The interaction between an inclined plane and level ice is a complex dynamic process, characterized by periodic shear extrusion, bending failure, rotational immersion and sliding. To investigate the interaction process between structures and ice and the ice-breaking mode, a mechanical test on the interaction between inclined structures and level ice was conducted in an ice tank at China Ship Scientific Research Center. A high-precision tactile sensor and strain balance were employed to simultaneously measure the distribution of the model ice load and overall ice load. The resistance of the inclined structure to ice and its load temporal and spatial distribution characteristics during the interaction with the level ice were determined. Furthermore, based on physical observations, the failure process and load distribution law governing the interaction between inclined structures and sea ice were analyzed.

Mooring lines are prone to fatigue damage or even fracture due to the long-term exposure of floating wind turbine to marine environmental loads. At present, the mainstream S-N/T-N curve methods have many defects, such as high discretization of results and inability to consider initial cracks. The fracture mechanics method can analyze the fatigue life of structures with initial cracks. However, the analysis of large structures by fracture mechanics is inefficient and complex, and it is difficult to achieve accurate prediction from time-domain load analysis to fatigue life using a single general software. In this paper, a framework based on PYTHON for fatigue crack propagation was constructed, and a fatigue crack propagation program for mooring lines was developed based on the fracture mechanics method in conjunction with SESAM, ABAQUS, and Franc 3D softwares, which enables the simulation of fatigue crack propagation processes under different sea conditions. Secondly, as an example, the fatigue life of No.1 mooring line of OC4 semi-submersible floating wind turbine was calculated by using this program. Finally, the parametric study of the anchor chain was carried out, based on the fatigue life calculation results of No.1 mooring line. The results show that the crack growth rate in the crown section of the mooring chain is the fastest, and the fatigue life is the shortest, which is about 74% and 36% of those in the bending section and the straight section, respectively. The initial crack morphology has a significant effect on the fatigue life of mooring cable. The increase of the initial crack size and the decrease of length-depth ratio both result in a decrease in the fatigue life of mooring lines. The research work can provide technical support for the design and analysis of mooring line of floating wind turbines.

With aquaculture equipment gradually moving from offshore to deep sea, "Deep Blue 2", a semi-submersible and column-stabilized cage with a total aquaculture volume of about 90 000 cubic meters, came into existence. In order to study its hydrodynamic performance and characteristics of motion response under the irregular wave combined with steady air and current, a numerical model suitable for the time domain analysis of the cage was established by combining the WADAM, SIMO and RIFLEX solvers. The numerical model was coupled from the hydrodynamic model of the main structure of the "Deep Blue 2" and the finite element model of the nets and the mooring system. The panel model and Morrison model were combined to solve the hydrodynamic force of the cage. The finite element method was used to analyze the nets and mooring system in time domain where the nets load was computed based on the Screen model. The time domain simulation shows that the nets have a significant effect on the hydrodynamic performance of the cage, which cannot be ignored. The maximum mooring tension of the cage with nets is about twice that without nets, and the range of horizontal drift is also wider. The difference-frequency force components of second order wave force have little effect on the mooring tension and horizontal drift. These conclusions may be useful for the evaluation and optimization of the hydrodynamic performance of new cages.

In this paper, numerical simulation and comparative verification tests of two ship models in heading regular waves, which was recommended by ITTC, were conducted. Based on the Reynolds time averaged method for solving the N-S equation, a calculation method of wave interference and 6DOF motions for two ships under horizontal mooring constraints was established. With the model and mooring parameters in the test taken as inputs, the numerical simulation of wave interference between the two ships under typical wave conditions was carried out. The time curves of 6DOF motions, wave surface rise between the two ships and mooring tension were obtained and compared with the results of model tests. The comparison shows that the motions of surge, heave, roll and pitch as well as the wave surface rise of the comparative conditions (wave period: 1.5 s) are in good agreement with the test results. There are relatively large errors in motions of sway and yaw compared with the test results, because these motions result from the coupling of wave system interference between two ships and mooring constraints, and the superposition of multi-factor simulation errors reduces calculation accuracy.

The line spectra noise radiated by cavity flows greatly deteriorates the acoustic stealth of naval ships, whose formation mechanisms are related to the flow and acoustic modal effects, as well as the acoustic-vibration and flow-sound coupling effects. In this paper, the transient flow, equivalent sound source and acoustic fields of the simple square and typical cavity flows were numerically simulated, based on the CFD/CHA hybrid approaches. The applicability of the numerical methods was verified by comparison with experimental data of water tunnel test. The characteristics of the flow and acoustic modes of the cavity flows were concluded, particularly the effects of the acoustic-vibration coupling of elastic cavity walls and the complexity of cavity inner shapes upon the acoustic mode frequencies were quantitatively calculated. The important regularity, which the line spectrum induced by the effect of the first acoustic mode is the "decisive line spectrum" in the far-field radiated noise spectrum, is summed up. The tendency of the acoustic mode frequencies to shifting sharply towards lower frequencies under the actual cavity conditions was analyzed, indicating the necessity of avoiding the flow-sound coupling. The necessary condition of the cross-sectional area ratio for the related acoustic experiments in water tunnels was quantitatively established through an analytical solution. The research has an important guiding value for the designs of experimental modals.

The pump-jet thrusters produce structural noise during operation.The pump-jet propulsors made of conventional materials often have heavy structure weights. And in this case it is difficult to balance the stern weight. The use of composite materials in the pump-jet propulsor structure can not only greatly reduce the overall weight, but also have good corrosion resistance and fatigue resistance. Focusing on the vibration control problem of composite duct structure of pump-jet propulsors, this paper presents the research on experimental modeling, algorithm optimization design, hardware platform construction and test for MFC-based structural vibration active control system construction and verification based on macro fiber composite (MFC). The genetic algorithm was applied to the optimization design of linear quadratic Gaussian (LQG) controller, and the control effects of the algorithm before and after optimization were compared by experiments. A model identification platform and an active control test platform were built for the composite duct. The control model was obtained by experimental modeling method and the active vibration control test under harmonic excitation was carried out in the air environment. The research attempts to push MFC-based active vibration control method to application scenarios.

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.

The Bend Stiffener (BSR) manufactured from polyurethane is generally used at the connection between nonbonded pipes and water surface platform. It is necessary to predict curvature distribution of BSR. This paper proposed a curvature prediction model that took into account the stress-strain nonlinearity of BSR and bending hysteresis of nonbonded pipes. Then, a nonlinear regression method was used to identify the Prony parameters which could be used to describe the stress relaxation behavior of BSR materials. Then the stress relaxation model was substituted into the curvature prediction model, so that the effect of BSR’s stress relaxation could be taken into considernation. Finally, an optimization criteria was proposed for BSR and conducts parameter analysis on regular shaped BSR.

A numerical method combining Lattice Boltzmann and Large Eddy Simulation (LBM-LES) is used to simulate the wind field of the unsimplified carrier model under different wind speeds and wind angles. By analyzing the distribution characteristics of the wind field on the ideal landing trajectory, it is found that the dimensionless time-averaged wind speed has a similar distribution pattern and magnitude along the trajectory under the same wind angle and different wind speed conditions. The vertical component has a typical "rooster tail" distribution, with the peak of the sinking airflow being about 10% of the incoming velocity. For the same incoming speed and different wind angles, the influence of the wake on the landing trajectory during port wind is significantly larger than that of the starboard wind. In addition, the vertical velocity on the landing trajectory is mainly sinking in port winds and both sinking and rising in starboard winds, but predominantly upwelling.

In order to accurately evaluate the influence of irregular current load on the safety of semi-submersible platform towing operation, based on the coupled time-domain analysis theory and potential flow theory, this paper presents an analysis of the influence of different current velocities and flow angles on the dynamic response and towing tension of semi-submersible platform towing under the same wave environment and towing speed through the semi-submersible platform-towing-tug coupling dynamic model. The results show that under certain wind and wave conditions, the current velocity and flow direction angle have little influence on the heave and pitch of the platform, but have great influence on the roll and towing tension. With the increase of flow velocity and flow direction angle, the platform heave gradually increases, with the platform roll and pitch angles under different flow velocities and flow angles fluctuating within ± 3.5°. The maximum towing tension is obtained when the flow angle is 90°. Therefore, the angle of 90° between the heading and the flow direction should be avoided during the towing process, and it is not suitable for towing when the flow rate reaches 1 m/s.