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.

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.

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.

This paper aims to propose an improved theory of homogenization for acoustic coatings, the acoustic coating with periodic cavities can be considered equivalent to a uniform layer, thus improving the computational efficiency of sound absorption. Based on the traditional homogenization theory, parameters of equivalent density, modulus, and thickness for the acoustic coating by are derived incorporating the potential flow theory and the Minnaert resonance scattering theory. The sound absorption coefficient of the coating is then obtained through analytical calculation. This paper specifically addresses the effectiveness, efficiency, and adaptability of the proposed algorithm, thus offering technical support for accurately predicting the sound absorption coefficient of acoustic coatings within the middle and low-frequency range.

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.

With the development of high flow turbopumps, the size and speed of impellers have increased rapidly, resulting in the coupling vibration phenomenon of the turbopump. In order to keep the turbopump running smoothly and reduce its vibration and noise, the coupling dynamics characteristics of the turbopump rotor system were studied in this paper. Firstly, based on the simplified finite element model of the turbopump, it was found that when the rotor frequencies of different orders approach each other in the Campbell chart, two coupling characteristics phenomena of curve turning and merging would occur. Further analysis of the rotor modes conducted for the coupling characteristic phenomenon showed the different orders of the coupling characteristic modes would affect each other. Secondly, a two-degree-of-freedom system was used to simulate the coupling characteristics of the rotor, and then the effects of coupling degree, damping and gyroscopic torque on the characteristics were analyzed. Finally, investigation on the coupling dynamic characteristics of the two-degree-of-freedom system revealed that the dynamic response would change abruptly when the curve turning and merging occurred, leading to the increase of the coupling vibration amplitude and even the instability of the system. The research results could provide theoretical guidance for the safe and stable operation of rotor systems.

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.

In view of the numerous and complex structures of ship machinery, equipment and the coupling of vibration transmission paths, a method of underwater radiated noise prediction based on BP (Back Propagation) neural network was proposed in this paper. A BP neural network based on gradient descent algorithm and Bayesian regularization algorithm was constructed respectively. Vibration data was taken as input, hull radiation noise was taken as output, and root mean square error (e_RMSE) and mean absolute error (e_MAE) were taken as evaluation indexes of model prediction accuracy. The results show that the generalization and robustness of Bayesian regularization BP neural network is better than that of gradient descent algorithm BP neural network. The error of Bayesian regularization is less than 3 dB, and the proposed method has good applicability in the field of ship radiation noise prediction.

In order to improve the propulsion performance of contra-rotating propellers and reduce the cavitation effect, an end plate was applied to the contra-rotating propeller. The cavitation performance and propulsion performance of the end-plate contra-rotating propeller were analyzed. The RANS method with Schnerr-Sauer cavitation model was used for analyzing. Then the propulsion performance of contra-rotating propellers composed of conventional skewed propellers and end-plate propellers were checked for comparison. It is found that the addition of an end-plate makes the contra-rotating propeller possess better anti-cavitation performance. The sheet cavitation range is reduced by about 59% in the bollard state (J=0), and the cavitation is delayed when J=0.1. In addition, under the condition of low advance speed, the end-plate contra-rotating propeller shows a higher propulsion efficiency by 0.9%~3.1% than the conventional one. The open water performance of the end-plate contra-rotating propeller was tested at different rotation speeds, and the data were in good agreement with the simulation results considering the cavitation model. In this study, an end plate is innovatively applied to the contra-rotating propeller, which is suitable for the propulsion and operation requirements of low-speed submersibles.

Aiming at the initial stress field generated by welding of ring-ribbed cylindrical shell structures with initial geometric defects after shape correction, this paper presents the study on the influence of initial stress field on the strength and stability of ring-ribbed cylindrical shell structures under the premise of considering geometric nonlinearity caused by large deformation. The finite element model of ring-ribbed cylindrical shell with initial geometric defects was constructed by using ANSYS software and the initial stress field was calculated. The strength and stability of ring-ribbed cylindrical shell with initial geometric defects and stress field were solved by arc length method. The comparison between the experimental results and the calculated results verifies the validity of the model. The analysis shows that the ultimate bearing capacity of the ring-ribbed cylindrical shell under hydrostatic external pressure is slightly reduced, and the regularity of the instability waveform is reduced, but the failure position remains unchanged.