To achieve energy efficiency and enhanced performance in the cruise ship industry, the lightweight design of large cruise ship superstructures has emerged as a critical research priority. To meet the specific lightweight requirements of the upper decks in large cruise ship superstructures, this study proposes a novel composite sandwich panel with steel stiffeners. Designed to replace conventional steel-stiffened panels, this innovative structure aims to achieve substantial weight reduction while maintaining or even improving structural strength and mechanical performance, thus contributing to the overall efficiency and competitiveness of large cruise ships.

To comprehensively evaluate the axial compression ultimate strength of the proposed panel, a series of experimental and numerical studies were conducted. In the experimental phase, a meticulously designed test model with specific dimensions was fabricated. Tensile tests were conducted to accurately determine material parameters, and the initial deformation of the specimen was measured with high precision prior to the test. During the axial compression test, the deformation processes and load-time histories were systematically recorded. For the numerical simulation, a highly refined finite element model was developed in Abaqus/Explicit. The experimentally measured initial deformation was incorporated into the model to enhance accuracy. The Tsai−Wu, Shokrieh−Hashin, and modified LaRC03 failure criteria, combined with instantaneous stiffness degradation models, were implemented through VUMAT subroutines. Displacement-controlled loading was applied to simulate the axial compression process observed in the experiments.

The results demonstrate strong agreement between numerical simulations and experimental data. Compared to the experimental values, the Shokrieh-Hashin and LaRC03 criteria, when combined with instantaneous stiffness degradation, predict the ultimate strengths with errors of 5.7% and 2.7% respectively, while corresponding displacement errors are 3.8% and 2.1%, all within an acceptable range. The LaRC03 criterion, which accounts for fiber-matrix interaction failures, predicts a larger damage area in the face sheet, a slightly lower ultimate load and greater deformation. In contrast, the Tsai−Wu criterion predicts premature failure, with an ultimate load error of 3.3% and a significant displacement error of 27.1%. The load-bearing behavior in the elastic phase of the simulation aligns well with experimental observations; but some differences still exist, with the simulated ultimate load exceeding the experimental value. Additionally, the composite sandwich panels with steel stiffeners achieve a remarkable 40% weight reduction compared to the conventional steel-stiffened panels.

The Shokrieh−Hashin criterion, in conjunction with the instantaneous stiffness degradation method, effectively predicts the ultimate strength of composite sandwich panels with steel stiffeners, demonstrating high accuracy for fiber-dominated failure modes. The LaRC03 criterion, incorporating additional considerations such as fiber-matrix directional failure, provides more precise predictions, although its applicability is primarily limited to compressive loading conditions. The proposed composite sandwich panel with steel stiffeners not only achieves an efficient lightweight design but also effectively lowers the ship's center of gravity. The experimental and numerical analysis of this structure establishes a valuable and effective methodology for the lightweight design and strength analysis of ship superstructures. Future research should focus on optimizing material parameters and geometric configurations of the composite sandwich panel with steel stiffeners to further enhance structural performance and reliability. Additionally, considering the effects of marine environmental factors on structural integrity can improve its practical applicability in ship superstructures.

This study aims to develop a concept design for an unmanned aerial-aquatic cross-medium vehicle that can fly in the air and navigate underwater, and features repeatable medium transitions and superior hydrodynamic performance.

After analyzing the shape of manta ray that evolved good fluid dynamics performance through natural selection, 3D scanning and mathematical fitting methods are employed to conduct a configuration study of the unmanned vehicle. To achieve covert propulsion underwater, numerical analysis methods are used to determine the propulsion amplitude and frequency by fitting the swimming gaits of manta ray. To protect the rotor blades and enhance airborne efficiency, an innovative soft hybrid cross-medium approach is developed that uses ducted rotor devices as flight propulsion units. The numerical simulation method is then employed to study the unmanned vehicle's rapid underwater movement, aerial performance, and cross-medium capabilities.

The results show that during underwater navigation, with a biomimetic fish fin swinging cycle of 2 seconds and a maximum swing angle of 15°, the unmanned vehicle achieves a speed of over 3 knots. During aerial flight, with an attack angle of 7° for the hybrid vehicle and rotor speed set at 3 000 r/min, the aerial speed exceeds 100 km/h. During the transition from air to water, the average load is 0.17 MPa, with the maximum load occurring at abrupt structural edges, reaching up to 0.46 MPa stress. Structural strength calculations are performed for applying 0.17 MPa load at the center bottom and 0.46 MPa load at the bottom edge of the vehicle. The maximum stress occurs at the center bottom, measuring 47.94 MPa, with maximum deformation of 0.02 mm.

The designed cross-medium unmanned aerial-aquatic vehicle satisfies the proposed requirements for both aerial and underwater operation. Furthermore, the fluid loads and structural safety during the air-water transition scheme are assessed, ensuring the vehicle's ability to safelyand repeatedly shift between aerial and aquatic environments.

As composite material design and structural design are separated in the "dual track" state, this paper proposes an integrated design method for composite materials in order to improve the ultimate strength of marine composite structures.

Based on the multi-scale method, the correlation between the meso-scale material and macro-scale structure is established, and the influence of the meso-scale parameters on the ultimate strength of macro-scale stiffened panels is explored, as well as the differences in mechanical properties between intra-layer and inter-layer hybrid carbon/glass fiber composite material. Through comparison, the superior structural form is obtained.

The proposed micro-meso-macro mechanical analysis method can improve the ultimate strength of macro-scale stiffened panels by enhancing the meso-scale parameters of composite materials. By adjusting the spacing and cross-sectional area of TC33 yarn, cross-sectional area of WR yarn, and mixing mode, the designed composite top-hat stiffened structure has better ultimate strength.

The results of this study show that the integrated design of material and structure can be realized through multi-scheme comparison and optimization while satisfying the requirements of the rules, providing theoretical guidance and technical support for the novel design of naval ships.

The analysis of small failure probability in the overall longitudinal strength of a ship's hull structure is a complex, high-dimensional and time-consuming task which is challenging to calculate accurately using traditional reliability analysis methods. To address the precise calculation of small failure probabilities in the reliability analysis of complex structures, this paper establishes a computational process for assessing structural small failure probabilities.

The subset simulation method is used to reduce the overall sample demand. Samples within each subset are generated through Markov Chain Monte Carlo (MCMC) sampling to cover all scenarios within the sample space, and precise computations are performed on these samples using the stochastic finite element method (SFEM), resulting in accurate sample response values which enhance the accuracy of the failure probability calculations. Furthermore, the introduction of the dynamic Kriging surrogate model significantly reduces the number of FEM computations within each subset.

The process is applied to a case study on the reliability analysis of an icebreaker's hull structure, and the analyzed lifecycle structural failure probability is 9.58 × 10⁻⁶.

The accuracy and efficiency of the proposed method are validated through comparisons with the computational results under various parameter settings.

A large opening on the swimming pool structure of a large cruise ship reduces the carrying capacity of the deck structure. The opening reinforcement is an effective approach to improve the structural strength. However, various forms of reinforcements pose a challenge to the optimal design of opening structures.

A variable density topology optimization method is used to optimize the opening reinforcement of a swimming pool, and a new form of opening reinforcement is obtained. Next, a size optimization method is used to obtain a more reasonable distribution of plate thicknesses, thereby achieving better weight reduction.

As the results show, compared with the prototype structure, the optimized structure has an increased ultimate bearing capacity of 1.1%, maximum stress reduction of 3.3% and weight reduction of 7.0%.

The proposed optimization design method can provide a reinforcement approach for designing the deck opening structures of cruise ships.

As composite materials have varied internal structures, an in-depth analysis of the damage mechanisms of their component materials can provide a research foundation for the ultimate strength analysis of composite stiffened panels.

The microscopic, mesoscopic and macroscopic mechanical analyses of marine glass fiber reinforced plastic (GFRP) composite stiffened panels are carried out using a multi-scale approach. Microscopic and mesoscopic representative volume element (RVE) models of chopped strand mat (CSM) and woven roving (WR) materials are established, and the macroscopic equivalent stiffness is obtained by homogenizing the RVE models. The ABAQUS VUMAT subroutine is used to code the progressive damage evolution model of the composite materials to derive the damage evolution mechanism of the microscopic and mesoscopic models respectively. The equivalent strength of macroscopic laminates is also obtained.

The multi-scale approach can be used to accurately evaluate the macroscopic mechanical properties of composite materials, and the ultimate strength of composite stiffened panels is mainly determined by fiber bundle failure.

The obtained macroscopic material parameters can be used to calculate the ultimate strength of composite stiffened panels, while the parametric study of the mesomechanics of composite materials can provide an analysis tool for investigating the influence of material processing technology.