An optimization method based on the evolutionary and topology approaches to reduce the mass of composite wind turbine blades

In optimization of transient problems, a robust, stable, and efficient numerical scheme for time integration is of much importance. Recently, the mixed Lag     

Two‐phase thermo‐mechanical and macrosegregation modelling of binary alloys solidification with emphasis on the secondary cooling stage of steel slab continuous casting processes

As an approach towards a better modelling of solidification problems, we introduce a thermo‐mechanical and macrosegregation model that considers a solidifying alloy as a binary mixture made of a liquid and a solid phase. Macroscopic conservation laws for mass, momentum and solute are obtained by spatial averaging of the respective microscopic conservation equations. Assuming local thermal equilibrium, a single equation for the conservation of the mixture energy is then written. A single equation can be obtained for the solute as well by invoking a proper microsegregation rule. The numerical implementation in a two‐dimensional finite element code is then detailed. Lastly, some examples of simulations of academic tests as well as industrial applications for continuous casting of steel slabs are discussed. They particularly enlighten the ability of the formulation to describe the formation of central macrosegregation during the secondary cooling of slab continuous casting processes. Copyright © 2006 John Wiley & Sons, Ltd.     

连铸板坯鼓肚变形与宏观偏析的有限元分析

鼓肚变形及因变形引起的中心线偏析是影响板坯质量的重要因素.法国冶金部和一些企业组织了优化钢铁生产的项目,采用数值方法研究和优化连铸工艺.介绍了巴黎高等矿业学校在连铸过程数值仿真方面的研究成果.     

Computational modelling of shaped metal deposition

Shaped metal deposition (SMD) is a novel process for rapid prototyping that employs tungsten inert gas (TIG) welding controlled by a robot inside an inert gas chamber to build parts by successive layer deposition. This process can be enhanced through modelling and control. Industries are interested in developing systematized models to explain observed phenomena and to predict processing conditions for process planning and optimization. In this work, thermal and mechanical finite element (FE) modelling of SMD is presented. The thermal problem is solved with linear tetrahedral finite FEs that take into account the liquid/solid phase change phenomenon. The mechanical problem is solved with hexahedral elements with tri‐linear interpolation of displacements and constant interpolation of mean stresses (Q1– P0). Special techniques to account for material addition were developed, based on activation/deactivation of FEs. Numerical tests were conducted to determine the heat source model parameters. An experiment using Ti‐6Al‐4V material was developed to validate the formulation. The test consisted of a TIG‐wash procedure (arc passing without wire feeding to preheat the plate) followed by a single welding layer. The results, including temperatures and residual displacements, are compared with those obtained with the finite element method (FEM) code. Finally, a multilayer SMD numerical example is presented. Copyright © 2010 John Wiley & Sons, Ltd.     

An enrichment scheme for solidification problems

A new enriched finite element formulation for solving isothermal phase change problems is presented. We propose a fixed mesh method, where the discontinuity in the temperature gradient is represented by enriching the finite element space through a function whose definition includes a gradient discontinuity. Generally, in these types of formulations, the enrichment location (the location of the solidification front) is determined through a level set auxiliary scheme. In this work, this position is determined implicitly by constraining the temperature at the phase change boundary to be equal to the melting temperature. Several numerical examples are presented to show the application of the method.     

Computational modeling of natural ventilation in low-rise non-rectangular floor-plan buildings

Natural ventilation (NV) is a relevant passive strategy for the design of buildings in seek of energy savings and the improvement of the indoor air quality and the thermal comfort. The main aim of this work is to present a comprehensive NV modeling study of a non-rectangular floor-plan dwelling. Given the arbitrary shape of the building, recourse is made to computational fluid dynamics (CFD) to determine the surface-averaged pressure coefficients (\(\overline {{C_p}} \)). The CFD model was calibrated to match experimental data from an extensive wind tunnel database for low-rise buildings. Then, \(\overline {{C_p}} \) computation via CFD is used to feed the building performance simulation software EnergyPlus, in replacement of the built-in Swami and Chandra parametric model that is only valid for estimating \(\overline {{C_p}} \) in rectangular floor-plan buildings. This computational tool is used to investigate the effect of NV on the thermal performance and the airflow rate in a social housing located in the Argentine Littoral region. Simulation results of the considered building show that NV enables to reduce even more than 65% of the cooling degree-hours. Furthermore, regarding to the \(\overline {{C_p}} \) source (either CFD or Swami and Chandra’s), it is also found that this data has a considerable effect on the airflow rates, but a little effect on the thermal performance.     

Finite-element modelling of heat transfer in shaped metal deposition and experimental validation

Shaped metal deposition (SMD) is a novel technology for building near-net-shaped components by successive layer deposition using a welding machine. The SMD rig consists of a robot with a tungsten inert gas welding torch and manipulator, both of which are housed inside a sealed chamber. A series of walls were made from Ti–6Al–4V alloy by SMD and the heat transfer problem during layer deposition was analysed in all cases. The specimens were built using a wide range of process parameters (number of layers, layer height, wire feed rate, travel speed, heat input, etc.) and wall dimensions. During the fabrication process, the SMD built part is subjected repeatedly to high temperature gradients and high heating and cooling rates, resulting in a unique morphology and microstructures usually not observed in conventional fabrication techniques. A finite-element model for the thermal analysis of this deposition process was constructed. The aims of this study are, firstly, to correlate the predicted temperature field to experimental observations to validate the numerical model of this complex process; and secondly, to explain on the basis of the computed temperature and temperature rate the appearance of characteristic microstructures on the top of the walls, and in the substrate and intermediate region.     

A fast convergent and accurate temperature model for phase‐change heat conduction

This work proposes a temperature‐based finite element model for transient heat conduction involving phase‐change. Like preceding temperature‐based models, it is characterized by the discontinuous spatial integration over the elements affected by the phase‐change. Using linear triangles or tetrahedrals, integration can be performed in a closed analytical way, assuring an exact evaluation of the discrete balance equation. Because of its unconditional stability, an Euler‐backward time‐stepping scheme is implemented. A crucial fact is the computation of the exact tangent matrices for the Newton–Raphson solution of the non‐linear system of discretized equations. Efficiency of the model is tested by means of the results obtained for the Neumann problem and the solidification of a steel ingot. Copyright © 1999 John Wiley & Sons, Ltd.     

Finite element modelling of inverse design problems in large deformations anisotropic hyperelasticity

This paper introduces a finite element model for the inverse design of pieces with large displacements in the elastic range. The problem consists in determining the initial shape of the piece, such that it attains the designed shape under the effect of service loads. The model is particularly focused on the design of parts with a markedly anisotropic behavior, like laminated turbine blades. Although the formulation expresses equilibrium on the distorted configuration, it uses a standard constitutive equations library that is expressed as usual for measures attached to the undistorted configuration. In this way, the modifications to a standard finite elements code are limited to the routines for the computation of the finite element internal forces and tangent matrix. Two examples are given, the first one for validation purposes, while the second is an application which has industrial interest for the design of turbine blades. Copyright © 2007 John Wiley & Sons, Ltd.