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• A numerical model is developed to analyze underwater explosion of slender explosive and structure responses. • Slender explosive will generate a directional pressure field in the surrounding water. • The shape of explosive strongly influences shock wave dynamics in the near-field. • The direction effect of pressure and energy flux is significant. • The response of a plate subjected to near-field underwater explosion of a slender explosive is studied. The shape of a high-explosive is an important factor to consider in the near-field and contact explosion, but this has been rarely studied previously. In this paper, we first conduct experiments to study the directional effects of the underwater explosion shock wave of slender explosives. A numerical model based on the multi-material arbitrary Lagrangian Eulerian (MM–ALE) technique is then developed to study the influence of the explosive slender ratio on the generated shock waves. The numerical model is validated by experiment data. Then, tests are conducted with constant-mass cylindrical explosives with slender ratios ranging from 2.0 to 9.2. By comparing with the center-detonated spherical explosive, the peak pressure, pulse duration, impulse and energy flux of the underwater explosion of slender explosives are analyzed in detail. Furthermore, the effectiveness of the fluid-structure interaction algorithm is verified through the experimental data of a plate subjected to underwater contact explosion. Finally, the response of plates subjected to the underwater explosion of a slender explosive at different azimuths is studied. The interaction between the plate and the directional loads is analyzed. We conclude that the loads and structure responses of the near-field underwater explosion of slender explosives are different from those of spherical explosives. The analyses and results provide a reference for the near-field underwater explosion loads and structural response studies. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The rigid motions of powders widely exist in powder-based laser additive manufacturing, like powder deposition, entrainment and spattering. These phenomena simultaneously happen as the laser melts these powders, and can have significant impacts on the quality of the printed products. However, existing models can hardly efficiently reproduce the co-existence of melting and rigid motion which greatly influences the molten pool and molten track evolution. The bottleneck therein lies in the demand that unresolved Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) has on the CFD grid size, that is, larger than 3 times of the particle diameter. However, this large size ratio (CFD grid cell vs particle diameter) handicaps the description of the particle deformation during melting. Hence in this paper, a kernel approximation-based semi-resolved CFD-DEM numerical model that allows the refinement of CFD grid is employed, and then coupled with the Volume of Fluid (VOF) method to reproduce the molten metal-gas interface. On this basis, the rigid motions of the powders, like entrainment and spattering, are finally simultaneously realized as the molten pool evolves at high efficiency. Powders remained in the unclosed molten pool trail defect are well explained with the proposed model as well. This model can also be applied to simulate the particle-fluid interactions in Directed Energy Deposition. It is believed that this semi-resolved VOF-DEM Additive Manufacturing model will serve as a good tool for future investigations into the particle behaviors in powder-based additive manufacturing. [Display omitted] • Semi-resolved VOF-DEM Additive Manufacturing model is developed. • Particle rigid motion is simultaneously modeled with molten pool evolution. • Spattered powders left in the defect are well explained. • Modeling of complex particulate flows in Directed Laser Deposition is realized. [ABSTRACT FROM AUTHOR]

• Semi-resolved CFD–DEM is extended to particulate flows with thermal convection. • Background fluid properties are corrected using kernel-based approximation. • Model A is adopted to address fluid-particle interaction with more force models. • Turbulence model is incorporated into the semi-resolved CFD–DEM. • The semi-resolved CFD–DEM provides better predictions and more details in modeling thermal particulate flows in fluidized bed. • Several phenomena observed in thermal fluidized bed are discussed. Particulate flows with heat transfer widely exist in industry including fluidized bed reactor and powder-based 3D printing, and are frequently modeled with CFD–DEM coupled approaches. Recently, we developed a semi-resolved CFD–DEM approach, which bridges the simulation gap between the resolved and unresolved CFD–DEM (Wang et al., 2019). The semi-resolved CFD–DEM is as efficient as the conventional unresolved CFD–DEM and as accurate as the resolved CFD–DEM, while it is validated for particulate flows with momentum exchange with Model B without heat exchange. In this paper, we further extend the semi-resolved CFD–DEM approach to model particulate flows with momentum exchange and thermal convection. Firstly, similar to background fluid velocity, background fluid temperature is corrected through kernel-based approximations on the neighboring fluid cells rather than simply taking values in the local cell containing the concerned particle. Secondly, Model A is adopted in the semi-resolved CFD–DEM, leading to more powerful capabilities in handling complicated flows. Force models like the Magnus force, virtual mass force are also included. Thirdly, turbulence model is incorporated into the semi-resolved CFD–DEM approach to address possible turbulence effects. Finally, the developed semi-resolved CFD–DEM is applied to modeling the complex particulate flows in fluidized bed. The obtained numerical results are compared with experimental data and results from other sources. It is demonstrated that the present semi-resolved CFD–DEM is effective in modeling particulate flows with thermal convection. Compared to the conventional unresolved CFD–DEM, this semi-resolved CFD–DEM can provide better predictions and more details on particle temperature distribution, mean temperature, solid/fluid fraction, velocity autocorrelation and vorticity field. [ABSTRACT FROM AUTHOR]

• We extend a third-order weighted vartiational rDG(P 1 P 2) to solve the incompressible flows on unstructured grids. • High-order DoFs are reconstructed by minimizing a weighted interfatial jump integration function using variational method. • This new rDG(P 1 P 2) method is able to achieve the designed optimal third order of accuracy. • The computational costs of this new rDG(P 1 P 2) method are significantly reduced compared to the standard DG(P 2) method. In this paper, a third-order reconstructed discontinuous Galerkin (DG) method based on a weighted variational minimization principle, which is denoted as P 1 P 2 (WVr) method, is presented for solving the incompressible flows on unstructured grids. In this method, the first-order degrees of freedom (DoFs) are obtained directly from the underlying second-order DG method, while the second-order DoFs are reconstructed through the weighted variational reconstruction. Specifically, we first introduce a weighted interfacial jump integration (WIJI) function which represents a measure of the jump between the reconstructed polynomial solutions from two neighboring cells. Then, we build the constitutive relations by minimizing this WIJI function using the variational method. A number of incompressible flow problems in both steady and unsteady forms are presented to assess the performance of the proposed P 1 P 2 (WVr) method. The numerical results demonstrate that the P 1 P 2 (WVr) method is able to achieve the designed optimal third-order accuracy at a significantly reduced computational costs. Moreover, when a suitable value of the weight parameter is chosen to be used, the P 1 P 2 (WVr) method outperforms the reconstructed DG methods based on either least-squares or Green-Gauss reconstruction for the simulations of incompressible flows. [ABSTRACT FROM AUTHOR]

The weakly compressible SPH (WCSPH) method has been widely used for solving hydrodynamic problems, in which the fluid is assumed to be weakly compressible through limiting the density deviation to a small value. Despite its simplicity and robustness in implementation, the WCSPH method is generally hindered by its poor accuracy and spurious oscillations in the pressure field which may lead to numerical instability. In order to dampen the spurious oscillations without introducing excessive dissipation, a Roe-type approximate Riemann solver with a low-dissipation limiter was proposed and applied to the WCSPH method by Zhang et al. (2017). The present paper aims to extend this low-dissipation Riemann solver to the finite particle method (FPM), which can be referred to an enhanced or modified version of the conventional SPH method, for reducing spurious pressure oscillations and meanwhile achieving higher order of accuracy. Numerical results demonstrate that the Riemann solver based FPM is effective in modeling incompressible flows and it produces a more accurate flow field than the conventional WCSPH and Riemann solver based WCSPH methods. [ABSTRACT FROM AUTHOR]

As a typical fluid–structure interaction (FSI) problem, water entry involves violent fluid flows and changing free surfaces, which presents great challenges for numerical modeling. Smoothed Particle Hydrodynamics (SPH) is a Lagrangian particle method that has natural advantages in modeling free surfaces and moving interfaces. However, SPH is computationally expensive due to the search of particle–particle interactions, and it causes great difficulties for performing large-scale simulations of 3D FSI problems. In this work, we present an accelerated SPH framework based on the Graphics Processing Unit (GPU) techniques to study water entry problems. The multi-threading programmed by Compute Unified Device Architecture (CUDA) is applied to enhance the computational performance in terms of efficiency and scale. Compared to the Single-CPU-based strategy, the newly presented GPU-accelerated SPH method is computationally more efficient with a speedup over hundreds times and enables a larger memory available for large-scale simulations of around ten million particles for three-dimensional cases. With the GPU-accelerated SPH method, the 3D water entry of a circular cylinder is investigated with some kinematic and dynamic characteristics explained. The results demonstrate that the rotational characteristic of a 3D cylinder in water entry is related to the dimensionless number γ defined as the ratio of the initial inclination angle to the initial velocity angle. The rotation of a cylinder changes from anticlockwise to clockwise with the increase in γ. A transition value of γ exists between the anticlockwise to clockwise rotation, which focuses on the range from 1.0 to 6.0. Meanwhile, the water entry of a 3D circular cylinder leads to a violent impact on the bottom of the cylinder, which causes a peak value of pressure being a maximum value at the early stage of the water entry. It is also indicated that the selection of the initial inclination angle has a great effect on the maximum pressure. • A GPU-accelerated SPH method for fluid–structure interaction problems is developed. • The GPU-accelerated SPH method can greatly improve the computational ability compared to CPU-based SPH. • The water entry characteristics of a 3D cylinder relate to the ratio of the initial inclination angle to velocity angle. • A cross-region that the trajectory of the centroid always passes through is determined by the initial velocity angle. [ABSTRACT FROM AUTHOR]

Finding analytical and semi-analytical solutions of two-dimensional nonlinear fractional-order problems arising in mathematical physics is a challenging task for research community. In this work, an innovative scheme is proposed based on the shifted Gegenbauer wavelets. For this purpose first, we introduce shifted Gegenbauer polynomials via suitable transformation. Then, we present three-dimensional shifted Gegenbauer wavelets using shifted Gegenbauer polynomials. We illustrate function approximation of three variables, for example, u (x , y , t) through shifted Gegenbauer wavelets. To compute the novel operational matrices of positive integer and non-integer order derivative of shifted Gegenbauer wavelets vector in one, two and three dimensionals piecewise functions are utilized. Moreover, we describe associated theorems to validate our newly proposed scheme mathematically. The proposed algorithm is innovative because of the incorporation of Picard iterative scheme to tackle highly nonlinear problems of fractional-order. The current computational scheme coverts a mathematical model to a system of linear algebraic equations that are easier to solve. To validate the accuracy, credibility, and reliability of the present method, we analyze various fractional-order problems, including Bloch–Torrey, Burgers, Schrödinger, Rayleigh–Stokes and sine-Gordon. We also conduct a detailed comparative study, which demonstrates that the proposed computational scheme is effective to find the analytical and semi-analytical solutions of the aforementioned problems. Moreover, the proposed computational method can be utilized to analyze the solutions of other higher dimensional nonlinear fractional or variable order problems of physical nature. [ABSTRACT FROM AUTHOR]

• A novel coupling approach of ES-FEM-SPH is developed for solving thermal-fluid-structure interaction (TFSI) problems. • The updated Lagrangian ES-FEM is developed for solving the coupled thermal elastic problems. • The SPH method, after integrating with particle shifting technique and kernel gradient correction, is robust and effective in modeling thermal fluid flows. • The ghost particle coupling algorithm is developed for treating fluid structure conjugate heat transfer. Thermal-fluid-structure interaction (TFSI) problems are significant in science and engineering, and usually pose great challenges for numerical simulations due to the coupled effects of thermal convection, fluid flow and structure deformation. In this paper, a novel coupling approach of smoothed finite element method (ES-FEM) with an improved smoothed particle hydrodynamic (SPH) method is developed for TFSI problems. In the coupling approach, the edge based ES-FEM is used to model solid domain and the Lagrangian SPH is used to model fluid flow. In ES-FEM, the temperature and velocity gradient smoothing technique are applied over the edge-based smoothing domain for thermal structure coupling problems. In SPH, some state-of-art algorithms including kernel gradient correction (KGC) and particle shift technique (PST) are integrated to ensure computational accuracy for simulating thermal fluid flows. A ghost particle coupling algorithm is developed to handle fluid-structure interaction and fluid-structure conjugate heat transfer, and the kinematic condition, dynamics conditions and conservation of energy are satisfied. Four numerical examples are tested to demonstrate the effectiveness of the present coupling approach of ES-FEM-SPH for TFSI problems. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• The CFD-DEM method combined with micro-scale reconstruction is used to study proppant transport in hydraulic fracture. • Typical flow behaviors of proppant particles and fracturing fluid in different fracture models are analyzed. • The surface area ratio is utilized to characterize the cross-scale relation between proppant distribution and fracturing parameters. • The parameter effects of fluid, proppant, and fracture on proppant migration in fracture are discussed. A comprehensive investigation of the dynamical characteristics of proppant-laden flow systems in hydraulic fractures is important for the development of unconventional oil and gas resources. In this paper, we combine the micro-scale reconstruction technique and CFD-DEM method to numerically investigate the mobility and distribution rules of proppant-laden fluid in rough hydraulic fractures. To characterize realistic fracture surface morphology, six synthetic fracture models were assembled based on optical scanning data of real shale from three sets of hydraulic fracturing experiments. In order to accurately simulate the fluid-particle two-phase flow in rough fractures, the lift forces and particle rolling effect are considered in the CFD-DEM model. First, the effectiveness of the used CFD-DEM solver was validated by comparing it to the experimental data. We then examined mechanisms for the typical flow behaviors of proppant particles and fracturing fluid in smooth and rough fractures. Subsequently, the surface area ratio of the synthetic fracture model is adopted to characterize the cross-scale relationship between the micro-scale proppant distribution and fracture's geometric features induced by the macroscale fracturing parameters (i.e., confining stress, fluid viscosity, flow rate, and sand ratio). Lastly, the parameter effects of the fracturing fluid, proppant particle, and fracture aperture on the dynamic characteristics of particulate flow in the hydraulic fracture are further discussed. In summary, the presented numerical model and findings can help better understand particle transport and distribution in real rock fractures and bridge the connectivity of the micro-scale particle flow and macroscopic fracturing parameter, which is vital for hydraulic fracturing process optimization. [ABSTRACT FROM AUTHOR]

• Natural thermal convection induces fluid motion. • Particle shape-effects do play an important role in the particle and overall system dynamics. • Thermal heat exchange significantly affects the motion of the two-phase flow. • Multi-grid FEM-FBM is robust and potentially powerful tool for real particulate flow simulations. In particulate flows, particle-particle collisions play a very important role in determining the flow behavior of the fluid-particle two-phase systems. Thus, it is very important in the numerical simulations of particulate flows to treat the particle-particle interactions with a felicitous method. In this paper, a recently developed direct numerical simulation (DNS) technique, the Finite Element Fictitious Boundary Method (FEM-FBM), for thermal convective particulate flows is used for the simulations of dense particulate suspensions of elliptic shaped particles. The momentum and temperature flow fields are coupled with the aid of Boussinesq approximation. The thermal and momentum interactions between solid and fluid phases are handled by using the Fictitious boundary method (FBM). The continuity, momentum, and energy equations are solved on a fixed Eulerian mesh which is independent of flow features by using a multi-grid finite element scheme. A modified collision model is proposed that can handle not only the interactions between the circular particles but also effectively treat the collisions between the elliptic shaped particles. Firstly, we validate the newly developed collision model for isothermal circular particles together with a comparative study of "drafting, kissing and tumbling" (DKT) motion of both elliptic and circular shaped isothermal particles. Then we investigated the DKT motions of the hot and cold elliptic particles with energy exchange and studied the lateral behavior of the particles in numerous settings. Further, we studied the DKT motion of catalyst particles and investigate the particles behavior at different Grashof numbers. Numerical tests are performed to show that the present method is robust and provides an efficient approach for the simulations of particulate flows with a large number of elliptic particles. [ABSTRACT FROM AUTHOR]

Abstract Composites are considered as effective materials in absorbing the energy of blast and impact, and have been often used in complex loading environments. A numerical model is developed to analyze the response and damage of S-2 glass/SC-15 epoxy composite laminate subjected to combined loadings with blast and fragments. A composite progressive failure model is used to investigate the damage and the failure of the material. The proposed numerical model is validated by its comparison with the experimental data obtained from the literature. Three different types of loading combinations: (1) ammunition fragments impact loading, (2) bare blast loading, and (3) the combinations of blast and fragments loading, correspond to the scenarios of the near-field and the far-field explosions. Moreover, the response and the damage evaluation of the composite are analyzed here. It is concluded that the damage modes of the laminate are correlated to the type of the loading. Furthermore, the synergetic effects for the composite laminate subjected to the combined blast loading and the fragments impact are verified and evaluated. By comparing the energy absorption and the damage zone in the laminate, the synergetic effect is attributed to the conjunction of damage and the continuous pressure of the detonation products. [ABSTRACT FROM AUTHOR]

This paper presents a direct numerical simulation (DNS) technique, the Finite Element Fictitious Boundary Method (FEM-FBM) for the simulation of fluid-solid two-phase flows with heat transfer. The heat transfer equation is introduced to study thermal convection in fluid-solid two-phase flows. The Boussinesq approximation is considered for the coupling of momentum and temperature flow fields. Multi-grid finite element solver is used to compute flow equations of mass, momentum, and energy on a fixed Eulerian mesh which is independent of time and the solid particles are allowed to move freely in the whole computational domain. Fictitious boundary method (FBM) is used to treat the particles inside the fluid, FBM takes account of the thermal and momentum interaction between the fluid and the particles. The accuracy and stability of presented method are validated by comparing our test cases results with the results reported in the available literature. Numerical tests are performed to show that this method is potentially powerful and provides an efficient approach to simulate complex thermal convective particulate flows with a large number of particles. [ABSTRACT FROM AUTHOR]

• The semi-resolved CFD-DEM with a multi-smoothing distance scheme is further developed for the polydispersed particle system. • Grain-scale reconstruction by μCT images is employed to quantitatively characterize the heterogeneous porous media. • Particle-scale migration process and distribution characteristics of fine particles in porous media are examined. • The influences of powder properties and anisotropy effects on migration processes and heat transfer are studied. A comprehensive understanding of the migrating phenomena of microscale particles associated with fluid flows and heat exchange in porous media is essential for developing unconventional geo-resources. In this work, we further develop the kernel-based semi-resolved CFD-DEM and combine it with grain-scale reconstruction to numerically investigate particulate flows and associated heat transfer processes in porous media. To characterize wide grain size distributions and heterogeneity of rock skeleton, a 3D spherical-packed model is quantitatively assembled based on CT images of real rock. After a series of validations, it is found that the results from the improved semi-resolved CFD-DEM, including motion, heat transfer, and pressure drop behaviors of particulate systems, match better with experimental observations and analytical solutions than that obtained from the unresolved CFD-DEM. On this basis, the particle-scale migration and distribution characteristics of fine particles are further studied. It is found that the penetration distance, temperature, and energy distributions of particle systems rely on the variation of powder properties (i.e., concentration and size) and the effects of matrix anisotropy. In a higher powder concentration system, more deposited particles at the upper of the packed bed prevent the downward migration of powder particles and lower the quantity of heat exchange between the fine and matrix particles. In addition, this can also lead to a more pronounced jamming phenomenon and reduce the seepage capacity of the packed bed. As the powder diameter increases, the heat transfer capacity of fine particles increases and gradually dominates the temperature of particulate systems. The deposition patterns and temperature variation behaviors of fine particles along the migration direction caused by the anisotropy of the porous medium are also identified. Therefore, the developed computational framework can be a powerful tool to reproduce the dynamics of fine particles in heterogeneous porous materials and reveal the underlying mechanisms. [ABSTRACT FROM AUTHOR]

The underwater explosion (UNDEX) phenomenon involves hydrodynamic behaviors with a wide range of spatial scales, from macroscopic cavitation regions to refined areas with fluid-structure interactions around the shock wavefront. Correct description of the refined shock wavefront is important for determining the shock wave position and pressure peak. In this work, the local discontinuous Galerkin (LDG) method for the two-dimensional wave equation, which allows for the local triangular meshes refinement and merging during the shock wave propagation process, is presented to model the UNDEX shock hydrodynamics. This article is an extension of our previous work, where we discretize the UNDEX total wave formulation in the LDG framework and simulate the UNDEX shock wave and cavitation phenomenon. In order to save computational cost (including CPU time and computational storage) and capture the shock wavefront more accurately, the LDG method is extended to be in combination with the mesh adaption technique. The troubled-cell indicator, depending on the local jump of the pressure, is adopted to identify elements which require to be refined or coarsened. Typical numerical examples are tested to assess the capability of the present h -adaptive LDG method for capturing the UNDEX shock wave. The numerical results clearly demonstrate that the mesh adaption technique enables us to dynamically increase the mesh resolution in close proximity to the flow discontinuities with a large pressure jump. The local increase of the mesh resolution results in a substantial increase in the accuracy of the pressure peak. In terms of the computational efficiency, the h -adaptive LDG method can save nearly half of the calculation time in comparison to the non-adaptive LDG method on uniform meshes, whose mesh resolution is the same as that of the maximum level of refinement of the h -adaptive LDG method. • An h -adaptive LDG method is presented for simulating the UNDEX shock hydrodynamics. • The mesh resolution is adaptive with the evolution of the UNDEX shock wavefront. • The present h -adaptive LDG method can well capture the UNDEX pressure peak at a relative small computational cost. [ABSTRACT FROM AUTHOR]

Existing studies of fluid-structure interaction (FSI) in ocean engineering mainly focus on the interaction between Newtonian fluids and structure. The FSI problems involving non-Newtonian fluids, especially viscoplastic fluids, have rarely been studied while the inherent dynamic behavior is not clear. In this paper, an immersed boundary-lattice Boltzmann method (IB-LBM) is developed for numerical investigations on FSI problems involving viscoplastic fluids. The present IB-LBM is integrated with a hybrid multiple relaxation times (MRT) scheme where different diagonal relaxation matrices are used for modeling Newtonian and non-Newtonian fluids, and are combined in a hybrid manner using a step function to achieve smooth transition for Newtonian to non-Newtonian fluid behavior at the FSI area. Four benchmark problems are used to validate the IB-LBM with hybrid MRT scheme. It is demonstrated that the numerical model can avoid numerical instability when modeling viscoplastic fluid flow and reduce the numerical boundary slip in the IB-LBM. The numerical model is further used to study the viscoplastic fluid flow around a fixed and moving cylinder (or particle). We show that the present IB-LBM with the hybrid MRT scheme is effective in modeling FSI involving viscoplastic fluids while the obtained phenomena are quite different from those with Newtonian fluids. [ABSTRACT FROM AUTHOR]

Heat transfer and flow structures for round jet impingement over rough surfaces have been investigated using the shear stress transport model (SST) with transition model. This model is first evaluated against the experimental data and other numerical results for the smooth surface with Reynolds number Re = 23,000 for the nozzle-plate spacing of 2. Based on the above evaluation, the effects of rough surfaces on the mean velocity, turbulence field, skin friction and heat transfer are investigated with equivalent sand grain roughness heights k s of 50, 100, 250 and 500 μm. Two trends of the effects of roughness on the velocity field are found. First, the mean velocity over rough surfaces becomes steeper than that over the smooth surface in very near the wall. However, for k s ≥ 250 μm, the velocity gradient in the axial direction does not increase with an increase of k s. Second, the decay of the mean velocity is found in the deceleration region, but minimal in the acceleration zone. In addition, it is observed that the increase of roughness height leads to the reduction of the wall shear stress in the stagnation region. On the contrary, downstream, large k s usually contributes to an augmentation of wall shear stress. For heat transfer, the enhancement of heat transfer due to roughness varies from 2.53% to 6.08% compared with the case of smooth surface. However, this enhancement is non-monotonic due to the change of the second peak of heat transfer which is believed to be the key factor. [ABSTRACT FROM AUTHOR]

Numerical simulation of fluid structure interaction (FSI) problems is one of the most challenging topics in computational fluid dynamics. In this paper, coupling edge-based smoothed finite element method (ES-FEM) and smoothed particle hydrodynamics (SPH) method (ES-FEM-SPH) is proposed for solving FSI problems, where the edge-based smoothed finite element method is used to model the movement and deformation of structures, and the smoothed particle hydrodynamics is used to model the fluid flow. In ES-FEM, the gradient smoothing technique is applied over the smoothing domain and it can effectively overcome the "overly-stiff" effect in conventional FEM model. Some correction algorithms including density correction, kernel gradient correction and particle shift technique are integrated into the SPH method to improve computational stability and accuracy. A virtual particle coupling scheme is used to implement the coupling of ES-FEM and SPH with complex geometry interface. As ES-FEM is more accurate than conventional FEM, and it is expected that this ES-FEM-SPH coupling approach should be superior than existing FEM-SPH coupling approaches. A number of test examples with FSI are investigated with the presented ES-FEM-SPH, and compared with results from other approaches including FEM-SPH. From the obtained numerical results, we can conclude that the ES-FEM-SPH coupling approach is effective to simulate FSI problems. • Coupling edge-based smoothed finite element method (ES-FEM) with SPH is proposed for solving FSI problems. • The coupling strategy is based on the automatically generated virtual particles. • The gradient smoothing technique in ES-FEM overcomes the "overly-stiff" effect in conventional FEM. • The SPH method with integrated algorithms is effective and robust in modeling fluid flows. • ES-FEM-SPH is demonstrated to be effective in modeling diversified FSI problems. [ABSTRACT FROM AUTHOR]

• Four integrated SPH models are presented and compared for simulating natural convection. • The most suitable SPH model for natural convection is provided. • Natural convection for R a = 10 9 and Pr = 0.71 is successfully modeled for the first time by using the SPH method. • Mechanisms of the natural convection in a square cavity at different Rayleigh numbers are discussed. This paper conducts the simulation of natural convection in a differentially heated square cavity at high Rayleigh numbers by using the smoothed particle hydrodynamics (SPH) method. Due to the decrease of the accuracy and stability, it is challenging for the SPH method to simulate natural convection at high Rayleigh numbers, and there are few reported SPH literatures of natural convection at R a > 10 6 for air (Pr = 0.71). In this study, four integrated SPH models are presented to simulate the natural convection and their accuracy and stability are assessed. These four SPH models are associated with Kernel Gradient Correction (KGC) to improve approximation accuracy and Particle Shifting Technology (PST) to regularize particle distribution while they are different in treating density diffusion and calculating the pressure term. The numerical results show that SPH model_4 (KGC, PST, δ -SPH and asymmetric pressure approximation) is the most suitable for simulating the closed natural convection problems, especially at high Rayleigh numbers. Good agreements with reference solutions are obtained by SPH model_4 for the natural convection at 10 4 ≤ R a ≤ 10 8. Furthermore, the simulation of natural convection at R a = 10 9 is conducted by SPH model_4. The evolutions of thermal convection are described in detail. It is found that dynamics characteristic reveals that the dominant force is the pressure gradient, rather than the buoyancy force before the quasi-steady state. In addition, the chaotic motion at R a = 10 9 has significant influence to the heat transfer characteristic in the vertical boundary layers. [ABSTRACT FROM AUTHOR]

In order to understand the protective mechanism of helmet against shock wave, a head model under far-field blast is investigated experimentally and numerically. The distribution of overpressure on the surface of the head model are obtained and compared. The numerical simulations are carried out using the Multi-Material Arbitrary Lagrangian Eulerian (MM-ALE) technique with suitable material models for a Kevlar helmet and soft pads. The differences in the distributions of overpressure on the head models with and without the protection of the helmet are analyzed. The interaction of shock waves around the head and the helmet is investigated. Our experimental observations and numerical results indicate that, if protected by a helmet in the case of a shock wave acting from the front, the peaks of overpressure on the head are reduced at the top area, but increased at the rear area. The numerical simulations also show that the enhancement of the overpressure at the rear is mainly due to the collision of the shock wave. The underwash phenomenon also occurs when the shock wave acts from the side or the rear. [ABSTRACT FROM AUTHOR]