1,356 research outputs found
Resistência à fadiga em misturas betuminosas para pavimentos rodoviários
Perante as cargas do tráfego, as camadas betuminosas dos pavimentos rodoviários estão sujeitas a um estado de tracção na sua base. A passagem repetida das cargas do tráfego provoca um fenómeno de fadiga das misturas betuminosas que origina o fendilhamento das misturas betuminosas e consequentemente dos pavimentos, afigurando-se este como a principal degradação que ocorre nos pavimentos. Desde os anos 60 que o fendilhamento dos pavimentos tem vindo a ser estudado tendo-se desenvolvido inúmeros ensaios para a sua avaliação. Dentre os mais conhecidos encontram-se o ensaio de flexão em quatro pontos sobre vigas prismáticas e o ensaio de tracção indirecta por compressão diametral em provetes cilÃndricos. A análise dos resultados destes ensaios relaciona o nÃvel de extensão ou tensão instalada no provete com o número de ciclos de carga que provoca a sua rotura. Este artigo apresenta a forma como a resistência à fadiga das misturas betuminosas é avaliada e considerada no dimensionamento de pavimentos e as tentativas para redução do tempo de ensaio
Hybrid UHF/UWB antenna for passive indoor identification and localization systems
WOS:000312996000040 (Nº de Acesso Web of Science)There is a growing interest for simultaneous identification and centimetre-resolution localization of multiple targets in indoor environments. A hybrid passive UHF/UWB RFID concept has been recently proposed that conciliates the potential from high resolution UWB impulse radio with the typical range from UHF-RFID identification systems. This paper proposes a new planar antenna for hybrid passive tag systems, which operates both in the UHF-RFID band and in the FCC UWB band. The co-designed UHF and UWB antenna elements are printed back-to-back on each side of a common substrate with appropriate topology for future integration with a single UHF-UWB RFID chip. Experimental tests have shown that both UHF-RFID and UWB performance of the hybrid antenna are comparable to available commercial solutions that work just on a single band. The antenna is adequate for low-cost mass production of hybrid passive tags. It aims at low-cost passive RFID systems combining the ability of item identification with precise tracking in indoor environments
A primer on CFD-DEM for polymer-filled suspensions
This work reports on an evaluation of the computational fluid dynamics–discrete element
method (CFD-DEM) numerical approach to study the behavior of polymer-filled suspensions in a
parallel-plate rheometer. For this purpose, an open-source CFD-DEM solver is used to model the
behavior of such suspensions considering different particle volume fractions and different types of
fluid rheology. We first validate the numerical approach for the single-phase flow of the continuum
phase (fluid phase) by comparing the fluid’s azimuthal velocity and shear stress components obtained
from the open-source solver against the analytical expressions given in cylindrical coordinates.
In addition, we compare the numerical torque given by the numerical procedure with analytical
expressions obtained for Newtonian and power law fluids. For both cases, there is a remarkable
agreement between the numerical and analytical results. Subsequently, we investigated the effects
of the particle volume fraction on the rheology of the suspension. The numerical results agree well
with the experimentally measured ones and show a yield stress phenomenon with the increase of the
particle volume fraction.This research was funded by FEDER through the COMPETE 2020 Programme and National Funds through FCT (Portuguese Foundation for Science and Technology) under projects
UID-B/05256/2020, UID-P/05256/2020, UIDB/ 00013/2020, UIDP/00013/2020, UIDB/00532/ 2020,
PTDC/EMS-ENE/3362/2014–POCI-01-0145-FEDER-016665
Integrated thermochronology and organic maturation studies in the South Portuguese Zone and Algarve Basin (South Portugal)
This PhD research project started in February this year. Its main goal is to combine
apatite fission track analysis (AFTA) with other low-temperature thermochronometers
(zircon fission track, (U-Th)/He apatite) to construct temperature-time paths for the
South Portuguese Zone and the Algarve Basin
Viability of wall-embedded tag antenna for ultra-wideband real-time suitcase localisation
WOS:000335152600007 (Nº de Acesso Web of Science)Viability of a conformal single-layer monopole antenna is studied for a wall-embedded tag in an ultra-wideband (UWB) suitcase localisation application based on impulse radio UWB. The performance of the embedded antenna is simulated and confirmed experimentally in real-time localisation (RTL) experiments carried out in a cluttered laboratory environment. Evaluation in the main planes shows average suitcase positioning error around 8 cm for worst-case conditions. RTL tests are made when the suitcase is empty, when it is filled with common travelling items and also when it is shadowed by a second suitcase. A vector network analyser-based measurement set-up is used for target localisation error evaluation. Additionally, the same tests are repeated using portable commercial time-domain transceivers with similar results
Efficiency prediction on a 2.5 MW wind turbine gearbox
This paper is a case study of the efficiency of a 2.5 MW wind turbine gearbox including
the influence of each gearbox element: gear tooth geometry, rolling bearings and oil
formulation. The power loss model used to predict the gearbox efficiency was
previously validated with experimental results. The calculations showed that the
efficiency of a wind turbine gearbox can be improved by selecting different wind turbine
gear oil formulations, modifying gear tooth geometry. The energy savings can be even
more significant if both gear tooth geometry and oil formulation are adequately
selected.The authors gratefully acknowledge the funding supported by:
National Funds through Fundação para a Ciência e a Tecnologia (FCT), under
the project EXCL/SEM-PRO/0103/2012;
COMPETE and National Funds through Fundação para a Ciência e a
Tecnologia (FCT), under the project Incentivo/EME/LA0022/2014;
Quadro de Referência Estratégico Nacional (QREN), through Fundo Europeu
de Desenvolvimento Regional (FEDER), under the project NORTE-07-0124-
FEDER-000009 - Applied Mechanics and Product Development;
without whom this work would not be possible
Geochemistry of the Baixo Alentejo Flysch Group, South Portuguese Zone: implications for provenance and palaeoweathering
The Baixo Alentejo Flysch Group (BAFG) is one of the
domains of the South Portuguese Zone, consisting of deepwater tubiditic sediments, with more than 5 km in thickness.
Stratigraphically the BAFG is subdivided into three
formations, from the bottom to the top: Mértola Formation,
Mira Formation and Brejeira Formation, with ages ranging
from Middle to Upper Carboniferous
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