The Effects Of Weighting System On The Hydrodynamics Of Gravity Cage

This master dissertation bases on the model experiment, which is sponsored by the National 863 Ocean High Technology Development Plan Project and National Nature Science Foundation Project. The effect of weighting system to the hydrodynamics of Gravity Cage under pure current, pure wave and current combined with wave is studied, which includes the mooring lines force, cage motion responses and the net volume loss.The experiments were carried out in The State Key Lab of Coastal and Offshore Engineering of Dalian University of Technology.Physical models were made with model scale of 1:20 according to the common Gravity Cage. The diameter of the inner floating ring is 79.6cm, The outer one is 84.6cm.The perimeter of the net system is 250cm,the deep is 40cm. Three kinds of weighting system includes: 1) sinking ring, lower ring and sinkers. 2) lower ring and sinkers.3) sinkers only. Total eight models were designed. A four-point mooring system was attached to the cage model,which was assembled symmetrically in the middle of the flume. The experiment conditions included that pure current, pure wave and following current combined with wave, adverse current combined with wave. The experiment results are analysed and listed as follow:1. Lightening the weight is available to decrease of the mooring line force in pure current and current combined with wave tests. The force increases after installed lower ring. In the pure wave tests different models present different change on the force after added weigh. After installed lower ring, the force decreased. Whether installed the sinking ring makes little difference on the mooring line force in all experiment conditions.2. The weigh's addtion would minish the bottom net's movement markly, but to the floating ring, can only influence the horizitional movement. The floating ring's horizitional's movement becomes acute after installed lower ring, and holds down the movements of the bottom net. In the pure wave condition, the height of the wave infiunces the vertical movement mostly, and the weihting form has less force. The floating ring or bottom net's horizitional movement becomes acute after installed of sinking ring or lower ring. In current combined with wave condition, the horizitional movement is direct radito to the height of wave and period, the vertical movement is direct radito to the height of wave, and the velocity makes no difference.3.Weigh's addition minishes the loss of net's volume in pure current, but makes no differnce in the pure wave condition. After installed of sinking ring or lower ring, the loss of net's volume is decreased. The loss of net volume is more in the current combined with wave condition than in the pure current condition.