Shields parameter

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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) g D},

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[edit]

By multiplying the top and bottom of the Shields parameter by D2, you can see that it is proportional to the ratio of fluid force on the particle to the weight of the particle.

References[edit]

External links[edit]

  • 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.