共查询到20条相似文献，搜索用时 671 毫秒
1.
三维地震波走时计算技术是三维地震反演、层析成像、偏移成像等诸多地震数据处理技术中非常重要的正演计算工具.为了获得精度高且兼顾效率的三维走时计算方法:首先,在常规双线性插值公式推导过程中,充分利用平面波双线性假设的结论,获得了二元极小值超越方程的解析解,进而推导出了准确的局部走时计算公式,同时构造性地证明了该计算公式满足地震波的传播规律和Eikonal方程;其次,引入迎风差分的基本思想,提出迎风双线性插值的局部走时计算策略,该计算策略能简化算法、提高效率且保证无条件稳定性;然后,将上述计算公式和迎风双线性插值策略与常规快速推进法中的窄带技术结合,获得了一种新的基于快速推进迎风双线性插值法的三维地震波走时计算方法;最后,通过精度和效率分析检验了新算法的精度、效率和正确性,并通过计算实例验证了算法在面对复杂介质时的稳定性和有效性. 相似文献
2.
大地电磁三维快速松弛反演并行算法研究(英文) 总被引：8，自引：1，他引：7
为了进一步提高大地电磁三维快速松弛反演的计算效率,在深入分析大地电磁三维快速松弛反演算法的基础上,结合MPI自身的优越性,确定了并行计算的思路,实现了三维快速松弛反演的并行计算。通过理论模型合成数据和实测数据对实现的三维快速松弛反演并行程序进行了试算,分析对比了在多种情况下程序的执行效率。测试结果表明,所实现的三维快速松弛反演并行程序运行结果正确,效率提高明显。此成果在普通微机上实现,推动了大地电磁三维反演技术的实用化,可为其它地球物理三维正反演研究所借鉴。 相似文献
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4.
实现大地电磁法快速三维反演的关键在于找到快速计算灵敏度矩阵的方案. 本文在对大地电磁三维张量阻抗表达式进行深入分析的基础上，获得了三维快速松弛反演算法的灵敏度函数表达式，解决了三维快速松弛反演的核心问题；为了减小反演解的多解性，针对三维问题定义了最小构造函数，实现了求最小构造的三维快速松弛反演算法. 对二维棱柱体、三维棱柱体理论模型的大地电磁合成数据进行了反演试算，反演结果与理论模型相吻合. 对日本Kayabe地区实测资料进行了XY模式反演，反演得到的地电模型较好地反映了地热资源的分布. 反演试算结果表明大地电磁三维快速松弛反演具有计算速度快、结果稳定可靠等特点；使三维快速松弛反演在普通微机上得以实现. 相似文献
5.
三维地质建模与可视化方法研究 总被引：48，自引：0，他引：48
设计了超体元实体模型、断层数学模型及褶皱几何模型, 以表达复杂地质构造的空间几何形态; 建立了面向应用的三维地质建模的体系结构, 提出以空间数据处理为基础、以实体建模技术为核心、以模型应用为目的的设计理念, 丰富和发展了三维地质建模的理论与方法. 根据这一理论方法, 提出基于特征的驾驭式可视化设计思路, 通过将数据库、图形库、知识库与三维动态模拟的系统集成, 直观、形象、准确地把握空间地质数据的局部特征与整体构架. 相似文献
6.
铸件的工业CT三维检测技术 总被引：2，自引：0，他引：2
通过对工业CT扫描得到的连续二维图片进行三维重建，得到试件的三维重建图像，从而可用于复杂构件的三维结构分析、缺陷硷测，并可与快速成型系统相结合，实现对复杂零件的快速复制，在产品开发及制造过程中起到了重要作用。 相似文献
7.
基于锥束CT的实时成像系统经常要求实时获得投影数据并快速重建,如何将获得的投影数据不丢失地快速传递到图像重建单元进行重建是系统设计的一个关键问题。本文提出了一种基于Linux和以太网的数据获取方案,通过在探测器和重建计算机之间引入投影数据缓存系统,较好地解决了重建计算机和CT采集模块间由于实时性能差异所造成的通讯不稳定和数据丢失。本方案所设计的系统成本低廉、易于实现并且具有较好的通用性,对一个快速数据获取和重建系统而言具有较强的实用价值。 相似文献
8.
瞬变电磁法的严格三维反演计算复杂、占用资源多,在普通计算机上难以实现.本文引入瞬变电磁矩变换的概念,提出一种快速三维反演方法.该方法基于阻性限制(resistive limit)特性,建立包含异常体的三维大地的一阶矩响应正演算法,根据不同约束条件,选择优化的最速下降法实现瞬变电磁快速三维反演.文中通过含异常体的三维大地正演一阶矩与仿真数据一阶矩的对比,验证了快速三维正演算法的有效性,之后在不同约束条件下,利用优化的最速下降法实现了对含噪声的仿真瞬变电磁数据的快速三维反演.结果表明,该方法能够在普通计算机上短时间内较为准确地反演出地下异常体的体积和位置,在瞬变电磁数据的实时解释工作中具有良好的应用前景. 相似文献
9.
一种地质体三维建模与可视化的方法研究 总被引：1，自引：0，他引：1
地质结构是在时间维内地质过程演变的产物,以三维形态存在自然界中,但是很多地质学家仍然依靠二维或一维的形式来记录和发布地质数据,丧失了很多空间信息,原因之一是现存方法在表达地下三维地质体有很大的局限性．为了分析和解译地质地图模型,基于现有的建模理论,提出了结点．层数据模型组织不同实体类型的地质数据,实现地质观测数据和几何模型的一体化表达与存储．在此基础上,通过快速构建多分辨率三维地质模型,实现大规模地质数据集的可视化方法,满足地质学家操作、分析和解译三维地质体的需要．实验证明,本文的方法能很好的实现大规模三维地质数据建模和自适应可视化,同时为实现空间数据的集成和共享提供了一条很好的解决途径． 相似文献
10.
高精度、快速有效的正演模拟算法是三维电磁正反演的前提.为了提高海洋电磁三维数值模拟的精度和效率,本文提出利用基于Gauss-Lobatto-Chebyshev（GLC）基函数的谱元法进行海洋可控源三维电磁正演模拟.谱元法结合有限元法和谱方法的优点.我们通过应用伽辽金加权残差法离散二次电场矢量亥姆赫兹方程,在单元内选择混合阶GLC多项式的张量积作为高阶矢量插值基函数,在求解大型稀疏线性方程组时利用直接求解器进行快速求解,从而实现了三维海洋可控源电磁快速高精度正演模拟.一维和三维模型正演结果验证了本文算法的有效性和准确性.典型模型的数值结果表明谱元法是一种有效的三维海洋可控源电磁正演数值方法,能在稀疏网格剖分情况下获得精确的海洋电磁正演模拟响应. 相似文献
11.
Fire in the natural environment is a widespread agent of geomorphological and biological change. Temperatures can exceed 1000°C. There is often a rapid rise from ambient conditions through a steep thermal gradient, promoting rock disintegration. Laboratory simulation studies have established that temperature changes which are representative of natural fires affect rock material properties, which can then be related to weathering susceptibility. This study extends previous work by more closely replicating the natural environment, (a) through the simulation of rainfall and (b) by encasing samples to reflect the exposure of a single rock face to a passing fire event. Rock samples collected on Cyprus were prepared and tested following previously reported procedures. Change in modulus of elasticity was monitored using a non-destructive ultrasonic method. The data corroborate previous work but with somewhat different degrees of change. The new results are more likely to be representative of natural conditions and real-world change. The rate of rock disintegration and effects such as case-hardening appear to be a function of rock thermal characteristics, material properties and environmental constraints such as diurnal temperature range. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
12.
This paper contains the results of a laboratory study that was designed to compare sorption of low (mg/L) concentrations of 11 organic solutes by six polymeric materials (acrylonitrile butadiene styrene [ABS], fluorinated ethylene propylene [FEP], fiberglass-reinforced epoxy [FRE] and fiberglass-reinforced plastic [FRP], polyvinyl chloride [PVC], and poly-tetrafluoroethylene [PTFE]).
During this six-week study, ABS sorbed analytes much more rapidly and to a greater extent than did the other materials, and PVC and FRE sorbed analytes more slowly and to a lesser extent than the other materials tested.
As the study progressed, an increasing number of spurious peaks were found in the high performance liquid chromatography (HPLC) chromatograms of some of our samples, indicating that leaching of some consituents had occurred. By the end of the study, there were 11 additional peaks in the ABS samples, five in the FRP samples, and one in the FRE samples. Analysis by purge and trap gas chromatography/mass spectrometry (GC/MS) of those samples and of well water samples that were exposed to the casings for 500 hours revealed the identity of some of the leached constituents; acrylonitrile and styrene (components of ABS), chloroform and ethylbenzene (an intermediate in the production of styrene) from the ABS pipe, and toluene, 1,1,1-trichloroethane, and ethylbenzene from the FRP casing. 相似文献
During this six-week study, ABS sorbed analytes much more rapidly and to a greater extent than did the other materials, and PVC and FRE sorbed analytes more slowly and to a lesser extent than the other materials tested.
As the study progressed, an increasing number of spurious peaks were found in the high performance liquid chromatography (HPLC) chromatograms of some of our samples, indicating that leaching of some consituents had occurred. By the end of the study, there were 11 additional peaks in the ABS samples, five in the FRP samples, and one in the FRE samples. Analysis by purge and trap gas chromatography/mass spectrometry (GC/MS) of those samples and of well water samples that were exposed to the casings for 500 hours revealed the identity of some of the leached constituents; acrylonitrile and styrene (components of ABS), chloroform and ethylbenzene (an intermediate in the production of styrene) from the ABS pipe, and toluene, 1,1,1-trichloroethane, and ethylbenzene from the FRP casing. 相似文献
13.
Outcrops of young, sedimentary, argillaceous rocks with well developed fabric display rapid changes in their properties when subject to tropical weathering. The change in the materials is often accompanied by mass movement activity and the geomorphological consequence in terms of landforms is usually the development of badlands topography. Detailed field and laboratory studies have been undertaken on the Joe's River Formation, Barbados, and the Lichi Melange, Taiwan. Both are sedimentary mudrocks with well developed, scaly fabrics. Physical and geotechnical laboratory tests have been conducted on samples collected from type site locations to elucidate associations between material properties, earth surface processes and landform development. While the inherent physical properties show little or no difference in the transition from unweathered to highly weathered materials, by applying the critical state model, the mudrock geotechnical properties can be shown to change significantly. As weathering commences, material strength surprisingly increases. Only after a period of more extensive weathering do mechanical properties confirm increasingly incompetent materials. The initial strength increase appears to be due to weathering-induced modification of the fabric. The subsequent strength drop is a product of weathering-induced modification of both the fabric and the in situ, intact sediment. It is suggested that by applying the critical state model, a greater consideration can be gained of the geotechnical response of the sediments to weathering. 相似文献
14.
Using geostatistical simulation to disaggregate air quality model results for individual exposure estimation on GPS tracks 总被引：1，自引：1，他引：0
Lydia E. Gerharz Edzer Pebesma 《Stochastic Environmental Research and Risk Assessment (SERRA)》2013,27(1):223-234
In this work, we address the mismatch in spatio-temporal resolution between individual, point-location based exposure and grid cell based air quality model predictions by disaggregating the grid model results. Variability of PM10 point measurements was modelled within each grid cell by the exponential variogram, using point support concentration measurements. Variogram parameters were estimated over the study area globally using constant estimates, and locally by multiple regression models using traffic, weather and land use data. Model predictions of spatio-temporal variability were used for geostatistical unconditional simulation, estimating the deviation of point values from grid cell averages on GPS tracks. The distribution of deviations can be used as an estimate of uncertainty for individual exposure. Results showed a relevant impact of the disaggregation uncertainties compared to other uncertainty sources, dependent of the model used for spatio-temporal variability. Depending on individual behaviour and variability of the pollutant, these uncertainties average out again over time. 相似文献
15.
Richard L. Johnson Christina N. Brow Reid O'Brien Johnson Holly M. Simon 《Ground Water Monitoring & Remediation》2013,33(2):38-43
A cryogenic coring system for the collection and preservation of biomolecules in unconsolidated subsurface solid samples is presented here. The sampler is based on existing direct‐push coring technology, with the addition of a cryogenic step to freeze the sample in situ. Once brought to the surface, the frozen cores can be packed in dry ice and shipped to the laboratory for further processing and analysis. The approach prevents redistribution of fluids during sample recovery and shipping, and because the cores are frozen in situ there is little loss of solid material during retrieval to ground surface. To evaluate the performance of the approach, DNA analyses of samples collected by cryogenic coring in a very large physical model are compared with results from water samples and horizontal core samples taken in close proximity. The data indicate that the vertical distribution of DNA within the cryogenic core can be measured at the centimeter scale, providing unprecedented characterization of subsurface biogeochemical interfaces. 相似文献
16.
三维电阻率探测的线性反演和非线性反演中均存在着多解性的固有难题.电阻率线性反演方法的效率较高,但反演结果对初始模型的依赖性较强,易陷入局部极小;而非线性反演方法不依赖初始模型,但搜索效率极低,尚未见到关于三维电阻率非线性反演的文献.针对上述问题,融合线性与非线性反演方法的互补优势,提出了最小二乘法(线性方法)与改进遗传算法(非线性方法)相结合的混合反演方法的概念和思想.首先,提出了将介质电阻率变化范围作为不等式约束引入反演方程的思路,以实现压制多解性、提高可靠性的目标.提出了宽松不等式约束和基于钻孔推断的局部严格不等式约束的获取及定义方法.在此基础上,分别提出了基于不等式约束的最小二乘线性反演方法和遗传算法非线性反演方法.其次,对于遗传算法在变异搜索方向控制、初始群体产生等方面进行了改进,优化了其搜索方向和初始群体多样性.然后,提出了混合反演方法及其实现方案,利用改进遗传算法进行第一阶段反演,发挥其对初始模型的依赖程度低的优势,搜索到最优解附近的空间,输出当前最优个体;利用最小二乘法进行第二阶段反演,将遗传算法得到的当前最优个体作为初始模型,在最优解附近空间执行高效率的局部线性搜索,最终实现地电结构的三维成像.最后,开展了合成数据与实际工程算例验证,与传统最小二乘方法进行了对比,发现混合反演方法在压制多解性、摆脱初始模型依赖和提高反演效果方面有较好效果. 相似文献
17.
— A new method for characterising the detailed fracture geometry in sandstone cores is presented. This method is based on the impregnation of samples with coloured resin, without significant disturbance of the fractures. The fractures are made clearly visible by the resin, thus allowing the fracture geometry to be examined digitally. In order to model the bulk hydraulic conductivity, the samples are sectioned serially perpendicular to the flow direction. The hydraulic conductivity of individual sections is estimated by summing the contribution of the matrix and each fracture from the digital data. Finally, the hydraulic conductivity of the bulk sample is estimated by a harmonic average in series along the flow path. Results of this geometrical method are compared with actual physical conductivity values measured from fluid experiments carried out prior to sectioning. The predicted conductivity from the fracture geometry parameters (e.g., fracture aperture, fracture width, fracture length and fracture relative roughness all measured using an optical method) is in good agreement with the independent physical measurements, thereby validating the approach. 相似文献
18.
Thierry Leviandier Stéphanie Madier Sylvain Payraudeau 《Stochastic Environmental Research and Risk Assessment (SERRA)》2012,26(4):557-568
Sampling strategies are necessary to minimise the cost of data acquisition. We consider the case when several samples must
be analysed at the same time, knowing rainfall data, optionally discharge data. We assume also that a rainfall-runoff and
pesticide transfer model is available. Three methods are presented based on behavioural sets calculated on prior events, which
provide optimal sampling times with respect to different statistical criteria, for a fixed number of samples. A methodology
to compare these strategies, adapted to a context of data scarcity is proposed for proper validation. We consider that the
combination of a model and a strategy is efficient if it does better than a strategy without a model based on equal volumes.
Even with a simple and relatively poor model, it can be concluded that the different strategies are efficient and show similar
efficiency in spite of their different levels of conceptual and algorithmic complexity. 相似文献
19.
Electromagnetic methods are routinely applied to image the subsurface from shallow to regional structures. Individual electromagnetic methods differ in their sensitivities towards resistive and conductive structures and in their exploration depths. If a good balance between different electromagnetic data can be be found, joint 3D inversion of multiple electromagnetic datasets can result in significantly better resolution of subsurface structures than the individual inversions. We present a weighting algorithm to combine magnetotelluric, controlled source electromagnetic, and geoelectric data. Magnetotelluric data are generally more sensitive to regional conductive structures, whereas controlled source electromagnetic and geoelectric data are better suited to recover more shallow and resistive structures. Our new scheme is based on weighting individual components of the total data gradient after each model update. Norms of individual data residuals are used to assess how much of the total data gradient must be assigned to each method to achieve a balanced contribution of all datasets for the joint inverse model. Synthetic inversion tests demonstrate advantages of joint inversion in general and also the influence of the weighting. In our tests, the controlled source electromagnetic data gradients are larger than those of the magnetotelluric and geoelectric datasets. Consequently, direct joint inversion of controlled source electromagnetic, magnetotelluric, and geoelectric data results in models that are mostly dominated by structures required by the controlled source electromagnetic data. Applying the new adaptive weighting scheme results in an inversion model that fits the data better and resembles more the original model. We used the modular system electromagnetic as a framework to implement the new joint inversion and briefly describe the new modules for forward modelling and their interfaces to the modular system electromagnetic package. 相似文献
20.
A combination of two indirect methods to measure sediment flux is presented in this study to evaluate suspended sediment transport in a hydropower reservoir. The acoustic backscatter signal (ABS) from an Acoustic Doppler Current Profiler (ADCP) is therefore applied in pre-defined transects within the reservoir in combination with a Laser In-Situ Scattering Transmissometry – stream lined device (LISST-SL). The stationary LISST-SL derived suspended sediment concentration (SSC) measurements are used to calibrate the ABS. From the LISST-SL measurements a time series of SSC is obtained. This enables, in addition, a comprehensive data analysis to evaluate the influence of natural fluctuations of the SSC on the calculated sediment flux, which should be taken into account when assessing sediment transport. Furthermore SSC measurements are done with the LISST-SL close to the reservoir bed. In areas close to the bed no information regarding the ABS is available from the ADCP measurements due to the side-lobe interference. In various studies the information from the last three valid cells is used for extrapolation. However, as result of a comparison of the LISST-SL measurements with extrapolated SSC values from the ADCP measurements it can be seen that, especially in deep reservoirs, this method has to be adapted to the in-situ conditions. 相似文献