significantly which in turn could lead to more stress on the installation and the
farmed candidates. The cage structure has additionally vertical steel pipes, which
also act as buoyancy device.
Spherical design: The coordination of crossbars and the entire skeleton to design
the spherical structure and its attachment device for the foundation piles simply
depends on the height of the cage. We planned to connect the cage with the piles at
least at six points to absorb axial forces and to avoid the generation of a kinematic
positioning. The connections to the support structure were installed in the upper and
lower third of the sphere (Figs. 11.35b and 11.36f, g). The cage volume of the
sphere is approx. 1,700 m
3 .
As levels in the internal space would create wedge-shaped units in the upper and
the lower third of the sphere, further developments would not include additional
levels. Further, these levels would not explicitly improve the stability of the cage.
The cage design with meridional bar direction (Fig. 11.36g) was rejected due to the
sharp angles on the top and the bottom of the age as well as due to its poor
load-bearing behaviour. Another design of the skeleton of the cage was the use of a
triangular bar interconnectedness of the spheres’ surface (Fig. 11.36f).
Triangular Prism: The height was calculated to be 17.5 m and an edge length of
13 m leading to a volume of about 1,250 m
3 (Fig. 11.35b). This is a comparably
small volume compared to the other cages, however, the advantage of this design is
the reduced tensile loads on the horizontal crossbars through the prevailing bearing
forces as the three edge cage piles spread the forces over the entire cage height.
Another disadvantage of this cage design is the existence of the three edges along
the entire cage height. In worst case scenarios with high waves and strong current
velocities these edges could function as energy focussing zones leading to the fact
that the fish could be pushed against the net, which in turn could lead to stress and
interference of the fish.
Tripile cage designs: This cage design relies on the structure of the tripile as the
foundation piles also function as the outer piles of the cage holding the net. In
comparison to the cylinder cage the height of the tripile cage would be only 15 m as
the distance from the cage bottom to the seafloor will be increased by 2.5–7.5 m to
avoid any scour effects. The volume of the cage would be 3,000 m
3 .
Large-scale cage design: These large cages are designed with a volume of
approx. 20,000 m
3 and could be installed in the vicinity of the tripile and connected
between 3 and 4 foundations (Fig. 11.36h).
11.4.3.2 Impact of the Integrated Cage on the Support Structure
To integrate a cage into the internal space of tripod foundation it is of the utmost
importance to get more insight about the impact of the fish cage on the
tripile-dynamics, such as an oscillatory instability of the foundation piles between
the water surface and the seabed.
To start the laboratory experiments BARD Engineering constructed a model
of the tripile, which was identical to the tripile used at the offshore wind farm
316
B.H. Buck et al.
farmed candidates. The cage structure has additionally vertical steel pipes, which
also act as buoyancy device.
Spherical design: The coordination of crossbars and the entire skeleton to design
the spherical structure and its attachment device for the foundation piles simply
depends on the height of the cage. We planned to connect the cage with the piles at
least at six points to absorb axial forces and to avoid the generation of a kinematic
positioning. The connections to the support structure were installed in the upper and
lower third of the sphere (Figs. 11.35b and 11.36f, g). The cage volume of the
sphere is approx. 1,700 m
3 .
As levels in the internal space would create wedge-shaped units in the upper and
the lower third of the sphere, further developments would not include additional
levels. Further, these levels would not explicitly improve the stability of the cage.
The cage design with meridional bar direction (Fig. 11.36g) was rejected due to the
sharp angles on the top and the bottom of the age as well as due to its poor
load-bearing behaviour. Another design of the skeleton of the cage was the use of a
triangular bar interconnectedness of the spheres’ surface (Fig. 11.36f).
Triangular Prism: The height was calculated to be 17.5 m and an edge length of
13 m leading to a volume of about 1,250 m
3 (Fig. 11.35b). This is a comparably
small volume compared to the other cages, however, the advantage of this design is
the reduced tensile loads on the horizontal crossbars through the prevailing bearing
forces as the three edge cage piles spread the forces over the entire cage height.
Another disadvantage of this cage design is the existence of the three edges along
the entire cage height. In worst case scenarios with high waves and strong current
velocities these edges could function as energy focussing zones leading to the fact
that the fish could be pushed against the net, which in turn could lead to stress and
interference of the fish.
Tripile cage designs: This cage design relies on the structure of the tripile as the
foundation piles also function as the outer piles of the cage holding the net. In
comparison to the cylinder cage the height of the tripile cage would be only 15 m as
the distance from the cage bottom to the seafloor will be increased by 2.5–7.5 m to
avoid any scour effects. The volume of the cage would be 3,000 m
3 .
Large-scale cage design: These large cages are designed with a volume of
approx. 20,000 m
3 and could be installed in the vicinity of the tripile and connected
between 3 and 4 foundations (Fig. 11.36h).
11.4.3.2 Impact of the Integrated Cage on the Support Structure
To integrate a cage into the internal space of tripod foundation it is of the utmost
importance to get more insight about the impact of the fish cage on the
tripile-dynamics, such as an oscillatory instability of the foundation piles between
the water surface and the seabed.
To start the laboratory experiments BARD Engineering constructed a model
of the tripile, which was identical to the tripile used at the offshore wind farm
316
B.H. Buck et al.