Applying an acoustic coating to the hull effectively reduces target strength while reducing both mechanical and hydrodynamic noise. In this study, a finite ribbed cylindrical shell is studied based on the modal superposition method. A computational model is developed to predict the acoustic scattering of a finite ribbed cylindrical shell with multilayer gradient acoustic coating in an infinite ideal fluid. The influence of characteristic impedance parameters—such as sound speed and density—on the scattering form function is examined, and an optimized impedance distribution for the multilayer gradient acoustic coating is proposed to suppress scattering across different frequency bands. In addition, the effects of frequency-dependent characteristic impedance of embedded-cavity acoustic coatings and stiffeners of cylindrical shells on the scattering form function are investigated. Results show that multilayer gradient acoustic coating with characteristic impedance gradually increasing from the inner to the outer surface can effectively reduce the scattering form function in lower frequency ranges. Furthermore, frequency-dependent acoustic coatings result in broadband scattering control from low to high frequencies, and applying an optimized layered coating to the rib-stiffened cylindrical shell yields a substantial reduction in its scattering form function for frequencies above 500 Hz.

The coexistence of waves and broken ice is a prominent feature in marginal ice zones. Ships navigating in these areas are subjected to combined loads from both ice and wave actions. While current research has obtained substantial findings on ship ice resistance characteristics under either single wave or ice conditions, studies on coupled wave-broken ice interactions remain relatively scarce, resulting in insufficient understanding of the ship-ice-wave interaction mechanisms and their impacts on vessel navigation performance. To investigate ice resistance characteristics in broken ice fields under wave effects, this study developed a numerical model by adopting a coupled Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) for ship navigation in wave-affected broken ice environments. The numerical wave tank was first established using the Finite Volume Method (FVM), while the broken ice model was developed through the Discrete Element Method (DEM). The validity of the ship resistance model under either single wave or ice conditions was verified through comparisons between theoretical solutions and experimental data. Subsequently, the ice resistance characteristics of ships navigating in wave-affected broken ice fields were systematically analyzed, with particular focus on the influences of wave parameters and ice concentrations. The results demonstrated that wave action significantly alters the ship-ice interaction process, inducing distinct periodic fluctuations in ice resistance. Notably, the ice resistance under combined wave-ice conditions consistently exceeds that observed in still water conditions with equivalent ice concentrations. Furthermore, the influence of key parameters including wavelength, wave height, and ice concentration on ice resistance behavior was also elucidated.

The flexible hose connecting the deep-sea mining vehicle and the relay station is a key link in the deep-sea mining system and is suspended in a curved configuration above the mining vehicle. This paper extends the applicable conditions of the model from the vertical pipeline to the flexible hose based on the one-dimensional model (VHT_1D), by discretizing the long-distance curved pipelines into a series of inclined pipelines for force analysis. The extended model is fully compared with the key parameters calculated by the two-way coupling method of fluid dynamics and discrete elements (CFD-DEM), and this model shows high accuracy. At the same time, the influence of input parameters such as feed concentration and mixture transport velocity on the flow state in the pipeline is further explored. A reasonable range of input parameters is determined, and the conveying efficiency of the pipeline system is optimized. In addition, the hydraulic gradients in the single-peak and double-peak long-distance curved pipes are compared and analyzed, providing a basis for the design of the conveying pump. The extended model significantly improves computational efficiency while maintaining high accuracy, particularly for long-distance pipeline applications.

In engineering applications, Very Large Floating Structures (VLFS) need to rely on mooring systems to achieve offshore positioning. However, due to their large length-to-width ratio, VLFS have low overall stiffness and are prone to significant elastic deformation under wave action. Based on the rigid body theory, the impact of such deformation on the mooring system cannot be taken into account, nor can the structural dynamic response of the floating structure in the moored state be easily predicted. To address this, this study established a coupled calculation model of the VLFS and the mooring system based on three-dimensional hydroelasticity theory and slender rod mooring dynamics theory. With this model, the structural response of the floating structure under mooring loads is calculable, and the dynamic response of the mooring system to the combined effects of the floating structure’s rigid body motion and elastic deformation is synchronously computable, thereby realizing the high-precision synchronous prediction of mooring tension and structural response. In this paper, this model is used to analyze the coupling performance of a three-module VLFS, and the floating structure’s load response of typical sections and the mooring line tensions are obtained. The results show that the elastic deformation of the floating structure significantly changes the displacement of the mooring points, leading to an increment in mooring line tension reaching the order of 10⁵ N, with the maximum increment being approximately 40% of its pretension.

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.

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.

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 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.