Alain Bastide

Bayesian and Sensitivity Analysis Approaches to Modeling the Direct Solar Irradiance

In this paper, emphasis is put on the design of a neural network (NN) to model the direct solar irradiance. Since, unfortunately, a neural network is not a statistician -in-a-box, building a NN for a particular problem is a nontrivial task. As a consequence, we argue that in order to properly model the direct solar irradiance, a systematic methodology must be employed. For this purpose, we propose a two-step approach to building the NN model. The first step deals with a probabilistic interpretation of the NN learning by using Bayesian techniques. The Bayesian approach to modeling offers significant advantages over the classical NN learning process. Among others, one can cite (i) automatic complexity control of the NN using all the available data and (ii) selection of the most important input variables. The second step consists of using a new sensitivity analysis-based pruning method in order to infer the optimal NN structure. We show that the combination of the two approaches makes the practical implementation of the Bayesian techniques more reliable.

Natural ventilation - A new method based on the Walton model applied to cross-ventilated buildings having two large external openings

Abstract In order to provide comfort in a low energy consumption building, it is preferable to use natural ventilation rather than HVAC systems. To achieve this, engineers need tools that predict the heat and mass transfer between the buildings interior and exterior. This paper presents a method implemented in some building software, and the results are compared to CFD. The results show that the knowledge model is not sufficiently well described to identify all the physical phenomena and the relationships between them. A model was developed which introduces a new building-dependent coefficient allowing the use of Waltons model, as extended by Roldan to large external openings, and which better represents the turbulent phenomena near large external openings. The formulation of the mass flow rates was inversed to identify modelling problems. It appears that the discharge coefficient is not the only or best parameter to obtain an indoor static pressure compatible with CFD results, or to calculate more realistic mass flow rates.

Aerodynamic and mechanical system modeling of a vertical axis wind turbine (VAWT)

The Savonious rotor is a slow running vertical axis wind turbine (VAWT) which gets stabilized after a certain period of functioning. This work aims to assess the results of an aerodynamic study concerning a Savonious rotor. The computational fluid dynamics (CFD) is a technique used to solve the airflow around the wind turbine rotor. In this paper, the turbulence models standard k-ε and shear stress transport (SST) k-ω are the turbulences models. A three-dimensional study of the problem has been conducted. Firstly, the moment of static forces acting on the rotor blades have been compared to with experimental results. Secondly, the integration of the equation of motion of the Savonious rotor with one degree of freedom (1-DOF) rigid body dynamics model. Implicit schemes for unsteady Euler equations have been used to perform dynamic simulation.

Impact of external surroundings on natural convection in a vertical channel asymmetrically heated

This paper reports a numerical study of natural convection problem between vertical plates with asymmetric heating. Influence of perturbation conditions outside of the channel on flow structure and on the heat transfer rate are investigated. The effect of temperature consists of considering a gradient of temperature between the bottom and top of the channel in order to obtain a thermal stratification. The effect of surface radiation on the laminar air flow with a thermal stratification is investigated by considering temperature of grey bodies. Results show that these weak perturbations outside the channel are a real influence on flow and that the influence of thermal stratification is more important than surface radiation. Numerical simulations have been carried out at modified Rayleigh number Ra=5.10 (laminar regime) and with Prandtl number Pr=0.71.