In order to select and optimize the skin friction reduction scheme for high-speed underwater vehicles, a better technical scheme of skin friction reduction test, the expression method of characteristic parameters and the technical way to improve the measurement accuracy were put forward in this paper. The feasibility of the above scheme and approach was demonstrated by the actual skin friction reduction test of PEO. The results can provide support for the selection and optimization of the skin friction reduction scheme for high-speed underwater vehicles.

Based on the boundary data immersion method (BDIM) and the fluid-structure coupling algorithm for rigid body motions, a numerical program for the vertical water-entry of a sphere was developed. The accuracy and effectiveness of the numerical method were verified by comparison with the experimental results. Based on the analysis of the numerical calculation results, the cavity development and corresponding flow structures with different impact velocities during vertical water entry, as well as the development of the splash were obtained. Different vortex identification criteria were adopted to investigate the development of vortex structures. The results show that the impact velocity of the sphere has a significant effect on the closure of the splash, the cavity shape and the evolution of the flow structures inside the cavity. The Q criterion can identify the complex vortex structure more accurately, and the entry velocity of the sphere will affect the vortex intensity inside the cavity.

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.

Hazardous noise of flight deck due to jet blast deflector impingement causes a serious damage to the health of crew members. An experiment of jet impinging on a blast deflector was carried out in a full anechoic chamber to study the acoustic characteristics. With a diameter (D) of 56.4 mm, a convergent nozzle was used to investigate a Mach number of 1.01 jet impingement. Flow visualization and far-field microphones were employed to observe the flow field and measure the far-field noise, respectively. The test was performed on a 600 mm×600 mm deflector and with three inclined angles (β) of 45°, 55°and 65°. The results show that the impact angle has a significant influence on the wall jet structure and overall sound pressure level (OASPL). With the increase of impact angle, the OASPL of upstream and downstream rise and fall respectively. It is found that the OASPL increases by 15 dB in the upstream direction and decreases by 7 dB in the downstream direction for β=65°. Flow visualization and spectra analysis indicate that downstream directions are radiated by low frequency noise originated from trailing edge of the deflector due to separation of the large scale vortex. Specifically, it can be illustrated by correlation analysis that the directivity of the trailing separation noise becomes more significant when the impact angle reduces. Upstream directions are dominated by impingement noise. Although impingement noise is significantly affected by impact angle, the radiation structure of impingement acoustic wave under different impact angles is similar to each other according to the correlation analysis. In addition, the deflector forms a low-pass filtering effect on the impingement noise, and the sideline spectra have steep peaks. The OASPL and spectra of sideline directions are less affected by the impact angle. The research results are expected to be helpful for noise pollution control on carrier deck.

Ship collision is the main risk for the large-scale floating offshore wind turbine's (FOWT) safety, especially in the deep water zones. The ship collisions for the monopile and jacket offshore wind turbines have been studied abundantly, and this paper focuses on the issue of the operation and maintenance vessel collision with FOWT. The coupled mathematical dynamic model of the vessel and FOWT was built based on the multi-body hydrodynamics in MATLAB/Simulink, and the impact force was simulated using the physical numerical modeling method. The collision process was modeled in the time domain assuming the dynamic positioning system was broken. And then, the effects of the relative impact velocity and the impact locations on the floaters’ response were analyzed. The results show that the magnitude of the impact force is proportional to the relative impact velocity. The dynamic response of roll and yaw degree of freedom of the ship is intense due to its small added mass.The impact location determines the kinetic energy redistribution and the magnitude of the impact force.

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 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.

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.

The complexity of the stern appendage of a four-screw ship and the differences in the spatial layout of the internal and external propellers will lead to the unbalanced load distribution of the internal and external propellers. Based on the CFD method, numerical prediction simulation for the viscous wake field of a ship with four propellers was carried out. According to wake field distribution and turbulence characteristics, the difference in wake fields between the inner and outer propellers was compared and analyzed, and also the results was contrasted with the test values. The study results show that the inner propeller in the turbulence zone is affected by the hull boundary layer, which makes the axial velocity at the inner propeller disk less than that at the outer propeller disk, resulting in uneven load distribution between the inner and outer propellers. The flow at the outer propeller is a mixed one of the hull boundary layer and the turbulent wake, which makes the wake at the outer propeller disk more uneven. The research can provide basis and support for four-screw ship design and stern layout optimization.

The directional dimensional analysis method is commonly used in the design of similar scale-down models of hull structures. However, the traditional dimensional analysis method based on elastic theory cannot reflect the nonlinear response process of a structure, which limits its application in the scale down model test of hull structures. In this paper, based on the finite similarity method, the scale-down factors of the geometric dimension, material density and time of a structure were obtained by matching the transport equations in the physical space and the trial space. The nonlinear similarity relationship between the scaled down model of the stiffened plate structure and the prototype was derived, and the influence of the material parameters on the nonlinear similarity process was analyzed. By calculating the ultimate strength of the stiffened plates subjected to plain compression, the effectiveness of the scaling criterion based on the finite similarity method was verified. The result shows that the present method can well reflect the nonlinear characteristics of materials, and achieve a good prediction on the ultimate strength of the original model through the results of the scale down model.