5.1. INTRODUCTION TO STRUCTURE MODELS
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• Impermeable Sloping Structures. A relative of the
rubble-mound structure is the impermeable sloping structure. These are most often encountered as revetments constructed of pre-cast blocks or as breakwaters and jetties
that have an asphalt cover. Wave energy is dissipated on
the slope as waves break, but wave runup is greater than
on a similarly-sloped permeable structure.
• Vertical-Wall Structures. Vertical-wall structures can
be built where foundation materials are strong enough to
support their weight. Vertical-wall structures are used as
breakwaters, seawalls, and bulkheads in harbors. The vertical structure accommodates port activities because ships
can be moored next to the structure to facilitate loading
and unloading activities. Generally, vertical structures are
designed to reflect the incident wave energy with little or
no overtopping. Some vertical structures have baffles or
other means to reduce wave reflection.
• Composite Structures. These structures usually combine a rubble-mound base through part of the water column, topped by a vertical monolithic structure. The rubble base of composite structures strengthens the foundation, and the vertical portion offers the mooring advantages
of vertical structures.
• Floating Structures. Floating breakwaters are the primary floating structures familiar to coastal engineers, and
they are not very common relative to the above structures.
(However, ocean engineers deal extensively with floating
structures such as tension-leg platforms.) Forces transmitted by ships through mooring linés are often concerns for
harbor designers.
• Pneumatic and Hydraulic Breakwaters. This is a
special class of structure that reduces wave heights by either a curtain of rising air bubbles that generates horizontal water currents (pneumatic) or by generating horizontal
currents with water jets forced through a series of nozzles placed near the free surface (hydraulic). Both of these
structures are uncommon, and hence, will not be further
discussed here. The interested reader should see Tekeli
and Maxwell (1980) for a discussion of physical modeling
of bubble screens and Hudson, et al. (1979) for scaling
relations and further information.
171
• Impermeable Sloping Structures. A relative of the
rubble-mound structure is the impermeable sloping structure. These are most often encountered as revetments constructed of pre-cast blocks or as breakwaters and jetties
that have an asphalt cover. Wave energy is dissipated on
the slope as waves break, but wave runup is greater than
on a similarly-sloped permeable structure.
• Vertical-Wall Structures. Vertical-wall structures can
be built where foundation materials are strong enough to
support their weight. Vertical-wall structures are used as
breakwaters, seawalls, and bulkheads in harbors. The vertical structure accommodates port activities because ships
can be moored next to the structure to facilitate loading
and unloading activities. Generally, vertical structures are
designed to reflect the incident wave energy with little or
no overtopping. Some vertical structures have baffles or
other means to reduce wave reflection.
• Composite Structures. These structures usually combine a rubble-mound base through part of the water column, topped by a vertical monolithic structure. The rubble base of composite structures strengthens the foundation, and the vertical portion offers the mooring advantages
of vertical structures.
• Floating Structures. Floating breakwaters are the primary floating structures familiar to coastal engineers, and
they are not very common relative to the above structures.
(However, ocean engineers deal extensively with floating
structures such as tension-leg platforms.) Forces transmitted by ships through mooring linés are often concerns for
harbor designers.
• Pneumatic and Hydraulic Breakwaters. This is a
special class of structure that reduces wave heights by either a curtain of rising air bubbles that generates horizontal water currents (pneumatic) or by generating horizontal
currents with water jets forced through a series of nozzles placed near the free surface (hydraulic). Both of these
structures are uncommon, and hence, will not be further
discussed here. The interested reader should see Tekeli
and Maxwell (1980) for a discussion of physical modeling
of bubble screens and Hudson, et al. (1979) for scaling
relations and further information.