The integration of renewable energy sources into modern power systems necessitates efficient and robust control strategies to address challenges such as power quality,stability,and dynamic environmental variations.Thi...The integration of renewable energy sources into modern power systems necessitates efficient and robust control strategies to address challenges such as power quality,stability,and dynamic environmental variations.This paper presents a novel sparrow search algorithm(SSA)-tuned proportional-integral(PI)controller for grid-connected photovoltaic(PV)systems,designed to optimize dynamic perfor-mance,energy extraction,and power quality.Key contributions include the development of a systematic SSA-based optimization frame-work for real-time PI parameter tuning,ensuring precise voltage and current regulation,improved maximum power point tracking(MPPT)efficiency,and minimized total harmonic distortion(THD).The proposed approach is evaluated against conventional PSO-based and P&O controllers through comprehensive simulations,demonstrating its superior performance across key metrics:a 39.47%faster response time compared to PSO,a 12.06%increase in peak active power relative to P&O,and a 52.38%reduction in THD,ensuring compliance with IEEE grid standards.Moreover,the SSA-tuned PI controller exhibits enhanced adaptability to dynamic irradiancefluc-tuations,rapid response time,and robust grid integration under varying conditions,making it highly suitable for real-time smart grid applications.This work establishes the SSA-tuned PI controller as a reliable and efficient solution for improving PV system performance in grid-connected scenarios,while also setting the foundation for future research into multi-objective optimization,experimental valida-tion,and hybrid renewable energy systems.展开更多
The forest industry operates in a dynamic and global market where change and competition are the rule rather than the exception. The color of wood is one of the most attractive features for the modem wood industry. Ev...The forest industry operates in a dynamic and global market where change and competition are the rule rather than the exception. The color of wood is one of the most attractive features for the modem wood industry. Even when wood is chosen for its structural qualities, attractive and decorative colors are usually an important factor. In many applications, particularly in furniture, decorative products, decorative veneers and flooring, accurate matching of the color of different samples is required. Wood attributes and properties are important because they have a direct bearing on market opportunities and consumer acceptance for many types of manufactured wood products. The aim of this review is to identify causes of wood discoloration and advances in drying technology to overcome this problem. Wood discoloration is a complex phenomenon, mainly affected by heat, light, physiological and biochemical reactions, as well as from attack by microorganisms.展开更多
A new method was denonstrated to determine stress in a single crystal for multicrystal material and this new method could be specially applied for any symmetric crystalline systems. The strain tensor e was determined ...A new method was denonstrated to determine stress in a single crystal for multicrystal material and this new method could be specially applied for any symmetric crystalline systems. The strain tensor e was determined by the change of the metric tensor G before the initial state and after the deformed state in the crystal reference system. Then stress tensor at grain scale was calculated by the HOOK's law. The stress evaluations were carried out in coarse grains of a thin galvanized coating on a steel substrate during tensile loading. This makes it possible to link the microstructure evolution to the elastic heterogeneity at grain scale or between the grains.展开更多
In the context of industrial competitiveness, taking into account the process design throughout the product life cycle is inevitable, from the expression of the need to recycle, the capitalization and knowledge manage...In the context of industrial competitiveness, taking into account the process design throughout the product life cycle is inevitable, from the expression of the need to recycle, the capitalization and knowledge management increasingly a target much sought after companies because of increased knowledge. Indeed, during the approval phase and use studies and scientific researches make have generated knowledge especially that concerning the reliability of system components. In this context, the capitalization and reuse of knowledge are necessary and have a particular interest in design and particularly in the preliminary design phase. Studies are already completed suggest a design process ranging from the need to solve the problem. At each phase of the process, structural characteristics are defined by the designer through the available knowledge already capitalized to make choice of component and their arrangement. This article proposes integrating the analysis of system reliability in this process. The objective is the use of knowledge in the vision safety and hazards of operating through the study of reliability and decision making for the selection of solution.展开更多
The decrease of wind velocity （wake losses） in downstream area of wind turbine is generally quantified using wake models. The overall estimated power of wind farm varies according to reliability of wake model used, ...The decrease of wind velocity （wake losses） in downstream area of wind turbine is generally quantified using wake models. The overall estimated power of wind farm varies according to reliability of wake model used, however it＇s unclear which model is most appropriate and able to give a high performance in predicting wind velocity deficit. In this subject, a qualification of three analytical wake models （Jensen, lshihara and Frandsen） based on three principal criteria is presented in this paper： （i） the parsimony which characterizes the inverse of model complexity, （ii） the accuracy of estimation in which wake model is compared with the experimental data and （iii） imprecision that is related to assumptions and uncertainty on the value of variables considered in each model. This qualitative analysis shows the inability of wake models to predict wind velocity deficit due to the big uncertainty of variables considered and it sensitivity to wind farm characteristic.展开更多
The aim of this work is to study and quantify the air mass flow exchanged between inside and outside of the greenhouse, in order to determine the ventilation openings layout and the design effect on greenhouse airflow...The aim of this work is to study and quantify the air mass flow exchanged between inside and outside of the greenhouse, in order to determine the ventilation openings layout and the design effect on greenhouse airflow and microclimate distribution. The study was conducted over a 945 m2 multi-chapels arched greenhouse with a polyethylene cover and has thirteen crop rows oriented from north to south;the greenhouse was equipped with side wall and roof vents openings. A simulation was performed using different arrangements and configurations of ventilation openings with the same wind direction. Numerical simulation has been adopted in three dimensions (CFD), using the Fluent computer code which relies on the resolution of the Navier-Stokes equations. These equations were solved in the presence of the turbulence model (k - ε) and the Boussinesq model equation adopted to incorporate buoyancy forces. The effects of solar and atmospheric radiation were included by solving the radiative transfer equation (RTE), using Discrete Ordinate (DO) model. The effects of the roof openings, the presence of anti-insect screens and crops orientation were investigated and quantified. In a 3-span greenhouse with an anti-aphid in-sect screen in the vent openings, combining roof and sidewall vents gave a ventilation rate per unit opening area that was 1.4 times more than with only side vents. In the latter case, the difference of temperature between the inside and the outside of the greenhouse was greater than 3°C. Numerical simulations with an anti-insect screen having a porosity of 56% showed that the air exchange rate with combined ventilation was reduced by 48%. Finally, the paper focused on the effect of vent arrangement on the efficiency of the ventilation and the distribution of the microclimate inside the greenhouse. Results showed that computed ventilation rates varied from 53.43 to 70.95 kg/s, whereas temperature differences varied from 7.15°C to 10.14°C. This study also showed that other characteristics such as climate heterogeneity must be investigated in order to define the best ventilation configuration.展开更多
This study aims to examine the effect of replacing vanadium by niobium and iron on the tribological behavior of hot-isostatic-pressed titanium alloy （Ti-6Al-4V） biomaterial, using a ball-on-disk-type oscillating tri...This study aims to examine the effect of replacing vanadium by niobium and iron on the tribological behavior of hot-isostatic-pressed titanium alloy （Ti-6Al-4V） biomaterial, using a ball-on-disk-type oscillating tribometer, under wet conditions using physiological solution in accordance with the ISO7148 standards. The tests were carried out under a normal load of 6 N, with an AISI 52100 grade steel ball as a counter face. The morphological changes and structural evolution of the nanoparticle powders using different milling times （2, 6, 12 and 18 h） were studied. The morphological characterization indicated that the particle and crystallite size continuously decrease with increasing milling time to reach the lowest value of 4 nm at 18-h milling. The friction coefficient and wear rate were lower in the samples milled at 18 h （0.226, 0.297 and 0.423; and 0.66 × 10-2, 0.87 × 10-2 and 1.51 × 10-2 μm3 N-1 i, tm-1） for Ti-6Al-4Fe, Ti-6A1-7Nb and Ti-6Al-4V, respectively. This improvement in friction and wear resistance is attributed to the grain refinement at 18-h milling. The Ti-6Al-4Fe samples showed good tribological performance for all milling times.展开更多
With their advantages, continuously variable transmissions have gained more popularity in the last decade by their use in mechanical transmission systems. The present paper aims to analysis the efficiency of the trans...With their advantages, continuously variable transmissions have gained more popularity in the last decade by their use in mechanical transmission systems. The present paper aims to analysis the efficiency of the transmission based on the mechanical efficiency of the planetary gear train integrated in such transmission. In this analysis, we consider the mechanical efficiency of the transmission has been determined considering how the efficiency of the CVT members changes as a function of the operating conditions. The efficiency of the planetary gear train as a function of the configuration, speeds in his three input/output shafts, and also with respect to the power flow type. Results are compared with those obtained from other methods performance evaluation of the transmission, available in the literature.展开更多
One of the difficulties encountered in the study of dusty plasmas is related to the knowledge of the size of the dust particles present. A variety of sources, physical and chemical mechanisms of formation, causes a wi...One of the difficulties encountered in the study of dusty plasmas is related to the knowledge of the size of the dust particles present. A variety of sources, physical and chemical mechanisms of formation, causes a wide variety of sizes and morphologies of dust. The diameter of a dust will not be unique but spread over several orders of magnitude. Its distribution in number, surface, mass or volume is called distribution. It is important to know this distribution in particle size because it strongly impacts the physical and radiative processes. To have a dust distribution in situ is very difficult;the reverse method can identify the particle populations from light extinction measures. In this study, we present an inversion procedure with a Tikhonov regularization dedicated to the determination of volume size distribution (V-PSD) from extinction measurements corresponding to the different wavelengths obtained by the Extinction Spectrometry technique.展开更多
Cooling by evaporation through transpiring porous walls is expanding in various industrial applications such as air conditioning. It is also used to cool water in a clay jug. This process deserves to be studied, under...Cooling by evaporation through transpiring porous walls is expanding in various industrial applications such as air conditioning. It is also used to cool water in a clay jug. This process deserves to be studied, understood and valued. This paper deals with the transpiration phenomenon through a saturated porous plate coupled with heat and mass transfer by natural convection. Conservation Equations (mass, momentum, energy and concentration), associated with adequate boundary conditions, have been numerically solved using an implicit finite difference iterative method. The numerical model has been validated by experimental measurements from holographic interferometry. The used method to obtain temperature and concentration profiles was explained. They are evaluated from the refractive index of moisture air in the boundary layer. The main numerical results presented are: Nusselt and Sherwood numbers, temperature, humidity, and velocity profiles within the boundary layer as well as the different heat fluxes exchanged between the plate and the surrounding environment. Besides, the present model allows showing the important effect of the equivalent thermal conductivity and the surface emissivity on temperature and heats flux.展开更多
In this paper,we theoretically investigate the total optical coefficient(TOAC)considering 1S-2P and 2S-2P conduction subband transitions in a single parabolic quantum well(SPQW)with an on-center hydrogen-like impurity...In this paper,we theoretically investigate the total optical coefficient(TOAC)considering 1S-2P and 2S-2P conduction subband transitions in a single parabolic quantum well(SPQW)with an on-center hydrogen-like impurity.Within the framework of the effective-mass approximation,the Schrödinger equation is solved numerically to obtain the eigenvalues and their corresponding eigenvectors using the finite difference method.The calculations are performed for finite confinement potential height,taking into account the dielectric and effective mass mismatches between GaN and InGaN materials under the considered electric field and temperature effects.The temperature dependence of the effective mass,dielectric constant and band gap energy are obtained accordingly.On the one hand,the results show that a significant shift is produced with the variation of both the temperature and the intensity of the electric field.On the other hand,the absorption spectrum is shifted to lower energies with increasing both electric field strength and temperature.Moreover,its amplitude is enhanced with an increase in the intensity of the electric field,and show a slight drop with increasing temperature for the two optical transitions considered.The results show that such parameters can be used to adjust the optical properties of single parabolic Quantum Well for solar cell applications.展开更多
To evaluate the residual stress in TiAl based alloys by X ray diffraction, X ray elastic constants (REC) of a γ TiAl alloy were determined. From these results, the stress state of a given phase in a duplex TiAl based...To evaluate the residual stress in TiAl based alloys by X ray diffraction, X ray elastic constants (REC) of a γ TiAl alloy were determined. From these results, the stress state of a given phase in a duplex TiAl based alloy under a uniaxial tensile loading has been characterized by X ray diffraction. The results show that the X ray elastic constants and the microscopic stresses of the given phase are different from the apparent elastic constants and the macroscopic stresses of the alloy. The reason of the different distribution of the alloy was also discussed. [展开更多
This paper reports that an atomic scale study of [^-110] symmetrical tilt grain boundary （STGB） has been made with modified analytical embedded atom method （MAEAM） for 44 planes in three noble metals Au, Ag and Cu...This paper reports that an atomic scale study of [^-110] symmetrical tilt grain boundary （STGB） has been made with modified analytical embedded atom method （MAEAM） for 44 planes in three noble metals Au, Ag and Cu. For each metal, the energies of two crystals ideally joined together are unrealistically hlgh due to very short distance between atoms near the grain boundary （GB） plane. A relative slide between grains in the GB plane results in a significaut decrease in GB energy and a minimum value is obtained at specific translation distance. The minimum energy of Cu is much higher than that of Ag and Au, while the minimum energy of Ag is slightly higher than that of Au. For all the three metals, the three lowest energies correspond to identical （111）, （113） and （331） boundary successively for two translations considered; from minimization of GB energy, these boundaries should be preferable in [^-110] STGB for noble metals. This is consistent with the experimental results. In addition, the minimum energy increases with increasing reciprocal planar coincidence density ∑, but decreases with increasing relative interplanar distance d/a.展开更多
The characteristic architecture in the oases of south-eastern Morocco is that of raw earth construction.This is done through two techniques:rammed earth and adobe.This work is carried out with the aim of preserving th...The characteristic architecture in the oases of south-eastern Morocco is that of raw earth construction.This is done through two techniques:rammed earth and adobe.This work is carried out with the aim of preserving this ancestral know-how by studying a construction dating back two centuries.The first step is to characterize a soil extracted from the remains of an old building,the grain size and plasticity of the soil showed that it was not very clayey and moderately plastic and that it was suitable for earth construction.Secondly,the study focuses on the mechanical resistance of blocks extracted from the remains studied,the result obtained satisfies all the standards.In order to characterize the durability of the adobe,we made samples of the earthen bricks with a similar soil and the study showed good durability of the adobe construction,the raw earth is a material that can stand in time.And finally,the reusability of the earth material from old buildings has been studied,the results have shown that raw earth is a perfectly reusable material,which makes it the ideal ecological material.展开更多
The proposedwork focuses on the in-depth study of convective heat transfer in the unconfined air gap of a discoidal rotor-stator system.The rotary cooling mechanism is achieved by the injection of two air jets,while t...The proposedwork focuses on the in-depth study of convective heat transfer in the unconfined air gap of a discoidal rotor-stator system.The rotary cooling mechanism is achieved by the injection of two air jets,while the cavity geometry is characterized by a dimensionless parameter G.The numerical analysis primarily concentrated on the effect of flow velocity and rotation on the heat exchange process.More precisely,the range of analysis extends from the rotational Reynolds number Re_(ω)=2.35×10^(5)to Re_(ω)=5.04×10^(5),while varying the Reynolds value of the jet in a range from 16×10^(3)to 55.46×10^(3).To carry out this analysis,a numerical simulation was conducted with Ansys-Fluent software,using the RSM turbulence model.The results of the study significantly reveal the impact of rotation on heat exchange transfer within the cavity,identifying two distinct zones of fluid recirculation.These zones exhibit remarkable heat transfer characteristics,contributing to a better understanding of the complexmechanisms governing heat transfer in this particular technological context.Additionally,the analysis of radial mean velocity distributions,as well as local and mean Nusselt numbers,provides further insight into the heat transfer performance of this unique configuration.展开更多
Asteroid research is of global security interest, we are more afraid about any impact of these asteroids on Earth. We seek through this work to provide a study on the effect of the asteroid’s shape on the gravity asp...Asteroid research is of global security interest, we are more afraid about any impact of these asteroids on Earth. We seek through this work to provide a study on the effect of the asteroid’s shape on the gravity aspect. Knowledge of the potential is crucial to bodies approaching the asteroid. There is a range of asteroid shapes to consider. Some well-known asteroids such Ceres, Vesta, Iris and Oumuamua are considered in this study. After determining the moment of inertia of the asteroids depending on their materials, the gravity fields and the potential gravity of the asteroids are established when varying their shapes. A representation of the gravity field is given in three dimensional coordinate systems. Also, the behavior of the potential gravity is drawing in the function of the object’s location. The second part is dealing with the interpretation of all the obtained results in order to deduce some rules and features which would be useful for the identification of the asteroids. Thus, by the best knowledge of the effect of the asteroid’s shape, we would be more informed in the survey of the hazardous near earth objects.展开更多
<span style="font-family:Verdana;">Understanding the environment of olive tree cuttings is a key factor in improving these plants’ rooting rate and survival. This study aims to develop </span>&l...<span style="font-family:Verdana;">Understanding the environment of olive tree cuttings is a key factor in improving these plants’ rooting rate and survival. This study aims to develop </span><span style="font-family:Verdana;"> a </span><span style="font-family:Verdana;">three-dimensional (3-D) Computational Fluid Dynamics (CFD) model for</span><span style="font-family:Verdana;"> numerically assessing air temperature and relative humidity in an olive cuttings </span><span style="font-family:Verdana;">greenhouse under Mediterranean climatic conditions. The results are deduced from a steady-state simulation performed with recorded boundary</span><span style="font-family:Verdana;"> conditions at 10:00 am, 12:00 pm, 02:00 pm, 04:00 pm, and 06:00 pm at different obser</span><span style="font-family:Verdana;">vation points. The calculations were validated using experimental data. The </span><span style="font-family:Verdana;">simulation errors of the air temperature were -0.8°C to 4.55°C, </span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">and errors of</span></span></span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;"> the leaf </span><span style="font-family:Verdana;">temperature were 0.07°C to 2.42°C, for the air relative humidity w</span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">as</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> <span style="font-family:Verdana;white-space:normal;">-</span>33.84% to <span style="font-family:Verdana;white-space:normal;">-</span>1.64%</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">,</span></span></span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;"> and <span style="font-family:Verdana;white-space:normal;">-</span>10.1% to <span style="font-family:Verdana;white-space:normal;">-</span>13.54% for the relative humidity of the leaf air. Contour maps were obtained from the 3-D CFD simulations to evaluate the distribution of humidity and air temperature inside the greenhouse </span><span style="font-family:Verdana;">and the vicinity of the plant canopy. This study suggests that the developed</span><span style="font-family:Verdana;"> 3-D CFD model can be a helpful tool to understand and optimize</span><span style="font-family:Verdana;"> greenhouse operation for better crop quality.</span></span></span></span>展开更多
Glasses of the compositions 20Li2O-(50 - x)Li2WO4-xFe2O3-30P2O5 where (x = 0, 1, 5, 8, 10, 15 mol%) were elaborated by the melt-quenching route. Synthesized glasses are characterized using X-ray diffraction (XRD), Fou...Glasses of the compositions 20Li2O-(50 - x)Li2WO4-xFe2O3-30P2O5 where (x = 0, 1, 5, 8, 10, 15 mol%) were elaborated by the melt-quenching route. Synthesized glasses are characterized using X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), differential scanning calorimetric?(DSC), and density determination. The XRD patterns confirmed the?amorphous nature of samples, and IR spectra showed the structural groups and highlight the depolymerization of phosphate network with the introduction of iron oxide. It is found that the structural unit Q2 converts to Q1 and Q0 as Fe2O3 replaces Li2WO4. Chemical durability tests on the glasses have shown that the compositions containing pyrophosphate (Q1) and orthophosphate (Q0) units are more water-resist. The electrical conductivity measurements were performed by complex impedance spectroscopy in the frequency range of 20 - 106 Hz at various temperatures from ambient to 400°C. It is found that the conductivity is activated thermally and follows an Arrhenius law. The obtained electrical data were analyzed by the modulus formalism and dielectric formalism. The determined asymmetric nature of? spectra suggested that the relaxation behavior is non-Debye and characterized by the stretched exponent parameter展开更多
文摘The integration of renewable energy sources into modern power systems necessitates efficient and robust control strategies to address challenges such as power quality,stability,and dynamic environmental variations.This paper presents a novel sparrow search algorithm(SSA)-tuned proportional-integral(PI)controller for grid-connected photovoltaic(PV)systems,designed to optimize dynamic perfor-mance,energy extraction,and power quality.Key contributions include the development of a systematic SSA-based optimization frame-work for real-time PI parameter tuning,ensuring precise voltage and current regulation,improved maximum power point tracking(MPPT)efficiency,and minimized total harmonic distortion(THD).The proposed approach is evaluated against conventional PSO-based and P&O controllers through comprehensive simulations,demonstrating its superior performance across key metrics:a 39.47%faster response time compared to PSO,a 12.06%increase in peak active power relative to P&O,and a 52.38%reduction in THD,ensuring compliance with IEEE grid standards.Moreover,the SSA-tuned PI controller exhibits enhanced adaptability to dynamic irradiancefluc-tuations,rapid response time,and robust grid integration under varying conditions,making it highly suitable for real-time smart grid applications.This work establishes the SSA-tuned PI controller as a reliable and efficient solution for improving PV system performance in grid-connected scenarios,while also setting the foundation for future research into multi-objective optimization,experimental valida-tion,and hybrid renewable energy systems.
文摘The forest industry operates in a dynamic and global market where change and competition are the rule rather than the exception. The color of wood is one of the most attractive features for the modem wood industry. Even when wood is chosen for its structural qualities, attractive and decorative colors are usually an important factor. In many applications, particularly in furniture, decorative products, decorative veneers and flooring, accurate matching of the color of different samples is required. Wood attributes and properties are important because they have a direct bearing on market opportunities and consumer acceptance for many types of manufactured wood products. The aim of this review is to identify causes of wood discoloration and advances in drying technology to overcome this problem. Wood discoloration is a complex phenomenon, mainly affected by heat, light, physiological and biochemical reactions, as well as from attack by microorganisms.
文摘A new method was denonstrated to determine stress in a single crystal for multicrystal material and this new method could be specially applied for any symmetric crystalline systems. The strain tensor e was determined by the change of the metric tensor G before the initial state and after the deformed state in the crystal reference system. Then stress tensor at grain scale was calculated by the HOOK's law. The stress evaluations were carried out in coarse grains of a thin galvanized coating on a steel substrate during tensile loading. This makes it possible to link the microstructure evolution to the elastic heterogeneity at grain scale or between the grains.
文摘In the context of industrial competitiveness, taking into account the process design throughout the product life cycle is inevitable, from the expression of the need to recycle, the capitalization and knowledge management increasingly a target much sought after companies because of increased knowledge. Indeed, during the approval phase and use studies and scientific researches make have generated knowledge especially that concerning the reliability of system components. In this context, the capitalization and reuse of knowledge are necessary and have a particular interest in design and particularly in the preliminary design phase. Studies are already completed suggest a design process ranging from the need to solve the problem. At each phase of the process, structural characteristics are defined by the designer through the available knowledge already capitalized to make choice of component and their arrangement. This article proposes integrating the analysis of system reliability in this process. The objective is the use of knowledge in the vision safety and hazards of operating through the study of reliability and decision making for the selection of solution.
文摘The decrease of wind velocity （wake losses） in downstream area of wind turbine is generally quantified using wake models. The overall estimated power of wind farm varies according to reliability of wake model used, however it＇s unclear which model is most appropriate and able to give a high performance in predicting wind velocity deficit. In this subject, a qualification of three analytical wake models （Jensen, lshihara and Frandsen） based on three principal criteria is presented in this paper： （i） the parsimony which characterizes the inverse of model complexity, （ii） the accuracy of estimation in which wake model is compared with the experimental data and （iii） imprecision that is related to assumptions and uncertainty on the value of variables considered in each model. This qualitative analysis shows the inability of wake models to predict wind velocity deficit due to the big uncertainty of variables considered and it sensitivity to wind farm characteristic.
文摘The aim of this work is to study and quantify the air mass flow exchanged between inside and outside of the greenhouse, in order to determine the ventilation openings layout and the design effect on greenhouse airflow and microclimate distribution. The study was conducted over a 945 m2 multi-chapels arched greenhouse with a polyethylene cover and has thirteen crop rows oriented from north to south;the greenhouse was equipped with side wall and roof vents openings. A simulation was performed using different arrangements and configurations of ventilation openings with the same wind direction. Numerical simulation has been adopted in three dimensions (CFD), using the Fluent computer code which relies on the resolution of the Navier-Stokes equations. These equations were solved in the presence of the turbulence model (k - ε) and the Boussinesq model equation adopted to incorporate buoyancy forces. The effects of solar and atmospheric radiation were included by solving the radiative transfer equation (RTE), using Discrete Ordinate (DO) model. The effects of the roof openings, the presence of anti-insect screens and crops orientation were investigated and quantified. In a 3-span greenhouse with an anti-aphid in-sect screen in the vent openings, combining roof and sidewall vents gave a ventilation rate per unit opening area that was 1.4 times more than with only side vents. In the latter case, the difference of temperature between the inside and the outside of the greenhouse was greater than 3°C. Numerical simulations with an anti-insect screen having a porosity of 56% showed that the air exchange rate with combined ventilation was reduced by 48%. Finally, the paper focused on the effect of vent arrangement on the efficiency of the ventilation and the distribution of the microclimate inside the greenhouse. Results showed that computed ventilation rates varied from 53.43 to 70.95 kg/s, whereas temperature differences varied from 7.15°C to 10.14°C. This study also showed that other characteristics such as climate heterogeneity must be investigated in order to define the best ventilation configuration.
文摘This study aims to examine the effect of replacing vanadium by niobium and iron on the tribological behavior of hot-isostatic-pressed titanium alloy （Ti-6Al-4V） biomaterial, using a ball-on-disk-type oscillating tribometer, under wet conditions using physiological solution in accordance with the ISO7148 standards. The tests were carried out under a normal load of 6 N, with an AISI 52100 grade steel ball as a counter face. The morphological changes and structural evolution of the nanoparticle powders using different milling times （2, 6, 12 and 18 h） were studied. The morphological characterization indicated that the particle and crystallite size continuously decrease with increasing milling time to reach the lowest value of 4 nm at 18-h milling. The friction coefficient and wear rate were lower in the samples milled at 18 h （0.226, 0.297 and 0.423; and 0.66 × 10-2, 0.87 × 10-2 and 1.51 × 10-2 μm3 N-1 i, tm-1） for Ti-6Al-4Fe, Ti-6A1-7Nb and Ti-6Al-4V, respectively. This improvement in friction and wear resistance is attributed to the grain refinement at 18-h milling. The Ti-6Al-4Fe samples showed good tribological performance for all milling times.
文摘With their advantages, continuously variable transmissions have gained more popularity in the last decade by their use in mechanical transmission systems. The present paper aims to analysis the efficiency of the transmission based on the mechanical efficiency of the planetary gear train integrated in such transmission. In this analysis, we consider the mechanical efficiency of the transmission has been determined considering how the efficiency of the CVT members changes as a function of the operating conditions. The efficiency of the planetary gear train as a function of the configuration, speeds in his three input/output shafts, and also with respect to the power flow type. Results are compared with those obtained from other methods performance evaluation of the transmission, available in the literature.
文摘One of the difficulties encountered in the study of dusty plasmas is related to the knowledge of the size of the dust particles present. A variety of sources, physical and chemical mechanisms of formation, causes a wide variety of sizes and morphologies of dust. The diameter of a dust will not be unique but spread over several orders of magnitude. Its distribution in number, surface, mass or volume is called distribution. It is important to know this distribution in particle size because it strongly impacts the physical and radiative processes. To have a dust distribution in situ is very difficult;the reverse method can identify the particle populations from light extinction measures. In this study, we present an inversion procedure with a Tikhonov regularization dedicated to the determination of volume size distribution (V-PSD) from extinction measurements corresponding to the different wavelengths obtained by the Extinction Spectrometry technique.
文摘Cooling by evaporation through transpiring porous walls is expanding in various industrial applications such as air conditioning. It is also used to cool water in a clay jug. This process deserves to be studied, understood and valued. This paper deals with the transpiration phenomenon through a saturated porous plate coupled with heat and mass transfer by natural convection. Conservation Equations (mass, momentum, energy and concentration), associated with adequate boundary conditions, have been numerically solved using an implicit finite difference iterative method. The numerical model has been validated by experimental measurements from holographic interferometry. The used method to obtain temperature and concentration profiles was explained. They are evaluated from the refractive index of moisture air in the boundary layer. The main numerical results presented are: Nusselt and Sherwood numbers, temperature, humidity, and velocity profiles within the boundary layer as well as the different heat fluxes exchanged between the plate and the surrounding environment. Besides, the present model allows showing the important effect of the equivalent thermal conductivity and the surface emissivity on temperature and heats flux.
基金This research received no specific grant from any funding agency in the public,commercial,or not-for-profit sectors.
文摘In this paper,we theoretically investigate the total optical coefficient(TOAC)considering 1S-2P and 2S-2P conduction subband transitions in a single parabolic quantum well(SPQW)with an on-center hydrogen-like impurity.Within the framework of the effective-mass approximation,the Schrödinger equation is solved numerically to obtain the eigenvalues and their corresponding eigenvectors using the finite difference method.The calculations are performed for finite confinement potential height,taking into account the dielectric and effective mass mismatches between GaN and InGaN materials under the considered electric field and temperature effects.The temperature dependence of the effective mass,dielectric constant and band gap energy are obtained accordingly.On the one hand,the results show that a significant shift is produced with the variation of both the temperature and the intensity of the electric field.On the other hand,the absorption spectrum is shifted to lower energies with increasing both electric field strength and temperature.Moreover,its amplitude is enhanced with an increase in the intensity of the electric field,and show a slight drop with increasing temperature for the two optical transitions considered.The results show that such parameters can be used to adjust the optical properties of single parabolic Quantum Well for solar cell applications.
文摘To evaluate the residual stress in TiAl based alloys by X ray diffraction, X ray elastic constants (REC) of a γ TiAl alloy were determined. From these results, the stress state of a given phase in a duplex TiAl based alloy under a uniaxial tensile loading has been characterized by X ray diffraction. The results show that the X ray elastic constants and the microscopic stresses of the given phase are different from the apparent elastic constants and the macroscopic stresses of the alloy. The reason of the different distribution of the alloy was also discussed. [
基金Project supported by the State Key Development for Basic Research of China （Grant No 2004CB619302） and the National Natural Science Foundation of China （Grant No 50271038）.
文摘This paper reports that an atomic scale study of [^-110] symmetrical tilt grain boundary （STGB） has been made with modified analytical embedded atom method （MAEAM） for 44 planes in three noble metals Au, Ag and Cu. For each metal, the energies of two crystals ideally joined together are unrealistically hlgh due to very short distance between atoms near the grain boundary （GB） plane. A relative slide between grains in the GB plane results in a significaut decrease in GB energy and a minimum value is obtained at specific translation distance. The minimum energy of Cu is much higher than that of Ag and Au, while the minimum energy of Ag is slightly higher than that of Au. For all the three metals, the three lowest energies correspond to identical （111）, （113） and （331） boundary successively for two translations considered; from minimization of GB energy, these boundaries should be preferable in [^-110] STGB for noble metals. This is consistent with the experimental results. In addition, the minimum energy increases with increasing reciprocal planar coincidence density ∑, but decreases with increasing relative interplanar distance d/a.
文摘The characteristic architecture in the oases of south-eastern Morocco is that of raw earth construction.This is done through two techniques:rammed earth and adobe.This work is carried out with the aim of preserving this ancestral know-how by studying a construction dating back two centuries.The first step is to characterize a soil extracted from the remains of an old building,the grain size and plasticity of the soil showed that it was not very clayey and moderately plastic and that it was suitable for earth construction.Secondly,the study focuses on the mechanical resistance of blocks extracted from the remains studied,the result obtained satisfies all the standards.In order to characterize the durability of the adobe,we made samples of the earthen bricks with a similar soil and the study showed good durability of the adobe construction,the raw earth is a material that can stand in time.And finally,the reusability of the earth material from old buildings has been studied,the results have shown that raw earth is a perfectly reusable material,which makes it the ideal ecological material.
文摘The proposedwork focuses on the in-depth study of convective heat transfer in the unconfined air gap of a discoidal rotor-stator system.The rotary cooling mechanism is achieved by the injection of two air jets,while the cavity geometry is characterized by a dimensionless parameter G.The numerical analysis primarily concentrated on the effect of flow velocity and rotation on the heat exchange process.More precisely,the range of analysis extends from the rotational Reynolds number Re_(ω)=2.35×10^(5)to Re_(ω)=5.04×10^(5),while varying the Reynolds value of the jet in a range from 16×10^(3)to 55.46×10^(3).To carry out this analysis,a numerical simulation was conducted with Ansys-Fluent software,using the RSM turbulence model.The results of the study significantly reveal the impact of rotation on heat exchange transfer within the cavity,identifying two distinct zones of fluid recirculation.These zones exhibit remarkable heat transfer characteristics,contributing to a better understanding of the complexmechanisms governing heat transfer in this particular technological context.Additionally,the analysis of radial mean velocity distributions,as well as local and mean Nusselt numbers,provides further insight into the heat transfer performance of this unique configuration.
文摘Asteroid research is of global security interest, we are more afraid about any impact of these asteroids on Earth. We seek through this work to provide a study on the effect of the asteroid’s shape on the gravity aspect. Knowledge of the potential is crucial to bodies approaching the asteroid. There is a range of asteroid shapes to consider. Some well-known asteroids such Ceres, Vesta, Iris and Oumuamua are considered in this study. After determining the moment of inertia of the asteroids depending on their materials, the gravity fields and the potential gravity of the asteroids are established when varying their shapes. A representation of the gravity field is given in three dimensional coordinate systems. Also, the behavior of the potential gravity is drawing in the function of the object’s location. The second part is dealing with the interpretation of all the obtained results in order to deduce some rules and features which would be useful for the identification of the asteroids. Thus, by the best knowledge of the effect of the asteroid’s shape, we would be more informed in the survey of the hazardous near earth objects.
文摘<span style="font-family:Verdana;">Understanding the environment of olive tree cuttings is a key factor in improving these plants’ rooting rate and survival. This study aims to develop </span><span style="font-family:Verdana;"> a </span><span style="font-family:Verdana;">three-dimensional (3-D) Computational Fluid Dynamics (CFD) model for</span><span style="font-family:Verdana;"> numerically assessing air temperature and relative humidity in an olive cuttings </span><span style="font-family:Verdana;">greenhouse under Mediterranean climatic conditions. The results are deduced from a steady-state simulation performed with recorded boundary</span><span style="font-family:Verdana;"> conditions at 10:00 am, 12:00 pm, 02:00 pm, 04:00 pm, and 06:00 pm at different obser</span><span style="font-family:Verdana;">vation points. The calculations were validated using experimental data. The </span><span style="font-family:Verdana;">simulation errors of the air temperature were -0.8°C to 4.55°C, </span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">and errors of</span></span></span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;"> the leaf </span><span style="font-family:Verdana;">temperature were 0.07°C to 2.42°C, for the air relative humidity w</span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">as</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> <span style="font-family:Verdana;white-space:normal;">-</span>33.84% to <span style="font-family:Verdana;white-space:normal;">-</span>1.64%</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">,</span></span></span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;"> and <span style="font-family:Verdana;white-space:normal;">-</span>10.1% to <span style="font-family:Verdana;white-space:normal;">-</span>13.54% for the relative humidity of the leaf air. Contour maps were obtained from the 3-D CFD simulations to evaluate the distribution of humidity and air temperature inside the greenhouse </span><span style="font-family:Verdana;">and the vicinity of the plant canopy. This study suggests that the developed</span><span style="font-family:Verdana;"> 3-D CFD model can be a helpful tool to understand and optimize</span><span style="font-family:Verdana;"> greenhouse operation for better crop quality.</span></span></span></span>
文摘Glasses of the compositions 20Li2O-(50 - x)Li2WO4-xFe2O3-30P2O5 where (x = 0, 1, 5, 8, 10, 15 mol%) were elaborated by the melt-quenching route. Synthesized glasses are characterized using X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), differential scanning calorimetric?(DSC), and density determination. The XRD patterns confirmed the?amorphous nature of samples, and IR spectra showed the structural groups and highlight the depolymerization of phosphate network with the introduction of iron oxide. It is found that the structural unit Q2 converts to Q1 and Q0 as Fe2O3 replaces Li2WO4. Chemical durability tests on the glasses have shown that the compositions containing pyrophosphate (Q1) and orthophosphate (Q0) units are more water-resist. The electrical conductivity measurements were performed by complex impedance spectroscopy in the frequency range of 20 - 106 Hz at various temperatures from ambient to 400°C. It is found that the conductivity is activated thermally and follows an Arrhenius law. The obtained electrical data were analyzed by the modulus formalism and dielectric formalism. The determined asymmetric nature of? spectra suggested that the relaxation behavior is non-Debye and characterized by the stretched exponent parameter
