The pump-jet thrusters produce structural noise during operation.The pump-jet propulsors made of conventional materials often have heavy structure weights. And in this case it is difficult to balance the stern weight. The use of composite materials in the pump-jet propulsor structure can not only greatly reduce the overall weight, but also have good corrosion resistance and fatigue resistance. Focusing on the vibration control problem of composite duct structure of pump-jet propulsors, this paper presents the research on experimental modeling, algorithm optimization design, hardware platform construction and test for MFC-based structural vibration active control system construction and verification based on macro fiber composite (MFC). The genetic algorithm was applied to the optimization design of linear quadratic Gaussian (LQG) controller, and the control effects of the algorithm before and after optimization were compared by experiments. A model identification platform and an active control test platform were built for the composite duct. The control model was obtained by experimental modeling method and the active vibration control test under harmonic excitation was carried out in the air environment. The research attempts to push MFC-based active vibration control method to application scenarios.

The line spectra noise radiated by cavity flows greatly deteriorates the acoustic stealth of naval ships, whose formation mechanisms are related to the flow and acoustic modal effects, as well as the acoustic-vibration and flow-sound coupling effects. In this paper, the transient flow, equivalent sound source and acoustic fields of the simple square and typical cavity flows were numerically simulated, based on the CFD/CHA hybrid approaches. The applicability of the numerical methods was verified by comparison with experimental data of water tunnel test. The characteristics of the flow and acoustic modes of the cavity flows were concluded, particularly the effects of the acoustic-vibration coupling of elastic cavity walls and the complexity of cavity inner shapes upon the acoustic mode frequencies were quantitatively calculated. The important regularity, which the line spectrum induced by the effect of the first acoustic mode is the "decisive line spectrum" in the far-field radiated noise spectrum, is summed up. The tendency of the acoustic mode frequencies to shifting sharply towards lower frequencies under the actual cavity conditions was analyzed, indicating the necessity of avoiding the flow-sound coupling. The necessary condition of the cross-sectional area ratio for the related acoustic experiments in water tunnels was quantitatively established through an analytical solution. The research has an important guiding value for the designs of experimental modals.

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.

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.

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.

Conventional resistance prediction method of proxy models takes main scale ratios, ship form coefficients, and other similar parameters as inputs. Compared to CFD calculations, in which the complete hull form is used as input, prediction method with lower information density of proxy models results in lower prediction accuracy. In this paper, a high-dimensional, high-precision resistance prediction method was proposed for ship hulls using 4108 sets of complete hull geometry feature tensors as input and employing neural networks as proxy models. The total resistance coefficient of the ship was taken as the output. Dimensionless treatment of the hull forms was conducted at first and feature tensors were extracted as inputs. Next, a neural network model was constructed, comprising input layers, hidden layers, and an output layer. Finally, the feature tensors of the hull forms and the corresponding total resistance coefficients were fed into the neural network, and the model was trained using error back propagation until the loss function converges. The research findings in this paper can provide theoretical and technical support for high-dimensional proxy model-based resistance performance prediction.

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 .

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.

In order to investigate the impact of the blowing rate and sequence of the main ballast water tank on the emergency surfacing characteristics of submarines, Suboff was taken as the research object. Based on RANS equation and overall dynamic grid technology, a simplified high-pressure air blowing model of the main ballast water tank was combined to construct a simulated calculation model for the emergency surfacing motion of submarines. By linearly applying buoyancy, the submarine emergency surfacing motion parameters varying with time were obtained under different blowing rates, blowing sequences, and time intervals at an initial speed of 1m/s. The results show that the faster the blowing rate of the main ballast water tank is, the faster the hull water flows out, the smaller the amplitude of the pitch angle is, and the larger the amplitude of the roll angle is. Blowing out the water tank in the order of the bow, middle, and stern groups, as well as the middle, bow, and stern groups, results in a larger longitudinal angle amplitude and faster upward buoyancy compared to simultaneous blowing out. Blowing out the water tank in the order of the bow, middle, and stern groups, results in faster water output compared to that in the order of the middle, bow, and stern groups. Under the same blowing sequence, the longer the time interval, the greater the amplitude of pitch angle and the surfacing time with an interval of 1.0 s is earlier than the other two working conditions. In all operating conditions, the highest point of surfacing occurred at 7.08 s in the condition of blowing out the water tank in the order of the bow, middle, and stern groups with a time interval of 1.0 s, which is 1.21 earlier than simultaneous blowing. The research results have certain guiding significance for the pressure design of high-pressure gas in submarines and the blowing strategy for emergency surfacing of real submarine.

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.