Fatigue problem as a common failure form in the engineering field has been widely concerned. The fatigue damage-crack size can be obtained by the fatigue analysis method based on fracture mechanics, but the calculation is relatively complicated. In this paper, aiming at the spectrum analysis based fatigue analysis of ocean engineering structures, the stress intensity factor (SIF) spectrum under random loading conditions of the same hot spot through genetic algorithm wavelet neural network (GAWNN) was established, and the network training with the SIF obtained from finite element analysis was conducted. The results show that the model can predict the SIF spectra under random loading conditions well. The method proposed in this paper can considerably reduce the repetitive finite element calculation and provide a reference for the fatigue life prediction of engineering structures under random load conditions by applying crack propagation method. Finally, combined with the unique crack growth rate curve model, the rapid prediction of crack growth under random loading conditions was realized.

Based on the OpenFOAM, a hybrid model coupling fully nonlinear potential flow theory (FNPT) with viscous flow method, and the propeller-rudder mode, the turn and zigzag maneuvers of a single-screw ship in waves were simulated. The FNPT was used to simulate the wave tank in the external field, while the viscous flow method was used to simulate the interaction between waves and ships in interal field. Then, the 6DOF ship maneuvers in waves was simulated. The KVLCC2 model was selected for simulation, and the method was validated by the tank test, and the maneuvers in beam waves were simulated. By various wavelengths, the effect of wavelength on the ship maneuvering performance in beam waves was investigated.

The cyclic void growth model (CVGM) based on microscopic fracture mechanism is an effective method to analyze and predict ultra-low cycle fatigue (ULCF) fracture. In this method, the void growth index and damage degradation parameters are important parameters to control the crack propagation process. Due to the influence of production technology, the void growth index and damage degradation parameters of different batches of steels are often unfixed, which leads to the insufficient accuracy of the ultra-low cycle fatigue fracture analysis. In order to solve this problem, smooth round bar, smooth notch round bar and notch samples were used to carry out experiments, the ultra-low cycle fatigue characteristics of steel were studied, and the cracking mechanism and damage evolution law of the samples were explored. Secondly, the VUSDFLD program based on the cyclic void growth model was written, and the finite element analysis was carried out based on the results of test to calibrate the void growth index and damage degradation parameters. Finally, the ultra-low cycle fatigue fracture of notched samples was studied, the crack initiation and crack propagation rates were analyzed, and the ultra-low cycle fatigue fracture life of the samples was predicted. The results show that the fracture process of ultra-low cycle fatigue matches well with the experimental results, which is suitable for the prediction of ultra-low cycle fatigue fracture life.

Tank sloshing is a common phenomenon in ship navigation, which not only affects the stability of a ship, but also poses a threat to the marine environment and human life. How to reduce the amplitude of tank sloshing has always been a key research problem in ocean engineering. In this paper, based on the improved moving particle semi-implicit method, BM-MPS method, the damping effect of vertical open-hole separator under lateral excitation was simulated and studied, and the influence of porosity and lateral amplitude of the separator on resonance period and impact duration curve morphology was discussed. The results show that the size of porosity has an obvious effect on the resonance period. The porosity of 15% is the point where the maximum impact pressure is the minimum when the resonance is reached, and the resonance period is in the transition period of obvious transformation. The impact duration curve is also closely related to porosity. With the increase of porosity, the impact duration curve changes from no peak to single peak and then to double peak. In addition, the amplitude of excitation is also one of the factors affecting the resonance period.

In order to effectively reduce the ‘window effect’ in the sound field reconstruction process of near-field acoustic holography (NAH) and accurately measure and locate the surface sound source of a submarine by using the limited measuring aperture, a patch NAH method based on two-level iteration was proposed. Firstly, patch NAH based on orthogonal spherical waves was improved, and a patch NAH method based on two-level iteration was proposed. Then, the reconstruction results of the two NAH methods were simulated and compared, and the influence of extrapolation error and extended measurement points on the reconstruction accuracy was studied. Finally, the experimental study of patch NAH based on two-level iteration was carried out in an anechoic tank using a small aperture holographic measuring surface. The results show that the patch NAH based on two-level iteration proposed in this paper can greatly reduce the ‘window effect’ and ‘aperture repetition effect’ errors caused by the limited measurement aperture, which verifies the advantages of the method and provides an important reference for NAH precise measurement of large size sound sources.

The effect of riblet wall on the two-phase turbulent boundary layer containing 355 μm polystyrene particles was investigated by using particle image velocimetry (PIV). The effects of riblet wall on the characteristics of two-phase turbulent boundary layer were analyzed by comparing the average velocity profile, turbulence and Reynolds shear stress of the flow over the riblet and smooth surface. The spatial multi-scale local average structure function and λ_ci vorticity identification criterion of hairpin vortex head (clockwise spanwise vortex) were used together to accurately identify the vortex center and extract the spatial topology of the surrounding fluctuating velocity and streamline. The numerical law of the forward vortices at different wall-normal heights was calculated. The results show that, compared with the smooth surface, the buffer layer of the average velocity profile of the riblet wall rises partly, the logarithmic region shifts outward, and the friction velocity and frictional shear stress of the riblet wall decrease, resluting in a drag reduction of 4.86%. At the same normal height, compared with the smooth wall, the clockwise vortexes detected on the riblet wall have smaller dip angles and fewer numbers, and the streamwise fluctuating velocity around the riblet wall is weak, showing that in two-phase flow, the riblet wall can weaken the intensity and finally decreases the drag.

Effective use of numerous wave energy resources in the ocean remains a problem to be solved. Due to the wave conditions for low periodic and small wave height in the South China Sea, a model combining a split heave point absorber with a tension leg platform (TLP) was proposed. Through a physical model test, the hydrodynamic characteristics and wave energy capture efficiency of the split float were measured and analyzed, then compared with the whole float. And the optimal wave energy capture of the split float was discussed. The results show that the split float presents different hydrodynamic characteristics, and the energy capture efficiency of the device for small periodic waves is greatly improved in the low sea state, but the pitch motion of the platform is significantly increased in the specific wave direction, which requires further optimization of the tension leg system.

Large-diameter monopiles are an important type of offshore wind turbines (OWTs) foundations, whose bearing capacities are the core issue in foundation design. In this paper, the BP neural network and Monte-Carlo simulation coupled method were improved and used to study the reliability of the bearing capacity of a large-diameter monopile wind turbine under serviceability limit state (SLS), considering the real geological condition and the correlation of wind speed, wave height and wave period. The bearing capacity analysis was conducted based on the monopile-soil contact surface model. The accuracy of the numerical model was verified in two conditions: sand and clay foundations, respectively. Then the finite element model was adopted to determine the values of the training points of neural network. Finally, with the LW 8MW OWT taken as an example, the reliability of the bearing capacity of the monopile-supported OWT under SLS was calculated. The improved method can provide a reference for the subsequent design and construction of offshore wind farms in China.

The hull form modelling progress in ship design is significantly relied on the parent hull database and the professional designers well trained with CAD software, and it is usually a time and experience costly work. The conditional generation of ship hull with both geometrical and locational features by training an artificial neural network was concerned by this paper. The geometrical feature means the overall shape variety of ship designs like bulbous bow, stern shaft, etc., the locational feature means the shape difference between stern, front and mid-body of ships. Firstly, a conditional deep-convolutional generative adversarial network (CDC-GAN) was constructed to distinguish the geometrical and locational features individually; Secondly, the CDC-GAN was well trained to learn and generate these features with different resolutions and categories, from easy to hard; In the end, the training cost and performance of networks were compared and concluded to prove the capability of CDC-GAN in solving ship hull form generating issues. This paper is based on authors’ previous investigation with regular GAN, and it provides a further exploration about the potential of CDC-GAN in ship design.

The installation of spool pieces of submarine pipelines is important in the construction of newly-laid submarine pipelines. Due to the manufacturing errors in the process of producing marine pipelines, as well as the offset between the spool piece and offshore riser or the submarine horizontal pipes, the problem concerning the limit size offset of spool piece naturally emerges during installations. In this paper, the finite element analysis software ABAQUS was employed to establish the simulation model of a spool piece with flange joint based on the practical structural configuration and material parameters. As for the three typical situations in the practical process of the spool piece installation, the stress and strain distribution of the structure were obtained. Furthermore, the limit size offsets of the spool piece were calculated under the condition of satisfying the practical strength requirement. The mechanics and deflections of the spool piece during installation were discussed and analyzed in detail. The relevant conclusions are expected to provide the corresponding theoretical basis for the practical construction of the offshore platforms. And the research could have some engineering significance for the development and construction of offshore oil and gas fields.