Research On Hydrodynamic Characteristics Of A Fish Cage Based On Jacket Structure

At present,with the end of the life of offshore oil and gas platforms or the end of oil production activities,a large number of jacket structures will lose their original value due to idle or abandoned;and as offshore wind power continues to advance into the deep sea,the application of jacket foundation will become more and more extensive,but still facing problems such as high construction and maintenance costs and low water surface utilization rate.At the same time,along with the continuous development and utilization of marine resources,coastal aquaculture space resources are constantly compressed,the breeding density becomes large,which leads to a series of problems such as disease and pollution.In view of the above problems,the combination of jacket structure and breeding cage can meet the synergistic development of different marine uses.However,the fish cage based has a complex response under the action of the ocean environment such as waves and ocean currents,and it is of great significance to carry out relevant hydrodynamic characteristics studies.The main structure studied in this paper is a large-span jacket structure,the research on the jacket structure and the whole fish cage structure mainly includes two aspects,one is to conduct physical model tests to research the change law of the horizontal wave force of the structure under different wave conditions;and the other is to use the finite element method to study the change law of wave phase angle and wave force component with the wave parameters,and use the least square method to solve the hydrodynamic coefficients.The research scope is described as follows:Firstly,the physical models of jacket and the whole fish cage were designed and the regular wave test was used to study the horizontal wave force of the two models under different wave heights,periods and incident angles,The results show that the large-span jacket structure is very sensitive to the change of the wave period,and there is also a big difference with the change of the wave incident angle,which is quite different from the related research of traditional offshore structures.Secondly,the finite element model of the jacket and the whole fish cage is established,and the phase angle search of the structure is carried out based on the Morison equation to analyze the relationship between the wave force and the wave phase angle;the transient dynamic analysis is performed to solve the horizontal wave force and its components.The results show that the phase angle corresponding to the peak wave force of the large-span jacket structure is basically unchanged with the wave height and varies greatly with the wave period,and there are also differences in the law of change with different wave incident angles;regarding the wave force component of the jacket,the proportion of the drag force increase gradually with the increase of wave height and period,and the inertial force cannot be ignored.For the netting,the inertial force is relatively small compared to the drag force,consider only using the drag force to approximate the total wave force.Finally,on the basis of the transient dynamic analysis combine with the corresponding test data,based on the nonlinear Morison equation,the least square method is used to fit the hydrodynamic coefficients of the structure.While the hydrodynamic coefficients of the structure change with the KC number,the influence of the wave incidence angle cannot be ignored;then calculate the corresponding drag force,inertial force and total wave force,compare the calculated wave force corresponding to the hydrodynamic coefficients and the test wave force,find that the method of calculating the hydrodynamic coefficients with the help of finite element method is effective,which can provide reference for related research.