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Combining the strengths of Lagrangian and Eulerian descriptions, the coupled Lagrangian–Eulerian methods play an increasingly important role in various subjects. This work reviews their development and application in ocean engineering. Initially, we briefly outline the advantages and disadvantages of the Lagrangian and Eulerian descriptions and the main characteristics of the coupled Lagrangian–Eulerian approach. Then, following the developmental trajectory of these methods, the fundamental formulations and the frameworks of various approaches, including the arbitrary Lagrangian–Eulerian finite element method, the particle-in-cell method, the material point method, and the recently developed Lagrangian–Eulerian stabilized collocation method, are detailedly reviewed. In addition, the article reviews the research progress of these methods with applications in ocean hydrodynamics, focusing on free surface flows, numerical wave generation, wave overturning and breaking, interactions between waves and coastal structures, fluid-rigid body interactions, fluid–elastic body interactions, multiphase flow problems and visualization of ocean flows, etc. Furthermore, the latest research advancements in the numerical stability, accuracy, efficiency, and consistency of the coupled Lagrangian–Eulerian particle methods are reviewed; these advancements enable efficient and highly accurate simulation of complicated multiphysics problems in ocean and coastal engineering. By building on these works, the current challenges and future directions of the hybrid Lagrangian–Eulerian particle methods are summarized. [ABSTRACT FROM AUTHOR]

Hypervelocity impact (HVI) on carbon fiber reinforced plastics (CFRPs) is associated with extreme impulse response of material as well as complex characteristics of the composites. It is a challenging task to predict the physical process of CFRP-HVI problems accurately. We apply a GPU-accelerated smoothed particle hydrodynamics (SPH) method which incorporates the composite material model and the decoupled finite particle method to simulate the CFRP-HVI processes. The presented SPH model is validated by simulating the processes of aluminum spheres impacting metallic plates. The simulation results agree well with available experimental and numerical results, and the GPU parallelization technique significantly improves the simulation efficiency (350 times faster than an equivalent serial SPH model). With such computational accuracy and efficiency, the model is extended to simulate CFRP laminate impact problems, and a particle convergence analysis is performed. It is shown that the model can obtain convergent results when modeling each CFRP layer with three SPH particles in the thickness direction and correspondingly using about twenty million particles in total. The simulation can be completed within several hours, and the dominant mechanisms of the CFRP-HVI can be captured quantitatively. To further investigate the protective performance of CFRP structures, HVI on a well-known shielding structure Whipple bumper is investigated numerically. The dynamic response of the structure is well reproduced, and the results show that the CFRP pressure wall is more effective than the metallic one. These simulation results demonstrate that the presented SPH model can model the CFRP-HVI problems accurately and efficiently. [ABSTRACT FROM AUTHOR]

Vehicle wading is a complex fluid-structure interaction (FSI) problem and has attracted great attention recently from the automotive industry, especially for electric vehicles. As a meshless Lagrangian particle method, smoothed particle hydrodynamics (SPH) is one of the most suitable candidates for simulations of vehicle wading due to its inherent advantages in modeling free surface flows, splash, and moving interfaces. Nevertheless, the inevitable neighbor query for the nearest adjacent particles among the support domain leads to considerable computational cost and thus limits its application in 3D large-scale simulations. In this work, a GPU-based SPH method is developed with an adaptive spatial sort technology for simulations of vehicle wading. In addition, a fast, easy-to-implement particle generator is presented for isotropic initialization of the complex vehicle geometry with optimal interpolation properties. A comparative study of vehicle wading on a puddle between the GPU-based SPH with two pieces of commercial software is used to verify the capability of the GPU-based SPH method in terms of convergence analysis, kinematic characteristics, and computing performance. Finally, different conditions of vehicle speeds, water depths, and puddle widths are tested to investigate the vehicle wading numerically. The results demonstrate that the adaptive spatial sort technology can significantly improve the computing performance of the GPU-based SPH method and meanwhile promotes the GPU-based SPH method to be a competitive tool for the study of 3D large-scale FSI problems including vehicle wading. Some helpful findings of the critical vehicle speed, water depth as well as boundary wall effect are also reported in this work. [ABSTRACT FROM AUTHOR]

This paper presents a profound study on the formation of three typical types of defects (i.e., lack of fusion, keyholes, and gas pores) observed in selective laser melting (SLM) printed Inconel 718 samples, along with their correlations with mechanical properties of the samples. Computed tomography, scanning electron microscopy, and mechanical property tests revealed that the three types of defects fall into three stages of porosity evolution classified by recently-proposed dimensionless numbers ηm (melting efficiency) and ηv (vaporization efficiency). Meanwhile, experimental tests verified that the mechanical properties of products, such as strength and elongation, are remarkably sensitive to lack of fusion. However, these properties are slightly affected by the keyholes and gas pores. An optimal process window characterized by dimensionless numbers is realized by adjusting the processing parameters and employing different powders. This process window allows products to have relatively low defects and high mechanical performances. A quantitative relation between processing parameters, dimensionless numbers, defects, and mechanical properties is established based on these observations. This relation, along with the optimal process window, is believed to enhance the quality of SLM products of Inconel 718 alloy and can be further extended to SLM with other metal materials. [ABSTRACT FROM AUTHOR]

Free-surface flows, especially those associated with fluid-structure interactions (FSIs), pose challenging problems in numerical simulations. The authors of this work recently developed a smoothed particle element method (SPEM) to simulate FSIs. In this method, both the fluid and solid regions are initially modeled using a smoothed finite element method (S-FEM) in a Lagrangian frame, whereas the fluid regions undergoing large deformations are adaptively converted into particles and modeled with an improved smoothed particle hydrodynamics (SPH) method. This approach greatly improves computational accuracy and efficiency because of the advantages of the S-FEM in efficiently treating solid/fluid regions showing small deformations and the SPH method in effectively modeling moving interfaces. In this work, we further enhance the efficiency of the SPEM while effectively capturing local fluid information by introducing a multi-resolution technique to the SPEM and developing an effective approach to treat multi-resolution element-particle interfaces. Various numerical examples demonstrate that the multiresolution SPEM can significantly reduce the computational cost relative to the original version with a constant resolution. Moreover, the novel approach is effective in modeling various incompressible flow problems involving FSIs. [ABSTRACT FROM AUTHOR]

Level set (LS) method is a widely used interface capturing method. In the simulations of incompressible two-phase flows, in order to avoid discontinuities at interfaces, the LS function is usually taken as a smeared-out Heaviside function bounded on [0, 1] and advected by a given velocity field u obtained from the solution of the incompressible Navier-Stokes equations. In the incompressible limit ∇ · u = 0 , the advection equation for the LS function can be written and discretized in conservative form. However, due to numerical errors, the resulting velocity field is in general not divergence free which leads to the solution of the advection equation in conservative form does not satisfy the maximum principle. To overcome this issue, in this work, we develop a high-order discontinuous Galerkin (DG) method to directly solve the advection equation for the LS function in non-conservative form. Moreover, we prove that by applying a linear scaling limiter, the proposed method together with a strong stability preserving (SSP) time discretization scheme can satisfy the strict maximum principle under a suitable CFL condition. Numerical simulations of several well-known benchmark problems, including the application to incompressible two-phase flows, are presented to demonstrate the high-order accuracy and maximum-principle-satisfying property of the proposed method. [ABSTRACT FROM AUTHOR]

As a promising powder-based additive manufacturing technology, selective laser melting (SLM) has gained great popularity in recent years. However, experimental observation of the melting and solidification process is very challenging. This hinders the study of the physical mechanisms behind a variety of phenomena in SLM such as splashing and balling effects, and further poses challenges to the quality control of the products. Powder-scale computational models can reproduce the multi-physics process of SLM. In this study, we couple the Finite Volume Method (FVM) and Discrete Element Method to model the deposition of powder particles, and use the FVM to model the melting process, both with ambient air. In particular, a cutting-edge sharp surface capturing technique (iso-Advector) is incorporated into the Volume of Fluid Model to reconstruct the interface between different phases during the melting process. Iso-Advector is then used to capture and reconstruct the interface between molten material and ambient air, which is further used as a solid boundary for spreading the next powder layer. As such, 3D geometrical data is exchanged between these two stages repeatedly to reproduce the powder spreading-melting process of SLM incorporating different scan paths on multiple powder layers. To demonstrate the effectiveness of the powder-scale multi-physics modeling framework, typical scenarios with different fabrication parameters (Ti-6Al-4V powder) are simulated and compared with experimental observations available in literature. [ABSTRACT FROM AUTHOR]

Flow through arrays of micropillar embedded inside microfluidic chip systems is important for various microfluidic devices. It is critical to accurately predict the mass flow rate through pillar arrays based on the pillar design. This work presents a dissipative particle dynamics (DPD) model to simulate a problem of flow across periodic arrays of circular micropillar and investigates the permeability of two types of micropillar arrays. The flow fields including horizontal and vertical velocity fields, the number density field, and the streamline of the flow are analyzed. The predicted solid volumes by the presented DPD simulation of both types of arrays are quite close to the actual counterparts. These quantitative agreements show usefulness and effectiveness of the DPD model in simulating arrays of micropillar. By comparing two types of micropillar arrangement patterns, we find that the arrangement pattern of micropillar does not have significant influence on the permeability of the array. [ABSTRACT FROM AUTHOR]

Mesoscale dispersed two-phase flows often involve complicated dynamic behaviors. Grid-based methods within the framework of continuum mechanics are usually difficult to capture certain degree of molecular-level effect, while the molecular dynamics is only practical at extremely small temporal and spatial scales. In this paper, dissipative particle dynamics (DPD) is extended to the investigation of a fluid-solid sphere system with inertia effect within two parallel plates through the modification of DPD weighting function and hence the dynamic parameters. The sphere and walls are composed of frozen DPD particles that are first treated to reach equilibrium state in the simulation. The force on the solid sphere is obtained from all the particles included in the sphere. The drag coefficient of the frozen sphere is evaluated and compared with the classical correlations. The initial value problem for the sedimentation of the sphere is then solved at certain Reynolds numbers, which is consistent with our direct numerical simulation results. [ABSTRACT FROM AUTHOR]

The ocean environment is protected from oil pollution usually by using floating booms, which involves water-oil two-phase flow and strong fluid-structure interaction. In this paper, a modified multi-phase smoothed particle hydrodynamics (SPH) method is proposed to model oil spill containment by using a moving boom. Four major influencing factors including oil type, moving velocity and skirt angle of the boom, and water wave are investigated. The SPH simulation results demonstrate different typical boom failure modes found in laboratory experiments. It is shown that the ability of a boom in containing oil is not only affected by its own characteristics, but also closely related to external environmental factors. It is found that boom failure is more likely to happen for heavy oil, high boom velocity, negative skirt angle, and/or in the presence of water waves. [ABSTRACT FROM AUTHOR]

As a popular meshfree particle method, the smoothed particle hydrodynamics (SPH) has suffered from not being able to directly implement the solid boundary conditions. This influences the SPH approximation accuracy and hinders its further development and application to engineering and scientific problems. In this paper, a coupled dynamic solid boundary treatment (SBT) algorithm has been proposed, after investigating the features of existing SPH SBT algorithms. The novelty of the coupled dynamic SBT algorithm includes a new repulsive force between approaching fluid and solid particles, and a new numerical approximation scheme for estimating field functions of virtual solid particles. The new SBT algorithm has been examined with three numerical examples including a typical dam-break flow, a dam-break flow with a sharp-edged obstacle, and a water entry problem. It is demonstrated that SPH with this coupled dynamic boundary algorithm can lead to accurate results with smooth pressure field, and that the new SBT algorithm is also suitable for complex and even moving solid boundaries. [ABSTRACT FROM AUTHOR]

In this work, we propose an efficient smoothed particle hydrodynamics (SPH) method for simulating laser powder bed fusion (LPBF). The multi-physics process of LPBF, including the heat transfer and phase change with complex boundaries, is accurately resolved by a novel heat source model and a modified continuous surface force based on a corrected surface delta function. Moreover, we also develop an efficient tensile instability control algorithm for preventing the pressure oscillations. The present method is implemented in a GPU-accelerated framework, and its performance is well demonstrated by simulating the LPBF processes with both single-layer and multi-layer powder beds (with the help of surface reconstruction). The numerical results are compared well with the experimental ones which clearly verify the ability of the present method in capturing the complex physical phenomenon of LPBF. [ABSTRACT FROM AUTHOR]