Numerical Study on the Heading Misalignment and Current Velocity Reduction of a Vessel-Shaped Offshore Fish Farm

Recently, the concept of a vessel-shaped fish farm was proposed for open sea applications. The fish farm comprises a vessel-shaped floater, five fish cages, and a single-point mooring system. Such a system weathervanes, and this feature increases the spread area of fish waste. Still, the downstream cages may experience decreased exchange of water flow when the vessel heading is aligned with the current direction, and fish welfare may be jeopardized. To ameliorate the flow conditions, a dynamic positioning (DP) system may be required, and its power consumption should relate to the heading misalignment. This paper proposes an integrated method for predicting the heading misalignment between the vessel-shaped fish farm and the currents under combined waves and currents. A numerical model is first established for the fish farm system with flexible nets. Current reduction factors are included to address the reduction in flow velocity between net panels. The vessel heading is obtained by finding the equilibrium condition of the whole system under each combined wave and current condition. Then, the Kriging metamodel is applied to capture the relation between the misalignment angle and environmental variables, and the probability distribution of this misalignment angle is estimated for a reference site. Finally, the requirement for the DP system to improve the flow condition in the fish cages is discussed.

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Predicting the Heading Misalignment of a Vessel-Shaped Offshore Fish Farm Under Waves and Currents

Volume 6: Ocean Space Utilization ◽

10.1115/omae2018-77476 ◽

2018 ◽

Cited By ~ 1

Author(s):

Lin Li ◽

Zhiyu Jiang ◽

Jungao Wang ◽

Muk Chen Ong

Keyword(s):

Reference Site ◽

Single Point ◽

Fish Farm ◽

Misalignment Angle ◽

Integrated Method ◽

Open Sea ◽

Waves And Currents ◽

Spread Area ◽

Fish Cages ◽

Current Reduction

A vessel-shaped fish farm concept for open sea applications has been proposed recently. The whole system consists of a vessel-shaped floater, fish cages positioned longitudinally along the floater, and a single-point mooring system. The whole system weathervanes; this feature increases the spread area for the fish waste. However, the downstream cages may experience reduced water exchange when the vessel is parallel to the currents. This situation may jeopardize the fish health. A dynamic positioning (DP) system may be necessary to improve the flow conditions. This paper investigates the misalignment angle between the heading of the vessel-shaped fish farm and the currents under combined wave and current conditions. The misalignment angle is critical for the estimation of the DP system consumption. A numerical model of the fish farm system with flexible nets is developed. Current reduction factors are included to account for the flow velocity reductions between the net panels. The heading of the system is obtained by finding the equilibrium condition of the whole system under each combined wave and current condition. An integrated method using metamodels is proposed and applied for the prediction of the misalignment angle for a reference site. The probability distribution of the misalignment angle between the vessel heading and the currents is calculated using the Kriging metamodel for the reference site. Based on the prediction, the requirement for the DP system to improve the flow condition in the fish cages is discussed.

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Numerical Analysis of a Floating Fish Cage With Feeding Systems

Volume 5: Ocean Space Utilization ◽

10.1115/omae2020-18112 ◽

2020 ◽

Author(s):

Lin Li ◽

Mathias Bruset ◽

Muk Chen Ong ◽

Xiaopeng Wu

Keyword(s):

Environmental Conditions ◽

Numerical Study ◽

Coupled System ◽

Feeding Tube ◽

Fish Farm ◽

Dynamic Responses ◽

Feeding System ◽

Solidity Ratio ◽

Sensitivity Studies ◽

Fish Cages

Abstract A modern marine-based fish farm normally consists of a feeding barge, several fish cages, and feeding tubes. Although many studies, both experimental and numerical, are available in the literature to investigate the global responses of the fish cages under wave and current conditions, research on the coupled system including both the fish cage and the feeding system is very limited. This paper presents a numerical study on the coupled system with a floating fish cage and the feeding system. The purpose is to study the dynamic responses of the coupled system under different environmental conditions and configurations of the fish farm. A numerical model is firstly established in the numerical program OrcaFlex, comprising of a feeding barge, a gravity-based floating fish cage with mooring systems, and a feeding tube between the barge and the cage. Time-domain simulations of this coupled system are then performed under environmental conditions corresponding to 1-year and 50-year return periods for a reference site. The deformation of the fish cage, the tensions in the anchor lines and in the feeding tube are compared under various conditions. Sensitivity studies on the solidity ratio of the fish net as well as the lengths of the feeding tube are addressed, and their influences on the responses of the coupled system are also discussed.

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Numerical Analysis of a Vessel-Shaped Offshore Fish Farm

Journal of Offshore Mechanics and Arctic Engineering ◽

10.1115/1.4039131 ◽

2018 ◽

Vol 140 (4) ◽

Cited By ~ 8

Author(s):

Lin Li ◽

Zhiyu Jiang ◽

Andreas Vangdal Høiland ◽

Muk Chen Ong

Keyword(s):

Wind Waves ◽

Single Point ◽

Fish Farm ◽

Mooring Line ◽

Mooring System ◽

Wave Loads ◽

Fish Farms ◽

Mooring Lines ◽

Environmental Loads ◽

Fish Cages

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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A Preliminary Study of a Vessel-Shaped Offshore Fish Farm Concept

Volume 6: Ocean Space Utilization ◽

10.1115/omae2017-61665 ◽

2017 ◽

Cited By ~ 2

Author(s):

Lin Li ◽

Zhiyu Jiang ◽

Muk Chen Ong

Keyword(s):

Wind Waves ◽

Single Point ◽

Open Water ◽

Fish Farm ◽

Mooring Line ◽

Mooring System ◽

Wave Loads ◽

Fish Farms ◽

Environmental Loads ◽

Fish Cages

The aquaculture industry is aiming to move fish farms from near-shore area 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 current. 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 frequency domain analysis. A preliminary mooring system was designed to avoid possible interactions with the fish cages. Time domain 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 in various waves and current conditions. The effects due to misalignment of waves and current directions on the responses were also studied.

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Optical Performance of Single Point-Focus Fresnel Lens Concentrator System for Multiple Multi-Junction Solar Cells—A Numerical Study

Energies ◽

10.3390/en14144301 ◽

2021 ◽

Vol 14 (14) ◽

pp. 4301

Author(s):

Yassir A. Alamri ◽

Saad Mahmoud ◽

Raya Al-Dadah ◽

Shivangi Sharma ◽

J. N. Roy ◽

...

Keyword(s):

Solar Cells ◽

Numerical Study ◽

Single Point ◽

Optical Element ◽

Fresnel Lens ◽

Electrical Performance ◽

High Concentration ◽

Three Dimensional Model ◽

Optical Efficiency ◽

Concave Lens

This paper investigates the potential of a new integrated solar concentrated photovoltaic (CPV) system that uses a solo point focus Fresnel lens for multiple multi-junction solar cells (MJSCs). The proposed system comprises of an FL concentrator as the primary optical element, a multi-leg homogeniser as the secondary optical element (SOE), a plano-concave lens, and four MJSCs. A three-dimensional model of this system was developed using the ray tracing method to predict the influence of aperture width, height, and position with respect to MJSCs of different reflective and refractive SOE on the overall optical efficiency of the system and the irradiance uniformity achieved on the MJSCs’ surfaces. The results show that the refractive homogeniser using N-BK7 glass can achieve higher optical efficiency (79%) compared to the reflective homogeniser (57.5%). In addition, the peak to average ratio of illumination at MJSCs for the reflective homogeniser ranges from 1.07 to 1.14, while for the refractive homogeniser, it ranges from 1.06 to 1.34, causing minimum effects on the electrical performance of the MJSCs. The novelty of this paper is the development of a high concentration CPV system that integrates multiple MJSCs with a uniform distribution of rays, unlike the conventional CPV systems that utilise a single concentrator onto a single MJSC. The optical efficiency of the CPV system was also examined using both the types of homogeniser (reflective and refractive).

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Numerical Study of a Single-Point Mooring Gravity Fish Cage With Different Deformation-Suppression Methods

Journal of Offshore Mechanics and Arctic Engineering ◽

10.1115/1.4046115 ◽

2020 ◽

Vol 142 (4) ◽

Author(s):

Hui Cheng ◽

Karl Gunnar Aarsæther ◽

Lin Li ◽

Muk Chen Ong

Keyword(s):

Current Velocity ◽

Numerical Study ◽

Single Point ◽

Local Environment ◽

Full Scale ◽

Tension Force ◽

Wave Loads ◽

Practical Advice ◽

Rigid Frame ◽

Positive Effect

Abstract Compared with the multipoint mooring fish cage, the single-point mooring (SPM) fish cage can spread out the fish wastes and uneaten feeds in a larger area, and it can also prevent the local environment from being overwhelmed. Thus, it has attracted much attention recently. In this research, different deformation-suppression methods are applied to the SPM system with a typical Norwegian fish cage aiming to increase the cultivation volume under the action of current and/or wave loads. A well-validated software, fhsim, is used to conduct the full-scale numerical study. The effects of the three deformation-suppression methods, i.e., (i) adding the lower bridles, (ii) adding the frontal rigid frame and (iii) adding the trawl doors, are analyzed under pure current and combined wave–current conditions. The results indicate that all the three deformation-suppression methods can improve the cultivation volume at least by 32% compared to the original SPM fish cage when the current velocity is larger than 0.5 m/s. In addition, moving the conjunction point close to the bottom ring can bring a positive effect on the cultivation volume maintaining with an only small increment in the tension force. This study can provide practical advice and useful guides for the SPM fish cage design.

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Drag on Nets Fouled With Blue Mussel (Mytilus Edulis) and Sugar Kelp (Saccharina Latissima) and Parameterization of Fouling

Volume 6: Ocean Space Utilization ◽

10.1115/omae2017-62030 ◽

2017 ◽

Author(s):

Lars C. Gansel ◽

Per Christian Endresen ◽

Kristine Braaten Steinhovden ◽

Stine Wiborg Dahle ◽

Eirik Svendsen ◽

...

Keyword(s):

Mytilus Edulis ◽

Structural Integrity ◽

Blue Mussel ◽

Numerical Models ◽

Flow Speed ◽

Saccharina Latissima ◽

Detailed Knowledge ◽

Fish Welfare ◽

Fish Cages ◽

The Relationship

Biofouling is a serious problem in marine finfish aquaculture with a number of negative impacts. Marine growth obstructs net openings, thereby reducing water exchange through the net and affecting fish welfare and health, as well as the spreading of dissolved nutrients, particles and pathogens. Furthermore, additional water blockage leads to increased hydrodynamic forces on fish cages, which potentially threaten the structural integrity of the fish farm. However, detailed knowledge about the effects of biofouling on the flow past, and the resulting forces on fish cages, is limited and systematic investigations of the effects of different types of fouling have been called for. This study investigates the effects of different amounts and sizes of two important fouling organisms in Norwegian aquaculture, blue mussel (Mytilus edulis) and kelp (Saccharina latissima) on the drag on net panels. Drag forces on a number of clean and fouled nets were measured in a flume tank at a flow speed of 0.1 m/s. Net solidity was calculated from images acquired of all nets in the current. The relationship between net solidity and drag was then found for clean nets and for each type of fouling, and biofouling was parameterized by comparing clean and fouled net results: for a given fouled net, a clean net can be found that experiences the same drag. The latter can then be used in numerical models to estimate the effect of fouling on net drag. That means existing models can be used to model the drag effect of fouling. This study found a solidity increase due to mussel and kelp fouling to affect drag roughly at the same rate as an increase in clean net solidity at a flow speed of 0.1 ms−1 and within the tested fouling size range for two net types. Therefore, existing models, describing the relationship between net solidity and drag, can be used directly or with minor alterations (especially at high solidities) to estimate effects of additional mussel and kelp fouling on drag. In contrast, wet weight seems to be unsuitable as a measure to estimate drag on nets fouled with seaweed or mussels. It should be noted that these findings are only valid under similar conditions, and that other fouling types and sizes, as well as test parameters and tank size can affect the relationship between solidity and drag.

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