Experimental Study on Sloshing Characteristics of Accumulator under Ocean Condition

The development of marine resources and the construction of coastal islands need a reliable energy supply. The floating nuclear power plant (FNPP) is a combination of small nuclear reactors and offshore platforms, and it can be used in many fields such as offshore power supply, combined heat and power, and seawater desalination treatment. FNPP has the advantages of high power density, sustainable power generation, and low carbon emission. But due to environmental factors such as wind and waves on the sea or ship navigation, FNPP will generate complex motions in actual sea conditions. Liquid sloshing will occur in accumulators and other liquid storage tanks subjected to additional inertial forces under moving conditions. The free surface fluctuation will disturb the measurement of critical parameters such as liquid level, and the fluid impact load will affect the operation and maintenance of equipment. So measurement experiments were carried out based on the 6-DOF motion platform to study the sloshing characteristics and pressure variation rule of the accumulator. The pressure surge was studied by multi-directional pressure sensors, the free surface sloshing process was obtained by the high-speed camera system, and the natural frequency of the accumulator was obtained according to the model equivalent and mathematical analysis. The results show that under rolling motions, the pressure variation period is consistent with the motion period and the pressure amplitude can be determined by motion angle. The motion forms of liquid surface are basically stationary waves and marginal hydraulic jump, and the pressure measurement results show a regular sine and cosine variation, so the system analysis model under rolling conditions can be reasonably simplified based on the above analysis and safety margin assessment. Under horizontal sloshing, the additional inertial force will induce many kinds of nonlinear liquid surface sloshing. Based on time and frequency domain analysis, it can be seen that the pressure variation rule is mainly dominated by natural frequency, excitation frequency, and frequency multiplication. The pressure variation amplitude increases sharply and reaches the peak value under resonance conditions. There are unstable evolution processes and chaotic sections of pressure surge under specific sloshing conditions, where the pressure variation has randomness and initial value sensitivity. In addition, the breaking and rotation of the free surface will occur near the resonance frequency. Under the coupled motion, the pressure at the measurement point is affected by the characteristics of single degree of freedom motion and the coupling form of different motion. The coupled motion can be disassembled and analyzed based on considering the phase difference. In summary, the study can provide an analytical basis for sloshing research of liquid storage equipment and provide a reference for structural improvement and sloshing suppression optimization.