L’établissement d’un modèle de comportement passe inévitablement par l’identification des paramètres qui le pilotent. Le présent article s’intéresse à la proposition d’un modèle rhéologique pour représenter le comportement viscoélastique-viscoplastique des thermoplastiques. Le modèle est un montage en série du mécanisme de Kelvin-Voigt et celui de Bingham. Des essais de fluage en flexion trois points sont conduits sur une poutre en polyamide 6. L’identification des paramètres du modèle est réalisée par une analyse inverse basée sur la technique des algorithmes génétiques. Les résultats test-modèle représentés par la courbure et sa vitesse sont confrontés et un bon accord est constaté.
The behavior of thermoplastics depends on several factors, mainly time and temperature. The present work is focused on an analysis of the time sensitivity of the viscoelastic and viscoplastic parameters of a rheological model. The material considered in this study is a polyamide 6. The analogical model is represented by the Kelvin-Voigt viscoelastic mechanism mounted in series with a viscoplastic branch of Bingham. After a mathematical formulation of the equations governing the model, tensile tests at different strain rates are conducted. The model parameters are then identified by inverse analysis. The technique of genetic algorithms has been favored. A nonlinear dependence of these parameters on the rate of strain has been observed. The dependence function has been established by a nonlinear regression technique. The comparison of the experimental results with those obtained by the model reveals a satisfactory agreement, hence the validation of the approach adopted.
The pivots of irrigation or the swiveling banisters of irrigation are metallic mobile devices with an important size intended for automatic irrigation of cultivated wide fields, they are composed by a central tower, mobile tower and a set of spans. In our country, these devices are made by a company having a complete line of production with a good level of integration of local raw materials including its production. However these devices do not really answer in global needs of a local market, indeed, the shape and the size of the produced and proposed model how is only the once receipts with the production unit. This work consists in clearing tools to modify and develop other models of more adapted pivots to reach this goal we proceed at first to checking the optimality of the shape of the current span, then, we propose the possibility of the weight reduction of this span by using the technique of the variation of geometrical form of the element defining the structure while assuring the quality of the product. The obtained results establish effective tools in the development of new pivots of irrigation; this also show the possibility of modification of the current geometrical configuration and gives relative importance of the choice of the geometrical variables and objectifs functions. In conclusion we were able to propose three models how in theory answer our aims.
In real, the vortices created behind the wind turbine and around the blades due to the induction flow created by the difference in pressure in rotation plan and the rotational the blade moves, which summarized in Glauert’s model as the axial and tangential induction factors. In this work, a Matlab code has been established to analyze the induction effect on the performance of wind turbine. This code based on the enhanced blade element momentum theory with considering the recent correction. The results demonstrate that the axial induction effect is the master responsible for increasing the mechanical stress effect that decreases the wind turbine performance at the low wind speed value. In another side the increasing of wind speed accompanied by the increasing of tangential induction effect at tip and root of blades with creating vortices, which put the rotor in the critical case with less efficiency
Previous research on the vertical axis turbines efficiency has used blades with a typical static camber to improve the turbines efficiency. Typically, the static camber increases the drag force, which affects negatively the optimal harvesting of energy. The present study proposes deformable blades that change their shape relative to their angular position. The new blade shape is achieved by deforming the airfoil camber line via a sinusoidal rounded arc. The computed results show that the present type of deformation involves two typical flow control mechanisms. Firstly, a leading edge control that alters the flow angle of attacks and therefore the leading edge vortex (LEV) time of growth. Secondly, this type of deformation comprises a trailing edge control that affects the physical size and strength of the LEV. The lift force can be effectively increased. As a main result, the turbine power coefficient appears to be higher by about 20% for the optimal operating conditions
Fixed speed wind turbines have the advantage of being robust and reliable. They allow a direct connection to the electric. The purpose of the article is to study the aerodynamic behaviour and determine the performance of a fixed speed wind turbine. The work presents an analysis method based on the theory of blade element moments (BEM). The variation of aerodynamic parameters is studied for a wide range of wind speeds. A case study is conducted for the design of a wind turbine adapted to the Adrar site which is located in the Algerian Sahara. The results obtained showed that the wind turbine has maximum efficiency just at the design speed. For speeds higher than the design speed, the efficiency is reduced by the stall effect with decreases in torque due to the fall of the lift force. At wind speeds lower than the design value, the thrust effect increases, which puts the rotor under high mechanical stress and blade rotation decreases with low efficiency.
An active flow control mechanism is proposed to improve the efficiency of the energy extraction for the vertical axis wind turbine. The proposed system consists of a vertical axis wind turbine with flexible blades. The conception is inspired from the vortex control mechanism utilized by the aero-/aqua animals to improve their performance via the flexion of their fins. The viscous non-stationary flow around the turbine is simulated using the ANSYS-FLUENT 15 software. The complex flapping motion is reproduced using a dynamic mesh technique and a user-defined function. The results show that, with this strategy of control, the turbine generates a higher moment coefficient due to the increase in the peaks of lift force caused by a better difference in the pressure between the two sides of the blade due to the flexure motion. The turbine power coefficient can reach 38 % enhancement for the optimal flow control conditions.
The works allows to studying theoretically (numerical method + solver Fluent) the flow around the profile. Our attention will be principally takes on the description of the parallel and homogeneous flow. In the same context and in the case of the potential flow, we will take the perturbed function φ caused by the presence of the profile. The mathematical formulation of the problem gives for different Mach number several forms of differential equations as (linear or non linear). The solution found for each Mach number interval allows a good understanding of the flow behaviors inside the studies field.