numbers is yet important to investigate how loadings develop under the additional
resistance due to marine fouling. Up-scaled overall forces that have to be absorbed
by the tripile structure are at least for stormy conditions in the mega newton range
and deemed clearly design relevant for the OWEC structure. For the chosen cases,
the connecting joints between the investigated fish cage variations are arranged so
that bending moments are also induced. In upcoming studies it is thus recommended to lower the connecting joints further down to the sea bottom in order to
greatly reduce the effects that aquaculture applications connected to the OWEC
would have.
In literature a number of theoretical approaches exist to deduce the maximum
scour depths at piles (Melville and Coleman 2000; Sumer and Fredsøe 2002) which
nowadays depict an important piece of information for the safety assessment of
OWEC. In case of complex marine constructions involving multi-use of an OWEC
with multiple, complex-shaped constructional members, the analytical approaches
are not easily applicable. Hence an optical method is applied which consists of
sediment gauges and image capturing. A manual post-processing routine is chosen
to estimate the local sea bed evolution. The local water depth of the modeled
OWEC structure and the chosen monochromatic waves limit the scour tendency.
Scour evolution is yet possible under the assumption that swell generated in a far
field arrives at the location of interest. Therefore additional experiments with an
elongated wave period of T = 3.0 s are conducted. In this case scour around the
tripile legs can be observed clearly. Under the assumed boundary condition relative
scour depth of S/D = 0.54 is determined at the front leg of the tripile whereas
relative scour depth of S/D = 0.36 is found below the tower of the OWEC for a
setup without a fish cage. Slightly different results are obtained under the presence
of fish cages mounted to the OWEC. Relative scour depth of S/D = 0.48 (front leg)
and S/D = 0.25 (central below tower of OWEC) are found. This reduction of scour
observed underneath the main tower of the OWEC below the tower can be
explained by a reduction of wave-induced flow velocities and shear stresses in this
area.
3.5 Discussion and Conclusions
In the following, not only are conclusions drawn from the single case studies but it
is highlighted how open ocean aquaculture might benefit from its transition towards
a multi-use concept. Direct benefits such as cost reductions through multiple usage
of anchor constructions as well as indirect ones like shared usage of supply vessels
or personnel indicate that time has come to move aquaculture industry further
offshore. Ongoing initiatives such as the European framework funded projects
MERMAID, H2OCEAN, and TROPOS are a vital indication of the present demand
for research and development in this area.
Open ocean shellfish farming is at a pivotal point at this time. Technology has
reached a point where economically viable commercial production is a real
90
N. Goseberg et al.
resistance due to marine fouling. Up-scaled overall forces that have to be absorbed
by the tripile structure are at least for stormy conditions in the mega newton range
and deemed clearly design relevant for the OWEC structure. For the chosen cases,
the connecting joints between the investigated fish cage variations are arranged so
that bending moments are also induced. In upcoming studies it is thus recommended to lower the connecting joints further down to the sea bottom in order to
greatly reduce the effects that aquaculture applications connected to the OWEC
would have.
In literature a number of theoretical approaches exist to deduce the maximum
scour depths at piles (Melville and Coleman 2000; Sumer and Fredsøe 2002) which
nowadays depict an important piece of information for the safety assessment of
OWEC. In case of complex marine constructions involving multi-use of an OWEC
with multiple, complex-shaped constructional members, the analytical approaches
are not easily applicable. Hence an optical method is applied which consists of
sediment gauges and image capturing. A manual post-processing routine is chosen
to estimate the local sea bed evolution. The local water depth of the modeled
OWEC structure and the chosen monochromatic waves limit the scour tendency.
Scour evolution is yet possible under the assumption that swell generated in a far
field arrives at the location of interest. Therefore additional experiments with an
elongated wave period of T = 3.0 s are conducted. In this case scour around the
tripile legs can be observed clearly. Under the assumed boundary condition relative
scour depth of S/D = 0.54 is determined at the front leg of the tripile whereas
relative scour depth of S/D = 0.36 is found below the tower of the OWEC for a
setup without a fish cage. Slightly different results are obtained under the presence
of fish cages mounted to the OWEC. Relative scour depth of S/D = 0.48 (front leg)
and S/D = 0.25 (central below tower of OWEC) are found. This reduction of scour
observed underneath the main tower of the OWEC below the tower can be
explained by a reduction of wave-induced flow velocities and shear stresses in this
area.
3.5 Discussion and Conclusions
In the following, not only are conclusions drawn from the single case studies but it
is highlighted how open ocean aquaculture might benefit from its transition towards
a multi-use concept. Direct benefits such as cost reductions through multiple usage
of anchor constructions as well as indirect ones like shared usage of supply vessels
or personnel indicate that time has come to move aquaculture industry further
offshore. Ongoing initiatives such as the European framework funded projects
MERMAID, H2OCEAN, and TROPOS are a vital indication of the present demand
for research and development in this area.
Open ocean shellfish farming is at a pivotal point at this time. Technology has
reached a point where economically viable commercial production is a real
90
N. Goseberg et al.