Nonlinear vertical accelerations of a floating torus in regular waves

Li, Peng; Faltinsen, Odd M.; Lugni, Claudio

doi:10.1016/j.jfluidstructs.2016.08.007

Cited by 24 publications

(23 citation statements)

References 7 publications

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“…Many investigations have been done for the fish farm system. For example, Dong et al (2010a) and Li et al (2016) studied experimentally and theoretically the vertical responses of an isolated elastic-circular, moored floater in regular waves. Lader and Fredheim (2006) applied a truss model to investigate the dynamic properties of a two-dimensional flexible net sheet exposed to waves and current.…”

Section: Introductionmentioning

confidence: 99%

Numerical study of a well boat operating at a fish farm in current

Shen

Greco

Faltinsen

2019

Journal of Fluids and Structures

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Dynamic response of a well boat operating at a fish farm in current is investigated numerically. An objective is to determine the operational conditions of the well boat. In terms of the fish farm, a realistic set-up (with single cage) is considered, including a floating collar, an elastic sinker tube, a flexible-closed net cage and a complex mooring system. A time-domain solution is used to find the steady configuration and response. Transverse viscous current loads are estimated using the cross-flow principle. The drag coefficients are obtained empirically by considering cross-sectional details, free surface and three-dimensional (3D) flow effects. The drag force is experimentally validated. The effect of the ship wake on the net loading is also assessed.The most critical scenario with the well boat placed at the weather side of the fish farm is analyzed in detail. Critical response variables for operational limits are the maximum anchor-line tensions and floater stresses. Numerical results show that the anchor loads will increase more than 40% in small current velocities and up to 90% in high current velocities due to the viscous current loads on the boat. There is also a strong increase of the floating collar deformations and stresses when the well boat is in contact with the floating collar.A sensitivity analysis has been carried out to identify the physical parameters affecting the anchor loads and the maximum stress in the floating collar. From our studies, the anchor loads are more sensitive to current direction, bottom weight system, sinker tube depth and mooring line properties (pretension load, anchor chain weight, etc.) and less sensitive to other parameters such as floating collar stiffness and crosssectional drag coefficients of the well boat. The shading effect of the well boat on the fish-farm inflow has been examined and appeared not negligible with 4% to 10% reduction of the anchor loads for the studied current conditions. The maximum stress in the floating collar is sensitive to well-boat loads related parameters (current direction, cross-sectional drag coefficient) and pretension load in the anchor line; not so sensitive to net loading related parameters such as sinker tube depth and sinker tube weight.Lastly, the operational conditions of the well boat at the fish farm were discussed. Numerical results show that the maximum stresses in the floating collar should be of major concern. The loads in the mooring lines are moderate compared with the corresponding breaking limits.

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Section: Introductionmentioning

confidence: 99%

Numerical study of a well boat operating at a fish farm in current

Shen

Greco

Faltinsen

2019

Journal of Fluids and Structures

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“…The CFD calculations illustrated that overtopping of waves and flow separation can matter. Li et al (2016Li et al ( , 2018) studied experimentally and theoretically vertical accelerations of a moored floating elastic torus without netting in regular waves of different steepness and periods in deep water. Wavelengths of practical interest are of the order of the torus diameter but long relative to the cross-sectional diameter.…”

Section: Wave and Current Load Effects On Floating Fish Farms With Nementioning

confidence: 99%

“…The sinker tube was attached directly to the net in the present study, without vertical chains between the floating collar and the sinker tube to avoid chafing between the chain and the net cage. Shen et al (2018) used the curved beam equations with axial tension to describe the radial and vertical deformations of the two concentric floating tubes similarly as Li et al (2016) did for an isolated elastic torus. The deformations were expressed as Fourier series.…”

Section: Mooring Loads Of Realistic Marine Fish Farmsmentioning

confidence: 99%

Wave and Current Effects on Floating Fish Farms

Faltinsen

Shen

2018

J. Marine. Sci. Appl.

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The paper is partly a review on hydrodynamic and structural aspects of fish farms. In addition, new numerical results are presented on the stochastic behavior of bending stresses in the floater of a realistic net cage in extreme wave conditions. The behavior of traditional-type fish farms with net cages and closed fish farms in waves and currents is discussed. Hydroelasticity can play a significant role for net cages and closed membrane-type fish farms. The many meshes in a net cage make CFD and complete structural modeling impracticable. As an example, a hydrodynamic screen model and structural truss elements are instead used to represent the hydrodynamic loading and the structural deformation of the net. In addition, the wake inside the net due to current plays an important role. The described simplified numerical method has been validated by comparing with model tests of mooring loads on a single net cage with two circular elastic floaters and bottom weight ring in waves and currents. It is discussed which parts of the complete system play the most important roles in accurately determining the mooring loads. Many realizations of a sea state are needed to obtain reliable estimates of extreme values in a stochastic sea. In reality, many net cages operate in close vicinity, which raises questions about spatial variations of the current and wave environment as well as hydrodynamic interaction between the net cages. Live fish touching the netting can have a non-negligible influence on the mooring loads. It is demonstrated by numerical calculations in waves and currents that a well boat at a net cage can have a significant influence on the mooring loads and the bending stresses in the floater. The latter results provide a rational way to obtain operational limits for a well boat at a fish farm. Sloshing has to be accounted for in describing the behavior of a closed fish farm when important wave frequencies are in the vicinity of natural sloshing frequencies. The structural flexibility has to be considered in determining the natural sloshing frequencies for a membrane-type closed fish farm. Free-surface non-linearities can matter for sloshing and can, for instance, result in swirling in a certain frequency domain for a closed cage with a vertical symmetry axis.

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“…It should be noted that polyethylene can be efficiently produced from recycled plastic waste (49). Numerical calculations and model testing have been performed of the dynamics of a single floating elastic torus structure interacting with water waves (50,51); an approximate linear treatment of torus deflections is presented in SI Appendix. Fig.…”

Section: Dynamics Of Floating Islandsmentioning

confidence: 99%

“…The fact that the deflection amplitudes calculated using the simple linear theory are of the same order as the incoming wave amplitude demonstrates the necessity of quantitative predictions of a more detailed, nonlinear analysis (51). This is particularly true with regard to the inherently nonlinear phenomena of "overtopping" (waves breaking over the upper torus surface) and "out of water" (protrusion of the torus above the water surface).…”

Section: Dynamics Of Floating Islandsmentioning

confidence: 99%

Renewable CO₂recycling and synthetic fuel production in a marine environment

Pàtterson

Borgschulte

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

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A massive reduction in CO 2 emissions from fossil fuel burning is required to limit the extent of global warming. However, carbonbased liquid fuels will in the foreseeable future continue to be important energy storage media. We propose a combination of largely existing technologies to use solar energy to recycle atmospheric CO 2 into a liquid fuel. Our concept is clusters of marinebased floating islands, on which photovoltaic cells convert sunlight into electrical energy to produce H 2 and to extract CO 2 from seawater, where it is in equilibrium with the atmosphere. These gases are then reacted to form the energy carrier methanol, which is conveniently shipped to the end consumer. The present work initiates the development of this concept and highlights relevant questions in physics, chemistry, and mechanics. renewable energy | carbon dioxide recycling | synthetic fuel | maritime structures L imiting anthropogenic global warming to below 2°C, a goal of the Paris Agreement of the United Nations Framework Convention on Climate Change (1), now ratified by 174 countries, will require within the coming decades the phasing out of carbon dioxide emissions from fossil fuel burning. However, in the foreseeable future, carbon-based liquid fuels will continue to play an important role, in particular for aeronautical, marine, and long-haul automotive mobility. It is therefore essential to investigate possibilities of using renewable energy to recycle CO 2 between the atmosphere and synthetic liquid fuel (2). Efforts to photochemically produce synthetic fuel from CO 2 and water (i.e., via artificial photosynthesis) show some promise (3). We propose an approach using more conventional methods, but with important unique aspects.Methanol, CH 3 OH or MeOH, is the simplest carbon-based fuel, which is liquid at ambient conditions (4). With approximately half the energy density of gasoline (15.6 MJ/L vs. 32.4 MJ/L), it can be used to power existing gas turbines, modified diesel engines, and direct methanol fuel cells. Methanol can serve as a feedstock for most petrochemical products, and by simple dehydration it can be converted to dimethyl ether, an attractive substitute for natural gas, and other hydrocarbon fuels. Methanol can be produced (5) by the catalytic hydrogenation of CO 2 [presently the largest methanol production facility using this technique is located in Iceland (6)], and MeOH burns in air to release CO 2 and water:An attractive scenario for the production of synthetic methanol fuel is the recycling of atmospheric CO 2 , the electrolytic produc-tion of H 2 , and their catalytic reaction to CH 3 OH, with all of these processes powered by renewable energy. As a concept for realizing this scenario, the present work proposes the production of H 2 and the extraction of CO 2 from seawater and their catalytic reaction to produce MeOH on clusters of artificial, marine-based photovoltaic (PV)-powered "solar methanol islands" (7) (Fig. 1). We present an initial implementation plan; in view of many uncertainties, much addition...

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Nonlinear vertical accelerations of a floating torus in regular waves

Cited by 24 publications

References 7 publications

Numerical study of a well boat operating at a fish farm in current

Numerical study of a well boat operating at a fish farm in current

Wave and Current Effects on Floating Fish Farms

Renewable CO₂recycling and synthetic fuel production in a marine environment

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Nonlinear vertical accelerations of a floating torus in regular waves

Cited by 24 publications

References 7 publications

Numerical study of a well boat operating at a fish farm in current

Numerical study of a well boat operating at a fish farm in current

Wave and Current Effects on Floating Fish Farms

Renewable CO2recycling and synthetic fuel production in a marine environment

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Product

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Renewable CO₂recycling and synthetic fuel production in a marine environment