The energy balance components of a greenhouse as well as the greenhouse design may strongly impact the greenhouse energy. Few studies were devoted to the description of the energy balance components of a greenhouse located in the semi arid region of the southern Mediterranean basin, and no attention was paid to the prediction of the inside air temperature. In this study, experiments were undertaken to investigate the response of a greenhouse to the outside climate conditions considering a naturally ventilated Venlo glasshouse with a tomato crop. The measurements show that the difference between inside and outside air temperature is strongly linked to the incoming solar radiation as well as to the wind speed. From these results a simplified model was established to predict the greenhouse air temperature, knowing the greenhouse characteristics and the outside climate variables. The model is based on the energy balance of the greenhouse. Using a parameter identification technique, the model was calibrated against the experimental results. A sensivity analysis was conducted to assess the impact of several physical parameters such as solar radiation, wind speed and cover transmission on the evolution of the inside air temperature. This model appears to be suitable for predicting the greenhouse air temperature satisfactorily.

Prediction of effective properties for multiphase composite is very important not only to analysis and optimization of material performance, but also to new material designs. In this paper, the effective elastic property of some complex particulate composites is analyzed and compared with numerical results, demonstrating the validity of the proposed approach. We propose the equivalent morphology concept for the numerical homogenization of random composites. In this study, this concept is extended for complex material. A home script based on Python codes is made to automate the generating of Representative volume element with various volume fraction.

A high emergence of wind energy into the electricity market needs a parallel efficient advance of wind power forecasting models. Determining optimal specific speed and drive-train ratio is crucial to describe, comprehend and optimize the coupling design between a wind turbine-rotor and an electric generator (EG) to capture maximum output power from the wind. The selection of the specific design speed to drive a generator is limited. It varies from (1-4) for vertical axis wind turbines and (6-8) for horizontal axis wind turbines. Typically, the solution is an iterative procedure, for selecting the adequate multiplier ratio giving the output power curve. The latter must be relatively appreciated to inlet and nominal rated wind speeds. However, instead of this tedious and costly method, in the present paper we are developing a novel heuristic coupling approach, which is economical, easy to describe and applicable for all types of variable speed wind turbines (VSWTs). The principle method is based on the fact that the mechanical power needed of the wind turbine (WT) to drive the EG must be permanently closer to the maximum mechanical power generated by the (WT).

A numerical homogenization technique and morphological analysis based on the finite element method are used to compute mechanical properties of porous materials. This is achieved by considering two–dimensional matrix containing random distribution of identical non–overlapping circular or elliptical voids. Several microstructure configurations are obtained by varying the voids morphology and the porosity of the matrix. The notion of the representative volume element is used for numerical simulations in order to estimate the morphology effects of the voids on the effective ultimate tensile strength of the called Lotus–Type Porous Metals. A confrontation of the obtained numerical results of the representative microstructures for different morphologies of voids and different porosities to an analytical model and experimental data is performed. Finally, a formula improving the Boccaccini model is proposed to estimate effective tensile strength of porous metals taking into account the voids morphology.

This paper presents an efficient method to automatically generate and mesh random non–periodic three dimensional (3D) microstructures for three classes of complex heterogeneous media having a wide range of important engineering applications, porous media, composites with interfacial debonding and composites with high density particles. The resulting 3D microstructure is intentionally constructed to be easily and efficiently implemented in standard finite element computational codes. Several examples of 3D representative volume elements are shown. The performance of the proposal in finite element analysis is demonstrated in numerical implementation to predict the effective non–linear elastic–plastic response of two–phase particulate composites reinforced with spherical particles. The main result achieved is the estimation of the effective plastic tangent modulus by a simple linear regression equation for different volume fractions.

The greenhouse design as well as the cover material properties in particular may strongly impact the greenhouse energy. To study the effect of these parameters, three typical unheated greenhouses equipped with rows of canopy were considered. Experiments were launched to establish the boundary conditions and validate the model. Two parametric studies were carried out: for the nocturnal period when the energy performance of each type of greenhouse was investigated, and for the diurnal period, when the sun path was simulated taking into account the type of the cover, its spectral optical and thermal properties. Results indicate that for the nocturnal period, the ambient air temperature in the tunnel and vertical wall greenhouse was relatively homogenous and warmer compared with the temperature distribution in the Venlo greenhouse. The plastic greenhouse, especially the tunnel one had better performances concerning the homogenization of the climate and the thermal energy storage. Concerning the diurnal period, and for both plastic greenhouses equipped with fully opened side vents, the air located between the rows of canopy and ground surfaces remained very slow, not exceeding 0.2 ms-1 ; for the Venlo glasshouse, the recirculation loop situated above the crop improved the air mixing and induced a good homogenization. Results indicate that the cover material with highest absorptivity, deteriorated the natural ventilation, increasing the air temperature by convection, and reduced the available Photosynthetically Active Radiation.

The present paper concerns a computational study of a three-dimensional (3D) unit cells with identical spherical voids in a von Mises matrix. The objective is to estimate the effective plastic flow surface of 3D microstructures. The work originality is to deal with identical spherical overlapping voids, covering a wide range of stress triaxiality ratios. The effective plastic flow surface is computed for nine distinct loadings on four distinct microstructures. The result indicates that the classical Gurson–Tvergaard–Needleman (GTN) model obtained using the Fritzen et al.parameters, matches with our numerical simulations.

A successful osseointegration involves the simultaneous optimization of the primary stability of the implant and the minimization of interfacial stresses bone - implant. In this context, the modeling of these stresses reports a great interest for researchers in last decades.The aim of this work is to study the effects of geometric parameters of a new model of titanium dental implant on the evolution of interfacial stresses bone /implant. For this, a dental implant of the second premolar in the lower jaw was considered, with different diameters, thread pitches and different thread forms. The profile of the interfacial stresses was presented for each case study, the results show a great similarity in the areas concerned, cortical bone, threaded region and cancellous bone, with the results obtained in the literature for other types of geometries.

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.

Greenhouses play an important role in the field of agriculture, allowing the grower to have more control on the environmental factors that govern the behaviour of crops. The interactions of the environmental factors on the inside climate of a greenhouse are complex and involve a set of physical mechanisms that constitute challenges to modellers. To better assess the greenhouse climatic behaviour, a CFD modelling approach was developed and combined with field surveys considering a Venlo, closed greenhouse, under semi arid conditions. Measurements were undertaken at different heights along a vertical cross-section at the centre of the greenhouse. The components of the greenhouse were then integrated inside a CFD distributed climate model. The boundary conditions were inferred from the outside climatic conditions, taking account both of radiative and convective transfers through the walls. Simulations were conducted under pseudo-steady state conditions (i.e., updating the boundary conditions at each time step) all day long, and several scenarios (clear or cloudy day) were simulated to analyse to what extent the inside climate of the green¬house responds to the outside climate conditions.