Polar ship icing is formed when supercooled droplets from the air or seawater fall onto ships. After the crystal nuclei in the supercooled droplet are formed, they solidify and release heat, so that the temperature returns to the freezing point and forms an ice water mixture, which is called recalescence. This process is the beginning of the freezing stage. The phase field method was used to simulate the recalescence process of water under different undercooling conditions, and the icing morphology and ice-phase proportion after recalescence were studied. The results show that the undercooling has a certain effect on the results of recalescence. The dendrite growth rate in the process of recalescence is fast at first and then becomes slow. The proportion of ice phase increases with the increase of undercooling. When the undercooling increases from 30K to 45k, the proportion of ice phase increases from 11.92% to 29.17%.

In this paper, the dynamic response characteristics of aluminium honeycomb sandwich panels under repeated rigid wedge impacts and ice wedge impacts were experimentally studied by using the horizontal impact test apparatus. The impact force-displacement curves and the structural deformation properties were obtained. Results show that with the increase of collision numbers, the peak value of collision force increases continuously, the contact time decreases significantly, the local indentation and global bending deformation of face sheet increase gradually, the compressive deformations of the honeycomb cores enlarge gradually and finally the densification phenomenon appears. Due to the ice fragmentation phenomenon in the collision process, the contact area under ice wedge impact increases. Compared with rigid wedge impact, the midpoint permanent deflection of top facesheet under ice wedge impact is smaller, but the local damage area is obviously larger. With the increase of collision numbers, the plastic accumulated deformation of honeycomb sandwich panel evolves from a plastic hinge line to an elliptic plastic zone.

Mn25Al7 steel is a new type of lightweight and high-strength marine steel, and the fatigue properties of Mn25Al7 steel have not been studied in relevant experiments. In this paper, the fatigue tests of typical nodes such as base metal, butt welded joint and T-welded joint of Mn25Al7 steel were carried out, and the fatigue grade curve of the typical nodes was obtained based on the nominal stress method and the hot stress method, respectively, and compared with the fatigue grade curve of the existing standard. The fracture morphology of the three samples was observed, and the crack propagation law and fracture mechanism were analyzed. The test results show that the fatigue life of Mn25Al7 steel base metal is higher than that of ordinary steel designed by the specification. The specification underestimates the fatigue life of butt weld joints of base metal and smoothed toes, but can accurately evaluate the fatigue life of T-weld joints. By comparing and analyzing the difference in damage rate of the three specimens, the fracture morphology was further systematically analyzed. It is found that the initial crack source and welding residue will reduce the fatigue strength. This study can provide a theoretical basis and experimental support for the prediction of fatigue life of marine high-strength steel.

A rigid polyurethane foam (RPUF) buffer was designed to reduce the load of a projectile during high-speed water entry. Based on the Hopkinson compression bar technique, the density and strain rate effects of RPUF under impact loading were obtained, and its macroscopic constitutive model was established. Based on the Arbitrary Lagrangian-Eulerian (ALE), the numerical simulation model of the projectile during high-speed water entry was established. The numerical simulation of the projectile during high-speed water entry with different densities of RPUF was carried out. The dynamic failure process and motion parameters of the buffer during the water entry were obtained, and the influence law of the density and thickness of RPUF on the load reduction characteristics was analyzed. It can be found that the strain rate effect of RPUF is not obvious, but the density effect is obvious, and that, as the density and thickness of RPUF increase, the load reduction performance of RPUF increases.

In this paper, for the demand of low-frequency hydrodynamic noise control in submarine sonar dome, based on the coupled vibration equations of the plate and acoustic cavity, the hydrodynamic self-noise calculation model of the multi-layer composite plate was established by using the acoustic vibration transfer matrix, modal expansion method and wave vector-frequency spectrum of turbulence boundary layer pressure. According to the analysis of dynamic vibration absorption characteristics, the vibration and noise equations of the plate under the control of distributed energy absorption unit were formed, and the hydrodynamic self-noise of the distributed power absorption composite sonar domes was evaluated. The hydrodynamic self-noise reduction effect was verified through the large cavitation channel tests, providing technical support for the design of advanced low-noise sonar domes.

The large number of internal solitary waves in the South China Sea seriously threaten the safety of offshore engineering operations. In this paper, the vector form intrinsic finite element (VFIFE) method was used to analyze the dynamic characteristics of deep-sea steel lazy wave risers (SLWR) under the action of internal solitary waves. The dynamic model of a deep-sea steel lazy wave riser considering soil reaction in touchdown zone and internal solitary wave load was established. The internal solitary wave load was solved according to the mKdV equation. Fortran calculation program was compiled based on vector form intrinsic finite element beam element. The displacement extremum and variation trends of tension and bending moment of a riser under different incident angles were analyzed. The dynamic characteristics of a steel lazy wave riser and a simple steel catenary riser under internal solitary waves were compared. The results show that under the action of internal solitary waves, the steel lazy wave riser will have a greater displacement response, especially the upper section will have a greater horizontal displacement. Compared with the simple steel catenary riser, the steel lazy wave riser has a more significant tension variation amplitude and a more complex bending moment variation trend.

The new conceptual artificial seabed can effectively improve the adaptability of disastrous marine environmental factors such as strong winds, huge waves and surface currents, but the considerable impact force generated by internal solitary waves is a key factor affecting the operation safety of the artificial seabed. This paper presents a study on hydrodynamic forces and flow field characteristics of the new conceptual artificial seabed under the action of internal solitary waves. First of all, the eKdV equation was used as the theoretical model. A three-dimensional numerical flume was established by using the wave-making method of velocity inlet, and the numerical wave-making of internal solitary waves was achieved. On this basis, the numerical waveform was compared with the theoretical and experimental waveforms, and the feasibility of the numerical method was verified. Finally, hydrodynamic forces exerted by internal solitary waves on the artificial seabed were calculated, the characteristics of forces induced by internal solitary waves of various amplitudes on the artificial seabed were studied in detail. Besides, the velocity field and the vorticity field around the artificial seabed were analyzed. The results show that, with the increase of the amplitude of the internal solitary wave, the drag force, vertical force and lift force on the artificial seabed gradually increase, and the drag force and vertical force are much greater than the lift force. When the internal solitary wave passes through the artificial seabed, both the particle velocity of the fluid and the vortex intensity around the artificial seabed increase. This study provides an effective numerical calculation method for the prediction of internal solitary wave forces and the analysis of flow field characteristics of large underwater engineering structures.

As wind speed and wave height are the main loading parameters in offshore facility operations, their accurate prediction is of great importance. In order to solve the problem of wind speed and wave height prediction with complex and changeable characteristics, a wave height forecast model was established based on prototype monitoring data and Long-Short-Term Memory (LSTM) neural network. Firstly, the correlation analysis of wind speed and wave height was carried out based on prototype monitoring data. Then, a one-step-ahead wind speed forecast model and wave height forecast method were established based on LSTM neural network. Different prediction models with different time intervals (t=0.5 h, 1 h, 3 h) were built to verify the accuracy. Finally, a joint prediction model based on two forecast models was obtained with a prediction error of only 0.12 m at the time interval of 0.5 h.

LNG cryogenic hoses are used for connecting floating structures to transport LNG efficiently and continuously in the process of LNG deep-sea transportation and unloading. Making sure that cryogenic flexible hoses operate safely and reliably is crucial for the LNG mining system. The main application conditions of LNG cryogenic hoses are ship-ship side-by-side (SBS) unloading, ship-ship tandem unloading, and ship-shore refueling. The hydrodynamic analysis and calculation of LNG cryogenic hoses were carried out according to these application conditions, and sensitivity analysis of the global layout parameters of the hoses was performed. The LNG cryogenic hose with a diameter of 12 inches was used as the object of study. Considering the combined effects of wind, wave and current marine environmental loads, the LNG cryogenic hose was modeled and subjected to finite element calculations, hydrodynamic analysis and computational checks under different application conditions based on Orcaflex software. The critical response was studied, and sensitivity analysis was performed on the global configuration design parameters of the cryogenic hose and the lifting speed. The results show that increasing the hose length and the distance between the connection points leads to an increase in the curvature extreme value and a decrease in the tension extreme value for both tandem and SBS unloading conditions. The lifting speed decreases the tension extreme value and increases the curvature extreme value during ship-shore refueling condition. The study can provide a theoretical basis for the design optimization of LNG cryogenic hoses and has reference significance for the configuration arrangement of FLNG unloading systems.

The damping-corrected potential flow theory was used to study the ship-to-ship transfer system. The CFD numerical model of ship-to-ship transfer system was established and the theory of potential flow was modified by applying viscous damping lid on the free water surface between two ships. The time domain results of ship-to-ship transfer system with and without correction were compared and analyzed. The results show that the calculation results of the motion response of each degree of freedom of the two ships and the force of each mooring or fender without viscosity correction are higher than the corrected results, and that it is very necessary to consider the correction of fluid viscosity.