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.

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.

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.

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.

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.

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.

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.

Sloshing experiment is crucial to determine the reaction performance of regeneration columns on an offshore floating platform. A novel type of column motion simulating device and a Marine Predator Algorithm-based Sliding Mode Controller (MPA-SMC) are proposed for such sloshing experiments. The simulator consists of a Stewart platform and a steel framework. The Stewart platform is located at the column's center of gravity (CoG) and supported by the steel framework. The platform's hydraulic servo system is controlled by a sliding mode controller with parameters optimized by MPA to improve robustness and precision. A numerical sloshing experiment is conducted using the proposed device and controller. The results show that the novel motion simulator has lower torque during the column sloshes, and the proposed controller performs better than a well-tuned PID controller in terms of target tracking precision and anti-interference capability.

In order to understand the influence of bow shape on ice resistance and provide guidelines for hull line design in the early design stage, an investigation of the impact of bow shape on ice resistance for the Arctic LNG carriers is carried out based on semi-empirical methods. Firstly, some typical semi-empirical formulas developed for ice resistance estimation of cargo carriers in different ice conditions are summarized. Then, formulas appropriate for ice resistance estimation of Arctic LNG carriers under different ice conditions are verified according to the result comparison between semi-empirical formulas and experimental tests. The comparison result indicates that the Lindqvist formula is appropriate for ice resistance estimation in level ice conditions, Zuev and Dobrodeev formula for ice resistance estimation in broken ice conditions, and Dobrodeev formula for ice resistance estimation in brash ice conditions. After that, the parameters considered in the selected formulas are summarized, and the influence of critical parameters on ice resistance is analyzed. Some parameters describing the ship's bow shape characteristic like ship breadth, waterline angle and stem angle greatly influence the ice resistance. Ice resistance increases with both the growth of ship breadth under all ice conditions and the growth of stem angle in level ice and broken ice conditions while ice resistance decreases with the development of waterline angle under all ice conditions. Finally, the optimization of the bow shape is discussed, and an optimized bow shape with both a large waterline angle and low stem angle is proposed. The optimized bow shape can decrease ice resistance by 9.9% in the level ice condition and reduce ice resistance by 11.3% in the brash ice condition.

High-static-low-dynamic stiffness (HSLDS) vibration isolators have been demonstrated to be an effective means of attenuating low-frequency vibrations, and may be utilized for ship shafting applications to mitigate torsional vibration. This paper presents the construction of a highly compact HSLDS torsional vibration isolator by connecting positive and negative stiffness components in parallel. Based on mechanical model analysis, the restoring torque of negative stiffness components is derived from their springs and connecting rods, while that of positive stiffness components is obtained through their circular section flexible rods. The quasi-zero stiffness characteristics of the HSLDS isolator are achieved through a combination of static structural simulation and experimental test. The torsional vibration isolation performance is assessed by means of numerical simulation and theory analysis. Finally, the frequency-sweep vibration test is conducted. The test results indicate that the HSLDS torsional vibration isolator exhibits superior low-frequency isolation performance compared to its linear counterpart, rendering it a promising solution for mitigating low-frequency torsional vibration in ship shafting.