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121.
Akinobu Miyakoshi Takeshi Hayashi Atsunao Marui Yasuo Sakura Shinichi Kawashima Masafumi Kawai 《International Journal of Earth Sciences》2008,97(2):401-411
Information on the distribution of subsurface temperature and hydraulic heads at 24 observation wells in and around the Tokyo
Lowland, the eastern part of the Tokyo Metropolitan area, were examined to make clear the relationship between groundwater
and the subsurface thermal environment in the urban area. Minimums in temperature–depth logs due to subsurface temperature
increasing at shallow parts were recognized in 21 wells. This fact shows subsurface temperature is affected by ground surface
warming in almost all of this area. Deeper than minimums, where the effects of surface warming became relatively small, regional
variation is observed as follows: high temperatures are shown in the central part to the southern part, and low temperatures
shown in the inland to eastern part. The high temperature area corresponds to an area where the lower boundary of groundwater
flow is relatively shallow. This area corresponds also to an area with severe land subsidence resulting from excessive groundwater
pumping. It is considered that this high temperature area is formed by the effects of upward groundwater flow affected by
hydrogeological conditions and pumping. On the other hand, a comparison between past data (1956–1967) and present data (2001–2003)
revealed widespread decreasing temperature in the inland area. This is explained by downward groundwater flow based on an
analysis of temperature–depth logs. This fact suggests that subsurface temperature is not only increasing from the effects
of surface warming but also decreasing from the effects of groundwater environment change due to pumping. 相似文献
122.
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
123.
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
124.
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
125.
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
126.
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
127.
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
128.
黄河下游断面形态与水沙输移关系及数学模拟方法 总被引:4,自引:0,他引:4
以前人对黄河下游的实测资料分析为基础,本文讨论断面形态与来水来沙关系、断面形态对输水输沙的影响,并根据实测资料,提出黄河下游弯段与直段断面冲淤变化的两种模式,建立了主流摆动及坍岸影响断面形态变化以及纵向冲淤量在断面的分布两种数学模拟方法。 相似文献
129.
渗流域内应用拉普拉斯变换(LT)建立相应的有限分析(FAM)方程,顾及渗流域内地下水流的初始条件和边界条件,可在LT空间构成一个封闭的以水头像函数为变量的线性方程组。将此方程组所得的解,通过Stehfest数值反演公式,可归化为时间域的解(水头)。由于时间t被隐含在数值方程内,从而克服了传统数值法按时段(△t)逐步迭代的缺陷,提高了计算效率,也为用嵌入法建立地下水流管理模型提供了一条捷径。 相似文献
130.
钻遇莫霍面是人类一直以来的梦想。深海海底是地球上离莫霍面最近的地方,目前有研究推测南海是世界上莫霍面深度最浅的海域之一,但缺乏足够的直接证据。深反射地震探测可以直接揭示岩石圈的构造形态,是莫霍面探测的重要手段。本文基于长达15000 km的深反射多道地震剖面的解释、处理、制图和分析,结合前人的研究,形成了南海海盆区莫霍面反射特征和空间分布的初步认识。① 南海东部次海盆南部早期经历了较快速扩张,岩浆供应充足,受扩张停止后岩浆活动影响较小,基底平坦,地质构造相对简单,同时洋壳地震速度结构不存在异常,且有较强的广角莫霍面反射波和可识别的地幔顶部折射波,具备莫霍面钻探的基本条件。② 南海海盆不同区域的莫霍面反射强度存在较大差异。其中东部次海盆莫霍面反射最为强烈且清晰,西北次海盆次之,西南次海盆仅有零星出现的清晰莫霍面反射且可信度不高。③ 识别南海海盆区莫霍面地震反射长度超过3500 km,首次形成了海盆区深度域莫霍面地震反射空间分布图。与重力反演的莫霍面深度相比,利用深反射多道地震计算的莫霍面深度细节更为丰富,并且可以在垂向上清晰刻画莫霍面的结构。整体上,南海海盆区莫霍面地震反射强烈和可信度高的区域中,深度较浅的区域之一是东部次海盆南部,最浅处仅约9. 5 km,其中水深4. 01 km,洋壳厚度仅5. 54 km。综合判断,东部次海盆南部是南海重要的莫霍面钻探备选区,这对南海莫霍面钻探选址具有重要意义。 相似文献