FallVelocity

This model is used to calculate Particle fall velocity.

Model introduction

This model calculate fall velocity for spheres. Uses formulation of Dietrich (1982).

Model parameters

• Input Files and Directories
• Run Parameters
• About

Parameter	Description	Unit
Input directory	path to input files
Site prefix	Site prefix for Input/Output files
Case prefix	Case prefix for Input/Output files

Parameter	Description	Unit
kinematic viscosity of water (ν)		m2 / s
Submerged specific gravity of sediment (R)		-
Grain size (D)		mm
Acceleration due to gravity (g)		-

Parameter	Description	Unit
Model name	name of the model	-
Author name	name of the model author	-

Uses ports

This will be something that the CSDMS facility will add

Provides ports

This will be something that the CSDMS facility will add

Main equations

• Explicit particle Reynolds number

$Re_{p} = {\frac{\sqrt { R g D } D}{\nu}}$

(1)

• Dimensionless fall velocity

$R_{f} = exp \left ( -b_{1} + b_{2} ln \left ( Re_{p} \right ) - b_{3} \left ( ln \left ( Re_{p} \right ) \right ) ^2 - b_{4} \left ( ln \left ( Re_{p} \right ) \right ) ^3 + b_{5} \left ( ln \left ( Re_{p} \right ) \right ) ^4 \right )$

(2)

• fall velocity

$R_{f} = {\frac{v_{s}}{\sqrt { R g D }}}$

(3)

Nomenclature

Symbol	Description	Unit
g	gravitational acceleration	L / T2
ν	kinematic viscosity of water	L2 / T
R	submerged specific gravity of sediment, defined as (ρs -ρ) /ρ	-
D	grain size	L
ρs	sediment density	M / L3
ρ	water density	M / L3

Output

Symbol	Description	Unit
vs	fall velocity	L / T
Rep	explicit particle Reynolds no.	-
Rf	dimensionless fall velocity	-

Notes

b₁, b₂, b₃, b₄, b₅ are all parameters from Dietrich(1982).

This formulation is only valid for Reynold’s numbers less than or equal to 2.5·10⁶. If Re_p is greater than this upper limit, the function will alert the user, and exit the program.

Examples

An example run with input parameters, BLD files, as well as a figure / movie of the output

Follow the next steps to include images / movies of simulations:

• Upload file: http://csdms.colorado.edu/wiki/Special:Upload
• Create link to the file on your page: [[Image:<file name>]].

See also: Help:Images or Help:Movies

Developer(s)

Gary Parker

References

Dietrich, E. W., 1982, Settling velocity of natural particles, Water Resources Research, 18 (6), 1626-1982.

Links

• Model:FallVelocity