Investigation On Hydrodynamic Characteristics Of Enclosure Mariculture Facilities

During the 13th Five-Year Plan period,it has become an important task to develop aquaculture equipment and accelerate the transformation and promotion of mariculture industry.A series of national strategies such as “Maritime Silk Road”,“Blue Granary” and “National Science and Technology Plan for Invigorating the Sea” have been introduced to support the work.As a new marine ecological aquaculture pattern,enclosure aquaculture is an important development trend of aquaculture in the future,which has some advantages compared with the traditional cage aquaculture,such as large effective breeding space,natural breeding quality and less pollution.The hydrodynamic response,flow and wave field characteristics of enclosure aquaculture facilities are of great significance to the material selection,design and breeding growth.Many researches on the hydrodynamic characteristics of the enclosure aquaculture facility components,but there are few basic studies on the whole enclosure aquaculture facilities.Therefore,this paper combined physical model experiment and numerical simulation to study the hydrodynamic characteristics of the enclosure aquaculture facilities.Firstly,the physical models of the floating rope enclosure and the pile-net enclosure are designed based on the variable scale gravity similarity criterion.The hydrodynamic characteristics of floating rope enclosure under currents and waves are analyzed by using dynamometers to collect the mooring line tension and CCD high-speed camera to collect the movement of net.In order to study the structural and flow field characteristics of the pile-net enclosure,dynamometers and acoustic Doppler velocimetry(ADV)are used to collect the force of the pile and the velocity of the monitoring point near the structure,respectively.The experimental data provide a basis for the verification of the numerical model below.Secondly,a numerical model is established based on the lumped mass method for the hydrodynamics of the floating rope enclosure.Physical model test results are used to verify the accuracy of the numerical model.The numerical model is used to analyze and compare the distribution of mooring line tension,net tension,net movement and volume retention rate of rectangular and circular floating rope enclosure under currents,waves and combined currents and waves.The results show that the mooring line tension at the four corners of the rectangular floating rope enclosure bears most of the load,and the maximum mooring line tension appears on the mooring line at the upstream corner.The distribution of mooring line tension of circular floating rope enclosure is more uniform than that of rectangular floating rope enclosure.Except for the horizontal motion amplitude,the mooring line tension,vertical movement amplitude,net tension and volume change rate of the rectangular floating rope enclosure are greater than those of the circular floating rope enclosure under the same conditions.Based on the numerical results of floating rope enclosure,a fast prediction model of hydrodynamic characteristics of floating rope enclosure is established based on support vector machine regression fitting method(SVR),and the influences of data normalization,kernel function and parameter optimization methods on the prediction results are discussed.It is found that ε-SVR model,RBF kernel function and cross-validation parameter optimization method are used to predict the hydrodynamic characteristics of floating rope enclosure have achieved good results.SVR has obvious advantages over artificial neural network(ANN)in prediction accuracy under the condition of small training samples.In addition,SVR has obvious advantages over artificial neural network(ANN)in prediction accuracy under the condition of small training samples.The applicability of SVR in predicting the hydrodynamic characteristics of the floating rope enclosure provides a theoretical basis for the early warning of the floating rope enclosure damage risk.Finally,a three-dimensional one-way fluid-solid coupling model of pile-net enclosure under the action of currents and waves is established.Under the flow velocity and wave parameters studied in this paper,the deformation of the pile-net enclosure has little influence on the flow field,so it is relatively reasonable to adopt the one-way fluid-structure coupling model without considering the influence of structural deformation on the surrounding flow field.The surface pressure of the structure in flow field simulation is transformed into the surface pressure load of the structure element through the nearest neighbor interpolation.Then the large deformation nonlinear finite element model is used to solve the dynamic problem of the structure,and the force and deformation results of the structure are obtained.The accuracy and applicability of the model are verified by physical model test.By using the three-dimensional one-way fluid-solid coupling model,the influences of the arrangement form,the intersection between current and pile-net and the pile-net spacing on the upstream and downstream velocity,wake,wake vortex and the structure stress and deformation of the pile-net structure under flow are discussed.The influence of net and pile-net row number on wave surface distribution,velocity distribution,structure stress and deformation under waves is analyzed.It is found that the presence of net decreases the velocity in front of the structure,intensifies the downstream velocity attenuation,and also significantly increases the stress and deformation of piles.The maximum axial stress appears at the connection between the net and pile,where tensile damage is most likely to occur,so the net at this location should be reinforced in practice.