Study On Hydrodynamic Characteristics Of Artificial Floating Reef Under Waves

It is of great importance and in urgent need of restoring and protecting the marine ecological environment due to the overfishing and serious environmental pollution.Artificial reef is a man-made structure,typically built to restore the marine environment and promote marine production.And artificial floating reef is mainly used to concentrate and protect fishes distributed in the middle and upper water layers,less restricted by seabed conditions,especially showing fairly good suitability in soft silt seabed.However,the floating reef can be greatly affected by the dynamic ocean environment such as wave and current for its main functional structure is just right set in the middle and upper water layers.Thus,structure safety and stability of the floating reef are the key points during design and installation process.In this research,model experiment and numerical simulation have been employed to study the hydrodynamic characteristics of cage-net floating reef under wave.Firstly,a model floating reef is made based on variable scale similarity law,and the motion of model under different wave heights is captured by using CCD image tracking technology.Then,a 1:1 mathematical model is established by using the lumped mass point method,the finite element method and the rigid body kinematics principle in order to simulate the motion of floating reef.The results show the trace point horizontal negative motion displacement error between numerical simulation and physical model is 13.95%,the positive motion displacement error is 2.42%,and the total motion displacement error is 8.08%.The results confirm this numerical model can well simulate the movement of the floating fish reef under waves.Finally,a full-scale numerical model is developed and used to study the hydrodynamic characteristics of the prototype floating reef under waves.The results indicate that the following parameters,floating reef horizontally offset,deflection angle and the maximum tension of the mooring line increase with the increasing wave height.The floating reef is almost at rest when the wave height is 1 m.Wave height has almost no effect on the maximum deflection angle of the floating reef and the cage does not deflect but moves forward and downward.The effect of wave height on the floating reef system can be easily seen in the aspect of force of the mooring line with four mooring lines having different forces.When the wave height is fixed,the floating reef horizontally offset,deflection angle and the maximum tension of the mooring line decrease with the increasing submergence depth.The floating fish reef movement tends to be stationary when submergence depth is two times larger than the wave height.This submergence depth can be used as a threshold for floating fish reef installation.In conclusion,the maximum horizontal offset of cage,the deflection angle of cage and the force of net and mooring line under wave are studied.The results can provide theoretical basis and reference for structural design,safety assessment and installation of artificial floating reefs.However,the artificial floating reefs in actual sea condition also can be affected by currents.The influence of current on the hydrodynamic characteristics of floating reefs needs further systematic and in-depth study.