Study On CFD Numerical Simulation Of Flow Field In The Working Tank Of A New Type Fishing Ship

During the working process of fish farming ships,the tank will respond to six degree of freedom coupling motion of the hull under the influence of external marine environment,which will lead to a complex sloshing phenomenon in the tank.The change of water state caused by sloshing directly determines the aquaculture ecological environment.Therefore,it is of great theoretical reference value for the selection of mother ship and the design of modification plan to carry out numerical simulation study of the flow field in the working tank of a fish farming ship,and to analyze the influence of hull motion and external flow field on the ecological environment of fish culture in the tank.Facing the urgent market demand of fishery culture in the South China Sea,some domestic shipping companies have proposed the plans of transforming retired old ships into fish farming ships.In this paper,a fish farming ship refitted from bulk carrier is taken as the research object.Based on CFD method,the flow field in the tank of the fish farming ship with multi degree of freedom coupling motion under external environmental conditions is simulated.The effects of hull motion and external marine conditions on the ecological environment of the fish farming ship are analyzed.The specific contents include:Firstly,based on the model test of enclosed tank,the model and algorithm of numerical calculation are determined.In addition,the uncertainty of sloshing problem is analyzed by using ITTC recommendation procedure combined with the test data of an enclosed tank,and the grid scale and time step scheme of numerical calculation are determined.The validation results of the closed tank model will be extended to the subsequent numerical simulation of the flow field in perforated tank.Secondly,according to the general layout of the fish farming ship,a two-dimensional hydrodynamic analysis model is established by selecting the typical cross section of the perforated tank.Numerical simulation of two typical motion modes with sloshing problems,rolling and heave,is carried out.The variation of flow field state in the perforated tank under the excitation of rolling and heave motions at different amplitudes and frequencies,as well as rolling-heave coupled motion at different phase angles is analyzed.The research results can provide reference for the selection of mother ship in the reconstruction scheme of fish farming ship.Then,based on the two-dimensional cross-section hydrodynamic analysis model,the flow fields inside the perforated tank under the actions of uniform flow field,wave field and wave-current combined field are simulated.The impacts of velocity,tank type and different waves on the flow field inside the perforated tank are analyzed.The research results can provide a reference for the design of fish farming ship reconstruction scheme.Finally,based on the three-dimensional boundary element theory of wave potential flow,a theoretical prediction method for the motion response of fish farming ship under complex wave loads is established.Considering the influence of ship motion and external flow field,a reliable numerical analysis model for the combined action of ship motion and external flow field is established,and the simulation of the flow field in perforated tank under actual sea conditions is realized.