Comparison of Subgrid-scale Viscosity Models and Selective Filtering Strategy for Large-eddy Simulations

Explicitly filtered large-eddy simulations (LES), combining high-accuracy schemes with the use of a selective filtering without adding an explicit subgrid-scales (SGS) model, are carried out for the Taylor-Green-vortex and the supersonic-boundary-layer cases. First, the present approach is validated against direct numerical simulation (DNS) results. Subsequently, several SGS models are implemented in order to investigate if they can improve the initial filter-based methodology. It is shown that the most accurate results are obtained when the filtering is used alone as an implicit model, and for a minimal cost. Moreover, the tests for the Taylor-Green vortex indicate that the discretization error from the numerical methods, notably the dissipation error from the high-order filtering, can have a greater influence than the SGS models

Google Earth Engine based monitoring of cork and holm oak woodlands NDVI trends in Portugal

ComunicaçãoThe Mediterranean area currently suffers a general decline of oak woodlands’ health and productivity. Cork oak (Quercus suber L.) and holm oak (Quercus ilex L.) are widely exploited in Portugal and are an important economical and ecological resource for the country. The Normalized Difference Vegetation Index (NDVI) is a common remote sensing index used as a proxy for vegetation biomass, chlorophyll activity, health and stress. NDVI can be monitored for 34 years (1984-2017) at 30-meter of resolution using Landsat imagery. The online platform Google Earth Engine (GEE) allows the free access and fast handling of this huge amount of satellite images. Objective: Providing to researchers, land owners and policy-makers a high-resolution map of cork and holm oak long-term trends for the whole PortugalN/

Modeling and simulation of damage in elastomer structures at high strains

International audienceA new model is proposed in order to simulate correctly the behaviour of elastomers for very large deformations. The hyperelastic Hart–Smith’s model is revisited in order to take into account the damage of elastomers and the opening and the closing of micro-defects. Applications concern structures with elastomer used in space industry. Shear loadings are typical solicitations for these structures. Whenever the material is able to undergo very large deformations (600–700%), the simulation of this type of experiment up to so high strains is not easy. The failure of industrial finite element code leads us to develop a prototype software using a non-incremental method (large time increment method) and a material formulation with “rotated” quantities. Some applications are shown for elastic or hyperelastic materials, especially for nearly incompressible materials

Synthesis and photochromic behaviour of new methyl induced linear and angular thieno-2H-chromenes

New methyl induced linear and angular thieno-2H-chromenes 4, 5 and 6 were prepared by reaction of new methylated 6-hydroxybenzo[b]thiophenes 2 (a, b and c) and propargylic alcohols 3a and 3b, using acidic Alumina Brockmann I as catalyst and drying agent. Compounds 2 were prepared in good to excellent yields in a “one pot” three step reaction from the corresponding bromo compounds 1. The photochromic behaviour of compounds 4, 5 and 6b was evaluated with the aid of a classical set of spectrokinetic parameters, and compared to reference compounds that are benzoannellated in the 5,6 and 6,7 positions of the chromene (naphthopyrans) and also to thieno-2H-chromenes 7 and 8, previously prepared, which are analogues of 5a. The resistance to fatigue (photodegradation) under continuous irradiation was also evaluated.Fundação para a Ciência e Tecnologia. Escola Superior de Tecnologia e Gestão do Instituto Politécnico de Bragança

Simulation des Grandes Échelles de l'interaction onde de choc / couche limite turbulente sur plaque plane

Une interaction onde de choc / couche limite turbulente (ICCLT) de forte intensité entraîne le décollement de la couche limite et la création d'un bulbe de recirculation. Ce type de configuration génère fréquemment l'apparition d'instationnarités basses fréquences. L'étude s'attaque par Simulation des Grandes Échelles au cas d'ICCLT instationnaire sur plaque plane. L'objectif est de démontrer que la dynamique basse fréquence est pilotée par la couche de mélange qui se développe le long du bulbe de recirculation

Produtividade dos montados em Portugal no período 1984-2017

Apresentação baseada nos trabalhos: Aubard, V., Paulo, J. A., Silva, J. M. N. 2019. Long-term monitoring of cork and holm oak stands productivity in Portugal with Landsat imagery. Remote Sensing 11(5):525. https://doi.org/10.3390/rs11050525 / Aubard, V. 2018. Monitoring cork oak woodlands through remote sensing with Google Earth Engine‘. MSc thesis. http://portaildoc-agro.vetagrosup. fr/Record.htm?idlist=2&record=19265660124910838429N/

Semi-Automatic Methodology for Fire Break Maintenance Operations Detection with Sentinel-2 Imagery and Artificial Neural Network

PTDC/CCI-COM/30344/2017 PCIF/SSI/0102/2017 UID/EEA/00066/2019 UIDB/00239/2020The difficult job of fighting fires and the nearly impossible task to stop a wildfire without great casualties requires an imperative implementation of proactive strategies. These strategies must decrease the number of fires, the burnt area and create better conditions for the firefighting. In this line of action, the Portuguese Institute of Nature and Forest Conservation defined a fire break network (FBN), which helps controlling wildfires. However, these fire breaks are efficient only if they are correctly maintained, which should be ensured by the local authorities and requires verification from the national authorities. This is a fastidious task since they have a large network of thousands of hectares to monitor over a full year. With the increasing quality and frequency of the Earth Observation Satellite imagery with Sentinel-2 and the definition of the FBN, a semi-automatic remote sensing methodology is proposed in this article for the detection of maintenance operations in a fire break. The proposed methodology is based on a time-series analysis, an object-based classification and a change detection process. The change detection is ensured by an artificial neural network, with reflectance bands and spectral indices as features. Additionally, an analysis of several bands and spectral indices is presented to show the behaviour of the data during a full year and in the presence of a maintenance operation. The proposed methodology achieved a relative error lower than 4% and a recall higher than 75% on the detection of maintenance operations.publishersversionpublishe

Fully automated countrywide monitoring of fuel break maintenance operations

PTDC/CCI-COM/30344/2017 PCIF/SSI/0102/2017 UIDB/00239/2020 UIDB/00066/2020Fuel break (FB) networks are strategic locations for fire control and suppression. In order to be effective for wildfire control, they need to be maintained through regular interventions to reduce fuel loads. In this paper, we describe a monitoring system relying on Earth observations to detect fuel reduction inside the FB network being implemented in Portugal. Two fast automated pixel-based methodologies for monthly monitoring of fuel removals in FB are developed and compared. The first method (M1) is a classical supervised classification using the difference and postdisturbance image of monthly image composites. To take into account the impact of different land cover and phenology in the detection of fuel treatments, a second method (M2) based on an innovative statistical change detection approach was developed. M2 explores time series of vegetation indices and does not require training data or user-defined thresholds. The two algorithms were applied to Sentinel-2 10 m bands and fully processed in the cloud-based platform Google Earth Engine. Overall, the unsupervised M2, which is based on a Welch t-test of two moving window averages, gives better results than the supervised M1 and is suitable for an automated countrywide fuel treatment detection. For both methods, two vegetation indices, the Modified Excess of Green and the Normalized Difference Vegetation Index, were compared and exhibited similar performances.publishersversionpublishe