Question

For the lab "Flow nets and Seepage model" write one paragraph each of the abstract, and introduction.

Answer 1

Flownet-

flownet is a graphical representation of two-dimensional steady-state groundwater flow through aquifers.

Construction of a flownet is often used for solving groundwater flow problems where the geometry makes analytical solutions impractical. The method is often used in civil engineering, hydrogeology or soil mechanicsas a first check for problems of flow under hydraulic structures like dams or sheet pilewalls. As such, a grid obtained by drawing a series of equipotential lines is called a flownet. The flownet is an important tool in analysing two-dimensional irrotational flow problems. Flow net technique is a graphical representation method.

Mathematically, the process of constructing a flownet consists of contouring the two harmonic or analytic functions of potential and stream function. These functions both satisfy the Laplace equation and the contour lines represent lines of constant head (equipotentials) and lines tangent to flowpaths (streamlines). Together, the potential function and the stream function form the complex potential, where the potential is the real part, and the stream function is the imaginary part.

The construction of a flownet provides an approximate solution to the flow problem, but it can be quite good even for problems with complex geometries by following a few simple rules (initially developed by Philipp Forchheimer around 1900, and later formalized by Arthur Casagrande in 1937) and a little practice:

• streamlines and equipotentials meet at right angles (including the boundaries),
• diagonals drawn between the cornerpoints of a flownet will meet each other at right angles (useful when near singularities),
• streamtubes and drops in equipotential can be halved and should still make squares (useful when squares get very large at the ends),
• flownets often have areas which consist of nearly parallel lines, which produce true squares; start in these areas — working towards areas with complex geometry,
• many problems have some symmetry (e.g., radial flow to a well); only a section of the flownet needs to be constructed,
• the sizes of the squares should change gradually; transitions are smooth and the curved paths should be roughly elliptical or parabolic in shape. Seepage flow-

  In hydrology, seepage flow refers to the flowof a fluid (water) in permeable soil layers such as sand. The fluid fills the pores in the unsaturated bottom layer and moves into the deeper layers as a result of the effect of gravity. The soil has to be permeable so that the seepage water is not stored.

• Seeepage is the key factor in the safety of dikes and earth-fill dams. It is crucial to identify
  and localize the seepage excesses at the early stages before it initiates the internal erosion process
  in the structure. A proper seepage monitoring system should ensure a continuous and wide area
  seepage measurement. Here, continuous monitoring of seepage at the laboratory-scale is achieved by
  a passive optical fiber Distributed Temperature Sensing (DTS) system. An experimental model was
  designed which consists of initially unsaturated sand model, water supply, seepage outflow, optical
  fiber DTS system, and water and air temperature measurement. Initially, the sand temperature was
  higher than the temperature of the seepage water. An optical fiber DTS system was employed with
  a high-temperature resolution, short sampling intervals and short time intervals for temperature
  monitoring in the sand model. In the system, the small variation in the temperature due to groundwater
  flow was detected. The numerical analysis was conducted for both the seepage process and the heat
  transfer progression in the sand model. The results of the heat flow simulation were evaluated and
  compared with the measured temperature by the optical fiber DTS. Obvious temperature reduction
  was obtained due to seepage propagation in the sand. The rate of temperature reduction was observed
  to be dependent on the seepage flow velocity.