Analysis On Coupling Effects Of Ship Motion And Tank Sloshing

With the development of liquid cargo like LNG, FPSO and FLNG, the effect of inner free surface and its sloshing inside the tank is becoming great concern to the ship’s motion. The numerical calculation research on the coupled motion of ship and tank sloshing is carried on, then compared with the FPSO model test results which is conducted by MARINE. To sum up, this thesis’s work can be divided into following several aspects:Firstly, numerical calculation on tank sloshing:tank sloshing on different conditions is calculated based on CFD software Fluent and compared with experiment results, which verifies the accuracy of numerical method in the thesis; the comparative analysis of2D tank and3D tank sloshing is conducted, the results show that when the length of tank is greater than the width of tank the2D model is accurate enough to accumulate the3D model; the research about the effect of mesh size and timestep on numerical calculation of the full size tank sloshing is conducted to supply some engineering evidence for the design of liquid container.Secondly research on coupling ship motion and tank sloshing in frequency domain: the frequency domain motion equation of tank sloshing coupling with ship motion is obtained through theoretical derivation, and hydrodynamic coefficients of FPSO are calculated by solving diffraction/radiation problem using a constant panel method program, called Hydrostar, then the frequency domain motion equation can be solved by inputting coefficients, and the motion RAOs solved by equation are compared with experiment results, the roll linear damping ratios of FPSO are determined by comparing the RAOs of calculating results and experiment results, lastly the impact of filling level of tank on ship motion is discussed.Finally, research on coupling ship motion and tank sloshing in time domain:solving the coupling problem of ship motion and tank sloshing in time domain is crucial and necessary because of the nonlinear phenomenon of tank sloshing, the time domain motion equation of tank sloshing coupling with ship motion is obtained through theoretical derivation, in the equation radiation force of ship can be obtained by using IRF method,and incident wave force in frequency domain can be converted into time domain by using FFT, and load of tank sloshing can be calculated by using CFD software Fluent. The motion RAOs are investigated by solving the time domain equation and compared with the results of frequency and experiment, which verifies the time domain method is more accurate than the frequency approach, then the effect of tank filling level on ship roll motion in time domain caused by regular wave are investigated.