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.

Thick-walled pipelines are widely used as transmission pipes for (ultra) deepwater petroleum and natural gas, and buckle arrestors for shallow water pipelines. However, the current international authoritative regulations may underestimate their ultimate bearing capacity significantly so that their economy and safety are hot topics in industrial circles. After deriving the calculation formula of vector form intrinsic finite element (VFIFE) method solid element, an analysis model of thick-walled pipelines considering the nonlinearity of geometry, material and boundary was established to solve the key mechanical problem of local collapse of thick-walled pipelines. And its accuracy was verified by comparison with 8 sets of thick-walled pipe scale tests, the DNV code, and ABAQUS simulations. Sensitivity analysis of diameter-to-thickness ratio, initial ovality and material yield strength were carried out to quantify the calculation errors of the DNV code method. Then, a more accurate formula for calculating the local collapse pressure of thick-walled pipes was obtained by fitting the VFIFE results. The results show that the simulation results of the VFIFE constant strain tetrahedral element are in line with the actual situation and can provide a new analysis strategy for the collapse behavior analysis of thick-walled pipelines. However, attention should be paid to determining the maximum load rate under the requirement of the quasi-static loading. Under high external pressure, the pipeline will collapse locally and propagate buckle dynamically and the deformation of the pipe section changes from an ellipse to a "dumbbell" shape with certain folds on the inner wall. During local collapse, the change trend of the stress distribution conforms to the general features of solid structure buckling instability. The calculation error of the DNV code of thick-walled pipelines’ local collapse pressure increases with the decrease of the diameter-to-thickness ratio, the decrease of the initial ovality, and the increase of the material yield strength respectively. The corrected formula for local collapse pressure calculation of thick-walled pipelines has a fitting error of -2.49%~1.72% for homologous data and a calculation error of -6.11%~1.70% for heterologous data. It can accurately calculate the local collapse pressures of deepwater pipelines with diameter-to-thickness ratio of 8~18, initial ovality of 0.5%~3.0%, and material yield strength of 300~500 MPa. The results can be used to guide the design and verification of submarine thick-walled pipelines.

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.

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.

Obtaining the divisional characteristics of ice resistance on the hull is the basis of hull form optimization for icebreakers. At present, neither the real ship measurement nor the ice tank model test can effectively obtain the divisional characteristics of ice resistances at each part of the hull. In order to explore the ice resistance during the icebreaking process, the icebreaker "XueLong 2" was taken as the research object in this paper, and the ice force carried by each parts of the hull during the icebreaking process was analyzed by constructing a discrete element numerical model of the interaction of ship and ice. Firstly, a discrete element model of level ice with random-arranged elements was established, and the microscopic parameters of the model were calibrated according to the typical strength values of Arctic sea ice. Then, the ice resistance of "XueLong 2" calculated based on discrete element method was compared with that based on Lindqvist empirical formula. On this basis, the ice force value of each region of the hull was obtained through calculating zonally the ice force in the interaction process of ship and ice. The calculation results show that the icebreaking resistance accounts for a large proportion among the ice resistance of the hull generated in the icebreaking process, and the friction resistance caused by the slip of crushed ices is relatively small. The ice resistance of the hull is mainly generated in the area of bow, and the stem bears a significant icebreaking load. The divisional calculation method of ice resistance of icebreaker established in this paper can provide technical support for the hull optimization based on icebreaking capability.

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.

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.

The structural design of the propulsion shafting of modern ships is relatively complex, and the structure size is an important factor affecting the whirling vibration characteristics. Taking a ship complex propulsion shafting as the object, the influence of changes in shaft segment hollowness on the whirling vibration characteristics of the shafting was studied in this paper. Based on the finite element method, a whirling vibration analysis model of the shafting was established, and the whirling vibration characteristics of the shafting were analyzed under the initial hollowness. On this basis, the range of hollowness values was determined through strength check calculation. Taking the hollowness of the stern shaft and propeller shaft as variables, the influence of changes in the hollowness of shaft segments on the critical speed of the whirling vibration was analyzed and the values range of hollowness was specified according to the requirements of shafting alignment. The results can provide a reference for structural design and whirling vibration control in the design process of ship propulsion shafting.

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 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.