Modeling the effect of sediment concentration on the flow-like behavior of natural debris flow     

《国际泥沙研究》2020,35(4):315-327

The rheological behavior of natural slurries consisting of fine-grained, reconstituted debris-flow deposits on pyroclastic terrains having different solid concentrations (ranging from 30 to 42%) has been investigated using a rotational rheometer equipped with a vane rotor system. Experiments were done by increasing the applied shear stress step by step; then a decreasing stress ramp was applied following the same shear stress levels. The slurry mixtures exhibit a typical yield-stress fluid behavior with a static yield stress larger than the dynamic yield stress. In the range of the shear rate corresponding to the flow-like behavior the slurry mixtures behave as a dilatant fluid at lower grain concentrations and as a pseudoplastic fluid in correspondence with the higher grain content, showing a strong discrepancy from the Bingham idealization. The rheological behavior is better interpreted by a Herschel-Bulkley model, whose rheological parameters strongly depend on the granular concentration. Therefore, a generalized Herschel-Bulkley model accounting for the bulk sediment concentration effect is proposed.  相似文献   

Crystal morphology and surface structures of orthorhombic MgSiO3 perovskite     

M. Alfredsson  J. P. Brodholt  D. P. Dobson  A. R. Oganov  C. R. A. Catlow  S. C. Parker  G. D. Price 《Physics and Chemistry of Minerals》2005,31(10):671-682

Orthorhombic MgSiO₃ perovskite is thought to be the most abundant mineral in the mantle of the Earth. Its bulk properties have been widely studied, but many geophysical and rheological processes are also likely to depend upon its surface and grain boundary properties. As a first step towards modelling these geophysical properties, we present here an investigation of the structures and energetics of the surfaces of MgSiO₃-perovskite, employing both shell-model atomistic effective-potential simulations, and density-functional-theory (DFT) calculations. Our shell-model calculations predict the {001} surfaces to be the energetically most stable surfaces: the calculated value of the surface energy being 2.2 J/m² for the MgO-terminated surface, which is favoured over the SiO₂-terminated surface (2.7 J/m²). Also for the polar surfaces {111}, {101} and {011} the MgO-terminated surfaces are energetically more stable than the Si-terminated surfaces. In addition we report the predicted morphology of the MgSiO₃ perovskite structure, which is dominated by the energetically most stable {001} and {110} surfaces, and which appears to agree well with the shape of grown single crystals.  相似文献   

Averaging on Earth‐Crossing Orbits     

G. F. Gronchi  A. Milani 《Celestial Mechanics and Dynamical Astronomy》1998,71(2):109-136

The orbits of planetcrossing asteroids (and comets) can undergo close approaches and collisions with some major planet. This introduces a singularity in the Nbody Hamiltonian, and the averaging of the equations of motion, traditionally used to compute secular perturbations, is undefined. We show that it is possible to define in a rigorous way some generalised averaged equations of motion, in such a way that the generalised solutions are unique and piecewise smooth. This is obtained, both in the planar and in the threedimensional case, by means of the method of extraction of the singularities by Kantorovich. The modified distance used to approximate the singularity is the one used by Wetherill in his method to compute probability of collision. Some examples of averaged dynamics have been computed; a systematic exploration of the averaged phase space to locate the secular resonances should be the next step.'Alice sighed wearily. I think you might do something better with the time she said, than waste it asking riddles with no answers(Alice in Wonderland, L. Carroll)  相似文献   

Sedimentology of the Krakatau 1883 submarine pyroclastic deposits     

C. W. Mandeville  S. Carey  H. Sigurdsson 《Bulletin of Volcanology》1996,57(7):512-529

The majority of tephra generated during the paroxysmal 1883 eruption of Krakatau volcano, Indonesia, was deposited in the sea within a 15-km radius of the caldera. Two syneruptive pyroclastic facies have been recovered in SCUBA cores which sampled the 1883 subaqueous pyroclastic deposit. The most commonly recovered facies is a massive textured, poorly sorted mixture of pumice and lithic lapilli-to-block-sized fragments set in a silty to sandy ash matrix. This facies is indistinguishable from the 1883 subaerial pyroclastic flow deposits preserved on the Krakatau islands on the basis of grain size and component abundances. A less common facies consists of well-sorted, planarlaminated to low-angle cross-bedded, vitric-enriched silty ash. Entrance of subaerial pyroclastic flows into the sea resulted in subaqueous deposition of the massive facies primarily by deceleration and sinking of highly concentrated, deflated components of pyroclastic flows as they traveled over water. The basal component of the deposit suggests no mixing with seawater as inferred from retention of the fine ash fraction, high temperature of emplacement, and lack of traction structures, and no significant hydraulic sorting of components. The laminated facies was most likely deposited from low-concentration pyroclastic density currents generated by shear along the boundary between the submarine pyroclastic flows and seawater. The Krakatau deposits are the first well-documented example of true submarine pyroclastic flow deposition from a modern eruption, and thus constitute an important analog for the interpretation of ancient sequences where subaqueous deposition has been inferred based on the facies characteristics of encapsulating sedimentary sequences.  相似文献   

气候变化对东北区粮食产量的影响及其适应性对策   总被引：38，自引：0，他引：38  

马树庆 《气象学报》1996,54(4):484-492

采用作物生长发育和产量形成对气温、降水等资源环境条件的反应函数，建立了在气候变化条件下粮食产量变率理论推算模式，分析了在主要农作物生长季气温升、降１—２℃与降水增、减１０％—２０％的各种组合条件下，东北各地粮、豆作物产量的变化，提出了适应气候变化的农业对策。结果表明，气候变化对产量影响较大，地域差异明显。气温升、降１℃，粮、豆单产将升、降２％－４０％，东北部变幅大于西南部；降水量增、减１０％，西、西南部粮食产量将增加或减少１０％左右，东南部则相反。各地应根据其影响情况采取不同的农业生产对策，如调整作物品种布局和种植结构，加强灾害防御，以确保粮食生产长期持续稳定地发展。  相似文献   

Transporting capacity of overland flow on plane and on irregular beds   总被引：2，自引：0，他引：2  

G. Govers  G Rauws 《地球表面变化过程与地形》1986,11(5):515-524

In this paper the transporting capacity of thin flows, in the laminar and transitional flow regime, is studied. Experiments were carried out on irregular as well as on plane beds, using two totally different set-ups. The results of these two types of experiment were convergent. In both cases, sediment concentration was clearly related to grain shear velocity and unit stream power, expressed as the product of mean velocity and slope (Yang, 1973). The data agreed with those of Kramer and Meyer (1969). For a sandy bed, the unit stream power relationship was able to predict reasonably well the sediment concentrations measured on a mulched surface. For laminar and transitional flows, both the unit stream power and the shear velocity are related in the same way to slope and unit discharge. The unit stream power is a parameter which in particular can be very easily measured and might therefore become useful in obtaining a quick estimate of the transporting capacity of a thin flow. However, before a sediment transport equation for thin flows can be developed, more information is needed about the influence of the flow regime and grain size and density.  相似文献   

岩石颗粒度测量方法的研究及其应用     

陈瑞君 《岩石学报》1989,5(4):76-82

本文介绍了三种不同岩石颗粒度的测量方法,点计法,线计法,带计法及两种不同计算程序。颗粒度测量结果研究表明三种不同测量方法及两种不同计算程序之间存在着差別,其中结合野外的实例,其应用结果带计法为最好,线段长度百分比要比颗粒的频率百分比计算程序要好,前者能较客观地反映颗粒的实际搬运时水介质动力条件和沉积物的沉积环境。  相似文献   

Morphological Investigations in the River Odra     

A. Schmidt 《洁净——土壤、空气、水》1999,27(5):268-273

Since 1992, the Federal Institute of Hydrology (Bundesanstalt für Gewässerkunde – BfG) performs morphological investigations in the river Odra downstream from the confluence of the river Neiße (Nysa Luzycka). The results of these investigations give a clear insight into the morphodynamic behaviour of this part of the river and indicate that on average 380 000 t of suspended solids and 130 000 t of bed load are transported by the river Odra at Hohensaaten per year, with a distinct seasonal variability in the case of suspended solids. Detailed studies on type and composition of the bed substrates have revealed that the river bottom is composed of very fine material: at Ratzdorf already 75 % of the bed material is finer than 2 mm, at Widuchowa almost all of the river bed material consists of sand finer than 0.63 mm. Because of the high sensitivity of the river bottom to discharge increases and the corresponding increases of bottom shear stress sand was found to be the dominating fraction of the suspended load in case of extreme flood events.  相似文献   

风成沙纹的研究进展     

庄燕美  哈斯  岳兴玲 《干旱区地理》2006,29(4):490-495

近半个多世纪以来国内外学者对沙纹各方面有了详尽的研究,使沙纹研究理论逐渐趋向系统化和完善化。在扼要回顾了风成沙纹的研究历史的同时,分别从沙纹形态、沙纹形成过程和沙纹形成中的颗粒分异机制等几方面阐述了沙纹研究的现状及主要进展。最后根据沙纹研究的现状和目前沙纹研究中存在的问题,对将来的研究趋势作了初步探讨。  相似文献   

渤海湾曹妃甸沙坝-泻湖海岸沉积物搬运趋势   总被引：11，自引：0，他引：11  

贾玉连  柯贤坤  许叶华  王艳 《海洋科学》1999,23(3):56-60

以沉积物粒度参数特征和区域沉积物搬运趋势模型为基础,分析了曹妃甸沙坝－泻湖海岸的沉积物搬运趋势,揭示沙坝区为沉积物辐聚区,东坑尖子沙坝后侧及泻湖区为沉积中心。  相似文献