296
CHA PTER 6. SEDIMENT TRA NS PORT MODELS
Froude criterion and sand grain size selected to preserve the prototype
value of the fall speed parameter. This model law was not tested in the
laboratory, but Dalrymple and Thompson stated that it appeared to be
most practical because it also preserves the wave steepness parameter. They
also recommended that sand be used as the model bed material to avoid
possible “alien” effects.
Noda13 (1978) conducted movable-bed model experiments in which the
value of Dean’s (1973) Version of the fall speed parameter, given as
13 Not the same person who developed the scaling criteria discussed earlier in this
section.
(6-105)
was kept the same in geometrically undistorted scale models using sand
as the model sediment. Preserving the value of the parameter given by
Eqn. 6.105 in an undistorted Froude-scaled model fulfills the scaling requirements suggested by Dalrymple and Thompson (1976). Noda used
sand sizes having median grain size diameters ranging between 0.17 mm
and 0.6 mm, and experiments were conducted in a 20-m-long by 0.5-mwide wave flume with a 0.4 m water depth. Experiments were designed to
maintain the same values of the fall speed parameter for values of length
scales ranging between Nl = 2 and Nl = 8.3.
Noda (1978) achieved good matches of equilibrium beach profiles between the different scale models when the fall speed parameter was the
same in the two models. Much poorer correspondence was found when
he compared profiles from models having the same value of the parameter
Ho/d$Q. Noda considered the possibility of geometrically distorted models
based on sediment fall speed, but did not draw any conclusions as to its
validity.
Kamphuis (1982) concluded that preservation of the fall speed parameter in models where significant sediment suspension is occurring eliminates
most of the scale effects associated with attempting to scale the grain size
diameter of quartz sand geometrically.
The scale requirement for maintaining similarity of the fall speed parameter between prototype and model is easily derived by equating prototype
and model values of the parameter, i.e.,
-ÜE- =
(6.106)
WmTm
CHA PTER 6. SEDIMENT TRA NS PORT MODELS
Froude criterion and sand grain size selected to preserve the prototype
value of the fall speed parameter. This model law was not tested in the
laboratory, but Dalrymple and Thompson stated that it appeared to be
most practical because it also preserves the wave steepness parameter. They
also recommended that sand be used as the model bed material to avoid
possible “alien” effects.
Noda13 (1978) conducted movable-bed model experiments in which the
value of Dean’s (1973) Version of the fall speed parameter, given as
13 Not the same person who developed the scaling criteria discussed earlier in this
section.
(6-105)
was kept the same in geometrically undistorted scale models using sand
as the model sediment. Preserving the value of the parameter given by
Eqn. 6.105 in an undistorted Froude-scaled model fulfills the scaling requirements suggested by Dalrymple and Thompson (1976). Noda used
sand sizes having median grain size diameters ranging between 0.17 mm
and 0.6 mm, and experiments were conducted in a 20-m-long by 0.5-mwide wave flume with a 0.4 m water depth. Experiments were designed to
maintain the same values of the fall speed parameter for values of length
scales ranging between Nl = 2 and Nl = 8.3.
Noda (1978) achieved good matches of equilibrium beach profiles between the different scale models when the fall speed parameter was the
same in the two models. Much poorer correspondence was found when
he compared profiles from models having the same value of the parameter
Ho/d$Q. Noda considered the possibility of geometrically distorted models
based on sediment fall speed, but did not draw any conclusions as to its
validity.
Kamphuis (1982) concluded that preservation of the fall speed parameter in models where significant sediment suspension is occurring eliminates
most of the scale effects associated with attempting to scale the grain size
diameter of quartz sand geometrically.
The scale requirement for maintaining similarity of the fall speed parameter between prototype and model is easily derived by equating prototype
and model values of the parameter, i.e.,
-ÜE- =
(6.106)
WmTm