地震作用下大型多岔调压井衬砌结构数值分析

针对地震作用下的深埋多岔圆形调压井,采用三维非线性有限元对其洞室开挖及衬砌结构受力特性进行了计算分析。引入岩石弹塑性损伤本构关系模拟地下调压井洞室的开挖效应;基于模拟结构支护的隐式锚杆、锚索单元,提出了复杂体型的调压井洞室开挖支护及衬砌开裂的计算方法;采用波动场拟静法对地震波作用下混凝土衬砌结构受力、变形特性进行了计算,给出了衬砌开裂的裂缝宽度和结构配筋的计算公式。通过小湾水电站调压井的工程实例计算,分析了空间多岔调压井衬砌结构在地震作用下的变形、开裂特性和应力分布规律,验证了模型的合理性与计算方法的可行性,为强震地区大型复杂调压井结构设计施工和安全校核提供了新思路和参考依据。     

Eruptive conditions and depositional processes of Narbona Pass Maar volcano,Navajo volcanic field,Navajo Nation,New Mexico (USA)

Phreatomagmatic deposits at Narbona Pass, a mid-Tertiary maar in the Navajo volcanic field (NVF), New Mexico (USA), were characterized in order to reconstruct the evolution and dynamic conditions of the eruption. Our findings shed light on the temporal evolution of the eruption, dominant depositional mechanisms, influence of liquid water on deposit characteristics, geometry and evolution of the vent, efficiency of fragmentation, and the relative importance of magmatic and external volatiles. The basal deposits form a thick (5–20 m), massive lapilli tuff to tuff-breccia deposit. This is overlain by alternating bedded sequences of symmetrical to antidune cross-stratified tuff and lapilli tuff; and diffusely-stratified, clast-supported, reversely-graded lapilli tuffs that pinch and swell laterally. This sequence is interpreted to reflect an initial vent-clearing phase that produced concentrated pyroclastic density currents, followed by a pulsating eruption that produced multiple density currents with varying particle concentrations and flow conditions to yield the well-stratified deposits. Only minor localized soft-sediment deformation was observed, no accretionary lapilli were found, and grain accretion occurs on the lee side of dunes. This suggests that little to no liquid water existed in the density currents during deposition. Juvenile material is dominantly present as blocky fine ash and finely vesiculated fine to coarse lapilli pumice. This indicates that phreatomagmatic fragmentation was predominant, but also that the magma was volatile-rich and vesiculating at the time of eruption. This is the first study to document a significant magmatic volatile component in an NVF maar-diatreme eruption. The top of the phreatomagmatic sequence abruptly contacts the overlying minette lava flows, indicating no gradual drying-out period between the explosive and effusive phases. The lithology of the accidental clasts is consistent throughout the vertical pyroclastic stratigraphy, suggesting that the diatreme eruption did not penetrate below the base of the uppermost country rock unit, a sandstone aquifer ∼360 m thick. By comparison, other NVF diatremes several tens of kilometers away were excavated to depths of ∼1,000 m beneath the paleosurface (e.g., Delaney PT. Ship Rock, New Mexico: the vent of a violent volcanic eruption. In: Beus SS (ed) Geological society of America Centennial Field Guide, Rocky Mountain Section 2:411–415 (1987)). This can be accounted for by structurally controlled variations in aquifer thickness beneath different regions of the volcanic field. Variations in accidental clast composition and bedding style around the edifice are indicative of a laterally migrating or widening vent that encountered lateral variations in subsurface geology. We offer reasonable evidence that this subsurface lithology controlled the availability of external water to the magma, which in turn controlled characteristics of deposits and their distribution around the vent. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Simplified methods for real-time prediction of storm surge uncertainty: The city of Venice case study

Providing reliable and accurate storm surge forecasts is important for a wide range of problems related to coastal environments. In order to adequately support decision-making processes, it also become increasingly important to be able to estimate the uncertainty associated with the storm surge forecast. The procedure commonly adopted to do this uses the results of a hydrodynamic model forced by a set of different meteorological forecasts; however, this approach requires a considerable, if not prohibitive, computational cost for real-time application. In the present paper we present two simplified methods for estimating the uncertainty affecting storm surge prediction with moderate computational effort. In the first approach we use a computationally fast, statistical tidal model instead of a hydrodynamic numerical model to estimate storm surge uncertainty. The second approach is based on the observation that the uncertainty in the sea level forecast mainly stems from the uncertainty affecting the meteorological fields; this has led to the idea to estimate forecast uncertainty via a linear combination of suitable meteorological variances, directly extracted from the meteorological fields. The proposed methods were applied to estimate the uncertainty in the storm surge forecast in the Venice Lagoon. The results clearly show that the uncertainty estimated through a linear combination of suitable meteorological variances nicely matches the one obtained using the deterministic approach and overcomes some intrinsic limitations in the use of a statistical tidal model.     

考虑SSI效应储油罐的子结构实验方法与数值模拟

提出了应用振动台子结构试验方法来研究考虑土-结构相互作用（SSI）效应储罐的抗震性能,该方法将土体简化为双自由度八参量集总参数模型进行模拟,储罐作为试验子结构应用振动台加载,两部分联机完成振动台子结构试验。该方法能完成大比例尺储罐试验,具有传统试验方法难以比拟的优势。然后,通过数值模拟分析了SSI效应对储罐动力响应的影响。分别研究了不同储液高度和不同地基刚度对储罐位移和加速度响应的影响。研究结果表明：考虑SSI效应时,罐体位移响应和加速度响应均有所减小,土质越软,效果越明显;随着储液高度的增高,位移、加速度反应呈现减小趋势。     

Flume tank studies to elucidate the fate and behavior of diluted bitumen spilled at sea

An economical alternative to conventional crudes, Canadian bitumen, harvested as a semi-liquid, is diluted with condensate to make it viable to transport by pipeline to coastal areas where it would be shipped by tankers to global markets. Not much is known about the fate of diluted bitumen (dilbit) when spilled at sea. For this purpose, we conducted dilbit (Access Western Blend; AWB and Cold Lake Blend; CLB) weathering studies for 13 days in a flume tank containing seawater. After six days of weathering, droplets detached from the AWB slick and were dense enough to sink in seawater. The density of CLB also increased, but at a slower rate compared to AWB, which was attributed to the high concentration of alkylated polycyclic aromatic hydrocarbons in it, which are more resistant to weathering. An empirical, Monod-type model was introduced and was found to closely simulate the increase in oil density with time. Such a model could be used within oil spill models.     

Enhancing hydrologic modelling through the representation of traditional rainwater harvesting systems: A case study of water tanks in South India

Water tanks as traditional rainwater harvesting systems for agriculture are widely distributed in South India. They have a strong impact on hydrological processes, affecting streamflow in rivers as well as evapotranspiration. This study aims at an accurate representation of water harvesting systems in a hydrologic model to improve model performance and assessment of the catchment water balance. To this end, spatio-temporal variations of water bodies between the years 2016 and 2018 and the months of January and May 2017 were derived from Sentinel-2 satellite data to parameterize the water tanks (reservoir) parameters in the Soil and Water Assessment Tool (SWAT+) model of the Adyar basin, Chennai, India. Approximately 16% of the basin is covered by water tanks. The initial model performance was evaluated for two model setups, with and without water tanks. The best model run was selected with a multi-metric approach comparing observed and modelled monthly streamflow for 5000 model runs. The final model evaluation was carried out by comparing estimated water body areas by the model and remote sensing observations for January to May 2017. The results showed that representing water tanks in the hydrologic model led to an improvement in the representation of the seasonal variations of streamflow for the whole simulation period (2004–2018). The model performance was classified as good and very good for the calibration (2004–2011) and validation (2012–2018) periods as NSE varies between 0.67 and 0.85, KGE varies between 0.65 and 0.72, PBIAS varies between −24.1 and −23.6, and RSR varies between 0.57 and 0.39. The best fit was shown for the high and middle flow segments of the hydrograph where the coefficient of determination (R²) ranges from 0.81 to 0.97 and 0.75 to 0.81, respectively. The monthly variation of water body areas in 2017 estimated by the hydrologic model was consistent with changes observed in remote sensing surveys. In summary, the water tank parametrization using remote sensing techniques enhanced the hydrologic model's efficiency and applicability for future studies.     

厦门港潮汐、风暴潮耦合模型

建立一个适合台湾海峡及小港湾,特别是能够反映小港湾的漫滩及潮汐、风暴潮耦合效应的数值模型,对小港湾风暴潮进行数值预报,有重要的社会和经济意义.文中以厦门港作为小港湾研究区域,在漫滩、风暴潮的耦合、开边界条件等方面对小港湾风暴潮数值计算作了一定的尝试,提出了一种能够模拟小港湾台风增水,潮位和流场变化情况的途径.     

近年风暴潮对山东海岸及海岸工程的影响

讨论了风暴潮对山东海岸的侵蚀及近年来山东海岸工程破坏的原因,并着重指出,采用较短年限潮位资料导致校核高潮位偏低是海岸工程破坏的重要原因之一。建议利用长系列资料重新推算不同重现期的校核高潮位。本文推荐胶州湾附近的50年一遇的校核高潮位为5．54m。     

贝壳堤的形成与风暴沉积——以广东台山长湾贝壳堤为例

台山市西南部沿海有一条由典型风暴潮沉积堆积形成,出露高度远高于现代风暴潮增水面的贝壳堤.根据贝壳堤出露的横向与纵向剖面以及横剖面上的3个钻孔的形成年代、沉积特征的分析表明风暴潮在贝壳堤发育过程中的不同阶段具有不同的侵蚀与堆积作用;贝壳堤风暴沉积也具有丘状层理、切割充填结构等典型的风暴沉积特征,但贝壳堤风暴沉积与浅海陆架上的风暴沉积在沉积过程、堆积层位、保存条件等方面具有明显的差异.长湾贝壳堤是由多次风暴加积而成,形成贝壳堤的风暴增水高度接近或高于历史最高记录.形成贝壳堤的风暴沉积堆积于平均海面之上,所以增     

考虑桩土作用的储罐模拟地震振动台试验

为研究考虑桩土相互作用的储液罐的动力响应及长周期地震波对储液晃动、储罐提离的影响,根据量纲分析法设计了桩-土-储罐模型进行了振动台试验。试验中采用4条基岩波、4条地表波进行振动台试验。试验显示基岩波与地表波输入时,体系变化规律基本一致,其结果表明:土体地表加速度被放大,且输入加速度峰值增加,地表加速度放大倍数减小;一般地震波时,随着输入加速度峰值的增加,储液晃动波高大致呈线性增加。长周期地震波下则为非线性增加,且晃动波较大。此外,液体产生的晃动波高与储罐类型相关。细高型储罐产生的波高稍大;储罐提离高度随着输入加速度峰值的增加呈非线性增长。长周期地震波激励下,储罐提离高度小于一般地震波时的提离高度。细高型储罐在长短周期地震波激励下,提离高度较为接近,而一般储罐在两种地震波激励下,提离高度相差较大。细高型储罐提离高度大于一般储罐的提离高度。建议在储罐设计时考虑长周期地震波的影响。