With the development of shipbuilding technology, composite materials have shown great potential in ship construction due to their excellent properties. However, the application of sandwich structures in ship main load-bearing structures has been limited due to the weak out-of-plane load-bearing capacity. The aim of this study is to design a novel foam-filled composite sandwich structure with reinforcing ribs (combined thick plate) to address this issue and explore its application prospects in ship main load-bearing structures. This research is of great significance for promoting the development of lightweight ships.

In this study, a series of mechanical property tests were carried out. First, according to the anisotropic characteristics of the combined thick plate, three-point bending and tensile tests were conducted along and perpendicular to the direction of the reinforcing ribs. For the bending tests, referring to the GB/T 1456−2021 standard, four types of bending test specimens were designed. These specimens were divided according to the number of cell reinforcing plates in the direction perpendicular to the ribs and the bending center position in the direction of the ribs. For the tensile tests, with reference to the GB/T 1040.5−2008 standard, four types of tensile test specimens were designed based on the tensile center position in the direction perpendicular to the ribs and the number of cell reinforcing plates in the direction of the ribs. Each type of specimen had 6 samples tested, and the mechanical property parameters such as bending strength, bending stiffness, and tensile modulus were calculated through specific formulas.

The experimental results reveal the significant anisotropy of the combined thick plate. In the direction perpendicular to the ribs, the bending strength of the structure is increased by 82% compared with that in the longitudinal direction, and the tensile modulus in the longitudinal direction is 22% higher than that in the perpendicular direction. The number of cell reinforcing plates and the loading center position have a remarkable impact on the bending strength, while having a relatively small effect on the tensile modulus. The adhesive strength between the panel, ribs, and foam plays a crucial role in determining the bending strength of the structure. In terms of failure modes under bending loads, the initial failure mode in the direction perpendicular to the ribs is the local debonding of the lower panel. In the direction of the ribs, it is the shear failure of the reinforcing plate. The number of cell reinforcing plates and the bending center position have no obvious influence on the initial failure mode. After the initial failure, the damage processes of the specimens in different directions are distinct. In the specimens bent in the direction perpendicular to the ribs, the upper panel will locally debond following the lower panel, and the final failure is caused by the complete debonding of one side of the lower panel. In the specimens bent in the direction of the ribs, some specimens fail due to the complete debonding of one side of the lower panel, while in others, the lower panel does not completely debond, and the panel gradually loses its load-bearing capacity during the loading process.

In conclusion, this research provides a technical reference for the promotion and application of composite sandwich reinforcement plates in ship main load-bearing structures. The obtained data and conclusions can guide the design and optimization of composite structures in shipbuilding, helping to improve the structural performance and safety of ships. It also offers valuable insights for further research on the mechanical properties of composite materials in marine engineering.

Against the backdrop of global warming, maritime activities in the Arctic region are increasing, and polar vessels inevitably encounter ice loads during navigation. A precise understanding of the deformation characteristics and failure mechanisms of hull plate structures under ice loads is crucial for ensuring the safe navigation of polar vessels. However, significant gaps remain in existing research, particularly regarding initial hull damage and the mechanisms of repeated ice loads. Based on this, this study aims to deeply explore the mechanical response characteristics of hull plate structures under ice loads, focusing on key scientific issues such as initial damage effect assessment and repeated ice load mechanisms, providing theoretical and technical support for the design of anti-ice structures and the safety assessment of polar vessels.

A repeated compression test on steel hull plates and ice was conducted using a simplified plate model based on the actual bow shoulder structure, with some specimens pre-fabricated with initial defects to simulate real service damage. During the test, triangular pyramid ice models were prepared using the filling-freezing method. A total of 12 test cases were designed to systematically examine the effects of variables such as plate thickness, stiffener arrangement, defect direction, and position offset. The plate was pressed vertically at a constant speed of 6 mm/min to repeatedly compress the ice. High-precision sensors were used to measure displacement, force, and strain in real time, while the plastic deformation of the structure was recorded after each loading cycle to fully characterize the structural response under ice loads.

The results show that plate thickness has a significant impact on structural strength. As plate thickness increases, the slope of the compression force-displacement curve increases, while the loading displacement at ice failure significantly decreases. Although the arrangement of stiffeners can effectively enhance anti-ice compression strength, their ability to compensate for strength reduction caused by longitudinal defects is limited. Notably, when the defect location aligns with the ice load area, especially for longitudinal defects, significant stress concentration occurs at the root, leading to defect propagation. A comparative analysis showed that under the same load conditions, transverse defects exhibit higher load-bearing capacity than longitudinal defects. Additionally, offsetting defects significantly alters stress distribution: a 200 mm longitudinal offset of a longitudinal defect can reduce root stress by about 74%, while a 75 mm transverse offset of a transverse defect can increase root stress to 202 MPa at one end while reducing it to 66 MPa at the other end. After the first loading, plastic deformation generally occurred in the plates, with plates of lower initial strength exhibiting greater strength improvement during the second loading, even potentially surpassing those with higher initial strength.

The study reveals the structural response characteristics of plate structures with initial damage under repeated ship−ice compression scenarios, providing valuable references for the design and evaluation of ice-resistant structures polar vessel structures.

Aiming at the problem of structure recovery difficulty caused by soil adsorption force in the process of submarine structure recovery, the model test method of submarine structure sitting bottom adsorption force is proposed.

By designing a series of marine structure base models, building a simple model test device to simulate the process of structure bottom lifting, and adopting a special loading device to quantitatively measure the adsorption force of bottom lifting, we investigated the influence of parameters such as soil type, time of bottom lifting, mass of bottom lifting, area of bottom lifting, and material of base lifting, etc. on the adsorption force of bottom lifting of the structures.

The test results show that the adsorption force is positively correlated with the sitting time and sitting weight, and negatively correlated with the sitting area; the adsorption force of sandy and simulated soils is about 50% and 80% of that of the sea-tested soils; the smoother the base material is, the smaller the adsorption force is.

The research in this paper can improve the design efficiency of submarine structures in China.

The sloshing load is one of the most important and complex loads in the LNG carrier cargo containment system, but it is difficult to calculate or measure accurately due to the simplifications in numerical simulations and model experiments. To obtain accurate time-history characteristics of the sloshing load and enable real-time health monitoring of the LNG carrier cargo containment system, the inverse impulse-space superposition method is used to measure the local response of the structure and deduce the sloshing load and the response of high-stress regions (hotspots).

Based on the improved inverse impulse-space superposition method, an inverse mathematical model of measuring point positions and sloshing load positions is established to predict loads in multi-regions. Using the time-shift property of the convolution integral, the Duhamel integral is reformulated and discretized into a matrix equation to predict sloshing loads at different time steps. The matrix equation is solved by least-squares. To address the instability due to noise interference and small singular values in the unit impulse load response matrix, the Tikhonov regularization method is adopted, with the optimal regularization parameter selected by the L-curve method. Based on the improved impulse-space superposition method, a response prediction mathematical model for sloshing load positions and hotspot positions is established to predict multi-hotspot stress, such as shear stress in the secondary plywood and vertical stress in the secondary polyurethane foam.

The algorithm's performance is systematically evaluated under both triangular and random load conditions. The application of multiple triangular sloshing loads with randomly generated characteristic shows that the predicted values agree well with actual measurements, indicating the method's ability to accurately predict multi-region triangular sloshing loads from any starting moment. For random loads, the investigation focuses on three prediction step sizes (0.5 ms, 0.25 ms, and 0.05 ms). The analysis shows a strong correlation between prediction accuracy and step-size reduction. At the finest resolution of 0.05 ms, the predicted load curve successfully captures all peak features of the actual load profile. While minor fluctuations occur in zero-value regions without prominent peaks, primarily due to noise interference and small singular values, comprehensive error analysis across all regions demonstrates that step-size reduction effectively minimizes prediction errors. Specifically, the maximum load peak pressure error for individual regions decreases from 21.861% to 9.530%, with corresponding average errors decreasing from 10.081% to 4.023%. Similarly, temporal accuracy improves significantly, with maximum load peak time errors decreasing from 0.900 ms to 0.050 ms and average errors decreasing from 0.256 ms to 0.022 ms. Stress prediction shows equally promising results. For both loading scenarios, the predicted curves for plywood shear stress and foam vertical stress agree well with actual measurements, particularly at smaller step sizes. The maximum stress peak prediction error remains within 1% for selected hotspots. In the most challenging cases, the maximum peak stress error reaches 5.267% for plywood shear stress and 2.644% for foam vertical compressive stress, with peak time errors not exceeding 0.15 ms.

The improved inverse impulse-space superposition method based on the Duhamel integral successfully inverts the sloshing load and the predicts hotspot stresses in the LNG carrier cargo containment system. This method combines the accuracy of experimental with the cost-effectiveness of numerical simulations, minimizing the negative effects of experimental measurement errors and numerical model simplifications. It provides a novel and reliable approach for assessing the safety of LNG carriers and other ship-ocean structures. Although the current study adopts a uniform load model and does not fully account for the internal non-uniformity of actual sloshing loads in different regions, it still serves as a valuable reference for future research in this field.

To solve the problem of applying thick carbon fiber laminates in naval architecture and marine engineering, this paper proposes a thick plate structure composed of thin carbon fiber laminates with reinforcing ribs and core material in the middle.

First, based on the theory of continuous damage mechanics, two-dimensional Hashin failure criterion and cohesive element technology, a finite element analysis model of a combined thick plate is established. Second, the bending performance of the combined thick plate in different directions is compared and analyzed. Next, the progressive damage process of the adhesive layer and carbon fibre-reinforced polymer (CFRP) is analyzed to investigate the failure behavior and mechanisms of the combined thick plate during the bending process in the direction perpendicular to the stiffeners. Finally, the influence of adhesive strength on the damage behavior of the combined thick plate is discussed.

The results indicate that the bending stiffness of the combined thick plate is higher in the direction perpendicular to the stiffeners compared to the parallel direction. During the bending process perpendicular to the reinforcing rib direction, the adhesive layer at the interface between the rib plate and panel is the first to suffer damage; it rapidly expands under shear force, ultimately forming a mixed failure mode where interface failure and panel 0° ply fiber tearing promote each other. When the adhesive strength is low, the adhesive layer breaks first; and when the adhesive strength is high, the laminates break first. The adhesive layer mainly bears shear action under Types II and III tearing modes, and the shear stress in the direction of the reinforcing rib is the primary cause of initial damage to the adhesive layer.

This study reveals the damage behavior of a new-type composite thick plates during bending perpendicular to the stiffener direction, thereby providing technical references for the promotion and application of thick composite plates with reinforcing ribs and core material in the middle in major load-bearing structures in the fields of naval architecture and marine engineering.

In view of the fact that the structural performance assessment method of the internal-pressure-resistant square cabin is not clear and the general specifications for naval ships are not fully applicable, the stress analysis method and strength assessment criteria applicable to the internal-pressure-resistant square cabin are studied.

Based on the theory of elasticity, the two yield criteria Mises and Tresca commonly applied in ASME BPVC were analyzed. According to the principle of safety, Tresca was determined to be the analysis criterion applicable to the internal-pressure-resistant square cabin. By taking the bulkhead grillage as the basic unit, the stress classification of the internal-pressure-resistant square cabin was carried out based on ASME BPVC, and four typical assessment locations were obtained: the center of the plate panel, the midpoint of the short side of the plate panel, the midpoint of the long side of the plate panel, and the corner of the plate panel. In order to reduce the amount of engineering calculation, the theoretical formula and numerical calculation method of stress components for plate element finite element analysis were proposed based on the stress linearization theory, and the solid finite element model of grillage was established for comparing the difference between the structural assessment results of two models.

Compared with the accurate results of the solid element model, the error of plate element stress analysis result is basically about 3%, and the results of plate elements are generally larger. Considering the safety conservative assessment principle of ships and nuclear structures, it can be considered that the strength assessment method of internal-pressure-resistant square cabins based on the plate element finite element model and ASME BPVC meets the engineering requirements.

This study can provide a reference for the stress analysis and strength assessment of the internal-pressure-resistant square cabin, and is of great significance for tackling the technical bottleneck faced by the ships using nuclear power plants.

With the continuous development of larger scale and more complex ships, the number of finite element model elements required to model hull structures at the cabin structure level and above is increasing dramatically, resulting in collision, impact, contact and other large-scale non-linear mechanical problems which are difficult to solve. To this end, a simplified method for the deformation of two-way stiffened plate structures based on orthotropic equivalent theory is proposed in order to simplify the modeling of ship structures.

First, the current well-established simplification method for the plane stress of one-way stiffened plates is extended to the more complex plane bending problem of two-way stiffened plates. The ratio of the total moment of inertia of stiffened plates to the moment of inertia of plates in the orthogonal direction is introduced to reflect the structural orthotropism. Next, the moment of inertia ratios are substituted into the equivalent constitutive equation for the plane bending of stiffened plates to achieve the transformation to physical orthotropism, thereby taking into account both the deformation resistance of the structure and the influence of the membrane forces generated by shifting the neutral surface at the mechanical level. Finally, finite element calculations are used to classify the deformation modes of the four-sided fixed stiffened plates according to different displacement distributions, and the actual results of the stiffened plates are analyzed in terms of error comparisons with the equivalent results of this method and the traditional method.

The result comparison shows that the proposed method can reduce the number of elements in two-way stiffened plates by up to 84%, and the equivalent errors in all three deformation modes can be controlled within 6%, which is much lower than those of the two traditional methods.

With high precision, a wide application range and greatly reduced calculation resources, the proposed method can provide a direct modeling and simulation calculation solution to address the nonlinear mechanical problems of large hull structures for practical engineering applications.

To identify the change in structural strength after an interaction between hull girders and ice, this paper puts forward an analytical technique which can determine the structural strength of hull girders after an ice riding accident and disclose the related structural strength features.

First, the hull girder structural strength analysis model and associated load analysis model are constructed in accordance with the characteristics of each section. To account for the buoyancy variations brought on by ice riding, the buoyancy distribution of the ice riding conditions is retrieved from the load analysis model and inserted into the structural strength analysis model. Gravity and the reaction force of the ice are then used to determine the structural strength. Finally, an analysis is carried out on the impact of lifting position and height on the buoyancy, shear force, bending moment and local stress distribution of the hull girders.

The results show that the sites of buoyancy and shear force of the hull girders are situated in the stern part and middle part, and unaffected by changes in the bow lifting height. The shell is closer to the vertical when the lifting position is at the bow of the bulbous bow, making it harder to resist the reaction force of the ice and resulting in the high stress areas becoming comparably larger and more dangerous.

The proposed method has high computation efficiency and can be used to estimate how hull girders will respond to a significant bow lift and make preliminary judgments on hull girder structural strength under risky ice riding conditions.