IMHE OpenIR  > 山地灾害与地表过程重点实验室
考虑侵蚀影响的泥石流两相动力学模型研究
其他题名A two-phase dynamic model of debris-flow that includes the effects of erosion
乔成
学位类型博士
导师欧国强
2018
学位授予单位中国科学院大学
学位授予地点北京
学位专业岩土工程
关键词两相泥石流 剪胀效应 虚自由面动力边界 动床侵蚀 动力学模型
摘要泥石流是山区尤其是山地地震区常见灾害之一,由于降雨、固体物源时空分异及地形(微地形)的影响,其发生时间、地点、规模目前难以预知,加之其具有宽级配、高浓度、直进性、大冲大淤、冲击力大、破坏力强等特点,屡屡造成严重的灾害损失。防范化解泥石流灾害风险的主要对策包括工程治理和动态监测预警,其前提条件是客观把握泥石流发生、运动物理过程及其动力学机制,方可科学规划防治工程布局、合理确定工程设计参数、有效构建预警避难体系,将灾害损伤降至最低。泥石流体是介于高含沙水流和滑坡等块体之间的非牛顿体,颗粒组成、细粒含量、体积浓度、运动速度、颗粒碰撞、摩擦、浆体粘滞等因素影响泥石流动力学特征和模型构建。在颗粒剪胀效应方面,Iverson等人假设粗颗粒和浆体速度相同,提出了描述颗粒剪胀效应的虚自由面概念,并建立了相应的深度积分泥石流动力学模型,但泥石流(特别是稀性、过渡性泥石流)运动过程中粗颗粒和浆体速度存在分异性,在泥石流动力学模型构建过程中需要考虑固液两相速度的差异;在动床侵蚀作用方面,Iverson和Ouyang在深度积分泥石流动力学模型中考虑了侵蚀项的的基本架构,但假定固液两相速度相同,且缺乏表述两相泥石流动床侵蚀过程的侵蚀动力学模型。因此,为了更客观、科学地构建描述泥石流运动过程中的颗粒剪胀效应和动床侵蚀作用的泥石流动力学模型,本文重点探讨了考虑固液两相速度差异的颗粒剪胀效应、表述泥石流动床侵蚀过程的侵蚀动力学模型,构建了考虑颗粒剪胀效应和动床侵蚀作用的深度积分泥石流两相动力学模型;在此基础上,基于有限体积法建立了数值仿真模型和算法,并借助相关的实验数据和深圳光明滑坡流态化实际案例对动力学模型进行了可靠性、合理性检验。取得的主要进展和成果如下:1. 针对两相泥石流动床侵蚀问题,基于侵蚀面上的力学平衡和动量传递特征进行理论分析,提出一种符合基本力学原理、包含两相泥石流基本变量的侵蚀率计算公式。泥石流动床侵蚀问题特别复杂,泥石流与动床之间在剪切运动过程中存在物质、动量和能量交换,进而影响泥石流的流速、流深、固相体积分数和侵蚀能力,且呈动态变化特征。泥石流动床侵蚀模型包括经验模型、半经验半理论模型和理论模型;以前常用的经验模型缺乏明晰的物理机制,无法描述侵蚀过程且没有普适性;半经验半理论模型含一定的物理机制,但需通过实验等对模型相关参数进行率定;理论模型具有明晰的物理机制和动力学依据,不仅能定量描述侵蚀动态变化过程,而且具有普适性。本研究分析的是在考虑固液两相速度差异情况下的两相泥石流动床侵蚀问题,将被侵蚀的底床看作与泥石流内部固相具有相同或接近的物理属性的固体物质,基于侵蚀面上侵蚀力和抗力的力学平衡以及泥石流与动床间的动量传递特征,对固液两相分别进行理论推导,获得了两相泥石流侵蚀率动力学模型,该模型主要反映了影响侵蚀的主要因素对侵蚀量的动态影响关系。2. 系统梳理了几种泥石流动力学模型的特点及不足,重点针对近年来广受关注的深度积分泥石流动力学模型中的剪胀效应问题,考虑泥石流中颗粒物与浆体的速度差异,提出了两相泥石流在虚自由面处需要满足的动力边界条件,建立了考虑剪胀效应的两相泥石流动力学模型。剪胀和剪缩是颗粒物在剪切变形过程中固有的特性,但目前仅有极少数泥石流动力学模型中考虑了颗粒剪胀的影响。泥石流中颗粒物的剪胀或剪缩变形导致浆体的液面出现高度上的起伏,给自由表面的定义带来了极大的困难。本文在Iverson 和 George的虚自由面概念(固液速度相同)的基础上提出了两相泥石流(固液速度不同)在虚自由面处需要满足的动力边界条件,该边界条件允许颗粒相和流体相在虚自由面上有不同的速度,同时满足边界上的动量平衡关系。基于该边界条件,结合泥石流各相的质量守恒和动量守恒方程以及适当的底床边界条件,通过深度积分建立了以固相速度、液相速度、流深和固相体积分数为基本变量、考虑剪胀效应的两相泥石流深度积分动力学模型。3.考虑剪胀和侵蚀效应的两相泥石流深度积分动力学模型的建立及数值求解,动力学模型验证和应用实例分析。将侵蚀率计算模型融入考虑剪胀效应的两相泥石流动力学模型,建立了考虑侵蚀作用和剪胀效应的两相泥石流深度积分动力学模型。引入侵蚀和挟带效应后,动力学模型的质量守恒和动量守恒方程都将发生变化,同时固相体积分数的演变方程也将发生变化;采用能够考虑颗粒物和流体相互作用以及两相之间速度差异,同时考虑侵蚀作用和剪胀效应的两相泥石流深度积分动力学模型,能更好的描述多种泥石流的动力学特征,具有更广泛的应用前景。基于Geoclaw软件平台进行二次开发,采用有限体积法对提出的深度积分两相泥石流动力学模型进行了数值建模,软件研发和数值求解。数值建模主要考虑满足动力学模型的双曲型特征结构;根据方程组的特征结构构造黎曼求解器,并将该自定义的黎曼求解器以Fortran文件的形式提供给Geoclaw软件,供编译使用。然后,将数值模型用于分析USGS水槽实验,将模拟获得的流深和压力特征与实验结果进行了对比,验证了本文提出的动力学模型及对应的数值模型的合理性和有效性。在此基础上,将两相泥石流深度积分动力学模型应用于深圳2015年光明弃渣场发生的滑坡流态化运动堆积过程的实际案例分析,并与Iverson 和 George模型计算结果进行对比,结果表明本文的动力学模型能更好地反演灾害运动堆积过程和影响范围。
其他摘要Debris flow is one of the common disasters in mountainous regions, especially in earthquake-prone regions. Due to rainfall, spatial and temporal variation of solid-source, and topography (micro-topography), the time, place, and scale of occurrence are difficult to predict, combined with its wide gradation and high concentration, straight forwardness, large flush and large deposit, large impact force, and strong destructive power, all these lead serious disaster losses from debris flows. The main countermeasures to prevent and resolve the risk of debris flow disasters include engineering governance, dynamic monitoring and early warning. The precondition for these is to objectively grasp the occurrence, physical processes of movement, and their dynamic mechanisms of mudslides before scientific planning of prevention and control project layout, rational determination of engineering design parameters, and effective construction of early warning evacuation system, and minimize disaster damage. Debris flow is a non-Newtonian fluid with properties intermediating in character between blocks of landslide and flow with hyperconcentration of sediment. Particle composition, fines content, volume concentration, velocity distribution, particle collisions, friction, slurry viscosity, etc. affect debris flow statics and dynamics characters and the construction of models. There are differences in the velocity of coarse particles and slurries during the movement of debris flow (especially for dilute and transitional debris flow). The analysis of this type of debris flow needs to take into account the velocity difference between solid and liquid phase. Iverson and Ouyang proposed the basic structure of the erosion term in the depth-integrated dynamic model of debris flow in terms of mobile bed erosion. However, it is assumed that the velocity of solid and liquid phase is the same, and the material composition characteristics of two-phase of the debris flow are not considered. This paper focuses on the erosion model of debris flow considering the characteristics of the composition and the velocity difference of solid-liquid phase, and constructs a depth-integrated two-phase dynamic model of the debris flow considering both the dilatancy effect and the erosion effect on mobile bed. Based on the finite volume method, a numerical simulation model was established, and the reliability and rationality of the dynamic model were verified using the data from experiment flumes and the event of fluidized landslide in the Guangming New District of Shenzhen. The major progress and results achieved are as follows:1. Aiming at the mobile bed erosion problem of two-phase debris flow, theoretical analysis was conducted based on the mechanical balance and momentum transfer characteristics on the erosion interface, and a formula of erosion rate based on basic mechanics principle and basic variable of two-phase debris flow was proposed. There are material, momentum, and energy exchanges between the debris flow and the mobile bed during the shearing process, which affects the flow velocity, flow depth, volume fraction of solids, and erosion capacity, all of which are change dynamically. The debris flow bed erosion models include empirical models, semi-empirical semi-theoretical models, and theoretical models; previously commonly used empirical models lack a clear physical mechanism to describe erosion processes and are not universal applicable; semi-empirical and semi-theoretical models contain certain physical mechanisms, but, the relevant parameters of the model need to be determined through experiments; the theoretical model has clear physical and dynamics mechanisms, and it can not only quantitatively describe the dynamic process of erosion, but also has universal applicability. This study considers the problem of two-phase debris flow mobile bed erosion under the condition of different solid-liquid two-phase velocity, and considers the erodible bed as a solid substance with the same or close physical properties as the internal solid phase of the debris flow. Based the mechanical balance of erosive force and resistance on the erosion interface, the characteristics of momentum transfer between the debris flow and the mobile bed, the theoretical derivation of the solid-liquid two phases has been carried out respectively. A dynamic model of the erosion rate of the two-phase debris flow was obtained, the model mainly reflects dynamic influence of the main factors on the erosion of mobile bed.2. The characteristics of several debris flow dynamics models and their deficiencies were analyzed respectively, with considering the dilatancy effect within the depth-integrated dynamics model of debris flow which has received widespread attention in recent years, the difference in solid-liquid two-phase velocity, a dynamic boundary condition that needs to be satisfied at the virtual free surface is established for two-phase debris flow. Based on these, a two-phase debris flow dynamics model considering the dilatancy and erosional effect is established. Dilatancy is an inherent characteristic of granular in the process of shear deformation. However, only a few debris flow dynamic models have considered the effect of dilatancy. The dilatancy or shear deformation of the debris flow debris causes the height of the liquid surface of the slurry to fluctuate, which brings great difficulties to the definition of the free surface. Based on Iverson & George's concept of virtual free surface (the same solid-liquid velocity), this paper proposes the dynamic boundary conditions that two-phase debris flow (different in solid-liquid velocity) needs to satisfy at the virtual free surface, which allows the particle phase and fluid phase have different speeds on the virtual free surface, while satisfying the balance of momentum on the boundary. Based on this boundary condition, combined with the mass conservation and momentum conservation equations of the each phases of the debris flow and the appropriate boundary conditions of the bed, a two-phase depth-integrated debris flow dynamic model with dilatancy effect was established, in which the solid-phase velocity, liquid phase velocity, flow depth, and volume fraction of the solid phase are taken as basic variables.3. A two-phase debris flow depth-integrated dynamics model considering dilatancy and erosion effects was established and solved numerically. The dynamic model validation and application examples were analyzed. The erosion rate calculation model was integrated into the two-phase debris flow dynamics model considering the dilatancy effect, and a two-phase debris flow depth-integrated dynamic model was established considering the effects of erosion and dilatancy. With the introduction of erosion and entrainment effects, both the mass conservation and momentum conservation equations of the kinetic model will change, and the evolution equation of the volume fraction of the solid phase will also change; the particle-fluid interaction can be considered and the velocity between the two phases can be considered. The difference, a two-phase debris flow depth integration dynamics model considering both erosion and dilatancy effects, can better describe the dynamic characteristics of various debris flows, and has a wider application prospect. A secondary development was carried out basing on the Geoclaw software platform, the finite volume method was used to numerically model the proposed depth-integrated two-phase debris flow dynamics model. The software was developed and numerically solved. The numerical modeling mainly considers that the hyperbolic characteristic structure of the dynamic model is satisfied; the Riemann solver is constructed according to the characteristic structure of the equation set, and the custom Riemann solver is provided to the Geoclaw software in the form of Fortran file for compilation. Then, the numerical model was used to analyze the USGS flume experiments. The flow depth and pressure characteristics obtained from the simulation were compared with the experimental results, which verified the rationality and effectiveness of the proposed dynamic model and the corresponding numerical model. On this basis, a two-phase debris flow depth-integrated dynamics model was applied to the real analysis of the fluidized landslide which occured at Shenzhen Guangming dump site in 2015, and compared with the calculation results of the Iverson & George model. The results show that the dynamic model can better reproduce the process and range of deposition of this disaster event.Key
页数163
语种中文
文献类型学位论文
条目标识符http://ir.imde.ac.cn/handle/131551/24796
专题山地灾害与地表过程重点实验室
作者单位中国科学院成都山地灾害与环境研究所
第一作者单位中国科学院水利部成都山地灾害与环境研究所
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乔成. 考虑侵蚀影响的泥石流两相动力学模型研究[D]. 北京. 中国科学院大学,2018.
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