Shields parameter

The Shields parameter, also called the shields criterion or shields number, is a nondimensional number used to calculate the initiation of motion of sediment in a fluid flow. It is a nondimensionalization of a shear stress, and is typically denoted $\tau _{\ast }$ or $\theta$. It is given by:

$\tau _{\ast }=\theta ={\frac {\tau }{(\rho _{s}-\rho )gD}},$

where:

$\tau$	is a dimensional shear stress;
$\rho _{s}$	is the density of the sediment;
$\rho$	is the density of the fluid;
$g$	is acceleration due to gravity;
$D$	is a characteristic particle diameter of the sediment.

Physical meaning

By multiplying the top and bottom of the Shields parameter by d^2, you can see that it is proportional to the ratio of fluid force on the particle to the weight of the particle.

References

• Shields, A. (1936). Anwendung der Aehnlichkeitsmechanik und der Turbulenzforschung auf die Geschiebebewegung (PDF). Mitteilungen der Preußischen Versuchsanstalt für Wasserbau (in German). Vol. 26. Berlin: Preußischen Versuchsanstalt für Wasserbau. {{cite book}}: Unknown parameter |trans_title= ignored (|trans-title= suggested) (help)
• Cao, Zhixian; Pender, Gareth; Meng, Jian (2006). "Explicit Formulation of the Shields Diagram for Incipient Motion of Sediment". Journal of Hydraulic Engineering. 132: 1097. doi:10.1061/(ASCE)0733-9429(2006)132:10(1097).

External links

• Southard, John. "Chapter 9 – Threshold of movement" (PDF). Lecture notes – Special topics: An introduction to fluid motions, sediment transport, and current-generated sedimentary structures. MIT Open Courseware. Retrieved 2011-01-31.