Investigation On The Coupling Characteristics Of Variable Mass Tank Sloshing And Ship Motion In Waves

Tank sloshing generally exists in the field of ships and marine engineering,especially in the offshore operation of oil and gas production and transportation equipment such as liquefied natural gas ship(LNG),liquefied natural gas floating production unit(FPU),liquefied natural gas floating storage unit(FSRU),large crude oil cargo ship(VLCC).With the development of offshore oil and gas resource exploitation activities,higher requirements are put forward for the operation safety of LNG,FPU,FSRU and other equipment.However,the tanker represented by LNG and VLCC will produce obvious sway movement under the dual influence of wave action and liquid real-time filling,resulting in violent sloshing of the inner tank.When the sloshing frequency of the liquid in the tank is close to the natural frequency of the tank,it will not only have a significant impact on the stability of the ship,but also cause a large local impact load on the tank bulkhead,resulting in the fracture and damage of the hull structure,which will directly affect the safe operation of the ship.Therefore,the research on the coupling characteristics of tank sloshing and ship motion in waves has practical engineering needs and theoretical research value for guiding marine equipment design and marine operation.In view of the above problems,this paper combs the cases of tanker navigation accidents caused by large tank sloshing,and summarizes the research progress at home and abroad in three aspects:Tank forced sloshing,tank sloshing considering liquid filling,and the coupling between tank sloshing and hull motion.The physical essence of these three types of Engineering problems is single body nonlinear dynamics Single body nonlinear nonstationary dynamics and multi-body nonlinear nonstationary dynamics.Aiming at these three scientific problems,this paper has carried out the research on the numerical simulation and frequency load characteristics of tank forced sloshing,the numerical simulation and frequency load characteristics of variable mass tank sloshing,the typical experimental research on the coupling characteristics of tank sloshing and ship motion,the numerical simulation research on the coupling characteristics of tank sloshing and ship motion,and the coupling characteristics of multi tank sloshing and ship motion.The main research contents are as follows:(1)The numerical simulation of tank forced sloshing is carried out by CFD method.Firstly,the numerical verification of tank micro amplitude sloshing and tank large amplitude sloshing test are carried out.The accuracy of the numerical simulation results is compared with the analytical solution and public test results respectively.It is proved that the numerical model can accurately capture the large deformation phenomenon of free surface and local pressure peak,and has good accuracy;Secondly,on this basis,the frequency characteristics of tank large sloshing load are studied,and the strong nonlinear characteristics in the process of large sloshing are analyzed.(2)The numerical simulation of forced sloshing of variable mass liquid tank is carried out by CFD method.Firstly,the forced sloshing test of variable mass tank is carried out,and the accuracy of the numerical simulation results is compared with the public test results;Secondly,based on the experimental verification,the numerical simulation of forced sloshing of single cabin with variable mass is carried out,and the effects of filling rate,sloshing amplitude and sloshing period on the sloshing process are discussed;Finally,the numerical simulation of variable mass multi tank forced sloshing is carried out,the influence of filling mode on sloshing process is discussed.(3)The tank test of the coupling between tank sloshing and ship motion is carried out,and its coupling characteristics are analyzed from the perspective of test,which provides a verification basis for the study of nonlinear and nonstationary dynamics numerical model of single tank ship.Firstly,the no-load test of liquid tank in transverse wave is carried out,and the influence of incident wavelength on ship rolling motion is discussed;Secondly,the typical experimental study on the coupling characteristics of single tank sloshing and ship motion in transverse waves is carried out,the physical quantities such as the change of bulkhead pressure and ship motion are monitored,and the effects of incident wavelength,tank size and other factors on the results are discussed;Finally,EMD-FFT method is used to decompose the pool test data in frequency domain,and the generation mechanism of high-frequency force and low-frequency force in the coupling process of tank sloshing and ship motion is revealed.(4)A fully nonlinear numerical model of internal field sloshing external field wave hull motion coupling is established by CFD method,and the nonlinear and nonstationary dynamics of single tank ship is studied.Firstly,the numerical simulation of motion characteristics of tankless ship in transverse waves is carried out,and the dimensionless roll angle and other numerical simulation results are compared with the pool test results;Secondly,the numerical simulation of the coupling characteristics of tank sloshing and ship motion in transverse waves is carried out,and the dimensionless rolling angle and sloshing pressure are compared with the pool test results;Finally,the coupling characteristics of tank sloshing and ship motion in oblique wave are analyzed,and the generation mechanism of high-frequency force and low-frequency force in the coupling process of tank sloshing and ship motion in oblique wave is revealed.(5)Taking KVLCC ship as the research object,the nonlinear and nonstationary dynamics of multi tank ship is studied based on the fully nonlinear numerical model of internal field sloshing external field wave hull motion coupling.Firstly,the coupling characteristics of multi tank sloshing and hull motion in waves are studied.The effects of wavelength,wave height,speed and whether there is a tank on the coupling characteristics of tank sloshing and hull motion are discussed.The effects of the number of tank devices and the liquid carrying rate of multi tank on the overall dynamic response of the ship are studied;Secondly,the coupling characteristics of variable mass multi tank sloshing and ship motion in waves are studied,the effects of liquid filling and ship motion on tank sloshing are analyzed,and then the effects of liquid.filling and tank sloshing on ship pitch and heave motion are discussed.