Environmental Engineering Reference
In-Depth Information
Mathematical model
Model that simulates a system's behaviour by a set of equations, per-
haps together with logical statements, by expressing relationships between
variables and parameters.
Mean depth
Average depth of a canal, being the cross sectional area divided by the
surface or top width.
Mean velocity
Average velocity in a canal, being the discharge divided by the cross
sectional (wetted) area.
Meandering
Single channel having a pattern of successive deviations in alignment that
results in a more or less sinusoidal course.
Mixing length
The mixing length is the characteristic distance travelled by a fluid
particle before its momentum is changed by the new environment; the
mixing length theory is a turbulence theory developed by Prandtl (1925).
Modelling
Simulation of some physical phenomenon or system with another system
believed to obey the same physical laws or rules in order to predict the
behaviour of the former by experimenting with the latter.
Momentum exchange
coefficient
Apparent kinematic (eddy) viscosity in turbulent flows; analogous to the
kinematic viscosity in laminar flows. Momentum exchange coefficient is
proportional to the shear stress divided by the strain rate. Also called eddy
viscosity or eddy coefficient (Boussinesq, 1877).
Navier
Louis Marie Henri Navier (1785-1835) - French engineer who extended
Euler's equations of motion (Navier 1823).
Navier-Stokes equation
Momentum equation applied to a small control volume of incompressible
fluid; usually written in vector notation. Navier first derived the equation
by a different method. De Saint-Venant in 1843 and Stokes in 1845 derived
it in a more modern manner.
Negative surge
A negative surge results from a sudden change in flow that decreases the
flow depth. It is a retreating wave front moving upstream or downstream.
Newton
Sir Isaac Newton (1642-1727) - English mathematician and physicist. His
contributions in optics, mechanics and mathematics were fundamental.
Nikuradse
J. Nikuradse - German engineer who investigated the flow in smooth and
rough pipes (1932).
Non uniform flow
Flow that varies in depth, cross-sectional area, velocity and hydraulic
slope from section to section.
Normal depth
Uniform equilibrium open channel flow depth; depth at a given point
in a canal corresponding to uniform flow, water surface and bed are
parallel.
Numerical modelling
Refers
to
the
analysis
of
physical
processes
(e.g.
hydraulic)
using
computational models.
Off-take
Structure with or without gates, that conveys water to a secondary canal or
tertiary unit.
One-dimensional flow
Neglects the variations and changes in velocity and pressure transverse to
the main flow direction.
One-dimensional model
Model defined with one spatial coordinate, the variables being averaged in
the other two directions.
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