In order to study the propeller cavitation and induced pressure fluctuation in non-uniform wake, a multi-field synchronous measurement system was used to carry out tests in a cavitation tunnel for a highly skewed propeller (HSP) and explore the influence of advance coefficient and cavitation number on the propeller cavitation performance and fluctuating pressure characteristics. The results show that the propeller cavitation appears in the test mainly in three types: back cavitation, face cavitation and tip vortex cavitation. Low-frequency pressure fluctuation is highly correlated to the cavity volume oscillation. Under non-cavitation condition, the first blade passing frequency is the main component of pressure fluctuation while the amplitude of higher blade passing frequency component can be ignored by comparing the contributions of each blade passing frequency component of the whole pressure fluctuation. Under cavitation condition, the unsteady cavitation has a great impact on the pressure fluctuation. The higher blade passing frequency components can be obviously observed, and the amplitude of main frequency pressure fluctuation increases significantly.The variation of pressure will become more observable with the increase of intensity of cavitation evolution process. The higher order blade frequency component of pulsating pressure increases obviously when tip vortex cavitation is present.

The propulsion mechanism and swimming performance are of great significance to the construction of fish migratory channels. By using computational fluid dynamics method combined with overlapping mesh technology, the two-dimensional fish autonomous swimming was simulated by compiling the UDF program for controlling fish body swing, analyzing the evolution process and parameter changes of fish body pressure field distribution and inverse Carmen vortex street structure, carrying out the changes of fish swimming performance and fish body force under different parameters of tail swing frequency, tail swing amplitude, fish body shape and tail fin size, etc., and revealing the swimming mechanism of fish in the process of autonomous swimming. The results show that: (1) the fish body’s tail fin periodically swings back and forth under the formation of anti-Carmen vortex street, which is the main source of the fish body forward thrust, and with the increase of tail swing frequency and tail swing amplitude, the fish body tail vortex street length and vortex street strength gradually increase, while the effect of tail swing amplitude on the vortex street width is greater; (2) with the increase of swinging frequency and swinging amplitude, the horizontal mean coefficient of synergy and the maximum lateral force coefficient increase, which makes the fish obtain a larger swimming speed, but the increase of mean coefficient of synergy and swimming speed is more obvious when the swinging frequency has been changed, and the increase of maximum lateral force coefficient is more obvious when the swinging amplitude has changed; (3) with the increase of body width index, the horizontal average coefficient of force gradually decreases, and the swimming resistance to be overcome increases, which makes the swimming speed of fish gradually decrease, while the maximum lateral force coefficient gradually increases; (4)and with the increase of caudal fin index, both horizontal mean coefficient of force and maximum lateral force coefficient increase, which leads to the gradual increase of swimming speed of fish. The results of the study can provide a support for fish habitat restoration.

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.

To study the influence of the pitching and translational coupling motion of underwater structure on its hydrodynamic pressure field, the potential flow theory was used to analyze the hydrodynamic pressure field of the coupling motion of the structure. The overlapping grid technology was used to analyze the hydrodynamic pressure field of the structure in the four motion states of translational motion, translational motion with attack angle, pitching motion, and pitching translation coupling. Taking elliptical structures of different axial length ratios as the research object, the hydrodynamic pressure field under different angular velocities was analyzed. The results show that the pitching motion of the elliptical structure will make the negative pressure peak of the hydrodynamic pressure field curve shift with time. The larger the angle of pitching oscillation is, the greater the negative pressure peak shifts. In addition, the axial length ratio of the elliptical structure will also affect the offset degree of the curve. The spectrum of the hydrodynamic pressure field caused by the pitching oscillation of the elliptical structure has a very low frequency spectrum peak. The frequency corresponding to the peak of the spectrum is consistent with that of the elliptical structure oscillation.

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.

In order to predict the critical buckling load of a filament winding thick composite cylindrical shell under hydrostatic pressure, the buckling governing equation of the thick cylindrical shell under hydrostatic pressure was obtained based on the nonlinear Sander theory, as well as the deformation geometry equation of the cylindrical shell and the constitutive relation of the filament-wound layer. An analytical method for predicting the critical buckling pressure of thick composite cylindrical shells under hydrostatic pressure was proposed by solving the governing equation. Then, critical buckling load of the thick shell with different filament-wound types and angles were calculated with FEM and compared with analytical results for verifying the accuracy and high efficiency of the analytical method. The influence of key parameters such as geometrical and material design on the critical buckling load of thick cylindrical shells was investigated based on the analytical method.

Based on the analysis of the lubrication performance of the eccentric stern bearing, an elasto-hydrodynamic coupling lubrication model for the local wear and stiffness of the stern bearing was established. The joint program of finite difference method and finite element method was compiled to solve the elastic deformation of the bearing, and the mass conservation boundary condition was used to replace the Reynolds boundary condition. The effects of local wear depth, bearing elastic modulus and other factors on the hydrodynamic pressure, liquid film thickness, cavitation area and friction law of the bearing were discussed in detail. The results show that when the local wear depth of rigid body bearing is lower than the threshold value, it is beneficial for bearing lubrication. When the local wear depth exceeds the threshold value, the maximum hydrodynamic pressure, friction force and cavitation area increase significantly. The influence of bearing elastic deformation on the calculation results cannot be ignored. Elastic deformation and local wear exist at the same time, and the change law is basically consistent with the change trend of local wear of rigid body bearings.

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.

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.