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Research Papers: Ocean Space Utilization

Numerical Analysis of a Vessel-Shaped Offshore Fish Farm

[+] Author and Article Information
Lin Li, Andreas Vangdal Høiland, Muk Chen Ong

Department of Mechanical and
Structural Engineering and Materials Science,
University of Stavanger,
Stavanger 4036, Norway

Zhiyu Jiang

Centre for Research-based Innovation of Marine
Operations (SFI MOVE),
Department of Marine Technology,
Norwegian University of Science
and Technology (NTNU),
Trondheim 7491, Norway
e-mail:  zhiyu.jiang1896@gmail.com

1Corresponding author.

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received August 4, 2017; final manuscript received December 12, 2017; published online February 23, 2018. Assoc. Editor: Theodoro Antoun Netto.

J. Offshore Mech. Arct. Eng 140(4), 041201 (Feb 23, 2018) (11 pages) Paper No: OMAE-17-1137; doi: 10.1115/1.4039131 History: Received August 04, 2017; Revised December 12, 2017

The aquaculture industry is aiming to move fish farms from nearshore areas to open seas because of many attractive advantages in the open water. However, one major challenge is to design the structure to withstand the environmental loads due to wind, waves, and currents. The purpose of this paper is to study a vessel-shaped fish farm concept for open sea applications. The structure includes a vessel-shaped hull, a mooring system, and fish cages. The shape of the hull minimizes the wave loads coming from the bow, and the single-point mooring system is connected to the turret at the vessel bow. Such a system allows the whole fish farm to rotate freely about the turret, reduces the environmental loads on the structure and increases the spread area of fish wastes. A basic geometry of the vessel hull was considered and the hydrodynamic properties were obtained from the frequency-domain (FD) analysis. A mooring system with six mooring lines was designed to avoid possible interactions with the fish cages. Time-domain (TD) simulations were performed by coupling the hull with the mooring system. A simplified rigid model of the fish cages was considered. The global responses of the system and the mooring line loads were compared under various wave and current conditions. The effects due to misalignment of wave and current directions on the responses were discussed. Finally, the responses using flexible and rigid net models were compared under steady current conditions.

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Figures

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Fig. 2

Main geometry of the submerged part of the vessel-shaped fish farm

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Fig. 1

Overview of the vessel-shaped fish farm concept [15]

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Fig. 5

Comparison of the added masses using different models

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Fig. 6

Comparison of the potential damping from model 1 and the linearized drag damping from models 2 to 4

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Fig. 3

Definition of the angle of attack of a net panel under a steady current

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Fig. 4

Illustration of models 2 and 4 for hydrodynamic analysis in WADAM: (a) M2 panel model with Morison elements on the hull and (b) M4 panel model with Morison elements on the hull and the simplified nets

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Fig. 7

Comparison of RAOs in heave, roll, and pitch from models 1 to 4 (wave direction = 135 deg)

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Fig. 14

Comparison of maximum tension MPM among six mooring lines (models 2 to 4, ECs 1 to 7)

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Fig. 12

Standard deviations of WF and LF components for horizontal motions using three models (for each EC, from left to right the bars correspond to M2, M3, and M4)

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Fig. 13

Comparison of mean, WF and LF components from vertical motions using three models (for each EC, from left to right the three bars corresponds to M2, M3, and M4)

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Fig. 8

Illustration of the coupled model (model 4) in simo-riflex for TD analysis with global coordinate system and mooring line numbers

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Fig. 9

Selected response time histories under EC4 using models 2 and 4

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Fig. 10

Comparison of mean drift motions of the global origin (turret center) under all ECs using three models

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Fig. 11

Mean angle difference between the vessel heading and the directions of waves and currents under all ECs

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Fig. 15

Comparison of the tension MPMs under different ECs (numerical model 4)

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Fig. 16

Comparison of mean, WF and LF components for tensions in mooring line 1 using three models (for each EC, from left to right the three bars corresponds to M2, M3, and M4)

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Fig. 17

The flexible fish net model using representative bar elements

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Fig. 18

Illustration of the deformation of flexible nets in steady currents (Sn = 0.2, each bottom weight is 4 tonnes): (a) Uc = 0.2 m/s, (b) Uc = 0.5 m/s, and (c) Uc = 0.8 m/s

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Fig. 19

Mooring line tension and drift motion of the turret center using rigid and flexible net models (for flexible models, Sn = 0.2, and each bottom weight is 4 tonnes)

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