Temporal variation of modulated-wave-train geometries and their influence on vertical bending moments of a container ship     

《Applied Ocean Research》2019

A towing experiment was conducted using a modulated wave train to investigate the vertical bending responses of a hydro-structural container ship model. In the experiment, a spatially periodic modulated wave train, as a model of a freak wave in successive high waves mimicking the so-called three sisters, was generated by the recently established higher-order spectral method wave generation (HOSM-WG) method. HOSM-WG enables us to control the location and timing of the maximum crest height in a wave tank. With precise control of the towing carriage, an experiment was conducted in which the timing of the encounters between the ship model and the modulated wave train was accurately determined. The maximum sagging moment (SM) was found to increase in proportion with the encounter wave height. However, because of differences in the relative depth of the fore and aft troughs, the maximum SM is highly variable for a given wave height. The temporal wave-geometry evolution caused the relative trough-depth to vary significantly within a wave period in the vicinity of the maximum crest height. As a result, depending on the encounter timing, the SM varied considerably for a given wave height. The temporal variation of the wave geometry is a robust feature of a modulated wave train and is common between the spatially periodic and temporally periodic modulated wave trains.  相似文献   

CFD modelling of a small–scale fixed multi–chamber OWC device     

《Applied Ocean Research》2019

Wave Energy Converters (WECs) have excellent potential as a source of renewable energy that is yet to be commercially realised. Recent attention has focused on the installation of Oscillating Water Column (OWC) devices as a part of harbor walls to provide advantages of cost–sharing structures and proximity of power generation facilities to existing infrastructure. In this paper, an incompressible three–dimensional CFD model is constructed to simulate a fixed Multi–Chamber OWC (MC–OWC) device. The CFD model is validated; the simulation results are found to be in good agreement with experimental results obtained from a scale physical model tested in a wave tank. The validated CFD model is then used for a benchmark study of 96 numerical tests. These investigate the effects of the PTO damping caused by the power take–off (PTO) system on device performance. The performance is assessed for a range of regular wave heights and periods. The results demonstrate that a PTO system with an intermediate damping can be used for all chambers in the MC–OWC device for most wave period ranges, except for the long wave periods. These require a higher PTO damping. An increased incident wave height reduces the device capture width ratio, but there is a noticeable improvement for long wave periods.  相似文献   

深海滑坡灾害的物质点法模拟     

董友扣  马家杰  王栋  RANDOLPH Mark 《海洋工程》2019,37(5):141-147

深海滑坡可以沿着斜坡搬运大量沉积物,是危害巨大的海洋地质灾害之一。评估深海滑坡的流滑机制并量化分析其对海底结构物的冲击对海洋资源的开发利用至关重要。采用物质点法对滑坡的滑动特性进行了总应力分析。设计了三组不同的土体、海床参数,展现了三种不同的滑动形态:延展、块体和扩张。随后复现了流滑体对部分暴露管线的冲击过程,并对冲击力的稳定值进行了分析,分析中考虑了流滑体的惯性、抗剪强度和静压力的影响。研究表明,物质点法能够用于模拟深海滑坡的流滑过程及其对海底结构物的冲击,可以为海洋工程中的实际设计工作提供服务。  相似文献   

Thorium-poor monazite and columbite-(Fe) mineralization in the Gleibat Lafhouda carbonatite and its associated iron-oxide-apatite deposit of the Ouled Dlim Massif,South Morocco     

《Gondwana Research》2020

Recent exploration work in South Morocco revealed the occurrence of several carbonatite bodies, including the Paleoproterozoic Gleibat Lafhouda magnesiocarbonatite and its associated iron oxide mineralization, recognized here as iron-oxide-apatite (IOA) deposit type. The Gleibat Lafhouda intrusion is hosted by Archean gneiss and schist and not visibly associated with alkaline rocks. Metasomatized micaceous rocks occur locally at the margins of the carbonatite outcrop and were identified as glimmerite fenite type. Rare earth element (REE) and Nb mineralization is mainly linked to the associated IOA mineralization and is represented by monazite-(Ce) and columbite-(Fe) as major ore minerals. The IOA mineralization mainly consists of magnetite and hematite that usually contain large apatite crystals, quartz and some dolomite. Monazite-(Ce) is closely associated with fluorapatite and occurs as inclusions within the altered parts of apatite and along cracks or as separate phases near apatite. Monazite shows no zonation patterns and very low Th contents (<0.4 wt%), which would be beneficial for commercial extraction of the REE and which indicates monazite formation from apatite as a result of hydrothermal volatile-rich fluids. Similar monazite-apatite mineralization and chemistry also occurs at depth within the carbonatite, although the outcropping carbonatite is barren, suggesting an irregular REE ore distribution within the carbonatite body. The barren carbonatite contains some tiny unidentified secondary Nb-Ta-U phases, synchysite and monazite. Niobium mineralization is commonly represented by anhedral minerals of columbite-(Fe) which occur closely associated with magnetite-hematite and host up to 78 wt% Nb₂O₅, 7 wt% Ta₂O₅ and 1.6 wt% Sc₂O₃. This association may suggest that columbite-(Fe) precipitated by an interaction of Nb-rich fluids with pre-existing Fe-rich minerals or as pseudomorphs after pre-existing Nb minerals like pyrochlore. Our results most strongly suggest that the studied mineralization is economically important and warrants both, further research and exploration with the ultimate goal of mineral extraction.  相似文献   

On the linear elastic responses of the 2D bonded discrete element model     

Gao-Feng Zhao  Qiuyue Yin  Adrian R. Russell  Yingchun Li  Wei Wu  Qin Li 《国际地质力学数值与分析法杂志》2019,43(1):166-182

The bonded discrete element model (DEM) is a numerical tool that is becoming widely used when studying fracturing, fragmentation, and failure of solids in various disciplines. However, its abilities to solve elastic problems are usually overlooked. In this work, the main features of the 2D bonded DEM which influence Poisson's ratio and Young's modulus, and accuracy when solving elastic boundary value problems, are investigated. Outputs of numerical simulations using the 2D bonded DEM, the finite element method, a hyper elasticity analysis, and the distinct lattice spring model (DLSM) are compared in the investigation. It is shown that a shear interaction (local) factor and a geometric (global) factor are two essential elements for the 2D bonded DEM to reproduce a full range of Poisson's ratios. It is also found that the 2D bonded DEM might be unable to reproduce the correct displacements for elastic boundary value problems when the represented Poisson's ratio is close to 0.5 or the long-range interaction is considered. In addition, an analytical relationship between the shear stiffness ratio and the Poisson's ratio, derived from a hyper elasticity analysis and applicable to discontinuum-based models, provides good agreement with outputs from the 2D bonded DEM and DLSM. Finally, it is shown that the selection of elastic parameters used the 2D bonded DEM has a significant effect on fracturing and fragment patterns of solids.  相似文献   

Extracting energy while reducing hydroelastic responses of VLFS using a modular raft wec-type attachment     

《Applied Ocean Research》2019

This paper presents the use of a modular raft Wave Energy Converter (WEC)-type attachment at the fore edge of a rectangular Very Large Floating Structure (VLFS) for extracting wave energy while reducing hydroelastic responses of the VLFS under wave action. The proposed modular attachment comprises multiple independent auxiliary pontoons (i.e. modules) that are connected to the fore edge of the VLFS with hinges and linear Power Take-Off (PTO) systems. For the hydroelastic analysis, the auxiliary pontoons and the VLFS are modelled by using the Mindlin plate theory while the linear wave theory is used for modelling the fluid motion. The analysis is performed in the frequency domain using the hybrid Finite Element-Boundary Element (FE-BE) method. Parametric studies are carried out to investigate the effects of pontoon length, PTO damping coefficient, gap between auxiliary pontoons, and incident wave angle on the power capture factor as well as reductions in the hydroelastic responses of the VLFS with the modular attachment. It is found that in oblique waves, the modular attachment comprising multiple narrow pontoons outperforms the corresponding rigid attachment that consists of a single wide pontoon with respect to the power capture factor and the reduction in the deflection of the VLFS. In addition, it is possible to have a considerable gap between pontoons without significantly compromising the effectiveness of the modular attachment.  相似文献   

Tectonomagmatic evolution of a Jurassic Cordilleran flare-up along the Korean Peninsula: Geochronological and geochemical constraints from granitoid rocks     

《Gondwana Research》2020

This study used new and published U-Pb geochronological, chemical, and Sr-Nd-Hf-O isotopic data (n > 2500) from Jurassic granite-granodiorite-diorite-monzonite-gabbro plutons in the southern part of the Korean Peninsula to assess the spatiotemporal evolution of a flare-up magmatism, its tectonic connection, and specific contributions of mantle and crustal reservoirs to the magmas generated. After a ~15 m.y. magmatic gap in the Late Triassic, calc-alkaline granitoids intruded into the outboard Yeongnam Massif, then magmatic activity migrated systematically toward the inboard Gyeonggi Massif. The early phase of the Jurassic magmatism is represented by relatively sodic plutons showing distinctly primitive isotopic signatures. The crustal signature of the plutons became increasingly prominent with decreasing age. Voluminous inboard plutons in the Gyeonggi Massif and the intervening Okcheon Belt are dominated by Middle Jurassic peraluminous granites that show isotopic compositions conspicuously shifted toward old crustal values. The Nd-Hf isotopic compositions of the inboard plutons are distinctly less radiogenic than those of Jurassic plutons in Southwest Japan and southeastern China, which corroborates the North China affinity of the Yeongnam and Gyeonggi massifs. The geochronological and geochemical data compiled in this study suggest a tectonomagmatic model consisting sequentially of (1) an extension-dominated arc system in the margin of the Yeongnam Massif (ca. 200–190 Ma); (2) low-angle subduction and the development of an advancing arc system (ca. 190–180 Ma); (3) continued low-angle subduction, extensive underthrusting of fertile crustal materials to the arc root, and consequent magmatic flare-up (ca. 180–170 Ma); and (4) flat subduction and the development of the Honam Shear Zone (ca. 170–160 Ma). The subsequent magmatic lull and previous dating results for synkinematic rocks and minerals indicate that the compressional arc system was maintained until the Early Cretaceous.  相似文献   

Zircon provenances provide paleogeographic constraints on models reconstructing the Paleoproterozoic Columbia Supercontinent     

《Gondwana Research》2020

Paleoproterozoic orogens of the North Australian Craton are related to the assembly of the Columbia Supercontinent. The roles of the distinct orogens in the Paleoproterozoic craton amalgamation are poorly understood due to the lack of surface exposure. The age and isotopic systematics of detrital zircon grains hosted in Paleoproterozoic sedimentary sequences are used to unravel the geological history of the craton, in terms of paleogeography and tectonic setting. The oldest (Early Paleoproterozoic) metasedimentary units are characterised by detrital zircon ages peaking at ca. 2500 Ma. The zircon ε_Hf values show large variations in the different orogens and range from −18 to +6. The overlaying youngest turbiditic units show minor accumulation of Archean detritus. Units from apparently different metasedimentary sequences have a major detrital zircon age population at ca. 1865 Ma, and a relatively restricted range of zircon ε_Hf values between −7.3 and +2.6. The isotopic distinctiveness of the oldest units is attributed to local variations in the depositional environment, probably due to horst-graben architecture of the early Paleoproterozoic basin. The youngest turbiditic units blanketed this early horst-graben architecture and in part have a local provenance. Potential detritus sources include South Australian Craton, Dharwar Craton and Aravalli-Lesser Himalayan terrains in India, South China, and Madagascar (Africa). This finding indicates that these regions might have been connected before the Columbia Supercontinent was formed. The ubiquitous ca. 2500 Ma magmatic event records the assembly of these cratonic fragments in a previous supercontinent called Kernorland. In addition, the data do not support a proximity of the North Australian Craton with the North China Block, Western Laurentia (North America), and Kaapvaal Craton (Africa) during Columbia amalgamation.  相似文献   

Towards Quantifying the Likelihood of Water Resource Impacts from Unconventional Gas Development     

Margaret Shanafield  Peter G. Cook  Craig T. Simmons 《Ground water》2019,57(4):547-561

Gas production from unconventional reservoirs has led to widespread environmental concerns. Despite several excellent reviews of various potential impacts to water resources from unconventional gas production, no study has systematically and quantitatively assessed the potential for these impacts to occur. We use empirical evidence and numerical and analytical models to quantify the likelihood of surface water and groundwater contamination, and shallow aquifer depletion from unconventional gas developments. These likelihoods are not intended to be exact. They provide a starting point for comparing the probabilities of adverse impacts between types of water resources and pathways. This analysis provides much needed insight into what are “probable” rather than simply “possible” impacts. The results suggest that the most likely water resource impacts are surface water and groundwater contamination from spills at the well pad, which can be as high as 1 in 10 and 1 in 100 for each gas well, respectively. For wells that are hydraulically fractured, the likelihood of contamination due to inter-aquifer leakage is 1 in 10⁶ or lower (dependent on the separation distance between the production formation and the aquifer). For gas-bearing formations that were initially over-pressurized, the potential for contamination from inter-aquifer leakage after production ceases could be as high as 1 in 400 where the separation between gas formation and shallow aquifer is 500 m, but will be much lower for greater separation distances (more characteristic of shale gas).  相似文献   

Assessing the performance of a large-scale irrigation system by estimations of actual evapotranspiration obtained by Landsat satellite images resampled with cubic convolution     

《International Journal of Applied Earth Observation and Geoinformation》2019

Remote sensing techniques allow monitoring the Earth surface and acquiring worthwhile information that can be used efficiently in agro-hydrological systems. Satellite images associated to computational models represent reliable resources to estimate actual evapotranspiration fluxes, ET_a, based on surface energy balance. The knowledge of ET_a and its spatial distribution is crucial for a broad range of applications at different scales, from fields to large irrigation districts. In single plots and/or in irrigation districts, linking water volumes delivered to the plots with the estimations of remote sensed ET_a can have a great potential to develop new cost-effective indicators of irrigation performance, as well as to increase water use efficiency. With the aim to assess the irrigation system performance and the opportunities to save irrigation water resources at the “SAT Llano Verde” district in Albacete, Castilla-La Mancha (Spain), the Surface Energy Balance Algorithm for Land (SEBAL) was applied on cloud-free Landsat 5 Thematic Mapper (TM) images, processed by cubic convolution resampling method, for three irrigation seasons (May to September 2006, 2007 and 2008). The model allowed quantifying instantaneous, daily, monthly and seasonal ET_a over the irrigation district. The comparison between monthly irrigation volumes distributed by each hydrant and the corresponding spatially averaged ET_a, obtained by assuming an overall efficiency of irrigation network equal to 85%, allowed the assessment of the irrigation system performance for the area served by each hydrant, as well as for the whole irrigation district. It was observed that in all the investigated years, irrigation volumes applied monthly by farmers resulted generally higher than the corresponding evapotranspiration fluxes retrieved by SEBAL, with the exception of May, in which abundant rainfall occurred. When considering the entire irrigation seasons, it was demonstrated that a considerable amount of water could have been saved in the district, respectively equal to 26.2, 28.0 and 16.4% of the total water consumption evaluated in the three years.  相似文献