Based on the open source programme OpenFOAM, a numerical model was established to investigate the behavior of the interaction between waves and the newly-developed open breakwaters with elliptical arc-plate. The numerical model was verified by using theoretical wave surface and previous experimental results. Focusing on the three types of open structures, such as double flat plate, flat-elliptical arc-plate and double elliptical arc-plate open breakwater, a total of 90 cases were designed to analyze their wave attenuation performance. Considering the indexes of transmission coefficient, reflection coefficient and energy dissipation coefficient comprehensively, the numerical results indicate that the open breakwater with flat-elliptical arc-plate exhibits a low-level transmitted wave energy and a high-level reflected wave energy, while the open breakwater with double elliptical arc-plate exhibits a high-level transmitted wave energy and a low-level reflected wave energy under most working conditions. Further analysis revealed that when the structure is placed above the hydrostatic level, the open breakwater with flat-elliptical arc-plate has higher wave attenuation performance compared with the double flat plate type and double elliptical arc-plate. Therefore, the open breakwater with flat-elliptical arc-plate could be selected when it is submerged at suitable depths based on hydrodynamic conditions in engineering practice. This research provides design references for the breakwaters which could simultaneously meet the requirements of wave attenuation and water permeability.

Currently, when predicting the ship maneuvering motion in waves based on the mathematical model of ship maneuvering motion, hydrodynamic coefficients are mostly obtained through the model test or numerical prediction in still water, without considering the influence of waves on ship maneuvering hydrodynamics. Therefore, establishing the prediction method of ship maneuvering motion hydrodynamics in waves is essential for accurately predicting ship maneuvering motion. In this paper, the multi-degree-of-freedom motion of ship in waves was numerically modeled based on the overset grid method. The hydrodynamic modeling, free surface treatment and wave simulation methods were presented. The numerical simulation method of ship maneuvering hydrodynamic forces in waves was established. The hydrodynamic model test and numerical prediction of S175-ship in regular waves were carried out, and the influence of waves on ship hydrodynamics was evaluated. The numerical prediction results were compared with the model test results to verify the reliability and practicability of the numerical simulation method. The research in this paper can provide a guidance for the improvement of the ship maneuvering prediction in waves.

To investigate the collision dynamics of a marine rotating machinery integrated with an airbag-raft-limiter system under the influence of heaving motions, a dynamic model of an asymmetric system incorporating a limiter was developed. This model took into account the effect of the ship heaving motion and the limiter gap on the coupled airbag-raft-limiter system. The equations of motion were given dimensionless treatment to facilitate computational analysis. The study examined the influence of rotor speed, heaving amplitude, and limiter gap on the system’s dynamics utilizing nonlinear dynamics analysis techniques including phase diagrams, spectral responses, and energy trajectory diagrams. The findings indicate that an increase in heaving amplitude leads to collisions between the system and the limiter, causing a significant amplitude decrease while triggering a transition of motion from quasi-periodic state to chaotic state. Additionally, the collision alters the energy trajectory of the system, moving from a uniform distribution towards the collision zone.

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.

This paper focuses on proposing a finite-time command filtered backstepping robust adaptive dynamic positioning control method to deal with the thruster dynamics, parameters uncertainty, input saturation and unknown external disturbance problems. The proposed method not only has the advantages of the command filtered backstepping, but also can guarantee the control system convergence in finite time. Firstly, adaptive neural network was used to estimate uncertain functions in the system. Secondly, the thruster input saturation issue was addressed with a finite-time auxiliary dynamic system. Finally, based on the uncertain estimation and the FTADS, a finite-time command filtered backstepping (FTCFB) control law was introduced, and the system tracking errors and parameter estimating errors were proved to be convergent in finite time by using Lyapunov stability theory. Additionally, the effectiveness of the proposed positioning control method was verified by numerical simulations.

In order to analyze the impact attack angle on the oblique water-entry performance of projectiles, the oblique water-entry tests of a projectile under multiple conditions were carried out based on the high-speed photography technology. The effects of the attack angle on the cavity evolution and motion characteristics of the projectile were studied. Based on finite volume method and overlapping grid technology, a numerical method for oblique water-entry of projectiles was established. The water-entry stability and force characteristics of the projectile were compared and analyzed with the attack angle set as 0°, ±0.5°, ±1.5°, ±2.5°, and ±3.5° respectively. The reliability of numerical simulation was validated by comparing the simulated results with the experimental results. It is shown that when the attack angle is positive, the projectile will deflect counterclockwise and deviate upward, while it will deflect clockwise and deviate downward when the attack angle is negative. When the attack angle is zero, the projectile motion is stable, and the simulation results under the same condition are consistent with the experimental ones. With the increase of the absolute value of the attack angle, the absolute value of the deviation and deflection of the projectile presents an increasing trend simultaneously, and the time of the tail-slapping of the projectile is gradually advanced. When the absolute value of the attack angle is the same, the first tail-slapping of the projectile occurs earlier when the attack angle is less than 0°, and the water-entry stability of the projectile is worse. Influenced by the attack angle, both the drag and lift of the projectile will shock violently at the early stage of water-entry. With the increase of the attack angle, the lift of the projectile presents a decreasing trend, while the drag is not significantly influenced by the attack angle, except that the drag is relatively large at attack angle of −3.5 °.

Reliable experimental data are crucial for understanding the performance of Floating Wind Turbine (FWT) systems in complex wind-wave-current marine environments. This paper presents the results from 1∶70 scale model tests conducted in a wave basin to investigate the motion response characteristics of a new 12 MW semi-submersible FWT. The experimental design incorporated improvements, including a large-scale wind generation system with a rectifier network, aiming to provide a stable wind field for the experiment. The experimental results indicate that wind loads primarily exert static effects, as reflected by changes in response mean values. On the other hand, increased wave parameters predominantly contribute to dynamic effects, which are demonstrated through changes in response standard deviations. Aerodynamic damping effect is primarily manifested in the coupling responses of pitch and surge, as well as at the natural frequency of pitch motion. The action of current significantly reduces response at the natural frequency of pitch, although it concurrently amplifies platform’s surge and yaw responses. This study contributes valuable insights into the dynamic behavior of large-scale semi-submersible FWTs under combined wind, wave and current conditions.

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 method of combining overlapping grid and sliding grid was applied to study the hydrodynamic performance and motion control of an underwater robot under incoming flow. The PID (Proportional, Integral, Differential) control method was used to realize the vertical heave motion under the presence of incoming flow through the joint operation of the umbilical cable and the ducted propeller, and the depth of the underwater robot was maintained under the condition of incoming flow change. The trim angle of the underwater robot could be adjusted by the propeller though PID method, maintaining the attitude close to balance at a fixed depth. Also the underwater robot can keep its trim angle constant throughout the entire movement process under the complicated heave working conditions.