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CHAPTER 6. SEDIMENT TRANSPORT MODELS
or more simply
Nf. = Ny,Nd
Ny,Nd
(6.63)
(6.64)
because JV71 = 1.
In a similar manner, the scale ratio of grain size Reynolds number, Nr, ,
is found to be
Nr, =
(^o)wave Nd
Np
N,
(NLy/< (Nd)W Nd
Np
N,
(6.65)
which reduces to
Nr, = N[,6Ndï/&
(6.66)
when water is the model fluid.
The necessary velocity scales for correct current reproduction in the
Offshore Sand ModeJ and the Inshore Sand Model are already given in
terms of NL and Nd by Eqns. 6.21 and 6.22, respectively (with Nki = Nd).
Sand Model Scale Effects
The Sand Model cures some of the scale effects introduced by the use
of lightweight materials, but not maintaining the prototype densimetric
Froude number in the model can lead to serious errors. Kamphuis (1985)
stated that nonsimilarity of Np, and Nr. in the Sand Model will give incorrect sediment transport at low velocities, and the period of no sediment
motion is exaggerated in the model during a wave cycle. This is particularly
pronounced in deeper water where the wave-induced bottom velocities are
decreased.
The Sand Model has potential for modeling coastal sediment transport,
but evaluation of scale effects is best done using a “scale series” or comparing model response to prototype measurements.
Example 6.3. Offshore Sand Model
After conducting numerous experiments in the three-dimensional, movable-bed
model described in Example 6.1, our intrepid researcher, “George" decides to abandon the Best Model guidelines and instead use the same model setup to represent a
prototype inlet having quartz sand with a median grain size of dp = 0.3 mm. For
CHAPTER 6. SEDIMENT TRANSPORT MODELS
or more simply
Nf. = Ny,Nd
Ny,Nd
(6.63)
(6.64)
because JV71 = 1.
In a similar manner, the scale ratio of grain size Reynolds number, Nr, ,
is found to be
Nr, =
(^o)wave Nd
Np
N,
(NLy/< (Nd)W Nd
Np
N,
(6.65)
which reduces to
Nr, = N[,6Ndï/&
(6.66)
when water is the model fluid.
The necessary velocity scales for correct current reproduction in the
Offshore Sand ModeJ and the Inshore Sand Model are already given in
terms of NL and Nd by Eqns. 6.21 and 6.22, respectively (with Nki = Nd).
Sand Model Scale Effects
The Sand Model cures some of the scale effects introduced by the use
of lightweight materials, but not maintaining the prototype densimetric
Froude number in the model can lead to serious errors. Kamphuis (1985)
stated that nonsimilarity of Np, and Nr. in the Sand Model will give incorrect sediment transport at low velocities, and the period of no sediment
motion is exaggerated in the model during a wave cycle. This is particularly
pronounced in deeper water where the wave-induced bottom velocities are
decreased.
The Sand Model has potential for modeling coastal sediment transport,
but evaluation of scale effects is best done using a “scale series” or comparing model response to prototype measurements.
Example 6.3. Offshore Sand Model
After conducting numerous experiments in the three-dimensional, movable-bed
model described in Example 6.1, our intrepid researcher, “George" decides to abandon the Best Model guidelines and instead use the same model setup to represent a
prototype inlet having quartz sand with a median grain size of dp = 0.3 mm. For