RIASSUNTO
ABSTRACT
The fluid induced dynamic properties of a floating raft system for oyster culture are investigated numerically and physically. In this numerical model, the whole raft system including floating raft and mooring lines are divided into numerous elements and nodes. The element is the basic solid unit subjected to external forces, while the node is treated as the center of lumped mass. A Morison type equation of relative motion is used to calculate environmental loadings such as waves and currents on the elements and then evenly distributing to neighboring nodes; other forces such as element’s weights, buoyant forces and contact forces are added to the common nodes to form a system of motion equations. A time marching scheme, 4th-order Runge-Kutta method, predicts the node’s displacement for the next time step. Based on these displacements on the mooring line, the elongation of the line can be determined and so is the tension force of the line. To verify the numerical model, a physical model was established in a wave/current tank (35×1×1.2 m). The comparison of the numerical predictions and experimental measurements of dynamic responses show good agreement. The results will help to undertake further studies on the in-situ oyster raft system.
INTRODUCTION
Oyster culture has being existed along the southern coastal area of Taiwan for centuries, and the aquaculture species is mainly the Pacific Oyster. Recently, the oyster culture is becoming an important income source for shellfish farmers, according to the Fisheries Statistics Annual Report of the production of information, from 1999 to 2007, increasing from 19,000 to 28,000 tons, equivalent to the economic value from NT $2.5 to 3.2 billion. This shows that the oyster raft system, shown in Fig. 1, is a great important infrastructure for raising shellfish in the sea. Oyster cluster is usually a basic harvested unit tied to the string of line.