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1.
以双座串联大跨度斜拉桥-珠海洪鹤大桥为背景,根据桥梁自振特性及场地效应,生成了三组人工波,采用纵向+2/3竖向的地震作用组合输入方式,通过非线性时程分析,系统的研究了粘滞阻尼器对双座串联大跨度斜拉桥减震性能的影响。同时为了确定粘滞阻尼器的最优参数,对粘滞阻尼器的阻尼系数C和速度指数α进行了参数敏感性分析。结果表明:设置纵向粘滞阻尼器能够显著减小双座串联斜拉桥的纵向位移响应,减小主梁在串联处发生碰撞的概率,同时改善主塔塔底结构受力情况,具有良好的耗能减震效果。综合考虑安全性、适用性和经济性等方面,最后给出针对洪鹤大桥的最优粘滞阻尼器参数:速度指数α为0.3,阻尼系数C为3 000kN/(m/s)0.3。  相似文献   
2.
以线性粘滞阻尼器加固剪切型规则框架结构为研究对象,基于能量原理提出附加阻尼系数正比于层间位移平方的分配方式。以六层和十二层钢筋混凝土框架为例,以确保结构在中震时保持弹性状态为设计目标,分别采用附加阻尼系数正比于层间位移平方的分配方式以及现有的分配方式,对结构进行消能减震设计。计算结果表明:有控结构均满足中震不坏的要求,层间位移角限值均未超过1/550,减震效果良好;附加阻尼系数正比于层间位移平方的分配方式得出的总阻尼系数最小,为最经济的设计结果。  相似文献   
3.
为了评估水库诱发地震震级上限,收集了150余例水库诱发地震的震例资料;利用改进的层次分析法优化了各评价指标的权重;应用模糊综合评价方法评估了水库诱发地震震级上限;结合二滩水电站水库诱发地震实例与目前评估水库诱发地震震级最常用的灰色聚类分析法的评价结果进行了对比分析。结果表明:层次分析法与模糊综合评价相结合的震级上限评估方法评价结果更加可靠,可对水库及水工建筑物的建设位置及抗震设防提供参考。  相似文献   
4.
The internal energies and entropies of 21 well-known minerals were calculated using the density functional theory (DFT), viz. kyanite, sillimanite, andalusite, albite, microcline, forsterite, fayalite, diopside, jadeite, hedenbergite, pyrope, grossular, talc, pyrophyllite, phlogopite, annite, muscovite, brucite, portlandite, tremolite, and CaTiO3–perovskite. These thermodynamic quantities were then transformed into standard enthalpies of formation from the elements and standard entropies enabling a direct comparison with tabulated values. The deviations from reference enthalpy and entropy values are in the order of several kJ/mol and several J/mol/K, respectively, from which the former is more relevant. In the case of phase transitions, the DFT-computed thermodynamic data of involved phases turned out to be accurate and using them in phase diagram calculations yields reasonable results. This is shown for the Al2SiO5 polymorphs. The DFT-based phase boundaries are comparable to those derived from internally consistent thermodynamic data sets. They even suggest an improvement, because they agree with petrological observations concerning the coexistence of kyanite?+?quartz?+?corundum in high-grade metamorphic rocks, which are not reproduced correctly using internally consistent data sets. The DFT-derived thermodynamic data are also accurate enough for computing the P–T positions of reactions that are characterized by relatively large reaction enthalpies (>?100 kJ/mol), i.e., dehydration reactions. For reactions with small reaction enthalpies (a few kJ/mol), the DFT errors are too large. They, however, are still far better than enthalpy and entropy values obtained from estimation methods.  相似文献   
5.
6.
Compositional zoning and exsolution patterns of alkali feldspars in carbonatite-bearing cognate syenites from the 6.3 km3 (D.R.E) phonolitic Laacher See Tephra (LST) deposit in western Germany (12.9 ka) are reported. These rocks represent the cooler outer portion and crystal-rich products of a cooling magma reservoir at upper crustal levels. Major and trace-element difference between cores and rims in sanidine crystals represent two generations of crystal growth separated by unmixing of a carbonate melt. Trace-element differences measured by LA–ICP–MS are in accordance with silicate–carbonate unmixing. Across the core–rim boundary, we extracted gray-scale profiles from multiple accumulations of back-scattered electron images. Gray scales directly represent K/Na ratios owing to low concentrations of Ba and Sr (<?30 ppm). Diffusion gradients are modeled to solve for temperature using known pre-eruptive U–Th zircon ages (0–20 ky) of each sample (Schmitt et al., J Petrol 51:1053–1085, 2010). Estimated temperatures range from 630 °C to 670 °C. For the exsolution boundaries, a diffusive homogenization model is constrained by the solvus temperature of ~ 712_725 °C and gives short time scales of only 15–50 days. Based on our results, we present a model for the temperature–time history of these rocks. The model also constrains the thermal variation across the cooling crystal-rich carapace of the magma reservoir over 20 ka and suggests a thermal reactivation of cumulates, the cooling carapace, and probably the entire system only a few years prior to the explosive eruption of the remaining molten core of the phonolitic magma reservoir.  相似文献   
7.
This paper investigates the origin of low-δ18O quartz porphyry dykes associated with the 144–133 Ma Koegel Fontein Igneous Complex, which was intruded during the initial phase of breakup of Africa and South America. The 25-km diameter Rietpoort Granite is the largest and youngest phase of activity, and is roofed by a 10-km diameter pendant of gneiss. Quartz porphyry (QP) dykes, up to 15 m in width, strike NW–SE across the complex. The QP dykes that intruded outside the granite have similar quartz phenocryst δ18O values (average 8.0‰, ± 0.7, n?=?33) to the granite (average 8.3?±?1.0, n?=?7). The QP dykes that intruded the roof pendant have quartz phenocrysts with more variable δ18O values (average 1.6‰, ± 2.1, n?=?55). In some cases quartz phenocrysts have δ18O values as low as ? 2.5‰. The variation in δ18O value within the quartz crystal population of individual dykes is small relative to the overall range, and core and rim material from individual quartz phenocrysts in three samples are identical within error. There is no evidence that quartz phenocryst δ18O values have been affected by fluid–rock interaction. Based on a ?quartz?magma value of 0.6‰, magma δ18O values must have been as low as ? 3.1‰. Samples collected along the length of the two main QP dykes that traverse the roof pendant have quartz phenocryst δ18O values that range from +?1.1 to +?4.6‰, and ? 2.3 to +?5.6‰, respectively. These δ18O values correlate negatively (r = ? 0.96) with initial 87Sr/86Sr, which can be explained by the event that lowered δ18O values of the source being older than the dykes. We suggest that the QP dykes were fed by magma produced by partial melting of gneiss, which had been variably altered at high temperature by 18O-depleted meteoric water during global glaciation at ~?550 Ma. The early melts had variable δ18O value but as melt pockets interconnected during melting, the δ18O values approached that of average gneiss. Variable quartz phenocryst δ18O values in the same dyke can be explained by vertical emplacement, at variable rates of ascent along the dyke. The lateral variation in quartz, and hence magma δ18O value at a particular point along a single dyke would depend on the rate of ascent of magma at that point along the dyke, and the ‘age’ of the particular magma batch.  相似文献   
8.
The hydroclimatology of the southeastern USA (AL, GA, NC, SC, and TN) is analyzed from a holistic perspective, including multiple climate drivers. Monthly precipitation modeled by the PRISM group and runoff data (1952–2011) from 18 basins are analyzed using a single-field based principal component’s analysis. Results indicate that the Atlantic Multidecadal Oscillation and El Niño-Southern Oscillation are the main atmospheric drivers of hydroclimate variability in the region, sometimes operating at several months’ lag. Their influence is the strongest in the fall through spring, which corresponds with the dry season in the southern parts of the study area thereby increasing pressure on already limited water resources. The Arctic Oscillation, North Atlantic Oscillation, and Pacific-North American patterns vary on shorter-term bases, and also show a significant, but temporally more sporadic influence. Insight is also brought to the ongoing discussion, confirming the disassociation of the Arctic and North Atlantic Oscillation. Findings can be used in water resources forecasting, giving an indication of expected water volumes several months ahead.  相似文献   
9.
The occurrence of flood and drought frequency is highly correlated with the temporal fluctuations of streamflow series; understanding of these fluctuations is essential for the improved modeling and statistical prediction of extreme changes in river basins. In this study, the complexity of daily streamflow fluctuations was investigated by using multifractal detrended fluctuation analysis (MF-DFA) in a large heterogeneous lake basin, the Poyang Lake basin in China, and the potential impacts of human activities were also explored. Major results indicate that the multifractality of streamflow fluctuations shows significant regional characteristics. In the study catchment, all the daily streamflow series present a strong long-range correlation with Hurst exponents bigger than 0.8. The q-order Hurst exponent h(q) of all the hydrostations can be characterized well by only two parameters: a (0.354 ≤ a ≤ 0.384) and b (0.627 ≤ b ≤ 0.677), with no pronounced differences. Singularity spectrum analysis pointed out that small fluctuations play a dominant role in all daily streamflow series. Our research also revealed that both the correlation properties and the broad probability density function (PDF) of hydrological series can be responsible for the multifractality of streamflow series that depends on watershed areas. In addition, we emphasized the relationship between watershed area and the estimated multifractal parameters, such as the Hurst exponent and fitted parameters a and b from the q-order Hurst exponent h(q). However, the relationship between the width of the singularity spectrum (Δα) and watershed area is not clear. Further investigation revealed that increasing forest coverage and reservoir storage can effectively enhance the persistence of daily streamflow, decrease the hydrological complexity of large fluctuations, and increase the small fluctuations.  相似文献   
10.
Multiphase solid inclusions in minerals formed at ultra-high-pressure (UHP) provide evidence for the presence of fluids during deep subduction. This study focuses on barian mica, which is a common phase in multiphase solid inclusions enclosed in garnet from mantle-derived UHP garnet peridotites in the Saxothuringian basement of the northern Bohemian Massif. The documented compositional variability and substitution trends provide constraints on crystallization medium of the barian mica and allow making inferences on its source. Barian mica in the multiphase solid inclusions belongs to trioctahedral micas and represents a solid solution of phlogopite KMg3(Si3Al)O10(OH)2, kinoshitalite BaMg3(Al2Si2)O10(OH)2 and ferrokinoshitalite BaFe3(Al2Si2)O10(OH)2. In addition to Ba (0.24–0.67 apfu), mica is significantly enriched in Mg (XMg ~ 0.85 to 0.95), Cr (0.03–0.43 apfu) and Cl (0.04–0.34 apfu). The substitution vector involving Ba in the I-site which describes the observed chemical variability can be expressed as BaFeIVAlClK?1Mg?1Si?1(OH)?1. A minor amount of Cr and VIAl enters octahedral sites following a substitution vector VI(Cr,Al)2VI(Mg,Fe)?3 towards chromphyllite and muscovite. As demonstrated by variable Ba and Cl contents positively correlating with Fe, barian mica composition is partly controlled by its crystal structure. Textural evidence shows that barian mica, together with other minerals in multiphase solid inclusions, crystallized from fluids trapped during garnet growth. The unusual chemical composition of mica reflects the mixing of two distinct sources: (1) an internal source, i.e. the host peridotite and its garnet, providing Mg, Fe, Al, Cr, and (2) an external source, represented by crustal-derived subduction-zone fluids supplying Ba, K and Cl. At UHP–UHT conditions recorded by the associated diamond-bearing metasediments (c. 1100 °C and 4.5 GPa) located above the second critical point in the pelitic system, the produced subduction-zone fluids transporting the elements into the overlying mantle wedge had a solute-rich composition with properties of a hydrous melt. The occurrence of barian mica with a specific chemistry in barium-poor mantle rocks demonstrates the importance of its thorough chemical characterization.  相似文献   
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