Study On Liquid Sloshing Characteristic In Elastic Side Wall Tank With Compound Excitation

FPSO is known as "offshore oil factory" because it can preliminarily process and store the oil extracted from the seabed.However,due to the influence of wind,wave,current and other factors,the ship is subject to external excitation in many directions,and the liquid in tank sloshes along with the ship's motion.When the external excitation frequency approaches the low-order natural frequency of the liquid in the tank,the phenomenon of liquid sloshing in tank is violent,and the impact load caused by the liquid sloshing may generate structure response with the tank structure,which is dangerous to the bulkhead in serve cases.It is one of the key problems in tank structure design.Aiming at the compound external excitation of rolling and pitching,which mainly affects the motion of ships,the problem of liquid sloshing in tank with elastic side wall is studied.The main work is as follows:Firstly,in this paper,a 300,000-ton FPSO medium cargo tank is taken as the prototype tank,and the flowing oil is taken as the research object.At the same time,according to the principle of dynamic similarity between model experiments and prototype experiments,Reynolds Number and Froude Number are selected as the criterion of dynamic similarity,and the appropriate scale ratio is selected to establish the physical model.Besides,the experimental oils were deduced by Reynolds Number and Froude Number,and experiments were designed according to different experimental purposes.Secondly,in the light of elastic side wall tank,the characteristics of liquid sloshing in elastic side wall tank under three typical conditions of non-resonance,resonance and super-resonance are studied.The evolution process of free surface waveform,the time-domain and frequency-domain characteristics of the sloshing impact pressure on the side wall are mainly analyzed.The results are compared with the experimental results of the rigid tank to reveal the effect of the structural response of side wall tank on liquid sloshing.Thirdly,In the light of compound external excitation and single rolling excitation,the characteristics of liquid sloshing in elastic side wall tank are studied.The waveform evolution of free surface and the frequency domain characteristics of liquid sloshing impact pressure on the side wall and the top of tank are made contrastive analysis between elastic side wall tank and rigid tank to get effect of compound excitation on liquid sloshing.Fourthly,considering the compound external excitation and the structural response of the side wall of the tank,the sloshing problem in the elastic side wall tank under the compound excitation is studied under different external excitation frequencies,amplitudes and loading rates.The evolution process of the free surface waveform,the frequency domain characteristics of the liquid sloshing impact pressure of the side wall and the spatial distribution of impact pressure are mainly analyzed,which reveals the characteristics of liquid sloshing in an elastic side wall tank under compound excitation.The experimental results show that the side wall of tank is subjected to large sloshing impact pressure with compound excitation and structural response at low-load liquid condition and near the first natural frequency of external excitation,which can absorb the kinetic energy of the liquid in the tank,resulting in the peak value of sloshing impact pressure on the elastic side wall being lower than that on the rigid side wall.For the single rolling and compound excitation,it is found that the liquid sloshing impact pressure on the side wall of tank is related to the loading rate,and the sloshing impact pressure on the top of tank is related to the external excitation frequency.At the same time,the liquid sloshing problems in elastic side wall tank under compound excitation are investigated with low liquid load and finite liquid load.It is found that when the loading rate is 30%,the liquid sloshing impact pressure on the side wall of tank is the greatest,besides,the bulkhead near the liquid free surface and the top of tank are susceptible to large liquid sloshing impact pressure.Therefore,the two parts should be considered in the design of the tank structure.