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 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.

This paper aims to study the influence of immersion and liquid filling on the acoustic radiation characteristics of cylindrical shells, and to provide theoretical basis and research methods for the evaluation and measurement of acoustic performance of liquid-filled shells near the interface. The frequency immersion depth spectrum of the radiated sound pressure of a semi-filled infinite cylindrical shell and the frequency liquid-filled height spectrum of a semi-immersed infinite cylindrical shell were calculated by using the finite element numerical simulation method. The results show that there are two obvious resonance phenomena, which are respectively excited by the bending waves and the low-order fluid additional waves. According to the dispersion curve of phase velocity, the prediction formula of resonance frequency was deduced, which can accurately predict the resonance phenomenon in the radiated sound field and provide theoretical support for the control and evaluation of the characteristics of the vibration acoustic radiation line spectrum of the internal tank structure in the mooring state.

The joined shell with complex boundary condition is widely employed in the marine propulsion. And the traveling wave mode of the joined shell with rotational motion usually plays an important role in the marine propulsion. For prompting the application of functionally graded materials (FGMs) in ships and ocean engineering, the boundary conditions of a shell structure were simulated by the spring, the dynamical model of the rotating FGMs joined conical-cylindrical shell was derived, and the traveling wave mode of the rotating FGMs joined conical-cylindrical shell was analyzed. Firstly, considering the influence of the Coriolis force and centrifugal force produced by rotation, energy equations of the joined shell with the boundary spring and connecting spring were derived based on the Love’s thin shell theory. Then, the displacement function could be assumed based the Chebyshev polynomial, and the modal frequency equation was derived. Finally, the modal frequency of the traveling wave was solved by the Rayleigh-Ritz method. Based on the convergence analysis, the stiffness values of corresponding springs and the truncated terms of the Chebyshev polynomial were given. The effects of the circumferential wave number, volume fraction exponent, cone angle, rotational speed and the general boundary condition on the traveling wave mode were discussed. Results indicate that the bifurcation behavior with respect to the forward wave and backward wave are notable with the increase of rotating speed; the stiffness of axial spring has a greater effect compared with other springs; compared with the traditional energy method, the efficiency can be reduced for the repeated calculation and the elastic boundary condition has a large influence on the traveling wave mode, meaning the necessity of employing the spring to simulate the boundary condition.

Aiming at the inherent bottleneck of low efficiency and narrow frequency band of energy capture for traditional linear hinged module floating wave energy converters (WEC), a simple negative stiffness mechanism for hinged two-module floating WEC was proposed, which could be used as a passive method to improve the energy capture efficiency. Firstly, a simple and compact negative stiffness device was proposed, which was realized by placing simple stretch elastic elements between articulated floating bodies. Secondly a dynamic model of two-module nonlinear WEC in the time domain was established based on linear wave theory and Cummins equation. At the same time, the convolution integral term induced by wave radiation force was replaced by the state space model to improve the calculation speed. Finally, the numerical simulation of the two-module nonlinear WEC was carried out, and its energy capture characteristics under regular waves were analyzed. The numerical results show that the equivalent natural frequency of the system can be effectively reduced by introducing the nonlinear negative stiffness mechanism. When the negative stiffness mechanism was adjusted to appropriate parameters, the elastic force of the system can form an elliptical potential well in the phase plane of pitch motion, and its long axis is close to the mode direction of pitch motion of the floating module. Thus the pitch motion of the two modules tends to anti-phase and the nonlinear negative stiffness mechanism plays the role of phase control. Due to the above mechanism, the nonlinear negative stiffness mechanism with appropriate parameters can effectively improve the energy capture efficiency and broaden the energy absorption band.

As a kind of body-force model capable of replacing real propellers, the Blade Element Momentum Theory (BEMT) has a great application potential in simulating propeller performance and hull-propeller interaction. In order to deal with the problem that the traditional BEMT based on the ideal fluid hypothesis cannot accurately represent the real propeller model in a wide range of working conditions when coupling with the viscosity solver, an improved induct factor calculation method based on the real propeller was proposed in this paper. Open-water simulation of KP505 propeller body-force model at J=0.4-0.8 was carried out, and the simulation results of the body-force model, such as open-water performance, propeller load distribution and induced velocity field, were compared with those of the real propeller model. The results show that the maximum error of open water performance is 1.05% at each advance ratio, and the induced velocity field of the improved body-force model can reflect the wake momentum transport of the real propeller.

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 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.

Pump jet thrusters have gradually become the first choice of modern submarines, and vector thrusters have also been widely used in the aerospace field. In order to solve the problems of low control efficiency under low speed and improve the turning performance of submarines based on traditional rudder control, the application of vector thrusters in submarines has gradually become a hot spot at home and abroad. In this study, considering the nonlinear influence of various parameters of submersibles under large rudder angle (nozzle deflection angle), a nonlinear model of the horizontal maneuvering motion of a submersibles was established. By analyzing the turning performance of the submersible under three different control methods of ship rudder propeller, ship vector propeller and ship rudder vector propeller, the simulation was carried out under three different conditions: low speed, controlling the rotating speed of the pump jet propeller and controlling the axial speed of the submersible. The simulation results show that the vector pump jet propeller can effectively improve the turning performance of the submersible.