Suppressing incipient cavitation in an underwater body is of great importance to reducing the adverse effects caused by cavitation. For the method of suppressing incipient cavitation by changing the surface roughness, the research on the optimal design of the rough band parameters based on surrogate model methods was conducted. Firstly, numerical calculation methods were used to analyze the influence mechanism of the rough band parameters on the incipient cavitation characteristics at the head of the underwater body, and an initial design range for the rough band parameters was established. Then, the surrogate model method was used for parameter optimization analysis. The results show that setting a rough band on the head surface of the body can change the pressure distribution. The front and rear boundaries of the roughness may cause slight pressure fluctuations, which can change the minimum pressure value and thereby affect the incipient cavitation characteristics. Through sensitivity analysis of the surrogate model, it can be observed that compared with the position and width of the rough band, its height has a greater influence on incipient cavitation. The final optimization results obtained were verified by numerical calculation, which can obviously reduce the incipient cavitation and achieve a better effect in suppressing it.

To study the time-averaged flow field characteristics of a cylinder under the action of periodic oscillating flow, the time-varying flow field around the cylinder was obtained by numerically solving the Navier-Stokes equations. The time-averaged flow field was obtained by averaging the velocity field over time. The time-averaged flow fields with different K_C numbers under a given Stokes number β=20 for Reynolds number Re< 200 were compared and analyzed. It is found that: (1) when K_C< 7 (Re<140), the oscillating flow vorticity source is always attached to the cylinder wall and gradually stretches along the oscillating flow direction; (2) the corresponding time-averaged flow field consists of four small-scale internal vortices with strong stable flow and four large-scale external vortices with weak flow; (3) the flow structure is of axisymmetric distribution; (4) when K_C> 7 (140<Re<200), the symmetry of the vorticity distribution around the cylinder is destroyed, while the oblique vortex street and dissipative behavior appear, the corresponding time-averaged flow field structure is seriously distorted, and the flow field structure is closely related to the vortex shedding mode around the cylinder, (5) the strength of the time-averaged flow field increases exponentially with the increase of K_C number, and (6) for double cylindrical tubes, the time-averaged flow fields under different arrangements and spacing ratios show rich flow field characteristics, and the gap flow intensity between tubes increases with the decrease of spacing ratio.

An accelerated creep test method for deep-sea equipment viewport window was proposed in this paper based on the sensitivity of PMMA (Polymethyl methacrylate) to temperature and stress. A modified creep constitutive equation based on aging theory was proposed by introducing the influence function of temperature. The uniaxial compressive creep tests at different temperature and stress levels were carried out, and the creep constitutive relation of PMMA was obtained by stepwise fitting method. The conversion relationship of the creep behavior of the viewport under different temperatures and pressures was obtained by the finite element creep analysis. The accelerated creep test method of the viewport model under the condition of raised temperature and increased pressure was proposed, and the comparison between the test results and the calculated results was completed. It is shown that the stress sensitivity of the uniaxial compressive creep behavior of PMMA is related to temperature. The finite element solution of the conversion coefficient of viewport’s creep deformation under different temperatures and pressures is different from the calculated value. The results of the viewport model are in good agreement with those of finite element creep analysis. In conclusion, in a certain temperature and stress range, the creep constitutive relation of PMMA obtained in this paper can well describe the law of uniaxial compressive creep behavior, and that of the viewport can be well simulated by the finite element creep analysis. The calculation results show that the conversion coefficient of viewport’s creep displacements between conditions of 25 °C & 26.6 MPa and 3 °C & 20 MPa is 12.2, and this coefficient can provide a basis for the accelerated creep test.

A structural reliability analysis method based on synthetic minority over-sampling technique (SMOTE) algorithm and Bayesian optimization (BO) neural network was proposed in this paper to improve the calculation accuracy and analysis efficiency of the impact resistance reliability of lubricating oil cooler. Firstly, the uniform design (UD) method and SMOTE algorithm were used to improve the utilization efficiency of the sample points. Secondly, the Bayesian optimization algorithm was used to optimize the hyperparameters, initial weights and initial biases of the BP neural network to improve the fitting accuracy and generalization ability of the model. Finally, the optimized surrogate model was combined with the Monte Carlo (MC) method to calculate the structural reliability. The results show that, compared with the traditional surrogate model method, the proposed method has the advantages of higher accuracy, shorter analysis time and lower calculation cost. The analysis method proposed in this paper has great applicability in the impact resistance reliability analysis of lubricating oil cooler. The analysis results provide technical guidance and theoretical support for the impact resistance design of lubricating oil cooler.

To investigate the collision dynamics of a marine rotating machinery integrated with an airbag-raft-limiter system under the influence of heaving motions, a dynamic model of an asymmetric system incorporating a limiter was developed. This model took into account the effect of the ship heaving motion and the limiter gap on the coupled airbag-raft-limiter system. The equations of motion were given dimensionless treatment to facilitate computational analysis. The study examined the influence of rotor speed, heaving amplitude, and limiter gap on the system’s dynamics utilizing nonlinear dynamics analysis techniques including phase diagrams, spectral responses, and energy trajectory diagrams. The findings indicate that an increase in heaving amplitude leads to collisions between the system and the limiter, causing a significant amplitude decrease while triggering a transition of motion from quasi-periodic state to chaotic state. Additionally, the collision alters the energy trajectory of the system, moving from a uniform distribution towards the collision zone.

The accurate assessment and analysis of nonlinear wave loads on ships and the high-frequency vibrational response of ship structures are requisites for determining the safety of ship structures. However, the reliability of numerical simulation and the analysis of their uncertainties have received relatively little attention. This paper presents a segmented keel beam hydroelastic model CFD-FEM simulation and experimental research to simulate and analyze the high-frequency response of a ship model in waves. Uncertainty analysis was performed on the simulation results to evaluate the reliability of the simulation model. The calculation results of numerical uncertainties can provide criteria for judging the convergence of results under different influencing factors and the level of uncertainty. The uncertainty levels of the impact pressure on the ship’s bow, the motion of the ship model, and the high and low-frequency wave bending moments of the ship hull are also clarified. A comparison between numerical simulation and experimental testing reveals that CFD-FEM two-way fluid-structure coupling simulation can accurately capture the high-frequency response of ship structures. The high-frequency bending moment component of the ship under cruising conditions can account for more than 49.95% of the low-frequency wave bending moment. The dynamic response of ships induced by impact loads cannot be ignored, and their influence must be considered in the structural design and safety assessment of such ships. This paper can provide a reference for the uncertainty analysis of high-frequency structural dynamic responses such as ship impact vibration.

Stiffened plates are the basic structural units of a ship hull, and the safety and reliability of such structures are of paramount importance during service. Therefore, accurate acquisition of physical parameters such as stress and strain in stiffened plate structures through real-time monitoring techniques can provide data support for the safety assessment and prediction of ship hull structures. By employing the inverse finite element method (IFEM) based on the least squares variational principle, strain-field reconstruction of stiffened plate structures was conducted. Initially, numerical simulations were performed on axially-loaded stiffened plates, and the simulation results were then input into the inverse finite element algorithm for strain field reconstruction. By designing different measurement point layout schemes, the errors between the reconstructed results and the simulation results were analyzed. Moreover, the Xgboost algorithm was applied to provide guidance for the selection of discrete measurement point quantities and locations. The results indicate that IFEM is applicable to strain reconstruction in stiffened plate structures of ship hulls, and by optimizing the positions of measurement points, a significant reduction in quantity of measurement points in the inverse finite element model can be achieved while maintaining high-precision reconstruction results. The findings of this study can provide technical support for the health monitoring and safety assessment of ship hull structures.

Marine risers are critical facilities connecting offshore oil and gas platforms to subsea wellheads, and vortex-induced vibration is the main cause of fatigue damage to risers. Therefore, a vibration suppression-energy harvesting turbine device was designed for risers to suppress vortex-induced vibration and harvest energy. Then experiments were conducted with the length of the blade of the turbine device’s impeller as a variable. On one hand, the vibration suppression and energy harvesting performance of the turbine device were verified; on the other hand, the influence of the impeller’s length of the blade on the device’s vibration suppression-energy harvesting performance was investigated. The results show that the overall vibration suppression efficiency of the turbine device is ideal, capable of reaching over 50%, with the best vibration suppression efficiency being 96.08%. The vibration suppression performance of the device increases positively with the increase in the impeller’s length of the blade, while the energy harvesting performance shows a negative trend. When the length of the blade is 12d, the vibration suppression-energy harvesting performance of the device increases synchronously with the increase in the incoming flow velocity.

In the formation process of a sonar array, position deviation between array elements is inevitable, and the sound-field coupling between array elements is strong under the close-packed condition, thus resulting in the amplitude and phase inconsistency between array elements. So it is necessary to carry out array online calibration after array formation. An anechoic pool in the lab can only be used to simulate free field in a certain frequency band, which is difficult to satisfy the need of low frequency underwater acoustic measurement. Therefore, the study in this paper focuses on the low frequency calibration problem of cylindrical array, and proposes a calibration method for array amplitude-phase consistency which combines holographic acoustic field reconstruction in finite space with matching search compensation. Based on the sound field separation technique of near-field acoustic holography (NAH) in finite space, the sound field in finite space was reconstructed firstly. Then, the amplitude-phase consistency search function was established with the sound field reconstruction results to realize the amplitude-phase consistency calibration for complex array elements by combining the optimization idea of matching search algorithm. In this paper, a small cylindrical array was taken as the analysis object, the theoretical modeling and simulation of the finite space sound field in the cylindrical cavity were carried out, and combined with intelligent optimization algorithm to calibrate the amplitude and phase consistency between array elements. The simulation results show that the proposed method based on NAH can be used for on-line calibration of low frequency amplitude-phase consistency after array formation in the laboratory.

An equivalent source method based on plane wave expansion and mirror imaging is proposed for predicting radiation from elastic structures in shallow water waveguide. This method uses the equivalent source framework and represents the Green’s function with plane wave expansion for virtual source intensities and far-field acoustic calculations. For seabed reflection coefficients dependent on incident angles, the Green’s function decomposes the spherical wave from a point source into plane waves, facilitating accurate reflection calculations on non-ideal boundaries. Comparisons with other Green’s function validate the computational accuracy. Numerical simulations of an elastic cylindrical shell under various excitation frequencies in shallow water waveguide confirm the method’s accuracy in sound field reconstruction.