LBM based flow simulation using GPU computing processor

Graphics Processing Units (GPUs), originally developed for computer games, now provide computational power for scientific applications. In this paper, we develop a general purpose Lattice Boltzmann code that runs entirely on a single GPU. The results show that: (1) simple precision floating point arithmetic is sufficient for LBM computation in comparison to double precision; (2) the implementation of LBM on GPUs allows us to achieve up to about one billion lattice update per second using single precision floating point; (3) GPUs provide an inexpensive alternative to large clusters for fluid dynamics prediction.     

Synthesis of (polyethylene terephthalate/poly?-caprolactone) copolyesters

Polyethylene terephthalate (PET) was alcoholised with ethylene glycol to synthesize hydroxytelechelic oligomers of PET. On the other hand, commercial hydroxytelechelic poly?-caprolactone was modified in order to synthesize carboxytelechelic poly?-caprolactone. The chemical structure of the products was investigated by ¹H NMR. Multiblock copolyesters were then synthesized by polyesterification of hydroxytelechelic PET and carboxytelechelic poly?-caprolactone oligomers, using several catalysts and different reaction conditions, which have been linked with the average molecular weight of the obtained block copolyesters. It appeared that residual distannoxane species coming from glycolysis step are best catalyst for polyesterification reaction. The chemical structure of the synthesized copolyesters was investigated by size exclusion chromatography and ¹H NMR. The thermal and thermomechanical behavior of the synthesized copolyesters was investigated by differential scanning calorimetry and by dynamic mechanical analyses. The ester-ester interchange reaction between the two types of oligopolyesters has been enlightened and estimated taking in account the different reaction parameters. This side reaction led to the miscibility of the two phases of the oligomers, that can be explained by a random structure of the copolyester, and prevented to obtain multiblock copolymer.     

Texture Evolution in Heavily Cold-Rolled FeCo-2V Alloy during Annealing

The recrystallization texture evolution in heavily cold-rolled (93%) FeCo-2V alloy with annealing temperature and time was investigated by X-ray diffraction and electron backscatter diffraction. It was found that the orientation density of α-fiber texture component fluctuates with increasing annealing temperature and time. The transmission electron microscopy images show that abundant precipitates appear inside the recrystallized grains and around the grain boundaries. The amount and size of the precipitate...     

Optical fibre musical instruments: making sense of the senseless

This paper demonstrates how the light transmitted through a stretched optical fibre may be used to detect its modes of vibration. In particular, replacing strings of a musical instrument with optical fibre allows the fabrication of a simple acoustic instrument with a single laser source and single detector. The detected signal contains rich harmonics of the vibrating fibre. This device may be used as a vibration, temperature or strain sensor, or simply as a musical instrument. Coating the optical fibre with novel materials such as PZLT may well allow a modification of vibration properties to enhance, suppress certain harmonics or lead to the development of simple electric field sensors.     

Stability Study of a Mixed Islanded Power Network

This paper presents the modelling, simulation and analysis of the dynamic behaviour of a mixed power network of 2.78 GW including hydro, thermal and wind power plants. The modelling of each power plant is described. The set of parameters of the turbine speed governor of the hydroelectric power plant is determined with a specific identification procedure to achieve stable operation for different cases such as interconnected, isolated or islanded operation. The analysis of the stability of the entire mixed islanded power plant is investigated through time domain simulations for different sets of controllers parameters and for different disturbances （load rejection and turbulent wind speed profile）.     

Deformation at ambient and high temperature of in situ Laves phases-ferrite composites

The mechanical behavior of a Fe₈₀Zr₁₀Cr₁₀ alloy has been studied at ambient and high temperature. This Fe₈₀Zr₁₀Cr₁₀ alloy, whoose microstructure is formed by alternate lamellae of Laves phase and ferrite, constitutes a very simple example of an in situ CMA phase composite. The role of the Laves phase type was investigated in a previous study while the present work focuses on the influence of the microstructure length scale owing to a series of alloys cast at different cooling rates that display microstructures with Laves phase lamellae width ranging from ～50 nm to ～150 nm. Room temperature compression tests have revealed a very high strength (up to 2 GPa) combined with a very high ductility (up to 35%). Both strength and ductility increase with reduction of the lamella width. High temperature compression tests have shown that a high strength (900 MPa) is maintained up to 873 K. Microstructural study of the deformed samples suggests that the confinement of dislocations in the ferrite lamellae is responsible for strengthening at both ambient and high temperature. The microstructure scale in addition to CMA phase structural features stands then as a key parameter for optimization of mechanical properties of CMA in situ composites.     

Modification of poly(styrene-b-(ethylene-co-butylene)-b-styrene) via free-radical grafting and its photo-crosslinking

Poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS) is functionalized via radical grafting with 4-vinyl-1-cyclohexene 1,2-epoxide (VCHO) initiated using 2,5-Bis(tert-butylperoxy)-2,5-dimethylhexane. The existence of the epoxide group on the SEBS backbone is evidenced by ¹H nuclear magnetic resonance. A size exclusion chromatography (SEC) study reveals some chain coupling, and this phenomenon is limited by controlling the quantities of peroxide and monomer reagents used during the radical grafting. Photo-crosslinking of SEBS-g-VCHO under ultraviolet irradiation in the presence of a cationic initiator is then successfully performed with resultant gel contents higher than 85%. Mechanical properties of SEBS and crosslinked materials are measured by tensile tests on thin films. On the one hand, those tests reveal a significant increase of Young's modulus of the crosslinked materials. On the other hand, the diminution of elongation at break is much more limited; crosslinked materials retain their elastomeric properties with an elongation at break greater than 200%. Finally, the photosensitive SEBS-g-VCHO is used to show the adhesion performance of the photo-crosslinking coating as well as a resin for the stereolithography process.     

Nanosecond reversible solid state switches capable of handling MJ of energy

The theoretical applicability of the Schottky thermionic emission model to electronic transport at tin dioxide grain boundaries is addressed. Firstly, the theoretical behaviour of the barrier height ?_(v) versus applied voltage V is determined for a single grain boundary. Next we predict the current density–voltage characteristics as a function of temperature, demonstrating good correlation between experimental and theoretical results. The model carried out has the advantage that it contains no adjustable parameters. Agreement with experimental results from optimised polycrystalline ceramics gives strong evidence for the double-depletion-layer/thermionic-emission model. Moreover, this study emphasises the importance of the direct large-bandgap of doped SnO₂ in surge-arrester applications, and gives credibility to the analogy between the apparent behaviour of doped SnO₂ and doped ZnO varistors. Doped polycrystalline tin oxide ceramic is the first material to compete with doped ZnO in the medium and high voltage applications for surge arresters.     

A numerical thermal approach to study the accelerated aging of a solar absorber material

Solar power tower receivers are exposed to highly-concentrated solar flux. The strong flux variations that they are exposed to during their service life enhance the physical–chemical aging mechanisms and cause the decrease of the material’s thermal performance. A material that is commonly used for these applications was selected for our study. It is used for the absorber tubes of a solar power tower receiver. This material is made of an alloy (Inconel 625) that is coated with a silicone-based paint coating (Pyromark 2500 black) to increase the solar radiation absorption capacity.With the aim of determining the optimal conditions to accelerate the aging of this two-layer material (metal + paint coating), an axisymmetric 2-D model reproducing its thermal behavior was developed. Several thermal indicators (temperature, thermal gradients, temporal gradient), which are representative of the thermal aging factors and the material’s thermal performance, are analyzed in different configurations of boundary conditions. One configuration was defined according to the normal working conditions of a particular solar power plant application; the others are associated with various boundary conditions with the potential to increase or modify the thermal stress factors to accelerate the aging mechanisms. Other aging factors such as humidity, pollutants, and dust are not investigated in this paper. Several simulations were run in permanent and variable regimes. The most influencing boundary conditions and material properties were highlighted by a sensitivity study. To design relevant aging tests, particular attention should be paid to the incident solar power and the cooling characteristics of the material. The surface total absorptance, the thermal conductivities and the thermal contact resistance between the paint and the metal layers are the parameters that most affect the material’s thermal behavior. The evolution of those material properties characterizes the aging and should be monitored. Irradiance cycles were simulated for their potential to increase the thermal fatigue. Depending on the average, the amplitude and the period of the cycle, the evolution of the thermal indicators were analyzed. They were compared to select the most appropriate aging tests that are to be performed. From there, two aging strategies were determined. To put them in practice, an experimental Solar Accelerated Aging Facility (SAAF) was built and is described in this paper. It enables to perform accelerated aging experiments with a 2-m-diameter parabola concentrating the sun radiation up to 16,000 times. A preliminary experiment to validate the model confirmed that the simulation results are in good agreement with the experimental.     

On the role of kinetic energy during unstable propagation in a heterogeneous peeling test

We study the dynamic debonding of a one-dimensional inextensible film, subject to a monotonic loading and under the hypothesis that the toughness of the glue can take only two values. We first consider the case of a single defect of small length in the glue where the toughness is lower than in the remaining part. The dynamic solution is obtained in a closed form and we prove that it does not converge to the expected quasi-static one when the loading speed tends to zero. The gap is due to a kinetic energy which appears when the debonding propagates across the defect at a velocity which is of the same order as the sound velocity. The kinetic energy becomes negligible again only when the debonding has reached a critical distance beyond the defect. The case of many defects is then considered and solved using an exact numerical solution of the wave equation and the Griffith law of propagation. The numerical results highlight the effects of the time evolution of the kinetic energy which induce alternate phases of rapid and slow debonding, these oscillations depending essentially on the volume fraction of the highest toughness.