With the continuous development and consumption of traditional land resources, the development and utilization of new water energy has become a new trend, and a large number of various floating structures have appeared. As the key to ensure the safe and stable operation of floating structures, mooring systems have always been the focus of the industry. In this paper, a large number of literature review and research were carried out on the existing floating structure mooring systems, the types of floating structures were summarized, the mooring system structures were analyzed from the aspects of the classification of the mooring systems, the way of chain distributions, the bottom anchorage foundation types and the new mooring systems, and the characteristics and advantages and disadvantages of various mooring cable materials were discussed. The static characteristics and dynamic response of the mooring systems were analyzed according to a large number of existing literatures, and the applicability evaluation and recommendation of various mooring methods were given through a comprehensive analysis of the water depth, seabed topography, geology, platform function, wind and wave conditions, economy and other aspects of the mooring engineering, and the shortcomings of the existing research were pointed out, and the current research direction still needs to be further developed.

Welding residual stress has a significant impact on the fatigue life of a welding structure. Meanwhile, welding residual stress is not invariable, but will be redistributed with crack propagation. Therefore, the coupling study of welding residual stress redistribution and crack propagation is very important to predict the fatigue life of a welded structure accurately. Based on thermal elastic-plastic finite element method and extended finite element method (XFEM), a fatigue life analysis method considering the coupling of residual stress redistribution and crack propagation was proposed in this paper. Taking the tensile fatigue sample of TC4 titanium alloy as an example, the redistribution of the welding residual stress along with crack propagation was studied with the extended finite element method. The welding residual stress distribution in front of the crack tip during crack propagation and the fatigue crack propagation a-N curve under the redistribution of weld residual stress were calculated by cyclic iteration. The calculation results show that the welding residual stress at the crack tip increases firstly and then decreases with the crack propagation. Compared with the results based on constant value of the residual stress, the extended finite element fatigue life analysis method considering the redistribution of the residual stress is more accurate to predict the fatigue lives of welding structures.

This paper presents an investigation on the target-guided coordinated control (TACC) of unmanned surface vehicles (USVs). In the scenario of tracking non-cooperative targets, the status information of the target can only be obtained by some USVs. In order to achieve semi-encirclement tracking of non-cooperative targets under maritime security conditions, a fixed-time tracking control method based on dynamic surface control (DSC) is proposed in this paper. Firstly, a novel TACC architecture with decoupled kinematic control law and decoupled kinetic control law was designed to reduce the complexity of control system design. Secondly, the proposed DSC-based target-guided kinematic control law including tracking points pre-allocation strategy and sigmoid artificial potential functions (SigAPFs) can avoid collisions during tracking process and optimize kinematic control output. Finally, a fixed-time TACC system was proposed to achieve fast convergence of kinematic and kinetics errors. The effectiveness of the proposed TACC approach in improving target tracking safety and reducing control output chattering was verified by simulation comparison results.

Ship motions induced by waves have a significant impact on the efficiency and safety of offshore operations. Real-time prediction of ship motions in the next few seconds plays a crucial role in performing sensitive activities. However, the obvious memory effect of ship motion time series brings certain difficulty to rapid and accurate prediction. Therefore, a real-time framework based on the Long-Short Term Memory (LSTM) neural network model is proposed to predict ship motions in regular and irregular head waves. A 15000 TEU container ship model is employed to illustrate the proposed framework. The numerical implementation and the real-time ship motion prediction in irregular head waves corresponding to the different time scales are carried out based on the container ship model. The related experimental data were employed to verify the numerical simulation results. The results show that the proposed method is more robust than the classical extreme short-term prediction method based on potential flow theory in the prediction of nonlinear ship motions.

In order to predict the critical buckling load of a filament winding thick composite cylindrical shell under hydrostatic pressure, the buckling governing equation of the thick cylindrical shell under hydrostatic pressure was obtained based on the nonlinear Sander theory, as well as the deformation geometry equation of the cylindrical shell and the constitutive relation of the filament-wound layer. An analytical method for predicting the critical buckling pressure of thick composite cylindrical shells under hydrostatic pressure was proposed by solving the governing equation. Then, critical buckling load of the thick shell with different filament-wound types and angles were calculated with FEM and compared with analytical results for verifying the accuracy and high efficiency of the analytical method. The influence of key parameters such as geometrical and material design on the critical buckling load of thick cylindrical shells was investigated based on the analytical method.

Path planning is one of the key technologies for autonomous navigation of unmanned vehicles. A good path planning method is of great significance to the intelligent development of unmanned vehicles. In the existing path planning research, the maneuvering performance of unmanned vehicles is not considered. In order to make the planned path have shorter voyage time, shorter path length and better path tracking ability, it is necessary to combine the maneuvering performance of unmanned vehicles with the path planning algorithm. In order to accurately predict the ship maneuverability, the channel-type unmanned catamaran was taken as the research object, and simulation tests of three planar motion mechanisms were carried out by CFD technology. Simulation results were fitted with different hydrodynamic models, and corresponding hydrodynamic derivatives were calculated. The MMG model was used to establish a mathematical model of ship maneuvering motion to simulate the turning motion and Z-shape motion of the unmanned catamaran. The influence of different hydrodynamic models on the simulation results was analyzed, and the maneuvering pre-diction of the unmanned catamaran was realized.

In recent years, shipowners have become increasingly concerned about the actual performance in the real marine environment. At present, ship design optimization is mainly conducted based on performance in still water which has a certain difference from real-sea performance. The factors influencing the powering performance of ships in wind and waves were investigated taking series oil tankers, bulk carriers, and container ships as the research subjects. The theory of two-dimensional strip was used to calculate the added resistance under typical sea states BF6 and BF8. The propeller was redesigned using graph method to research the influence of light running margin in the wind and waves. The results show that the principal dimensions have a significant impact on the added resistance of oil tankers and bulk carriers, and have a relatively small impact on container ships. Therefore, it is necessary to consider the ship type separately when optimizing the powering performance in wind and waves. In addition, with the increase of the light running margin, the reserved space for power becomes increasingly sufficient.

The omnidirectional waterjet propeller, as a lateral thruster or dynamic positioning device, has attracted more and more attentions. Its hydrodynamic characteristics are a key factor in meeting the application requirements. However, there are limited related studies. The numerical simulation of hydrodynamic performance of the omnidirectional waterjet propeller was carried out in this paper. Based on the STAR-CCM+ software, the steady RANS method was applied to investigate the hydrodynamic performance of an omnidirectional waterjet propeller under two conditions, i. e. static water and flowing water. The results show that the hydrodynamic performance of both thrust magnitude and directionality is greatly affected by the magnitude and direction of incoming flow, and the influence is greater when the rotational speed is lower. The research in this paper reveals the thrust loss mechanism of the omnidirectional waterjet propeller. Its hydrodynamic performance should be evaluated according to its working conditions, and the low rotational speed operation should be avoided to ensure that hydrodynamic performance requirements are met.

Some ship equipment with weak anti-shock properties has the flowing characteristics such as small space proportion, variable and large shock loads, dynamic load changes, rigid-flexible state transitions and passive operation. Howerver, these needs cannot be met by traditional vibration isolation devices. Therefore, this paper proposed a novel integrated bi-directional vibration isolation device and conducted the corresponding structural design. Then, the dynamic model of the vibration isolation device was established to predict the dynamic response under complex loading and to explore the effects of frequency and damping ratio on the anti-shock properties of the device. Finally, the test bench for the vibration isolation device was built to verify the validity of the structural design and theoretical analysis. The results show that the direction of the impact load and dynamic sway load affects the anti-shock properties of the vibration isolation device, When the loads act in the same direction, the anti-shock performance will be improved, whereas when the performance will be decreased if the loads act in opposite directions. As the frequency or damping ratio increases, the anti-shock properties of the vibration isolation device gradually decrease, thus requires optimization based on key performance indicators. The test results of the vibration isolation device have smooth curves without distortion, and the overall trend is basically the same as that of the theoretical calculation results, which can verify the validity of the structural design and theoretical analysis. The results of the study can provide useful guidance for the design of vibration isolation and anti-shock for weak ship equipment.

In order to understand the influence of bow shape on ice resistance and provide guidelines for hull line design in the early design stage, an investigation of the impact of bow shape on ice resistance for the Arctic LNG carriers is carried out based on semi-empirical methods. Firstly, some typical semi-empirical formulas developed for ice resistance estimation of cargo carriers in different ice conditions are summarized. Then, formulas appropriate for ice resistance estimation of Arctic LNG carriers under different ice conditions are verified according to the result comparison between semi-empirical formulas and experimental tests. The comparison result indicates that the Lindqvist formula is appropriate for ice resistance estimation in level ice conditions, Zuev and Dobrodeev formula for ice resistance estimation in broken ice conditions, and Dobrodeev formula for ice resistance estimation in brash ice conditions. After that, the parameters considered in the selected formulas are summarized, and the influence of critical parameters on ice resistance is analyzed. Some parameters describing the ship's bow shape characteristic like ship breadth, waterline angle and stem angle greatly influence the ice resistance. Ice resistance increases with both the growth of ship breadth under all ice conditions and the growth of stem angle in level ice and broken ice conditions while ice resistance decreases with the development of waterline angle under all ice conditions. Finally, the optimization of the bow shape is discussed, and an optimized bow shape with both a large waterline angle and low stem angle is proposed. The optimized bow shape can decrease ice resistance by 9.9% in the level ice condition and reduce ice resistance by 11.3% in the brash ice condition.