World Aquaculture Society Meetings

Add To Calendar 25/02/2016 14:30:0025/02/2016 14:50:00America/ChicagoAquaculture 2016INFLUENCE OF WAVE KINEMATICS STRETCHING METHODS ON FORCES OVER A CAGE UNDER REGULAR WAVES AND CURRENT.   Versailles 3The World Aquaculture Societyjohnc@was.orgfalseanrl65yqlzh3g1q0dme13067DD/MM/YYYY


Cristian Cifuentes *, M.H.Kim
Ocean Engineering Program
Department of Civil Engineering
Texas A&M University
College Station, Texas, USA

The response of a single cage under regular waves, and wave/current interaction loading is calculated and compared to experimental data. The cage consists of a surface collar, netting, ballast and mooring lines. The numerical calculations are carried out using the commercial software OrcaFlex v9.6. In this tool, forces are calculated using a modified version of Morison equation able to account for the relative motion between cage elements and fluid. Waves are modeled using linear wave theory, besides current profiles, constant over water depth, are included. Shielding effect, due to the loss of momentum of the flow when crossing the net, is incorporated into the numerical model. Given the relevance of inertia load and deformations of the surface collar over tension on mooring lines, special attention is given to the numerical representation of this cage component. Inertia coefficients for the surface collar are selected according to each wave condition; in addition, bending stiffness of the floater is included; hence, it deforms as wave propagates. Calculations are done considering vertical, Wheeler and extrapolation wave kinematics stretching methods. Results show the significance of the method's selection over mooring line tension. Based on the numerical results, it can be concluded that, when using a Morison force model, Wheeler stretching shows high accuracy when compared to experimental data.

For the numerical model of the net, a combination of lines, six and three degree of freedom buoys have been used. Projected area, wet mass and axial stiffness are matched between physical and numerical nets. Lines represent the net and collar components of the system as well as the mooring lines. Buoys are used to connect the lines and generate a model that reacts to the environment loads as a single unit. Of primary relevance on the determination of drag forces in nets, is the selection of drag coefficient for each element in the numerical model. This is achieved by the use of a method that updates Cd at each time step during the simulation using the normal relative velocity between each line element and the fluid field. The drag force is then determined by using Morison equation considering the mass and inertia properties of each element.

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