Flow-Induced Vibration (FIV) energy harvesting is an effective approach for harnessing low-velocity ocean currents. Using a maglev support system to replace traditional metal springs enables better stiffness adjustment and improves underwater operation and maintenance performance. To enhance energy output and stability, dual-oscillator designs are widely used in vortex-induced vibration energy harvesters. However, the vibration characteristics of dual oscillators supported by maglev systems remain underexplored. This study establishes a coupled numerical model that integrates the FIV of rigid cylindrical oscillators with a maglev support system to investigate the influence of the spacing ratio (G/D) on their vibration responses. Results show that a smaller spacing ratio (G/D=2) intensifies hydrodynamic interactions, leading to a downstream oscillator's amplitude reaching over twice that of a single oscillator. The oscillation frequencies decrease monotonically with increasing spacing ratios, and distinct frequency variation patterns are observed between upstream and downstream oscillators. Vortex analysis reveals that the upstream wake reconstructs the flow field and strengthens the excitation forces on the downstream oscillator, thereby amplifying its vibration response. The maglev effect enhances the oscillators' responsiveness to flow field changes through nonlinear magnetic forces, further improving vibration performance and system stability. This study provides theoretical insights for optimizing dual-oscillator FIV energy harvesters with maglev support.

The phenomenon of flow-induced vibrations with small amplitude and strong fluid-structure interaction is commonly found in both nature and engineering practice. This paper proposes a frozen boundary method, which keeps the boundary fixed and represents the boundary vibration effects using mass sources and momentum sources. This method is applied to calculate forced vibrations and vortex-induced vibrations of a circular cylinder with a single degree of freedom. The results show that in forced vibrations, the frozen boundary method improves computation speed compared to the dynamic mesh method while ensuring calculation accuracy, thus validating the reliability of the method. For the single degree of freedom vortex-induced vibration of the circular cylinder, the phenomenon of lock-in was successfully computed. Due to the resonance effects within the lock-in region, the lateral fluctuations of the cylinder's wake field are considerable. The wake-vortex lock-in results from the competition between the vibrating vortex system and the detached vortex system. When the vibrating vortex system dominates, it manifests as frequency locking, leading to resonance. The frozen boundary method provides a new perspective and implementation approach for calculating fluid-structure interaction problems.

To investigate the feasibility of determining submarine hydrodynamic derivatives through wind tunnel experiments, this study focuses on the SUBOFF AFF-8 model proposed by the David Taylor Model Basin (DTMB). Using the linear and rotary oscillation mechanisms equipped in the FL-10 wind tunnel of Harbin Aerodynamics Research Institute, AVIC, wind tunnel tests were conducted to obtain the hydrodynamic derivatives in the vertical plane of the SUBOFF AFF-8 model. A data processing method for evaluating submarine vertical-plane hydrodynamic derivatives based on wind tunnel testing is proposed. The validation results indicate that the hydrodynamic coefficients obtained from the wind tunnel tests exhibit trends consistent with those from the DTMB measurements. For the hydrodynamic coefficients used in vertical-plane maneuvering and stability predictions, the discrepancies are all within 10% except the pitch moment coefficient with respect to angular velocity. This demonstrates the feasibility of the experimental principle and methodology. The work lays a technical foundation for further studies on wind tunnel test methods for submarine hydrodynamic derivatives at large angles of attack.

In this paper, the large eddy simulation and level-set/volume-of-fluid (CLSVOF) coupled interface capture method is used to calculate the ventilated cavity flow of porous flat plate under two wall contact angles (90° and 160°), and the influence of wall superhydrophobicity on the development characteristics of ventilated cavity fusion of flat plate is studied. The results show that compared with the typical experimental results, the numerical calculation method can better simulate the shape of ventilated cavitation and the wall superhydrophobicity. Compared with the flat plate with a contact angle of 90°, it is found that the flat plate with a contact angle of 160° will have a near-wall velocity slip phenomenon, which will increase the spanwise velocity of the cavity and promote the fusion of the cavity, so that the position of the cavity fusion is advanced by 41%. The pressure fluctuation of the cavity after fusion is smaller, and the resistance of the plate with a contact angle of 160° is smaller than that of the plate with a contact angle of 90°.

The real-time prediction of ship motion is one of the key technologies to ensure safe and efficient navigation of ships. Based on the Higher Order Dynamic Mode Decomposition (HODMD) algorithm, this paper constructs an improved Reduced-Order Model (ROM) for real-time prediction of ship maneuvering motion. The improved ROM enhances the correlation between maneuvering motion parameters of similar frequencies by separately incorporatng the parameters into high-frequency and low-frequency input samples according to their frequency features. The prediction of ship maneuvering motion under environmental influences is conducted by using the ship motion data of a 35° turning circle maneuver of the ship YUKUN at sea. The comparative analysis of prediction accuracy between the improved ROM and the original ROM shows that the improved ROM exhibits significantly higher accuracy in predicting low-frequency motion and a slight improvement in predicting high-frequency motion compared to the original ROM.

Reduced-order models (ROMs) offer an effective means to extract the dominant features of flow fields while significantly reducing computational resources, which provides an important means for the analysis and interpretation of nonlinear complex flow field information. Although ROMs have been widely applied to reconstruct fields of steady-state flows with different geometries or transient flows with one geometry, the study on reconstructing transient flow fields with different geometries remains limited. In this study, a novel flow field reconstruction method combining Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD) is proposed, and then applied to reconstruct the wave field of a trimaran under different side hull layouts at a wave length equal to the ship length. The results indicate that the reconstructed flow fields exhibit lower errors compared with the original flow fields by high-fidelity simulation, which validates the reasonableness and feasibility of the proposed method, laying a solid foundation for subsequent studies on flow field prediction and optimization for hull forms.

Aiming at the limitation that the single-factor model ignores the combined effect of internal pressure and internal fluid weight in the traditional submarine pipeline buckling theory, this study proposed a multi-factor joint analytical solution optimization method based on secondary buckling analysis. Firstly, by combining the Coulomb friction law, Maltby formula and Hobbs and Taylor buckling theory, an analytical model for the secondary buckling deformation of the pipeline under the combined action of temperature-internal pressure-internal fluid weight was established, and the analytical solution of the cap-shaped buckling mode was derived. Secondly, through the thermal-solid coupled finite element model, the pipe-soil contact stiffness and boundary condition parameters were calibrated with experimental data to ensure the equivalence between the numerical model and the actual working conditions. On this basis, the empirical coefficient K₁ in the analytical solution is corrected by comparing the theoretical solution with the simulation results, so that the error in the buckling displacement prediction is reduced to less than 2%. The results show that the contribution rate of the internal fluid weight to the axial compression of the pipeline is 35.89%, a factor that significantly affects the critical buckling threshold. The prediction accuracy of the modified analytical solution is improved to more than 98% under the combined condition. The results provide a high-precision theoretical tool for the anti-buckling design of deep-sea pipelines, and lay a methodological foundation for the stability analysis of pipelines under the combined action of multiple physical fields.

In the multi-objective optimization of slender ring-stiffened cylindrical shells, it is difficult to balance the structural lightweight and critical pressure for overall instability, which restricts the improvement of the performance of Autonomous Underwater Vehicle. In this paper, a data-driven multi-objective optimization strategy is proposed, which can improve the critical pressure for overall instability and reduce the weight of the structure. Firstly, based on the error convergence criterion and accuracy requirement, the appropriate training set size is found in this strategy through iteration, and a low-cost and high-precision surrogate model is constructed. Then, the second-generation non-dominated sorting genetic algorithm is used to obtain the Pareto solution set. The non-inferior solution is screened by the minimum distance method based on maximum and minimum normalization, and the optimal design scheme with a well-balanced performance is obtained by combining the local accuracy enhancement strategy of the surrogate model. Using the optimization strategy proposed in this paper, the structural weight of the slender ring-stiffened cylindrical shell is reduced by 9.1%, and the critical pressure for the overall stability is increased by 13.4%. An effective design to improve the stability of the ring-stiffened cylindrical shell without increasing its weight is to increase the thickness of the cylindrical shell, increase the height of the stiffeners, and reduce their number.

The propulsion shaft system of a ship is a critical component of the powertrain, subjected to direct contact between the shaft and bearing under various operating conditions, such as low speed, heavy load, and startup/shutdown phases. These conditions can lead to friction-induced vibrations and even result in issues such as flutter and noise. In this paper, a four-degree-of-freedom coupled model of the ship propulsion shaft system is developed on the basis of modal coupling theory to investigate the modal coupling phenomenon in detail. A combined complex modal analysis and the fourth-order Runge-Kutta method are applied to analyze modal coupling instability and identify the critical friction factor. The results indicate that the minimum critical friction coefficient is a crucial parameter influencing the stability of the system. The impact of both proportional and non-proportional damping conditions on the critical friction coefficient is examined. Furthermore, the effects of various damping parameters on the modal coupling instability of the system is summarized. These findings provide important theoretical support for vibration control and stability optimization in propulsion shaft systems, significant value for advancing theoretical models and optimizing practical engineering applications.

To address the issues of excessive structural redundancy, severe ice debris accumulation, and strong ice-induced vibrations of traditional jacket platform cone structures, a novel jacket platform cone structure design is proposed. This design aims to reduce structural damage to jacket platforms caused by ice accumulation and ice-induced vibrations. Using the JZ20-2NW single-pile leg platform as the research object, the DEM-FEM coupling method based on LS-DYNA software was employed to simulate the interaction between sea ice and both traditional and novel cone structures. A comparative analysis was conducted on ice failure modes, ice loads, and the platform's ice-induced vibration responses and structural responses. The results indicate that the novel cone structure can effectively inhibit ice debris accumulation after climbing, improve ice removal efficiency, decrease ice loads, reduce the ice-induced vibrations of the platform, and improve the safety performance of the cone structure. The study shows that the innovative cone structure demonstrates significant advantages in improving the ice-resistant performance of jacket platforms, providing a theoretical basis for optimizing platform structures in ice regions.

This paper investigates the influence of initial geometric defects on the ultimate load capacity and failure mode of thin-walled titanium alloy ring-ribbed cylindrical shells. The study combines key geometric parameters, including the radius-to-thickness ratio (R/t), length-to-radius ratio (L/R), and rib spacing (u), to conduct structural design calculations and analyze failure modes, supported by experimental verification. A welded model (with initial defects) and a precision-machined model (without defects) were designed and fabricated. Theoretical analysis and numerical simulations were performed to obtain the structural stress distribution and critical buckling pressure at critical locations on both models. Subsequently, hydrostatic external pressure tests were conducted to evaluate the structural strength and ultimate load capacity, revealing the stress distribution characteristics, failure pressure, and failure modes of each model. By comparing the theoretical, numerical, and experimental results, the impact of initial shape defects on structural performance was assessed. This comparison provides a robust basis for the design, calculation, and evaluation of thin-walled titanium alloy ring-ribbed cylindrical shell structures.

In order to establish a comprehensive planar Real-Time Nearfield Acoustic Holography (RT-NAH) system and effectively avoid overdependence on the Laplace transform table when deriving impulse response functions, an alternative method based on the Rayleigh integral is proposed. Firstly, the pressure-pressure, normal velocity-pressure, normal acceleration-pressure, and normal displacement-pressure impulse response functions are systematically derived based on the Rayleigh integral. Then, a comprehensive planar RT-NAH system is constructed based on the obtained impulse response functions. Finally, simulation of a simply supported thin aluminum plate is performed to evaluate the correctness of the derived impulse response functions. The analysis of the reconstruction results demonstrates that high accuracy is achieved when reconstructing pressure and normal velocity, whereas relatively lower accuracy is observed for normal acceleration and displacement. The primary factors contributing to the lower accuracy when reconstructing the normal acceleration and displacement are further investigated.

The classical finite element method (FEM) is known to suffer from significant accuracy degradation under large wavenumber conditions due to dispersion error effects. Furthermore, the reliability of FEM solutions heavily depends on mesh quality, particularly in regions with steep gradient fields or complex geometric features. While high-quality meshes are essential for obtaining credible results, their generation remains computationally intensive and time-consuming. To address these limitations, this study proposes a modified radial point interpolation meshless method (MRPIM) for three-dimensional acoustic-structure interaction analysis. By introducing a novel interpolation node selection scheme, the method constructs continuous approximation functions within individual integration cells, effectively reducing numerical integration errors. Results demonstrate that the modified method achieves notable improvements in computational accuracy compared to the conventional method (RPIM) while exhibiting superior efficiency. Additionally, the computational overhead of MRPIM is comparable to that of FEM, highlighting its promising potential for engineering applications.