Abstract

A finite element model has been developed for the 3D simulation of the sintering of a single track during a selective laser sintering process (SLS). The model takes into account both the thermal and the sintering phenomena involved in the process. Owing to the continuous movement of the laser beam the model takes also into account the transient nature of the problem. This is transformed into a pseudo‐static one through a transformation of the coordinates system of the equations. Nevertheless, this transformation introduces a convective term into the heat equations that produces instabilities in the solution. These instabilities have been solved by using a stream upwind Petrov Galerkin (SUPG) strategy together with a shock capturing scheme. Finally, a fixed point strategy is used for the solution of the analysis. The model has been tested through the solution of some examples.

Abstract

Residual stresses and distortions are two technical obstacles for popularizing the additive manufacturing (AM) technology. The evolution of the stresses in AM components during the thermal cycles of the metal depositing process is not yet clear, and more accurate in situ measurements are necessary to calibrate and validate the numerical tools developed for its simulation. In this work a fully coupled thermo-mechanical analysis to simulate the laser solid forming (LSF) process is carried out. At the same time, an exhaustive experimental campaign is launched to measure the temperature evolution at different locations, as well as the distortions and both the stress and strain fields. The thermal and mechanical responses of single-wall coupons under different process parameters are recorded and compared with the numerical models. Good agreement between the numerical results and the experimental measurements is obtained. Sensitivity analysis demonstrates that the AM process is significantly affected by the laser power and the feeding rate, while poorly influenced by the scanning speed.

Abstract

Abstract

In this paper, we firstly introduce a nodal-integration-based finite element method. The method allows the use of first-order tetrahedral elements without suffering from the volumetric locking problem. The most important advantage of tetrahedral meshes is that they can be automatically generated for complex geometries using existing reliable meshing tools. The method is then applied to 3 types of applications. The first application is a large displacement, large strains elastic-plastic simulation on a notched specimen. The second application is an elastic-plastic bending problem. And the last example concerns the numerical simulation of the thermo-mechanical problem. In all the cases, the solution given by the nodal-integration-based FEM is compared to more classical FEM results.

Abstract

The aviation industry found that a number of engine power-loss events were related to the ice crystal icing, and the research on ice crystal icing had gradually attracted the attention of scholars. In this work, the compressor and ice crystals ingested are regarded as study objects, and the trajectories of particles are calculated based on the Lagrangian approach. Moreover, the two-way coupling method is applied to solve the heat and mass transfer process between ice crystals and the flow field. The variation of particle diameter and temperature under different MVD (Medium Volume Diameter), RH (Relative Humidity) and TWC (Total Water Contents), and the variation of temperature, velocity and pressure of internal flow field are also studied. The result indicates that the MVD, RH and TWC play an important role in the ice crystals motion. Moreover, the temperature and velocity of internal flow field are also greatly affected by the three parameters while the pressure is little affected. In addition, without considering the ice crystal icing, the ice crystals ingested by the compressor would reduce the total temperature at the outlet of compressor, and improve the isentropic efficiency and mass flow rate. 

Abstract

 The Pseudo-Direct Numerical Simulation (P-DNS) method is a numerical approach to solve multiscale fluid dynamics phenomena overcoming the computational burden associated with direct numerical resolution of the governing equations. In P-DNS, both the coarse scale and the fine scale are solved numerically. The most expensive part of the computations, the solutions of the fine scale, are parametrized to be performed offline and store their results in dimensionless databases. This latter allows us to construct synthetic models to emulate the fine scale behavior when coarse scale solutions are computed. In this work, a multiphase representative volume element (RVE) is designed for the specific case of a dispersed flow of heavy particles in air. Making use of high performance computing facilities, a set of numerical experiments for a wide range of volume fractions, particle distribution sizes, and inertial forces introduced as shear loads are carried out. Quantitative results of the statistically stationary turbulent state are obtained. This brings insights into the turbulence modulation phenomenon, i.e. the change of the kinetic energy of the carrier flow due to the presence of the particles. The database of RVE results is stored in an artificial neural network to facilitate its use in general flow solvers via a fast interpolation technique. Global case studies of particulate flows are analyzed, highlighting the differences and similarities found using the fine-scale model developed vis-a-vis a standard turbulence modeling.