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101.
本文改进并验证了大地电磁测深数据的三维反演算法和并行计算程序,程序对计算机物理内存和CPU速度及数量要求较低,使普通家用机进行三维反演计算成为可能.本文在Newman和Alumbaugh(2000)提出的三维非线性共轭梯度算法和Rodi和Mackie(2001)给出的大地电磁场二维NLCG反演预处理方法的基础上实现了大地电磁场NLCG三维反演算法,改进了的预处理方法,将反演计算对初始模型的依赖性降到最低,并且通过理论模型验证了程序的正确性,并根据日本KAYABE地区实测数据的反演结果验证了算法的实用性. 相似文献
102.
This paper reports the methodology and computational strategy for a forest cover disturbance alerting system. Analytical techniques from time series econometrics are applied to imagery from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor to detect temporal instability in vegetation indices. The characteristics from each MODIS pixel's spectral history are extracted and compared against historical data on forest cover loss to develop a geographically localized classification rule that can be applied across the humid tropical biome. The final output is a probability of forest disturbance for each 500 m pixel that is updated every 16 days. The primary objective is to provide high-confidence alerts of forest disturbance, while minimizing false positives. We find that the alerts serve this purpose exceedingly well in Pará, Brazil, with high probability alerts garnering a user accuracy of 98 percent over the training period and 93 percent after the training period (2000–2005) when compared against the PRODES deforestation data set, which is used to assess spatial accuracy. Implemented in Clojure and Java on the Hadoop distributed data processing platform, the algorithm is a fast, automated, and open source system for detecting forest disturbance. It is intended to be used in conjunction with higher-resolution imagery and data products that cannot be updated as quickly as MODIS-based data products. By highlighting hotspots of change, the algorithm and associated output can focus high-resolution data acquisition and aid in efforts to enforce local forest conservation efforts. 相似文献
103.
We discuss various strategies for parallelizing streamline simulators and present a single-phase shared memory implementation.
The choice of a shared memory programming model is motivated by its suitability for streamline simulation, as well as the
rapid advance of multicore processors, which are readily available at low-cost. We show that streamline-based methods are
easily parallelizable on shared memory architectures through their decomposition of the multidimensional transport equations
into a large set of independent 1D transport solves. We tested both a specialized explicit load balancing algorithm that optimizes
the streamline load distribution across threads to minimize the time that any of the threads are idle, and the dynamic load
balancing algorithms provided by OpenMP on the shared memory machines. Our results clearly indicate that built-in schedulers
are competitive with specialized load balancing strategies as long as the number of streamlines per thread is sufficiently
high, which is the case in field applications. The average workload per thread is nominally insensitive to workload variations
between individual streamlines, and any load balancing advantage offered by explicit strategies is not sufficient to overcome
associated computational and parallel overhead. In terms of the allocation of streamlines or streamline segments to threads,
we investigated both the distributed approach, in which threads are assigned streamline segments, and the owner approach,
in which threads own complete streamlines. We found that the owner approach is most suitable. The slight advantage that the
distributed approach has in terms of load balancing is not enough to compensate for the additional overheads. Moreover, the
owner approach allows straightforward re-use of existing sequential codes, which is not the case for the distributed approach
in case of implicit or adaptive implicit solution strategies. The tracing and mapping stages in streamline simulation have
low parallel efficiency. However, in real-field models, the computational burden of the streamline solves is significantly
heavier than that of the tracing and mapping stages, and therefore, the impact of these stages is limited. We tested the parallelization
on three shared memory systems: a 24 dual-core processor Sun SPARC server; an eight-way Sun Opteron server, representative
of the state-of-the-art shared memory systems in use in the industry; and the very recently released Sun Niagara II multicore
machine that has eight floating point compute units on the chip. We test a single-phase flow problem on three heterogeneous
reservoirs with varying well placements (this system gives the worst case scenario as the tracing and mapping costs are not
negligible compared to the transport costs). For the SPARC and Opteron system, we find parallel efficiencies ranging between
60 and 75 for the tracer flow problems. The sublinear speedup is mostly due to communication overheads in the tracing and
mapping stages. In applications with more complex physics, the relative contributions of these stages will decrease significantly,
and we predict the parallel performance to be nearly linear. On the Niagara II, we obtain almost perfect linear scalability
even for the single-phase flow problem thanks to the lowered communication costs on these architectures that have a shared
cache. This result is all the more satisfactory considering that future server designs will be akin to this system. 相似文献
104.
This paper summarises the evidence for glacial ice advance into lower Glen Spean during the Loch Lomond Stadial which involved the blockage of westward-flowing drainage to form a series of ice-dammed lakes, the former surfaces of which are marked by prominent shorelines. Detailed mapping of glacigenic landforms and instrumental levelling of the shorelines reveals a dynamic interplay between the glacier margins and lake formation. Subsequent deglaciation led to lowering of the lake levels, at times by catastrophic drainage beneath the ice (jökulhlaup). The abandoned shorelines have been warped and dislocated in numerous places as a result of glacio-isostatic deformation, faulting and landslip activity. The pattern of retreat of the ice can be deduced from the mapped distributions of retreat moraines and the levelled altitudes of numerous kame and fluvial terrace fragments. The sequence of events outlined in this paper provides important context for understanding the evolution of the landscape of the Glen Roy area during the Loch Lomond Stadial, and a prelude to more recent studies reported in other contributions to this thematic issue. 相似文献
105.
数值天气预报业务模式现状与展望 总被引:36,自引:5,他引:31
20 0 4年是数值天气预报理论提出 10 0周年 ,同时也是数值天气预报业务化应用 5 0周年。经过百年的发展历程 ,数值天气预报学科有了飞跃的发展。特别是最近 10多年来 ,大气科学以及地球科学的研究进展 ,高速度、大容量的巨型计算机及网络系统的快速发展 ,更加快了数值天气预报的发展步伐。文中从模式动力框架、物理过程参数化、模式程序软件等方面对数值天气预报业务模式现状进行了简要综述 ,对存在的问题进行了探讨 ,并对数值天气预报业务模式的未来发展作了展望。当前数值天气预报业务模式发展的特点有 :(1) 2 0世纪 90年代中期以来 ,各国的全球和区域模式水平和垂直分辨率都有明显提高 ,且模式物理过程也同步进行改进 ;数值预报业务模式已进入了大规模并行计算的阶段 ;(2 )主要发达国家和中国都正在致力于研发各自的新业务数值预报模式———非静力 (多尺度 )一体化模式或非静力中尺度模式 ,部分国家的新一代天气 气候一体化数值模式已业务运行 ;(3)业务数值预报模式正在朝着不断完善的方向发展。随着模式分辨率的提高 ,云物理过程、陆面过程和湍流过程、考虑坡度 -坡向因子的辐射过程等在模式中的参数化方案 ,以及模式垂直坐标的选择越来越受重视 ,这些物理过程的描述成为业务数值模式改进的重点和 相似文献
106.
Three-dimensional finite-difference (3D-FD) simulations of earthquake wave propagations in the Yanhuai area were performed for the 1720 Shacheng earthquake (Ms 7.0) using a stochastic finite-fault model, running on a parallel supercomputer Hitachi-SR8000 (http://www.lrz-muenchen.de). A stochastic finite-fault model was implemented into the 3D-FD program. The basic idea of the stochastic finite-fault model is that the fault plane can be subdivided into several subfaults (or elements, sources). Radiation from a large earthquake is the sum of contributions from all subfaults with proper time delays, each of which acts as a small independent double-couple point source. Heterogeneity of the fault rupture process was modeled by randomizing the location of initial rupture (hypocenter), slip vectors (slip, rake), and rise-times of subfaults in this study. A 3D velocity model of the Yanhuai area was constructed based on studies that analyzed available geological and geophysical information. A grid increment of 75 m in three directions was used in the 3D-FD simulation, which made it possible to capture the short period information with a resolution as low as 0.5 s in sediment regions. The uncertainties of simulated results caused by the stochastic finite-fault model were studied with a homogeneous 3D model. We found that the effects of the randomness of source on simulated ground motions are only limited in near-fault-region including the surface exposure of the fault and its vicinities, which occupies about 5% of the whole study area. This article presents an integrated approach for simulating the strong ground motions for engineering purpose using the 3D-FD method. Such simulations would be useful for hazard mapping, land using planning, insurance rate assessment, particularly in planning, preparedness, and coordinating emergency response, which must be based on realistic situations induced by concrete (historic or scenario) earthquakes. 相似文献
107.
Marcin Idczak Patrice Mestayer Jean-Michel Rosant Jean-Francois Sini Michel Violleau 《Boundary-Layer Meteorology》2007,124(1):25-41
In order to investigate the microclimatic conditions in a street canyon, a physical model was used to conduct the Joint ATREUS-PICADA
Experiment (JAPEX) in situ experimental campaign. Four lines of buildings simulated by steel containers were installed to
form three parallel street canyons at 1:5 scale, with width/height aspect ratio approximately 0.40. The reference wind and
atmospheric conditions were measured, as well as the flow velocity and direction in the street. Preliminary results concern
street canyon ventilation and thermal effects on in-canyon airflow, and show that vortical motions appear for reference wind
directions perpendicular to the street axis. The presence of adjacent rows of buildings did not appear to significantly influence
the flow character within the canyon for the case of a low aspect ratio corresponding to a skimming flow regime. The flow
structure was not significantly affected by the thermal effects although some slight interference occurred in the lower part
of the canyon. An analysis of horizontal temperature gradients indicated that a thin boundary layer develops near the heated
facade. These facts imply that the thermal effects are considerable only very close to the wall. 相似文献
108.
GPS"射线打靶”模式的并行计算 总被引:3,自引:0,他引:3
全球定位系统(GPS)“射线打靶”模式是GPS/MET(气象)资料变分同化中联系GPS原始观测与大气状况的一种自成一体的观测算子,但因其计算量非常巨大而一直没能得到实用。为了克服这一困难,我们建立一个并行版本的 GPS“射线打靶”模式,并在国家重点基础研究发展规划项目“大规模科学计算研究”资助下研制的微机机群系统(LSSC)上成功地实现了并行计算,取得了理想的加速比和并行效率,而且具有良好的可扩展性,为该观测算子达到实用迈出了实质性的一步。 相似文献
109.
为了寻求一种操作简单、低成本的岩体应力测试方法, 本文提出了一个依据控制致裂钻孔应力变化的量测推算原岩应力的改进平行钻孔法。本文阐明了平行钻孔法岩体应力量测的特点和控制致裂法的原理。介绍了依据控制致裂钻孔应力变化确定岩体应力的基本理论。 相似文献
110.