online_fall_velocity: Fall velocity of a spherical sediment particle

Formulas
w = {(4/3)[(gd _{s})/C _{D}][(γ _{s}  γ)/γ]} ^{1/2}
R = (w d_{s})/ν
Reference

DESCRIPTION
This program calculates the fall velocity [w] of a spherical sediment particle using an iterative procedure, with the following steps:
 The particle Reynolds number [R] is assumed equal to 100.
 For the given Reynolds number, the drag coefficient C_{D} is obtained from Fig. 151 in the text, assuming a spherical particle.
 The fall velocity is calculated with Eq. 152, assuming γ_{s} = 2.65 (quartz particles).
 The particle Reynolds number is calculated with Eq. 153.
 The absolute difference between assumed and calculated Reynolds number is compared to a specified tolerance (0.0001).
If the difference is greater than the tolerance, replace assumed with calculated value, and return to Step 2.
 Otherwise, stop and report results of last iteration.
Output is the number of iterations, and the last drag coefficient, particle
Reynolds number, and fall velocity (in m/s or fps) calculated.
Default units is SI (metric). The program can take U.S. Customary units.

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