In this paper, a numerical homogenization technique is used to estimate the effective thermal conductivity of random two-dimensional two-phase heterogeneous materials. The thermal computational leads essentially bring out the effect of the voids/inclusions morphology on the effective physical properties. This is achieved using two different heterogeneous materials: microstructure 1 with non-overlapping spherical pores and microstructure 2 with non overlapping spherical rigid inclusions taking into account five different volume fractions from each case. The notion of the representative volume element is introduced for numerical simulations using periodic boundary conditions and uniform gradient of temperature conditions. The obtained effective material properties on the representative microstructures are compared with different analytical models as: series model, parallel model, effective medium theory and Maxwell models, for different morphologies of rigid inclusions and voids. This paper compares the performance of several classical effective medium approximations. Finally, an analytical expression developing the Maxwell model is proposed to estimate the effective thermal conductivity of heterogeneous materials taking into account the inclusion morphology.

Rotary machines have many rotating structures necessity design-optimization. Their structure motions are controlled at low-frequency by rigidity, at high-frequency by inertia and at resonance level by damping. Using modal model, dynamic design of the structure developed can be predicted, analyzed and improved. Recently, H-Darrieus wind turbine (HDWT) has received considerable attention due to its inherent structural characteristics. This machine intends a promising design of renewable energy conversion system in urban and isolatedareas. Though, the system suffers fromseveral dynamic problems caused by geometry, centrifugal and aerodynamic cyclic loadings. Present paper investigated dynamic design-optimization of a three-bladed (HDWT) based on its natural structural parameters using 3D-CAD-FEA using SolidWorks modeling and simulationsoftware. From simulation results obtained, (i) the minimum static safety factor of the wind turbine materials is equal to 1.4. It is greater than that recommanded by the international standard IEC61400-1, assessing an acceptable value to1.35 when the mass of the system is not obtain by weighting; (ii) the first three natural frequencies of the system are (17.73, 17.99 and 21.07Hz), the resultant mass participates (10.55, 10.44 and 0.04%), the modal damping (9.19, 9.17 and 9.05%), also resonant amplification (5.44, 5.44 and 5.52), magnitude ratios (100, 97.13 and 70.82%)are calculated and mode shapes associated are predicted and analyzed; and (iii) critical operating conditions of wind turbine under forced excitations due to the wind speeds at various regimes are also treated and assessed. The static and dynamic stability and reliability of the system are shown since all quality indicators tested are consistent according to structure dynamics standards made in steel materials.

The main goal of this paper is to predict the elastic modulus of partially intercalated and exfoliated polymer-clay nano-composites using numerical homogenization techniques based on the finite element method. The representative volume element was employed here to capture nano-composites microstructure, where both intercalated exfoliated and clay platelets coexisted together. The effective macroscopic properties of the studied microstructure are obtained with two boundary conditions: periodic boundary conditions and kinematic uniform boundary conditions. The effect of particle volume fractions, aspect ratio, number and distribution of particles and the type of boundary conditions are numerically studied for different configurations. This paper investigate also the performance of several classical analytical models as Mori and Tanaka model, Halpin and Tsai model, generalized self consistent model through their ability to estimate the mechanical properties of nano-composites. A comparison between simulation results of polypropylene clay nano-composites, analytical methods and experimental data has confirmed the validity of the set results.

Sun tracking systems (STS) are one of the main components of large-scale photovoltaic (PV)-projects (PV farms) worldwide. PV farms comprise thousands of STS that are subjected to a number of high variable loads, e.g. the loading due to wind. It is also subjected to mechanical and aerodynamic cyclic stresses that can induce fatigue, thus shortening its lifetime. The main objective of this paper is to perform structural stress and fatigue analyses on the dual axis sun tracking system (azimuth-elevation) under selfweight and critical wind loading of 36 m/s (130km/h). Plain carbon steel is considered as the material structure. The static stress, damage distributions and fatigue life are obtained by means of Finite Element Analysis (FEA). FEA is carried out using the linear static approach. Fatigue analysis is performed using the Stress-Life method. Simulation results show that the stress resistance of the most fragile material is checked with a safety factor higher than 2 and the structure of the STS can withstand a maximum of 11.905 blocks (repeats) after the specified variable amplitude loading event before fatigue will become an issue. These evaluation results indicate that the sun tracking systems satisfy the design requirements of static strength and are safely within its designed fatigue life.