Homogenization of degenerate coupled transport processes in porous media with memory terms

In this paper we establish a homogenization result for a doubly nonlinear parabolic system arising from the hygro-thermo-chemical processes in porous media taking into account memory phenomena. We present a meso-scale model of the composite (heterogeneous) material where each component is considered as a porous system and the voids of the skeleton are partially saturated with liquid water. It is shown that the solution of the meso-scale problem is two-scale convergent to that of the upscaled problem as the spatial parameter goes to zero.Comment: 27 pages, 1 figur

Large-scale effects on meso-scale modeling for scalar transport

The transport of scalar quantities passively advected by velocity fields with a small-scale component can be modeled at meso-scale level by means of an effective drift and an effective diffusivity, which can be determined by means of multiple-scale techniques. We show that the presence of a weak large-scale flow induces interesting effects on the meso-scale scalar transport. In particular, it gives rise to non-isotropic and non-homogeneous corrections to the meso-scale drift and diffusivity. We discuss an approximation that allows us to retain the second-order effects caused by the large-scale flow. This provides a rather accurate meso-scale modeling for both asymptotic and pre-asymptotic scalar transport properties. Numerical simulations in model flows are used to illustrate the importance of such large-scale effects.Comment: 19 pages, 8 figure

Afromaison. Project objective, work progress and achievements project management : Core part of the mid-term report

Natural resources are essential for maintaining or improving people's livelihood, especially in Africa. Integrated management of natural resources (INRM) is a way to maintain ecosystems capacity to produce a broad range of goods and services considering African socio-economic conditions and institutional frames. Despite the availability of many tools, expertise, local practices and indigenous knowledge, the concept of INRM has hardly been brought into practice and the building blocks in many cases still need to be integrated. Effective INRM in many cases is not achieved due to a lack of exchange of information and a lack of coordination between many actors involved at different scales. Furthermore, external pressures are affecting the availability of natural resources. Many of the poorest people in the world typically are highly vulnerable to external shocks (e.g. drought, floods, famine, disease outbreaks). AfroMaison is making use of what is available to contribute to a better integration of the main components of natural resource management into a coherent integrated and adaptive management process at meso-scale. We define the meso-scale as that level (sub-national) to which power has shifted after decentralization in many countries in Africa. Due to the relative youth of mesoscale authorities and institutions, their capacity for integrated natural resources management (INRM) needs to be strengthened. From a natural resources point of view, the meso-scale corresponds to a landscape, ecosystems or a river (sub)basin. The challenge of AFROMAISON is to provide a holistic toolbox and operational framework for INRM that can be applied in a variety of environmental and socioeconomic conditions in Africa. At the same time, following a participatory analysis of opportunities and challenges, it provides participatory management options for operational INRM, which are both embedded in local traditions and culture, and are scientifically sound. (Résumé d'auteur

Meso-scale modelling of 3D woven composite T-joints with weave variations

A meso-scale modelling framework is proposed to simulate the 3D woven fibre architectures and the mechanical performance of the composite T-joints, subjected to quasi-static tensile pull-off loading. The proposed method starts with building the realistic reinforcement geometries of the 3D woven T-joints at the mesoscale, of which the modelling strategy is applicable for other types of geometries with weave variations at the T-joint junction. Damage modelling incorporates both interface and constituent material damage, in conjunction with a continuum damage mechanics approach to account for the progressive failure behaviour. With a voxel based cohesive zone model, the proposed method is able to model mode I delamination based on the voxel mesh technique, which has advantages in meshing. Predicted results are in good agreement with experimental data beyond initial failure, in terms of load-displacement responses, failure events, damage initiation and propagation. The significant effect of fibre architecture variations on mechanical behaviour is successfully predicted through this modelling method without any further correlation of input parameters in damage model. This predictive method will facilitate the design and optimisation of 3D woven T-joint preforms