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71.
The dynamics of jacket supported offshore wind turbine (OWT) in earthquake environment is one of the progressing focuses in the renewable energy field. Soil-structure interaction (SSI) is a fundamental principle to analyze stability and safety of the structure. This study focuses on the performance of the multiple tuned mass damper (MTMD) in minimizing the dynamic responses of the structures objected to seismic loads combined with static wind and wave loads. Response surface methodology (RSM) has been applied to design the MTMD parameters. The analyses have been performed under two different boundary conditions: fixed base (without SSI) and flexible base (with SSI). Two vibration modes of the structure have been suppressed by multi-mode vibration control principle in both cases. The effectiveness of the MTMD in reducing the dynamic response of the structure is presented. The dynamic SSI plays an important role in the seismic behavior of the jacket supported OWT, especially resting on the soft soil deposit. Finally, it shows that excluding the SSI effect could be the reason of overestimating the MTMD performance. 相似文献
72.
73.
The effects of a building's density on urban flows are investigated using a CFD model with the
RNG k-ε turbulence closure scheme. Twenty-seven cases with different building's density parameters
(e.g., building and street-canyon aspect ratios) are numerically simulated. As the building's density parameters
vary, different flow regimes appear. When the street canyon is relatively narrow and high, two counter-rotating
vortices in the vertical direction are generated. The wind speed along streets is mainly affected by the
building's length. However, it is very difficult to find or generalize the characteristics of the street-canyon
flows in terms of a single building's density parameter. This is because the complicated flow patterns appear
due to the variation of the vortex structure and vortex number. Volume-averaged vorticity magnitude is a very
good indicator to reflect the flow characteristics despite the strong dependency of flows on the variation of
the building's density parameters. Multi-linear regression shows that the volume-averaged vorticity magnitude
is a strong function of the building's length and the street-canyon width. The increase in the building's
length decreases the vorticity of the street-canyon flow, while, the increase in the street-canyon width
increases the vorticity. 相似文献
74.
韩国济洲岛下西归浦组的时代归属一直存在着争论。该段地层中浮游有孔虫 Globigerina calida calida、Beella digitata、 Globigerina bermudezi和 Globoquadrina conglomerata的发现表明了它应为中更新世 (晚 N 2 2带、即 Globigerina calida calida亚带 ,不晚于 40万年前 )的沉积。底栖、浮游有孔虫的定量统计分析揭示了下西归浦组沉积环境的变化 :下部的沉积环境为岸外中陆架暖水 ,而向上则演变成近岸内陆架温凉水。有孔虫组合的更替反映了下西归浦组沉积是一个由次一级的 3个亚海退和 2个亚海进组成的海退序列。 相似文献
75.
朝鲜半岛北部显生宙花岗岩成因研究及地质意义 总被引:1,自引:3,他引:1
朝鲜半岛北部图们江褶皱带和冠帽地块发育大面积的花岗岩,长期被认为形成于晚古生代二叠纪-早中生代三叠纪。采用锆石原位微区U-Pb测年技术(SIMS U-Pb),对6个代表性岩体的16个样品进行了侵位年龄测定,结合早期发表的年代学数据,确定朝鲜北部花岗岩主要形成于中生代的侏罗纪(199~173Ma),少部分为晚二叠世(265~263Ma)和早三叠世(248~240Ma)。岩石学及地球化学特征表明,朝鲜北部花岗岩以钙-碱性岩石系列为主,其成因类型为I型,且少数为高分异I型。锆石Hf-O同位素特征明显分为两类:图们江褶皱带及冠帽地块中的侏罗纪花岗岩、冠帽地块中晚二叠世片麻状花岗岩具有正的εH f(t)值(4.7~13.5)和年轻的二阶段Hf模式年龄(367~784Ma),O同位素组成δ~(18)O集中分布在5.7‰~7.4‰,表明其源区物质为新生地壳,且该地壳物质来自于亏损型的软流圈地幔;而冠帽地块中晚二叠世和早三叠世花岗岩通常具有负的εH f(t)值(-10.9~3.8)和古老的二阶段Hf模式年龄(889~1651Ma),O同位素组成变化较大,δ~(18)O分布在5.6‰~9.2‰,推测其主要为古老地壳物质重熔的产物。区域对比研究表明,图们江褶皱带和冠帽地块具有相同的地质演化历史,应归属于同一个整体,其上发育的花岗岩与我国吉黑造山带花岗岩在年代学格架、岩石学及地球化学特征、成因类型及岩浆源区都具有极大的相似性,可以进行对比。由此可见,朝鲜北部图们江褶皱带和冠帽地块为中亚造山带的组成部分,且朝鲜北部晚二叠世-早三叠世花岗岩形成于古亚洲洋闭合阶段,由于西伯利亚板块与华北板块的碰撞拼合,在华北地台北缘形成了同碰撞型花岗岩。侏罗纪中国东北及朝鲜开始进入环太平洋构造域演化阶段,在太平洋板块俯冲的挤压体制下形成大面积花岗岩。 相似文献
76.
朝鲜狼林地体是中朝克拉通的重要组成部分,其早前寒武纪基底岩系的岩石组成、形成和变质作用时代,直接影响到人们对古元古代辽吉活动带乃至整个华北克拉通地质演化历史的理解和认识。本文选取位于狼林地块东南缘,狼林群变质杂岩中的3个花岗片麻岩样品进行锆石U-Pb定年分析。锆石的LA-ICPMS和SIMS定年结果显示,3个片麻岩原岩的岩浆结晶时代为2521~2567Ma,并且它们都经历了古元古代1.87~1.89Ga的构造热事件改造,表现为原始岩浆锆石不同程度的铅丢失以及变质锆石的形成。基于这一认识,并结合其他学者的最新研究结果可知,太古宙片麻岩存在于狼林地块平南盆地的南缘和东缘地区,由此推测狼林地块太古宙基底岩系的规模可能远大于目前所识别的这几个地区。这些太古宙片麻岩普遍遭受了古元古代强烈变质作用(深熔作用)改造,并且变质作用的时代可以与华北克拉通三条古元古代活动带的变质-深熔作用时代相对比,表明狼林地块可能至少在古元古代之前,就已经与华北克拉通组成了统一的大陆。 相似文献
77.
安徽铜陵地区中酸性侵入岩及其岩石包体中的矿物包裹体研究 总被引:14,自引:2,他引:14
铜陵地区是长江中、下游铁、铜、硫、金成矿带的重要组成部分。笔者对铜陵地区中酸性侵入岩及其岩石包体中的包裹体进行了较系统的岩相学、显微测温和激光拉曼光谱研究。通过岩相学观察发现了 3类包裹体 ,即晶质熔融包裹体、流体熔融包裹体和流体包裹体。显微测温资料表明 ,本区的岩浆流体成矿演化可分为 3个阶段 :岩浆阶段 ( >12 5 0~ 90 0℃± )、过渡岩浆阶段 ( 90 0~ 75 0℃± )和岩浆期后热液阶段 ( <75 0℃ )。部分熔浆的温度之高 (可达 12 5 0℃ ) ,表明其可能是底侵幔源岩浆同熔下地壳形成的。在老庙基岩体、小铜官山岩体、鸡冠石岩体和小陶家岩体中产有晶质熔融包裹体、流体熔融包裹体和流体包裹体这 3种包裹体 ,表明相应的岩浆流体演化具有连续性、继承性和阶段性 ,其对应的成矿溶液以岩浆热液为主 ;与此不同的是 ,在鸡冠山岩体和白芒山岩体中仅产有晶质熔融包裹体和流体包裹体两种类型的包裹体 ,表明相应的岩浆流体演化不具连续性 ,其对应的成矿溶液以天水热液为主。此外 ,在小铜官山岩体和鸡冠石岩体的中酸性侵入岩中 ,发现了不混溶包裹体 ,其可能是在压力释放条件下形成的。 相似文献
78.
79.
KIM AARIS-SBRENSEN 《Boreas: An International Journal of Quaternary Research》1995,24(4):355-365
Investigations at a Late Weichselian freshwater basin in northwestern Jutland, Denmark, yielded a fairly rich assemblage of vertebrate remains, mostly bones and teeth of small mammals. The remains are primarily allochthonous and the bones have been subjected to different taphonomic pathways and agents. AMS 14 C-dates on terrestrial organic remains provided ages of Middle to Late Allerød time. Identifications revealed the first fossil record in Scandinavia of Rana arvalis, Sorex minutus, Ochotona cf. pusilla, Microtus gregalis, Microtus oeconomus , and Sicista cf. betulinu. Spermophilus cf. major and Desmana moschata , previously found only once and twice respectively, were retrieved, and Sorex araneus and Arvicola terrestris were recovered for the first time beyond the Atlantic chronozone. Ecologically, the Nørre Lyngby small mammal fauna can be characterized by its very high and almost equal proportions of boreal forest and steppe elements followed by a relatively high proportion of tundra elements. The fossil species share a modern area of sympatry north of the Caspian Sea from the river Volga in the west to the southern and western slopes of the Urals. If, however, the large Allerød mammals are added, the fauna is without modern analogues. The Nørre Lyngby fauna can be seen as a last expansion of the North European glacial fauna. Provided that an absolute chronology and a differentiated sea-level curve for the area can be established, the Nsrre Lyngby fauna could become important for studies in mammalian dispersal and migration rates. 相似文献
80.
Based on the maximum-entropy(ME)principle,a new power spectral estimator for random waves is derived in the form of S~(ω)=a/8H~2(2π)~(d 1)ω~-~((d 2))exp[-b(2π/ω)~n],by solving a variational problem subject to some quite general constraints.This robust method is comprehensive enough to describe the wave spectra even in extreme wave conditions and is superior to periodogram method that is not suitable to process comparatively short or intensively unsteady signals for its tremendous boundary effect and some inherent defects of FFT.Fortunately,the newly derived method for spectral estimation works fairly well,even though the sample data sets are very short and unsteady,and the reliability and efficiency of this spectral estimator have been preliminarily proved. 相似文献