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211.
212.
Application of FLATModel, a 2D finite volume code, to debris flows in the northeastern part of the Iberian Peninsula 总被引:7,自引:3,他引:4
FLATModel is a two-dimensional shallow-water approximation code with corrections and modifications that create a simulation
tool adapted to debris-flows behaviour. FLATModel uses the finite volume method with the numerical implementation of the Godunov
scheme and includes correction terms regarding the effect of flow over high slopes and curvature. Additionally, the stop-and-go
phenomenon, the basal entrainment and a correction regarding the front inclination of the final deposit are incorporated into
FLATModel. In addition, different flow resistance laws were integrated in the numerical code including Bingham, Herschel–Bulkley
and Voellmy fluid model. Firstly, our numerical model was validated using analytical solutions of a dam-break scenario and
published data on a laboratory experiment. Secondly, three real events, which occurred in the northeastern part of the Iberian
Peninsula, were back-calculated. Although field observations of the three events are not very detailed, the back-analyses
revealed interesting patterns on the flow dynamics, and the numerical results generally showed good agreement with field data.
Comparing the different flow resistance laws, the Voellmy fluid model presents the best behaviour regarding both the flow
behaviour and the deposit characteristics. Preliminary simulation runs incorporating the effect of basal entrainment offered
satisfactory results, although the final volume is rather sensitive on the selected friction angle of channel-bed material.
The outcomes regarding the correction of the calculated front inclination of the final deposit showed that this implementation
strongly improves the simulation results and better represents steep fronts of final deposits. 相似文献
213.
均匀设计与灰色理论在边坡稳定性分析中的应用 总被引:1,自引:1,他引:0
采用均匀设计安排试验,运用灰色理论中的灰色关联分析考察边坡稳定性影响因素的主次.结果表明,边坡稳定性影响因素的敏感性由大到小依次为:粘聚力、内摩擦角、重度、预应力、锚索间排距、锚索长度、锚固段长度、锚固角.可见,岩体的抗剪强度指标是影响边坡稳定性的最重要参数,其次是岩体的容重,而预应力锚索的设计参数对边坡的稳定性也有一定影响.这一分析结果为边坡开挖设计和加固方案的优化提供了重要依据. 相似文献
214.
鄂尔多斯高原地下水流系统的多层结构循环模式—来自深孔中PACKER系统分层水头测定的证据 总被引:1,自引:0,他引:1
地下水流系统和循环模式分析是研究地下水形成机理的基础,对正确认识和评价地下水资源具有重要意义。鄂尔多斯高原在含水系统和众多地下水排泄区的控制下,形成了多个不同规模、不同循环深度、相互独立的地下水流系统。PACKER系统分层试验测定的不同深度水头的数据证明,鄂尔多斯高原地下水流系统存在托斯多层水流模式,区域性水流系统一般包含浅循环、中间循环和深循环3个循环系统。浅循环系统的发育深度在200m以内,深循环系统的发育深度大于400m。 相似文献
215.
Non-Linear Theory and Power-Law Models for Information Integration and Mineral Resources Quantitative Assessments 总被引:7,自引:0,他引:7
Qiuming Cheng 《Mathematical Geosciences》2008,40(5):503-532
Singular physical or chemical processes may result in anomalous amounts of energy release or mass accumulation that, generally,
are confined to narrow intervals in space or time. Singularity is a property of different types of non-linear natural processes
including cloud formation, rainfall, hurricanes, flooding, landslides, earthquakes, wildfires, and mineralization. The end
products of these non-linear processes can be modeled as fractals or multifractals. Hydrothermal processes in the Earth’s
crust can result in ore deposits characterized by high concentrations of metals with fractal or multifractal properties. Here
we show that the non-linear properties of the end products of singular mineralization processes can be applied for prediction
of undiscovered mineral deposits and for quantitative mineral resource assessment, whether for mineral exploration or for
regional, national and global planning for mineral resource utilization. In addition to the general theory and framework for
the non-linear mineral resources assessment, this paper focuses on several power-law models proposed for characterizing non-linear
properties of mineralization and for geoinformation extraction and integration. The theories, methods, and computer system
discussed in this paper were validated using a case study dealing with hydrothermal Au mineral potential in southern Nova
Scotia, Canada. 相似文献
216.
Inversely-Mapped Analytical Solutions for Flow Patterns around and within Inclined Elliptic Inclusions in Fluid-Saturated Rocks 总被引:1,自引:0,他引:1
Chongbin Zhao Bruce E. Hobbs Alison Ord Shenglin Peng Liangming Liu 《Mathematical Geosciences》2008,40(2):179-197
In this paper, an inverse mapping is used to transform the previously-derived analytical solutions from a local elliptical
coordinate system into a conventional Cartesian coordinate system. This enables a complete set of exact analytical solutions
to be derived rigorously for the pore-fluid velocity, stream function, and excess pore-fluid pressure around and within buried
inclined elliptic inclusions in pore-fluid-saturated porous rocks. To maximize the application range of the derived analytical
solutions, the focal distance of an ellipse is used to represent the size of the ellipse, while the length ratio of the long
axis to the short one is used to represent the geometrical shape of the ellipse. Since the present analytical solutions are
expressed in a conventional Cartesian coordinate system, it is convenient to investigate, both qualitatively and quantitatively,
the distribution patterns of the pore-fluid flow and excess pressure around and within many different families of buried inclined
elliptic inclusions. The major advantage in using the present analytical solution is that they can be conveniently computed
in a global Cartesian coordinate system, which is widely used in many scientific and engineering computations. As an application
example, the present analytical solutions have been used to investigate how the dip angle of an inclined elliptic inclusion
affects the distribution patterns of the pore-fluid flow and excess pore-fluid pressure when the permeability ratio of the
elliptic inclusion is of finite but nonzero values. 相似文献
217.
This article presents a micromechanical approach to the problem of unsaturated water flow in heterogeneous porous media in
transient conditions. The numerical formulation is based on the two-scale model obtained previously by periodic homogenization.
It allows for a coupled solution of the non-linear flow equations at macroscopic and microscopic scales and takes into account
the macroscopic anisotropy of the medium and the local non-equilibrium of the capillary pressure. The model was applied to
simulate two-dimensional water infiltration at constant flux into an initially dry medium containing inclusions of square
and rectangular shapes. The numerical results showed the influence of the inclusion–matrix conductivity ratio and the local
geometry on the macroscopic behavior. The influence of the conductivity ratio manifested itself by the acceleration or retardation
of the onset of the macroscopic water flux at the outlet, while the local geometry (anisotropy) significantly affected the
macroscopic spatial distribution of the water flux. Such type of approach can be extended to simulate coupled phenomena (for
example hydro-mechanical problems) with evolving local geometry. 相似文献
218.
The dynamics and thermodynamics of large ash flows 总被引:6,自引:6,他引:0
Ash flow deposits, containing up to 1000 km3 of material, have been produced by some of the largest volcanic eruptions known. Ash flows propagate several tens of kilometres
from their source vents, produce extensive blankets of ash and are able to surmount topographic barriers hundreds of metres
high. We present and test a new model of the motion of such flows as they propagate over a near horizontal surface from a
collapsing fountain above a volcanic vent. The model predicts that for a given eruption rate, either a slow (10–100 m/s) and
deep (1000–3000 m) subcritical flow or a fast (100–200 m/s) and shallow (500–1000 m) supercritical flow may develop. Subcritical
ash flows propagate with a nearly constant volume flux, whereas supercritical flows entrain air and become progressively more
voluminous. The run-out distance of such ash flows is controlled largely by the mass of air mixed into the collapsing fountain,
the degree of fragmentation and the associated rate of loss of material into an underlying concentrated depositional system,
and the mass eruption rate. However, in supercritical flows, the continued entrainment of air exerts a further important control
on the flow evolution. Model predictions show that the run-out distance decreases with the mass of air entrained into the
flow. Also, the mass of ash which may ascend from the flow into a buoyant coignimbrite cloud increases as more air is entrained
into the flow. As a result, supercritical ash flows typically have shorter runout distances and more ash is elutriated into
the associated coignimbrite eruption columns. We also show that one-dimensional, channellized ash flows typically propagate
further than their radially spreading counterparts.
As a Plinian eruption proceeds, the erupted mass flux often increases, leading to column collapse and the formation of pumiceous
ash flows. Near the critical conditions for eruption column collapse, the flows are shed from high fountains which entrain
large quantities of air per unit mass. Our model suggests that this will lead to relatively short ash flows with much of the
erupted material being elutriated into the coignimbrite column. However, if the mass flux subseqently increases, then less
air per unit mass is entrained into the collapsing fountain, and progressively larger flows, which propagate further from
the vent, will develop.
Our model is consistent with observations of a number of pyroclastic flow deposits, including the 1912 eruption of Katmai
and the 1991 eruption of Pinatubo. The model suggests that many extensive flow sheets were emplaced from eruptions with mass
fluxes of 109–1010 kg/s over periods of 103–105 s, and that some indicators of flow "mobility" may need to be reinterpreted. Furthermore, in accordance with observations,
the model predicts that the coignimbrite eruption columns produced from such ash flows rose between 20 and 40 km.
Received: 25 August 1995 / Accepted: 3 April 1996 相似文献
219.
Extreme value analysis provides a semiparametric method for analyzing the extreme long tails of skew distributions which may be observed when handling mining data. The estimation of important tail characteristics, such as the extreme value index, allows for a discrimination between competing distribution models. It measures the thickness of such long tailed distributions, if only a limited sample is available. This paper stresses the practical implementation of extreme value theory, which is used to discriminate a lognormal from a mixed lognormal distribution in a case study of size distributions for alluvial diamonds. 相似文献
220.
Jacek A. Majorowicz 《Pure and Applied Geophysics》1996,147(1):1-24
The results of precision temperature logs made to depths of several hundred meters in some 80 wells in Western Canada, most of which are located in the Prairie Provinces, show evidence of warming at the ground surface in the 0.5 K to 3.5 K range (average=2.2±0.7 K, for 80 unevenly distributed sites). Modeling shows that this warming mostly pertains to this century and it has been most substantal in the last four decades if the ramp function of the linear increase of surface temperature is assumed. Using the step function model's increase of surface temperature (land clearing, forest fires, etc.) the calculated onset of warming would pertain mostly to the last two decades. Contour maps of ground temperatures currently and previously and a contour map of the ground warming magnitude dilineate a large regional character of the ground temperature change at the southern marigin of permafrost for the large area of the Prairie Provinces. In many cases however, the magnitude of ground warming is much larger than the magnitude of air warming. This is especially evident for the northern areas of Alberta in the boreal forest ecoprovince. The magnitude of ground warming is equal to the magnitude of surface air warming in southern Alberta in the grassland and aspen parkland ecoprovinces. The analysis of the temperature depth response to the surface warming from well data shows the integrated effect of surface air warming together with the increases in ground temperature due to natural terrain effects and other anthropogenical changes to the surface of the earth. 相似文献