The Minqin oasis is surrounded on three sides by the Tengger Desert and the Badanjilin Desert, and it prevents these two deserts from converging. However, in recent years it has become the worst ecological environment...The Minqin oasis is surrounded on three sides by the Tengger Desert and the Badanjilin Desert, and it prevents these two deserts from converging. However, in recent years it has become the worst ecological environment in the Lake area due to deficient water resources, continual declines in the groundwater level and quality （increasing mineralization and salination）, which are causing in- creasing desertification. In this study, Landsat Thematic Mapper （TM） remote images from 1992, 1998, 2002, and 2006 of the Lake area of the Minqin oasis are interpreted to analyze the desertification evolution. A combination of an ArcObjects module and a cellular automata model is used to build a model simulating the desertification dynamics; the forecasting accuracy of this model is shown to reach up to 90%. The desertification situation in 2012 is forecasted by this model, and the results showed that, from 2006 to 2012, the green land area will be reduced by 999.92 hm2 （l.59 percent of the total oasis area）, the desertification land area will be reduced by 3,000.68 hrn2 （4.78 percent of the total oasis area）, and sand land area will increase by 4,000.6 hm2 （6.37 per- cent of the total oasis area）. The sand land is predicted to become more widespread, and more than 18% sand land will be distrib- uted in the center of green land in the Lake area. In other words, more and more abandoned green land （mined farm land） will be transformed into sand land, and this will intensify the desertification.展开更多
A description of a mathematical algorithm for simulating grain structures with straight and hyperbolic interfaces is shown. The presence of straight and hyperbolic interfaces in many grain structures of metallic mater...A description of a mathematical algorithm for simulating grain structures with straight and hyperbolic interfaces is shown. The presence of straight and hyperbolic interfaces in many grain structures of metallic materials is due to different solidification conditions, in- eluding different solidification speeds, growth directions, and delaying on the nucleation times of each nucleated node. Grain growth is a complex problem to be simulated; therefore, computational methods based on the chaos theory have been developed for this purpose. Straight and hyperbolic interfaces are between columnar and equiaxed grain structures or in transition zones. The algorithm developed in this work involves random distributions of temperature to assign preferential probabilities to each node of the simulated sample for nucleation according to previously defined boundary conditions. Moreover, more than one single nucleation process can be established in order to gen- erate hyperbolic interfaces between the grains. The appearance of new nucleated nodes is declared in sequences with a particular number of nucleated nodes and a number of steps for execution. This input information influences directly on the final grain structure （grain size and dislribution）. Preferential growth directions are also established to obtain equiaxed and columnar grains. The simulation is done using rou- tines for nucleation and growth nested inside the main function. Here, random numbers are generated to place the coordinates of each new nucleated node at each nucleation sequence according to a solidification probability. Nucleation and growth routines are executed as a func- tion of nodal availability in order to know if a node will be part of a grain. Finally, this information is saved in a two-dimensional computa- tional array and displayed on the computer screen placing color pixels on the corresponding position forming an image as is done in cellular automaton.展开更多
A modified cellular automata （CA） model of dynamic recrystallization （DRX） and a flow stress-based nucleation parameter identification method have been developed. In the method, the modified CA model, which takes ...A modified cellular automata （CA） model of dynamic recrystallization （DRX） and a flow stress-based nucleation parameter identification method have been developed. In the method, the modified CA model, which takes the role of deformation degree on nucleation behavior into consideration, is coupled with an adaptive response surface model （ARSM） to search for the optimum nucleation parameter. The DRX behavior of an oxygen free high conductivity （OFHC） copper with different initial grain sizes has been taken as an example to validate the model. Good agreement is found between the simulated and the experimental results, which demonstrates that the new method can effectively improve the simulation accuracy.展开更多
针对船舶超大空间火灾对人员疏散能力的影响难以量化问题,本文基于元胞自动机理论,构建了一种行人个体自主分析火灾环境下温度和能见度影响的疏散模型(cellular automata model considering visibility and temperature, CAVT)。CAVT模...针对船舶超大空间火灾对人员疏散能力的影响难以量化问题,本文基于元胞自动机理论,构建了一种行人个体自主分析火灾环境下温度和能见度影响的疏散模型(cellular automata model considering visibility and temperature, CAVT)。CAVT模型采用Sigmoid函数和历史实验数据建立温度、能见度与人员运动能力的映射关系,基于FDS数值模拟结果建立火灾环境场对人员个体运动能力影响的时空耦合关系,使用熵值法计算温度场和能见度场在火灾环境场中的权重。以某客船超大空间为例开展研究分析,结果表明:火灾环境下人员疏散时间受火源功率影响较大,火源位置影响较小,出口宽度大于3 m,不影响疏散效率。与Pathfinder软件相比,CAVT模型可更准确模拟人员因高温和低能见度导致的运动能力的动态下降反馈。展开更多
基金supported by the National Natural Science Foundation of China (No. 40501073)the Fundamental Research Funds for the Central Universities (Nos. 11CX05015A and 10CX04047A)
文摘The Minqin oasis is surrounded on three sides by the Tengger Desert and the Badanjilin Desert, and it prevents these two deserts from converging. However, in recent years it has become the worst ecological environment in the Lake area due to deficient water resources, continual declines in the groundwater level and quality （increasing mineralization and salination）, which are causing in- creasing desertification. In this study, Landsat Thematic Mapper （TM） remote images from 1992, 1998, 2002, and 2006 of the Lake area of the Minqin oasis are interpreted to analyze the desertification evolution. A combination of an ArcObjects module and a cellular automata model is used to build a model simulating the desertification dynamics; the forecasting accuracy of this model is shown to reach up to 90%. The desertification situation in 2012 is forecasted by this model, and the results showed that, from 2006 to 2012, the green land area will be reduced by 999.92 hm2 （l.59 percent of the total oasis area）, the desertification land area will be reduced by 3,000.68 hrn2 （4.78 percent of the total oasis area）, and sand land area will increase by 4,000.6 hm2 （6.37 per- cent of the total oasis area）. The sand land is predicted to become more widespread, and more than 18% sand land will be distrib- uted in the center of green land in the Lake area. In other words, more and more abandoned green land （mined farm land） will be transformed into sand land, and this will intensify the desertification.
文摘A description of a mathematical algorithm for simulating grain structures with straight and hyperbolic interfaces is shown. The presence of straight and hyperbolic interfaces in many grain structures of metallic materials is due to different solidification conditions, in- eluding different solidification speeds, growth directions, and delaying on the nucleation times of each nucleated node. Grain growth is a complex problem to be simulated; therefore, computational methods based on the chaos theory have been developed for this purpose. Straight and hyperbolic interfaces are between columnar and equiaxed grain structures or in transition zones. The algorithm developed in this work involves random distributions of temperature to assign preferential probabilities to each node of the simulated sample for nucleation according to previously defined boundary conditions. Moreover, more than one single nucleation process can be established in order to gen- erate hyperbolic interfaces between the grains. The appearance of new nucleated nodes is declared in sequences with a particular number of nucleated nodes and a number of steps for execution. This input information influences directly on the final grain structure （grain size and dislribution）. Preferential growth directions are also established to obtain equiaxed and columnar grains. The simulation is done using rou- tines for nucleation and growth nested inside the main function. Here, random numbers are generated to place the coordinates of each new nucleated node at each nucleation sequence according to a solidification probability. Nucleation and growth routines are executed as a func- tion of nodal availability in order to know if a node will be part of a grain. Finally, this information is saved in a two-dimensional computa- tional array and displayed on the computer screen placing color pixels on the corresponding position forming an image as is done in cellular automaton.
基金supported by the National Basic Research Program of China (No. 2006CB705401)the National Natural Science Foundation of China (No.51075270)the Natural Science Foundation of the Jiangsu Higher Education Institutions of China (No.10KJD460003)
文摘A modified cellular automata （CA） model of dynamic recrystallization （DRX） and a flow stress-based nucleation parameter identification method have been developed. In the method, the modified CA model, which takes the role of deformation degree on nucleation behavior into consideration, is coupled with an adaptive response surface model （ARSM） to search for the optimum nucleation parameter. The DRX behavior of an oxygen free high conductivity （OFHC） copper with different initial grain sizes has been taken as an example to validate the model. Good agreement is found between the simulated and the experimental results, which demonstrates that the new method can effectively improve the simulation accuracy.
文摘针对船舶超大空间火灾对人员疏散能力的影响难以量化问题,本文基于元胞自动机理论,构建了一种行人个体自主分析火灾环境下温度和能见度影响的疏散模型(cellular automata model considering visibility and temperature, CAVT)。CAVT模型采用Sigmoid函数和历史实验数据建立温度、能见度与人员运动能力的映射关系,基于FDS数值模拟结果建立火灾环境场对人员个体运动能力影响的时空耦合关系,使用熵值法计算温度场和能见度场在火灾环境场中的权重。以某客船超大空间为例开展研究分析,结果表明:火灾环境下人员疏散时间受火源功率影响较大,火源位置影响较小,出口宽度大于3 m,不影响疏散效率。与Pathfinder软件相比,CAVT模型可更准确模拟人员因高温和低能见度导致的运动能力的动态下降反馈。
文摘文章的目的是对格子玻尔兹曼方法进行系统的介绍,格子玻尔兹曼方法(Lattice BoltzmannMethod)的出现直接来源于20世纪60年代的元胞自动机(Cellular Automata)思想,而这一方法用于解决流动现象时,又可以追溯到19世纪的分子运动论,求解的是Boltzmann提出的玻尔兹曼输运方程,因此将这一方法称为格子玻尔兹曼方法,之前也被称为格子气自动机(Lattice Gas Automa-ton)。该方法多用于研究复杂现象,如材料晶体凝聚时的生长过程、城市土地利用的演化等方面。在20世纪70年代由Hardy、Pomeau和Pazzis建立了第一个用于研究流体运动的格子气自动机,此后,这一方法被广泛用来模拟各种流动问题,诸如二相流、孔隙介质中的渗流等,并根据这一方法开发了相应的商业软件PowerFlow。同时,格子玻尔兹曼方法由于其在微观水平描述运动的特点,成为研究湍流的一个很好的数值计算工具,特别是用其进行直接数值模拟(DNS)计算,成为继传统的差分法、有限体积法和谱方法之后的又一有力的手段。而作为大气运动的一个主要现象的大气湍流,比普通湍流更加复杂,在这里着重介绍了大气湍流的特点和应用格子玻尔兹曼方法模拟湍流的发展过程。
