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61.
Within the framework of activities of the EC funded Project ‘Processes of Vertical Exchange in Shelf Seas’ (PROVESS), the seasonal thermal behaviour during 1998 at a station in the North Sea has been investigated using COHERENS, a three-dimensional fully non-linear hydrodynamic model. Extensive hydrographic measurements were carried out at the Northern North Sea (NNS) station, located at (59°20′N, 1°E). The collected data are used to validate the model results, showing an acceptable agreement between modelled temperatures and those obtained from CTDs and moored thermistors. This is valid both for surface and bottom temperatures, while the mixed layer thickness appears to be underestimated. A series of 3-D runs, testing different turbulence schemes, an internal wave mixing (IWM) parameterisation and the sensitivity to an increase of the surface stress, have been performed with the aim of assessing the relative importance of the advective and mixing processes. The model comparisons mostly evidenced differences in the behaviour of the bottom layer temperature during the last part of the year, which may be due to advection processes. The adoption of an internal wave mixing parameterisation, though managing to reproduce a deeper thermocline, overestimates the mixing around the period of the thermocline breakdown. The run adopting a wind stress increased by 50% provides a better agreement between observed and modelled thermocline. This applies also for surface velocities when compared to Acoustic Doppler Current Profiler (ADCP) measurements, while the bottom ones appear slightly underestimated only in the U-component. The Northern North Sea site appears to be located close to a gyre induced by thermal fronts. Comparisons with nearby wind data measured by an oil rig and by the ships operating in the area seem to confirm that the wind forcing values adopted during the integration are underestimated. 相似文献
62.
63.
Sandro Rinaldi Sihem Louati Hocine Bendjoudi Ghislain de Marsily 《Hydrogeology Journal》2014,22(4):943-956
Industrially sourced dense non-aqueous phase liquids (DNAPLs) contaminated an alluvial aquifer in France decades ago. The location(s) and nature of the pollution source zone(s) were unknown, and the dissolved concentrations of volatile organic compounds in the monitoring wells varied greatly with time. The aquifer was in hydraulic equilibrium with an artificial canal whose water level was highly variable (up to 5 m). These variations propagated into the aquifer, causing changes in the groundwater flow direction; a transient numerical model of flow and solute transport showed that they correlate with the concentration variations because the changes in the flow direction resulted in the contaminant plume shifting. The transient hydrogeological numerical model was built, taking into account solvent biodegradation with first-order chain, since biodegradation has a significant influence on the pollutant concentration evolution. The model parameterization confirms the position of the source zones among the potential troughs in the bedrock where DNAPLs could have accumulated. The groundwater model was successfully calibrated to reproduce the observed concentration variations over several years and allowed a rapid validation of the hypotheses on the functioning of the polluted system. 相似文献
64.
65.
A number of parameterisations for the simulation of mixing processes in the thermocline are compared and tested against the microstructure data of the PROVESS campaigns, conducted in the northern part of the North Sea during the autumn of 1998. The transport term in the turbulent kinetic energy equation is parameterised via the introduction of a third stability function Sk for turbulent energy diffusion. The formulations are compared with a simpler scheme based upon limiting conditions for turbulence variables. Improved results are obtained with a new form of Sk. The best agreement is, however, found with the simpler limiting scheme. This is explained in terms of a turbulence length scale theory for stably stratified turbulence. In agreement with previous laboratory and ocean data it is found that the ratios of the Thorpe and Kolmogorov scales to the Ozmidov length scale approach critical limiting values in the thermocline. The first of these conditions is satisfied when limiting conditions are implemented into the scheme, providing the necessary minimum value for the dissipation rate, whereas the schemes without limiting conditions fail to produce this critical ratio. The basic reason for this failure is that the Thorpe scale is overestimated, which is shown to be connected to an even larger overprediction of the dissipation rate of temperature variance. To investigate the impact of non-resolved advective processes and salinity stratification on the turbulence predictions, additional numerical experiments were conducted using a simple scheme for data assimilation. The best agreement is found again with the limiting scheme, which is able to make reasonable predictions for the dissipation rate without knowing the detailed shape of the mean stratification profile. It is shown that advective transport due to tidally and wind-driven motions has a non-negligible impact on vertical mixing. This is seen in the data and the models by periodic enhancements of turbulent mixing inside the thermocline. 相似文献
66.
Rodolfo Puglia Dario Albarello Antonella Gorini Lucia Luzi Sandro Marcucci Francesca Pacor 《Bulletin of Earthquake Engineering》2011,9(6):1821-1838
This paper describes the analyses of the single-station ambient-vibration measurements performed on the Italian accelerometric
network to detect site resonance phenomena potentially affecting earthquake recordings. The use of low cost, high quality
microtremor measurement can be helpful to discriminate among soil classes, since several classification schemes based on resonance
frequencies were proposed in the last decades. Operatively, in the framework of the Italian Strong Motion Database project
(DPC-INGV 2007–2009 S4; ), soil resonance frequencies have been evaluated from more than 200 ambient vibration measurements in correspondence of accelerometric
stations included in ITACA (). The noise recordings have been analyzed using the same numerical protocol in order to standardize the results. Particular
attention has been paid to evaluate the quality of measurements and to develop an on-purpose mathematical tool to automatically
estimate the peaks in the horizontal-to-vertical spectral ratio (HVSR) curve. The reliability of the resonance frequencies
from HVSR has been tested by comparing estimates provided by independent methods (modeling or earthquake recordings). The
test confirmed the reliability of the microtremor HVSR for assessing the resonance frequencies of the examined sites. 相似文献
67.
Use of biomarkers indices in a sediment core to evaluate potential pollution sources in a subtropical reservoir in Brazil 总被引:1,自引:0,他引:1
The presence of PAHs, n-alkanes, pristane, and phytanes in core sediment from the Vossoroca reservoir (Parana, southern Brazil) was investigated. The total concentration of the 16 PAHs varied from 15.5 to 1646 μg kg−1. Naphthalene was present in all layers (3.34–74.0 μg kg−1). The most abundant and dominant n-alkanes were n-C15 and n-C36, with average concentrations of 198.1 ± 46.8 and 522.9 ± 167.7 μg kg−1, respectively. Lighter n-alkanes were distributed more evenly through the layers and showed less variation, specially n-C9, n-C12, and n-C18, with average concentrations of 14.6 ± 3.0, 31.6 ± 1.9, and 95.0 ± 5.2 μg kg−1, respectively; heavier n-alkanes were more unevenly distributed. 相似文献
68.
The Italian strong motion network 总被引:2,自引:2,他引:0
Antonella Gorini Mario Nicoletti Paolo Marsan Riccardo Bianconi Rita De Nardis Luisa Filippi Sandro Marcucci Franco Palma Elisa Zambonelli 《Bulletin of Earthquake Engineering》2010,8(5):1075-1090
The Italian Strong Motion Network is a permanent monitoring system run by the Italian national emergency management department
(Dipartimento della Protezione Civile, DPC). The network is known as RAN (Rete Accelerometrica Nazionale). An extensive project
for updating and improving the technology of RAN instruments as well as the number of recording points was performed in the
last 10 years. A wide site selection survey was carried out from eastern Sicily along the Italian peninsula, covering high
seismic risk areas. The recording station density and the choice of high-quality digital strong motion instruments ensure
reliability of the RAN network in the long-term. At the end of 2008, the free field sites selection and instruments installation,
planned in the project, were quite completed. In planning and drawing the new RAN, special attention has been devoted to the
robustness of the transmission systems, and to the distribution of new stations in order to ensure plenty of data during a
seismic emergency. We spent special care both in the estimation of the RAN site responses and in the diffusion of the strong
motion data. In order to better identify damaged earthquake areas, improved ground motion parameters need to be set. Such
parameters will also assist future progress for engineering seismic design techniques as well as disaster mitigation. 相似文献
69.
The paper presents a numerical model for the dynamic analysis of pile groups with inclined piles in horizontally layered soil deposits. Piles are modelled with Euler–Bernoulli beams, while the soil is supposed to be constituted by independent infinite viscoelastic horizontal layers. The pile–soil–pile interaction as well as the hysteretic and geometric damping is taken into account by means of two‐dimensional elastodynamic Green's functions. Piles cap is considered by introducing a rigid constraint; the condensation of the problem permits a consistent derivation of both the dynamic impedance matrix of the soil–foundation system and the foundation input motion. These quantities are those used to perform inertial soil–structure interaction analyses in the framework of the substructure approach. Furthermore, the model allows evaluating the kinematic stress resultants in piles resulting from waves propagating in the soil deposit, taking into account the pile–soil–pile interactions. The model validation is carried out by performing accuracy analyses and comparing results in terms of dynamic impedance functions, kinematic response parameters and pile stress resultants, with those furnished by 3D refined finite element models. To this purpose, classical elastodynamic solutions are adopted to define the soil–pile interaction problem. The model results in low computational demands without significant loss of precision, compared with more rigorous approaches or refined finite element models. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
70.
Debora Bellafiore Edoardo Bucchignani Silvio Gualdi Sandro Carniel Vladimir Djurdjević Georg Umgiesser 《Ocean Dynamics》2012,62(4):555-568
Modeling studies of future changes in coastal hydrodynamics, in terms of storm surges and wave climate, need appropriate wind
and atmospheric forcings, a necessary requirement for the realistic reproduction of the statistics and the resolution of small
scale features. This work compares meteorological results from different climate models in the Mediterranean area, with a
focus on the Adriatic Sea, in order to assess their capability to reproduce coastal meteorological features and their possibility
to be used as forcings for hydrodynamic simulations. Five meteorological datasets are considered. They are obtained from two
regional climate models, implemented with different spatial resolutions and setups and are downscaled from two different global
climate models. Wind and atmospheric pressure fields are compared with measurements at four stations along the Italian Adriatic
coast. The analysis is carried out both on simulations of the control period 1960–1990 and on the A1B Intergovernmental Panel
for Climate Change scenario projections (2070–2100), highlighting the ability of each model in reproducing the statistical
coastal meteorological behavior and possible changes. The importance of simulated global- and regional-scale meteorological
processes, in terms of correct spatial resolution of the phenomena, is also discussed. Within the Adriatic Sea, the meteorological
climate is influenced by the local orography that controls the strengthening of north-eastern katabatic winds like Bora. Results
show indeed that the increase in spatial resolution provides a more realistic wind forcing for the hydrodynamic simulations.
Moreover, the chosen setup and the global climate models that drive the regional downscalings appear to play an important
role in reproducing correct atmospheric pressure fields. The comparison between scenario and control simulations shows a small
increase in the mean atmospheric pressure values, while a decrease in mean wind speed and in extreme wind events is observed,
particularly for the datasets with higher spatial resolution. Finally, results suggest that an ensemble of downscaled climate
models is likely to provide the most suitable climatic forcings (wind and atmospheric pressure fields) for coastal hydrodynamic
modeling. 相似文献