03.运动-1达西.pptVIP

* * Darcy flow: assumes that flow occurs through the entire cross section of the material without regard to solids and pores. 具有与实际水 流相同的： 断面流量、 水位 水力阻力。 * * 能量守恒 测压管水头： 在水流通过空隙介质时，由于摩擦阻力导致能量损失 能量守恒方程： 忽略动能项： 水流总是由高水头流向低水头 * 水头梯度： I=(H1-H2)/L=dH/dn 水力坡度： 大小等于水头梯度 I，方向沿着等水头线的法线方向、指向水头降低方向的矢量定义为水力坡度，记为J。 * K is also known as “Darcy’s proportionality constant” or “coefficient of permeability”. whereas in unsaturated flow K is a function of soil moisture, soil and fluid properties, in saturated flow it a function of soil and fluid properties only. * 水力坡度描述了能量损失的速度 * 实质：水流在孔隙介质中流动消耗的能量与流速和渗流长度成正比，与含水层渗透系数成反比。 位能Z 压能 热能 机械能 动能 * * 水流的动能不能忽略，机械能不再随距离按线性损失。 Will Darcy’s Law still valid？ * * Reynolds number(雷诺数) The Reynolds number has been employed to establish the limit of flows described by Darcy’s Law. Where, ρ is the fluid density, ν the velocity, μ the (dynamic) viscosity of fluid, d the diameter(of a pipe). In porous media, Darcy velocity is employed for v and an effective grain size(d10) is substituted for d。 * 达西定律成立的上限： 大量的试验表明，达西定律仅仅在黏滞力占优的条件下成立，亦即，雷诺数介于1~10之间。 大孔隙 岩溶 抽水井附近 … 大多数天然地下水流 * 达西定律成立的下限： 对低渗透性介质（如黏性土），存在起始水力梯度J0。当J小于J0时，几乎不发生流动。 * * 为了对多孔介质中的地下水运动作连续性近似，引入了REV的概念。 优点： 将实际上并不处处连续的水流当作连续水流进行研究，使流体力学的研究成果能够被引用、借鉴。 * The discussion of hydraulic conductivity assumed that the geologic material was homogeneous (均质的) and isotropic (各向同性的), implying that the value of K was the same in all directions. However, anisotropic (各向异性的) is the rule where directional properties of hydraulic conductivity exist. Homogeneous medium (均质)： the distribution of K must be monomodal Inhomogeneous medium (非均质)： hydraulic properties change spatially Isotropic medium (各向同性介质)： A porous medium has equal intrinsic permeability in all directions Anisotropic medium (各向异性介质)： the pattern of voids allows for a path of least resistance If an xyz coordinate system is setup along the principal directions: Kx=Ky=Kz is an isotropic situation Kx…Ky…Kz is an an