In this paper, three kinds of long-line aquaculture structure layouts including the position of buoys, the length of mooring lines, the layout depth of lantern nets are put forward for offshore long-line aquaculture. Physical model experiment is used to study the hydrodynamic characteristics of these kinds of long-line aquaculture structures to propose a relatively stable structure layout in waves. By analyzing and comparing the stress conditions of the windward mooring lines and the movement of the mainline under different wave conditions to determine which layout will be the safest for the long-line aquaculture structure.
Raft farming comes from Japan and it is widely used in the aquaculture of oysters, scallops and large algae. The long-line aquaculture facility is a form of raft farming, which is generally adopted in the industrial aquaculture of shellfish. Due to the excessively high breeding density and the deficiency of nutrition, which result in the high mortality of shellfish in shallow sea, it is imperative for long-line aquaculture to be developed towards the open sea to expand breeding space. However, the intense sea conditions, such as the high waves and the urgent currents, are great challenges for the safety of the offshore aquaculture facilities. Studying the hydrodynamic characteristics of aquaculture facilities and designing the most stable facility structures are essential to ensure the safety of aquaculture facilities.
The designs have a great influence on the hydrodynamic characteristics of the long-line structures and the growth of the shellfish. Lien and Fred Heim (2001) introduced a new material, PEH tube, used in the development of the mussel systems for cultivation of mussels. Díaz (2006) studied the effect of different longline farming designs, including longline with buoys---continuous sleeves or independent sleeves, longline with IIPPII tubes or HDPE tubes---continuous sleeves, independent sleeves and net, over the growth of Mytilus Chilensis at Llico Bay. Drapeau (2006) discussed the association between the spacing of the longlines and individual socks and mussel productivity in Prince Edward Island, Canada. On the numerical simulation, Jan Aure modelled current speed and carrying capacity in long-line blue mussel farms. Raman-Nair and Colbourne (2003) used Kane's formalism and Morison's equation to model the coupled dynamics of a mussel long-line system approximately. About hydrodynamics of the long-line aquaculture facilities, Craig Stevens (2008) explored the effect of the flow (waves and currents) on the long-line farm and the reverse perspectives of the farm on the flow. Lin (2016) studied the hydrodynamic effect of a mussel suspended aquaculture farm on tidal currents off Gouqi Island, outside the Changjiang Estuary in China, by observational data. Stevens (2007) discussed the mooring loads, within-structure variability, measurement techniques and local oceanography and implications for farm productivity in the context of observations. Gagon (2017) observed the forces and motion of a mussel long line at an open ocean to determine the drag coefficient of the droppers, the shielding effect on the bulk drag force exerted by steady currents on the long line.
