Advanced Analysis of Marine Structures

In the analysis and design of marine structures, one of the key issues is the accurate prediction of their strength under various load conditions, particularly impact and ultimate and fatigue strength. The advanced analysis of marine structures involves the mechanical analyses of advanced materials such as alloys and composite materials; it also involves the strength analyses of novel structures such as sandwich structures, in order to render marine structures lightweight, safe, and economical throughout their lifetimes.

The present Special Issue contains 19 articles; in total, 11 papers belong to the area of impacts and dynamic responses of ships and offshore structures, 3 papers are related to the fatigue strength of marine structures, 3 papers cover the various aspects of the strength assessment of ships and offshore structures, 1 paper revolves around the analysis of gravity anchors, and 1 paper deals with the sound absorption capability of marine equipment.

The fracture prediction of steel-plated structures is a key issue in impact strength analysis. Cerik and Choung [Contributions 1] carried out a validation study on a recently proposed rate-dependent shell element fracture model using both quasi-static and dynamic impact tests on square hollow sections made from offshore high-tensile-strength steel. A rate-dependent forming limit curve was used to predict the membrane loading-dominated failure, while a rate-dependent ductile fracture locus was applied for predicting the failure that is governed by bend loading.

The cruciform structure is a typical form in the double-hull ships. Liu et al. [Contributions 2] presented an experimental, numerical, and analytical study of the cruciform structure subjected to a local in-plane load, in order to investigate its crushing deformation and resistance.

For reducing accidental consequences, specific consideration is required to optimize the crashworthiness design. Qiu et al. [Contributions 3] proposed a novel method that addresses multi-working conditions and combines orthogonal testing with a backpropagation neural network to establish an efficient surrogate model for collision optimization.

Ice loading is a hot topic in the field of impact engineering, focusing on the safety of polar navigation. Liu et al. [Contributions 4] selected two numerical benchmark tests to validate the fluid–structure coupling approach and its program. During the ice-breaking simulation, the generation and propagation of radial and circular cracks in level ice are modeled, and the influence of ship speed and ice thickness on the ice load are investigated and analyzed. Chen et al. [Contributions 5] analyzed the dynamic response of a submarine during surface navigation in floating ice channels under special conditions. The fluid–structure coupling method was employed to simulate the structure–ice interaction of a submarine.

In polar engineering, the low temperature affects a ship’s safety, focusing on the changing of the mechanical properties of steel materials. Zhang et al. [Contributions 6] performed a series of quasi-static and dynamic tests to investigate the behavior of EH36 steel at temperatures ranging from 20 °C to −60 °C; the variations of yield and ultimate tensile stress are given.

Impact analysis has been widely used to evaluate the strength of various types of structures, such as floating pontoons. Khalifa et al. [Contributions 7] analyzed the dynamic response of a steel ferry exposed to side explosions with different explosive charges at certain stand-off distances. An innovative mitigation system has been proposed to dissipate the blast energy of the explosion based on the scientific theory of impedance using sacrificial cladding.

Box girders can be seen as simplified ship structures that are able to withstand a vertical bending moment. Shi et al. [Contributions 8] analyzed the dynamic elastic–plastic response and ultimate strength of a box girder under a bending moment. Based on published experimental results, the nonlinear finite element analysis method is validated to determine the ultimate strength of a box girder under a bending moment.

Hydroelastic analysis is often used to analyze the hydrodynamic and structural response characteristics of marine structures, an example of which is a large multi-body floating offshore structure. Gu et al. [Contributions 9] used a method based on a CFD-FEA (computation fluid dynamics–finite element analysis) coupling simulation to evaluate the hydroelastic response of the flexible floating structures.

The dynamic response of steel catenary risers used in offshore platforms is difficult to analyze due to their complicated loadings. Yu et al. [Contributions 10] proposed a novel experimental platform to conduct dynamic loading tests on a truncated-model steel catenary riser within the touchdown zone. The facilities of the platform include a soil tank, a loading system, and a soil stirring system.

Codends are the posterior components of trawl nets; they collect the catch, and play a crucial role in the selectivity process. Zhang et al. [Contributions 11] investigated the effects of various catch configurations on the hydrodynamic characteristics, geometrical profile, and fluttering motions of a codend in a flume tank. A codend structure was designed and tested using various catch configurations, including grooved-type configurations (canvas, green canvas, and basketballs) and spherical configurations (table tennis balls filled with water, balloons filled with water, and balls made of twine) in the flume tank.

Fatigue failure is one of the main fracture modes in ships and offshore structures. To comprehensively understand the distribution pattern of the hot spot stress method at spatial tubular joints, Wang et al. [Contributions 12] selected to research the typical joints by performing hot spot stress testing.

Low cycle fatigue damage has received attention in relation to ship structures experiencing high stresses and large deformations. Qin et al. [Contributions 13] carried out experimental and numerical studies on the crack propagation behavior of cracked plates under low cycle fatigue loads, in order to explain the fatigue crack propagation mechanism. The effect of the stress ratio and maximum applied load on the crack propagation behavior was investigated.

The lumping block equivalent method has been widely used to reduce the computational effort in the fatigue damage assessment of offshore structures. Guo et al. [Contributions 14] proposed a novel wave energy equivalence-based lumping block equivalent method to accurately determine the wave parameters of the representative sea states. The novelty of the proposed method is that a compact relationship between the input wave energy component and mooring lines’ fatigue damage is derived.

The superstructure of cruise ships is designed to be plumper with numerous decks and complex structural forms. To control the weight and the center of gravity, the bending stiffness of the superstructure is always designed to be weaker than that of the main hull, resulting in a stiffness step. Pei et al. [Contributions 15] conducted an experimental analysis to investigate the stiffness step between the main hull and the superstructure of a typical cruise ship. By comparing the longitudinal stress distribution characteristics both with and without the stiffness step with the theoretical results, the influence of the stiffness step on the longitudinal strength is investigated.

Fires and explosions in ships and offshore platforms cause serious human, economic, and environmental damage. Zong et al. [Contributions 16] experimentally and numerical evaluated the fire resistance of A-60-class ship bulkheads and decks through two sets of standard fire resistance tests.

The inflated membrane structures satisfy the demands of maritime salvage and military transportation for long-distance delivery and rapid response. Ye et al. [Contributions 17] comprehensively investigated the bending and failure behavior of inflated membrane structures.

Moreover, gravity anchors are widely used in ships and offshore platforms. Less attention has been paid to the bearing properties of gravity anchors in clay. Yu et al. [Contributions 18] investigated gravity anchors by conducting scaled model tests; the bearing process of gravity anchors in clay was simulated through the finite element method.

For marine equipment, their low-frequency broadband sound absorption capability is an important characteristic. Hu et al. [Contributions 19] designed a novel sound absorption structure with cavities by adding resonators and honeycombs to traditional sound absorption structures with cavities. The approximate multilayer sound absorption theoretical model based on the modified transfer matrix method is used to verify the accuracy of finite element calculations.

In summary, the articles presented in this Special Issue cover broad research topics related to the advanced analysis of marine structures, guiding readers through the best analysis approach.