Dynamic response and sliding distance of composite breakwaters under breaking and non-breaking wave attack     

Giovanni Cuomo  Giorgio Lupoi  Ken-ihiro Shimosako  Shigeo Takahashi 《Coastal Engineering》2011

Over the last 15 years improved awareness of wave impact induced failures has focused attention on the need to account for the dynamic response of maritime structures to wave impact load. In this work a non-linear model is introduced that allows evaluating the effective design load and the potential sliding of caisson breakwater subject to both pulsating and impulsive wave loads. The caisson dynamics is modelled using a time-step numerical method to solve numerically the equations of motion for a rigid body founded on multiple non-linear springs having both horizontal and vertical stiffness. The model is first shown to correctly describe the dynamics of caisson breakwaters subject to wave attack, including nonlinear features of wave–structure–soil interaction. Predictions of sliding distances by the new method are then compared with measurements from physical model tests, showing very good agreement with observations. The model succeeds in describing the physics that stands behind the process and is fast, accurate and flexible enough to be suitable for performance design of caisson breakwaters.  相似文献   

The development of the Space Environment Viability of Organics (SEVO) experiment aboard the Organism/Organic Exposure to Orbital Stresses (O/OREOS) satellite     

Nathan E. Bramall  Richard Quinn  Andrew Mattioda  Kathryn Bryson  Julie D. Chittenden  Amanda Cook  Cindy Taylor  Giovanni Minelli  Pascale Ehrenfreund  Antonio J. Ricco  David Squires  Orlando Santos  Charles Friedericks  David Landis  Nykola C. Jones  Farid Salama  Louis J. Allamandola  Søren V. Hoffmann 《Planetary and Space Science》2012,60(1):121-130

The Space Environment Viability of Organics (SEVO) experiment is one of two scientific payloads aboard the triple-cube satellite Organism/ORganic Exposure to Orbital Stresses (O/OREOS). O/OREOS is the first technology demonstration mission of the NASA Astrobiology Small Payloads Program. The 1-kg, 1000-cm³ SEVO cube is investigating the chemical evolution of organic materials in interstellar space and planetary environments by exposing organic molecules under controlled conditions directly to the low-Earth orbit (LEO) particle and electromagnetic radiation environment. O/OREOS was launched on November 19, 2010 into a 650-km, 72°-inclination orbit and has a nominal operational lifetime of six months. Four classes of organic compounds, namely an amino acid, a quinone, a polycyclic aromatic hydrocarbon (PAH), and a metallo-porphyrin are being studied. Initial reaction conditions were established by hermetically sealing the thin-film organic samples in self-contained micro-environments. Chemical changes in the samples caused by direct exposure to LEO radiation and by interactions with the irradiated microenvironments are monitored in situ by ultraviolet/visible/near-infrared (UV/VIS/NIR) absorption spectroscopy using a novel compact fixed-grating CCD spectrometer with the Sun as its light source. The goals of the O/OREOS mission include: (1) demonstrating key small satellite technologies that can enable future low-cost astrobiology experiments, (2) deploying a miniature UV/VIS/NIR spectrometer suitable for in-situ astrobiology and other scientific investigations, (3) testing the capability to establish a variety of experimental reaction conditions to enable the study of astrobiological processes on small satellites, and (4) measuring the chemical evolution of organic molecules in LEO under conditions that can be extrapolated to interstellar and planetary environments. In this paper, the science and technology development of the SEVO instrument payload and its measurements are described.  相似文献   

Artificial equilibrium points for a generalized sail in the elliptic restricted three-body problem     

Generoso Aliasi  Giovanni Mengali  Alessandro A. Quarta 《Celestial Mechanics and Dynamical Astronomy》2012,114(1-2):181-200

Different types of propulsion systems with continuous and purely radial thrust, whose modulus depends on the distance from a massive body, may be conveniently described within a single mathematical model by means of the concept of generalized sail. This paper discusses the existence and stability of artificial equilibrium points maintained by a generalized sail within an elliptic restricted three-body problem. Similar to the classical case in the absence of thrust, a generalized sail guarantees the existence of equilibrium points belonging only to the orbital plane of the two primaries. The geometrical loci of existing artificial equilibrium points are shown to coincide with those obtained for the circular three body problem when a non-uniformly rotating and pulsating coordinate system is chosen to describe the spacecraft motion. However, the generalized sail has to provide a periodically variable acceleration to maintain a given artificial equilibrium point. A linear stability analysis of the artificial equilibrium points is provided by means of the Floquet theory.  相似文献   

A Bonded Particle Model Simulation of Shear Strength and Asperity Degradation for Rough Rock Fractures   总被引：3，自引：3，他引：0  

Mohammad Sadegh Asadi  Vamegh Rasouli  Giovanni Barla 《Rock Mechanics and Rock Engineering》2012,45(5):649-675

Different failure modes during fracture shearing have been introduced including normal dilation or sliding, asperity cut-off and degradation. Attempts have been made to study these mechanisms using analytical, experimental and numerical methods. However, the majority of the existing models simplify the problem, which leads to unrealistic results. With this in mind, the aim of this paper is to simulate the mechanical behaviour of synthetic and rock fracture profiles during direct shear tests by using the two-dimensional particle flow computer code PFC2D. Correlations between the simulated peak shear strength and the fracture roughness parameter D _R1 recently proposed by Rasouli and Harrison (2010) are developed. Shear test simulations are carried out with PFC2D and the effects of the geometrical features as well as the model micro-properties on the fracture shear behaviour are studied. The shear strength and asperity degradation processes of synthetic profiles including triangular, sinusoidal and randomly generated profiles are analysed. Different failure modes including asperity sliding, cut-off, and asperity degradation are explicitly observed and compared with the available models. The D _R1 parameter is applied to the analysis of synthetic and rock fracture profiles. Accordingly, correlations are developed between D _R1 and the peak shear strength obtained from simulations and by using analytical solutions. The results are shown to be in good agreement with the basic understanding of rock fracture shear behaviour and asperity contact degradation.  相似文献   

Chromite alteration processes within Vourinos ophiolite     

Giovanni Grieco  Anna Merlini 《International Journal of Earth Sciences》2012,101(6):1523-1533

The renewed interest in chromite ore deposits is directly related to the increase in Cr price ruled by international market trends. Chromite, an accessory mineral in peridotites, is considered to be a petrogenetic indicator because its composition reflects the degree of partial melting that the mantle experienced while producing the chromium spinel-bearing rock (Burkhard in Geochim Cosmochim Acta 57:1297–1306, 1993). However, the understanding of chromite alteration and metamorphic modification is still controversial (e.g. Evans and Frost in Geochim Cosmochim Acta 39:959–972, 1975; Burkhard in Geochim Cosmochim Acta 57:1297–1306, 1993; Oze et al. in Am J Sci 304:67–101, 2004). Metamorphic alteration leads to major changes in chromite chemistry and to the growth of secondary phases such as ferritchromite and chlorite. In this study, we investigate the Vourinos complex chromitites (from the mines of Rizo, Aetoraches, Xerolivado and Potamia) with respect to textural and chemical analyses in order to highlight the most important trend of alteration related to chromite transformation. The present study has been partially funded by the Aliakmon project in collaboration between the Public Power Corporation of Greece and Institute of Geology and Mineral Exploration of Kozani.  相似文献   

Multitemporal Landsat-MODIS fusion for cropland drought monitoring in El Salvador     

Nguyen Thanh Son  Chi Farn Chen  Cheng Ru Chen  Mario Giovanni Molina Masferrer 《国际地球制图》2013,28(12):1363-1383

Abstract

This study aims to develop an approach to characterize cropland drought conditions in El Salvador, Central America. The data were processed for 2016–2017 through three main steps: (1) reconstructing MODIS land-surface temperature (LST), (2) Landsat-MODIS data fusion and (3) drought delineation using the temperature vegetation dryness index (TVDI). The results of LST reconstruction using the random forests (RF) indicated the median RMSE value of 0.5?°C. The fusion results achieved from the STARFM compared with the reference Landsat data revealed close agreement with the correlation coefficient (r) values higher than 0.84. The TVDI results verified with that from the reference Landsat data indicated r values of 0.85 and 0.75 for 2016 and 2017, respectively. The larger very dry area was observed for the 2016 primera season due to prolonged droughts. Approximately 11.5% and 10.7% of croplands were, respectively, associated with very dry moisture condition in the 2016 and 2017 primera seasons.  相似文献   

Modeling the morphodynamic response of tidal embayments to sea-level rise   总被引：1，自引：1，他引：0  

Barend van Maanen  Giovanni Coco  Karin R. Bryan  Carl T. Friedrichs 《Ocean Dynamics》2013,63(11-12):1249-1262

Sea-level rise has a strong influence on tidal systems, and a major focus of climate change effect studies is to predict the future state of these environmental systems. Here, we used a model to simulate the morphological evolution of tidal embayments and to explore their response to a rising sea level. The model was first used to reproduce the formation of channels and intertidal flats under a stable mean water level in an idealised and initially unchannelled tidal basin. A gradual rise in sea level was imposed once a well-developed channel network had formed. Simulations were conducted with different sea-level rise rates and tidal ranges. Sea-level rise forced headward erosion of the tidal channels, driving a landward expansion of the channel network and channel development in the previously non-inundated part of the basin. Simultaneously, an increase in channel drainage width in the lower part of the basin occurred and a decrease in the overall fraction of the basin occupied by channels could be observed. Sea-level rise thus altered important characteristics of the tidal channel network. Some intertidal areas were maintained despite a rising sea level. However, the size, shape, and location of the intertidal areas changed. In addition, sea-level rise affected the exchange of sediment between the different morphological elements. A shift from exporting to importing sediment as well as a reinforcement of the existing sediment export was observed for the simulations performed here. Sediment erosion in the inlet and the offshore transport of sediment was enhanced, resulting in the expansion of the ebb-tidal delta. Our model results further emphasise that tidal embayments can exhibit contrasting responses to sea-level rise.  相似文献   

The heartbeat of the volcano: The discovery of episodic activity at Prometheus on Io     

Ashley Gerard Davies  Lionel Wilson  Giovanni Leone  Windy Jaeger 《Icarus》2006,184(2):460-477

The temporal signature of thermal emission from a volcano is a valuable clue to the processes taking place both at and beneath the surface. The Galileo Near Infrared Mapping Spectrometer (NIMS) observed the volcano Prometheus, on the jovian moon Io, on multiple occasions between 1996 and 2002. The 5 micron (μm) brightness of this volcano shows considerable variation from orbit to orbit. Prometheus exhibits increases in thermal emission that indicate episodic (though non-periodic) effusive activity in a manner akin to the current Pu'u 'O'o-Kupaianaha (afterwards referred to as the Pu'u 'O'o) eruption of Kilauea, Hawai'i. The volume of material erupted during one Prometheus eruption episode (defined as the interval from minimum thermal emission to peak and back to minimum) from 6 November 1996 to 7 May 1997 is estimated to be ∼0.8 km³, with a peak instantaneous volumetric flux (effusion rate) of ∼140 m³ s⁻¹, and an averaged volumetric flux (eruption rate) of ∼49 m³ s⁻¹. These quantities are used to model subsurface structure, magma storage and magma supply mechanisms, and likely magma chamber depth. Prometheus appears to be supplied by magma from a relatively shallow magma chamber, with a roof at a minimum depth of ∼2-3 km and a maximum depth of ∼14 km. This is a much shallower depth range than sources of supply proposed for explosive, possibly ultramafic, eruptions at Pillan and Tvashtar. As Prometheus-type effusive activity is widespread on Io, shallow magma chambers containing magma of basaltic or near-basaltic composition and density may be common. This analysis strengthens the analogy between Prometheus and Pu'u 'O'o, at least in terms of eruption style. Even though the style of eruption appears to be similar (effusive emplacement of thin, insulated, compound pahoehoe flows) the scale of activity at Prometheus greatly exceeds current activity at Pu'u 'O'o in terms of volume erupted, area covered, and magma flux. Whereas the estimated magma chamber at Prometheus dwarfs the Pu'u 'O'o magma chamber, it fits within expectations if the Pu'u 'O'o chamber were scaled for the greater volumetric flux and lower gravity of Io. Recent volumetric eruption rates derived from Galileo data for Prometheus were considerably smaller than the rate that produced the extensive flows formed in the ∼17 years between the Voyager and Galileo missions. These smaller eruption rates, coupled with the fact that flows are not expanding laterally, may mean that the immediate heat source that generates the Prometheus plume is simultaneously running out of available volatiles and the thermal energy that drives mobilization of volatiles. This raises the question of whether the current Prometheus eruption is in its last throes.  相似文献   

The Ischia debris avalanche: first clear submarine evidence in the Mediterranean of a volcanic island prehistorical collapse     

Francesco Latino Chiocci  Giovanni De Alteriis 《地学学报》2006,18(3):202-209

Sector or flank collapse with related debris avalanches is increasingly recognized as a relatively common volcanic behaviour, in particular, for large, hot‐spot related oceanic islands. Here, we report the case of a catastrophic collapse that occurred at Ischia volcanic island in prehistorical times and was driven by the volcano‐tectonic uplift of Mt Epomeo, the major relief of the island. The collapse left a subaerial to submarine horseshoe scar on the southern flank of the island and generated a debris avalanche incorporating thousands of giant blocks dispersed as far as 50 km from the island. During the emplacement, part of the debris avalanche evolved into a debris flow covering an area of 250–300 km². This constitutes the first, clear evidence of a submarine debris avalanche in the Mediterranean Sea. The major collapse was followed, and probably also preceded, by recurrent, less catastrophic terrestrial and underwater failures. Two other undersea hummocky deposits are found north and west of the island and might tentatively be correlated to the major southern collapse. Such volcanic behaviour, previously unknown for Ischia Volcano, has likely triggered tsunami waves over the entire Bay of Naples raising the question of their impact on prehistorical/historical communities.  相似文献   

Geological structure of a long‐living geothermal system,Larderello, Italy     

Giovanni Bertini  Michele Casini  Giovanni Gianelli  Enrico Pandeli 《地学学报》2006,18(3):163-169

We have examined the data of 600 geothermal wells and re‐interpreted approximately 500 km seismic profiles through the field of Larderello, Italy. We conclude that the two main seismic reflectors present below the geothermal area host two different fluids: (1) superheated steam in the upper H‐horizon (reached by drillholes) and (2) supercritical fluid in the deeper K‐horizon (reached by few unproductive or damaged wells). The superheated steam has the physical and chemical connotation of the geothermal fluid exploited so far at Larderello, whereas the supercritical fluid represents a potential unconventional deep‐seated resource still to be assessed. The high temperatures existing in correspondence of the K‐horizon suggest that the silica‐rich rocks are close to a plastic state and the fluids should remain confined in a medium sealed to the confining rocks, unless occasional fluid overpressure and abrupt high strain rates occur.  相似文献