共查询到20条相似文献，搜索用时 15 毫秒
1.
岩土工程可靠度分析中,功能函数往往呈隐式且具有强非线性性质,而目前最为实用的矩方法,如JC法、二次二阶矩法,主要适用于显式功能函数情形。为此,将高效的统计矩估计方法和可靠度分析的高阶矩法相结合,提出了一种岩土工程可靠度分析的改进四阶矩方法。首先,通过引入变量的独立化变换和线性变换将功能函数转换为参考变量的函数,并结合多变量函数的单变量降维近似方法和参考变量计算节点与权系数的确定方法,建立了功能函数前四阶矩的高效点估计法。然后,将上述统计矩与立方正态变换假设相结合,提出了易于实现的岩土工程可靠度分析的改进四阶矩方法。最后,由数学算例验证了统计矩估计方法的效率和精度,并通过经典的岩土工程算例验证了建议的改进四阶矩方法具有高效率、高精度且操作简单等特点。 相似文献
2.
提出了基于支持向量机（SVM）的边坡可靠度分析新算法。该方法采用均匀设计确定样本点,通过一定数量的确定性计算来训练SVM,拟合边坡的功能函数;采用一阶可靠度方法（FORM）和迭代算法优化SVM模型,获得可靠度指标和验算点信息;在SVM模型基础上进一步通过二阶可靠度方法（SORM）和蒙特卡罗模拟（MCS）计算边坡的失稳概率。以两个典型边坡为例,通过与其他方法比较,证明了该方法的准确性和高效性。结果表明：提出的在标准正态空间（U空间）中取样并构建SVM,在原始空间（X空间）中计算功能函数的算法,有效地解决了具有相关非正态分布变量的可靠度分析问题,并且可很容易扩展到SORM的计算。算例结果证明,该方法的精度高于FORM;而效率优于MCS。分析过程中,边坡安全系数计算和可靠度分析相互独立。因此,该方法既适用于具有显式功能函数的简单问题,也适用于需要软件计算安全系数的实际边坡问题。 相似文献
3.
Two advanced Kriging metamodeling techniques were used to compute the failure probability of geotechnical structures involving spatially varying soil properties. These methods are based on a Kriging metamodel combined with a global sensitivity analysis that is called in literature Global Sensitivity Analysis-enhanced Surrogate (GSAS) modeling for reliability analysis. The GSAS methodology may be used in combination with either the Monte Carlo simulation (MCS) or importance sampling (IS) method. The resulting Kriging metamodeling techniques are called GSAS-MCS or GSAS-IS. The objective of these techniques is to reduce the number of calls of the mechanical model as compared with the classical Kriging-based metamodeling techniques (called AK-MCS and AK-IS) combining Kriging with MCS or IS. The soil uncertain parameters were assumed as non-Gaussian random fields. EOLE methodology was used to discretize these random fields. The mechanical models were based on numerical simulations. Some probabilistic numerical results are presented and discussed. 相似文献
4.
As numerical models are increasingly used as a design tool in geotechnical engineering, it is highly desirable if geotechnical reliability analysis can be conducted based on numeral models. Currently, the practical use of geotechnical reliability analysis-based numerical models is still quite limited. In this study, an easy to access method is derived to conduct geotechnical reliability analysis based on numerical models. To facilitate its application, a procedure is outlined to implement the suggested method such that geotechnical reliability analysis can be automated using existing geotechnical numerical packages. The procedure is illustrated in detail with an example, and the source codes provided can be easily adapted to analyze other similar problems. The method described in this paper is used to study the reliability of a deteriorating reinforced concrete drainage culvert in Shanghai, China. The suggested method provides a convenient means for reliability analysis of complex geotechnical problems. 相似文献
5.
可靠度分析中梯度求解方法的研究 总被引：2，自引：0，他引：2
在岩土工程的可靠度分析中，功能函数的形式非常复杂，甚至是隐式的。而对于常用的可靠度分析方法，如一阶可靠性方法（FORM）、二阶可靠性方法（SORM）等，一个重要的问题是求功能函数对基本随机变量的梯度。因此，对于隐式的或复杂的显式功能函数，必须采用数值微分方法来求解功能函数的梯度。对于可靠度分析中常用的有限差分法（FDM）及有理多项式法（RPT）这两种数值微分方法，本文详细研究了二者问的异同及其求导结果与步长的关系，指出了对于相同的步长控制系数及取样方式，FDM是RPT在线性情况下的特例；对于连续的线性功能函数，可直接用3点FDM求导：对于连续的非线性功能函数，可用5点RPT求导；对于非连续的功能函数，应采用RPT求导。建议取步长控制系数等于1。 相似文献
6.
A reliability analysis method based on the combination of the first-order reliability method (FORM) and hybrid particle swarm optimization (SACPSO) is presented for the reliability optimization calculation. The new reliability method, named as SACPSO-FORM, can be utilized for those complex reliability problems with correlated non-normal variables and implicit performance functions. Three examples are performed to verify its validation, and stability reliability analysis on the complicated rock foundation of a practical gravity dam is demonstrated. The results show that the proposed method is accurate, stable, flexible and efficient for reliability analysis in engineering applications. 相似文献
7.
Polynomial chaos expansions (PCEs) have been widely employed to estimate failure probabilities in geotechnical engineering. However, PCEs suffer from two deficiencies: (a) PCE coefficients are solved by the least-square minimization method which easily causes overfitting issues; (b) building a high order PCE is often computationally expensive. In order to overcome the aforementioned drawbacks, the Bayesian regression technique is employed to evaluate PCE coefficients, which not only provides a sparse solution but also avoids overfitting. With the aid of the predictive means and variances given by Bayesian analysis, a learning function is proposed to sequentially select the most informative samples that are critical to build a PCE. This sequential learning scheme can highly enhance the computational efficiency of PCEs. Besides, importance sampling (IS) is incorporated into the sequential learning (SL)-PCEs to deal with geotechnical problems with small failure probabilities. The proposed method of SL-PCE-IS is applied to three illustrative examples, which shows that the improved PCE method is more effective and efficient than the common PCEs method, leading to accurate estimations of small failure probabilities using fewer training samples. 相似文献
8.
相关型岩土参数分析和选用 总被引：2，自引：0，他引：2
岩土参数与应力环境、沉积条件、风化程度和埋藏条件等因素相关,其统计值具有空间变异性和相关性,采用非相关型岩土统计参数进行岩土工程设计具有不经济性。通过分析岩土参数的变化规律及与其相关的主要因素,说明岩土参数可用深度或参数与地层顶面或底面的距离作为相关参数进行相关型判别,论述相关型参数的判定标准和相关型标准值的计算方法,采用图解法分析相关型参数多种取值方法的可靠性。以华南某核电厂常规岛地基和某变电站边坡为例,介绍了相关型岩土参数标准值经验公式在岩土设计优化中的应用。分析表明：具有规律性变化的岩土参数宜选择恰当的相关参数划分为相关型,相关参数可取参数与地层顶面或底面的距离,相关型岩土参数标准值可使岩土设计方案更具合理性和经济性。 相似文献
9.
针对岩土工程的功能函数强非线性且难以显式表达的特点,提出了基于人工神经网络的四阶矩法,充分利用了基本随机变量的统计信息。首先利用神经网络对结构的隐式功能函数进行拟合,求得基本随机变量在均值点处的功能函数值及其偏导数,然后利用泰勒级数展开的方法由基本随机变量的前四阶矩求得功能函数的前四阶矩,并借助于Pearson系统获得功能函数的更高阶矩。在此基础上,通过最大熵原理确定以功能函数各阶矩为约束的功能函数的概率密度函数,最后由一次积分得到结构的失效概率。通过数值算例和工程实例不同方法的对比分析,表明基于神经网络的结构可靠度分析四阶矩方法是可行的,有效的,能够满足岩土工程可靠度分析的要求。 相似文献
10.
相关情况下Hasofer_Lind可靠度指标的求解 总被引：15，自引：0，他引：15
岩土工程的可靠度计算中, 基本变量之间往往存在着较强的相关性。 阐述了相关情况下 Hasofer-Lind 可靠度指标计算的几种方法: 正交变换法; 改进的验算点一次二阶矩法; Monte-Carlo 模拟法; 优化求解法。 在用优化方法求解可靠度指标 β 时, 利用 Microsoft Excel 中的规划求解器来进行优化求解, 避免了相关变量的独立变换以及求极限状态函数对基本变量的偏导数这两个问题。 实例比较了不同方法的求解结果。 相似文献
11.
受工程勘察成本及试验场地限制,可获得的试验数据通常有限,基于有限的试验数据难以准确估计岩土参数统计特征和边坡可靠度。贝叶斯方法可以融合有限的场地信息降低对岩土参数不确定性的估计进而提高边坡可靠度水平。但是,目前的贝叶斯更新研究大多假定参数先验概率分布为正态、对数正态和均匀分布,似然函数为多维正态分布,这种做法的合理性有待进一步验证。总结了岩土工程贝叶斯分析常用的参数先验概率分布及似然函数模型,以一个不排水黏土边坡为例,采用自适应贝叶斯更新方法系统探讨了参数先验概率分布和似然函数对空间变异边坡参数后验概率分布推断及可靠度更新的影响。计算结果表明：参数先验概率分布对空间变异边坡参数后验概率分布推断及可靠度更新均有一定的影响,选用对数正态和极值I型分布作为先验概率分布推断的参数后验概率分布离散性较小。选用Beta分布和极值I型分布获得的边坡可靠度计算结果分别偏于保守和危险,选用对数正态分布获得的边坡可靠度计算结果居中。相比之下,似然函数的影响更加显著。与其他类型似然函数相比,由多维联合正态分布构建的似然函数可在降低对岩土参数不确定性估计的同时,获得与场地信息更为吻合的计算结果。另外,构建似然函数时不同位置处测量误差之间的自相关性对边坡后验失效概率也具有一定的影响。 相似文献
12.
LHS方法在边坡可靠度分析中的应用 总被引：8，自引：0，他引：8
Monte Carlo（MC）法在目前边坡可靠度分析中是一种相对精确的方法,应用广泛,受问题限制的影响较小,适应性很强,其误差仅与标准差和样本容量有关。但其精度受随机抽样的可靠性和模拟次数制约,收敛速度慢,影响了实际使用。在极限平衡方法的基础上,用拉丁超立方抽样（Latin hypercube sampling,LHS）方法代替MC法的随机抽样,考虑边坡参数的变异性和相关性进行边坡可靠度分析。讨论了LHS法、MC法中可靠指标的各种计算方法,建议以破坏概率、安全系数均值和标准差作为评价指标。算例显示LHS法较MC法效率上有很大改善：较少的抽样样本就能反映参数的概率分布,可靠度分析收敛快,不需要大量的模拟,因此,值得在边坡可靠度分析中推广应用。也将工程上常用的均匀设计和正交设计用于边坡可靠度分析,结果表明,正交设计结果和中心点法比较接近,而均匀设计得到的结果则是不可靠的。 相似文献
13.
在有限数据条件下,可靠度敏感性分析是研究各种不确定性因素对边坡失稳概率影响规律的重要途径。基于直接蒙特卡洛模拟和概率密度加权分析方法提出了一种高效边坡稳定可靠度敏感性分析方法。所提出的方法通过随机场表征岩土体参数的空间变异性,并采用局部平均理论建立岩土体参数的缩维概率密度函数,用于概率密度加权分析中高效、准确地计算不同敏感性分析方案对应的边坡失稳概率。最后,通过一个工程案例--詹姆斯湾堤坝说明了所提出方法的有效性和准确性。结果表明：在敏感性分析过程中,所提出的方法只需要执行一次直接蒙特卡洛模拟,避免了针对不同敏感性分析方案重新产生随机样本和执行边坡稳定分析,节约了大量的计算时间和计算资源,显著提高了基于蒙特卡洛模拟的敏感性分析计算效率;在概率密度加权分析中采用岩土体参数的缩维概率密度函数能够准确地计算边坡失稳概率,避免了有偏估计,使概率密度加权分析方法适用于考虑空间变异性条件下的边坡稳定可靠度敏感性分析问题。 相似文献
14.
《地学前缘(英文版)》2018,9(6):1631-1638
To meet the high demand for reliability based design of slopes, we present in this paper a simplified HLRF(Hasofere Linde Rackwitze Fiessler) iterative algorithm for first-order reliability method(FORM). It is simply formulated in x-space and requires neither transformation of correlated random variables nor optimization tools. The solution can be easily improved by iteratively adjusting the step length. The algorithm is particularly useful to practicing engineers for geotechnical reliability analysis where standalone(deterministic) numerical packages are used. Based on the proposed algorithm and through direct perturbation analysis of random variables, we conducted a case study of earth slope reliability with complete consideration of soil uncertainty and spatial variability. 相似文献
15.
Explicit dynamic relaxation is an efficient tool that has been used to solve problems involving highly non-linear differential equations. The key feature of this method is the ability to use explicit dynamic algorithms in solving static problems. Few attempts have been made to date to apply this technique in conventional geotechnical engineering. In this study, an algorithm that incorporates the application of a stiffness dependent time step scheme is proposed. The algorithm has been successfully used to solve 2D and 3D non-linear geotechnical engineering problems. To calibrate the developed algorithm, numerical simulations have been conducted for a strip and square footings supported by Mohr–Coulomb material. Performance of four different types of brick elements used in collapse load calculation is examined in terms of convergence speed and accuracy. In addition, the role of employing adaptive time steps in reducing the number of iterations needed for convergence is also evaluated. 相似文献
16.
The first order reliability method (FORM) is efficient, but it has limited accuracy; the second order reliability method (SORM) provides greater accuracy, but with additional computational effort. In this study, a new method which integrates two quasi-Newton approximation algorithms is proposed to efficiently estimate the second order reliability of geotechnical problems with reasonable accuracy. In particular, the Hasofer–Lind–Rackwitz–Fiessler–Broyden–Fletcher–Goldfarb–Shanno (HLRF–BFGS) algorithm is applied to identify the design point on the limit state function (LSF), and consequently to compute the first order reliability index; whereas the Symmetric Rank-one (SR1) algorithm is nested within the HLRF–BFGS algorithm to compute good approximations, yet with a reduced computational effort, of the Hessian matrix required to compute second order reliabilities. Three typical geotechnical problems are employed to demonstrate the ability of the suggested procedure, and advantages of the proposed approach with respect to conventional alternatives are discussed. Results show that the proposed method is able to achieve the accuracy of conventional SORM, but with a reduced computational cost that is equal to the computational cost of HLRF–BFGS-based FORM. 相似文献
17.
M. H. Hashemi 《Geomechanics and Geoengineering》2015,10(4):243-248
One of the significant problems in geo-environmental and geotechnical engineering is the unsaturated flow of soil in unsaturated soils. The model of this phenomenon in porous media is governed by the Richards equation. In this paper a new, efficient, iterative method is used to handle the Richards equation. This new technique is obtained from the variational iteration method by a simple reconstruction that is the Laplace iteration method (LIM). In order to evaluate the efficiency and accuracy of the solutions obtained by the proposed method, two representative examples were investigated. The obtained results show that the Laplace iteration method is a very effective method, simplifies the difficulty of classical techniques and is quite accurate for systems of partial differential equations. 相似文献
18.
A first‐order Taylor series method including direct derivative coding (DDC) is presented as a computationally efficient method for producing the probability distribution associated with calculated geotechnical performance. The probability distribution is employed in reliability analyses to calculate the probability of failure, valuable information that is not typically associated with deterministic analyses. The probability distribution also is used to identify important input parameters and to direct sampling efforts. Another approach to generate the probability distribution is the Monte Carlo (MC) method, however, Taylor series results generally are calculated in less time than the MC approach. One key to the implementation of the Taylor series approach is efficient approximation of the sensitivities required by the Taylor series calculation. DDC provides the technique to produce an efficient Taylor series algorithm. Directly coding the sensitivity analysis into the engineering model is accomplished by automatic and hand programming of derivatives. ADIFOR 2.0 was employed to automatically add derivatives to an existing engineering analysis model. For this paper a meshing program and 3D FEM for soil deformation is used to demonstrate the DDC approach. Although DDC requires a large up‐front programming effort, it is not site or data specific. Therefore, once the derivative programming has been performed, the numerical model can be applied to a wide variety of problems without additional user intervention. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
19.
岩土工程随机—模糊可靠度的概念和方法 总被引：6，自引：0，他引：6
岩体最基本属性之一是其力学性质的随机——模糊性。针对这种情况,本文分析了岩土工程随机可靠度理论面临的问题,提出了岩土工程随机——模糊可靠度的概念和计算方法。这种方法将模糊数学原理引入确定性分析,实现模——精结合,既充分考虑了岩石的客观属性,又满足了对工程稳定性定量评价的需要。 相似文献
20.
传统有限元强度折减法在边坡稳定性数值分析中取得了一定的成功,但由于未考虑岩土体材料参数的变异性等不确定性因素,尚不能直接应用于边坡稳定性特别是动力稳定性可靠性分析问题。为此提出了基于有限元强度折减法的地震边坡动力稳定性可靠性分析方法。将有限元极限分析法、动力分析法和可靠性分析法三者耦合,分析求解边坡在地震作用下的动力稳定性可靠性问题,并将这一过程在数值计算程序中得以实现。在计算分析过程中,克服了原方法需不断人工试算才能得到边坡安全系数而无法量化处理问题,并对边坡动力失效准则进行了适用于程序化的改进,使其计算过程完全实现自主运行。结合典型算例分析结果表明,该方法显著的特点是能较全面地反映岩土体的动力特性和边坡岩土体材料强度参数的变异性及相关性,所得结果相对更加合理且更符合工程实际。该方法既是对有限元强度折减法的应用范围的有益推广,也为边坡动力稳定性可靠性问题研究提供了一条新的有效途径。 相似文献