4.2. SHORT-WAVE HYDRODYNAMIC MODELS
101
Wave Transmission. If rubble-mound structures and wave absorbers
are modeled with the stone sizes and core material geometrically reduced
from prototype scale, there will be relatively less wave transmission through
the model structures. Frictional losses are greater in the model as the wave
travels through the structure, and this comes particularly pronounced at
the scales used for harbor models (Hudson, et al. 1979). This scale effect
is countered by increasing the size of the model stones over that dictated
by geometric scaling6 so that
6 Increasing stone size means that the model will not correctly simulate stone stability
under wave attack.
y2- =
or
Nl = KNd
(4.34)
where L is the geometrically undistorted model characteristic length, D is
the stone size linear dimension, K is a factor greater than unity, and p and
m represent prototype and model, respectively.
Le Méhauté (1965) and Keulegan (1973) have proposed methods for
sizing model rubble-mound structure protective armor layers and core material to give correct wave transmission. Hudson, et. al (1979) recommend
that the scale factor, K, be calculated by both methods, and an average be
used in Eqn. 4.34.
Le Méhauté (1965) used analytical considerations and available data
to develop a nomogram method for selection of an appropriate value for
K in Eqn. 4.34. He assumed that scale effects are negligible in the outer
armor layers, and that the prototype and model have the same gradation
in core material sizes. His method, therefore, corrects for scale effects arising from flow through the core of the structure. Le Méhauté’s nomogram
(reproduced from Hudson, et.al 1979) is given in Figure 4.4
The solid lines in Figure 4.4 are lines of constant values of the factor,
K. The ordinate is the geometric length scale, Nl = Lp/Lm, and the
abscissa is a dimensional factor that combines several parameters of the
rubble-mound structure. This factor is
jj 3p 5
AL p p
(4.35)
where
101
Wave Transmission. If rubble-mound structures and wave absorbers
are modeled with the stone sizes and core material geometrically reduced
from prototype scale, there will be relatively less wave transmission through
the model structures. Frictional losses are greater in the model as the wave
travels through the structure, and this comes particularly pronounced at
the scales used for harbor models (Hudson, et al. 1979). This scale effect
is countered by increasing the size of the model stones over that dictated
by geometric scaling6 so that
6 Increasing stone size means that the model will not correctly simulate stone stability
under wave attack.
y2- =
or
Nl = KNd
(4.34)
where L is the geometrically undistorted model characteristic length, D is
the stone size linear dimension, K is a factor greater than unity, and p and
m represent prototype and model, respectively.
Le Méhauté (1965) and Keulegan (1973) have proposed methods for
sizing model rubble-mound structure protective armor layers and core material to give correct wave transmission. Hudson, et. al (1979) recommend
that the scale factor, K, be calculated by both methods, and an average be
used in Eqn. 4.34.
Le Méhauté (1965) used analytical considerations and available data
to develop a nomogram method for selection of an appropriate value for
K in Eqn. 4.34. He assumed that scale effects are negligible in the outer
armor layers, and that the prototype and model have the same gradation
in core material sizes. His method, therefore, corrects for scale effects arising from flow through the core of the structure. Le Méhauté’s nomogram
(reproduced from Hudson, et.al 1979) is given in Figure 4.4
The solid lines in Figure 4.4 are lines of constant values of the factor,
K. The ordinate is the geometric length scale, Nl = Lp/Lm, and the
abscissa is a dimensional factor that combines several parameters of the
rubble-mound structure. This factor is
jj 3p 5
AL p p
(4.35)
where