The silt seabed can undergo liquefaction under wave action, resulting in the liquefied silt seabed exhibiting nonNewtonian fluid characteristics and fluctuating in phase with the overlying waves. The fluctuation of the liquefied silt seabed can impose periodic forces on the buried pipelines, posing a significant threat to their safety. This study achieves the measurement of the non-Newtonian fluid rheological properties of wave-induced liquefied silt, through the improvement of the falling-ball method. The improved falling-ball method enables in situ measurement of the rheological properties of liquefied silt in fluctuation state. This method is applied in two wave flume experiments to investigate the effects of wave intensity and the liquefaction process on the rheological properties of liquefied silt. Building on this foundation, a computational fluid dynamics (CFD) numerical model is developed to simulate the wave-liquefied silt interaction, utilizing the rheological properties of the liquefied silt obtained from experimental measurement. The model is used to evaluate the fluctuation velocity of the liquefied silt under field conditions and its forces acting on buried pipelines. The research findings provide foundational data for more accurate simulations of the movement of wave-induced liquefied silt and its effects on structures.

Solid particles may experience different kinds of cohesive forces, which cause them to form agglomerates and affect their flow in multiphase systems. When such systems are simulated through computational fluid dynamics (CFD) programs, appropriate modelling tools must be included to reproduce this feature. In this review, these strategies are addressed for various systems and scales. After an introduction of the different forces (van der Waals, electrostatic, liquid bridge forces, etc.), the modelling approaches are categorized under three methodologies. For diluted slurries of very fine particles, many researchers succeeded with pseudo-single phase approaches, employing a model for the non-Newtonian rheology. This was especially popular for sludges in anaerobic digestions or certain types of soils. In other cases, continuum-based approaches seem to be more adequate, including cohesiveness in the kinetic theory of granular flows or the restitution coefficient. Geldart-A particles experiencing van der Waals forces are the primary focus of such studies. Finally, when each particle is modelled as a discrete element, the cohesive force can be directly specified; this is especially widespread for the wet fluidization case. For each of these approaches, a general overview of the main strategies, achievements, and limits is provided.

Vegetation barriers are an important environmental characteristic of spent fuel road transportation accidents. Spent fuel vessels may be affected by force majeure factors during transportation, which leads to damage to spent fuel assemblies and containers and can cause radionuclides to gradually release from assemblies to vessels to the external environment. In this work, considering the growth periods of coniferous vegetation barriers and vessel type, a radionuclide dispersion model based on computational fluid dynamics (CFD) was established by adding a decay term and a pressure loss term. The simulations showed that, first, compared to the small (Type-II) vessel, the effects of fluid flow around the large vessel (Type-I) have a more significant impact on radionuclide dispersion. The backflow around the Type-I vessel causes leaked radionuclides to disperse towards the vessel, and the larger the vessel is, the more significant the rise of the leaked radionuclide plume tail will be due to the increased negative pressure gradient area. Moreover, the area contaminated exceeding the maximum allowable concentration by radioactivity for the Type-I vessel is reduced gradually with the growth of coniferous vegetation barriers due to the weakening of the backflow effect by growing vegetation. Second, compared to vegetation barriers of 15 years and 23 years, the horizontal distance exceeding the maximum allowable concentration of the leaked I-131 dispersion from Type II vessels near vegetation barriers for 12 years is the longest. The older the vegetation barrier is, the shorter the horizontal dispersion range, and the shape of radionuclide dispersion gradually transforms from flat to semicircular with vegetation barrier growth, but this could cause a greater radioactive accumulation effect near the leakage point, and the maximum concentration of leaked I-131 reached 0.54 kBq center dot m(-3) for leaked radionuclides from the Type II vessel under vegetation barriers of 23 years. In addition, improvement suggestions based on the proposed method are presented, which will enable the Standards Institutes to apply the research methodologies described herein across various scenarios. Environmental Implication: Compared to nonradioative pollutants, radioactive pollutants are intercepted by vegetation barriers and then migrate to the soil through leaves, stems, and roots, which can contaminate the surrounding environment. Considering the effects of vessel type and coniferous vegetation growth, a radionuclide dispersion model based on CFD was established. Suggestions for decontaminating radioactive pollution areas have been proposed based on the simulation results of hypothetical scenarios. The scenario applicability improvements based on the proposed model could assist relevant Standards Institutes to making improving measures.

Marine and underwater structures, such as seawalls, piers, breakwaters, and pipelines, are particularly susceptible to seismic events. These events can directly damage the structures or destabilize their supporting soil through phenomena like liquefaction. This review examines advanced numerical modeling approaches, including CFD, FEM, DEM, FVM, and BEM, to assess the impacts of earthquakes on these structures. These methods provide cost-effective and reliable simulations, demonstrating strong alignment with experimental and theoretical data. However, challenges persist in areas such as computational efficiency and algorithmic limitations. Key findings highlight the ability of these models to accurately simulate primary forces during seismic events and secondary effects, such as wave-induced loads. Nonetheless, discrepancies remain, particularly in capturing energy dissipation processes in existing models. Future advancements in computational capabilities and techniques, such as high-resolution DNS for wave-structure interactions and improved near-field seismoacoustic modeling show potential for enhancing simulation accuracy. Furthermore, integrating laboratory and field data into unified frameworks will significantly improve the precision and practicality of these models, offering robust tools for predicting earthquake and wave impacts on marine environments.

Seismic-induced submarine landslides pose significant risks to offshore structures. To enhance our understanding of this phenomenon, we have developed a CFD-MPM capable of simulating complete mechanisms behind earthquake induced submarine landslide. Recent centrifuge tests have demonstrated that the permeability of marine sediment is a critical factor in determining the failure mechanism of submarine landslides. Specifically, a lower permeability increases the likelihood of a slope transitioning from failure to gravity debris flow. Our CFDMPM, validated with centrifuge tests, supports this conclusion. Moreover, we conducted a sensitivity analysis of seismic-induced submarine landslides using the CFD-MPM. In the case of contractive soil, a lower permeability leads to slower dissipation of excess pore water pressure, resulting in longer submarine debris flow runouts. Additionally, in the case of softening soil, a lower permeability increases the chances of spreads as a failure mechanism, while a higher permeability favours retrogressive flow slides. This study sheds light on the diverse effects of sediment permeability on submarine landslide mechanisms, offering crucial insights for hazard assessment and mitigation strategies in offshore engineering and coastal management.

To comprehensively understand the explosion risk in underground energy transportation tunnels, this study employed computational fluid dynamics technology and finite element simulation to numerically analyze the potential impact of an accidental explosion for a specific oil and gas pipeline in China and the potential damage risk to nearby buildings. Furthermore, the study investigated the effects of tunnel inner diameter (d = 4.25 m, 6.5 m), tunnel length (L = 4 km, 8 km, 16 km), and soil depth (primarily L-soil = 20 m, 30 m, 40 m) on explosion dynamics and on structural response characteristics. The findings indicated that as the tunnel length and inner diameter increased, the maximum explosion overpressure gradually rose and the peak arrival time was delayed, especially when d = 4.25 m; with the increase in L, the maximum explosion overpressure rapidly increased from 1.03 MPa to 2.12 MPa. However, when d = 6.5 m, the maximum explosion overpressure increased significantly by 72.8% from 1.25 MPa. Evidently, compared to the change in tunnel inner diameter, tunnel length has a more significant effect on the increase in explosion risk. According to the principle of maximum explosion risk, based on the peak explosion overpressure of 2.16 MPa under various conditions and the TNT equivalent calculation formula, the TNT explosion equivalent of a single of the tunnel was determined to be 1.52 kg. This theoretical result is further supported by the AUTODYN 15.0 software simulation result of 2.39 MPa (error < 10%). As the soil depth increased, the distance between the building and the explosion source also increased. Consequently, the vibration peak acceleration and velocity gradually decreased, and the peak arrival time was delayed. In comparison to a soil depth of 10 m, the vibration acceleration at soil depths of 20 m and 30 m decreased by 81.3% and 91.7%, respectively. When the soil depth was 10 m, the building was at critical risk of vibration damage.

Simulation and accurate modeling of the mixing process of the high-pressure jet-cutting clay by the water-air coaxial nozzle is significantly important for the performance optimization of the triple fluid jet grouting. In this paper, a numerical model considering the soil rheological properties is proposed to investigate the mixing process of the high-pressure jet-cutting clay. The cohesive force model of clay is obtained based on the solution of the power law index and consistency factor by coupling the Herschel-Bulkley and soil logarithmic models. The interaction model among the gas phase, the liquid phase, and the clay medium is further established through use of the drag force model. A laboratory device of high-pressure jet-cutting transparent clay is developed to prove the feasibility of the proposed model for the mixing process of the high-pressure jet-cutting clay. Finally, using the validated numerical model, the mixing process of the high-pressure jet-cutting clay by the water-air coaxial nozzle with varying radial spacings between the air nozzle and water nozzle is numerically investigated, and the axial stability of the jet, the width of the cross-sectional profile, and the variation of the central axis velocity field of the mixing process are analyzed. Results demonstrated that the variation trend of the jet in both simulations and experiments is consistent, and the maximum error in jet depth is better than 3.3%, validating the accuracy of the numerical model of the mixing process of the high-pressure jet-cutting clay. The optimal radial spacing size for a water-air coaxial nozzle in high-pressure jetting of clay medium is 1.4 mm, which provides the best axial stability, the narrower jet cross-section, and the slowest decay of jet velocity along the central axis.

Characterisation of the permeability of soils is of practical importance and, for cohesionless or granular soils, it can be predicted from the void ratio and the particle size distribution (PSD). However, the effect of fabric anisotropy on the permeability is rarely discussed. Restricting consideration to granular (cohesionless) soil, this study combines a variety of numerical methods to investigate (1) how the anisotropy of the permeability evolves as the soil fabric anisotropy evolves in triaxial deformation and (2) establish a link between the anisotropy of the permeability and the fabric anisotropy. The Discrete Element Method (DEM) was employed to create linearly graded virtual samples of spheres (Cu of 1 to 2). Initially isotropic sphere packings were subjected to triaxial compression or triaxial extension up to 30% of absolute axial strain to induce an anisotropic fabric. Pore Network Models (PNMs) present a computationally efficient option for simulation of flow through the pore space. A PNM models fluid flow between pores (nodes) connected by pipes ( edges) whose geometry is defined by the topology of the connected pores and the mass balance equation is solved at each pore. After demonstrating the accuracy of the PNM framework adopted here, this contribution presents data from PNM simulations that used the positions of individual particles in the sheared spherical packings as input data. The fabric and permeability anisotropies during triaxial shear deformation were compared at axial strain intervals of 1%. Detailed microscale analyses suggest that the anisotropy in the permeability can be attributed to an increase in the local conductance of fluid pipes in the direction of the major principal stress, which is related to the evolution of the pore topologies during the shear deformation.

Cyclic loading has a significant effect on soil properties and seriously threatens geotechnical engineering. However, it remains unclear how cyclic loading affects the suffusion behavior in gap-graded granular soils. In this study, we performed systematic numerical simulations of suffusion in soil samples subjected to triaxial compression coupled with computational fluid dynamics (CFD) and discrete element method (DEM) approaches, i.e., coupled CFD-DEM. The proposed method is able to simulate the suffusion process in gap-graded soils under cyclic loading and reveal the evolution of the fluid fields. The suffusion of gap-graded soil samples was achieved by imposing a downward seepage flow. The results indicated that cyclic loading induces greater erosion mass and fluid velocity during the suffusion process compared to simulations under fixed external forces. The erosion curve can be divided into two stages. In the first stage, the particle loss rate is high, but only lasts for a very short period of time. Then, the particle loss rate slows down and enters the second stage. In this stage, compared to a non-vibrating sample, the sample subjected to cyclic loading still has a large eroded mass, which persists until the end of the simulation. The sensitivity analysis indicated that the first stage of suffusion is more sensitive to an increase in vibration amplitude, whereas the second stage is more responsive to an increase in frequency.