Model help:FallVelocity

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

[math]\displaystyle{ Re_{p} = {\frac{\sqrt { R g D } D}{\nu}} }[/math]

(1)

• Dimensionless fall velocity

[math]\displaystyle{ 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 ) }[/math]

(2)

• fall velocity

[math]\displaystyle{ R_{f} = {\frac{v_{s}}{\sqrt { R g D }}} }[/math]

(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