Two-Point Closure Strategy in the Mapping Closure Approximation Approach

A two-point closure strategy in mapping closure approximation (MCA) approach is developed for the evolution of the probability density function (PDF) of a scalar advected by stochastic velocity fields. The MCA approach is based on multipoint statistics. We formulate a MCA modeled system using the one-point PDFs and two-point correlations. The MCA models can describe both the evolution of the PDF shape and the rate at which the PDF evolves.

基于USB接口的无线温湿度监测系统

针对环境温湿度检测的需求,设计了一种点对多点的星型无线温湿度监控网络。以无线通信模块nRF401为基础,配合AT89C2051和数字温湿度传感器SHT11构建了从机,以P89C51RD2BN单片机和USB接口芯片PDIUSBD12构建了主机。对系统的硬件原理及温湿度采集方法进行了介绍,对无线通信协议及USB固件设计方法进行了较详细分析。经上位机软件测试,系统运行稳定,具有较好实用性,可应用于多种场合的无线温湿度监测。

典型人类活动对边坡变形及稳定性的影响研究

China is a mountainous country in which geological hazards occurred frequently, especially in the east of China. Except the geology, topography and extreme climate, the large scale human activities have become a major factor to landslides. Typical human activities which induced landslides are fill, cut and underground mining. On the topic of the deformation mechanism and slope stability, taking three different man-made slopes as examples, deformation mechanism and slope stability were studied by several methods, such as field work, numerical modeling and monitor. The details are as following: (1) The numerical modeling approach advantages over other conventional methods such as limit methods, so the numerical modeling is the major tool in this thesis. So far, there is no uniform failure criterion for numerical simulation. The failure criterion were summarized and analyzed firstly, subsequently the appropriate criterion was determinated. (2) Taking 220kV Yanjin transformation substation fill slope as example, the deformable characteristic, unstable mode and laboratory tests were studied systematically. The results show: the slope deformation was probably caused by a combination effect of unfavorable topographic, geological and hydro geological conditions, and external loading due to filling. It was concluded that the creep deformation of the slope was triggered by external loading applied at the back of the slope. In order to define the calculating parameters, a set of consolidated drained (CD) tests, consolidated undrained (CU) tests, repeated direct shear tests and UCS tests were carried out. The stability of the slope before and after reinforcement was assessed using 3D numerical modeling and shear strength reduction technique. The numerical modeling results showed: the factor of safety (FOS) of the slope was 1.10 in the natural state, and reduced to 1.03 after fill, which was close to the critical state and it caused creeping slip or deformation under rainfall. The failure surface in the slope is in active shear failure, whereas tensile failure occurs at the slope crest. After the site was reinforced with piles, the FOS was 1.27. Therefore, the slope is stable after reinforcement measures were taken. (3) The cut slope stability is a complex problem. Taking the left cut slope of Xiangjiaba as example in this thesis, the deformation and slope stability were studied systematically by numerical modeling and monitor methods. The numerical results show: the displacement is gradually increasing along with the cutting, and the largest displacement is 27.5mm which located at the bench between the elevation 340 and 380. Some failure state units distribute near the undermining part and there is no linked failure state occurred from crest to bottom during cutting. After cutting, some failure units appeared at the ground surface between elevation 340 and 360. The increasing tense stress made the disturbed rock failed. The slope is stable after cutting by the monitor method, such as surface monitor, multipoint displacement meter, inclinometer and anchor cable tensometer. (4) The interaction between underground mining and slope stability is a common situation in mountainous. The slope deformation mechanism induced by underground mining may contributed significantly to slope destabilization. The Mabukan slope in xiangjiaba was analyzed to illustrate this. Failure mechanism and the slope stability were presented by numerical modeling and residual deformation monitor. The results show: the roof deformed to the free face and the floor uplift lightly to the free face. The subsidence basin is formed, but the subsidence and the horizontal movement is small, and there is no failure zone occurred. When the underground mining is going on, the roof deformation, subsidence and the horizontal movements begin increasing. The rock deformation near the free face is larger than the ground surface, and the interaction between these coal seams appeared. There are some tensile failures and shear failures occurred on the roof and floor, and a majority of failure is tensile failure. The roof deformation, subsidence and the horizontal movements increased obviously along with the underground mining. The failure characteristic is shear failure which means the tensile stress transformed to the compressive stress. So the underground mining will induced tensile stress first which lead to structure crack, subsequently the compressive stress appeared which result in slippage. The crest was subjected to horizontal tension which made the rock crack along with the joint. The long term residual deformation monitor demonstrates that the slope is stable after the underground mining stopped.