Modeling of two-phase flow in porous media with heat generation

The main purpose of this work is investigation of coolability of a boiling debris bed. The main governing equations are derived using volume averaging technique. From this technique some specific interfacial areas between phases are appeared and proper relations for modeling these areas are proposed. Using these specific areas, a modification for the Tung/Dhir model in the annular flow regime is proposed. The proposed modification is validated and the agreements with experimental data are good. Finally, governing equations and relations are implemented in the THERMOUS program to model two-phase flow in the debris bed in the axisymmetric cylindrical coordinate. Two typical configurations including flat and mounted beds are considered and the main physical phenomena during boiling of water in the debris bed are studied. Comparing the results with the one-dimensional analysis shows higher specific power of the bed.     

泥石流预测、预报技术方法的研究现状浅析

泥石流灾害的预测、预报是减灾防灾重要环节和基础。在充分研究泥石流形成条件基础上 ,正确预测、预报泥石流 ,是目前最大限度减少泥石流灾害损失所采取的主要方法。本文综合了当前泥石流预测预报的方法 ,分析了泥石流长期、中期、短期预报及泥石流预报的原理 ,不同时期泥石流预报的特征及存在的问题。我国是受泥石流危害最为严重的国家之一。每年由泥石流造成的直接经济损失约达几十亿元之多 ,减少泥石流灾害造成的损失主要取决于预测预报工作等。     

Lie symmetry solutions for two-phase mass flows

We apply Lie symmetry method to a set of non-linear partial differential equations, which describes a two-phase rapid gravity mass flow as a mixture of solid particles and viscous fluid down a slope (Pudasaini, J. Geophys. Res. 117 (2012) F03010, 28 pp [1]). In order to systematically explore the mathematical structure and underlying physics of the two-phase mixture flow, we generate several similarity forms in general form and construct self-similar solutions. Our analysis generalizes the results, obtained by applying the Lie symmetry method to relatively simple single-phase pressure-driven gravity mass flows, to the two-phase mass flows that include several dominant driving forces and strong phase-interactions. Analytical and numerical solutions are presented for the symmetry-reduced homogeneous and non-homogeneous systems of equations. Analytical and numerical results show that the new models presented here can adequately describe the dynamics of two-phase debris flows, and produce observable phenomena that are consistent with the physics of the flow. The solutions are strongly dependent on the choice of the symmetry-reduced model, as characterized by the group parameters, and the physical parameters of the flows. These solutions reveal strong non-linear and distinct dynamic evolutions, and phase-interactions between the solid and fluid phases, namely the phase-heights and phase-velocities.     

贵州关岭大寨崩滑碎屑流灾害初步研究

2010年6月28日,贵州省关岭县岗乌镇大寨村发生特大型崩滑碎屑(石)流灾害,造成99人死亡或失踪。通过现场考察崩滑区的地质环境与斜坡岩体结构,认为斜坡体由似"干砌块石结构"的裂隙化岩体组成是发生崩溃式破坏的主要内在原因。超常暴雨(过程雨量237mm)条件下斜坡岩体后缘裂缝充水形成持续的"水楔作用"是斜坡岩体松动、倾倒垮塌的主要外部引发因素。碎屑(石)流块度的空间分布具有从源头向沟口逐次减小,碎屑(石)流运动冲击高度逐步降低,冲击速度逐步减小,并显示4个能级4个冲程的特点。根据动势能守恒定律,计算了每个冲程的最大速度,得出第1冲程为高速崩滑,其它冲程属于碎屑(石)流动冲击。未发现区域天然地震、光照水库诱发地震与外围历史采矿活动与本次事件相关的直接证据。由于滑坡后缘仍存在不稳定岩体,碎屑(石)流堆积体上多处分布直径3~5m的堰塞塘,说明碎屑(石)空隙的排泄能力不足,在未来暴雨条件下引发新的崩滑或形成沟谷型泥石流的可能性是存在的。     

甘肃省舟曲8.7特大泥石流调查研究

本文通过对甘肃省舟曲县城后山三眼峪沟和罗家峪沟特大泥石流灾害的现场调查,从泥石流形成的地形、地质和降雨条件入手,分析了特大泥石流灾害的特征与成因：三眼峪沟和罗家峪沟泥石流形成区在2010年8月7日23～24时的1h降雨量达77.3mm,暴雨形成强大洪水依次冲毁两条沟内的天然堆石坝和人工拦挡坝,形成规模巨大的高容重黏性泥石流,泥石流冲出总量和泥沙总量分别为 144.2×10⁴m³和97.7×10⁴m³; 泥石流携带具有强大冲击力的巨石冲毁房屋5500余间; 在白龙江内形成长约550m,宽约70m,高约10m的堰塞坝并形成堰塞湖,堰塞湖回水长3km,使县城一半被淹; 泥石流造成1744人死亡和失踪。分析研究表明,三眼峪沟和罗家峪沟泥石流如果在近期遭遇强降雨还会暴发泥石流,但规模比87特大泥石流小;如果强降雨发生在数年后,暴发的泥石流规模比87特大泥石流略小;在20a或更长的时期内,没有发生新的地震影响下,在三眼峪沟和罗家峪沟经历一次大规模泥石流暴发后,泥石流的规模将回到汶川地震前的水平。     

舟曲泥石流源区土壤分散性高光谱探测模型

通过开展土壤分散性高光谱测量实验,首次明确了舟曲泥石流源区土壤分散性敏感波段位置、建立了土壤分散性高光谱探测模型、探讨了土壤分散性高光谱探测机理。结果表明,（1）傅里叶变换可以将光谱从时间域转换为频率域,实现对光谱信号与噪声的分离。通过开发矿物组分精细鉴别系统,实现了光谱去噪,为构建土壤分散性高光谱探测模型提供了高保真数据源; （2）基于多元线性回归分析法建立的土壤分散性高光谱探测模型在研究区具有较好的预测能力,所确定的敏感波段位置及其反射率与土壤分散性具有较高的相关性; （3）分析矿物光谱结果表明,土壤分散性高光谱探测的敏感波段位置实际上反映了土壤矿物组分及其所吸附的离子类型,揭示了导致土壤分散的深层原因： 与舟曲泥石流源区土壤分散性关系最为密切的是钠离子,其次是方解石、蒙脱石和伊利石,与绿泥石、高岭石、pH值、石英、钾长石、斜长石等的相关性较弱。其原因主要是与钠离子所具有的离子价低、半径小、水化力强的特点,方解石所具有的水溶性特点,蒙脱石所具有的层间结合力极弱、易吸附钠离子的特点,伊利石在高PH值条件下所具有的强吸附阳离子、高土壤分散性的特性有关。     

汶川震区北川县城泥石流源地特征的遥感动态分析

针对一种充气前缘(inflatable leading edge, ILE)增升技术,建立了其充气结构与流场耦合作用的运动方程. 将方程写成状态空间形式, 采用时域推进方法求解. 对使用了变前缘增升技术的NACA 63-212翼型进行了充气结构静变形的数值计算,结果表明充气结构的刚度对翼型的气动特性 有明显影响. 与原翼型相比,在不考虑充气结构变形时, 该增升技术大约能使翼型的失速迎角 增加30{\%},最大升力系数增加22{\%};考虑结构变形后增升效果有所降低. 刚度较低的薄 膜在前缘吸力峰的作用下会隆起形成鼓包,容易引起流动分离.     

汶川地震后四川省绵竹市清平乡文家沟泥石流灾害调查研究

在2008年5月12日汶川地震后的地震灾区暴发了许多泥石流灾害,其中以四川省绵竹市清平乡文家沟泥石流最为显著。文家沟原来不是泥石流沟,在汶川地震时由于滑坡形成的巨大的滑坡-碎屑流堆积体改变了文家沟的泥石流形成条件,在此后的3个雨季内,文家沟先后暴发了5次大规模和特大规模的泥石流灾害,其中以8 ·13文家沟泥石流规模和危害最大。8 ·13文家沟泥石流暴发时的总降雨量为227mm,泥石流持续时间约2.5h,泥石流总量约310×10⁴m³; 泥石流造成7人死亡, 5人失踪, 39人受伤, 479户农房被掩埋,直接经济损失4.3亿元。5次大规模和特大规模的泥石流以及洪水仅带走了16%的可以很容易形成泥石流的滑坡-碎屑流堆积物,文家沟如再遭遇较大降雨还会暴发泥石流。即使在今后的雨季中暴发几次规模如8 ·13泥石流一样大的特大规模泥石流,文家沟在较大降雨下仍然可能暴发泥石流灾害,因此对文家沟泥石流的防治工作将是一个长期的工作。     

A model for the aerodynamic coefficients of rock-like debris

This study presents a model to determine the aerodynamic forces on an irregularly shaped object for prediction of trajectories of debris. We classify the debris according to shape and use wind tunnel tests to create a database of aerodynamic forces of similarly sized objects. We have then validated the database results against wind tunnel measurements of aerodynamic coefficients of rock-like debris objects. Although the individual errors may be significant, the results show a generally good agreement with our model prediction and a small average error.     

Optimal systems of Lie subalgebras for a two-phase mass flow

We apply the Lie symmetry method to a two-phase mass flow model (Pudasaini, 2012 [18]) and construct one-, two- and three-dimensional optimal systems of Lie subalgebras corresponding to the non-linear PDEs. As an optimal system contains structurally important information about different types of invariant solutions, it provides precise insights into all possible invariant solutions emerging from infinitesimal symmetries. We use the optimal system of one-dimensional Lie subalgebras to reduce the two-phase mass flow model to other systems of PDEs. Using the fact that the Lie bracket contains information about further reduction, we further reduce to systems of ODEs and PDEs. We solve a system numerically and present results for different physical and Lie parameters. Simulations reveal fluid and solid dynamics are distinctly sensitive to different Lie parameters, whereas both phases are influenced by the solid and the fluid pressure parameters. Higher pressure gradients result in higher flow velocities and lower flow heights. Fluid velocities dominate solid velocities, but the solid heights are higher than the fluid heights. Results provide an overall picture of the physical process, and the coupled dynamics of the solid and fluid phase velocities and the flow heights. These are physically meaningful results in sheared inclined channel flow of coupled two-phase mixture. This confirms the consistency of the obtained similarity solutions and potential applicability of the models and the constructed optimal systems.