A flow net is a graphical representation of two-dimensional steady-state groundwater flow through aquifers. … As such, a grid obtained by drawing a series of equipotential lines is called a flow net. The flow net is an important tool in analysing two-dimensional irrotational flow problems.
What are the uses of flow nets?
- Flow net applications include Calculation of uplift pressure, Exit gradient / Piping, Heaving and Pore Water pressure.
- Flow net represents the flow of water through a soil graphically. …
- It is pore water pressure and it acts vertically upward direction due to residual pressure head.
What are the components of flow net?
A flow net consists of two sets of lines which must always be orthogonal (perpendicular to each other): flow lines, which show the direction of groundwater flow, and equipotentials (lines of constant head), which show the distribution of potential energy.
Why flow net is important?
Flow nets provide a general knowledge of the regional groundwater flow patterns that the hydrologist can use to determine such information as areas of recharge and discharge. Freeze and Cherry (1979, pg. 168) have stated that flow nets are an important concept of hydrology.
Which is the most commonly used method of construction of flow net?
But for that first we need to solve the laplace equation, which is not a very easy task to do. So, we try to obtain our flow net for two dimensional flow using next method. This is the most commonly used method of flow net construction because it is easy and it provides nearly accurate results.
What is Flow Net in geotechnical engineering?
A Flow net is a graphical representation of flow of water through a soil mass. It is a curvilinear net formed by the combination of flow lines and equipotential lines.
What is NF and ND?
Nd = number of potential drops Nf = number of flow channels h = total head loss q = total quantity of unit flow.
What are the various methods for obtaining flow nets?
- Graphical method.
- Electrical flow Analogy method.
- Sand Model.
- Capillary flow Model.
- Solution of Laplace equation/Analytical method.
What are the limitations of flow net?
The flow net analysis cannot be applied in the region closed to the boundary where the effects of viscosity are predominant. The flow net is not applied to sharply diverging flow , as the actual flow pattern is not represented by the flow net.
How do you draw a line in flow nets?
- First identify the hydraulic boundary conditions. …
- Draw a trial flow line ABC adjacent to boundary line. …
- Starting from the upstream end, divide the first flow channel into approximate squares.
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Which of the following method is used to draw the flow net?
Methods of Drawing Flow nets: (1) Analytical Method → The flow net can be drawn from the expression for ϕ and ψ in term of x and y and plotting them. (2) Hydraulic Models: streamlines can be traced by injecting a dye in a seepage model or Hele-shaw appartus.
Which of the following are used to determine flow net?
Flow nets are drawn based on the boundary conditions only. They are independent of the permeability of the soil and the head causing flow. The space formed between two flow lines and two equipotential lines is called a flow field. It should be in a square form.
What is phreatic line in earth dam?
The top flow line of a saturated soil mass below which seepage takes place, is called the Phreatic line. Hydrostatic pressure acts below the phreatic line whereas atmospheric pressure exists above the phreatic line. … For an earthen dam, the phreatic line approximately assumes the shape of a parabola.
Who was the first to give a graphical method of flow net construction?
3. Who was the first to give a graphical method of flow net construction? Explanation: The graphical method of flow net construction first given by Forchheimer in 1930, based on trial sketching.
What is exit gradient?
The disturbing force at any point is proportional to the gradient of pressure of water at that point (i.e. dp/dl). This gradient of pressure of water at the exit end is called the exit gradient. In order that the soil particles at exit remain stable, the upward pressure at exit should be safe.
What is permeability coefficient?
Definitions. The coefficient of permeability of a soil describes how easily a liquid will move through a soil. It is also commonly referred to as the hydraulic conductivity of a soil. This factor can be affected by the viscosity, or thickness(fluidity) of a liquid and its density.
What is isotropic soil?
If soil consisted of perfectly spherical grains, flow rates would be isotropic – the same in all directions, other factors being equal. … Depending on the physical properties of the soil, preferential flow could occur in any direction, but the tendency is for higher horizontal rates.
What is Flow Net how it is useful in seepage analysis in earthen dam?
Flow nets are the graphical representation of water movement through the soil and it is used to analyze the uplift water pressure and seepage amount. The flow nets are comprised of flow lines and equipotential lines, which is a graphical representation of Laplace’s equation.
What are the properties of flow net Mcq?
- The flow lines and equipotential lines meet at right angles to each other.
- Two flow line never cross each other.
- Two equipotential lines never cross each other.
- Flow and equipotential lines are smooth curves.
- The quantity of water flowing through each flow channel is the same.
What does high hydraulic conductivity mean?
DEFINITIONS OF HYDRAULIC CONDUCTIVITY In theoretical terms, hydraulic conductivity is a measure of how easily water can pass through soil or rock: high values indicate permeable material through which water can pass easily; low values indicate that the material is less permeable.
How do you calculate hydraulic gradient?
The hydraulic gradient is the change in total head divided the distance over which the change occurs. average pore water velocity v = -K/n(∆h/∆L) The average velocity of the water is the Darcy equation divided by the porosity of the sediment.
What are groundwater equipotential lines?
The equipotential lines represent the height of the water table or potentiometric surface above mean sea level or other datum plane. Add flow lines to depict the movement of groundwater at the site. Groundwater follows the path of steepest groundwater gradient.
What is difference between laminar and turbulent flow?
Laminar flow or streamline flow in pipes (or tubes) occurs when a fluid flows in parallel layers, with no disruption between the layers. … Turbulent flow is a flow regime characterized by chaotic property changes. This includes rapid variation of pressure and flow velocity in space and time.
Is flow net analysis is applicable for rotational flow?
Flow net is very much useful in analysing the two dimensional, irrotational flow problems. … (ii) The flow should be irrotational, which is possible only when flowing fluid is an ideal fluid (having no viscosity) or it has negligible viscosity.
What does the momentum equation State?
The momentum equation is a mathematical formulation of the law of conservation of momentum. It states that the rate of change in linear momentum of a volume moving with a fluid is equal to the surface forces and the body forces acting on a fluid.
Does hydraulic gradient have units?
The hydraulic gradient is the driving force that causes groundwater to move in the direction of maximum decreasing total head. It is generally expressed in consistent units, such as feet per foot. For example, if the difference in water level in two wells 1000 feet apart is 2 feet, the gradient is 2/1000 or 0.002 (Fig.
WHAT IS A in Q kIA?
Q = Discharge (L3/T) v = water velocity (L/T) A = Cross sectional area (L2)
What is the importance of exit gradient?
Increasing the seepage velocity at the downstream end of hydraulic structures, may cause the movement of soil particles and accordingly accelerates piping and soil erosion. The exit gradient is the main design criterion in determining the safety of hydraulic structures against the piping phenomenon.
