The dynamic response of a three-leg articulated tower

Articulated towers are a compliant type of platform particularly suited for deep water applications. In the design of articulated towers, it is very important that the motion characteristics include sufficient stability, less acceleration in the deck and the smallest possible loading on the articulated joint. The mass distribution along the tower also plays an important role in the motion characteristics of the tower. Multi-leg articulated towers with three or more towers (legs or shafts), which have been developed from the conventional single tower have reduced horizontal movements and have more deck area compared to the single-leg articulated towers. The experimental and analytical investigations on such towers are not available in the published literature. In this paper, both analytical treatment and an experimental program for a three-leg articulated tower model have been reported. The effect of mass distributions on the variations of the bending moment and the deck accelerations are also presented. The model has been tested in a 2 m wave flume for various wave frequencies and wave heights of regular waves. The model is also analysed using a computer program developed, and the comparison of theoretical results with the experimental results is presented.     

新疆中强震预报的探讨

利用物理意义清晰、彼此间及与地震目录关联度小的预测方法,进行了在新疆预测中强地震及其发震地点和发震条件的探讨.结果表明:3级地震频次维持3个月以上低值和5级地震维持6个月平静反映了6级以上地震的中短期发震背景,地震对应率大于83%;将地震活跃期6级地震发生后3个月内研究区发生的4级地震作为响应地震,其250 km范围内一年内发生中强震的为62%,两年内发生中强震的为79%;以响应区6值出现低值一回返作为预备震源可能发震的条件,其后一年内发震的为75%,2年内发震的为92%.     

论金铜钨锡成矿与花岗岩的关系

金铜钨锡成矿与花岗岩的关系是学术界关心的话题。按照流行的岩浆热液成矿理论,钨锡是高温热液矿床,金铜是中温热液矿床,铅锌是低温热液矿床,它们与花岗岩时空和成因有关,可以围绕岩体分布,近岩体处为钨锡,向外为金铜,远处为铅锌。在一个成矿带中,钨锡金铜铅锌可以共存,且有众多矿床实例为佐证。我们的研究表明,金铜与埃达克型和喜马拉雅型花岗岩有关,形成于加厚地壳;钨锡与南岭型花岗岩有关,形成于减薄的地壳。在一个地区同时不可能地壳又加厚又减薄,因此,埃达克型花岗岩与南岭型花岗岩不可能同时同地共存,所以,在一个地区不可能同时既有金铜又有钨锡成矿,大量矿床实例也证明金铜与钨锡是相悖的。至于在许多地方出现的金铜钨锡铅锌等在一起的现象,可能有两种解释:要么它们是不同时代成矿互相叠加在一起的;要么它们正好处于地壳厚度急剧变化的地方。为了查明金铜钨锡成矿究竟是相伴还是相悖的,至少需要掌握3个方面的资料:(1)不同矿床成矿的时代;(2)不同矿床与花岗岩的关系及花岗岩的地球化学特征和同位素年龄;(3)不同矿床的成因及矿床类型。     

An approach to digitize analog form of accelerograms recorded at Tarbela—Pakistan

Pakistan has a long history of seismological activity. The devastation caused by Kashmir earthquake has been administered all over the world. In Pakistan first seismological network, consisting of analog accelerograms and seismographs, was setup in early 1969 at Tarbela, where the largest water reservoir of the country is located. An approach to convert analog ground motion records into digital form is explained using a simple technique. The digitized data was compared with the original analog record and found in good agreement. The data has been used to plot response spectra. The digitized data will be available for seismic response analysis of structures and seismic risk analysis of the region.     

安徽庐枞盆地西湾铅锌矿床闪锌矿中镉的赋存状态和富集机制研究

镉(Cd)是一种重要的关键金属元素, 对国家安全和新兴产业发展具有重大意义。闪锌矿是最具经济意义的富镉矿物, 查明闪锌矿中镉的赋存状态, 对研究镉的富集机制具有重要的意义; 但受限于研究手段, 闪锌矿纳米尺度上镉的赋存状态研究仍相对薄弱。西湾矿床是长江中下游成矿带庐枞矿集区内新发现的大型铅锌矿床, 矿床中产出富镉闪锌矿。本次研究使用LA-ICP-MS对闪锌矿进行原位微量元素含量和Mapping分析, 查明闪锌矿微米尺度镉的分布规律; 在此基础上使用扫描透射电镜(STEM)查明纳米级闪锌矿的微观形貌和高分辨原子像, 明确纳米尺度镉的赋存状态。研究结果表明, 西湾矿床闪锌矿中镉含量的变化范围为2186×10^-6~9859×10^-6, 镉在闪锌矿中分布不均匀, 闪锌矿孔洞发育的区域相对富镉, 而闪锌矿均质区域相对贫镉。通过高分辨原子像的晶面间距和原子线扫描结果, 确定西湾矿床闪锌矿中Cd原子以原位替代Zn原子的形式赋存在闪锌矿晶格中, 未发现纳米级镉的独立矿物。对比金顶和牛角塘等富镉铅锌矿床, 长江中下游成矿带的铅锌矿床中平均镉含量不高, 推测成矿带可能缺乏充足的镉物质来源。

     

羌塘盆地中生代钾盐矿成矿预测

位于青藏高原腹地的羌塘盆地是我国最大的中生代海相含油气盆地,盆地发育多套生储盖组合,其中蒸发岩的膏盐层往往作为油气藏研究的盖层。但盆地内蒸发岩大多只达到硫酸盐沉积阶段,盆地内是否存在古钾盐矿？最佳的钾盐矿成矿有利区域具体位于何处？保存的远景资源量有多少？通过青藏高原形成过程中微地块的碰撞和拼合历史。研究羌塘盆地中生代沉积和演化过程,厘清羌塘盆地钾盐主要富集在中生代侏罗系的局限台地相区域。结合地震勘探和构造演化史恢复,阐明只有在逆冲推覆构造之下的区域才可能保存钾盐矿。根据羌塘盆地侏罗系夏里组沉积相带分布范围,推测保存钾盐矿的两个有利区主要位于安多县北西方向,面积约8 000 km²。综合地表膏盐层分布和地球物理勘探推断的羌塘盆地中侏罗统石膏层厚度分布图,根据海水中析出石膏和钾盐的比例,结合推覆构造对侏罗系夏里组的保存比例,推测羌塘盆地保存的钾盐资源量约为11亿吨。该研究为进一步勘查古钾盐矿提供了明确的范围和方向。     

中国萤石矿床流体包裹体研究进展

流体包裹体研究是揭示成矿流体来源与演化的重要手段,而萤石是流体包裹体研究的理想对象。本文选取中国主要萤石矿集区32个典型矿床为研究对象,总结了流体包裹体岩相学特征,并按不同矿床类型统计原生流体包裹体显微测温结果,探讨了萤石沉淀成矿机制。结果表明,岩浆期后热液型、火山—次火山热液型及热卤水型萤石矿床流体包裹体均一温度（集中在120℃~240℃）、密度（主要为0.8~1.0 g/cm³）相近,热卤水型萤石矿床成矿流体盐度高于岩浆期后热液型和火山—次火山热液型矿床。从成矿早期到晚期,大多数矿床成矿流体的盐度、温度逐渐降低。中国萤石矿床总体呈现浅成低温热液成矿的特征。地质事实和已有文献资料表明,萤石沉淀成矿的主要的机制可能不是水—岩反应,而是降温冷却和流体混合,不同矿床萤石主要沉淀成矿机制可能不同。水—岩反应主要在成矿物质集聚过程起重要作用。在总结前人研究的基础上,本文认为当前萤石矿床流体包裹体研究面临的主要问题是：1）流体包裹体组合（FIA）方法在显微测温上应用不足;2）流体包裹体成分分析以定性为主;3）成矿压力、深度估算方法适用性较低。针对这些问题,提出了相应的解决建议,以期推动萤石矿床流体包裹体研究进一步发展。

     

A study of the seismic response of the city of Benevento (Southern Italy) through a combined analysis of seismological and geological data

A previous analysis [Improta, L., G. Di Giulio, and A. Rovelli (2005). Variations of local seismic response in Benevento (Southern Italy) using earthquakes and ambient noise recordings, J. Seism. 9, 191–210.] of small magnitude earthquakes recorded at 12 sites within the city of Benevento has stressed the significant role played by near-surface geology in causing variability of the ground motion. In this paper, we extend the study of the seismic response from 12 sites to the entire urban area. Based on inferences from the comparison at the 12 sites between earthquake and ambient vibration results, we have collected ambient noise at about 100 sites within the city, intensifying measurements across the main shallow geological variations. We use borehole data to interpret ambient noise H/V spectral ratios in terms of near-surface geology comparing H/V curves to theoretical transfer functions of 1D models along five well-constrained profiles.

On the basis of geological, geotechnical, and seismic data, we identify three main typologies of seismic response in the city. Each type of response is associated to zones sharing common soil conditions and similar soil classes according to building codes for seismic design. Moreover, we find that the spatial variation of the seismic response in the ancient town area is consistent with the damage pattern produced by a very destructive, well-documented historical earthquake that struck the city in 1688, causing MCS intensity of IX–X in Benevento.

Finally, we use ground motions recorded during the experiment by Improta et al. [Improta, L., G. Di Giulio, and A. Rovelli (2005). Variations of local seismic response in Benevento (Southern Italy) using earthquakes and ambient noise recordings, J. Seism. 9, 191–210.] to generate synthetic seismograms of moderate to strong (Mw 5.7, Molise 2002 and Ms 6.9, 1980 Irpinia) earthquakes. We calibrate the random summation technique by Ordaz et al. [Ordaz, M., J. Arboleda, and S.K. Singh (1995). A scheme of random summation of an Empirical Green's Function to estimate ground motions for future large earthquakes, Bull. Seism. Soc. Am. 85, 1635–1647.] using recordings of these earthquakes available in Benevento. After a satisfactory fit between observed and synthetic seismograms, we compute response spectra at different sites and speculate on effects of the geology class at large level of shaking, including soil nonlinearity. We find that large discrepancies from design spectra prescribed by seismic codes can occur for a wide sector of Benevento, especially for periods < 0.5 s.     

基于ANSYS和响应面法的抗滑桩结构可靠性分析

在深入分析可靠度指标的几何意义和响应面法的基本思想的基础上,提出了基于ANSYS和响应面法的可靠度算法与步骤。分析了陕西省吴起县大路沟巨型黄土滑坡的工程地质条件,根据滑坡的工程地质勘察资料和滑坡治理工程的设计资料,建立了基于ANSYS的抗滑桩桩土体系有限元模型,经过自重作用下桩土结构有限元分析,验证了该有限元模型的有效性。在此基础上,选取滑体土重度、滑面土内聚力c和内摩擦角、滑面以下土的压缩模量Es;4个随机变量,基于响应面(中心复合设计CCD)法和通用有限元软件ANSYS平台,建立了抗滑桩的可靠度分析模型,并研制了对应算法。工程算例结果表明:当试验点数量N=25时,抗滑桩结构的失效概率Pf=0.35%,可靠度指标=2.70,从而验证了基于ANSYS和CCD响应面法建立抗滑桩可靠度计算模型及算法是可行的。     

西藏尼雄矿田滚纠铁矿成矿作用机制：来自矿物学和稳定同位素证据

本文分析了冈底斯成矿带西段尼雄矿田滚纠铁矿石榴子石、辉石、绿泥石成因矿物学特征,结果显示矿区石榴子石多为钙铁榴石,并存在一定量的钙铝榴石;辉石主要为透辉石、次透辉石和铁次透辉石,表明成矿流体早期为酸性、高温和高氧逸度环境。矽卡岩内接触带富钙铝榴石,外接触带富钙铁榴石,反映成矿流体由矽卡岩内接触带运移至矽卡岩外接触带过程中,温度逐渐降低,而pH和氧逸度逐渐升高。绿泥石主要为富铁贫镁的铁镁绿泥石,其在低温(206~268℃)、低pH值、还原环境下形成。方解石C-O同位素揭示成矿流体δ¹³C_∑C为-2.6‰~-0.7‰,δ¹⁸O_V-SMOW为+9.8‰~+12.0‰。石榴子石、磁铁矿、石英δD_V-SMOW值为-121‰~-105‰,成矿流体δ¹⁸O_H2O为8.7‰~11.3‰,反映成矿流体主要来源于花岗质岩浆。磁铁矿矿石中黄铁矿弱富铁亏硫,S/Fe为1.05~1.07,Co/Ni>1,指示为岩浆热液成因;黄铁矿δ³⁴S为4.2‰~11.1‰,与花岗质岩浆硫相当,综合反映成矿物质也来源于花岗质岩浆。结合前人研究资料,认为高温、高氧逸度使金属元素大量进入岩浆,岩浆上升侵位、分异出富含成矿物质的流体。成矿流体运移过程中遭遇围岩,并与之反应形成矽卡岩和退化蚀变矿物,导致成矿流体物理化学性质改变,在温度(180~400℃)、氧化-弱氧化和弱碱性-碱性条件下,发生磁铁矿沉淀。