Symmetric matrix-valued transmitting boundary formulation in the time-domain for soil–structure interaction problems     

《Soil Dynamics and Earthquake Engineering》2014

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防浪建筑物影响下珊瑚礁海岸波浪传播变形试验     

贾美军  姚宇  陈松贵  郭辉群 《海洋工程》2020,38(6):53-59,123

通过测试一系列不规则波工况研究了防浪建筑物存在下珊瑚礁海岸附近短波、低频长波和增水的变化规律，并对比了防浪建筑物的不同位置情况。分析结果表明：波浪在沿礁传播过程中，短波波高沿礁坪持续衰减，低频长波波高沿礁坪逐渐增大，波浪增水则沿礁坪基本保持不变；海岸附近短波随着防浪建筑物与礁缘距离的变大而减小，低频长波则在防浪建筑物处于礁坪后部时达到最大，防浪建筑物位置的变化对于礁坪波浪增水的影响可以忽略。通过理论分析证明了珊瑚礁地形上低频长波是由于群波破碎造成的破碎点移动而产生的；当特定波况作用于特定位置的防浪建筑物时，低频长波在礁坪上会发生一阶共振效应导致其能量在海岸附近达到最大值。  相似文献   

基于稀疏表示的地面磁共振信号提取方法          下载免费PDF全文

王琦  田宝凤  张健  蒋川东 《地球物理学报》2018,61(8):3446-3456

在多孔隙含水层中地面磁共振（surface nuclear magnetic resonance，SNMR）信号呈现多弛豫衰减特性，常规盲源分离方法和单指数拟合方法引起信号严重失真和信息缺失等问题.本文提出了基于稀疏表示的随机噪声背景下多弛豫SNMR信号的提取方法.根据SNMR信号的衰减特征，设计了精确刻画SNMR信号且与随机噪声不相关的离散衰减余弦冗余字典.其次，针对多弛豫SNMR信号稀疏度未知的问题，通过设置合理的残差比阈值控制迭代次数，改进了广义正交匹配追踪（generalized orthogonal matching pursuit，gOMP）算法，使得该方法应用于SNMR信号的提取时，具有更好的自适应性和普适性.再次，鉴于SNMR测量数据为多次独立重复采集的结果，提出了基于数据流的SNMR信号提取策略，在提高算法鲁棒性的同时，保证了信号提取结果的唯一性.最后，通过仿真和实测数据证明了基于gOMP算法的稀疏表示方法可以显著地提升多弛豫SNMR信号的提取质量，降低随机噪声对含水层反演结果的影响，提高SNMR探测能力.  相似文献   

Measuring hydrological connectivity inside a soil by low field nuclear magnetic resonance relaxometry   总被引：1，自引：0，他引：1       下载免费PDF全文

Pellegrino Conte  Vito Ferro 《水文研究》2018,32(1):93-101

Hydrological connectivity inside the soil is related to the spatial patterns inside the soil (i.e., the structural connectivity). This, in turn, is directly associated with the physical and the chemical processes at a molecular level (i.e., the functional connectivity). Nuclear magnetic resonance (NMR) relaxometry can be successfully applied to reveal both structural and functional components of soil hydrological connectivity. In the present study, the low field NMR relaxometry was applied on water suspended soils sampled at the upstream‐ and downstream‐end of three different length plots. Also the sediments collected from the storage tanks at the end of each plot were water suspended and monitored by NMR relaxometry. The results from the NMR investigations were elaborated by using a mathematical approach in order to quantify both the functional and structural connectivity components. In particular, following integration of the T₁ distribution curve, an S‐shaped curve was obtained. It revealed two plateaus corresponding to the shortest (low component) and the longest (high component) intervals of relaxation times, respectively. According to relaxometry theory, the two T₁ intervals, associated to the different plateaus, were attributed to micro and macro soil pores, respectively. The two T₁ intervals were used to define a functional connectivity index, while the central part of the S‐shaped distribution was used to define a structural connectivity index. Here we provide the physical meaning of the our mathematical approach, thereby revealing that functional connectivity index increases with plot length, as a result of a selective eroded particle transport. Moreover, the relationship structural connectivity index versus plot length resulted quasi‐independent of grainsize distribution, whereas the values of the structural connectivity index for the sediment samples resulted lower than those obtained for the corresponding soils.  相似文献   

Petrophysical characterisation of tight sandstone gas reservoirs using nuclear magnetic resonance: a case study of the upper Paleozoic strata in the Kangning area,eastern margin of the Ordos Basin,China     

Y. Y. Huyan  T. S. Liu  F. J. Jiang  X. Z. Chen  X. Q. Ma 《Australian Journal of Earth Sciences》2018,65(6):863-875

Residual and movable porosity are significant parameters for characterising petrophysical properties, especially in tight reservoirs. Eight tight sandstone samples from the upper Paleozoic gas-bearing strata in the Kangning area, from the eastern margin of the Ordos Basin, were analysed using nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), petrography, and porosity and permeability tests. The lithology and pore types were identified and classified using petrography and SEM. The residual and movable porosity were obtained with NMR. In addition, NMR was used to visualise pore structure and pore size distribution. The results suggest that the upper Paleozoic sandstones in the study area mainly comprise feldspathic litharenite and litharenite. The sandstone porosity and permeability are low, with means of 5.9% and 0.549 mD, respectively. Four pore types exist in the tight sandstones: residual primary pores, grain dissolution pores, micropores (clay-dominated) and microfractures. The T₂ spectra under water-saturated conditions correlate with pore size and can be used to distinguish small and large pores based on the transverse relaxation time cutoff value of 10 ms, which corresponds to a pore diameter of 0.232 μm. Small pores account for 72% of the pores in the tight sandstones. The continuous bimodal T₂ spectra suggest good connectivity between small and large pores, despite the low porosity and permeability. In this study, the movable porosity of the major tight sandstone gas reservoirs is higher than the residual porosity, which confirms the effective evaluation of movable porosity to tight sandstone reservoirs, based on NMR experiments.  相似文献   

Revisiting natural and laboratory electron spin resonance (ESR) dose response curves of quartz from Chinese loess     

《Quaternary Geochronology》2022

Natural and laboratory ESR dose response curves (DRCs) of [AlO₄/h]⁰ and [TiO₄/M⁺]⁰ were investigated for samples of quartz from the Luochuan loess-palaeosol master section, Chinese Loess Plateau. The natural and laboratory DRCs show a clear divergence above ∼1000 Gy, with much lower D₀ values and saturation levels observed for the natural DRCs, which is in agreement with the previous study by Tsukamoto et al. (2018). Young (<15 ka) samples from Luochuan and Jingbian – another site of the Chinese Loess Plateau, together with two modern samples of Chinese loess, were used to investigate the residual signals of [AlO₄/h]⁰ and [TiO₄/M⁺]⁰ centres. Our results are in line with published studies and show that the significant residual signals corresponding to several tens to hundreds of Gy are present in both Al and Ti centres. These need to be taken into account before laboratory DRC construction. ESR pulse annealing experiments performed on samples irradiated with different doses show an apparent dose-dependent thermal instability of [AlO₄/h]⁰ and [TiO₄/M⁺]⁰, with the signals for higher doses decaying faster with increasing temperature. We attribute the change in D₀ with preheat reported in Tsukamoto et al.2018, as well as the difference between laboratory and natural DRCs, to this apparent dose-dependent thermal instability of the signals. The saturation level of the natural DRC, being the result of reaching the equilibrium between filling of the traps and emptying them due to thermal decay, is therefore additionally affected at higher doses, due to the increased thermal instability. The inability to recreate in the laboratory the same response to irradiation as the one observed in nature questions the accuracy of dating samples beyond ∼1000 Gy.  相似文献   

车装全液压钻机桅杆模态分析及拓扑优化          下载免费PDF全文

杜垚森  和国磊  冯起赠  赵远  师敏  宋志彬  朱芝同  刘晓林  许本冲  秦如雷  马汉臣  伍晓龙  高鹏举  汤小仁  王晓赛 《探矿工程》2022,49(3):70-75

车装全液压钻机具有自动化程度高、工艺适用范围广、机动性好及施工效率高等优点,因此被广泛应用于煤层气抽采井、水井等钻井施工。桅杆作为钻机的重要构件,支撑着动力头的回转钻进工作,桅杆工作振动的稳定性对钻机工作的可靠性具有十分重要的影响。通过对桅杆进行模态分析,明确了桅杆的固有频率和模态振型,结果表明桅杆可能发生共振现象;通过对桅杆进行拓扑优化分析,并且根据桅杆的实际功能,得到优化模型,静力分析和模态分析结果均表明优化效果显著,满足结构强度要求且避免了共振的发生。桅杆的有限元分析,为桅杆的结构设计提供了理论支撑,同时提供了一种现代机械结构设计方法,具有一定的参考意义。  相似文献   

城市密集建筑群对沉积谷地地震动放大效应的影响          下载免费PDF全文

贺晨蕊  严磊  刘中宪 《地震工程学报》2019,41(4):1035-1045

采用有限元模拟方法建立了建筑群-沉积谷地二维模型,并在土体截断边界上施加粘弹性人工边界,在频域与时域中对比分析此体系和单独沉积谷地的地震反应,观察地震时沉积谷地与建筑群之间的动力相互作用规律。分析表明,沉积谷地中建筑群对谷地本身的地震反应具有显著影响。入射波频率较低时,由于共振效应的存在,在部分区域处建筑群-沉积谷地体系的地表位移响应幅值会大于单独沉积谷地,但随着入射波频率的增加,建筑群的存在又会对地震反应产生明显的减弱效果;建筑群对谷地的影响还与建筑高度和建筑间距有关,且不同位置处的响应也存在很大差异。计算结果可为沉积谷地中设防烈度的设置以及工程抗震设计提供部分理论依据。  相似文献   

日本“3·11”海啸引起的乐清湾共振研究          下载免费PDF全文

刘勇  卢文芳  应超  李新文  姚文伟 《海洋学研究》2019,37(3):31-39

本文基于TELEMAC-2D模型建立太平洋区域海啸传播模型,模拟2011年日本“3·11”海啸事件下海啸波的传播。使用实测数据对该模型进行验证,在模型验证良好的基础上分析日本“3·11”海啸事件对乐清湾的影响。通过频谱分析得到“3·11”海啸激发的乐清湾内240、180和103 min这3个主导模态的幅值及其相位。通过白噪声实验对乐清湾的固有共振特征进行估算,进一步支持了乐清湾在上述3个模态发生共振这一结论。白噪声实验还表明,海啸等海洋灾害发生时会在乐清湾湾顶及湾口处产生较大的增水,该结论对乐清湾内海洋灾害风险防范具有指导意义。  相似文献   

On the interest of using the multiple center approach in ESR dating of optically bleached quartz grains: Some examples from the Early Pleistocene terraces of the Alcanadre River (Ebro basin,Spain)     

《Quaternary Geochronology》2015

The present work reports the first numerical ages obtained for the two highest fluvial terraces (Qt1 and Qt2) of the Alcanadre River system (Northeastern Spain) representing the earliest remnants of Quaternary morphosedimentary fluvial activity in the Ebro basin. ESR dating method was applied to optically bleached quartz grains and both the Al and Ti centers were measured, in accordance with the Multiple Center approach. The results are overall in good agreement with the existing preliminary chronostratigraphic framework and our interpretation indicate that terraces Qt1 and Qt2 have an ESR age of 1276 ± 104 ka and 817 ± 68 ka, respectively. These data provide some chronological insights on the beginning of the fluvial sedimentary processes in a scenario of incision maintained over Quaternary in the Ebro Basin. These are among the first numerical ages obtained for such high terraces in the Iberian Peninsula.Our results demonstrate the interest of using the Multiple Center approach in ESR dating of quartz, since the two centers provide complementary information, i.e. an independent dose control. The overall apparent consistency between the ESR age estimates and the existing preliminary chronostratigraphic framework may be considered as an empirical evidence that the Ti–Li center may actually work for Early Pleistocene deposits, whereas the Ti–H center shows some clear limitations instead. Finally, these results demonstrate the interest of using ESR method to date Early Pleistocene fluvial terraces that are usually beyond the time range covered by the OSL dating method.  相似文献