In ship and ocean engineering, structures inevitably encounter crack damage due to material defects or microcracks generated during their service time, which causes stress concentration and structural failure. To better simulate the crack propagation behavior of steel members with defects, Q345 steel was taken as the research object in this paper, an improved two-parameter peridynamic (PD) model was proposed based on the PD theory. The internal length effect of long-range forces was considered and the corresponding expressions of coefficient were deduced firstly. Furthermore, the basic form of the constitutive force function of the two-parameter PD was constructed based on the linear and nonlinear mechanical behaviors of the failure process of Q345 steel with defects. The crack propagation behaviors of Q345 steel with different crack distance, length and angle were studied and compared with the experimental results, which verified the accuracy of the present work. Then, the calculation method of fatigue crack propagation under alternating load was given. The research results may provide a reference for the optimization design and failure prevention of steel members in ocean engineering.

To explore the influence of the blocking environment on the ice-class propeller's hydrodynamic and cavitation characteristics and to help the optimization design of ice-class propellers, a test platform was built under the ice blocking environment in a large cavitation channel. The hydrodynamic loads of the whole propeller and a single blade were measured while cavitation patterns with different blocking parameters were observed under ambient pressure and depressurized conditions. The test results show that the hydrodynamic performance of the propeller under ice blocking conditions is the result of the combined effects of the ice blocking parameters, the cavitation environment and the propeller operating conditions. Under the combined influence of ice blocking effect, proximity effect, propeller suction, reflux zone and the "Pirouette effect", the conjoined vortex between the ice and the propeller blade will be induced and severe fluctuations are caused in the propeller's hydrodynamic performance.

The multi-spherical shells composite structure is a common structurural form of manned submersibles. A vibro-acoustic coupling model of multi-spherical shells system considering acoustic field coupling between shells was established by using the translationnal addition theorem for spherical wave function. The acoustic field coupling characteristics and their influencing factors of a series of spatially-distributed spherical shells were studied. The results show that the acoustic field interaction can change the coupling between the modes of the spherical shells. The contribution of a single mode to the vibration of the spherical shell is no longer limited to a single peak, and thus affects the spectral characteristics of the acoustic radiation. Both shells of the double spherical shells system generate acoustic radiation. There is a strong field coupling effect between two spherical shells under axial excitation. When the excitation force deviates from the axial direction, the field coupling effect gradually weakens. The double spherical shells system composed of spherical shells with different scales expands the frequency range of effective coupling, and the modal characteristics of both shells appear in the acoustic field. When the spherical shells are arranged in series, the acoustic field coupling has a transmission effect. While the spherical shells are distributed at different angles, the spatial distribution of acoustic field becomes more complex.

In this paper, the Bonora damage model based on continuum damage mechanics was adopted to analyze the pressured spherical hulls of deep-sea manned submersibles. Firstly, the loading and unloading test of TA31 titanium alloy was committed to investigating the parameters of Bonora model. Then, a calibration method of model parameters was proposed, and the model parameters of TA31 titanium alloy were determined according to the experimental data. Finally, the Bonora model was embedded into the finite element software in the form of VUMAT subroutine, and the analysis of ultimate strength of titanium alloy pressured spherical hull was carried out. The results show that the method based on Bonora model can accurately simulate the failure mode and ultimate strength of the pressured spherical hull. In this model, the effects of yield strength, tensile strength and maximum plastic strain were considered in the constitutive relation of materials, and the physical meaning of structural failure was more explicit, which has guiding significance for the optimization and promotion of material properties.

The interaction between level ice and offshore pile structures is a complex process, which often involves the breaking, failure and accumulation of sea ice. The issure of level ice failure is essentially a problem related to brittle failure of ice materials. However, the failure mechanism of traditional finite element method has great limitations in this problem, which cannot reasonably reflect the deformation and motion state of broken ice. Therefore, it is necessary to explore the existing numerical simulation technology and establish a reasonable modeling method to solve the key points related to level ice damage problems. In this paper, a user-defined constitutive model was introduced to simulate mechanical properties of sea ice material, and the cohesive elements were used to refect the generation and propagation of ice cracks. Through the simulation of the interaction between pile structures and level ice, the failure mode of ice material and the interaction load between pile structures and level ice were analyzed, and the reliability of the proposed method was verified by comparing with the relevant model tests. The results show that the method used in this paper can effectively simulate the compression and bending failure of level ice under the action of pile structures, and the ice load can be accurately predicted. The relevant conclusions are of great significance for ice load prediction and the structure design of offshore pile structures.

In recent years, more and more researchers have applied machine learning to predict the performance of ship propellers, but the prediction effectiveness of surrogate model is often affected by the quantity and quality of data used for training. At present, the quantity and quality of the ship propeller performance data are unsatisfactory, and the distribution of data corresponding parameters is relatively centralized and seriously uneven. Therefore, these facts may affect the accuracy and reliability of surrogate models. In order to solve this problem, this paper presents a sample expansion method based on empirical knowledge, and applies it to the prediction of ship propeller hydrodynamic performance. The results show that the sample expansion method can generate the data sample quickly, and improve the reliability and accuracy of the forecasting surrogate model.

In order to improve the velocity of torpedoes, the transient calculation model of a torpedo launching propulsion pump during rapid start-up process was established based on the Reynolds average N-S equation and SST k-ω turbulence model in present paper. The hydraulic characteristics and the flow field evolution of the propulsion pump under three start-up time conditions were studied by numerical method. The results show that the flow rate and the thrust continue to increase with time. The head, the axial force, the axial moment and the power increase at first and then decrease. The efficiency firstly increases and then remains stable. The maximum values of the head, the axial force, the axial moment and the power appear at the end of acceleration, and the maximum values decrease with the increase of start-up time. At the beginning of start-up, there are serious inflow impact, flow separation and vortex structure in the impeller area, and the flow field tends to be stable gradually with time. Start-up time has a significant effect on the flow field evolution of the propulsion pump. The smaller the start-up time is, the faster the flow field reaches stable state. In order to ensure that the propulsion pump has no cavity and the internal flow field runs to stable state in a relatively short time during star-up process, it is recommended to start propulsion pump by 0.2 seconds start-up time.

Developing a reliable potential flow solver is necessary for the ship CAE software. The method on the three-dimensional time-domain Green function of ships with forward speed in infinite depth was studied. Firstly, a three-dimensional transient free-surface Green function was introduced, and its Rankine part was calculated by Hess & Smith’s method, and its free-surface memory part was calculated by the method of Beck team from the University of Michigan, US. Secondly, the memory part of the Green function and its derivatives were obtained in the mathematical expressions for making the program in five regions. Thirdly, the source method was used to calculate the source and the radiation potential, and then the radiation force was obtained by integrating the pressure around the floating body. Finally, the radiation force of the Wigley I ship was calculated, and compared with the published experimental and numerical results. The reliability of the method and the code in this paper is confirmed.