Inspired by the“casing treatment”in turbomachinery, a rectangular groove structure is applied to the inner surface of ducted propeller to reduce the strength of the tip vorticity and inhibit the cavitation of tip vorticity, which is expected to improve the hydrodynamic and cavitation performance. The unsteady numerical calculation of Ka4-70 propeller operating inside duct 19A, with or without grooves, was carried out by using computational fluid dynamics (CFD) method. The influence of groove structure on tip pressure, tip vortex strength, tip vortex structure and hydrodynamic performance of blades was studied. The results show that the groove structure can significantly change the tip vortex of duct propeller, weaken the strength of vortex, increase the minimum pressure at the tip of blade, and almost have no effect on the propulsion performance. The results provide a new solution for tip vortex control and vibration and noise reduction of the ducted propeller.

Free surface impact of complex structures, such as airdrop torpedo, the diving of unmanned underwater vehicles, and the water impact of high-speed ships, has always been a research hotspot in the field of ocean engineering. This paper presents the simulation of water impact of complex structures by combining the ghost cell method and the gradient augmented level set method (GALS). A time semi-implicit finite difference method was used to solve the incompressible Navier-Stokes equations, the ghost cell method was used to enforce the no-slip boundary conditions by interface reconstruction, and the gradient augmented level set method was used to capture nonlinear free surfaces such as wave overturning and jet flows. The slamming of a two-dimensional cylinder at constant speed was simulated to validate the accuracy of this numerical method by comparing the present results with the experimental data. Upon simulation of the slamming of a two-dimensional hull section, the variation rules of the impulsive pressure, the motion response, the pressure distribution, and the free surface motion with respect to the relative impact angle were analyzed. Also, some typical impact phenomena were observed such as the flow separation, the jet flow, and the ventilation for a small impact angle.

Prediction of ice force acting on the hull is a key to assess the navigation performance of ice-going ships. An ice-going ship was used to conduct the manoeuvring oblique test, the circular synthetic ice made of polypropylene was adopted, the forces of hull in water and medium and high floe ice concentration region were given by model test, the characteristics of force under different speeds and drift angles were investigated, the data repeatability was analyzed based on typical conditions, and the synthetic ice model test technology was developed. The model test results show that increasing ice concentration, speed and drift angle will cause the larger force acting on the ship, the contact area of the ship and ice is larger in higher ice concentration and larger drift angle, the repeatability of data is also better.

Two-dimensional numerical simulation was conducted to investigate the characteristics of fluid-induced vibration of a D-section prism with two degrees of freedom at an attack angle of 90°and a mass ratio of 2.6. The RANS equations were solved with the SST k-ω turbulent model closure. Uniform acceleration of inlet velocity and Newmark-β method were incorporated. Firstly the sensitivity analysis of the grid and time step in the present numerical model was carried out, then the comparisons with published experimental results were made to validate the existing numerical model. Then, a systematic analysis of response amplitude, vibration frequency, hydrodynamic coefficient, wake vortex shedding mode and average position-offset was made. The D-section prism exhibits combined response of VIV and galloping modes at a reduced velocity range of U_r=8-14, with vortex shedding pattern alternating between 2S and S+2S. The response amplitude of the two-degree-of-freedom prism is often stronger than that of the one-degree-of-freedom one. The lift force is inclined to the straight side of the section, and more than one frequency multiplications were found for the lift force. The average position-offsets of both cross-flow and downstream direction have maximum values exceeding one characteristic length.

Stingers bear the alternating load during operation, and the fatigue failure of the structure can not be ignored. Therefore, based on the wave spectrum and real-time monitoring data, the fatigue problem of a stinger was studied. The comparison and analysis of the calculation results suggest the fatigue damage calculation based on the wave spectrum is conservative due to the strong randomness of the wave load, so this method is suitable for the prediction and evaluation of the fatigue life of the structure in the design stage. However, the fatigue damage calculation based on the real-time monitoring data is relatively more accurate, so it is suitable for real-time assessment of the immediate fatigue damage of the structure. Finally, this paper puts forward appropriate repair and maintenance suggestions accordingly.

The significant life reduction of mechanical components during non-proportional loading compared to proportional loading results from the additional damage. In this study, the factors affecting the fatigue life under non-proportional loading were analyzed, and a new non-proportional damage factor was proposed. A novel fatigue life prediction model based on equivalent strain was established with the maximum shear plane as the critical plane. The new multiaxial fatigue life prediction model not only considers the effect of normal stress on the critical plane on the material crack initiation and crack propagation, but also reflects the non-proportional loading on the multiaxial fatigue life by introducing the non-proportional hardening coefficient of the materials and non-proportionality of the load paths. Experimental data under multiaxial loading of five materials were used to verify the accuracy of the novel model, and were also compared with two classical models. The results show that the prediction accuracy of the proposed model is higher.

Sandwich structures have been widely used in fields of sound insulation panels and vibration reduction structure design due to their lightweight, excellent performance in vibration reduction and sound insulation. Usually, sandwich panels in vibration tend to exhibit bending vibration modes in the low frequency band.However, the properties of sandwich skin materials and core materials often differ significantly, resulting in rich vibration modes in the midium and high frequency bands. Therefore, it is necessary to establish a theoretical prediction method for sandwich panel vibration applicable to various frequency bands. In this paper, a new theoretical calculation method for sandwich panel vibration was developed, in which three-dimensional elastic mechanics theory was applied to core material of sandwich panel while thin plate theory was applied to skin material. The theoretical method presented in this paper can reflect the bending deformation mode and dilatational deformation mode of sandwich panels, and allow for normal deformation of sandwich panels. As a result, the method can significantly improve the accuracy of vibration prediction calculation for medium and high frequency bands. Comparison of the calculation results of the theoretical method in this paper with those of other theoretical calculation methods and finite element method by an example proved the effectiveness and advantages of the theoretical method in this paper.

The underwater acoustic radiation of air cushion vehicles (ACVs) is a complex process considering hull structure-aircushion-water three-phase interaction and vibro-acoustic coupling, which has complex transmission characteristics and is the key and difficult issue in the ACV acoustic analysis. With an ACV taken as a computational example, the vibro-acoustic finite element method (FEM) and the analytical method were used to analyze the transmission characteristics of the underwater radiation noise of the ACV. To calculate the underwater acoustic field for mechanical noise sources and airborne sources of lift fans, a vibro-acoustic FEM numerical model considering structure-air-water interaction was established and calibrated by the natural frequency of the hull obtained from the tests. The analytical formulas were used to calculate the underwater acoustic field for airborne sources of other equipment. The overall sound pressure level (OASPL) at points 1 m from the port and starboard sides was adopted as an evaluation index. The research shows that the underwater radiation noise of the ACV is broadband noise. The underwater acoustic pressure calculated by the FEM increases with the increase of frequency, and the pressure is concentrated on the aircushion-water interaction surface at low frequencies. With the increase of frequency, the underwater acoustic field calculated by the FEM gradually presents an irregular interference distribution. The underwater radiation noise caused by the acoustic excitation of equipment like air propellers is mainly near-field and low-frequency noise, accounting averagely for 40% of that of the ACV within the sound radiation range of the equipment. The transmission characteristics of underwater radiation noise of ACVs revealed in this paper has important guiding significance for the vibration and noise reduction of ACVs.

The air lubrication drag reduction is a flow control method for energy-saving and carbon reduction. Under the background of “carbon peaking, carbon neutrality” strategy in China, the air lubrication drag reduction is essential for the development of low-carbon and zero-carbon ships since it can effectively reduce the ship resistance. In this paper, the background of the air lubrication drag reduction technology both at home and abroad is introduced. The definition and classification of air lubrication drag reduction are clarified based on the air-water flow regime and drag reduction mechanisms, i.e. dispersed bubble drag reduction and continuous air layer drag reduction. The progress of dispersed bubble drag reduction and continuous air layer drag reduction in two-phase flow regimes, drag reduction characteristics and mechanisms are summarized respectively. Finally, the status of air lubrication drag reduction is summarized and the future opportunities in this field are discussed.

With an 80 000 DWT bulk carrier taken as the optimization object, two new hull lines design technologies based on the hull fusion method and regional feature analysis were applied by combining ship CFD resistance and self-propulsion assessment for the research on hull lines design and performance analysis, aiming at the hydrodynamic performance under design draft. With the whole design process starting with the reference ship, the hull line automatic deformation designs of the bow and stern part were made respectively in order to reduce the resistance and improve the wave making and stern wake distribution. By analyzing the CFD numerical simulation evaluation results under the same model scale, a series of design hulls with good performance were successfully obtained. Finally, the simulation results were verified by model test under the design draft in still water. Compared with the design prototype, the received power trial prediction of the final design scheme at the speed of 14.0 kn was reduced by about 5.6%.