In ships’voyaging conditions, the global hull girder is subjected to the combination action of cargo loads on ship decks, still water moment and wave moment on hull bottom, and correspondingly partial ship stiffened panels suffer complex loads including longtudinal, transverse forces and pressures. Lateral loads could to some degree influence the ultimate compressive strength in the longitudinal and transverse directions. Thus, it is needed to establish the interaction formulae of ultimate strength for stiffened panels under combined loads. The stiffened panel structures in hull bottom of bulk carrier was selected as the research object. Based on the two-bays-and-two-spans geometrical extent model of stiffened panel with periodic boundary conditions, a nonlinear numerical method was employed to investigate the interaction formulae of ultimate strength for hull girder structures under longitudinal, transverse and lateral loads. It is found that lateral loads always reduce the ultimate strength in longitudinal and transverse directions, meanwhile the larger the lateral loads are, the more the ultimate strength decreases. It is suggested to increase stiffener size and plate thickness for improving the longitudinal and transverse ultimate strength under lateral pressures, respectively. The interaction formulae were developed to assess the ultimate strength of stiffened panels under combined loads and the interaction relationship of ultimate strength under multiple loads. It can be used to perform rapid calculation on the structural strength design under complex combined loads.

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.

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.

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.

Flow-induced vibration of valves is the main source of vibration and noise in pipeline system. The characteristics of flow-induced vibration of liquid valves are important for analyzing vibration and noise in pipeline system, designing and establishing low-noise system. By taking ball valve as the research object, a three-way spring and beam element model was used to simulate the elasticity bolt connection of ball valve inlet and outlet flange end face. Constrained boundary conditions of valves under actual working conditions were established though correcting constrained boundary stiffness with measured dry-humid modal results. Based on Finite Element Method (FEM) and Computational Fluid Dynamics (CFD) theory, the flow-induced vibration analysis model of ball valves was established to research the flow field and fluid-induced vibration characteristics and the correlative influence law of ball valve under variable opening and mass flow conditions. The results show that the three-way spring and beam element model can better simulate the actual installation boundary conditions of ball valve in water pipe. With the decrease of ball valve opening or the increase of mass flow rate, the disturbance of flow field becomes more obvious, and the vibration acceleration level at each measuring point increases.

Based on the STAR-CCM+ software, CFD-DEM method was used to simulate the process of a type of an actual built transport ship sailing in a brash ice channel. The influence of different drafts on the resistance performance of the ship was studied. The interaction between the ship and water was obtained using CFD method. A numerical brash ice particle model was established using DEM method, the ship-ice collision phenomena and the brash ice resistance were studied. The results show that the distribution pattern of brash ice particles obtained based on the above method agrees well with that of the test conducted in Hamburg Ship Model Basin (HSVA). The total resistance of the numerical prediction varies little from the model test results. Also, the numerical method performs much better than the FSICR empirical formula's prediction, which verifies the reliability of the present method. The ice resistance of the whole ship does not show a monotonically decreasing trend with the decrease of draft, but increases significantly when a specific draft is reached. At a small draft, the change in trim has a little effect on the ice resistance of the whole ship, but has a large effect on the proportion of ice resistances of the fore, middle, aft and bottom parts of the hull.

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.

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.

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.

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.