Geography requires a comprehensive understanding of both natural and human factors,as well as their interactions.Due to the complexity and multiplicity of geographic problems,various theories and methods for geographi...Geography requires a comprehensive understanding of both natural and human factors,as well as their interactions.Due to the complexity and multiplicity of geographic problems,various theories and methods for geographic modelling and simulation have been proposed.Currently,geography has entered an era in which quantitative analysis and modelling are essential for understanding the mechanisms of geographic processes.As the basic idea of quantitative spatial analysis,the specified space often needs to be partitioned by a series of small computational units(cells),i.e.,grids.Thus,there is a close relationship between the grids and geographic modelling.This article reviews the mainstream and typical grids used for modelling and simulation.In addition to classification,the derived theories and technologies,including grid generation methods,data organization strategies,multi-dimensional querying methods,and grid adaptation techniques,are discussed.For integrated geographic simulation to explore comprehensive geographic problems,we argued that it is reasonable to build bridges among different types of grids(e.g.,transformation strategies),and more powerful grids that can support multi-type of numerical computation are urgently needed.展开更多
Two of the main challenges in optimal control are solving problems with state-dependent running costs and developing efficient numerical solvers that are computationally tractable in high dimensions.In this paper,we p...Two of the main challenges in optimal control are solving problems with state-dependent running costs and developing efficient numerical solvers that are computationally tractable in high dimensions.In this paper,we provide analytical solutions to certain optimal control problems whose running cost depends on the state variable and with constraints on the control.We also provide Lax-Oleinik-type representation formulas for the corresponding Hamilton-Jacobi partial differential equations with state-dependent Hamiltonians.Additionally,we present an efficient,grid-free numerical solver based on our representation formulas,which is shown to scale linearly with the state dimension,and thus,to overcome the curse of dimensionality.Using existing optimization methods and the min-plus technique,we extend our numerical solvers to address more general classes of convex and nonconvex initial costs.We demonstrate the capabilities of our numerical solvers using implementations on a central processing unit(CPU)and a field-programmable gate array(FPGA).In several cases,our FPGA implementation obtains over a 10 times speedup compared to the CPU,which demonstrates the promising performance boosts FPGAs can achieve.Our numerical results show that our solvers have the potential to serve as a building block for solving broader classes of high-dimensional optimal control problems in real-time.展开更多
Rasterization is a conversion process accompanied with information loss, which includes the loss of features＇ shape, structure, position, attribute and so on. Two chief factors that affect estimating attribute accura...Rasterization is a conversion process accompanied with information loss, which includes the loss of features＇ shape, structure, position, attribute and so on. Two chief factors that affect estimating attribute accuracy loss in rasterization are grid cell size and evaluating method. That is, attribute accuracy loss in rasterization has a close relationship with grid cell size; besides, it is also influenced by evaluating methods. Therefore, it is significant to analyze these two influencing factors comprehensively. Taking land cover data of Sichuan at the scale of 1：250,000 in 2005 as a case, in view of data volume and its processing time of the study region, this study selects 16 spatial scales from 600 m to 30 km, uses rasterizing method based on the Rule of Maximum Area （RMA） in ArcGIS and two evaluating methods of attribute accuracy loss, which are Normal Analysis Method （NAM） and a new Method Based on Grid Cell （MBGC）, respectively, and analyzes the scale effect of attribute （it is area here） accuracy loss at 16 different scales by these two evaluating methods comparatively. The results show that： （1） At the same scale, average area accuracy loss of the entire study region evaluated by MBGC is significantly larger than the one estimated using NAM. Moreover, this discrepancy between the two is obvious in the range of 1 km to 10 km. When the grid cell is larger than 10 km, average area accuracy losses calculated by the two evaluating methods are stable, even tended to parallel. （2） MBGC can not only estimate RMA rasterization attribute accuracy loss accurately, but can express the spatial distribution of the loss objectively. （3） The suitable scale domain for RMA rasterization of land cover data of Sichuan at the scale of 1：250,000 in 2005 is better equal to or less than 800 m, in which the data volume is favorable and the processina time is not too Iona. as well as the area accuracv loss is less than 2.5%.展开更多
Based on the theory of optimization,we use edges and angles of cells to represent the geometric quality of computational grids,employ the local gradients of the flow variables to describe the variation of flow field,a...Based on the theory of optimization,we use edges and angles of cells to represent the geometric quality of computational grids,employ the local gradients of the flow variables to describe the variation of flow field,and construct a multi-objective programming model.The solution of this optimization problem gives appropriate balance between the geometric quality and adaptation of grids.By solving the optimization problem,we propose a new grid rezoning method,which not only keeps good geometric quality of grids,but also can track rapid changes in the flow field.In particular,it performs well for some complex concave domains with corners.We also incorporate the rezoningmethod into anArbitrary Lagrangian-Eulerian(ALE)method which is widely used in the simulation of high-speed multi-material flows.The proposed rezoning and ALE methods of this paper are tested by a number of numerical examples with complex concave domains and compared with some other rezoning methods.The numerical results validate the robustness of the proposed methods.展开更多
This paper presents issues and trepidations associated with transferring from conventional methods of electricity monitoring and distribution to the cyberspace, especially in developing countries like Nigeria where cu...This paper presents issues and trepidations associated with transferring from conventional methods of electricity monitoring and distribution to the cyberspace, especially in developing countries like Nigeria where current approaches have failed to provide regular, reliable electric power. The Smart Power Grid is a developing concept already put to test, successfully, in very advanced countries. The implementation of the Smart Grid will include the deployment of many new technologies and multiple communication infrastructures. Connecting the electricity grid to the Internet can provide a lot of advantages in terms of control, data viewing and generation. However, in Nigeria, the proposal to transfer conventional methods to the Smart Grid has perhaps not hit the deck yet because of excessive focus on power generation, and because of the annotated reservations associated with the Internet, as the Smart Grid involves circulation and dispersal via inter-networking structures. This paper describes the key technologies that support Power Grid substation automation, summarizes the mode of implementation into the existing Nigerian electrical infrastructure and brings fore issues and mitigating approaches to provide a seamless and securitised transfer of the current power grid to the Smart Grid.展开更多
Due to the inference of the uneven shallow water seabed and the surrounding islands,the wind-generated waves around or in a reef lagoon are rather complicated,and critical to the safety of floating structures deployed...Due to the inference of the uneven shallow water seabed and the surrounding islands,the wind-generated waves around or in a reef lagoon are rather complicated,and critical to the safety of floating structures deployed near islands or inside a lagoon.This paper aims to find a feasible analysis tool for the wave simulations near islands and reefs.The proposed three methods of grid techniques of WAVEWATCH III(WW3)are assessed by using on-site measured data which was collected and accumulated for about 5 years since August 2014 by a wave observation system deployed inside and outside a reef lagoon in South China Sea.In the assessments,the wave statistics including the correlation coefficients,root mean square errors,and their variances are used to quantify the precisions of the simulation results of the significant wave heights,mean wave periods,and peak wave directions at two sites.Among the three methods,the Multi-scale Zone and Multi-scale grid Technique(MZMGT)established on unstructured triangular grids exhibits better results in terms of the accuracy and CPU cost.In addition,the bimodal feature of wave spectra was observed at both sites of the reef lagoon in different typhoon events.The wave characteristics inside the reef lagoon and open sea are also analyzed.展开更多
基金supported by the Excellent Young Scientists Fund(Grant No.41622108)the National Basic Research Program of China(973Program)(Grant No.2015CB954103)the Priority Academic Program Development of Jiangsu Higher Education Institutions(Grant No.164320H116)
文摘Geography requires a comprehensive understanding of both natural and human factors,as well as their interactions.Due to the complexity and multiplicity of geographic problems,various theories and methods for geographic modelling and simulation have been proposed.Currently,geography has entered an era in which quantitative analysis and modelling are essential for understanding the mechanisms of geographic processes.As the basic idea of quantitative spatial analysis,the specified space often needs to be partitioned by a series of small computational units(cells),i.e.,grids.Thus,there is a close relationship between the grids and geographic modelling.This article reviews the mainstream and typical grids used for modelling and simulation.In addition to classification,the derived theories and technologies,including grid generation methods,data organization strategies,multi-dimensional querying methods,and grid adaptation techniques,are discussed.For integrated geographic simulation to explore comprehensive geographic problems,we argued that it is reasonable to build bridges among different types of grids(e.g.,transformation strategies),and more powerful grids that can support multi-type of numerical computation are urgently needed.
基金supported by the DOE-MMICS SEA-CROGS DE-SC0023191 and the AFOSR MURI FA9550-20-1-0358supported by the SMART Scholarship,which is funded by the USD/R&E(The Under Secretary of Defense-Research and Engineering),National Defense Education Program(NDEP)/BA-1,Basic Research.
文摘Two of the main challenges in optimal control are solving problems with state-dependent running costs and developing efficient numerical solvers that are computationally tractable in high dimensions.In this paper,we provide analytical solutions to certain optimal control problems whose running cost depends on the state variable and with constraints on the control.We also provide Lax-Oleinik-type representation formulas for the corresponding Hamilton-Jacobi partial differential equations with state-dependent Hamiltonians.Additionally,we present an efficient,grid-free numerical solver based on our representation formulas,which is shown to scale linearly with the state dimension,and thus,to overcome the curse of dimensionality.Using existing optimization methods and the min-plus technique,we extend our numerical solvers to address more general classes of convex and nonconvex initial costs.We demonstrate the capabilities of our numerical solvers using implementations on a central processing unit(CPU)and a field-programmable gate array(FPGA).In several cases,our FPGA implementation obtains over a 10 times speedup compared to the CPU,which demonstrates the promising performance boosts FPGAs can achieve.Our numerical results show that our solvers have the potential to serve as a building block for solving broader classes of high-dimensional optimal control problems in real-time.
基金The Independent Research of the State Key Laboratory of Resource and Environmental Information System,No.O88RA100SAThe Third Innovative and Cutting-edge Projects of Institute of Geographic Sciences andNatural Resources Research, CAS, No.O66U0309SZ
文摘Rasterization is a conversion process accompanied with information loss, which includes the loss of features＇ shape, structure, position, attribute and so on. Two chief factors that affect estimating attribute accuracy loss in rasterization are grid cell size and evaluating method. That is, attribute accuracy loss in rasterization has a close relationship with grid cell size; besides, it is also influenced by evaluating methods. Therefore, it is significant to analyze these two influencing factors comprehensively. Taking land cover data of Sichuan at the scale of 1：250,000 in 2005 as a case, in view of data volume and its processing time of the study region, this study selects 16 spatial scales from 600 m to 30 km, uses rasterizing method based on the Rule of Maximum Area （RMA） in ArcGIS and two evaluating methods of attribute accuracy loss, which are Normal Analysis Method （NAM） and a new Method Based on Grid Cell （MBGC）, respectively, and analyzes the scale effect of attribute （it is area here） accuracy loss at 16 different scales by these two evaluating methods comparatively. The results show that： （1） At the same scale, average area accuracy loss of the entire study region evaluated by MBGC is significantly larger than the one estimated using NAM. Moreover, this discrepancy between the two is obvious in the range of 1 km to 10 km. When the grid cell is larger than 10 km, average area accuracy losses calculated by the two evaluating methods are stable, even tended to parallel. （2） MBGC can not only estimate RMA rasterization attribute accuracy loss accurately, but can express the spatial distribution of the loss objectively. （3） The suitable scale domain for RMA rasterization of land cover data of Sichuan at the scale of 1：250,000 in 2005 is better equal to or less than 800 m, in which the data volume is favorable and the processina time is not too Iona. as well as the area accuracv loss is less than 2.5%.
文摘Based on the theory of optimization,we use edges and angles of cells to represent the geometric quality of computational grids,employ the local gradients of the flow variables to describe the variation of flow field,and construct a multi-objective programming model.The solution of this optimization problem gives appropriate balance between the geometric quality and adaptation of grids.By solving the optimization problem,we propose a new grid rezoning method,which not only keeps good geometric quality of grids,but also can track rapid changes in the flow field.In particular,it performs well for some complex concave domains with corners.We also incorporate the rezoningmethod into anArbitrary Lagrangian-Eulerian(ALE)method which is widely used in the simulation of high-speed multi-material flows.The proposed rezoning and ALE methods of this paper are tested by a number of numerical examples with complex concave domains and compared with some other rezoning methods.The numerical results validate the robustness of the proposed methods.
文摘This paper presents issues and trepidations associated with transferring from conventional methods of electricity monitoring and distribution to the cyberspace, especially in developing countries like Nigeria where current approaches have failed to provide regular, reliable electric power. The Smart Power Grid is a developing concept already put to test, successfully, in very advanced countries. The implementation of the Smart Grid will include the deployment of many new technologies and multiple communication infrastructures. Connecting the electricity grid to the Internet can provide a lot of advantages in terms of control, data viewing and generation. However, in Nigeria, the proposal to transfer conventional methods to the Smart Grid has perhaps not hit the deck yet because of excessive focus on power generation, and because of the annotated reservations associated with the Internet, as the Smart Grid involves circulation and dispersal via inter-networking structures. This paper describes the key technologies that support Power Grid substation automation, summarizes the mode of implementation into the existing Nigerian electrical infrastructure and brings fore issues and mitigating approaches to provide a seamless and securitised transfer of the current power grid to the Smart Grid.
基金supported by the Ministry of Industry and Information Technology(Grant Nos.[2016]22,[2019]357)supported by the Ministry of Science and Technology(Grant No.2013CB36100)+3 种基金the National Key Research and Development Programof China(Grant No.2017YFB0202701)the Jiangsu Province Science Foundation for Youths(Grant No.BK20190151)the Natural Science Foundation of Hunan Province(Grant No.2019JJ50633)the Southern Marine Science and Engineering Guangdong Laboratory(Zhanjiang)(Grant No.ZJW-2019-08).
文摘Due to the inference of the uneven shallow water seabed and the surrounding islands,the wind-generated waves around or in a reef lagoon are rather complicated,and critical to the safety of floating structures deployed near islands or inside a lagoon.This paper aims to find a feasible analysis tool for the wave simulations near islands and reefs.The proposed three methods of grid techniques of WAVEWATCH III(WW3)are assessed by using on-site measured data which was collected and accumulated for about 5 years since August 2014 by a wave observation system deployed inside and outside a reef lagoon in South China Sea.In the assessments,the wave statistics including the correlation coefficients,root mean square errors,and their variances are used to quantify the precisions of the simulation results of the significant wave heights,mean wave periods,and peak wave directions at two sites.Among the three methods,the Multi-scale Zone and Multi-scale grid Technique(MZMGT)established on unstructured triangular grids exhibits better results in terms of the accuracy and CPU cost.In addition,the bimodal feature of wave spectra was observed at both sites of the reef lagoon in different typhoon events.The wave characteristics inside the reef lagoon and open sea are also analyzed.
