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.

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.

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.

A numerical study of vortex-induced vibration (VIV) related to a flexible pipe system subjected to external current and internal flow was performed mainly to investigate the complex vibration response of the flexible pipe due to the coupled effect of external current and varying-density internal flow. The numerical model was validated through mesh dependency and fluid-structure interaction (FSI) analysis. A coupled correlation analysis method, combined with a 3D position-frequency-energy (PFE) spectral analysis technique, was proposed to reveal the spatial multi-mode competition along the flexible pipe span. It is shown that the increase in the velocity and density of internal flow amplifies the spanwise in-line mean deflection, but has limited effect on the dominant vibration mode. The vibration modes at the amplitude peak and trough are significantly different. High order vibration modes, characterized by classical“8”-shaped vibration trajectories, are dominant around the amplitude peak, but low order vibration modes become predominant, and phenomena of spatial multi-mode competition with chaotic vibration trajectories are favorable at the amplitude trough.

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.

A hull structure is prone to local deformation and damage due to the pressure load on the surface. How to simulate surface pressure is an important issue in ship structure test. The loading mode of hydraulic actuator combined with high-pressure flexible bladder was proposed, and the numerical model of the loading device based on flexible bladder was established. The design and analysis method of high-pressure flexible bladder based on aramid-fiber reinforced thermoplastic polyurethane was proposed to break through the surface pressure loading technology of ship structures. The surface pressure loading system based on flexible bladder was developed. The ultimate strength verification test of the box girder under the combined action of bending moment and pressure was carried out to systematically verify the feasibility and applicability of the loading system. The results show that the surface pressure loading technology can be used well for applying uniform pressure to ship structures. Compared with the traditional surface loading methods, the improved device can be applied with horizontal constant pressure load, with rapid response and safe process, and the pressure load is always stable with the increase of the bending moment load during the test. The requirement for uniform loading in the comprehensive strength test of large structural models is satisfied and the accuracy of the test results is improved by this system.

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.

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.

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.

To further investigate the forming mechanism and springback characteristics of strips under multi-square punch forming (MSPF) considering partial-unloading effects, a series of concave forming tests of strips are conducted on the MSPF machine. This paper aims to reveal the physical mechanism of the elastic-plastic deformation in the MSPF process considering the effect of the forming approaches, and derive appropriate mathematical interpretations. The theoretical model is firstly established to analyse the concave forming mechanism and springback characteristics of the strip, and its accuracy is then validated by experimental data. The forming history and load evolutions are depicted to explore the required forming capacity through the proposed analytical method. Besides, the parametric studies are carried out to discuss their effects on the springback of the strip. The results suggest that the deformation paths of the strip are influenced by the forming approach, and the springback of the strip in convex forming is larger than that in concave forming.