Photogrammetric 3D modelling and mechanical analysis of masonry arches: An approach based on a discontinuous model of voussoirs

This article shows the application of close range photogrammetry to the generation of accurate 3D geometric models for the subsequent evaluation of the condition state of historical masonry bridge arches by means of numerical analysis. The arch geometry in the model was obtained from each individual voussoir or ashlar with its own contour geometry, which was obtained by close range photogrammetry. From this precise geometrical model, mechanical modelling tools and finite elements analysis were applied to accomplish two main goals: to estimate the failure load considering the arch stability using a discontinuous model of voussoirs assembled without tension at the interfaces, and to obtain the distribution of stresses into each voussoir. The obtained results by means of this procedure are compared with those obtained by rigid blocks limit analysis with regular geometry.     

1D and 3D numerical simulations in PEM fuel cells

The potential of fuel cells for clean and efficient energy conversion is generally recognized.The proton-exchange membrane (PEM) fuel cells are one of the most promising types of fuel cells. Models play an important role in fuel cell development since they enable the understanding of the influence of different parameters on the cell performance allowing a systematic simulation, design and optimization of fuel cells systems. In the present work, one-dimensional and three-dimensional numerical simulations were performed and compared with experimental data obtained in a PEM fuel cell. The 1D model, coupling heat and mass transfer effects, was previously developed and validated by the same authors [1] and [2]. The 3D numerical simulations were obtained using the commercial code FLUENT - PEMFC module.The results show that 1D and 3D model simulations considering just one phase for the water flow are similar, with a slightly better accordance for the 1D model exhibiting a substantially lower CPU time. However both numerical results over predict the fuel cell performance while the 3D simulations reproduce very well the experimental data. The effect of the relative humidity of gases and operation temperature on fuel cell performance was also studied both through the comparison of the polarization curves for the 1D and 3D simulations and experimental data and through the analysis of relevant physical parameters such as the water membrane content and the proton conductivity. A polarization curve with the 1D model is obtained with a CPU time around 5 min, while the 3D computing time is around 24 h. The results show that the 1D model can be used to predict optimal operating conditions in PEMFCs and the general trends of the impact on fuel cell performance of several important physical parameters (such as those related to the water management). The use of the 3D numerical simulations is indicated if more detailed predictions are needed namely the spatial distribution and visualization of various relevant parameters.An important conclusion of this work is the demonstration that a simpler model using low CPU has potential to be used in real-time PEMFC simulations.     

Assessing the anthocyanic composition of Port wines and musts and their free radical scavenging capacity

The anthocyanic composition of must and different types of Port wine (Ruby, LBV and Tawny from nine producers) was evaluated by HPLC. In addition, the radical scavenging activity of these Port wines was evaluated by using DPPH radical microassay. Musts, Ruby and LBV Port wines presented similar qualitative profiles of anthocyanins and quantitative differences, ranging from 382-601, 92-156 and 32-78 mg of malvidin-3-O-glucoside equivalent/l, respectively. Anthocyanins in Tawny Port wines ranged between not detected and 51 mg of malvidin-3-O-glucoside equivalent/l. Principal component analysis was applied to the percentage (in weight) of each compound in relation with the total content of anthocyanins. PCA yielded two components explaining 90.9% of the total variance. The first PC correlates positively with the glucoside derivatives of delphinidin, cyanidin, petunidin and malvidin. The second PC correlates positively with pyruvic acid adducts of anthocyanins that resulted from vinification process. Ruby and LBV presented low amounts of glucoside derivatives and variable amounts of pyruvic acid adducts of anthocyanins. Acid hydrolysis allowed the identification of five anthocyanidins. Malvidin was the most abundant one. LBV Port wine showed the strongest antiradical activity, while Tawny Port wines revealed the lowest ones, with these wines presenting lower amounts of anthocyanic compounds owing to their “oxidative” aging in wooden barrels. These results suggest that aging process is an important factor influencing the antioxidant activity of Port wines.