Hazard in the environment - Woordenlijst

13 important questions on Hazard in the environment - Woordenlijst

What does 'Polarity of water molecules' mean?

depends mostly on the attraction between water molecules. Water behaves as a fluid of low viscosity as long as the temperatures are between 1 and 40 °C).

What does shear strain rate (ṡ)?

The rate of water, which is its degree of deformation (for example stretching out) will increase until the flow stops

What is a laminar flow?

Motion of the fluid partiles is very orderly , all particles moving in straight lines parallel to the pipe walls. Stroomsnelheid over de diepte bepalen kan met de laminaire stroming.


Newtoniaanse stroming staat gelijk aan laminaire stroming. Dit is een hele rustige vorm van stroming.
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What is meant by 'elements at risk' and 'specific risk'?


Element at risk: means the population, properties, economic activities and so on, at risk in a given area
Specific risk: means the expected degree of loss due to a particular (natural) phenomenon (e.g. a forest fire)

What is a steady non-uniform flow?

Conditions change from point to point in the stream, but do not change with time. For example, flow in a tapering pipe with constant velocity at the inlet.

What is an unsteady, non-uniform flow?

Every condition of the flow may change from point to point and with time at every point. For example, waves in a channel.

What is an unsteady uniform flow?

At a given instant in time, the conditions at every point are the same, but will change with time. For example, a pipe of constant diameter connected to a pump pumping at a constant rate, which is then switched off.

Boundary layer separation: what are divergent flows and how does this work?

Divergent flows: positive pressure gradients.
Pressure increases in the direction of the flow. The fluid in the boundary layer has so little momentum that it is brought to rest, and possibly reversed in direction. Reversal lifts the boundary layer. Therefore, turbulence is increasing and the other flow is losing energy.

What is flow velocity?

strain change per time unit, therefore also seen as the speed of the flow. Formula for this is: dV = v * A * dt

What is dynamic viscosity?

SI unit is Poise (P). Water of 20 °C has a viscosity of 1 cP (centipoise).

What is kinematic viscosity?

Dynamic viscosity / density (in Stokes). Stokes is written as St. 1 St := 10−4 m²/s.

What is the Venturi Experiment?

This experiment demonstrates that when the flow velocity increases, the pressure decreases. To have a detailed view of what exactly happens, please see again the syllabus. Friction is neglected with this experiment. This experiment can also be used to understand why objects on a riverbed can be carried along in a current by flowing water. This is because when water flows over an object, the flow is accelerated due to the saved energy. Now, the pressure directly above this object will decrease. Due to the reduced pressure, an upward directed stress is applied on the object.

What is logistic flow velocity?

When water crosses the critical velocity, it start behaving chaotic and becomes turbulent. Small vortices (draaikolken) start to appear. The more turbulence, the bigger the vortices get. How turbulent a fluid gets, has to do with viscosity of the fluid and inertia of it (mass, density, volume).

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