188
CHAPTER 5. COASTAL STRUCTURE MODEL
sponds to monochromatic wave height (//) when determining minimun
armor unit Reynolds numbers.
Reflection and Transmission Scale Effects in Rubble-Mounds
Wave reflection and transmission are important in laboratory studies c
coastal rubble-mound structures. Correct simulation of wave transmissio
is an important requirement of semi-permeable structures such as break
waters and jetties, and properly modeled wave reflection is important fc
all structures. Structures such as rubble revetments dissipate wave energ
within the structure’s voids, and correct model simulation of wave runu
on these structures requires that wave transmission and wave reflection i
the model be in close similitude with the prototype equivalent.
Geometrically scaled physical models of porous, rubble-mound strut
tures, in which the model armor unit Reynolds number is too low, general]
have relatively more wave energy reflected from the model structure an
relatively less wave energy transmitted through the model structure tha
in their prototype-scale equivalent (Wilson and Cross 1972). This is cause
by having laminar flows in interior portions of the model structure th<
should be fully turbulent in order to conform with the prototype situatioi
The methods of Le Méhauté (1965) and Keulegan (1973), given in fl
Short-Wave Model Laboratory and Scale Effects section of Chapter 4, ai
used to determine a material diameter for the underlayers and core i
rubble-mound structure models so that wave transmission is in proper simi
itude. As mentioned, the best procedure is to test at larger scale to confin
the empirical distortion of the structure core material size.
Likewise, wave reflection in a model can be reduced to be in accordai
with prototype values by using wire screens to create turbulent flow throuj
outer layers of the structure armor. This procedure was also discussed
the Short-Wave Model Laboratory and Scale Effects section of Chapter
in conjunction with short-wave hydrodynamic models. Many models a
conducted at large enough scales that little correction is required to fl
geometrically scaled rubble-mound cross-section.
Water Density Effect in Rubble-Mound Structures
Most rubble-mound structure models are conducted using fresh water rath
than salt water to avoid salt-water corrosion of expensive wave generate
or other metal parts of the model facility. If the prototype happens to
in salt water (which is most often the case), a correction to the model <
mor units must be made using the scaling relationship given by Eqn. 5.
(see Example 5.1). Failure to make this compensation could result in no
negligible errors that could be as much as 10 - 15% (Le Méhauté 1976).
CHAPTER 5. COASTAL STRUCTURE MODEL
sponds to monochromatic wave height (//) when determining minimun
armor unit Reynolds numbers.
Reflection and Transmission Scale Effects in Rubble-Mounds
Wave reflection and transmission are important in laboratory studies c
coastal rubble-mound structures. Correct simulation of wave transmissio
is an important requirement of semi-permeable structures such as break
waters and jetties, and properly modeled wave reflection is important fc
all structures. Structures such as rubble revetments dissipate wave energ
within the structure’s voids, and correct model simulation of wave runu
on these structures requires that wave transmission and wave reflection i
the model be in close similitude with the prototype equivalent.
Geometrically scaled physical models of porous, rubble-mound strut
tures, in which the model armor unit Reynolds number is too low, general]
have relatively more wave energy reflected from the model structure an
relatively less wave energy transmitted through the model structure tha
in their prototype-scale equivalent (Wilson and Cross 1972). This is cause
by having laminar flows in interior portions of the model structure th<
should be fully turbulent in order to conform with the prototype situatioi
The methods of Le Méhauté (1965) and Keulegan (1973), given in fl
Short-Wave Model Laboratory and Scale Effects section of Chapter 4, ai
used to determine a material diameter for the underlayers and core i
rubble-mound structure models so that wave transmission is in proper simi
itude. As mentioned, the best procedure is to test at larger scale to confin
the empirical distortion of the structure core material size.
Likewise, wave reflection in a model can be reduced to be in accordai
with prototype values by using wire screens to create turbulent flow throuj
outer layers of the structure armor. This procedure was also discussed
the Short-Wave Model Laboratory and Scale Effects section of Chapter
in conjunction with short-wave hydrodynamic models. Many models a
conducted at large enough scales that little correction is required to fl
geometrically scaled rubble-mound cross-section.
Water Density Effect in Rubble-Mound Structures
Most rubble-mound structure models are conducted using fresh water rath
than salt water to avoid salt-water corrosion of expensive wave generate
or other metal parts of the model facility. If the prototype happens to
in salt water (which is most often the case), a correction to the model <
mor units must be made using the scaling relationship given by Eqn. 5.
(see Example 5.1). Failure to make this compensation could result in no
negligible errors that could be as much as 10 - 15% (Le Méhauté 1976).