This study proposed a stiffener layout adjustment method for the box-girder model under compression effects, which could be used to increase spaces of adjacent stiffeners in box-girder sections, and thus improving processing feasibility and precision of ship structure experimental tests. The method is the combination of critical parameter-based similarity theory and neural network-based surrogate model by considering the coupled geometric distortion effects from essential plate components in box-girder sections. For obtaining reliable surrogate model, more than 5000 scenarios were included in the finite element-based numerical parametric analyses. Systematic experimental and numerical validation analyses were finally conducted to validate the effectiveness of the proposed method in keeping identical loading characteristics and ultimate strengths between box girders with and without stiffener layout adjustments. Good performance of proposed method could be observed from experimental and numerical validation results in terms of both the collapse modes and the ultimate strengths. This research could be beneficial for the practical experiments and the scaled-down model design of ship structures.

This study investigates near-wall cavitation loading on sandwich structures subjected to underwater shock waves through a combined numerical-experimental approach and systematic parametric analysis. A custom-built transparent shock tube apparatus was designed to examine cavitation loads induced by underwater blasts in the vicinity of sandwich structures. After confirming the reproducibility of shockwave loading through pressure history tests, experiments were performed on both water-backed and rigid-backed sandwich configurations. A numerical framework, was developed to capture shockwave propagation, cavitation inception, growth, and collapse, as well as fluid-structure interactions and dynamic compression in sandwich structures with cellular cores. Comparative analysis demonstrated strong agreement between numerical and experimental results in terms of wet-face pressure histories and cavitation evolution. Across all datasets, the maximum deviations between numerical and experimental results were 17.8 % for peak cavitation pressure, 16.5 % for cavitation load impulse, and 14.7 % for core compression, with corresponding average deviations of 9.9 %, 10.1 %, and 10.7 %. A parameter sensitivity analysis revealed that dimensionless core strength and the fluid-structure interaction parameter are the dominant factors influencing cavitation collapse impulse. The cavitation collapse impulse accounted for 75 % to 87 % of the total impulse. Under rigid boundary conditions, cavitation collapse impulses were consistently greater than those observed for water-backed boundaries, with rigid boundary values exceeding their water-backed counterparts by approximately 8.7 % to 9.0 %. Core strength exhibited a pronounced effect on the position and propagation speed of the closing front, with higher core strength accelerating its advancement, whereas the fluid-structure interaction parameter had a negligible impact on cavitation evolution.

Al/PTFE reactive material have emerged as promising candidates for warhead casings due to their dual capability of structural integrity and chemical energy release. The energy release characteristics of Al/PTFE casing under explosive loading were investigated through confined explosion experiments integrated with high-speed data acquisition and 3D deformation scanning. Comparative analysis between bare charges and cased charges revealed distinct pressure profiles in confined spaces, complemented by numerical simulations elucidating target plate deformation dynamics. Experimental results demonstrated that reactive casings enhanced quasi-static pressure and temperature in confined explosions, with recorded increases of 57% and 52% respectively, with target plate residual deformation peaking at 46% under enhanced loading. Numerical modeling uncovered a non-monotonic trend: structural responses were overestimated in small-charge scenarios but underestimated in large-charge conditions. This characteristic indicated that the afterburning behavior of Al/PTFE reactive materials affected structural responses not through simple energy superposition, but via synergistic interactions between time-delay energy release mechanisms and evolving explosion environmental parameters. Further analysis indicated a 5.8% reduction in casing combustion efficiency due to energy competition between detonation products and reactive fragments. Notably, RDX-driven casings exhibited triple the combustion efficiency of TNT-driven counterparts, with fragment-induced deflagration accounting for approximately 70% of total energy release from casing combustion. These findings provide critical insights into reactive material explosions in confined spaces, offering theoretical foundations and optimization strategies for advanced warhead design and naval compartment blast protection.

This study investigates the hydrodynamic performance of an 80 kW semi-submersible offshore floating photovoltaic platform using model tests and numerical simulations. A quadrilateral platform with a semi-taut hybrid mooring configuration is tested at a 1:10 scale under various regular wave conditions. Time-domain numerical simulations, based on potential flow theory and a lumped-mass mooring model, are conducted and validated against experimental measurements of platform motions and mooring tensions for the single-module configuration. Then, multi-module configurations are analyzed numerically using the validated model. Comparisons with the single-module system show that hydrodynamic interference and wave-shielding effects reduce platform motions under moderate sea states. However, larger wave heights and certain wave headings significantly increase mooring and connector tensions. The lower inter-connection rope is identified as the critical component governing extreme load transfer. In addition, connector stiffness affects the balance between inter-module constraint and relative motion, and an intermediate stiffness range leads to lower platform motions and connector tensions. Platform spacing mainly influences hydrodynamic interaction between adjacent modules, and increasing spacing generally reduces platform motions and connector tensions.

Composite-armor structures have been proven to enhance the protective performance of pure steel plates against fragment penetration. However, the protective capability and failure mechanisms of composite armor under the combined loading of shock waves and fragment clusters from explosions with cased charge in confined spaces remain unclear. This study presents a novel experimental investigation comparing the failure behavior of composite armor and steel plates subjected to explosions from both cased charge with reactive material (CCRM) and cased charge with inert material (CCIM) in a confined space. Under shock-wave loading alone, the deformation of the composite-armor structure was comparable to that of a steel plate with equivalent areal density. However, under coupled shock wave and fragment loading, the composite armor exhibited no through-thickness perforation, whereas the steel plate was perforated, demonstrating the effectiveness protective capability of composite armor. Furthermore, this study proposes a convolutional neural network (CNN) model for predicting armor perforation and full-field deformation. The performance of this method was compared with the proper orthogonal decomposition-artificial neural network (POD-ANN) prediction approach, as well as the CNN prediction framework based solely on data error terms. The results indicate that it preserves localized features more faithfully and achieves higher prediction accuracy.

Slamming induced whipping responses significantly amplifies dynamic stresses of ship structures under extreme waves. Analyzing the characteristics of whipping and dynamic responses of structure remains challenging, particularly for full-scale structures. Conventional structural strength simulations often simplify wave induced loads as sinusoidal time histories, neglecting high frequency (HF) components and whipping responses. Conversely, a decoupled approach neglects the interaction of structural deformation and hydrodynamic loads, thus particularly underestimating whipping responses of full-scale ships. To address these limitations and characterize structural dynamic responses of full-scale ship, this research conducted CFD-FEM numerical simulations combined with hydroelastic model experiments. The spatiotemporal characteristics of slamming pressure and whipping responses were analyzed, and the dynamic responses of a full-scale ship were investigated with whipping effects taken into account. Results demonstrate that the whipping component constitutes 33.8% of the wave frequency (WF) component. When the wave height reaches to 10 m, the HF responses increase the hogging bending moment by 92.65% relative to the WF condition, while the structural stress amplitude increases by 70.36%. This research reveals the dynamic response characteristics of full-scale ship structures under extreme waves utilizing a hydroelastic method that considering whipping effects, which providing a valuable insight for ship structural safety assessment.

Confined trinitrotoluene (TNT) explosions exhibit a short shock-dominated stage followed by a millisecond-scale quasi-static pressure rise driven by secondary combustion of detonation products. In such flows, repeated shock reflections, wave superposition, and the continued interfacial interaction between hot fuel-rich products and surrounding air govern the transition from an initially non-uniform compressible wave field to a late chamber-scale pressure buildup. In this work, these processes are modeled within a three-dimensional Euler framework solved by a Runge-Kutta discontinuous Galerkin method. Afterburning is represented by a single progress variable with a first-order rate law, interpreted as an effective chamber-scale closure for unresolved mixing-controlled energy release. The model is validated against nitrogen-filled chamber tests, in which afterburning is suppressed, and against air-filled chamber tests, in which afterburning raises the quasi-static plateau and accumulated impulse. For the present chamber, inversion of Unified Facilities Criteria quasi-static correlations gives afterburning energies about 80% higher for 90 g TNT and about 70% higher for 160 g TNT than a correlation derived from confined-explosion measurements; the latter is therefore adopted for subsequent analysis. With the calibrated rate constant, the predicted cumulative impulse in nitrogen is within about 3%-15% of the measurements, and the quasi-static plateaus and impulses in air are reproduced within about 5% over the tested charge masses. Parametric results show that afterburning has only a minor influence on the earliest shock peaks but substantially elevates the quasi-static pressure level while preserving the qualitative dependence of the loads on chamber volume, charge position, and charge mass.

In deep-water environments, the coupled effects of hydrostatic pressure, explosion-induced shock waves, and bubble pulsation can produce complex nonlinear dynamic responses and instability in stiffened cylindrical shells. Clarifying these response mechanisms is critical for the safety assessment and blast-resistant design of deep-sea equipment. In this study, an acoustic-structure coupled numerical method was developed for stiffened cylindrical shells subjected to underwater explosion loading and validated using deep-water explosion tests conducted in a pressure vessel. The results show that the proposed method predicts the dynamic response of stiffened cylindrical shells under deep-water explosion loading with satisfactory accuracy. Based on this validated model, a systematic investigation was conducted to evaluate the effects of hydrostatic pressure, stand-off distance, shell-plate thickness, and stiffener number on the deep-water explosion response of stiffened cylindrical shells. The findings provide practical guidance for blast-resistant design and parameter optimization of deep-water stiffened cylindrical shells.

The present study aims to establish a framework for developing a practical design diagram based on an advanced ultimate limit state (ULS) analysis methodology for stiffened plates subjected to combined loads, namely compression, shear, and lateral pressure. The proposed approach consists of two parts: the design diagram and the explicit formulation. The necessary datasets for stiffened plate scenarios were generated through comprehensive numerical parametric analyses, providing valuable insights for enhancing existing safety assessment frameworks in ocean mobility. In total, 144 sets of design diagrams were derived, representing the relationships between ultimate shear and compressive strengths under various combined loading levels for conservative design applications. Furthermore, concise design formulas for predicting the ULS of stiffened plates under combined loads were proposed using symbolic regression (SR) algorithms. Unlike black-box intelligent models or conventional curve-fitting techniques, symbolic regression provides explicit equations that achieve a balanced trade-off between accuracy, interpretability, and complexity, thereby facilitating practical engineering applications. As the combined loading conditions considered herein more closely reflect the actual loading environments of stiffened plates in ships and offshore structures, the present work serves as a meaningful extension and complement to existing ULS assessment methodologies.

Under severe sea states with significant bow emergence and immersion, violent ship relative motion induces substantial bow structural slamming loads. Slamming loads induce structural whipping response, sharply increasing overall structural stress and severely threatens ship safety. In order to investigate characteristics of slamming loads and whipping response under wave, this research conducted segmented variable cross-section backbone hydroelastic model experiment, in which were firstly utilized FBG (Fiber Bragg Grating) method to measure and analyze the whipping response of the ship. The research analyzes slamming loads on the ship bow by integrating the bow wave entry motion. Furthermore, it investigates the whipping response and explores the correlations between slamming loads and whipping response. The results confirmed the reliability of FBG method in measuring whipping response. Severe slamming loads on the bow caused the 2nd harmonic response component amplitude to reach 60.81 % of the wave frequency component. The superposition of multi-order harmonic responses leads to a 72.35 % increase in the sagging bending moment. This research analyzes the bow motion, slamming loads, whipping response and ship structural responses by FBG method. It provides a reference for the application of FBG method in measuring the whipping response under nonlinear wave loads.

ObjectiveTo reduce the damage range of traditional spliced composite armor, a novel composite armor structure composed of titanium alloy faceplate, silicon carbide （SiC） ceramic, ultra-high-molecular-weight polyethylene（UHMWPE） laminate, and integrated titanium alloy lattice and back plate is proposed. And we employ optimal design of the structure to achieve the enhancement of the ballistic resistance and weight reduction. MethodComparative studies on the ballistic resistance of the novel composite armor is conducted by numerical methods. A high-accuracy surrogate model is established to rapidly predict the ballistic performance of the composite armor, and correlation analysis is performed between structural parameters and residual velocity and areal density. The structural parameters of the composite armor are optimized based on the NSGA-II multi-objective genetic optimization algorithm. ResultsThe results indicate that, compared with traditional spliced composite armor, the new composite armor reduces the residual velocity of the projectile by 11.7% and the damage range by 60.9% due to the presence of the integrated titanium alloy lattice and back plate. The damage range is confined to the inside of the grill, while the rest of the structure maintains better integrity. The anti-penetration performance of the areas with weak protection located at the splices is improved. After optimization, the residual velocity of the projectile is reduced by 21.0%, while the areal density decreases by 5.3%. The residual velocity of the projectile shows the strongest correlation with the thickness of the UHMWPE laminate and the weakest correlation with the thickness of the titanium alloy back plate. The optimized structural design scheme is as follows: the thickness of SiC ceramic is 4.25 mm, the thickness of UHMWPE laminate thickness is 10.65 mm, and the thickness of titanium alloy backplate thickness is 0.52 mm. After optimization, the residual velocity of the projectile is reduced by 21.0%, while the areal density reduced by 5.3%. Conclusion Compared with the traditional spliced composite armor, the novel composite armor structure demonstrates superior anti-penetration performance. The method for structural optimization design of composite armor based on the SVR surrogate model and NSGA-II algorithm is effective and feasible.

Full-scale testing remains most effective to investigate deck dynamic buckling, yet scaled-model testing is widely adopted by researchers due to economic and spatial constraints. The key challenge is developing reliable scaled design to predict Full-scale prototypes’ dynamic responses. In the current study, a universal similarity method for different structural forms, impact loading types and material constitutive equations was proposed according to the finite similitude theory. By scaling physical systems through mapping of Full-scale and scaled-down spaces, the scopes of application of the proposed similarity method were expanded to various structure forms, loading types and material constitutive relations, and thus facilitating the similarity design and prediction of structural responses under dynamic load. To verify the proposed method, systematic numerical validation analyses were conducted, including all the cases of stiffened plates under impact mass loads, the cases of stiffened plates under simplified sinusoidal triangular loads, and the cases of box girder models under simplified sinusoidal triangular loads. The validation results indicated that the proposed similarity approach had acceptable effects in keeping the same dynamic structural responses between prototype and scaled-down models. This study could be regarded as the supplement to the existing similarity research of dynamic responses of ship and ship-like structures.

Cased charges are usually simplified as equivalent bare charges to characterize the energy dissipation and conversion caused by fragmentation and initial kinetic energy of metal casing under the driven force from inner detonation pressure. However, this conventional simplification method inherently neglects the afterburning effects of detonation products, introducing significant risks when applying cased charge analytical models to confined explosions. In this paper, three different configurations of cased charge were employed to investigate the energy release characteristic in confined explosion scenarios experimentally and numerically. In addition, comparative analyses were performed between bare charges and cased charges. The test results reveal that the initial peak overpressure of cased charge was significantly lower than that of the bare charge, but the quasi-static pressures were very close to each other, maintaining differences within 6 %. Numerical simulations employing the Smooth Particle Hydrodynamics (SPH) method were conducted to quantify the energy dissipation caused by casing fragmentation. Based on detonation energy conservation principles, equivalent bare charges with mass reductions of approximately 30 % compared to the initial cased charges were derived. However, pressure load analysis demonstrates substantial discrepancies exceeding 50 % in quasi-static pressure predictions between equivalent bare charges and cased charge configurations. To address this limitation, a reactive flow-based model was developed, explicitly incorporating chemical reactions and casing-product interactions. The proposed model achieved excellent agreement with experimental pressure histories in both temporal evolution and magnitude. Furthermore, a two-phase pressure load simplification framework was established based on pressure distribution and evolution patterns, which successfully reconciled with dynamic responses of target plate recorded in experiments. Furthermore, the critical role of quasi-static pressure in governing structural dynamic responses within confined spaces was identified through numerical analysis.

Although the underwater salvo is more efficient than the single launch, the flow-mediated interaction between slender bodies makes the launch more complicated. To address the highly nonlinearity in fluid-structure interactions and the coupling motions of structures, a numerical method is proposed for analyzing the underwater salvo of two slender bodies under transverse flow. The three-degree-of-freedom (3-DOF) motion model of structures, combined with the cavitation and collision models, is adopted. The model is initially validated and verified through a comparison with the experimental results. Subsequently, the applicability of the model in flows is analyzed, and the effects of the launch time interval (zt) and spatial interval (zs) on the salvo are discussed. The findings demonstrate the effectiveness of proposed model, particularly in high-speed transverse flow and the strong flow-mediated interaction. When z t and z s are large, the slender bodies are mainly affected by the transverse flow, reducing success of salvo due to the collision between the bodies and their barrels. It is recommended that z t = 0 with z s >= 2D (diameter of slender bodies) be employed to achieve both efficiency and success in the salvo. The peak pressures within the barrels especially when z t =0 should also be considered in the structural design.

This study proposed a geometrical distortion solution for the similarity design of box-girder under longitudinal compression load. The corrected distortional method by considering the plate thickness distortion effect was proposed to mitigate the similarity error caused by distortion effect during the similarity design process. The distortional method was based on the numerically obtained empirical formula for the stiffened plate component in the box-girder structure. A similarity procedure by combing the corrected geometrical distortional method and the previous material transformation method was finally put forward. The application of the similarity procedure was expected to reduce the distortion effect and improve the experiment test precision. The effectiveness of the proposed corrected distortional method and similarity procedure were well validated by both the experimental and numerical analyses in the current study.

In the design of small-scale test models for hull structures, the directional dimensional analysis method is commonly employed. However, conventional dimensional analysis based on elasticity theory may be insufficient to capture the nonlinear behaviors of structural materials under dynamic loading, which restricts its applicability in ultimate strength tests for small-scale hull structure models. This paper presents a scaling method grounded in the theory of finite similitude. Based on the finite similitude theory, this paper deduces similarity scaling criteria applicable to the static and dynamic responses of box girders and designs a series of trial models of box girders. The scaling criteria are verified and analyzed through numerical tests conducted under static and dynamic loads. On the basis of the numerical test results of dynamic responses, the dynamic response similarity criteria considering the similarity relationship of material constitutive parameters are modified and verified. By applying the static response scaling criteria in this paper to select appropriate materials, the prediction deviation of the box girder trial models under static loads is less than 2%. With the modified dynamic response scaling criteria proposed in this paper, the prediction deviations of each trial model under dynamic loads are less than 2% and 7%. A comprehensive analysis of material parameters was conducted to examine their impact on the nonlinear similarities observed in the processes. To validate the ultimate strength and nonlinear response scaling criterion based on the finite similitude approach, numerical experiments were performed to assess the ultimate strength and dynamic buckling response characteristics of the box girder across various scaling ratios and material parameters. The analysis demonstrated that the ultimate strength scaling criterion and the nonlinear response scaling criterion derived from the finite similitude approach effectively captured material nonlinearity. The results from the small-scale model provided accurate predictions of the ultimate strength of the full-scale model.

This study experimentally and numerically investigated the ultimate behaviours of the large-span double-layer structures with large openings on modern passenger ships under different types of loading conditions. The ultimate strength experimental research of the objective structure under combined bending and lateral pressure conditions was first conduced. A comprehensive parametric study containing 216 scenarios were then carried out based on the experimentally validated finite element method. Besides the sagging conditions, both the hogging and torsion conditions were further considered in the numerical parametric analyses. The parametric results indicated that the openings on upper decks exhibited a significant deteriorating effect on the ultimate strengths of the objective structure, while the influences of the lateral pressure could vary between deterioration and enhancement effects depending on the types of loading conditions. A simplified polynomial-shaped empirical formula was finally proposed based on these parametric results, which could be utilized to predict the ultimate strengths (sigma byu and sigma txu) of the objective structures under both the hogging bending and torsion conditions by considering the influences of large openings (LO/LC and BO/B) and lateral pressures (qE/sigma 2Y). The developed empirical formula could be useful for the lightweight design and safety assessment of structures on modern large passenger ships.

In numerical simulations of underwater explosions, inaccuracies in the parameters of the Jones–Wilkins–Lee (JWL) equation of state often result in significant deviations between predicted shock wave pressure peaks or bubble pulsation periods and experimental or empirical results. To achieve the precise forecasting of underwater explosion loads, a corrected method for adjusting the initial conditions of explosives is proposed. This method regulates explosion loads by correcting the initial density and initial internal energy per unit mass of the explosive, offering a straightforward implementation and easy extension to complex scenarios. In addition, the accuracy and feasibility of the proposed method were validated through comparisons with experimental data and empirical formulas from international studies. The numerical framework employs the Runge–Kutta Discontinuous Galerkin (RKDG) method to solve the one-dimensional Euler equations. The spatial discretization of the Euler domain is achieved using the discontinuous Galerkin (DG) method, while temporal discretization utilizes a third-order Runge–Kutta (RK) method. The results demonstrate that the proposed correction method effectively compensates for load discrepancies caused by inaccuracies in the JWL equation of state parameters. After correction, the maximum error in the shock wave pressure peak is reduced to less than 4.5%, and the maximum error in the bubble pulsation period remains below 1.9%.

The digital twin refers to a virtual representation of a physical object, system, or process using digital techniques like sensors and simulation models. The successful structural digital twin of ship structures is expected to provide designers with high-frequency feedback and reliable predictive results, thereby enhancing safety assessments of the structures. However, there are still many gaps in existing techniques in achieving these expectations. One prominent problem is that existing boundary methods in numerical analyses cannot accurately describe the boundary constraint effects on the objective structures. This would inevitably cause significant errors in the predictions from finite element analysis-based surrogate models. This study aims to improve existing finite element analysis-based surrogate model strategies by proposing a precise method for describing boundary constraints based on elastic boundaries. A boundary-driven model-updating approach was subsequently proposed together with an enhanced framework for establishing integrated surrogate models. Finally, an experimental case study was conducted to validate the proposed approach. This study can be regarded as an essential foundation and complement to future structural digital twins of ship structures.