| About 71% of the earth is covered by the ocean,which contains very rich natural resources.With the consumption of land resources,all over the world have turned their attention to the ocean.How to exploit and utilize the ocean resources more properly has become an important way to solve the problem of resource shortage.The quantity of wild seafood can no longer meet people's demand,so the Marine aquaculture industry is developing rapidly.However,due to the rapid development of population and industry in coastal areas and the saturation of the quantity of nearshore aquaculture,the aquaculture environment of the shallow water is gradually harsh,so the development of far-reaching marine culture has become an inevitable trend.Compared with the shallow water,the environment of the deep sea is more serious,so the fish cage in the deep see need better hydrodynamic performance.Although many scholars around the world have done a lot of research on the hydrodynamic performance of cage in the past decades,there are still many problems that need to be studied further.The characteristics of the flow field inside and around the fish cage are not only related to the environment around the cage,but also related to the quality and living environment of cultured fish.At present,the research on the flow field of the cage mainly adopts two methods: model test and field measurement.In this thesis,the internal flow field of the cage is researched.The numerical simulation of the internal flow field and the reduction of the water flow in the cage is carried out.In the numerical simulation of the cage,the amount of calculation depends on the diameter of the net wire of the net cloth.If the same reduction ratio is used for the main shape of the net and the cage,the net is too small,which will cause too much calculation or even impossible Calculate,therefore use different reduction ratios for the main dimensions of net clothing and cages.In order to explore how different mesh shrinkage ratios will have on the numerical simulation calculations,this thesis also carried out an analysis of the influence of mesh shrinkage ratio changes on the flow field.In the first Chapter of this thesis,the research background and significance of the subject are introduced,the structure of the cage and the current status of the research on cage flow field at home and abroad.The second part introduces the basic theory of numerical simulation: governing equations,turbulence model and finite element method.In Chapter 3,the validity of the numerical simulation method is verified by comparing the numerical results with the test results of the two experiments : the experimental study of the flow field effect of circular gravity cages by Liu Chao et al.and the two-dimensional flow field of square cages based on PIV technology by Cui Yong et al.In Chapter 4 uses two cages as the parent model,and initially designs a circular gravity cage.The basic structure,main dimensions and hydrodynamic performance of the cage are given.In order to compare the shapes of different cages the effect on the flow field gives the size of a square cage with the same breeding volume.The fifth chapter mainly discusses the influence of different mesh-shrinkage ratios on the flow field of circular gravity cages,and selects the appropriate mesh-shrinkage ratio for numerical simulation.Chapter 6 uses a suitable net-shrinkage ratio to establish a numerical calculation model for square cages,simulates the flow field of square cages,and analyzes the difference in distribution and reduction of flow in the flow field of round and square fish cages.Through research,it is found that when the scaled model is used in STAR-CCM+ to numerically simulate the cages,the scale ratio of netting is 2;the flow field distribution in the square cages is more regular,and the overall environment is more stable than the circular cages;The netting on the side of the round cage is subjected to greater water pressure than the square cage,which provides an important reference for subsequent cage design. |
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