Bi-metallic mechanical clad pipes are one of the main measures for anti-corrosion control of oil and gas field gathering and transmission pipelines. The failure of their liner layers restricts the clad pipes' engineering application. In order to explore the buckling failure mechanism of liner layers of bi-metallic mechanical clad pipes, the mechanical model of a clad pipe under bending load was established. The influence of forming pressure, working pressure and composite pipe structural parameters on the failure mode of the liner layer lining was studied. The results show that the buckling resistance of the liner layer is improved by increasing the residual contact pressure. The buckling time of the liner layer is delayed and the fold amplitude is reduced by increasing the working pressure. The reduction of the initial layers gap of the clad pipe before forming is beneficial to improve the buckling resistance of the liner layer. With the increase of the wall thickness of the outer base pipe, the wall thickness of the lining pipe and inner diameter of the clad pipe, the buckling resistance of the lining pipe increases.

Mono-shell submarine's acoustical coating is supposed to possess the multifunctional characteristics of mechanical noise, hydrodynamic noise and acoustic target intensity control. Two difficulties need to be addressed for this purpose: the first one is to improve the mechanical noise low-frequency control effect; the other one is to achieve multifunctional compatibility of acoustical coating. In this paper, from the perspective of reducing the sound radiation of mechanically excited shells, modal superposition method was adopted to establish the vibro-acoustic coupling and sound radiation model of multilayer graded acoustical coating and finite length ribbed cylindrical shell in ideal aqueous medium of infinite size. Based on the acoustic coating modal transfer function characteristics, the acoustic coating gradient distribution characteristics, thickness, the number of layers and other parameters were analyzed to reduce sound radiation of the ribbed cylindrical shell. The characteristic acoustic impedance asymptotic parameter distribution of the layered gradient acoustic cover was given and compared with the sound reduction characteristics of laying a uniform acoustic cover. The results indicate that the acoustic coating with increased acoustic impedance and slow wave velocity from the inner to the outer layer of the ribbed cylindrical shell has the property of reducing the vibration displacement of the outer surface more effectively than the uniform coating, which can significantly increase the sound reduction effect and extend the low frequency range of noise reduction. Optimisation of the acoustic coating should increase the acoustic impedance mismatch of the inner layer and the outer layer adaption effect, in order to help reduce the low frequency acoustic radiation of the ribbed cylindrical shell and to take the reduction of the acoustic target intensity into account.

Double-layer gearbox casings can not only provide elastic support for the gear transmission system, but have a good performance in the reduction of vibration noise. To efficiently and accurately predict the control effect of the vibration noise for double-layer gearbox casings, the flexible dynamic condensation model of a marine double-layer gearbox casing with vibration isolators was established based on the modal synthesis method. The condensation model was verified by calculating the natural characteristics of the complete finite element model of the double-layer gearbox casing. The vibration isolation performance of the double-layer gearbox casing was evaluated by analyzing the modal decoupling rate, modal contribution, vibration level difference, and inner casing inclination of the established condensation model. The results show that the modal decoupling rate of the double-layer gearbox casing in the translation direction is above 94.9%. The modal contribution is mainly dominated by the second to sixth mode shapes. The maximum vibration level difference can reach 34.2 dB in the excitation frequency range of 1-6000 Hz. The excitation frequency has a significant effect on the variations of the vibration level difference and inner casing inclination when the excitation frequency is less than 2000 Hz.

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 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.

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.

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.

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.

For the influence of cavitation effect on the forward and reverse performance of two-way propellers, the ice-class propeller model test in a cavitation tunnel was adopted to discuss the hydrodynamic effects of the cavitation number and the advance coefficient on the propeller forward and reverse performance in the uniform flow environment, as well as the effects of the cavitation number, advance coefficient and ice-propeller spacing in ice blockage environment. The results show that in the uniform flow environment with constant flow speed and variable rotating speed, severe cavitation phenomenon reduces more thrust and torque than the increase of thrust and torque due to the increase of rotating speed. In the ice blockage environment with constant rotating speed and variable flow speed, the thrust and torque of the propeller are affected by the ice blockage and cavitation. When the cavitation is severe, the thrust and torque no longer increase with the decrease of the blockage distance. The reverse performance of the two-way propeller is worse than the forward performance. The larger the advance coefficient is, the greater the performance difference is. When the advance coefficient is 0.7 in the uniform flow environment, the difference of the thrust coefficient is about 80%. With the increase of ice-propeller spacing, the hydrodynamic difference increases insignificanty. Cavitation is continuously generated on the blades, and quickly collapses when it is separated from the blades. With the decrease of the ice-propeller spacing, the cavitation phenomenon on the surface of the blade near the ice is more serious, the larger the area of cavitation is, the more irregular the shape of the cavitation will be.