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Due to their high bending stiffness, high torsional stiffness, and high local stability, rectangular section members of Al alloy space structures are frequently utilized as load-bearing elements. However, the joint construction is more complex because of the closed cross-section. To join rectangular section members without drilling holes in them, a variety of blind bolts that can be placed and fastened on one side have been devised. The blind bolts researched in this paper is known as BOM bolt. The shear resistance of BOM-bolted Al alloy connections is investigated using shear testing and finite element calculations of individual bolts and bolt groups. According to the test and numerical simulation results, the formulas for the compressive strength of the aluminum plate and the shear capacity reduction factor of BOM-bolted long connections are derived. [ABSTRACT FROM AUTHOR]

The unfixed flame propagation velocity of a gas explosion and the fixed response time of explosion suppression devices are the important reasons for the poor protective effect of active explosion suppression. A flexible explosion suppression method based on buffer energy absorption is detailed in this study. The explosion suppression system consists of an explosive characteristic monitoring system, an explosion suppression agent system, and an explosion suppression airbag. An empty pipe experiment and an explosion suppression experiment with a flexible-airbag gas-explosion suppression device were conducted in a 20.5 m-long pipe with an inner diameter of 180 mm. The flame propagation velocity and maximum overpressure values were compared between the two groups of experiments. The experimental results show that the flame wave propagation can be completely suppressed by the explosion suppression device under certain pressure. The occurrence time of maximum overpressure at each pressure measuring point is also analyzed. P3 is generally later than P4, which verifies the existence of energy absorption and explosion suppression effect of airbag. Finally, the energy absorption effect of the airbag is analyzed theoretically. The shock wave overpressure calculated in the sealing limit state of the airbag is 0.3432 MPa, and the maximum error is 7.8%, which provides reliable guidance and prediction for the experimental process in the future. [ABSTRACT FROM AUTHOR]

The Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) model integrated with the Volume of Fluid (VOF) method is applied to study the complex gas-fluid-particle coupled system. To enhance the model's feasibility, the efficiency and accuracy improvement approaches are implemented into the model, including the coarse-grained method, porous medium replacement and semi-resolved method. To validate the effectiveness and accuracy of the model, simulations of the particle water entry and dam break scenarios are conducted, Subsequently, the VOF-CFD-DEM model is utilized to study the sediment transportation under breaking waves. A comparison of various turbulence models reveals that the stabilized k - ω model can simulate the breaking wave with acceptable efficiency and accuracy. The study examines the flow characteristics, forces acting on slopes, and typical sediment movements, providing detailed case studies and data relevant to gas-fluid-particle systems. This work extends the application of the VOF-CFD-DEM model to extreme conditions in ocean engineering, offering a mesoscopic perspective on complex engineering challenges. [ABSTRACT FROM AUTHOR]

The hydrodynamic behaviours and progressive collapse phenomenon of the submerged floating tunnel (SFT) under anchor cable breakage are experimentally investigated in this study. A physical scale segment model of the SFT under wave and current loadings is designed and studied in wave-current flume. A specially designed anchor cable breakage device is presented. The experimental data are observed to conform well to the numerical calculation results. The dynamic performance of the SFT under anchor cable breakage is comprehensively investigated based on varying effect factors. The results from the test indicate that the response variation assessment, transient effect, force redistribution and impact force in different cases are the key factors to determine the probability of instability and progressive collapse of the SFT under cable breakage. The results can provide valuable design and construction recommendations to avoid potential engineering risks and ensure the safety and stability for the SFT under marine environment. [ABSTRACT FROM AUTHOR]

This study proposes a theoretical analysis model to analyse the marine riser's coupled cross-flow/in-line vortex induced vibration (VIV) under heave-induced time varying parametric vibration. Combining with the linear-wave theory, the stochastic phase spectrum method is used to simulate the stochastic multi-frequency parametric excitation in the time-domain to reproduce the real sea conditions. The nonlinearities are considered to capture the geometrical coupling of cross-flow/in-line displacements excited by hydrodynamic lift/drag forces and the wake-riser interaction. A generally good agreement between the proposed approach and other analyses can be observed. A parametric study is conducted, it is found that the drag coefficient is of significance for the riser's VIV, and the lift coefficient is affected by vortex shedding. The wave form, in terms of wave height and wave period, need to be considered with caution in design of a riser to avoid the occurrence of resonance under stochastic parametric excitation. [ABSTRACT FROM AUTHOR]

Prestressed concrete cylinder pipe (PCCP) is widely used in hydraulic engineering. The bell‐and‐spigot joint is a weak point along a PCCP pipeline, since damage of joint can affect the operation of the whole pipeline. In this paper, a three‐dimensional numerical model of buried PCCP, considering the simulation of rubber gasket in bell‐and‐spigot joint is established. The fluid–structure coupling of PCCP is accomplished using the Mesh‐based parallel Code Coupling Interface (MpCCI), where the pipe and the surrounding soil are characterized in the software ABAQUS, and the pressurized water is modeled in the software FLUENT. The force and rotation angle at joints of PCCP under different conditions, including surcharge load, loading location, cover depth, and internal pressure, are analyzed. It is shown that the rotation angle of joint exceeds the allowable value, when the surcharge load is greater than 180 kPa. Compared with the effect of surcharge load, the offset distance (i.e., distance between the loading position and the pipe axis) has a greater influence on the development of horizontal displacement and rotation angle. As the offset distance increases, both the horizontal displacement and rotation angle at joints increase first, and they decrease after the peak. [ABSTRACT FROM AUTHOR]

Offshore pipelines are often suspended or partially-buried during operating process. Understanding the scouring mechanism of the suspended and partially-buried pipelines is important for protecting the pipelines. The numerical models of pipelines under steady flow are established, in which Reynolds Averaged Navier-Stocks equation (RANS) with the k-ω turbulence closure, as well as the sediment transport equation, are solved with the finite volume method. After experimental verification, the models are applied to a series of parametric analysis for the suspended and partially-buried pipelines under steady flow. The effect of different variables such as the pipe diameter D , the suspension height e , the pipe shape, the embedment depth, on the scour process of the pipelines are investigated in detail based on more than 150 simulation results. For the suspended pipelines, the gap-to-diameter ratio e / D is the key parameter to predict scour depth. The pipe shape has an influence on the scour depth and the position of the scour hole. A formula to predict scour depth in terms of e/D and the relation between gap velocity and scour depth is obtained. For the partially-buried pipelines, the block height and the curvature of the pipeline is proposed as the key parameters to analyze the flow field around the pipeline. • The numerical model of pipelines under steady flow are established and verified. • Effect of different parameters on scour process of offshore pipelines are studied. • Formula to predict scour depth in terms of e / D is proposed for suspended pipelines. • Block height and curvature are key data to analyze flow of partially-buried pipelines. [ABSTRACT FROM AUTHOR]

The risks posed by local scour around offshore monopile foundations are substantial and threaten the structural safety of these installations. It is therefore essential to study the mechanisms of local scour to mitigate these risks. Numerical simulation is an effective tool to help us understand the mechanisms of local scour. However, the accurate modeling of the local scour process remains to be challenging due to the complexity of sediment transportation, in which the continuity threatment of sediment phase is typically used, the discrete behavior of the sediment is hard to be described. Therefore, in this paper, in order to conduct the deepin investigation into the mechanism of the local scour around monopile, a three-dimensional CFD-DEM model was established by coupling the computational fluid dynamic method (CFD) and discrete element method (DEM). To increase the efficiency and accuracy of the CFD-DEM model, the coarse grain method (CGM) was used to decrease the number of required DEM particles in the simulation, and the angle of repose was used to calibrate the contact parameters between DEM particles. During the validation process of the numerical model, it was found that the development of the scour depth and the morphology of scour pit obtained by the CFD-DEM model showed good agreement with the previously published results. The CFD-DEM simulation revealed that seepage-induced vertical drag force plays a crucial role in the initial stage of local scour. Two sediment transportation processes, "Pile toe erosion-Slope avalanche" and "Push-Accumulation-Wash", were observed and the relationship between bedload sediment flux and the Shields number was quantified. In the end of this paper, the critical evaluation of the CFD-DEM method was conducted. • The first time that the CFD-DEM method is used to research the sediment motion during the local scour around monopile. • The coarse grain method is used to improve the efficiency of CFD-DEM coupling method. • The seepage-induced vertical drag force was proved to be crucial in the early stage of local scour around monopile. • The "Pile toe erosion-Slope avalanche" and "Push-Accumulation-Wash" process of sediment transportation were observed. • A method is proposed to convert the parameters of discrete phase into the continuous phase parameters. [ABSTRACT FROM AUTHOR]

Local scour refers to the erosion or migration of sedimental particles around bridge piers or abutments under the action of water flow. It can potentially undermine the hydraulic structures, resulting in catastrophic damage or even collapse. Under various hydraulic conditions, monopiles with diverse cross-sectional shapes have increasingly been applied to marine foundations. This study aims to investigate the effect of monopile shapes on scour development, and to establish a cross-scale connection between the macroscopic evolution of scour pits and the microscopic characteristics of sediments. The scour processes around monopiles are simulated using a coupled computational fluid dynamics and discrete element method (CFD-DEM). Four monopile shapes are examined, including circular, square, square with rounded corners, and diamond. Macroscopic characteristics such as seabed morphology, maximum scouring depth, and scour areas are analyzed, along with the microscopic characteristics such as the kinetic energy, drag force, and mechanical coordination number. The outcomes highlight that the diamond-shaped pile results in the greatest scour depth and widest scour areas compared to the other shapes. The incorporation of rounded pile corners improves flow characteristics and mitigate scour pit development. Furthermore, the local scour at different areas around the monopiles varies under the influence of different flow features. [ABSTRACT FROM AUTHOR]