11.4.1.2 Mussel Longlines: Forces Induced by Collectors
As the distance between wind turbine foundations within an offshore wind farm are
expected to be between 700 and 2500 m, the forces induced by the longline can be
estimated to be very high. Additionally to the investigation on forces impinging on
the foundations by the attached longlines, the forces induced by the hundreds of
fully grown, market-sized Blue mussel collectors was calculated as well. To get
more insight into these forces the drag coefficient of this type of collector had to be
investigated. First tests were conducted in a towing tank of the Hamburg Ship
Model Basin (HSVA, Hamburg) to determine the drag coefficient (C D ) for the
collectors (Fig. 11.21a–i). The length of the tank allowed sufficiently long measuring times (length 80 m, width 3.8 m, and depth 3 m). Mussel collectors, with
mussels and without mussels (naked) were prepared for measurements of drag by
attaching the proximal end of the collector to a string. This string was directed over
a guide reel fixed to the bottom of a beam. A cavity within the beam allowed the
thread to be hooked onto the digital gauge, which was placed on the control panel
of the carriage. The beam was fastened to the base frame of the towing tank’s
carriage. It was lowered 1 m deep into the tank filled with water. Collectors tied to
Fig. 11.21 a–i Towing tank at the HSVA (Hamburg Ship Model Basin). a Main carriage with the
operation desk and the equipment holding the collectors; b carriage under way; c carriage
displaying the Bosch-profile, which holds the experimentals; d single holdings device to which
different collector types (artificial, mussel) in various modes (single, double, V-shape) can be
attached; e operation desk controlling the speed of the carriage; f V-shape artificial collector pair to
be tested; g carriage with V-shape artificial collector pair under way; h V-shape artificial collector
pair during high speed under way; i walkable platform to manage the experimentals. Images
AWI/Prof. Dr. Bela H. Buck and Björn Hendel
292
B.H. Buck et al.
As the distance between wind turbine foundations within an offshore wind farm are
expected to be between 700 and 2500 m, the forces induced by the longline can be
estimated to be very high. Additionally to the investigation on forces impinging on
the foundations by the attached longlines, the forces induced by the hundreds of
fully grown, market-sized Blue mussel collectors was calculated as well. To get
more insight into these forces the drag coefficient of this type of collector had to be
investigated. First tests were conducted in a towing tank of the Hamburg Ship
Model Basin (HSVA, Hamburg) to determine the drag coefficient (C D ) for the
collectors (Fig. 11.21a–i). The length of the tank allowed sufficiently long measuring times (length 80 m, width 3.8 m, and depth 3 m). Mussel collectors, with
mussels and without mussels (naked) were prepared for measurements of drag by
attaching the proximal end of the collector to a string. This string was directed over
a guide reel fixed to the bottom of a beam. A cavity within the beam allowed the
thread to be hooked onto the digital gauge, which was placed on the control panel
of the carriage. The beam was fastened to the base frame of the towing tank’s
carriage. It was lowered 1 m deep into the tank filled with water. Collectors tied to
Fig. 11.21 a–i Towing tank at the HSVA (Hamburg Ship Model Basin). a Main carriage with the
operation desk and the equipment holding the collectors; b carriage under way; c carriage
displaying the Bosch-profile, which holds the experimentals; d single holdings device to which
different collector types (artificial, mussel) in various modes (single, double, V-shape) can be
attached; e operation desk controlling the speed of the carriage; f V-shape artificial collector pair to
be tested; g carriage with V-shape artificial collector pair under way; h V-shape artificial collector
pair during high speed under way; i walkable platform to manage the experimentals. Images
AWI/Prof. Dr. Bela H. Buck and Björn Hendel
292
B.H. Buck et al.