盾构掘进引起地表沉降的多因素敏感性分析   总被引：3，自引：0，他引：3  

安永林  彭立敏  赵丹 《工程地质学报》2007,15(5):689-693

为了研究各因素在盾构法施工中对地表沉降的影响程度,基于敏感性分析原理,针对一地铁盾构实例,选取土体弹性模量、土仓压力、地下水等3个影响地表沉降的因素,通过变化某一基准参数,让其余影响因素固定,分析研究了盾构施工引起地表沉降对各因素的敏感性。结果如下:弹性模量提高10%时,地表累积最大沉降量可减小15%～20%;在地下水存在的情况下,地表沉降显著增大;而对于砂性土而言,土仓压力越高地表沉降值略有增加。研究结果表明:地表沉降对穿越地层的弹性模量和地下水比较敏感,而对土仓压力敏感性较小。  相似文献   

Correction of soil parameters in calculation of embankment settlement using a BP network back-analysis model   总被引：3，自引：0，他引：3  

Zhi-liang Wang  Yong-chi Li  R.F. Shen 《Engineering Geology》2007,91(2-4):168-177

Finite element method (FEM) have been widely used for the calculation of settlement of embankment on soft soils in the last decade. However, due to the complexity of construction, spatial inhomogeneity of soils, as well as sensitivity of numerical results to the variation of soil parameters, large discrepancy typically exists between numerical outputs and field observations. This paper presents a novel method, combining FEM and an improved back-propagation (BP) neural network, for correction of soil parameters in numerical prediction of embankment settlement. Duncan–Chang hyperbolic soil model is adopted with the sensitivity of eight constitutive parameters numerically investigated. The soil parameters with large sensitivity are identified, and together with the representative settlements, are used for the training of the improved BP neural network which, once established, generates correction factors of soil parameters for subsequent more accurate FEM forward predictions. It is demonstrated that the proposed numerical back-analysis framework is very efficient in practical engineering applications to calculate highway settlement.  相似文献   

导电性影响的地面核磁共振反演   总被引：11，自引：2，他引：11       下载免费PDF全文

翁爱华  王雪秋  刘国兴  莫修文  王德利 《地球物理学报》2007,50(3):890-896

导电性影响对实际的地面核磁共振反演非常重要. 在导电条件下，导出了地面核磁共振感应电动势的平方是含水率分布的二次型. 通过进一步分析，我们将其对含水率的灵敏度用显式表示出来，为由核磁感应电动势利用迭代技术快速求解含水率分布奠定了理论基础. 数值模拟结果表明，在自由空间与导电条件下，采用非线性反演技术获得的含水率分布与理论模型都有非常好的一致性.  相似文献   

霰粒子参数对强对流云降水和催化影响的数值模拟研究   总被引：1，自引：0，他引：1  

楼小凤  孙晶  史月琴  师宇 《大气科学》2015,39(3):474-488

本文利用三维对流云AgI催化模式, 开展了霰粒子密度和落速参数的敏感性模拟试验, 以研究高凇附度时霰粒子参数的选取对催化模拟结果的影响。敏感性试验中对七个霰微物理过程进行了调整。分析发现改变霰落速参数和霰密度, 可以引起3小时模拟的总降水量增加4.9%。催化后改变了敏感性试验中霰落速和上升气流的配置, 并影响到霰碰并云水和冰晶的过程, 及霰融化成雨水的过程。在高凇附度云中如果只增加霰密度而没有增加相应的落速系数, 将使云中霰含量大幅增加。霰参数也影响了自然云和催化云的降水效率。过量催化使得催化云的降水效率低于自然云。增加霰密度的同时也增加霰落速系数, 将使其降水效率高于对照试验, 从而影响催化效果。在高凇附度云中采用大密度和较大下落系数, 并且利用比数浓度平均落速计算霰粒子比数浓度的下落过程, 会使催化效率从25%减少到15%, 极大地改变催化效果。所以在高凇附度的暴雨个例中, 应当采用高霰密度和相应的高霰落速, 否则减雨的催化效果将会被大幅夸大。  相似文献   

Stochastic simulations of ocean waves: An uncertainty quantification study     

《Ocean Modelling》2015

The primary objective of this study is to introduce a stochastic framework based on generalized polynomial chaos (gPC) for uncertainty quantification in numerical ocean wave simulations. The techniques we present can be easily extended to other numerical ocean simulation applications. We perform stochastic simulations using a relatively new numerical method to simulate the HISWA (Hindcasting Shallow Water Waves) laboratory experiment for directional near-shore wave propagation and induced currents in a shallow-water wave basin. We solve the phased-averaged equation with hybrid discretization based on discontinuous Galerkin projections, spectral elements, and Fourier expansions. We first validate the deterministic solver by comparing our simulation results against the HISWA experimental data as well as against the numerical model SWAN (Simulating Waves Nearshore). We then perform sensitivity analysis to assess the effects of the parametrized source terms, current field, and boundary conditions. We employ an efficient sparse-grid stochastic collocation method that can treat many uncertain parameters simultaneously. We find that the depth-induced wave-breaking coefficient is the most important parameter compared to other tunable parameters in the source terms. The current field is modeled as random process with large variation but it does not seem to have a significant effect. Uncertainty in the source terms does not influence significantly the region before the submerged breaker whereas uncertainty in the incoming boundary conditions does. Considering simultaneously the uncertainties from the source terms and boundary conditions, we obtain numerical error bars that contain almost all experimental data, hence identifying the proper range of parameters in the action balance equation.  相似文献   

阿克苏河灌区作物需水量对气候变化的敏感性分析     

王志成 《沙漠与绿洲气象(新疆气象)》2018,12(3):33-39

阿克苏河灌区是中纬度干旱区典型的绿洲灌溉系统,同时也是新疆第二大灌区,了解灌区作物需水量可为灌区种植结构调整、水资源优化配置提供科学依据。本研究基于联合国粮农组织(FAO)的Penman-Monteith蒸散发模型,结合作物系数法估算了阿克苏灌区作物需水量的时空变化及其对气候因子和作物种植结构的敏感性。结果表明,1960—2015年阿克苏灌区多年平均作物需水量为586 mm,且呈显著上升趋势,上升速率为38.43 mm/10 a。随着气候变化和作物种植结构的改变,1990—2015年间作物需水量急剧增加,增加速率高达99.37 mm/10 a。对于不同作物类型,果林的需水量最大,高达829.8 mm,其次是棉花、水稻和玉米,小麦需水量最低。阿克苏灌区的作物需水量对日最高气温和日照时数较为敏感,而对最低气温、风速和水汽压的敏感度较低。当日最高气温升高2℃时,作物需水量增加4%,当日照时数增加10%时,作物需水量将增加3.2%。另外,作物需水量对作物种植结构非常敏感,当果林的种植面积比例增加10%时,作物需水量增加了12.1%。  相似文献   

Effect of soil parameter uncertainty on seismic demand of low-rise steel buildings on dense silty sand     

Prishati Raychowdhury 《Soil Dynamics and Earthquake Engineering》2009

Focusing on low-rise steel buildings supported by shallow isolated foundations on dense silty sand, this study demonstrates the effect of uncertainty in soil parameters on seismic response of structures. Considering a set of 20 ground motions representing 10% in 50 years hazard level and concentrating on peak base moment, base shear and interstory drift as the demand variables of interest, it is found that uncertainty in soil parameters may result in significant response variability of the structures, especially when vertical factor of safety is low and the structure is relatively stiff. Uncertainty in friction angle results in significant variability of the peak base moment and base shear, while peak interstory drift ratio is found to be virtually unaffected by uncertainty in soil parameters. It is also found that a linear soil–structure-interaction (SSI) model will not be able to predict such response variability under these set of ground motions.  相似文献   

有限频率地震层析成像方法及研究进展   总被引：1，自引：0，他引：1  

杨峰  黄金莉 《地震》2009,29(4):52-62

本文从基于射线理论的走时地震层析成像的发展引出有限频率地震层析成像, 说明两者最为本质的差别是有限频率灵敏度核函数。 概述了有限频率层析成像方法和基本原理, 详细阐述了国内外有关有限频率层析成像方法的研究进展和应用成果, 强调有限频率层析成像对全球地幔柱研究的重要意义, 最后指出有限频率层析成像方法在理论上的诸多优点目前还没有在实际应用中得到充分体现, 还存在一些问题需要解决。  相似文献   

Sensitivity-guided reduction of parametric dimensionality for multi-objective calibration of watershed models   总被引：1，自引：0，他引：1  

Kathryn van Werkhoven  Thorsten Wagener  Patrick Reed  Yong Tang 《Advances in water resources》2009

Problem complexity for watershed model calibration is heavily dependent on the number of parameters that can be identified during model calibration. This study investigates the use of global sensitivity analysis as a screening tool to reduce the parametric dimensionality of multi-objective hydrological model calibration problems while maximizing the information extracted from hydrological response data. This study shows that by expanding calibration problem formulations beyond traditional, statistical error metrics to also include metrics that capture indices or signatures of hydrological function, it is possible to reduce the complexity of calibration while maintaining high quality model predictions. The sensitivity-guided calibration is demonstrated using the Sacramento Soil Moisture Accounting (SAC-SMA) conceptual rainfall–runoff model of moderate complexity (i.e., up to 14 freely varying parameters). Using both statistical and hydrological metrics, optimization results demonstrate that parameters controlling at least 20% of the model output variance (through individual effects and interactions) should be included in the calibration process. This threshold generally yields 30–40% reductions in the number of SAC-SMA parameters requiring calibration – setting the others to a priori values – while maintaining high quality predictions. Two parameters are recommended to be calibrated in all cases (percent impervious area and lower zone tension water storage), three parameters are needed in drier watersheds (additional impervious area, riparian zone vegetation, and percent of percolation going to tension storage), and the lower zone parameters are crucial unless the watershed is very dry. Overall, this study demonstrates that a coupled, multi-objective sensitivity and calibration analysis better captures differences between watersheds during model calibration and serves to maximize the value of available watershed response time series. These contributions are particularly important given the ongoing development of more complex integrated models, which will require new tools to address the growing discrepancy between the information content of hydrological data and the number of model parameters that have to be estimated.  相似文献   

Uncertainty in the Specification of Surface Characteristics, Part ii: Hierarchy of Interaction-Explicit Statistical Analysis     

Devdutta S. Niyogi  Sethu Raman  Kiran Alapaty 《Boundary-Layer Meteorology》1999,91(3):341-366

The uncertainty in the specification of surface characteristics in soil-vegetation- atmosphere-transfer (SVAT) schemes within planetary boundary-layer (PBL) or mesoscale models is addressed. The hypothesis to be tested is whether the errors in the specification of the individual parameters are accumulative or whether they tend to balance each other in the overall sense for the system. A hierarchy of statistical applications is developed: classical one-at-a-time (OAT) approach, level 1; linear analysis of variance (ANOVA), level 1.5; fractional factorial (FF), or level 2; two-factor interaction (TFI) technique, or level 2.5; and a non-linear response surface methodology (RSM), or level 3. Using the First ISLSCP Field Experiment (FIFE) observations for June 6, 1987 as the initial condition for a SVAT scheme dynamically coupled to a PBL model, the interactions between uncertainty errors are analyzed. A secondary objective addresses the temporal changes in the uncertainty pattern using data for morning, afternoon, and evening conditions. It is found that the outcome from the level 1 OAT-like studies can be considered as the limiting uncertainty values for the majority of mesoscale cases. From the higher-level analyses, it is concluded that for most of the moderate surface scenarios, the effective uncertainty from the individual parameters is balanced and thus lowered. However, for the extreme cases, such as near wilting or saturation soil moisture, the uncertainties add up synergistically and these effects can be even greater than those from the outcomes of the OAT-like studies. Thus, parameter uncertainty cannot be simply related to its deviation alone, but is also dependent on other parameter settings. Also, from the temporal changes in the interaction pattern studies, it is found that, for the morning case soil texture is the important parameter, for afternoon vegetation parameters are crucial, while for the evening case soil moisture is capable of propagating maximum uncertainty in the SVAT processes. Finally, a generic hypothesis is presented that an appropriate question for analysis has to be rephrased from the previous 'which parameters are significant?’ to 'what scenarios make a particular parameter significant?’  相似文献