This study presents a combined experimental and numerical investigation of the wave attenuation performance of a bottom-fixed aquaculture cage equipped with double-layer side nets. A porous media model is adopted to simulate the hydrodynamic effect of nets, and the numerical method is validated through scaled-down model experiments. A series of simulations is conducted to investigate the effects of net layering, net solidity, differential inner-outer net arrangements and draft depth on wave attenuation. The results show that, compared with the single-layer side net, a double-layer net arrangement can more effectively attenuate wave propagation. Several net cage configurations with different solidity values between the inner and outer side nets are studied. Wave attenuation is affected not only by overall solidity but also by the location of the denser net layer. Moderate drafts achieve greater attenuation than excessively shallow or deep configurations, with the best performance observed between 1.1 m and 1.3 m for this study. The findings suggest that a well-designed set of side netting layers and an adjustment of net solidity are relatively feasible ways to control wave propagation and attenuation. The results provide some references for optimising the hydrodynamics of cages deployed in wave-exposed regions.

The hydrodynamic responses and mooring characteristics of an aquaculture vessel are evaluated using the AQWA software based on potential theory and the Morison equation. The numerical accuracy is validated through comparison with experimental data. A frequency-domain analysis is first conducted to obtain the hydrodynamic coefficients and to investigate the effects of the net and bottom plate on the motion responses. The results indicate that the motion amplitudes are more pronounced under low-frequency wave conditions, and the presence of nets increases heave, pitch, and roll responses. The installation of the bottom plates of the truss structure will reduce pitch response but increase heave response. Furthermore, a time-domain analysis is performed for the vessel with a single-point mooring system using the lumped mass method. The influences of the net, draft depth and environmental water depth on the mooring performance are analysed. The findings reveal that the presence of nets amplifies sway and roll motions and increases the maximum mooring force to approximately 1.35 times that of the case without nets. An increase in draft enhances sway but reduces heave motion response. In addition, increasing water depth from 15 m to 30 m reduces the maximum mooring force by about 22%-34%.

This study addresses key challenges for hyperloop trains, such as high surface temperatures and pressures on the carbody; shock wave effects and airflow choking inside the tubes. Based on the three-dimensional compressible Navier-Stokes equations coupled with the SST k-ω turbulence model, and employing the Roe spatial discretization scheme along with hybrid meshing techniques, a numerical computational model for aerodynamics of hyperloop trains was established to systematically investigate the evolution of flow fields, aerodynamic forces and aerothermal characteristics on the carbody surface and inside the tubes, under operating speeds ranging from 400 km/h to 2 500 km/h and in-tube pressures from 1 atm (101 325 Pa) down to 0.005 atm (506.625 Pa). Results show that the largest positive pressure zones on the carbody surface occur at the nose tip and the leading edge of the bottom mover plate of the head car; the mover region experiences strong compression, resulting in local pressure increases of 12% to 17% compared to the stagnation point on the head car. At a fixed blockage ratio of 0.057 42, a clear Kantrowitz limit appears when the Mach number ranges from 0.793 to 1.370 (corresponding to train speeds of approximately 971 km/h to 1 677 km/h), potentially triggering airflow choking and causing nonlinear jumps in the aerodynamic drag coefficient. Furthermore, increasing the vacuum level in the tubes significantly reduces shock wave intensity and aerothermal loads; at extremely low pressures between 0.05 atm (5 066.25 Pa) and 0.005 atm (506.625 Pa), aerodynamic drag falls to 5%–0.5% of that under atmospheric conditions. Therefore, a high-acceleration operating strategy is recommended to rapidly traverse choking speed ranges, and targeted thermal protection for the underside of the head car is emphasized for the design. These findings provide theoretical support for selecting optimal vacuum levels, optimizing vehicle contours, and ensuring safe operation of Hyperloop systems.

As the core load-bearing component of underwater hull structures, studying the buckling failure characteristics and their transformation laws of stiffened cylindrical shells under deep-water explosions is of great significance. In this paper, static and acoustic-structural coupling analysis methods were employed to conduct a numerical study on the dynamic buckling of underwater internally stiffened cylindrical shells subjected to the coupled action of deep-water explosion loads. The dynamic buckling modes of the internally stiffened cylindrical shell during the shock wave and two bubble pulsation stages were analyzed, and the buckling components were quantitatively assessed based on critical buckling displacement and the internal energy of the plate, shell, and ribs. Finally, the buckling evolution process of the internally stiffened cylindrical shell for each mode was examined. The research demonstrated that at the same water depth, as the explosion distance decreased, the primary damage area of the structure shifted from both ends to the middle. When the hydrostatic pressure was excessively high, damage occurred solely at both ends, and circumferential instability was likely to ensue. The buckling instability evolution laws of the internally stiffened cylindrical shell under shock wave loads exhibited similarities. During the first-stage bubble pulsation load, local buckling and aggravated deformation occurred in different parts for each mode. The second-stage bubble pulsation load further exacerbated the instability. Ribs tended to buckle in shallow water, whereas the plate-shell was more vulnerable in deep water.

Stiffened panel structures can achieve both weight reduction and enhanced structural strength by utilising composite materials for panel elements while retaining steel stiffeners as primary load-bearing components. To assess the impact of material substitution, a composite sandwich panel with steel stiffeners is developed, derived from a conventional steel stiffened panel prototype. Experimental and finite element analyses are performed to evaluate their ultimate compressive strengths and failure modes, in terms of the force-displacement curves and permanent deformations. Experimental results show that the composite sandwich panel with steel stiffeners achieves a 7.8% increase in ultimate strength and reduces the weight of its plate components by 30.3%, compared to the conventional steel panels. Various failure criteria of composite materials are calibrated by the finite element analysis, and the numerical results demonstrate that the modified LaRC03 failure criterion combined with the instantaneous stiffness degradation method provides the most accurate numerical predictions. The effects of lateral, transverse and shear loads on the ultimate compressive strength of stiffened panels are discussed. This investigation offers practical insights for lightweight design applications in ship superstructures.

The present analysis examines the effects of net layers, inflow angles and bow geometry on the flow field and drag force of a ship-type truss aquaculture cage. The porous media method is adopted to establish the numerical ship model. To validate the accuracy of this numerical approach, the drag force and flow velocity of a net at different inflow velocities and attack angles are simulated and compared with experimental data. This paper focuses on the flow field distribution and drag variation of the cages with and without nets, and with single- and double-layer nets. Then it compares the drag force and flow field characteristics of the three ships under different inflow angles. Subsequently, the influence of bow structure on the drag and flow improvement is analysed. The results indicate that the number of net layers has little influence under head-on inflow but a strong influence under oblique and lateral inflows. Three flat-bow configurations are proposed as design alternatives for comparison with the original sharp bow. The results indicate that the flat bow produces a more uniform velocity distribution inside the ship-type truss aquaculture cage. These findings can provide insight into the hydrodynamic optimisation of ship-type truss aquaculture cages.

This study presents a numerical investigation of the flow field distribution of a large semi-submersible hybrid aquaculture vessel in uniform flow. A coupled numerical framework is developed to simulate viscous flow behaviour inside and around the vessel. The influences of three key factors, such as the existence of the fishing net, the net solidity and the net-to-truss spacing on the flow field distribution are evaluated. The results indicate that the presence and arrangement of the fishing net have a pronounced influence on flow velocity and flow-field uniformity. It suggests that a reasonable combination of net types can effectively reduce drag force and optimize flow uniformity around the aquaculture vessel. Net solidity should be optimised to ensure both structural stability and breeding environment quality. Furthermore, the net-to-truss spacing plays a relatively important role in the spatial distribution of internal flows. The research also demonstrates the role of the fore and aft buoyancy tanks in attenuating velocity and in vortex development within and around the aquaculture vessel. This study elucidates the flow-field characteristics under different net configurations, providing insights for the design and optimisation of fishing nets.

[Objective]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 propos-es 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 im-proving structural strength and mechanical performance,thus contributing to the overall efficiency and com-petitiveness of large cruise ships.[Method]To comprehensively evaluate the axial compression ultimate strength of the proposed panel,a series of experimental and numerical studies were conducted.In the experi-mental 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 mea-sured 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 experi-ments.[Results]The results demonstrate strong agreement between numerical simulations and experimen-tal 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 cri-terion,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 be-havior 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 convention-al steel-stiffened panels.[Conclusion]The Shokrieh-Hashin criterion,in conjunction with the instanta-neous 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 predic-tions,although its applicability is primarily limited to compressive loading conditions.The proposed compos-ite 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 valu-able 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 sand-wich panel with steel stiffeners to further enhance structural performance and reliability.Additionally,consid-ering the effects of marine environmental factors on structural integrity can improve its practical applicability in ship superstructures.

This paper employs a combined approach of numerical simulation and experimental verification to evaluate the flow field characteristics around a bottom-supported net cage. The present study simplifies fishing nets into porous, permeable panels by setting appropriate coefficients for viscous drag and inertial resistance based on the porous medium method. Model tests are carried out in a flume to validate the numerical method. The study comprehensively analyses the impact of different factors on the flow field, including the effects of double-layer nets, net solidity and the combination of different solidities in inner and outer nets. The results show that double-layer side nets help reduce downstream velocities and improve the uniformity of the downstream flow field distribution. When multiple cages are deployed in an array, the double-layer nets can mitigate the impact on the flow field of downstream cages to some extent. Increasing net solidity promotes velocity attenuation and enlarges the size of the low-velocity region. The solidity of the outer net mainly affects the downstream average velocity, and the solidity of the inner net primarily affects the wake characteristics. Results show that optimising the net solidity and the number of side nets is necessary to balance the flow field distribution for efficient water exchange.

The safety of ships sailing through bridge areas has received significant attention, and the ship model without propeller and rudder (H-model) is widely used nowadays. To further elucidate the sailing mechanism in the bridge area, a coupled hull-propeller-rudder model (C-model) is proposed. Specifically, secondary development based on Fluent is undertaken. The governing equations of the ship are embedded using the user-defined function (UDF) module, and a modified multiple reference frame (MRF) model is employed to solve the coupled translational and rotational motions of the propeller. Compared to the motion parameters obtained by the H-model, the additional flow-mediated interactions among the propeller, rudder and pier lead to a smaller yaw angle and a greater lateral displacement. The reasons for these changes are given by analyzing the flow evolution and ship motions. The effects of flow velocity and ship velocity are also given. In front of the pier, the lateral displacement and yaw angle of the ship increase with the flow velocity and decrease with the ship velocity. Behind the pier, the yaw angles increase continuously under conditions of the low flow velocity and high ship velocity, thereby increasing the risk of the stern of the ship sweeping against the pier.

This paper focuses on the mechanical structure design of amusement rides, elucidating the application of fundamental theories such as statics and fatigue strength analysis. It introduces special requirements like impact and alternating stress, explores methods for structural safety assessment and their limitations. The paper also covers principles for selecting indicators, the construction of a grading evaluation system, and the application of various materials and technologies in amusement rides, emphasizing the importance of structural safety and future development directions.

Glass fibre-reinforced polymer (GFRP) hat-stiffened panels have been widely used in high-speed vessels. Using carbon fibre-reinforced polymer (CFRP) as hybrid composites can improve structural stiffness and strength by adopting reasonable material design methods. To show the advantages of the designability of composite materials, the integrated design of materials and structures has to be adopted. This paper establishes the multiscale analysis framework to assess the ultimate strength of marine carbon/glass fibre-reinforced hybrid composite hat-stiffened panels with diverse composite designability. The equivalent material properties at the meso-scale obtained by a multiscale method define the macro-scale ultimate strength in finite element analyses. The investigation is focused on integrating material and structural design variables to optimise the ultimate strength of marine hat-stiffened panels. The response surface method is used to establish a surrogate model of the ultimate strength of marine hat-stiffened panels, and the multi-objective optimisation design is performed using Non-dominated Sorted Genetic Algorithm - II (NSGA-II) with structural mass and ultimate load as optimisation objective functions. The analysis procedure provides the integrated design method of materials and structures to achieve the optimal design of composite stiffened structures.

A composite panel with steel stiffeners, instead of the traditional steel panel, can reduce the weight of the superstructure in large passenger ships. In this study, the buckling and ultimate strength of composite sandwich panels with steel stiffeners are analysed by the nonlinear finite element method, compared to the one of prototype steel stiffened panel. Using the preliminary alternative design, the structural mass is reduced by 40.3% and the ultimate strength is increased by 14.1%. Afterwards, the RSM method is used to establish the surrogate model of the ultimate strength of structure under combined loads, and the multi-objective optimisation design is performed using NCGA algorithm with structural mass and ultimate load as optimisation objective functions. The results show that the structural mass is reduced by 4.1% and the ultimate strength is increased by 9.2%. The investigation aims to establish a procedure for optimising the structural mass and ultimate strength of GFRP sandwich panel with steel stiffeners.

Full-scale ship collision experiments have been conducted to investigate the structural damage of two LLDPE navigation buoys struck by a ship under varying colliding angles. The LLDPE material is selected to replace mild steel due to its lightweight and excellent mechanical properties. One of the buoys is a conventional design fabricated using heat fusion joining techniques, while the other is a modular buoy assembled from standardised components. Three collision scenarios are examined: hull side scraping, stern right-angle collision and side large-angle collision. In the experiments, the dynamic motion and permanent structural damage of struck buoys and the structural response of striking bow are recorded. These experimental data facilitate a comparative analysis of the collision behaviour between the two buoy designs. Furthermore, the experimental results are compared with finite element simulations performed using the LS-DYNA solver. A 6-DOF coupled finite element model is developed incorporating the external dynamics and internal mechanics of ship collisions. A good agreement is observed between experimental and numerical results, validating the accuracy of the external dynamics modelling defined in the simulations. These analyses demonstrate that the LLDPE buoy structures exhibit exceptional collision resistance and superior safety performance in inland waterways.

This paper evaluates the responses of equivalent stiffened panels made of steel, an aluminum alloy, and the glass fiber – reinforced plastic (GFRP) composite under extreme slamming loads. These panels are designed for bow flare structures in high-speed crafts. Their equivalence is established with respect to their designs using the same classification society rules. The analysis methods used in this work are illustrated, and slamming loads and inelastic structural responses are analyzed separately. Slamming loads are evaluated using a two-dimensional rigid bow flared section, with dynamic structural deformation and stress responses assessed through nonlinear finite-element analysis. The structures constructed of various materials are verified to meet design requirements. The primary objective of this work is to investigate the safety margin of bow flare structures constructed of steel, an aluminum alloy, and the GFRP composite under extreme sea conditions. The results show that the equivalent composite structures with larger scantlings, particularly the GFRP flat-bar stiffened structure, still exhibit considerably weaker impact strength under extreme slamming loads. The investigation of the structural responses and damage characteristics of equivalent stiffened plates under extreme slamming loads provides a reference for the potential limit state design of the bow flare structures of high-speed crafts.

This study presents an integrated experimental and numerical investigation into the collapse characteristics of a cracked box girder subjected to bidirectional cyclic bending moments. An experimental test involving a box girder specimen with a prefabricated transverse crack on the deck panel is conducted under four-point bending to evaluate the influence of cracking on ultimate strength under cyclic loading. The findings are reported through load–displacement curves, strain measurements, and observations of both global and localised structural failure modes, demonstrating strong consistency with finite element simulations conducted using ABAQUS software (version 2022). The results reveal that cyclic loading prior to ultimate capacity induces negligible stiffness reduction in the box girder structure, consistent with the structural behaviour under monotonic loading. The initial failure mechanism is attributed to local buckling of the deck plate, subsequently followed by significant plastic deformation around the crack tips, ultimately leading to global collapse. Parametric studies are carried out to evaluate the influence of key variables on the girder’s residual strength, such as crack length, cyclic load amplitude and pattern.

In this paper, the experimental and numerical simulation of a bottom-fixed cage equipped with double-layer nets is carried out to analyse the wave field characteristics under regular waves. The accuracy of the numerical method is rigorously validated by comparing simulation outcomes with experimental data under identical wave conditions. The effects of wave period, wave height, angle of attack and the absence of net on the wave field of the cage are studied. The results demonstrate that when the wave period is kept constant, the wave transmission coefficient decreases as the wave height increases. In contrast, when the wave height remains unchanged, the transmission coefficient increases as the wave period becomes longer. The change of wave direction from 0 degrees to 22.5 degrees mainly leads to relatively small differences in transmission coefficients inside the net cage. The configuration of a double-layer side net shows better wave attenuation performance than the single-layer side net. With the decrease of the side net layer, the wave transmission coefficient tends to increase gradually. The influence of the bottom net on wave attenuation is relatively insignificant. These conclusions can offer some insights for the structural configuration and hydrodynamic optimisation of aquaculture platforms and cages.

In the advanced design of novel structures used in marine, mechanical, and structural engineering, a pivotal challenge lies in accurately predicting their strength, amidst the integration of new materials and structures, within the context of extreme marine environments and potential accidents [...]

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 [...]

To study the influence of opening ratio on the shear performance of steel-bamboo composite cellular beams (SBCC), taking the opening size as the basic parameter, experimental research was carried out on five test beams. The failure modes and deformation characteristics of the specimens were observed, and the influence and law of the change of hole size on the shear performance of steel-bamboo composite cellular beams were analyzed. Through nonlinear finite element simulation calculation, multi-parameter analysis was carried out on the composite cellular beams, and the contribution of flanges to the shear performance of cellular composite beams was studied. The results show that the integrity of steel-bamboo composite cellular beams is good. The failure is mainly manifested as the fracture of bamboo web at the beam hole area, the buckling of section steel and the debonding and separation of steel-bamboo interface. The opening ratio has a great influence on the shear performance of steel-bamboo composite cellular beams. The thickness of bamboo flange cannot be ignored for the shear contribution of cellular beams. The shear capacity of cellular beams is shared by flanges and webs. The larger the opening ratio, the greater the shear contribution of flanges to composite cellular beams.