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CHAPTER 5. COASTAL STRUCTURE MODELS
5.4 Vertical-Wall Structures
Vertical-wall structures discussed in this section can be either impervious,
and thus nearly perfect reflectors of normally-incident waves, or caissontype structures that allow a portion of the flow to penetrate the structure.
The vertical face usually extends to the sea floor except in the case of a
composite structure where the vertical portion rests upon a rubble-mound
base.
5.4.1 Vertical-Wall Structure Scaling
One of the main reasons for testing a vertical-wall structure in a physical
model is to determine the pressure forces developed on the structure under
hydrodynamic wave loading. There are a few instances, such as normallyincident, nonbreaking waves on a flat bottom, when analytical calculations
will provide sufficient design values. Likewise, recent numerical modeling
advances have expanded our capability for estimating forces on vertical
structures. However, when alternate techniques are lacking and there is a
need to confirm design loading assumptions, physical models offer a viable
alternative.
Nonbreaking Waves
Under nonbreaking wave conditions, vertical walls and caissons are modeled
according to Froude scaling. Generally, scale effects are small for the case of
nonbreaking waves, but care must be taken in modeling permeable caissontype structures to assure that flow Reynolds numbers in the interior of the
model structure are in the fully-turbulent flow range (assuming the flow in
the prototype is also turbulent).
Measured forces and pressures in Froude-scaled models will be in similitude with prototype equivalents provided the model does not experience
any impact or impulsive loading from waves breaking directly on the structure.
Breaking Waves
Vertical-wall structures are often located at a shoreline position where it
is possible for waves to break directly on the structure in some situations.
This results in short-duration, high-intensity shock pressures on the wall
that need to be considered by the design engineer. The complexity of this
process is beyond present analytical methods, and a physical model must
be employed. Also, wave breaking conditions can lead to overtopping of
the vertical wall, which can be quantified with a physical model.
CHAPTER 5. COASTAL STRUCTURE MODELS
5.4 Vertical-Wall Structures
Vertical-wall structures discussed in this section can be either impervious,
and thus nearly perfect reflectors of normally-incident waves, or caissontype structures that allow a portion of the flow to penetrate the structure.
The vertical face usually extends to the sea floor except in the case of a
composite structure where the vertical portion rests upon a rubble-mound
base.
5.4.1 Vertical-Wall Structure Scaling
One of the main reasons for testing a vertical-wall structure in a physical
model is to determine the pressure forces developed on the structure under
hydrodynamic wave loading. There are a few instances, such as normallyincident, nonbreaking waves on a flat bottom, when analytical calculations
will provide sufficient design values. Likewise, recent numerical modeling
advances have expanded our capability for estimating forces on vertical
structures. However, when alternate techniques are lacking and there is a
need to confirm design loading assumptions, physical models offer a viable
alternative.
Nonbreaking Waves
Under nonbreaking wave conditions, vertical walls and caissons are modeled
according to Froude scaling. Generally, scale effects are small for the case of
nonbreaking waves, but care must be taken in modeling permeable caissontype structures to assure that flow Reynolds numbers in the interior of the
model structure are in the fully-turbulent flow range (assuming the flow in
the prototype is also turbulent).
Measured forces and pressures in Froude-scaled models will be in similitude with prototype equivalents provided the model does not experience
any impact or impulsive loading from waves breaking directly on the structure.
Breaking Waves
Vertical-wall structures are often located at a shoreline position where it
is possible for waves to break directly on the structure in some situations.
This results in short-duration, high-intensity shock pressures on the wall
that need to be considered by the design engineer. The complexity of this
process is beyond present analytical methods, and a physical model must
be employed. Also, wave breaking conditions can lead to overtopping of
the vertical wall, which can be quantified with a physical model.