With the rapid development of the transportation industry, ship-bridge collision accidents occur from time to time and bring about loss of life and property. Ship-bridge anticollision facilities can reduce the damage of ships while protecting the bridge structure. In view of the shortcomings of traditional steel box, such as high stiffness and unchangeable protection position, a new self-floating ship-bridge anti-collision device is designed based on gradient foam aluminum composite sandwich structure. A ship-anticollision device-bridge pier collision model considering pile-water-soil coupling effect was established by finite element software LS-DYNA. The damage characteristics of ship-anticollision device-pier under typical collision loads were studied, and the crashworthiness of anticollision device under cases with different ship speed and ship collision angle were evaluated. The results show that the anticollision device has excellent buffering and energy absorption characteristics, which can effectively reduce the peak value of collision force, prolong the collision time, reduce the damage of pier and effectively reduce the damage of bow structure.

As an important hub connecting offshore oil and gas fields and offshore platforms, unbonded flexible pipes play a vital role in marine production. As one of the main bearing parts of flexible pipes, the failure of the tensile armor layer will threaten the integrity of a pipeline system. Therefore, it is of great theoretical significance and engineering practical value to clarify the influence mechanism of various defects on the mechanical properties of the tensile armor layer and to study the mechanical behavior of the tensile armor layer. The axial compression performance of the tensile armor layer of an unbonded flexible pipe with defects was studied by numerical simulation method. A five-layer unbonded flexible pipe axial compression finite element model was established. The effects of non-metallic layer defect size, interlayer friction coefficient and steel strip fracture on the axial compression stiffness and critical buckling load of the flexible pipe were studied. The research results show that the decrease in the friction coefficient caused by the increase in the annular water content will significantly reduce the critical buckling load, and that the defects in non-metallic layer and the fracture of steel strip will significantly reduce the axial compression stiffness and critical buckling load. Therefore, in engineering, more attention should be paid to the annular water content and the structural integrity of each layer. The results can provide a reference for flexible pipe design and integrity management.

The control of low-frequency broadband excitation and acoustic radiation of ship thrusters is of great significance for the acoustic stealth performance of ship. The control of low-frequency broadband excitation and induced sound radiation in a combination thruster with a front stator was investigated in this paper. Starting from the theoretical prediction model of low-frequency broadband excitation for rotors, the influence of parameters such as flow field, geometry, and operating conditions on the broadband force of rotors was systematically calculated and analyzed. Three directions to control the broadband excitation of rotors were proposed: (1) improving the distribution of turbulent flow fields to make them as uniform as possible; (2) improving the geometric design of the rotor to reduce the pulsating load component;(3) improving the matching design of various components of the thruster and reducing the rotational speed at the same speed of ship. Based on several research achievements, control research was conducted on the low-frequency broadband force and sound radiation of the rotor of a combined thruster. It is concluded that the optimization of the hydrodynamic shape of the stern appendage and the optimization of rotor geometric parameters combined with the efficiency enhancement design of the duct and stator can control the low-frequency broadband force and sound radiation of the rotor to a certain degree, and that the optimization scheme reduces the peak and integral values of the low-frequency broadband noise of the rotor by about 3 dB. The research can provide certain reference for the control of low-frequency broadband force and induced sound radiation of ship thrusters.

The outboard discharge process of an underwater vehicle navigating in water results in an interaction between cross-flow and jet. The fluid dynamic characteristics generated by jet in cross-flow are important topics in the field of fluids. Based on Reynolds average and large eddy simulation method, a numerical calculation model of jet in cross-flow was established in this paper. Then the flow field characteristics of jet in cross-flow were explored in detail. The accuracy of the current method was verified by comparing the results of averaged velocity and fluctuating pressures with those in related references. The velocity and vorticity characteristics of the near-wall surface upstream and downstream of the orifice were investigated based on the results of numerical simulation. Additionally, the characteristics of the sound field in the vicinity of the orifice were analyzed. The results indicate that the impact of jet in cross-flow on the upstream near wall was confined within the range of 6 times the aperture from the orifice. Flow separation occurs in the downstreams of the orifice within a range of 2-14 times the bore size. Under the interaction between the crossflow and the jet flow, the characteristic vortex structure of counter-rotating vortex pairs (CVP) are formed in the downstreams of the orifice. The CVP is formed near the lower edge of the orifice and persists downstream. The vortex core gradually moves away from the wall along the flow distance, and the influence area gradually expands. The primary source of acoustic energy resulting from the interaction between the cross-flow and the jet is situated in close proximity to the wall. The acoustic energy level near the orifice is higher and exhibits a detached characteristic from the wall. Furthermore, the sound pressure level in the downstreams of the orifice is considerably higher than that upstream. The radiation of the sound field is dependent on the direction of flow and exhibits obvious directional characteristics.

In this paper, a fast prediction model was established for ship motion and load based on Gated Recurrent Neural Networks (GRU). GRU neural network is a concise and efficient recurrent neural network that captures the temporal information of training samples to establish a model for predicting unknown samples. The forecast model consisted of two independent GRU neural networks used to predict ship motion and load respectively. The historical ship pitch and heave data were jointly used as the input of the motion prediction model to predict the ship pitch and heave in the next few seconds. The motion prediction results were used as the input of the load prediction model to achieve the prediction of the vertical bending moment in the midship. The method was validated through model test data, and the results showed that the prediction results at different lead times were in good agreement with the test results in terms of amplitude and phase, verifying the feasibility of the established ship motion and load prediction model.

In order to understand the motion characteristics of amphibious aircraft planing in head waves, in this paper, the Chinese numerical tank-Cartesian grid finite difference method was used to study the planing motion response characteristics of an amphibious aircraft in waves under different wave conditions. The effects of wavelength and wave height on heave and pitch response of the aircraft and the vertical overload of mid-ship and stem were summarized. Based on the step-by-step method, the Navier-Stokes equation was discretized in space. The immersed boundary method was used to capture the boundary of complex objects and accurately simulate its large motion. At the same time, the THINC/SW algorithm was used to effectively simulate the violent motion of free surface. The results show that the wavelength and wave height have a great influence on the planing motion response of the amphibious aircraft. With the increase of planing speed, the pitch resonance wavelength increases, and the heave resonance wavelength decreases first and then increases, while the linear correlation between the heave and pitch response of the aircraft, the vertical overload of the mid-ship and stem and the wave height will also be weakened.

Based on the SPH numerical simulation method, this paper presents an analysis of the wave variation of regular and irregular waves propagating along an inshore island reef with a floating structure, and the dynamic response of a tethered floating structure under the island reef topography, respectively. The results show that the floating structure attenuates irregular waves better than regular waves when a tethered floating structure is installed in front of the shore reef, and changes in wave height have little effect on the attenuation of floating structure wave height. However, changes in wave period have a greater impact on the attenuation effect of the floating structure, and the floating structure is less effective in attenuating the wave height of long-period waves. The maximum vertical displacement, maximum longitudinal rocking angle and maximum transverse oscillation values of the floating structure all show an increasing trend with wave height increasing under different regular wave height conditions, with the maximum longitudinal rocking angle being the most sensitive to changes in wave height and the maximum vertical displacement being the least sensitive.

In order to investigate the hydrodynamic performance of ships in restricted channel of polar regions, a hybrid Green’s function method based on three-dimensional potential flow theory was established, in which, the free-surface Green’s function was taken as the kernel function in the fluid domain of channel. The ice sheet on both sides of the channel was modeled as a thin elastic plate. The ice-surface Green’s function, which automatically satisfies the ice-covered water surface, seabed and radiation conditions, was adopted in the fluid domain below the ice. The boundary integral equations were established with the two kernel functions above respectively. To improve the efficiency of computation, the influence coefficients related to the wave component of the ice-surface Green’s function were obtained based on its analytical integral over vertical line segment. On the basis of above method, a computer program was developed. By taking a barge with available computational data as the research object, the effects of control surface length and mesh density on the convergence of calculation were first discussed, and the reliability of the method and program was verified. Then further calculations and analysis were conducted on the hydrodynamic coefficients under different channel widths and ice thicknesses. From the numerical results the oscillatory phenomenon was observed in the hydrodynamic forces of the ship in water channel confined by ice sheets. And with the decrease of channel width and increase of ice thickness, the oscillation becomes stronger.

Numerical modelling based on Navier-Stokes equations and model experiment for studying liquid sloshing have the limits of low computational efficiency and high economic cost. Therefore, to predict the hydrodynamic pressure and wave height, the time-histories to numerical and experimental results were reconstructed in this paper through the neural network model. The total numerical and experimental pressures and free surface elevations were taken as training samples, and CNN, RNN and LSTM with strong repretational ability were used to reproduce the sloshing responses. The internal structural parameters of the neural network were systematically adjusted, besides, the errors and correlations between the predicted and actual values were analyzed. The results show that the error is lower than 4% and the correlations of both RNN and LSTM reach 0.88, which is in general superior to CNN, and that LSTM is optimal in predicting the long sequence data. Overall, three surrogate models can well predict the sloshing wave height and pressure, and are promising in the study of liquid sloshing.

For a ship turning in the ice area, the bow shoulder and stern of the ship are more vulnerable to ice load of large amplitude, posing a threat to the safety of the hull structure. In this paper, the sea ice circumferential crack expansion analysis method was used to simulate the dynamic process of ship-ice interaction for ice breaking ship during turning. The random characteristics of ship-ice collision in different hull areas were analyzed, making an identification of the typical local ice pressure time course, to obtain the main characteristics of different types of ice pressure, such as period, amplitude and distribution law, and analyze the danger degree of each hull area under turning ice breaking scenario. The results show that there is a negative correlation between the period and amplitude of local loads, and that in the bow area, the short period "pure triangle" type loads account for 63.79% of the total and the peak value accounts for 82.4% of the whole ship. So the bow area is the key area of a ship in the turning ice breaking scenario. The method adopted in this paper provides an effective means to study the ship-ice interaction, and the relevant calculation results can be used as load input for the design of ice-resistant structures of polar ships.