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81.
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83.
This paper describes the development of a computational model to predict the response of synthetic-fiber ropes under both monotonic and cyclic loads. The model addresses the issue of damage to a rope cross-section and its effect on rope response. Isotropic damage is assumed and is therefore characterized by a scalar quantity known as the damage index. The damage index is used to quantify the amount of deterioration that takes place in a damaged rope throughout its loading history. For the current study, data obtained from static tension tests are used to determine the evolution relationship for the damage index. This relationship is based on the stiffness ratio between experimental data and simulation of rope response without any source of damage and is assumed to be described by an exponential equation. Numerical simulations of damaged rope behavior compare well with experimental results. 相似文献
84.
Factors controlling the vegetation distribution and coal‐forming environments in a strike‐slip basin. The Pennsylvanian Peñarroya‐Belmez‐Espiel Basin,southern Spain
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Coal‐forming environments require humid to perhumid conditions. Tectonics governs the size, location and availability of coal seams developed in such environments. While large Pennsylvanian paralic basins generated thick and continuous coal seams, many other small coeval basins, which were tectonically active, developed a puzzling succession, with carbonaceous deposits that varied in size, thickness and the nature of the coal‐forming flora. This study, conducted in the Peñarroya‐Belmez‐Espiel coalfield, a Variscan strike‐slip basin in the south of Spain, provides insights into this subject. The coal seams analysed, generated in different depositional environments, have quantitatively different palynological assemblages. Lacustrine coals are dominated by lycopsids; distal alluvial plain/marginal lacustrine coals are dominated by sphenophytes and tree ferns, and middle alluvial fan coals are dominated by sphenophytes, tree ferns and lycopsids. This means that when conditions were favourable for peat accumulation, peat accumulated regardless of the nature of the available flora. 相似文献
85.
Andre Frossard Pereira de Lucena Roberto Schaeffer Alexandre Salem Szklo 《Global Environmental Change》2010,20(2):342-350
Global climate change induced by the emission of greenhouse gases may pose challenges to energy security. The vulnerability of energy sources, in particular of renewable sources, to climate change raises the need to identify adaptation measures. This paper applies an integrated resource planning approach to calculate least-cost adaptation measures to a set of projected climate impacts on the Brazilian power sector. The methodology used has the advantage of finding optimal solutions that take into consideration the whole energy chain and the interactions between energy supply and demand. Results point in the direction of an increased installed capacity based, mostly, on natural gas, but also sugarcane bagasse, wind power and coal/nuclear plants, to compensate for a lower reliability of hydroelectric production, amongst other impacts. The indirect effect of these results is the displacement of natural gas from other consuming sectors, such as industry, in favor of its use for power generation. Results obtained are, however, based on the techno-economic premises used in the simulation, which may vary in the long term. 相似文献
86.
The model proposed in this article relates permeability to porosity measurements that can easily be performed in the laboratory. The pore size distribution (PSD) curve is updated with strains and damage. The updated volumetric fractions of natural pores and cracks are introduced in the expression of permeability. Contrary to classical permeability models based on PSD integrations, the model proposed in this article accounts for possible changes in the porosity modes: one mode for undamaged samples and two modes for cracked samples. The proposed approach also accounts for varying states of damage, as opposed to classical fracture network models, in which the cracks pattern is fixed. The only material parameters that are required to describe the microstructure are the lower and upper bounds of the pores size for both natural pores and cracks. All the other PSD parameters involved in the model are related to macroscopic parameters that can easily be determined in the laboratory, such as the initial void ratio. The framework proposed in this article can be used in any damage constitutive model to determine the permeability of a brittle porous medium. Drained triaxial compression tests have been simulated. Before cracks initiation, permeability decreases while the larger natural pores are getting squeezed. After the occurrence of damage, permeability grows due to the increase of cracks density. The model performs well to represent the influence of the confining pressure on damage evolution and permeability variations. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
87.
de Luna Rejane Maria Rodrigues dos Anjos Garnés Silvio Jacks da Silva Pereira Cabral Jaime Joaquim dos Santos Sylvana Melo 《Natural Hazards》2021,106(3):1821-1837
Natural Hazards - Recife Metropolitan Region, in the northeast of Brazil, is formed by a coastal plain bounded by hills and by the Atlantic Ocean. Recife Metropolitan Region has about 4 million... 相似文献
88.
Pereira E Abreu SN Coelho JP Lopes CB Pardal MA Vale C Duarte AC 《Marine pollution bulletin》2006,52(11):1450-1457
The main objective was to study the seasonal variation of mercury concentrations in different tissues (muscle, hepatopancreas and gills) of Carcinus maenas from low and high Hg contaminated areas, a valuable resource in temperate estuaries and a possible pathway for human uptake. Individuals of two size classes (around 35 and 55 mm cephalothorax wide) were captured monthly between March 1999 and May 2000 in two areas of Ria de Aveiro: in the main navigation channel that connects the lagoon to the sea, and in the inner lagoon area heavily contaminated by mercury (maximum Hg in sediments of 5.4 microg g(-1)). Pronounced decreases in salinity and temperature and reduced food availability in winter seemed to be the responsible for the decline of the crab condition index (0.75-0.45) in larger individuals. Muscle and hepatopancreas exhibited higher mercury concentrations than gills, with concentrations in the contaminated site ranging from 0.03 to 0.63 microg g(-1) and 0.02 to 0.34 microg g(-1), respectively. Linear regressions between muscle and hepatopancreas (r=0.94, p<0.001) and muscle and gills (r=0.97, p<0.001) suggested a rapid redistribution of mercury inside the organism. During winter, a rapid elimination of mercury was found in the three analysed tissues followed by uptake. Larger crabs presented elimination rates from 18 to 34 ng g(-1) per week, while the smaller crabs showed lower elimination rates (10-24 ng g(-1) per week). The uptake was similar in both size classes (11-15 ng g(-1) and 8.1-15 ng g(-1) per week, respectively for large and small crabs). Our results suggest that C. maenas harvested in the contaminated areas must be considered with caution, since Hg concentrations were found to exceed the threshold concentration allowed for human consumption (0.5 microg g(-1)). 相似文献
89.
Ramalhosa E Pato P Monterroso P Pereira E Vale C Duarte AC 《Marine pollution bulletin》2006,52(3):353-356
90.
Ray-traced slant factors for mitigating the tropospheric delay at the observation level 总被引:3,自引:2,他引:1
Landon?UrquhartEmail author Felipe?G.?Nievinski Marcelo?C.?Santos 《Journal of Geodesy》2012,86(2):149-160
Three-dimensional ray tracing through a numerical weather model has been applied to a global precise point positioning (PPP)
campaign for modeling both the elevation angle- and azimuth-dependence of the tropospheric delay. Rather than applying the
ray-traced slant delays directly, the delay has been parameterized in terms of slant factors, which are applied in a similar
manner to traditional mapping functions, but which can account for the azimuthal asymmetry of the delay. Five strategies are
considered: (1) Vienna Mapping Functions 1 (VMF1) and estimation of a residual zenith delay parameter; (2) VMF1, estimation
of a residual zenith delay and estimation of two tropospheric gradient parameters; (3) three-dimensional ray-traced slant
factors and estimation of a residual zenith delay; (4) using only ray-traced slant factors and no estimation of any tropospheric
parameters and; (5) using both ray-traced slant factors and estimating a residual zenith delay and two tropospheric gradient
parameters. The use of the ray-traced slant factors (solution 3) showed a 3.8% improvement in the repeatability of the up
component when compared to the assumption of a symmetric atmosphere (solution 1), while the estimation of two tropospheric
gradient parameters gave the best results showing an 7.6% improvement over solution 1 in the up component. Solution 4 performed
well in the horizontal domain, allowing for sub-centimeter repeatability but the up component was degraded due to deficiencies
in the modeling of the zenith delay, particularly for stations located at equatorial latitudes. The magnitude of the differences
in the mean coordinates between solution 2 and solution 3, and the strong correlation with the differences between the north
component and the ray-traced gradients (coefficient of correlation of 0.83), as well as the impact of observation geometry
on the gradient solution indicate that the use of the ray-traced slant factors could have an implication on the realization
of reference frames. The estimated tropospheric products from the PPP solutions were compared to those derived from ray tracing.
For the zenith delay, a root mean square (RMS) of 5.4 mm was found, while for the gradient terms, a correlation coefficient
of 0.46 for the N–S and 0.42 for the E–W was found for the north–south and east–west components, suggesting that there are
still important differences in the gradient parameters which could be due to either errors in the NWM or to non-tropospheric
error sources leaking into the PPP-estimated gradients. 相似文献