For low-frequency line spectrum control in naval and other engineering fields, a nonlinear energy sink vibration isolation system dynamics model considering a flexible foundation was established, and the nonlinear dynamics of the system was analyzed using the harmonic balance method and Runge-Kutta method. The influence of the foundational parameters on the amplitude-frequency characteristics of the system was explored, and the nonlinear dynamical behavior of the system at the resonant frequency was analyzed. The influence law of mass ratio, cubic stiffness, and damping on the damping effect of nonlinear energy sink was explored with vibration power flow as the evaluation parameter. For the computational model analyzed, research shows: when the foundation stiffness is weak, the nonlinear energy sink has a large effect on the amplitude and frequency response characteristics of the equipment; for specific parameters, the state of motion of the base and the equipment at the first order resonant frequency may be different; the nonlinear energy sink has a superior damping effect, reducing the peak power flow to the base by 13.95 dB in this example.

High-resolution time variant flow field data is the key to the study of turbulence flow. Limited by measurement methods, simulation efficiency and data storage, it is still difficult to obtain high-resolution turbulent flow data directly in some circumstances. In this paper, based on the low-dimensional representation model of flow time-history data, a neural network-based feature coding prediction model and high-resolution turbulence flow reconstruction method were proposed. Firstly, a low-dimensional representation model of the turbulence flow was established based on the one-dimensional convolution networks; then, an artificial neural network model was employed to establish the mapping between the measuring point coordinates and feature coding system, and the prediction of feature coding for the unknown measuring points was realized; finally, based on feature coding, the decoder in the representation model was utilized to generate turbulence flow time history data at unknown positions. Turbulence flow with Re=2.2×10⁴ around a square cylinder was studied, and the low dimensional representation model and flow generation model were trained and verified. The method proposed in this paper is a high-precision turbulence flow data reconstruction method which can be widely used in one-point-based sensor data processing. It is a new approach for the reconstruction of turbulence flow field time-history data.

Liquid sloshing load is one of the key loads for the structural design of tank in Liquefied Natural Gas (LNG) carrying vehicle. When the sloshing load is too large, it will lead to local damage of the tank structure, which will cause liquid leakage and even the overturning of LNG vehicle. In this paper, based on the previous numerical results, two kinds of wall structures, i.e. trapezoid and square, were proposed. Liquid sloshing in tanks with different wall structures was experimentally studied. For the free-surface evolution and the distribution characteristics of impact load, with the help of statistical analysis, the effectiveness of wall structures in suppressing liquid sloshing was qualitatively and quantitatively analyzed. The results show that the presence of wall structures has changed the flow field. And instead of direct impact by water, an indirect impact by gas-containing liguid occurs. During the sloshing and impact of air-containing liquid, a large number of air-liquid mixtures and bubbles are generated, effectively reducing the impact load. Furthermore, the square wall structure is better than the trapezoidal wall structure for suppressing impact load.

Based on the principle of "attribute subdivision and knowledge encapsulation", the application process research of virtual test of ship resistance performance based on RANS equation by encapsulating virtual test expert knowledge was carried out, The application process of virtual test of ship resistance performance was established and compared to the physical pool model test process. Precise prediction of resistance performance can be carried out by only inputting the geometric surface and the main scale parameters of test object, which has the characteristics of high prediction accuracy and good effect. Compared with the traditional CFD resistance numerical calculation, the evaluation efficiency of ship resistance performance is greatly improved, the research cycle of ship performance is shortened, and the barrier to entry is significantly lowered .

Submerged waterjet propulsion is a variant of conventional waterjet propulsion, whose inlet duct is fully integrated into the bottom plate of hull, reulting in a more complex coupled flow field behind. In order to meet the development requirements of submerged waterjet propulsion, the differences in mechanical control system between two types of waterjet propulsion were studied. Numerical simulations were conducted for both conventional and submerged waterjet propulsion at designed speed point. The comparison results show that submerged waterjet propulsion has larger flow obtaining area, higher inlet duct efficiency and less impact on the ship motion while the thrust reduction fraction is larger.

An umbilical cable serves as a crucial link between the water surface and subsea units in offshore engineering. In this paper, a model test method for the lateral buckling of an umbilical cable armor layer under bending and compression was proposed, and the model was constrained by a sheath to induce lateral buckling. Model tests were carried out under the conditions of straight and bending radii of 2 m, 1.7 m, and 1.4 m. The accuracy of the proposed model test method was verified by the comparison between the theoretical values and experimental results in previous literature, and comparing with the numerical simulation results of this paper. The experimental study revealed that the critical displacement and critical buckling load for lateral buckling of the umbilical cable armor layer increased as the bending radius decreased, and the location of lateral buckling moved toward the fixed end with decreasing bending radius. For the umbilical cable in a bent and compressed state, lateral buckling of the armor wires with the initial winding position on the concave surface of the bend was more pronounced. The lateral buckling model test method proposed in this paper can be used to study the failure mechanism and mode of the umbilical cable armor layer under lateral buckling and to validate numerical simulation analysis.

In order to improve the anti-explosion protection performance of ships and explore the damage mechanism of marine sandwich structure under impact load, the close-range air explosion test of U-shaped folded sandwich plate was designed and carried out. The deformation and failure mode of the sandwich plate under shock wave load were analyzed, and the finite element simulation analysis was carried out. On this basis, the damage characteristics of sandwich plates under the combined action of shock wave and fragments were studied by prefabricating fragments at the bottom of explosives. The influence of panel thickness and detonation distance on the anti-explosion performance of sandwich plates was discussed from three aspects: panel break size, vertical displacement and energy absorption. The results show that the failure modes of the upper panel of the sandwich plate under the combined action of shock wave and fragment are large deflection, boundary tearing, plug break and scattered perforation. The bottom panel is dominated by large deflection and pits, and the shape of the upper panel break changes from' butterfly' to' circular' with the increase of the thickness of the upper panel. At this time, the upper panel and the core layer are the main energy absorbing components. The deformation of the central region of the sandwich plate is more sensitive to the decrease of the detonation distance, while the deformation of the edge region has no significant change. The total energy absorption of the sandwich plate, the energy absorption and proportion of the lower panel and the core layer increase with the decrease of the thickness of the upper panel. The change of the thickness of the lower panel and the core layer has little effect on the overall energy absorption of the sandwich plate and the proportion of each part.

For floating structures deployed in waters near the coast or island lagoons, the shallow water depth makes the impact of seabed topography changes on the mooring system non-negligible, and the seabed can no longer be simplified as flat when exploring the characteristics of the mooring system. To study the static characteristics of the anchor chain under the condition of uneven seabed terrain, an anchor chain model was established based on the lumped mass method, and effects of the seabed inclination angle and the arrangement of the anchor chain on the tension and the tension angle at the top of the anchor chain, and the length of the catenary were discussed through numerical simulation, in an attempt to guide the design and safety performance evaluation of floating mooring system in shallow waters.

The deep-sea pressure structure gradually presents the characteristics of a medium-thick shell, and their structural stress characteristics are significantly different from those of a traditional thin shell. Taking a deep-sea unmanned system head cover reinforced with rectangular ribs as the object, the strength of medium-thick shells was studied based on the three dimensional stress analysis method of ring-stiffened cylindrical shells. Firstly, the correctness of the calculation of the three dimensional stress method on the cylindrical shell was tested by examples in other literatures, then the typical stress calculation of the main structure of head cover and the stress characteristics of the medium-thick shell were studied, and finally the stress level and distribution of the shell and rib in the typical area of the head cover were calculated based on the assumption of the equivalent rib spacing. Compared with the finite element simulation calculation and model test results, the three dimensional stress analysis method has good applicability and engineering accuracy for the stress calculation of medium-thick shell pressure structures, which can provide a reference for the strength analysis of deep-sea pressure structures and the theoretical research of medium-thick shells.

In order to explore the lubrication characteristics of the main bearing under heavy load and its interaction mechanism with wear, based on the micro-contact and fatigue damage mechanism of micro-convex body, the wear model of bearing material was constructed, and combined with the mixed thermal elastohydrodynamic lubrication theory, the coupling analysis model of mixed thermal elastohydrodynamic lubrication and wear of the main bearing was established, based on which, the wear distribution and evolution law of the main bearing under specific load at the time of ignition were investigated, and the effects of wear on lubrication characteristic parameters such as oil film pressure, oil film thickness and rough contact pressure were discussed. The effects of load, radius clearance, micro-convex friction coefficient and rotational speed on the wear characteristics of the main bearing were obtained. The results show that with the increase of wear time, the wear area increases from the center of the bearing zone along the circumferential direction of the bearing, the contact pressure decreases and the minimum oil film thickness increases, and that the increase of radius clearance and micro-convex friction coefficient and the decrease of rotational speed will aggravate the wear of bearing bush.