The influence of the bend ratios on the hydrodynamic characteristics in the tank of aquaculture vessel
In order to improve the hydrodynamic characteristics of aquaculture tanks with top and bottom compartments and low diameter-to-depth ratio,so as to improve the welfare of aquaculture animals and the economic benefits. In this study,a new structural optimization parameter was proposed,namely the parameter of the bend ratios a/B(a/B,a is the corner wall side length,B is the culture liquid bulkhead side length),to evaluate the improvement effect of the flow field inside the aquaculture tank. Based on computational fluid dynamics (CFD) simulation technology,the effects of the parameter of the bend ratios a/B (0-0. 40) and water inlet velocity (0. 8-1. 2 m/s) on the hydrodynamic characteristics in the aquaculture tank were studied. Firstly,in order to verify the correctness of the numerical model and the accuracy of the simulation results,a physical test model of the square aquaculture tank was established,and a numerical model of equal proportions was constructed. Next,the numerical simulation results of the water flow velocity in the aquaculture tank were compared with the test results of the physical model. On this basis,a 40:1 scale was carried out on the prototype of the Japan Bulk Carrier to construct a numerical model of the aquaculture ship. Next,the flow field under 9 bend ratios a/B and 3 inlet velocity conditions of the aquaculture tank system were numerically simulated. Under the same inlet velocity,the hydraulic retention time of each tank was basically equal by adjusting the number of water inlets,so as to quantitatively analyze the influence of the bend ratios a/B on the hydrodynamic of the aquaculture tank. (1) The average flow velocity (v) in the tank increases with the increase of the bend ratios a/B,and the trend is the same under the three inlet velocities. When the bend ratios a/B=0. 25-0. 40,the average flow velocity of each section in the aquaculture tank is 35％ higher than that of the original square aquaculture tank,and the velocity of each section is large and evenly distributed,and there is no obvious low flow velocity area. (2) The uniform distribution coefficient γA in the aquaculture tank decreases first and then increases with the increase of the bend ratios a/B. When the the bend ratios a/B=0- 0. 1 and 0. 25-0. 40,the uniform distribution coefficient γA is increased by 7％ compared with a/B= 0. 1-0. 25. (3) The energy utilization coefficient ηe in the aquaculture tank increases with the increase of the the bend ratios a/B.When the bend ratios a/B=0. 3- 0. 40,the energy effective utilization coefficient ηe is 70％ higher than that of the original square aquaculture tank. (4) With the increase of the bend ratios a/B,the vortex column in the center of the aquaculture tank gradually stabilizes,so that the water can move regularly in the tank,and a large vortex ring gradually appears. From the color shading of the velocity,it can be seen that the flow velocity is higher near the tank wall. In aquaculture tanks with smaller bend ratios a/B,large-scale vortex structures break down into many smaller-scale structures,vortex filaments,and irregular vortex distributions. The aquaculture tanks with the bend ratios a/B in the range of 0. 25-0. 40 have the characteristics of high average flow velocity,uniform flow field distribution,and no low flow velocity area. They also have a good water environment,high energy effective utilization rate and efficient utilization of aquaculture space. The results of this study have certain guiding significance for optimizing the design of aquaculture tank systems on aquaculture vessels and improving production efficiency. In practical applications,the flow field environment inside the aquaculture tanks can be adjusted based on the bend ratios a/B to maintain good water quality,improve aquaculture efficiency,and reduce operational costs.
the bend ratiosaquaculture vesselaquaculture tankhydrodynamic characteristicscomputational fluid dynamics
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