Submerged waterjet propulsion is a variant of conventional waterjet propulsion, whose inlet duct is fully integrated into the bottom plate of hull, reulting in a more complex coupled flow field behind. In order to meet the development requirements of submerged waterjet propulsion, the differences in mechanical control system between two types of waterjet propulsion were studied. Numerical simulations were conducted for both conventional and submerged waterjet propulsion at designed speed point. The comparison results show that submerged waterjet propulsion has larger flow obtaining area, higher inlet duct efficiency and less impact on the ship motion while the thrust reduction fraction is larger.

To cope with the difficulties of fault warning in current engineering practice, such as the challenges of constructing sensitive feature combinations, scarcity of complete fault samples, and inaccurate warning threshold settings, etc., a rolling bearing fault warning method based on Adversarial Autoencoder (AAE) and adaptive threshold was proposed. Firstly, the preprocessed normal sample spectrum data was utilized as AAE training data for autoencoder network and adversarial network training, and the autoencoder reconstruction error was calculated and the coding network was retained; Then, the low-dimensional features obeying the prior distribution was extracted layer by layer using the encoder, and the health indicator was constructed by combining the reconstruction error and similarity measure, and the probability density distribution of the health indicator was fitted based on the beta distribution to determine the threshold adaptively; Finally, the test data was processed by the same steps and compared with the threshold to discriminate abnormalities. The proposed method was verified by using two types of rolling bearing datasets, and the experimental results show that the proposed method has excellent fault warning performance and adaptability, and can realize early warning of weak fault.

Abrupt annular shear flows induced by internal solitary waves will cause submersibles to produce a large depth drop and pitch motion, threatening the safety and operation performance of submersibles. Based on the velocity inlet wave generation method and overset grid technique of CFD, the motion response prediction method of submersibles in internal solitary wave was established. With the prediction results compared with the experimental results, it is proved that the method can accurately simulate the large amplitude motion of submersibles in internal solitary waves. Through the simulation analysis of motion process of unpowered floating submersibles at the stratified interface under the action of internal solitary waves, the mechanism of depth drop and pitch motion of submersibles in internal solitary waves was revealed, and the effects of stratified thickness ratio, wave amplitude and depth of navigation on the longitudinal motion of unpowered floating submersibles were investigated. The results show that the amplitude of depth drop and pitch of the submersibles in internal solitary waves were determined by the wave amplitude and the maximum slope of wave surface; The factors such as amplitude, stratified thickness ratio and depth of navigation have great influence on the longitudinal motion property of submersibles.

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.

In order to improve the anti-explosion protection performance of ships and explore the damage mechanism of marine sandwich structure under impact load, the close-range air explosion test of U-shaped folded sandwich plate was designed and carried out. The deformation and failure mode of the sandwich plate under shock wave load were analyzed, and the finite element simulation analysis was carried out. On this basis, the damage characteristics of sandwich plates under the combined action of shock wave and fragments were studied by prefabricating fragments at the bottom of explosives. The influence of panel thickness and detonation distance on the anti-explosion performance of sandwich plates was discussed from three aspects: panel break size, vertical displacement and energy absorption. The results show that the failure modes of the upper panel of the sandwich plate under the combined action of shock wave and fragment are large deflection, boundary tearing, plug break and scattered perforation. The bottom panel is dominated by large deflection and pits, and the shape of the upper panel break changes from' butterfly' to' circular' with the increase of the thickness of the upper panel. At this time, the upper panel and the core layer are the main energy absorbing components. The deformation of the central region of the sandwich plate is more sensitive to the decrease of the detonation distance, while the deformation of the edge region has no significant change. The total energy absorption of the sandwich plate, the energy absorption and proportion of the lower panel and the core layer increase with the decrease of the thickness of the upper panel. The change of the thickness of the lower panel and the core layer has little effect on the overall energy absorption of the sandwich plate and the proportion of each part.

With the continuous development of large-scale offshore floating structures, the rain load of large-scale offshore floating structures in extreme environment has become one of the focus issues of designers. Based on the discrete particle model, the motion prediction of wind driven rain field was made and the distribution law of spatial characteristic parameters of rain field was quantified. The calculation formula of structural rain load was deduced, and the rain load prediction of offshore platform under different wind speed and rainfall intensity combination conditions was completed. The research results show that the rain load of offshore platforms under the action of DNV wind profile and Davenport wind spectrum follows Gamma distribution. Compared to the average wind load, when the rainfall intensity R is 800 mm/h, the significant value of rain load accounts for 5.07%, and the maximum value accounts for 8.87%; when the rainfall intensity R is 20 mm/h, the significant value of rain load accounts for 0.36%, and the maximum value accounts for 0.6%. The research results of this paper can provide guidance for the design of offshore structures and their mooring systems.

A shallow water interface interference separation and sound field reconstruction method based on the equivalent source method was proposed. The combination of the ray acoustic virtual source method with the equivalent source method can effectively separate the impact of interface reflected sound in shallow water conditions, and accurately reconstruct the radiated sound field of structural sound sources. The virtual source method model was briefly described in this paper, the basic principle and algorithm implementation process of the interference stripping equivalent source method were given, the impact of different frequencies and holographic surface configurations on the algorithm was illustrated through simulation, and the advantages and applicability of this method compared to conventional equivalent source methods were summarized.

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.

The floating cylindrical structures, such as the floating frame of the fish farming and the floating bodies of wave energy convertor and so on, are generally semi-submerged. However, the investigation on the hydrodynamics on such floating cylinders are few. This status makes the design and analysis of the relevant new structures face the essential problems of the force input uncertainty. The hydrodynamic forces on a semi-submerged cylinder were experimentally investigated under the combined influence of steady and oscillatory flow. To simulate the equivalent combined flow, the cylinder towed by the carriage was forced to oscillate with different amplitudes and periods. A significant mean downward lift force was observed for the semi-submerged cylinders, which was obviously larger than that of the mean drag force. Moreover, the relationship between the hydrodynamic coefficients and multi-sensitive parameters was revealed. It is confirmed that the KC number has a weak influence on the coefficients. The Froude number is seen to be the most important parameter affecting the hydrodynamic coefficients. The empirical models for predicting hydrodynamic coefficients in combined flow are initially developed. This work can provide useful references for the design of the related marine structures and serve as the valuable guideline for future research.

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.