Dynamic amplification factors for a system with multiple-degrees-of-freedom     

Zhang Chao  Hao Hong  Bi Kaiming  Yan Xueyuan 《地震工程与工程振动(英文版)》2020,19(2):363-375

It is well-known that the responses of a structure are different when subjected to a static load or a sudden step load. The dynamic amplification factor (DAF), which is defined as the ratio of the amplitude of the vibratory response to the static response, is normally used to depict the dynamic effect. For a single-degree-of-freedom system (SDOF) subjected to a sudden dynamic load, the maximum value of DAF is 2. Many design guidelines therefore use 2 as an upper bound to consider the dynamic effect. For a civil engineering structure, which is normally a multiple-degrees-of-freedom (MDOF) system, the DAF may exceed 2 in certain circumstances. The adoption of 2 as the upper bond as suggested by the design guidelines therefore may lead to unsafe structural design. Very limited studies systematically investigate the DAF of a MDOF system. This study theoretically investigates the DAF of a MDOF system when it is subjected to a step load based on the fundamental theory of structural dynamics. The condition on which the DAF may exceed 2 is defined. Two numerical examples and one experimental study of a cable-stayed bridge subjected to sudden cable loss are presented to illustrate the problem.  相似文献   

Ground motion duration effect on responses of hydraulic shallow-buried tunnel under SV-waves excitations     

Sun  Benbo  Zhang  Sherong  Wang  Chao  Cui  Wei 《地震工程与工程振动(英文版)》2020,19(4):887-902

Although intensive research of the influence of ground motion duration on structural cumulative damage has been carried out, the influence of dynamic responses in underground tunnels remains a heated debate. This study attempts to highlight the importance of the ground motion duration effect on hydraulic tunnels subjected to deep-focus earthquakes. In the study, a set of 18 recorded accelerograms with a wide-range of durations were employed. A spectrally equivalent method serves to distinguish the effect of duration from other ground motion features, and then the seismic input model was simulated using SV-wave excitation based on a viscous-spring boundary, which was verified by the time-domain waves analysis method. The nonlinear analysis results demonstrate that the risk of collapse of the hydraulic tunnel is higher under long-duration ground motion than that of short-duration ground motion of the same seismic intensity. In a low intensity earthquake, the ground motion duration has little effect on the damage energy consumption of a hydraulic tunnel lining, but in a high intensity earthquake, dissipation of the damage energy and damage index of concrete shows a nonlinear growth trend accompanied by the increase of ground motion duration, which has a great influence on the deformation and stress of hydraulic tunnels, and correlation analysis shows that the correlation coefficient is greater than 0.8. Therefore, the duration of ground motion should be taken into consideration except for its intensity and frequency content in the design of hydraulic tunnel, and evaluation of seismic risk.

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Modeling the westward transversal current in the southern Yellow Sea entrance: a case study in winter 2007     

Ding  Yang  Bao  Xianwen  Zhou  Lingling  Bi  Congcong  Yao  Zhigang  Ma  Chao  Chu  Qinqin 《Ocean Dynamics》2020,70(6):803-825

Ocean Dynamics - The westward transversal current (TC) in the southern Yellow Sea entrance was investigated during winter 2007 using a numerical ocean model. The three-dimensional structures and...  相似文献   

2018年2月12日河北永清4.3级地震强震动记录分析     

郭秋娜  温超  周月玲  李姜 《震灾防御技术》2020,15(2):329-338

2018年2月12日河北省廊坊市永清县发生4.3级地震,震中位于廊固凹陷内的河西务断裂附近,国家强震动台网中心获取74组强震动记录,本文对触发台站进行场地分类,结果显示大部分为Ⅰ类场地(51.35%),其次为Ⅱ类场地(35.14%)和Ⅲ类场地(13.51%)。根据5个典型台站加速度时程记录及反应谱分析本次地震强震动特征,并对各台站峰值加速度反应谱与方位角和震中距的关系进行分析。采用克里格插值方法绘制地震仪器烈度分布图,由于台站分布不均,导致极震区附近烈度影响场计算缺值现象,本文通过拟合本次地震强震动记录得到该地区地震动衰减关系,在空白区域建立空间随机假设台站进行补点插值,解决了计算缺值问题,为缺少台站记录的震区提供准确快速制作烈度分布图的思路,为震害调查和地震应急救援提供重要依据。  相似文献   

Origin of the springtime South China Sea Warm Current in the southwestern Taiwan Strait: Evidence from seawater oxygen isotope     

Chen  Dongyu  Lian  Ergang  Shu  Yeqiang  Yang  Shouye  Li  Yalong  Li  Chao  Liu  Pengfei  Su  Ni 《中国科学:地球科学(英文版)》2020,63(10):1564-1576

Oxygen isotope(δ~(18)O) of seawater is an excellent proxy for tracing the origins of water masses and their mixing processes. Combining with hydrographic observation, hybrid coordinate ocean model(HYCOM) analysis data, and seawater oxygen isotope, we investigated the source of the South China Sea Warm Current(SCSWC) in the southwestern Taiwan Strait and its underlying mechanism. Results show that the Kuroshio subsurface water(KSSW) can intrude the continental slope in the southwestern Taiwan Strait, and thereby climb up the continental slope coupled with upwelling. The δ~(18)O-salinity relationship further indicates that in spring, the SCSWC in the southwestern Taiwan Strait originates from the upslope deflection of the slope current formed by the KSSW intrusion into the South China Sea, rather than from the west segment of the SCSWC formed to the east of Hainan Island. In addition, the southward flowing Zhe-Min Coastal Current(ZMCC) can reach as far as the Taiwan Bank(TB) and deflects offshore over the western TB at approximately 23.5°N, to some extent affecting the SCSWC. Moreover, this study reveals that seawater δ~(18)O is exquisitely sensitive to the determination of the origin and transport of water masses as compared with traditional potential temperature-salinity plot(θ-S) and HYCOM analysis data. In addition, their coupling can more reliably interpret the mixing processes of shelf water masses.  相似文献   

Metallogenesis and major challenges of porphyry copper systems above subduction zones   总被引：1，自引：0，他引：1  

Chen  Huayong  Wu  Chao 《中国科学:地球科学(英文版)》2020,63(7):899-918

Porphyry copper±molybdenum±gold deposits(PCDs) are the most representative magmatic-hydrothermal metallogenic system above subduction zones with important economic value. Previous studies revealed that large PCDs are generally formed from initial arc magmas(from subduction-induced partial melting of the mantle wedge), which eventually ascend to the shallow crust(3–5 km) for mineralization after a series of complex evolution processes. These processes include(1) the dehydration or partial melting of subducting slab, which induces partial melting of the metasomatized mantle wedge;(2)the ascent of mantle-derived magma to the bottom of the lower crust, which subsequently undergoes crustal processes such as assimilation plus fractional crystallization(AFC) or melting, assimilation, storage and homogenization(MASH);(3) the magma chamber formation at the bottom of the lower, middle and upper crust;(4) the final emplacement and volatilization of porphyry stocks; and(5) the accumulation of ore-forming fluids and metal precipitation. Despite the many decades of research, many issues involving the PCD metallogenic mechanism still remain to resolve, such as(1) the tectonic control on the geochemical characteristics of ore-forming magma;(2) the reason for the different lifespans of the long-term magmatic arc evolution and geologically "instantaneous" mineralization processes;(3) the source of ore-forming materials;(4) the relative contributions of metal pre-enrichment to mineralization by the magma source and by magmatic evolution; and(5) the decoupling behaviors of Cu and Au during the pre-enrichment. These issues point out the direction for future PCD metallogenic research, and the resolution to them will deepen our understanding of the metallogenesis at convergent plate boundaries.  相似文献   

人为干扰对越冬后期稻田中小天鹅(Cygnus columbianus)昼间能量消耗的影响     

于超  周立志  宋昀微 《湖泊科学》2019,31(1):195-201

能量的消耗模式是动物适合度的重要体现,动物的日常行为和栖息地特征共同影响日能量消耗.稻田生境是越冬水鸟重要的觅食场所之一,同时又容易受到人为干扰,越冬水鸟应对日间不同的人为干扰因素而合理进行能量消耗配置,对于在越冬后期为迁徙而贮备能量的水鸟来说尤为迫切和重要.本文采用焦点动物取样法,观测越冬后期稻田中小天鹅（Cygnus columbianus）在干扰和非干扰环境中昼间行为的时间分配,推算其能量消耗.结果表明,小天鹅在干扰环境中警戒行为的时间分配和能量消耗、单次警戒时间和警戒频次均显著大于非干扰环境,游泳频次也是如此;在稻田中的昼间警戒能耗随干扰时间增加而增加,随干扰距离增加而降低.干扰造成小天鹅减少高能耗的取食行为,增加低能耗的警戒行为,降低昼间总能量的消耗.  相似文献   

TOVS水汽及演的误差分析及其订正          下载免费PDF全文

王超  张凤英 《应用气象学报》1996,(3)

该文利用同步物理反演法以６小时数值预报场为背景场对１９９２年１月份ＮＯＡＡ－１２卫星垂直探测（ＴＯＶＳ）资料进行了大气参数反演，并对水汽反演误差进行了检验和分析．以常规观测作为检验的标准，检验结果按３条轨道统计，发现反演的相对湿度平均误差与背景场的误差密切相关，均为负值；在高层和高纬度，误差绝对值随高度的增加而增加，随纬度的升高而增加；误差的日际变化在高层比较稳定，低层振动较大．对反演误差进行订正后的结果表明，在５００ｈＰａ以上反演均比背景质量要好，尤其轨道Ａ所有层次上订正后的反演比背景场好．  相似文献   

湖泊沉积有机碳同位素与环境变化的研究进展   总被引：22，自引：2，他引：20  

余俊清  王小燕  李军  安芷生 《湖泊科学》2001,13(1):72-78

湖泊沉积有机质稳定碳同位素（δ^13Corg)在区域气候与环境变化方面的应用近年来发展迅速,成果令人瞩目,保存在各类湖泊岩芯中的δ^13Corg记录揭示了晚更新世以来大气CO2浓度的变化、湖泊水位波动、湖区生态与植被的变迁以及气温变化等重要环境信息,由于造成δ^13Corg值变化的影响因素较多,确定个湖与环境变化有关的主导因素时常有赖于其它证据的帮助,诸如地球化学、古湖沼学、孢粉学、分子同位素地层学等等,前人通过研究来自不同类型湖泊、具不同曲线形态特征的δ^13Corg记录,提出了多种环境解释模型,本文对此作了归纳和评述。鉴别和澄清湖泊沉积有机质的源物质以及有机物源随环境变化而发生过的变化,是研究δ^13Corg记录环境意义至关重要的基础性工作,由于有机质含量、碳氮比值、氢指数、生物残留物鉴别等常能提供有关有关湖泊有机质来源、产率、成岩作用等方面的有用信息,这方面的研究结果应该尽可能一并提供,以利于恰当地应用现有的环境解释模型,或者建立个湖新模型,单体生物标志化合物鉴别通常也能为区分湖积有机质中陆生、水生、细菌生等不同碳的来源提供有用信息,特定化合物同位素分析技术近年来成功地应用于建立单体生物标志化合物碳同位素地层学,为湖积有机碳同位素在生态环境演变研究方面的应用提供了思路,我国许多湖泊的湖底沉积岩芯尚未钻取,那些对过去全球变化研究有价值的δ^13Corg记录有待我们去获取和研究。  相似文献   

双平板式透空堤消能效果评价方法     

张之晨  李雪艳  王庆  高浩杰  谢天  战超  王玉坤 《海洋科学》2021,45(4):159-169

双平板式透空堤具有较为优越的消浪性能备受专家学者关注。目前关于其消浪性能的评价多采用透射波高法开展,仅考虑波高一个参数。本文采用透射波高法、波浪能量法和波能流法分别对平板式透空堤的消能效果进行评价,结果表明,综合考虑波高、水深和周期三个参数的波能流法更加全面与深入。探讨了双平板式透空堤迎浪向与背浪向处波能流的主要影响因素,结果表明,相对板宽、位置参数和波高大小对波能流的影响较板间距和潜深更加显著。  相似文献