The Role of Instantaneous Forces in Particle Movement

Many methods and equations have been developed to predict bed load transport rates, most of which use some comparison between shear stress and critical shear stress. The critical shear stress is determined by the point of incipient motion. Researchers have attempted to predict bed load transport both deterministically with mean parameters and stochastically attempting to take into account the fluctuations of velocity at points near threshold. This work attempts to show that more than simple force balances are needed to determine the point at which a particle will move. Turbulent fluctuations in velocity seem to have an effect of particle entrainment. The fluctuations in velocity can be several times greater than their time averaged counterparts. These short durations of high velocity often result in particle movement even though the mean flow may be less than or very near critical conditions. Through experiments of a single spherical particle on a simple bed geometry in air without the effects of water, it is shown that time duration of force has an effect on entrainment. This shows that there may be a constant force-time combination, or impulse, required to entrain sediment.

Name thesis:degree_name

Master of Science

Level thesis:degree_level

masters

Discipline thesis:degree_discipline

Civil Engineering

Department dc:contributor.department

Civil Engineering

Grantor dc:publisher

Virginia Tech

Year dc:date.issued

2006

Author dc:creator

• Greer, Krista

Chairs dc:contributor.committeechair

• Dancey, Clinton L.
• Diplas, Panayiotis

Committee member dc:contributor.committeemember

• Little, John C.

• incipient motion
• sediment transport
• impulse
• electromagnet

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Dc Identifier Other

etd-09072006-083326

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/34957