical method to simulate fluid flow in single fractures with contacts is developed. In this method, the fracture is discretised into a system composed of cell elements. Different apertures, i.e., zero for contacts and non-zero for voids, are assigned to each cell element. Therefore, the contribution of the cell elements in a contact on a cell’s transmissivity can be ignored completely. The local transmissivity is assumed to conform to the cubic law. The fluid flow in a fracture with different contact situations is then modelled using the method established in this paper. The fluid flow path, flow velocity and fluid head distributions as well as the channel flow in the fracture are well-modelled. The flow behaviour of the fracture strongly depends on the effective fluid flow path.  相似文献   

Investigations on the influence of pore‐space geometry on concentration patterns and transportation properties of dissolved oxygen in a bioactive sandy sediment by a lattice Boltzmann automaton model     

R. Haußels  Th. Klenke  J. Kropp  W. Ebenhh 《水文研究》2001,15(1):81-96

A lattice Boltzmann automaton (LBA) is used as a modelling approach to investigate the influence of pore‐space geometry on intrinsic processes and component distributions in recent tidal sediments. The simulations are performed on real pore‐space structures obtained from scanning electron photomicrographs, which document the mesoscopic geometry of bioactive sandy surface sediments. The discrete transport–reaction model for dissolved oxygen shows that in advective controlled systems oxygen concentration properties can be clearly related to the pore‐space geometry. Variability of measured high‐resolution concentration gradients can therefore can be attributed to the structural heterogeneity of pore‐space geometry. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

An extended cellular automaton using case‐based reasoning for simulating urban development in a large complex region     

Xia Li  Xiaoping Liu 《International journal of geographical information science》2013,27(10):1109-1136

Rule‐based cellular automata (CA) have been increasingly applied to the simulation of geographical phenomena, such as urban evolution and land‐use changes. However, these models have difficulties and uncertainties in soliciting transition rules for a large complex region. This paper presents an extended cellular automaton in which transition rules are represented by using case‐based reasoning (CBR) techniques. The common k‐NN algorithm of CBR has been modified to incorporate the location factor to reflect the spatial variation of transition rules. Multi‐temporal remote‐sensing images are used to obtain the adaptation knowledge in the temporal dimension. This model has been applied to the simulation of urban development in the Pearl River Delta which has a hierarchy of cities. Comparison indicates that this model can produce more plausible results than rule‐based CA in simulating this large complex region in 1988–2002.  相似文献   

Integrated modelling of population,employment and land-use change with a multiple activity-based variable grid cellular automaton     

Roger White  Inge Uljee  Guy Engelen 《International journal of geographical information science》2013,27(7):1251-1280

A constrained cellular automaton (CA) framework is used to model both land use and, at the same resolution, densities of population and economic activity. The multi-scale processes determining the location of population, economic activity and land use are captured in a variable grid CA, in which the neighbourhood of each cell includes the entire modelled area. The transition rules generating the spatial dynamics incorporate both the land use and the activities, and because they cover the entire modelled area, they represent interaction effects at all spatial scales; effectively, they are distance decay functions. In general, any particular cell hosts a number of activities (population, employment in various sectors) regardless of its land use, so in effect multiple land uses are modelled as multiple activities, although activity levels are normally highest on cells of the corresponding land use. The model is applied to both the urban-centred Greater Dublin Region and the country of Belgium, which consists of the entire polycentric urban system and its rural matrix. Results for both applications are good, as measured by the errors of both predicted populations and fractal dimensions, and the model outperforms the best existing models by these measures.  相似文献   

基于应变率场的全球地震活动特征模拟探索     

王武星  石耀霖 《地震》2013,33(4):123-134

本文提出利用全球应变率资料模拟全球地震活动特征的基本思想, 并作了初步探索。 利用GSRM的全球应变率场结果, 初步设计了模拟全球地震活动时空分布特征的细胞自动机模型。 该模型把地球考虑为一个自组织的整体系统, 制定了细胞自动机的演化规则, 获得了模拟的人工地震目录。 初步的模拟结果基本反映了全球地震活动的主要分布特征, 体现了全球构造活动强弱的主要格局, 初步达到了利用GPS等实测资料计算的应变率作为细胞自动机网格状态及其改变量来模拟复杂的全球地震活动特征的实验目的。  相似文献