Peter Nielsen

Sediment transport by dam-break waves and other steady bores and surges.

This project involves both experimental work in the Civ Eng Hydraulics lab and theory.

THE SUBJECT MATTER IS NEW. NOT LIKE SEDIMENT TRANSPORT IN STEADY RIVER FLOWS, NOT LIKE SEDIEMT TRANSPORT UNDER WAVES.

What you will generate and study here is the sediment transport, which occurs under progressing dam-break tips, where very large bed shear stresses and correspondingly high sediment transport rates occur for a very short period (shorter than 1 second) just after the passage of the shock front.

Finite Mixing Length Effects and the importance of coherent flow structures in Geophysical and Industrial Fluid Mechanics

It is well known that the simple gradient diffusion model fails in relation to many geophysical and industrial mixing processes where the important eddies are not infinitesimally small compared to the scales considered. Finite mixing length models are therefore an active area of research, e g Nielsen & Teakle (2004).

The present project will be mainly experimental, studying concentration profiles of light (rising) versus heavy (sinking) particles with numerically similar rise/sinking velocities in the same flow.

Stratification effects on suspended sediment concentrations under waves

Much of the sand which migrates along the beaches travels in suspension.

The mechanisms which govern such sediment suspensions are therefore of interest.

For some combinations of wave and sand parameters stratification plays an important role. That is, for these parameter combinations, the density of the water-sand-mixture near the bed is sufficiently increased to dampen the turbulence significantly.

The thesis work involves litterature review and laboratory experiments.

Tornados and other buoyant rotating plumes

The project will experimentally investigate the conditions under which tornado-like flows form naturally or may be triggered.

Of special interest are

1. Conditions for the building of tornadoes with angular momentum originating in the clouds: Possibly the reason why tornados can exist.
2. Fire tornadoes, which act like 'a chimney without walls'
3. Rotating plumes of nutrient rich water, venting from the seabed, which has the potential to sustain large-scale fish production if prevented from mixing too rapidly with surrounding water so that, it can get up to the light- and oxygen-rich environment above the thermocline.
4. Oil-spils which, if made to rotate, will maintain enough buoyancy to come to the surface for easy cleanup