Search

Selective laser melting (SLM) is a promising additive manufacturing (AM) technique that has been attracting more and more attention both in academia and industry. The complex physics inherent in SLM processes, such as fluid flow, heat transfer, and phase change, pose great challenges to the quality control of AM products and a profound understanding of the mechanism of SLM is, therefore, significant. The existing literature mainly focuses on experimental investigations or numerical simulations where the provided results are usually limited and not applicable to general cases. To tackle this problem, we present a dimensionless analysis on SLM in this paper. Firstly, a theoretical analysis through normalization of the energy equation of the SLM process is conducted. Secondly, four key dimensionless numbers are proposed to characterize the thermo-dynamical behaviors of SLM including welding parameter, melting and vaporization efficiency, and track size parameter. Thirdly, a set of commonly-used processing parameters are employed to estimate these dimensionless numbers that provides a qualitative understanding of their physical significances. Finally, the presented dimensionless numbers are employed to analyze the SLM process and to reveal that these dimensionless numbers are effective in describing and predicting the physics of SLM for continuous track forming, porosity evolution, and track size. [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]

• 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]

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]

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]