Aquaculture Europe 2021

October 4 - 7, 2021

Funchal, Madeira

Add To Calendar 07/10/2021 10:20:0007/10/2021 10:40:00Europe/LisbonAquaculture Europe 2021OYSTER LONGLINE DESIGN OPTIMIZATION: AQUACULTURE PILOT STUDY IN THE BELGIAN PART OF THE NORTH SEABerlim-HotelThe European Aquaculture Societywebmaster@aquaeas.orgfalseDD/MM/YYYYaaVZHLXMfzTRLzDrHmAi181982

OYSTER LONGLINE DESIGN OPTIMIZATION: AQUACULTURE PILOT STUDY IN THE BELGIAN PART OF THE NORTH SEA

 A.  B. K. Pribadi1*, G. Verao Fernandez1 , A.M. Declercq2 ,  B. Stechele2 , N. Nevejan2 ,
B. Groenendaal3 , S. Debels3 , D. Delbare4, D. Vandercammen5, S. Petit6 , T. Kerkhove7 ,
J. Vanaverbeke7 , S. Degraer7 , E. Lataire1

 

1Maritime Technology Division, Ghent University, Ghent (Belgium).

2 Laboratory of Aquaculture and Artemia Reference Center, Ghent University, Ghent (Belgium). 3Brevisco, Hendrik Baelskaai 38, 8400 Oostende (Belgium).
4 Research Institute for Agriculture, Fisheries and Food, Ankerstraat 1, 8400 Oostende (Belgium).  5 Parkwind, Sint Maartenstraat 5, 8400 Oostende  (Belgium).
6Jan De Nul NV, Tragel 60, 9308 Hofstade-Aalst (Belgium).
7 Marine Ecology and Management, Operational Directory Natural Environment, Royal Belgian Institute of Natural Sciences, Vautierstraat 29, 1000 Brussel (Belgium)

 E-mail: ajiebramakrishna.pribadi@UGent.be

 



Introduction

As part of the European Horizon 2020 project  UNITED (UNITED, 2021) , an offshore longline  system (Morse and Rice, 2010 ) will be installed to assess the feasibility of cultivating European flat oysters (Ostrea edulis) in the Belgian part of the North Sea 25 n autical miles off shore . Five different culture systems  are studied :  SEAPA  baskets stacked on a ladder frame ; oysters glued on dropper lines ;  frames consisting  of horizontal and vertical grow-out sticks ; frames as spat collectors ; trays on dropper lines. To accommodate these culture systems, a mooring configuration suitable for the harsh offshore environment  is  designed. The main cultivation line is 57 m long, making up the total length of 263 m  of  mooring and backbone ropes  from South-West  screw anchor to the North-East  screw anchor. The distance between both anchors is 250  m. The water depth at the test location is  at  -30.1 m Mean Lower Low Water Spring.

Materials and methods

A set of boundary conditions are defined based on the operational limitations, space available and guidelines’ recommendations. Fig.1 shows the flowchart of the mooring design iterative process. T he longline  system  will be installed  with anchors  within  a zone of four wind turbines. Taking this into account , during  the operational conditions, the area taken by the mooring system has to be less than 0.12 km2. This governs the longline design characteristics as initial input. Then , a hydro static calculation is performed to ensure that the cultivation line can be lifted 5 m above still water level  and the lifting capacity of the vessel is adequate to perform maintenance/installation operations . Lastly , dynamic simulations  incorporating waves and current induced load  are performed for various scenarios to  determine the material properties of the mooring components.  Numerical simulations are performed utilising an in-house mooring dynamic solver based on  the lumped-mass approach to discretize the lines (Hall and Goupee, 2015; Pribadi et.al, 2019)  and the Morison Equation  (Morison, 1950) to model the hydrodynamic forces. The Morison coefficients are taken from the  guidelines set in  the DNV GL OS301 (DNVGL, 2018 ). The sea states used for the U ltimate L imit States (ULS)  calculation  and safety factors for the line elements  are taken from the recommendations provided in the NS9415  document (Norwegian Standard, 2010 ).

Results

The ULS simulation that is taking the 50-year return period of waves () and current (  parallel to the longline, is giving the maximum predicted tension of 125 kN on the mooring lines.  The state of the mooring system during  the  ULS simulation at  = 63.8 s is shown in Fig. 2. A maximum load of 71 kN is calculated for the 1-year return period of waves () and current parallel ( to the system. The load time-series of the two sea states are shown in Fig. 3.

Discussion and conclusion

 An iterative design process has been performed to define the technical requirements needed to install a  mooring system for the cultivation of flat oyster in  an  offshore wind farm . The mooring system is designed with a “set and forget” principle, meaning that the system will start with an excess buoyancy on day-1 of installation. By the winter season  when  the worst storm occurs, the backbone would be fully submerged up to 10 m  of depth,  due to the increase of biomass (oysters and biofouling), making it less exposed to the wave actions. Then, a fter one year of installation, a maintenance operation  will be needed to adjust  the  buoyancy.

References

UNITED: Multi-Use offshore platforms demoNstrators for boostIng cost-effecTive and Eco-friendly proDuction in sustainable marine activities. Retrieved April 1, 2021, from https://www.h2020united.eu/

 Morse, D. and Rice, M. A., 2010. Mussel aquaculture in the Northeast. NRAC Publication, 211.

 Hall, M. and Goupee, A., 2015. Validation of a lumped-mass mooring line model with DeepCwind semisubmersible model test data. Ocean Engineering, 104: 590-603. DOI: 10.1016/j.oceaneng.2015.05.035.

Pribadi, A.B.K., Donatini, L., Lataire, E., 2019. Numerical modelling of a mussel line system by means of lumped-mass approach. Journal of Marine Science and Engineering, vol. 9. DOI: 10.3390/jmse7090309.

 Morison, J.R., O’Brien, M. P., Johnson, J. W., and Schaaf,  S. A., 1950. The force exerted by surface waves on piles. J. Pet. Technol., vol. 2.

Det Norske Veritas Germanischer Lloyd (DNV-GL), 2018. OS-301 Position mooring.

Norwegian Standard, 2010. NS 9415.E:2009 Marine fish farms requirements for site survey, risk analyses, design, dimensioning, production, installation and operation.

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