Numerical Simulation Of Sediment Precipitation In VLCC Ballast Water Tank

When ballast water is pumped into the ship’s ballast water tanks, it always contains large amounts of sediment. The movement and accumulation of sediment bring a series of problems like the structure corrosion, wear and environmental pollution. Reduction of the distribution of sediment in the tank and the scope of the destruction to structure is always a pursue. Experts have conducted extensive research on this issue, but only on a beginning stage.With the booming of the CFD computational fluid dynamics, the means of numerical simulation has been proved accurate to solve the motion of fluid. In order to understand the ballast water flowing process and the sediment’s final distribution, this paper uses commercial software Fluent to simulate the items above. Standard k-ε model has been used to simulate the turbulence model, while Mixture model is for the simulation of three-phase mixed flow of air, water and sediment.The object is taken from a VLCC side ballast water tank; this paper simulates the whole process of ballast water being pumped into this tank. Results of water flow, sediment distribution and sediment escape at various times are obtained. Based on the final sediment distribution, this paper analyzes the influence of the manholes and overflow holes’size and location to the fluid velocity field and turbulence field, and meanwhile the influence of velocity and turbulence to sediment precipitation. Finally, an improved ballast water tank modal has been proposed to optimize sediment’s distribution and precipitation effect.Through the analysis and comparison of simulation results, some conclusions can be drew here:(l)Velocity field is not well-distribution during the whole process, the velocity shows a decreasing trend from the bottom to the top;(2) Sediment distributes mainly at bottom and platforms, and shows a decreasing tendency along the vertical direction in the whole tank;(3) because of the block of the solid webs, high concentrations of sediment is found at weld lines and corners near the webs;(4) Sediment precipitation is highly influenced by the flow velocity and turbulence intensity, the gentler velocity and turbulence field is the more likely sediment largely precipitates;(5) the more reasonable inner holes’location and size are designed the more optimized velocity and turbulence field will be got, as well as a better precipitation effect, this paper increases the size of the manholes and adjusts overflow holes’ location and number to enhance the precipitation rate and optimize the distribution of sediment.