Modeling of dynamic behavior of a single-point moored submersible fish cage under currents

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The submergence behavior of a small volume fish cage in a single-point mooring system under currents is investigated using a numerical model. Results are validated by comparing to a scaled physical model tow test. The current induced submergence depth, as a function of net chamber solidity for various water velocities is examined. The system remains at the surface at low water velocities until the solidity dependent threshold is reached. At higher currents, the system enters an unstable submergence regime where a small change in the system design could significantly impact the predicted submergence depth. The distribution of current throughout the water column also plays an important role in the steady state response of the structure.Analytical formulas to approximate the dependence of normal drag coefficient for cylinders and spheres on Reynolds number (Re) are proposed. The formulas for cylinders expand the expressions of Choo and Casarella (1971) to account for the decrease in drag forces experimentally observed for 2×105<Re<106. Modeling of this effect is important for proper interpretation of Froude scale physical modeling data.