4,433 research outputs found
Experimental study on the cyclic resistance of a natural loess from Northern France
In order to analyze the instability phenomenon observed along the Northern
High Speed Line of R\'eseau Ferr\'e de France (RFF), soil blocks were taken at
a site near the railway, at four different depths (1.2, 2.2, 3.5 and 4.9 m).
Cyclic triaxial tests were carried out on saturated and unsaturated soil
specimens. The results from tests on initially saturated specimens showed that
the soil taken at 2.2 m depth has the lowest resistance to cyclic loading, in
relation to its highest porosity and lowest clay fraction. This soil was then
studied at unsaturated state with various initial water contents. Unsaturated
soil specimens were first subjected to cyclic loadings to decrease their
volume. These cyclic loadings was stopped when the volume decrease was
approximately equal to the initial pore air volume, or when the pores filled by
air were eliminated and the soil was considered to become saturated.
Afterwards, the back-pressure tubing was saturated with de-aired water and
cycles were applied under undrained condition. Significant effect of initial
water content was evidenced: the lower the initial water content, the higher
the cyclic resistance. This can be explained by the densification of the soil
during the initial cyclic loadings
Energy Storage Technologies for Smoothing Power Fluctuations in Marine Current Turbines
With regard to marine renewable energies, significant electrical power can be extracted from marine tidal current. However, the power harnessed by a marine current turbine varies due to the periodicity of the tidal phenomenon and could be highly fluctuant caused by swell effect. To improve the power quality and make the marine current generation system more reliable, energy storage systems will play a crucial role. In this paper, the power fluctuation phenomenon is described and the state of art of energy storage technologies is presented. Characteristics of various energy storage technologies are analyzed and compared for marine application. The omparison shows that high-energy batteries like sodiumsulphur battery and flow battery are favorable for smoothing the long-period power fluctuation due to the tide phenomenon while supercapacitors and flywheels are suitable for eliminating short-period power disturbances due to swell or turbulence phenomena. It means that hybrid storage technologies are needed for achieving optimal performance in marine current energy systems
Microstructural characterization of a Canadian oil sand
The microstructure of oil sand samples extracted at a depth of 75 m from the
estuarine Middle McMurray formation (Alberta, Canada) has been investigated by
using high resolution 3D X-Ray microtomography (CT) and Cryo Scanning
Electron Microscopy (CryoSEM). CT images evidenced some dense areas
composed of highly angular grains surrounded by fluids that are separated by
larger pores full of gas. 3D Image analysis provided in dense areas porosity
values compatible with in-situ log data and macroscopic laboratory
determinations, showing that they are representative of intact states. CT
hence provided some information on the morphology of the cracks and disturbance
created by gas expansion. The CryoSEM technique, in which the sample is freeze
fractured within the SEM chamber prior to observation, provided pictures in
which the (frozen) bitumen clearly appears between the sand grains. No evidence
of the existence of a thin connate water layer between grains and the bitumen,
frequently mentioned in the literature, has been obtained. Bitumen appears to
strongly adhere to the grains, with some grains completely being coated. The
curved shape of some bitumen menisci suggests a bitumen wet behaviour
- …