二氧化氯对煤储层物性改变的机理研究     

郭红玉  拜阳  夏大平  王惠风  陈俊辉  马俊强 《煤田地质与勘探》2015,43(1):26-29

二氧化氯在作为煤储层压裂破胶剂的同时,兼具降低煤的亲甲烷能力和化学增透作用。查明二氧化氯对煤储层物性改变的内在机理,对深部煤储层改造摒弃传统活性水改用高粘压裂液有重要意义。通过对二氧化氯改性前后的不同变质程度煤样的压汞和Raman光谱测试,对比分析了煤样改性前后的孔隙结构和化学结构的变化特征。测试结果表明:煤样改性后孔隙度和孔容不同程度增加,比表面积降低;改性后煤的脂肪链的支链化程度和芳香环的缩合程度均降低,煤结构单元缺陷增加,芳碳总量相对减少。可见,煤储层物性改变的机理在于煤孔隙结构及其大分子结构发生了相应变化。   相似文献   

近磁尾TC-1观测到伴随有高速流的ULF波及不稳定性分析   总被引：2，自引：2，他引：0       下载免费PDF全文

马玉端  曹晋滨  符慧山  杨俊英  吕浩宇  杨建  王志强 《地球物理学报》2014,57(11):3754-3765

2004年8月3日近地TC-1卫星在磁尾X_GSM~－12R_E的等离子体片内,观测到了伴随着高速流的低于离子回旋频率的波,即超低频波(ULF,Ultra Low Frequency).该波垂直分量的振幅在高速流及其振荡减速期间大致相当;而平行分量振幅在高速流时明显大于其振荡减速时. 利用一个扰动双流模型对完全磁化离子横场漂移驱动的电磁不稳定性计算后,预测结果表明:(1)对于垂直分量来说,横场漂移速度与Alfvén速度的比值影响不稳定性增长率和激发波频率,随其比值增加,增长率变大,激发波频率从负值增加到正值.(2)对于平行分量来说,温度各向异性时等离子体热速度与Alfvén速度比值只影响不稳定性增长率和激发波频率,未改变不稳定性模类别;而温度各向同性时离子横场漂移速度与Alfvén速度比值既影响不稳定性模的种类及其分支,又影响激发波频率.进一步将卫星观测到的等离子体密度、温度、整体流速和磁场代入模型方程,进行数值计算与上述预测结果对比后发现:卫星观测中垂直分量的功率谱密度(PSD,Power Spectrum Density)增强时间和频段与理论模型中由β_//、β_⊥和v_⊥/V_A引起不稳定性激发的波一致;卫星观测中平行分量的功率谱密度增强时间与理论模型基本相符,但是前者的频率明显地低于后者.因此,除了需考虑平行磁场的离子整体流速对不稳定性激发波频率的可能影响,还需要统计上进一步核实伴随有高速流的ULF波与不稳定性的相关性.  相似文献   

Development and validation of nonlinear computational models of dispersed structures under strong earthquake excitation          下载免费PDF全文

Armen Derkevorkian  Sami F. Masri  Yozo Fujino  Dionysius M. Siringoringo 《地震工程与结构动力学》2014,43(7):1089-1105

Structural health monitoring of large multispan flexible bridges is particularly important because of their important role in civil infrastructure and transportation systems. In this study, the response of the Yokohama Bay Bridge (YBB), a three‐span cable‐stayed bridge, to the 2011 Great East Japan Earthquake is used to perform multi‐input multi‐output system identification studies. The extensive multicomponent measurements are also used to develop and validate data‐driven nonlinear mathematical models that can predict the response of YBB to various earthquake records and can accurately estimate its damping characteristics when the system is driven into the nonlinear response range. A combination of least‐square (parametric) and neural network (nonparametric) approaches is used to develop the mathematical models, along with time‐marching techniques for dynamic response calculations. It is shown that the nonlinear mathematical models perform better than the equivalent linear models, both for response prediction and damping estimation. The importance of having an accurate approach for quantifying the damping due to the variety of nonlinear features in the YBB response is shown. This study demonstrates the significance of constructing robust mathematical models that can capture the correct physics of the underlying system and that can be used for computational purposes to augment experimental studies. Given the lack of suitable data sets for full‐scale structures under extreme loads, the availability of the long‐duration measurements from the 2011 Great East Japan Earthquake and its many strong aftershocks provides an excellent opportunity to perform the analyses presented in this study. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Evaluation of a recently proposed record selection and scaling procedure for low‐rise to mid‐rise reinforced concrete buildings and its use for probabilistic risk assessment studies          下载免费PDF全文

Bekir Özer Ay  Sinan Akkar 《地震工程与结构动力学》2014,43(6):889-908

This paper evaluates a recent record selection and scaling procedure of the authors that can determine the probabilistic structural response of buildings behaving either in the elastic or post‐elastic range. This feature marks a significant strength on the procedure as the probabilistic structural response distribution conveys important information on probability‐based damage assessment. The paper presents case studies that show the utilization of the proposed record selection and scaling procedure as a tool for the estimation of damage states and derivation of site‐specific and region‐specific fragility functions. The method can be used to describe exceedance probabilities of damage limits under a certain target hazard level with known annual exceedance rate (via probabilistic seismic hazard assessment). Thus, the resulting fragility models can relate the seismicity of the region (or a site) with the resulting building performance in a more accurate manner. Under this context, this simple and computationally efficient record selection and scaling procedure can be benefitted significantly by probability‐based risk assessment methods that have started to be considered as indispensable for developing robust earthquake loss models. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

1D System identification of a 54‐story steel frame building by seismic interferometry          下载免费PDF全文

Mohammadtaghi Rahmani  Maria I. Todorovska 《地震工程与结构动力学》2014,43(4):627-640

A 54‐story steel, perimeter‐frame building in downtown Los Angeles, California, is identified by a wave method using records of the Northridge earthquake of 1994 (M_L = 6.4, R = 32 km). The building is represented as a layered shear beam and a torsional shaft, characterized by the corresponding velocities of vertically propagating waves through the structure. The previously introduced waveform inversion algorithm is applied, which fits in the least squares sense pulses in low‐pass filtered impulse response functions computed at different stories. This paper demonstrates that layered shear beam and torsional shaft models are valid for this building, within bands that include the first five modes of vibration for each of the North–South (NS), East–West (EW), and torsional responses (0–1.7 Hz for NS and EW, and 0–3.5 Hz for the torsional response). The observed pulse travel time from ground floor to penthouse level is τ ≈1.5 s for NS and EW and τ ≈ 0.9 s for the torsional responses. The identified equivalent uniform shear beam wave velocities are β_eq ≈ 140 m/s for NS and EW responses, and 260 m/s for torsion, and the apparent Q ≈ 25 for the NS and torsional, and ≈14 for the EW response. Across the layers, the wave velocity varied 90–170 m/s for the NS, 80–180 m/s for the EW, and 170–350 m/s for the torsional responses. The identification method is intended for use in structural health monitoring. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Computational study of self‐centering buckling‐restrained braced frame seismic performance          下载免费PDF全文

Matthew R. Eatherton  Larry A. Fahnestock  David J. Miller 《地震工程与结构动力学》2014,43(13):1897-1914

Recent research developed and experimentally validated a self‐centering buckling‐restrained brace (SC‐BRB) that employs a restoring mechanism created using concentric tubes held flush with pretensioned shape memory alloy rods, in conjunction with a buckling‐restrained brace (BRB) that dissipates seismic energy. The present computational study investigated how the SC‐BRB can be implemented in real buildings to improve seismic performance. First, a computational brace model was developed and calibrated against experimental data, including the definition of a new cyclic material model for superelastic NiTi shape memory alloy. A parametric study were then conducted to explore the design space for SC‐BRBs. Finally, a set of prototype buildings was designed and computationally subjected to a suite of ground motions. The effect of the lateral resistance of gravity framing on self‐centering was also examined. From the component study, the SC‐BRB was found to dissipate sufficient energy even with large self‐centering ratios (as large as 4) based on criteria found in the literature for limiting peak drifts. From the prototype building study, a SC‐BRB self‐centering ratio of 0.5 was capable of reliably limiting residual drifts to negligible values, which is consistent with a dynamic form of self‐centering discussed in the literature. Because large self‐centering ratios can create significant overstrength, the most efficient SC‐BRB frame designs had a self‐centering ratio in the range of 0.5–1.5. Ambient building resistance (e.g., gravity framing) was found to reduce peak drifts, but had a negligible effect on residual drifts. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

2008年汶川M_S8.0地震反应谱平台值衰减特性研究          下载免费PDF全文

万卫  薄景山  郭晓云 《地震学报》2014,36(6):1032-1042

2008年汶川M_S8.0地震获得了大量的强震动记录, 为研究反应谱特征参数衰减特性提供了重要的基础资料. 本文对已知场地条件的174个台站的记录进行研究, 计算其加速度反应谱并按照最小二乘分段拟合方法进行标定, 进而拟合了反应谱平台值的衰减关系;对比分析了水平方向与竖直方向反应谱平台值的衰减特性, 提出用“平台值的场地衰减影响系数”来定量研究不同场地类型对反应谱平台值的影响, 用“衰减曲线下降速率”来定量分析不同衰减曲线的衰减速率. 通过计算得出水平向Ⅰ, Ⅱ, Ⅲ类场地的平台值场地衰减影响系数平均值分别为0.5358, 1和1.579, 且Ⅲ类场地的加速度平台值衰减曲线的衰减速率最小.   相似文献   

Nonlinear dynamic analysis of Meloland Road Overpass using three-dimensional continuum modeling approach     

《Soil Dynamics and Earthquake Engineering》2014

This paper presents a three-dimensional (3D) continuum nonlinear analysis of the Meloland Road Overpass (MRO) near El Centro, California. The modeling methodology and the computational tools are discussed in detail. The performance of the computational model is evaluated by comparing the computed responses with the responses recorded at the bridge site during the 1979 Imperial Valley and 2010 El Mayor-Cucapah earthquakes. Amongst the recorded earthquake events at the bridge site, these two events caused the strongest shaking. The comparison shows that the 3D model is potentially an effective tool for detailed analysis of a full bridge system including foundation soils, pile foundations, embankments, supporting columns, and the bridge structure itself in a unified system without relying on any ancillary models such as Winkler springs. Additional response parameters such as displacements, rockings, and bending moments are also evaluated although none of these was measured during the seismic events.  相似文献   

Effect of soil depth on inelastic seismic response of structures     

《Soil Dynamics and Earthquake Engineering》2014

Effect of depth of soil stratum on estimated inelastic displacement of three typical structures, viz. a four storey building, a continuous bridge, and a tower, is studied and adequacy of the site amplification models of the current design codes and available empirical relationships is examined. The structures are assumed to be located on well-defined sites with varying bedrock depths, and effect of depth on elastic response spectrum, site amplification factor, displacement modification factor and inelastic displacement is studied, numerically, for two values of PGA. It is observed that soil depth has a significant effect on elastic as well as inelastic response of the structures; however, the effect of soil amplification on inelastic response is not as pronounced as in case of elastic response. Therefore, use of empirical site amplification models based on elastic response may be too conservative, for estimating inelastic response.  相似文献   

Learning of pore pressure response and dynamic soil behavior from downhole array measurements     

《Soil Dynamics and Earthquake Engineering》2014

Downhole arrays are deployed to measure motions at the ground surface and within the soil profile, with some arrays instrumented to also record the pore pressure response within soft soil profiles during excitation. The measurements from these arrays have typically been used in conjunction with parametric and nonparametric inverse analysis approaches to identify soil constitutive model parameters for use in site response analysis or to identify averaged soil behavior between locations of measurement. The self-learning simulations (SelfSim) inverse analysis framework, previously developed and applied under total stress conditions, is extended to effective stress considerations and is employed to reproduce the measured motions and pore pressures from downhole arrays while extracting the underlying soil behavior and pore pressure response of individual soil layers. SelfSim is applied to the 1987 recordings from the Imperial Valley Wildlife Liquefaction Array. The extracted soil behavior suggests a new functional form for modeling the degradation of the shear modulus with respect to excess pore pressures. The extracted pore pressure response is dependent on the number and amplitude of shear strain cycles and has a functional form similar to current strain-based pore pressure generation models.  相似文献