Forces on a cruciform/sphere structure in uniform current

Lader, Pål; Enerhaug, Birger; Fredheim, Arne; Klebert, Pascal; Pettersen, Bjørnar

doi:10.1016/j.oceaneng.2014.03.007

Cited by 34 publications

(18 citation statements)

References 5 publications

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“…However, a net structure consists of both twine sections and knots. It has been shown that these knots give a larger contributions to the overall force on the net, than what could be assumed if the net is considered to be made up of individual twines only (Fredheim, 2005;Lader et al, 2014). Therefore, it is important to also study the added effect of the knots, and how the hydroids affect this added effect, and for this reason, cruciform configurations of the twine models were also studied.…”

Section: Methodsmentioning

confidence: 99%

Drag on hydroid-fouled nets — An experimental approach

et al. 2015

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The present study investigated the drag increase on aquaculture nets due to biofouling of the colonial hydroid Ectopleura larynx. It had two main parts: firstly the growth characteristics of E. larynx were investigated by use of field tests at a Norwegian aquaculture site; secondly the hydrodynamic drag on the fouled twines was studied in a towing tank by using fabricated models of net twines with artificial hydroid fouling. In the field tests, the growth of the hydroids was first measured after three weeks of immersion and then again after six weeks. During this interval, the density of hydroids and the thickness of the hydroid stem were almost constant (1.4 hydroids/mm and 0.29 mm, respectively), while the average length of the hydroids increased from 6.4 to 11.2 mm. The hydroid length followed a Rayleigh distribution, while the thickness was normal (Gaussian) distributed. Replicas of twines with three different levels of hydroid growth were made (1.5 hydroids/mm twine, hydroid length 9 mm, 16 mm and 20 mm), and the drag on these twines was measured at different towing velocities (0.1 to 1.4 m/s) and with different twine configurations. For the twine with the shortest hydroids (9 mm), the drag was from 1.5 times (Re=4000) to 2.2 times (Re=1000) the drag on a clean twine. For the longest hydroids (21 mm), the drag was 2 times and 3.8 times, respectively.

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Section: Methodsmentioning

confidence: 99%

Drag on hydroid-fouled nets — An experimental approach

et al. 2015

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“…To test the performance of the flow around a 3D structure, a cruciform case (Fig. 3a), which has been investigated in [19] numerically and in [12] experimentally, is used to validate the accuracy of REEF3D. The results are shown in Fig.…”

Section: Figurementioning

confidence: 99%

“…The deviation between the results in [19] and REEF3D are small, which showed the current cell configuration was acceptable to continue the research. Reynolds number for REEF3D and the laboratory experiment on a cruciform element [12].…”

Section: Figurementioning

confidence: 99%

“…Except for the Morison model, the screen net model, which calculates the deformation of nets based on hydrodynamics of net panel, was developed in [11]. In [12], flume experiments were adopted to analyze the hydrodynamics of a cruciform structure representing a single net mesh. Moreover, a semi-empirical formula was derived experimentally by studying hydrodynamics of plane nets, combining Sn with AOA and Re [13~14].…”

Section: Introductionmentioning

confidence: 99%

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Numerical Simulation of Hydrodynamics Around Net Meshes Using Reef3d

Wang¹,

Martín²,

Huang³

et al. 2021

Preprint

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Hydrodynamics and turbulence around net meshes have drawn more and more attention because it is closely related to forces on the structures and safety issues of offshore fish farms. In terms of numerical modeling of forces on nets, Morison or screen force model is ordinarily adopted to account for its hydrodynamics. However, these methodologies mainly rely on empirical experimental or cylindrical hydrodynamic coefficients, neglecting flow interactions between adjacent cruciforms or net bars. In this study, REEF3D open-source hydrodynamic toolbox is adopted to analyze flow around net meshes explicitly and investigate the hydrodynamics related to forces on the structure. The simulation accuracy is in good agreement with flume experiments and previous research. Flow velocity and vorticity around net bars and knots are investigated. The results demonstrate that 2×2 or 3×3 mesh cases are more reliable when studying turbulence around net meshes, flow interactions around adjacent net bars, knots should be taken into consideration. Two patterns to control Sn, one is to change the diameter of net bars and the other is to control length, have different effects on the flow around meshes. This paper presents a first step in the aim to derive a new empirical formula for Cd depending on Sn, and Re, which are more related to the physics in offshore conditions.

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“…Despite the fact that aquaculture operators have one of the most dangerous professions in Norway, only limited research efforts have been made towards improving occupational safety in this industry, and statistics and in-depth analysis of occupational fatalities are missing. Structural properties of marine fish farms, both nets and cages, have been more thoroughly investigated than occupational safety [12][13][14][15]. Structural analysis has been especially important in relation to preventing the escape of fish from net cages [16], which has received a wide focus because of the negative implications from interactions with wild salmon [17,18].…”

Section: Introductionmentioning

confidence: 99%

Occupational safety in aquaculture – Part 2: Fatalities in Norway 1982–2015

et al. 2018

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This article presents an overview of reported fatalities in the Norwegian aquaculture industry focusing on the production of Atlantic salmon and trout, which dominate the fish farming industry in Norway. The data on fatalities from 1982-2015 are registered by SINTEF Ocean, which is the only data source available. The fatality data set includes information on the incidents leading to fatalities, activities conducted at the time of fatalities, and the time of year the fatalities were registered. The article discusses the fatality trends in light of the characteristics and changes in the Norwegian fish farming industry during the last three decades. This provides useful information for determining the most important current safety challenges and for developing efficient safety management in aquaculture.

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Forces on a cruciform/sphere structure in uniform current

Cited by 34 publications

References 5 publications

Drag on hydroid-fouled nets — An experimental approach

Drag on hydroid-fouled nets — An experimental approach

Numerical Simulation of Hydrodynamics Around Net Meshes Using Reef3d

Occupational safety in aquaculture – Part 2: Fatalities in Norway 1982–2015

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