For a ship turning in the ice area, the bow shoulder and stern of the ship are more vulnerable to ice load of large amplitude, posing a threat to the safety of the hull structure. In this paper, the sea ice circumferential crack expansion analysis method was used to simulate the dynamic process of ship-ice interaction for ice breaking ship during turning. The random characteristics of ship-ice collision in different hull areas were analyzed, making an identification of the typical local ice pressure time course, to obtain the main characteristics of different types of ice pressure, such as period, amplitude and distribution law, and analyze the danger degree of each hull area under turning ice breaking scenario. The results show that there is a negative correlation between the period and amplitude of local loads, and that in the bow area, the short period "pure triangle" type loads account for 63.79% of the total and the peak value accounts for 82.4% of the whole ship. So the bow area is the key area of a ship in the turning ice breaking scenario. The method adopted in this paper provides an effective means to study the ship-ice interaction, and the relevant calculation results can be used as load input for the design of ice-resistant structures of polar ships.

In order to understand the motion characteristics of amphibious aircraft planing in head waves, in this paper, the Chinese numerical tank-Cartesian grid finite difference method was used to study the planing motion response characteristics of an amphibious aircraft in waves under different wave conditions. The effects of wavelength and wave height on heave and pitch response of the aircraft and the vertical overload of mid-ship and stem were summarized. Based on the step-by-step method, the Navier-Stokes equation was discretized in space. The immersed boundary method was used to capture the boundary of complex objects and accurately simulate its large motion. At the same time, the THINC/SW algorithm was used to effectively simulate the violent motion of free surface. The results show that the wavelength and wave height have a great influence on the planing motion response of the amphibious aircraft. With the increase of planing speed, the pitch resonance wavelength increases, and the heave resonance wavelength decreases first and then increases, while the linear correlation between the heave and pitch response of the aircraft, the vertical overload of the mid-ship and stem and the wave height will also be weakened.

In view of the numerous and complex structures of ship machinery, equipment and the coupling of vibration transmission paths, a method of underwater radiated noise prediction based on BP (Back Propagation) neural network was proposed in this paper. A BP neural network based on gradient descent algorithm and Bayesian regularization algorithm was constructed respectively. Vibration data was taken as input, hull radiation noise was taken as output, and root mean square error (e_RMSE) and mean absolute error (e_MAE) were taken as evaluation indexes of model prediction accuracy. The results show that the generalization and robustness of Bayesian regularization BP neural network is better than that of gradient descent algorithm BP neural network. The error of Bayesian regularization is less than 3 dB, and the proposed method has good applicability in the field of ship radiation noise prediction.

Aiming at the initial stress field generated by welding of ring-ribbed cylindrical shell structures with initial geometric defects after shape correction, this paper presents the study on the influence of initial stress field on the strength and stability of ring-ribbed cylindrical shell structures under the premise of considering geometric nonlinearity caused by large deformation. The finite element model of ring-ribbed cylindrical shell with initial geometric defects was constructed by using ANSYS software and the initial stress field was calculated. The strength and stability of ring-ribbed cylindrical shell with initial geometric defects and stress field were solved by arc length method. The comparison between the experimental results and the calculated results verifies the validity of the model. The analysis shows that the ultimate bearing capacity of the ring-ribbed cylindrical shell under hydrostatic external pressure is slightly reduced, and the regularity of the instability waveform is reduced, but the failure position remains unchanged.

In order to improve the propulsion performance of contra-rotating propellers and reduce the cavitation effect, an end plate was applied to the contra-rotating propeller. The cavitation performance and propulsion performance of the end-plate contra-rotating propeller were analyzed. The RANS method with Schnerr-Sauer cavitation model was used for analyzing. Then the propulsion performance of contra-rotating propellers composed of conventional skewed propellers and end-plate propellers were checked for comparison. It is found that the addition of an end-plate makes the contra-rotating propeller possess better anti-cavitation performance. The sheet cavitation range is reduced by about 59% in the bollard state (J=0), and the cavitation is delayed when J=0.1. In addition, under the condition of low advance speed, the end-plate contra-rotating propeller shows a higher propulsion efficiency by 0.9%~3.1% than the conventional one. The open water performance of the end-plate contra-rotating propeller was tested at different rotation speeds, and the data were in good agreement with the simulation results considering the cavitation model. In this study, an end plate is innovatively applied to the contra-rotating propeller, which is suitable for the propulsion and operation requirements of low-speed submersibles.

Thick-walled pipelines are widely used as transmission pipes for (ultra) deepwater petroleum and natural gas, and buckle arrestors for shallow water pipelines. However, the current international authoritative regulations may underestimate their ultimate bearing capacity significantly so that their economy and safety are hot topics in industrial circles. After deriving the calculation formula of vector form intrinsic finite element (VFIFE) method solid element, an analysis model of thick-walled pipelines considering the nonlinearity of geometry, material and boundary was established to solve the key mechanical problem of local collapse of thick-walled pipelines. And its accuracy was verified by comparison with 8 sets of thick-walled pipe scale tests, the DNV code, and ABAQUS simulations. Sensitivity analysis of diameter-to-thickness ratio, initial ovality and material yield strength were carried out to quantify the calculation errors of the DNV code method. Then, a more accurate formula for calculating the local collapse pressure of thick-walled pipes was obtained by fitting the VFIFE results. The results show that the simulation results of the VFIFE constant strain tetrahedral element are in line with the actual situation and can provide a new analysis strategy for the collapse behavior analysis of thick-walled pipelines. However, attention should be paid to determining the maximum load rate under the requirement of the quasi-static loading. Under high external pressure, the pipeline will collapse locally and propagate buckle dynamically and the deformation of the pipe section changes from an ellipse to a "dumbbell" shape with certain folds on the inner wall. During local collapse, the change trend of the stress distribution conforms to the general features of solid structure buckling instability. The calculation error of the DNV code of thick-walled pipelines’ local collapse pressure increases with the decrease of the diameter-to-thickness ratio, the decrease of the initial ovality, and the increase of the material yield strength respectively. The corrected formula for local collapse pressure calculation of thick-walled pipelines has a fitting error of -2.49%~1.72% for homologous data and a calculation error of -6.11%~1.70% for heterologous data. It can accurately calculate the local collapse pressures of deepwater pipelines with diameter-to-thickness ratio of 8~18, initial ovality of 0.5%~3.0%, and material yield strength of 300~500 MPa. The results can be used to guide the design and verification of submarine thick-walled pipelines.

Obtaining the divisional characteristics of ice resistance on the hull is the basis of hull form optimization for icebreakers. At present, neither the real ship measurement nor the ice tank model test can effectively obtain the divisional characteristics of ice resistances at each part of the hull. In order to explore the ice resistance during the icebreaking process, the icebreaker "XueLong 2" was taken as the research object in this paper, and the ice force carried by each parts of the hull during the icebreaking process was analyzed by constructing a discrete element numerical model of the interaction of ship and ice. Firstly, a discrete element model of level ice with random-arranged elements was established, and the microscopic parameters of the model were calibrated according to the typical strength values of Arctic sea ice. Then, the ice resistance of "XueLong 2" calculated based on discrete element method was compared with that based on Lindqvist empirical formula. On this basis, the ice force value of each region of the hull was obtained through calculating zonally the ice force in the interaction process of ship and ice. The calculation results show that the icebreaking resistance accounts for a large proportion among the ice resistance of the hull generated in the icebreaking process, and the friction resistance caused by the slip of crushed ices is relatively small. The ice resistance of the hull is mainly generated in the area of bow, and the stem bears a significant icebreaking load. The divisional calculation method of ice resistance of icebreaker established in this paper can provide technical support for the hull optimization based on icebreaking capability.

Flow-induced vibration of valves is the main source of vibration and noise in pipeline system. The characteristics of flow-induced vibration of liquid valves are important for analyzing vibration and noise in pipeline system, designing and establishing low-noise system. By taking ball valve as the research object, a three-way spring and beam element model was used to simulate the elasticity bolt connection of ball valve inlet and outlet flange end face. Constrained boundary conditions of valves under actual working conditions were established though correcting constrained boundary stiffness with measured dry-humid modal results. Based on Finite Element Method (FEM) and Computational Fluid Dynamics (CFD) theory, the flow-induced vibration analysis model of ball valves was established to research the flow field and fluid-induced vibration characteristics and the correlative influence law of ball valve under variable opening and mass flow conditions. The results show that the three-way spring and beam element model can better simulate the actual installation boundary conditions of ball valve in water pipe. With the decrease of ball valve opening or the increase of mass flow rate, the disturbance of flow field becomes more obvious, and the vibration acceleration level at each measuring point increases.

Based on the STAR-CCM+ software, CFD-DEM method was used to simulate the process of a type of an actual built transport ship sailing in a brash ice channel. The influence of different drafts on the resistance performance of the ship was studied. The interaction between the ship and water was obtained using CFD method. A numerical brash ice particle model was established using DEM method, the ship-ice collision phenomena and the brash ice resistance were studied. The results show that the distribution pattern of brash ice particles obtained based on the above method agrees well with that of the test conducted in Hamburg Ship Model Basin (HSVA). The total resistance of the numerical prediction varies little from the model test results. Also, the numerical method performs much better than the FSICR empirical formula's prediction, which verifies the reliability of the present method. The ice resistance of the whole ship does not show a monotonically decreasing trend with the decrease of draft, but increases significantly when a specific draft is reached. At a small draft, the change in trim has a little effect on the ice resistance of the whole ship, but has a large effect on the proportion of ice resistances of the fore, middle, aft and bottom parts of the hull.

The structural design of the propulsion shafting of modern ships is relatively complex, and the structure size is an important factor affecting the whirling vibration characteristics. Taking a ship complex propulsion shafting as the object, the influence of changes in shaft segment hollowness on the whirling vibration characteristics of the shafting was studied in this paper. Based on the finite element method, a whirling vibration analysis model of the shafting was established, and the whirling vibration characteristics of the shafting were analyzed under the initial hollowness. On this basis, the range of hollowness values was determined through strength check calculation. Taking the hollowness of the stern shaft and propeller shaft as variables, the influence of changes in the hollowness of shaft segments on the critical speed of the whirling vibration was analyzed and the values range of hollowness was specified according to the requirements of shafting alignment. The results can provide a reference for structural design and whirling vibration control in the design process of ship propulsion shafting.