Nonlinear Model of Mean Free Surface of Waves     

Nicholas DODD 《中国海洋工程》1999,(2)

-A nonlinear model of mean free surface of waves or wave set-up is presented.The model isbased on that of Roelvink(1993),but the numerical techniques used in the solution are based on theWeighted-Average Flux(WAF)method(Watson et al,1992),with Time-Operator-Splitting(TOS)usedfor the treatment of the source terms.This method allows a small number of computational points to beused,and is particularly efficient in modeling wave set-up.The short wave(or primary wave)energy equa-tion is solved by use of a more traditional Lax-Wendroff technique.A nonlinear wave theory(James,1974)is introduced.The model described in this paper is found to be satisfactory in most respects whencompared with the measurements conducted by Stive(1983)except in modeling the mean free surface veryclose to the mean shoreline.  相似文献   

Influence of deterioration modelling on the seismic response of steel moment frames designed to Eurocode 8          下载免费PDF全文

Antonios Tsitos  Miguel A. Bravo‐Haro  Ahmed Y. Elghazouli 《地震工程与结构动力学》2018,47(2):356-376

This paper assesses the influence of cyclic and in‐cycle degradation on seismic drift demands in moment‐resisting steel frames (MRF) designed to Eurocode 8. The structural characteristics, ground motion frequency content, and level of inelasticity are the primary parameters considered. A set of single‐degree‐of‐freedom (SDOF) systems, subjected to varying levels of inelastic demands, is initially investigated followed by an extensive study on multi‐storey frames. The latter comprises a large number of incremental dynamic analyses (IDA) on 12 frames modelled with or without consideration of degradation effects. A suite of 56 far‐field ground motion records, appropriately scaled to simulate 4 levels of inelastic demand, is employed for the IDA. Characteristic results from a detailed parametric investigation show that maximum response in terms of global and inter‐storey drifts is notably affected by degradation phenomena, in addition to the earthquake frequency content and the scaled inelastic demands. Consistently, both SDOF and frame systems with fundamental periods shorter than the mean period of ground motion can experience higher lateral strength demands and seismic drifts than those of non‐degrading counterparts in the same period range. Also, degrading multi‐storey frames can exhibit distinctly different plastic mechanisms with concentration of drifts at lower levels. Importantly, degrading systems might reach a “near‐collapse” limit state at ductility demand levels comparable to or lower than the assumed design behaviour factor, a result with direct consequences on optimised design situations where over‐strength would be minimal. Finally, the implications of the findings with respect to design‐level limit states are discussed.  相似文献   

Oceanic influence on the precipitation in Venezuela under current and future climate     

Nele Tim  Lelys Bravo de Guenni 《Climate Dynamics》2016,47(1-2):211-234

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鲁西沂南金场夕卡岩型金铜矿床矿化时代与成矿流体研究   总被引：3，自引：1，他引：2  

胡芳芳  王永  范宏瑞  郑小礼  焦鹏 《岩石学报》2010,26(5):1503-1511

沂南金场金铜矿床是鲁西地区夕卡岩型矿床的典型代表,矿床产于燕山期中酸性杂岩体与新太古界-寒武系地层的内外接触带附近,受岩浆岩、地层岩性以及构造的复合控制。由石榴子石和透辉石构成了早夕卡岩阶段矿物组合,而绿帘石+磁铁矿+镜铁矿±透闪石±阳起石±石英构成了晚夕卡岩-磁铁矿阶段矿物组合。利用早夕卡岩期黑云母以及晚夕卡岩期与碳酸盐伴生的黑云母样品进行单颗粒云母超低本底Rb-Sr等时线测试,分别获得了133±6Ma和128±2Ma年龄数据,它们与金场岩体的形成时间十分一致,说明该矿床与侵入体有密切的成因联系。流体包裹体研究表明,沂南金场金铜矿床各成矿阶段矿石中的流体包裹体主要有四种类型:含子矿物三相包裹体、富气包裹体、H2O-CO2包裹体和气液两相包裹体。从早夕卡岩阶段石榴石捕获的含子矿物包裹体中获得了很高的均一温度(530～570℃)和盐度(39.9%～60.4%)值,而晚夕卡岩阶段透辉石中含子矿物包裹体也显示较高的均一温度(451～580℃)和盐度(39.3%～60.7%)值。石英-硫化物阶段石英中包裹体均一温度分为两个区间,分别为320～450℃和108～291℃。石榴石内含子矿物包裹体,其子矿物可能为赤铁矿或磁铁矿,结合该矿床的矿石矿物组成特征,沂南金场为岩浆热液流体形成的氧化型夕卡岩金铜矿床。  相似文献   

胶东石城金矿床成矿流体特征及成矿作用   总被引：1，自引：1，他引：0  

蓝廷广  范宏瑞  胡芳芳  杨奎锋  刘玄  刘振豪  宋玉波  于虎 《岩石学报》2010,26(5):1512-1522

石城金矿位于胶东牟平-乳山成矿带南端,为多金属硫化物型金矿床。其成矿流体阶段可分为3个,相应的流体包裹体特征为:(1)成矿早期(第1阶段)富CO2包裹体;(2)主成矿期(第2阶段)H2O包裹体和含CO2包裹体;(3)成矿后期(第3阶段)H2O包裹体。第1阶段均一温度为256～360℃,盐度3.71%～6.88%NaCl,第2阶段均一温度为168～270℃,盐度4.49%～10.24%NaCl,第3阶段均一温度为123～178℃,盐度0.35%～7.59%NaCl。其中主成矿期为中低温、低盐度的CO2-H2O-NaCl流体体系。H、O同位素表明石城金矿成矿流体为岩浆水与大气水形成的混合热液,C、O同位素则反映了地幔富CO2流体参与了成矿作用,而S同位素进一步揭示了金矿的成矿物质来源为壳幔相互作用的结果。石城金矿的出现表明研究区至少存在两期成矿事件,早期成矿时代约120Ma,主要为石英+黄铁矿型矿石,晚期成矿时代小于111Ma,主要为多金属硫化物型矿石,以石城金矿为代表。  相似文献   

白云鄂博地区碳酸岩脉侵位序列与稀土元素富集机制   总被引：5，自引：2，他引：3  

杨奎锋  范宏瑞  胡芳芳  王凯怡 《岩石学报》2010,26(5):1523-1539

白云鄂博地区发育大量的火成碳酸岩脉。按照矿物组成,碳酸岩脉可分为白云石型、白云石-方解石共存型和方解石型。野外穿插关系表明,白云石型碳酸岩脉形成得早,而方解石型碳酸岩脉形成得晚。白云鄂博地区的碳酸岩浆存在由白云石型到共存型再到方解石型的先后结晶顺序和演化趋势。碳酸岩脉的主量、稀土和微量元素组成特征表明,随着碳酸岩脉中方解石矿物组分的增加,轻稀土元素的含量呈明显富集趋势,而长期的结晶分异作用正是稀土元素,尤其是轻稀土元素在晚期岩浆中强烈富集的内在机制。  相似文献   

Evolution of polar coronal holes and sunspots during cycles 21 and 22     

S. Bravo  G. Stewart 《Solar physics》1994,154(2):377-384

A very good correlation between the evolution of polar coronal hole size and sunspot number half a solar cycle later was found by Bravo and Otaola for solar cycle 21. In this paper we use a more complete set of data to reanalyse the relationship for solar cycle 21 and investigate the same relationship for solar cycle 22. We find that the complete set of data for cycle 21 yields a slightly different time shift for the best correlation between sunspots and holes and that the time shift for cycle 22 is different from that of cycle 21. However, because of limited availability of data of cycle 22, we consider it necessary to wait until the end of this cycle in order to decide if the difference is statistically significant or not. We also found that the time between successive peaks of smoothed polar hole area and smoothed sunspot number is the same in both cycles. This may provide a useful tool for the forecasting of future sunspot maxima. The constant of proportionality between polar coronal hole area and sunspot number can be seen to be different in both cycles. We discuss this difference and interpret it in terms of a different magnitude of the polar field strength in the two cycles.  相似文献   

Community Structure of the Subtidal Macroinfauna in an Estuarine Mussel Bed in Southern Chile     

Eduardo  Jaramillo  Carlos  Bertrán Alejandro  Bravo 《Marine Ecology》1992,13(4):317-331

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SIXE: A Payload for MINISAT-02     

Jordi Gómez-Gomar  Jordi Isern  Eduardo Bravo  Franco Giovannelli  Cesare De La Padula 《Astrophysics and Space Science》1998,263(1-4):389-392

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Different Types of Coronal Mass Ejections At Minimum and Maximum of Solar Activity and Their Relation to Magnetic Field Evolution     

Bravo  S.  Blanco-Cano  X.  Nikiforova  E. 《Solar physics》1998,180(1-2):461-471

Coronal mass ejections (CMEs) are considered to be associated with large-scale, closed magnetic field structures in the corona. These structures change throughout the solar activity cycle following the evolution of the general solar magnetic field. To study the variation of CME characteristics with the evolution of coronal magnetic structures, we compute the 3-D coronal magnetic field at minimum and maximum of activity with a source-surface potential field model. In particular, we study the central latitude distribution of CMEs and the frequency of occurrence of the different CME types in these two periods. We find that most CMEs are indeed associated with large-scale, magnetically closed structures, and their latitudinal distribution follows the solar cycle latitudinal changes of the location of these structures. We also find that different CME types, which constitute different fractions of the total during the maximum and the minimum, are associated with different shapes and orientations of the closed structures at different times of the solar cycle.  相似文献