Numerical Simulation And Anti Rolling Mechannism Of Rectangular Anti Rolling Tank

With the continuous expansion of human demand for marine resources,ocean engineering ships have been greatly developed.The rolling motion of marine engineering ships has attracted more and more attention.Human have invented various anti roll tanks to reduce the roll motion of the ship.Among them,passive rectangular anti roll tank has the advantages of no additional energy consumption,simple structure,space saving,easy maintenance,low price and low technical requirements.In this thesis,the numerical simulation and the mechanism of the passive rectangular anti roll tank are studied.In the frequency domain,based on the balance principle of moving object,the coupled rolling motion equation of ship anti rolling tank is established and the analytical solution is obtained.The moment acting on the ship by the rectangular anti rolling tank is regarded as a part of the restoring moment of the ship’s rolling motion.The Ikeda method is used to obtain the rolling damping moment coefficient,and the Hydro D module of DNV.SESAM is used to calculate the hydrodynamic coefficient of the ship,including the added mass,added damping(wave damping)and wave load.The anti rolling effect of rectangular anti rolling tank under full load and ballast load is studied in frequency domain.The results show that under full load and ballast conditions,the rectangular anti rolling tank has anti rolling effect in a small range of wave circle frequency,and each wave circle frequency corresponds to a tank depth,which makes the rectangular anti rolling tank achieve the best anti rolling effect.In the time domain,this thesis based on the principle of impulse response superposition,the ship rolling motion equation is constructed by using indirect time domain method.The sloshing motion load of anti rolling tank solved by CFD method is added to the ship rolling motion equation as an external force term to form the ship anti rolling tank coupling rolling motion equation and solve the ship motion state.The motion state of the ship is taken as the excitation condition for CFD to solve the sloshing motion of the anti rolling tank,which further causes the sloshing motion of the tank and produces the force of the rectangular anti rolling tank on the ship,which affects the rolling motion of the ship.In this way,the rolling reduction effect of rectangular anti rolling tank under full load and ballast in regular waves is obtained and compared with the frequency domain method.The results show that under full load and ballast conditions,the frequency domain calculation results are basically consistent with the time domain simulation trend changes.When the rectangular anti-rolling tank is at the optimal loading depth,there is a big difference between the frequency domain calculation results of the anti-rolling effect and the time domain simulation results.At this time,the time domain simulation is more accurate.This thesis based on the two parameter P-M spectrum simulation of random waves,the anti rolling effect of rectangular anti rolling tank under full load survival condition,full load operation condition,ballast survival condition and ballast operation condition is studied in time domain.The results show that in random waves,when the water depth of rectangular anti rolling tank is about half,the anti rolling effect is the best.On this basis,the length and width of rectangular anti rolling tank and damping grid are studied.The results show that the length and width of rectangular anti rolling tank should not be too long or too short,and scheme 13 has the best anti rolling effect.