Aluminum alloys have been widely used in the ship industry for their low density, high specific strength and specific stiffness. However, compared with steel, the strength of aluminum alloy is low. To improve its strength, JDA1b aluminum alloy, which is often used in die casting and outfitting parts of ships, was taken as the research object. Pre-strain tensile, pre-bend tests and dynamic tensile tests were carried out to investigate the effects of pre-strain and pre-bend on the mechanical performance of JDA1b alloy, and the effects of strain rate on the flow behaviors of the alloy were also investigated. The results show that increasing the strain rate can increase the flow stress and tensile strength of the material; the yield stress and tensile strength of this material increase with the increase of pre-strain, and the elongation decreases, and that the increase of pre-bend is favorable to improve the bending yield load, bending stiffness and damage displacement of the material. A new dynamic constitutive model considering ultimate stress and critical strain was proposed, which allows the flow stress to be predicted more precisely at various strain rates over a wide range of 1~800/s, and the fitting goodness-of-fit value reached 0.999. This study provides methods to improve the strength of aluminum alloys, and the proposed constitutive model is conducive to the improvement of the accuracy of the simulation of mechanical performance of parts.

For floating structures deployed in waters near the coast or island lagoons, the shallow water depth makes the impact of seabed topography changes on the mooring system non-negligible, and the seabed can no longer be simplified as flat when exploring the characteristics of the mooring system. To study the static characteristics of the anchor chain under the condition of uneven seabed terrain, an anchor chain model was established based on the lumped mass method, and effects of the seabed inclination angle and the arrangement of the anchor chain on the tension and the tension angle at the top of the anchor chain, and the length of the catenary were discussed through numerical simulation, in an attempt to guide the design and safety performance evaluation of floating mooring system in shallow waters.

Ships are susceptible to wind and waves causing the declines of installation accuracy and maintenance safety of offshore wind turbines. The most seriously affected case is the non-stationary ship roll motion under long-peaked random wave spectrum. To ensure the stability of offshore operations under complex sea conditions, it is necessary to improve the generalization of the prediction model. In this paper, a preferential feature federation method was proposed. Firstly, the non-stationary ship roll motion was decomposed into multi-component stationary sequences by using the variable modal decomposition method. Then, the long and short-term memory neural network with attention mechanism was used to build a local multi-dimensional multi-step prediction model with error correction. Finally, in order to improve the prediction effect of new type ship motions in complex sea conditions, a federation method was used to combine some ship motion data holders for best model parameters, which were selected with the maximum mean discrepancy method with high similarity for preferential feature federated training. The experimental results show that the federated model has higher prediction accuracy and better generalization ability, which can help the stability control of wave compensation during offshore wind turbines installation.

In this paper, the open-source computational fluid dynamics software OpenFOAM was used to simulate the effect of plunging breaker waves and non-breaking waves on the typical column of an offshore platform in the extreme ocean environment. The purpose was to compare and analyze the variation of wave loads and structural stress in the column under the above two wave types. The motion of the fluids was simulated based on the Reynolds-averaged Navier-Stokes equations combined with k-ω SST turbulence model. The numerical results show that the breaking wave load on the column is much higher than the non-breaking wave load under the same design wave parameter input. The maximum stress values for each structure of the column under non-breaking wave loads are less than the yield limit of material. However, under the plunging breaker load, the maximum stress of some structures exceeds the yield limit of materials and cannot meet the requirements of structural safety. Therefore, the impact of breaking wave load on structural strength should be considered in the safety design of marine structures to ensure that the structure has sufficient safety margins.

In order to explore the lubrication characteristics of the main bearing under heavy load and its interaction mechanism with wear, based on the micro-contact and fatigue damage mechanism of micro-convex body, the wear model of bearing material was constructed, and combined with the mixed thermal elastohydrodynamic lubrication theory, the coupling analysis model of mixed thermal elastohydrodynamic lubrication and wear of the main bearing was established, based on which, the wear distribution and evolution law of the main bearing under specific load at the time of ignition were investigated, and the effects of wear on lubrication characteristic parameters such as oil film pressure, oil film thickness and rough contact pressure were discussed. The effects of load, radius clearance, micro-convex friction coefficient and rotational speed on the wear characteristics of the main bearing were obtained. The results show that with the increase of wear time, the wear area increases from the center of the bearing zone along the circumferential direction of the bearing, the contact pressure decreases and the minimum oil film thickness increases, and that the increase of radius clearance and micro-convex friction coefficient and the decrease of rotational speed will aggravate the wear of bearing bush.

The exciting forces generated by the propeller during ship operation will cause the vibration of propulsion shafting, and the shafting vibration will also have feedback to the propeller, causing complex spatial motion. There is a two-way fluid-structure coupling problem in the propeller-shafting system. To investigate this complex dynamic problem, the numerical model for simulating the coupling of shafting multi-degree-of-freedom vibration and propeller viscous flow field was established in this paper, based on the finite element (FEM) and computational fluid dynamics (CFD) methods. The iterative solution of the two-way coupling was realized by carrying out secondary development in the flow field solver, and several numerical examples were simulated to study the variation characteristics of fluid exciting and vibration response. The results show that, the simulation method proposed in this paper has practical values, and the convergence and accuracy of the two-way fluid-structure coupling simulation can meet the engineering requirements. The computing speed for solving the coupling system of this method is fast, and no additional computing resources are required. The two-way coupling effect and unbalanced mass have significant influence on the amplitudes at rotating frequency while the non-uniform inflows have significant influence on the amplitudes at blade passing frequency.

Welding residual stress has a significant impact on the fatigue life of a welding structure. Meanwhile, welding residual stress is not invariable, but will be redistributed with crack propagation. Therefore, the coupling study of welding residual stress redistribution and crack propagation is very important to predict the fatigue life of a welded structure accurately. Based on thermal elastic-plastic finite element method and extended finite element method (XFEM), a fatigue life analysis method considering the coupling of residual stress redistribution and crack propagation was proposed in this paper. Taking the tensile fatigue sample of TC4 titanium alloy as an example, the redistribution of the welding residual stress along with crack propagation was studied with the extended finite element method. The welding residual stress distribution in front of the crack tip during crack propagation and the fatigue crack propagation a-N curve under the redistribution of weld residual stress were calculated by cyclic iteration. The calculation results show that the welding residual stress at the crack tip increases firstly and then decreases with the crack propagation. Compared with the results based on constant value of the residual stress, the extended finite element fatigue life analysis method considering the redistribution of the residual stress is more accurate to predict the fatigue lives of welding structures.

The mooring system is the key structure of a floating platform, which plays an important role in ensuring the safe production of the platform. It is of profound significance to understand and evaluate the safety status and risk level of the mooring system in time. Aiming at the difficulties of real-time in-situ detection of mooring lines under the platform field operation states, a reliability assessment method of catenary mooring system based on prototype monitoring information is proposed in this paper. Compared with the conventional Monte Carlo simulation, the proposed reliability assessment model can improve the calculation efficiency to meet the requirements of real-time reliability analysis. Firstly, based on the catenary equation, a numerical simulation analysis of the forcing behavior of the mooring line was performed considering the influence of the current load. Then, a reliability assessment modelling method for strength analysis and fatigue analysis of mooring system was proposed based on Enhanced Monte Carlo (EMC) method. Finally, based on the prototype monitoring data of a semi-submersible platform in the South China Sea, the reliability assessment of the mooring line was performed by taking into consideration the impact of the corrosion. The simulated results indicate that the present real-time reliability assessment method could provide a superior ability for the guidance of the safety assessment and maintenance of catenary mooring system.

Under the welding process specifications that meet the structural strength requirements, welding energy input and welding sequence result in different welding residual stress and deformation, which significantly impact the typical bidirectional stiffened plate structure’s vibration and acoustic radiation. In order to explore the influence of welding process parameters on the vibro-acoustic characteristics of typical bidirectional stiffened plate structures, the accuracy of the welded structure test method was verified by combining numerical simulation and experiment, several tests of stiffened plate structures were carried out regarding the modal, underwater vibration, and acoustic radiation under different welding energy inputs. The results show that under the same welding sequence, different welding energy inputs have a large effect on the natural frequency of thin plates and a relatively small effect on the natural frequency of thick plates. For stiffened thick plate structures, under the same welding sequence, with the increase in welding energy input, the impact on the natural frequency shows a trend of first decreasing and then increasing, and the overall vibration acceleration level and radiated sound pressure level in the same frequency band decrease first and then increase. Under the symmetrical welding sequence, the optimal welding parameters cover a welding current of 200 A, a welding voltage of 25 V, a welding speed of 3.02-3.06 mm/s, and a welding energy input of 167 J/cm. This study can provide guidance for the design of low-noise processes for acoustic stealth of ships and marine structures.

It is inevitable to use various high-strength materials with brittle characteristics in the construction of ship structures. In order to study the fracture and crack propagation behavior of marine brittle materials, a coupling model of FEM and peridynamics was proposed based on the peridynamic theory. Firstly, the long-range force attenuation effect correction was considered on the basis of peridynamics. Then, the sharing node method was used to couple the FEM with the improved peridynamics, and a new fracture criterion was derived. Finally, the accuracy of the coupling model was verified by three examples. The results show that the coupling model improves the computational accuracy of the traditional peridynamic model greatly, and eliminates the“surface effect”, and it overcomes the FEM singularity when dealing with discontinuities. The calculation results of the coupling model are in good agreement with the experimental results, and the present model is feasible to study the fracture of marine brittle materials.