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211.
A numerical model has been developed for the simulation of turbidity currents driven by nonuniform, non cohesive sediment and flowing over a complex three dimensional submarine topography. The model is based on an alternative approach known as Cellular Automata paradigm. The model is validated by comparing a simulation with a reported field-scale event. The chosen case is a turbidity current which occurred in Capbreton Canyon and was initiated by a storm in December 1999. Using data from recent oceanographic cruises, the deposit of the event has been precisely described, which constrain values of model parameters. The model simulates the 1999 turbidity current over the actual canyon topography and related turbidite using three different types of particle. The model successfully simulates areas of erosion and deposition in the canyon. It predicts the vertical and longitudinal grain size evolution, and shows that the fining-up sequence can be deposited by several phases of deposition and erosion related to the current energetic variation during its evolution. This result could explain the presence of intrabed contacts or the frequent lack of facies in Bouma sequences. 相似文献
212.
213.
Carlos Sainz Ismael Fuente Luis Quindós Jose Luis Gutierrez Jose Luis Arteche Luis Santiago Quindós 《Acta Geophysica》2010,58(5):957-962
People working with ionising radiation are receiving radiation coming from artificial and natural sources. In Spain, as in
many other countries, there is a serious control by the national authorities, Spanish Nuclear Safety Council, of the dose
the workers receive from artificial sources. However, until the publication of the European Basic Safety Standards Directive,
96/29/EURATOM, the old criteria referring to the “above natural background” were widely used. This directive was incorporated
to the Spanish legislation in July 2001 (BOE 178); in its Title VII it recommends to evaluate the dose coming from natural
sources and take it into account for establishing the safety criteria. It is noteworthy to assess the natural doses received
at homes and the dose received by workers of radioactive installations subject to regulations, and to compare the two results.
The social and economical implications of the results derived can be important in the practical application of the recommendations
included in the above-mentioned BOE 178 Directive. 相似文献
214.
Francisco Mota de Sá Mónica Amaral Ferreira Carlos Sousa Oliveira 《Bulletin of Earthquake Engineering》2016,14(7):2047-2067
Earthquakes are a permanent threat to urban environments worldwide. The communication of the related risk demands accurate damage model simulations and an interactive visualization of results. The aim of this paper is to provide a realistic problem-solving environment for earthquake discussions among decision makers, stakeholders, and the general public. QuakeIST® is an integrated earthquake simulator developed by Instituto Superior Técnico (Lisbon University), oriented towards the performance of risk calculations concerning damage propagations that use the Disruption Index concept. This software imports data stored in a GIS environment, handles different ground motion scenarios, and deals with a complex situation of different soils and vulnerabilities of various layers of civil structures (buildings, lifelines, and other urban structures). It models interdependencies between several infrastructures and between infrastructures and the urban tissue. The computer programme is very versatile, written in separate modules, allowing an experimented user to incorporate new formulations. Results can be treated with any statistical application and most common GIS commercial environments can produced their geographic visualization. Current progress and new upcoming are briefly described at the end of the paper. 相似文献
215.
216.
217.
The viability of a complete structural characterization of civil structures is explored and discussed. In particular, the identification of modal (i.e. natural frequencies, damping ratios and modal shapes) and physical properties (i.e. mass and stiffness) using only the structure’s free decay response is studied. To accomplish this, modal analysis from free vibration response only (MAFVRO) and mass modification (MM) methodologies are engaged along with Wavelet based techniques for optimal signal processing and modal reconstruction. The methodologies are evaluated using simulated and experimental data. The simulated data are extracted from a simple elastic model of a 5 story shear building and from a more realistic nonlinear model of a RC frame structure. The experimental data are gathered from shake table test of a 2-story scaled shear building. Guidelines for the reconstruction procedure from the data are proposed as the quality of the identified properties is shown to be governed by adequate selection of the frequency bands and optimal modal shape reconstruction. Moreover, in cases where the structure has undergone damage, the proposed identification scheme can also be applied for preliminary assessment of structural health. 相似文献
218.
Marianne Holmer Núria Marbà Morgane Lamote Carlos M. Duarte 《Estuaries and Coasts》2009,32(3):456-466
Species of the macroalgae Caulerpa sp. are increasingly being observed in meadows of the endemic Mediterranean seagrass Posidonia oceanica, and in particular Caulerpa taxifolia, has been considered as an invasive species leading to seagrass decline. Studies have so far failed to reveal the underlying
mechanisms of the success of the macroalgae, and here, we examine how biogeochemical changes of the environment associated
to indigenous (Caulerpa prolifera) and non-indigenous (Caulerpa racemosa and C. taxifolia) species affect the habitat of P. oceanica. Two of the species (C. prolifera and C. racemosa) affect the sediment biogeochemical conditions by increasing organic matter pools, microbial activity, and sulfide pools
of the sediments, and limited effects were found for C. taxifolia. Biomass of the macroalgae contributed to the extent of impacts, and high sulfide invasion into the seagrasses and regression
of the meadow were pronounced at the location with the highest Caulerpa biomass. This suggests that Caulerpa invasion contributes to seagrass decline probably because Caulerpa thrives better than the seagrasses in the modified environment. 相似文献
219.
Carlos M. Duarte Daniel J. Conley Jacob Carstensen María Sánchez-Camacho 《Estuaries and Coasts》2009,32(1):29-36
The implicit assumption of many scientific and regulatory frameworks that ecosystems impacted by human pressures may be reverted
to their original condition by suppressing the pressure was tested using coastal eutrophication. The response to nutrient
abatement of four thoroughly studied coastal ecosystems that received increased nutrient inputs between the 1970s and the
1980s showed that the trajectories of these ecosystems were not directly reversible. All four ecosystems displayed convoluted
trajectories that failed to return to the reference status upon nutrient reduction. This failure is proposed to result from
the broad changes in environmental conditions, all affecting ecosystem dynamics, that occurred over the 30 years spanning
from the onset of eutrophication to the reduction of nutrient levels. Understanding ecosystem response to multiple shifting
baselines is essential to set reliable targets for restoration efforts. 相似文献
220.
Anisotropic visco-hypoplasticity 总被引:5,自引:5,他引:0
Andrzej Niemunis Carlos Eduardo Grandas-Tavera Luis Felipe Prada-Sarmiento 《Acta Geotechnica》2009,4(4):293-314
Apart from time-driven creep or relaxation, most viscoplastic models (without plastic and viscous strain separation) generate
no or a very limited accumulation of strain or stress due to cyclic loading. Such pseudo-relaxation (or pseudo-creep) is either
absent or dwindles too fast with increasing OCR. For example, the accumulation of the pore water pressure and eventual liquefaction
due to cyclic loading cannot be adequately reproduced. The proposed combination of a viscous model and a hypoplastic model
can circumvent this problem. The novel visco-hypoplasticity model presented in the paper is based on an anisotropic preconsolidation
surface. It can distinguish between the undrained strength upon triaxial vertical loading and horizontal loading. The strain-induced
anisotropy is described using a second-order structure tensor. The implicit time integration with the consistent Jacobian
matrix is presented. For the tensorial manipulation including numerous Fréchet derivatives, a special package has been developed
within the algebra program MATHEMATICA (registered trade mark of Wolfram Research Inc.). The results can be conveniently coded using a special FORTRAN 90 module for tensorial operations. Simulations of element tests from biaxial apparatus and FE calculations are also shown. 相似文献