Reliability analysis for aeroengine turbine disc fatigue life with multiple random variables based on distributed collaborative response surface method

The fatigue life of aeroengine turbine disc presents great dispersion due to the randomness of the basic variables,such as applied load,working temperature,geometrical dimensions and material properties.In order to ameliorate reliability analysis efficiency without loss of reliability,the distributed collaborative response surface method(DCRSM) was proposed,and its basic theories were established in this work.Considering the failure dependency among the failure modes,the distributed response surface was constructed to establish the relationship between the failure mode and the relevant random variables.Then,the failure modes were considered as the random variables of system response to obtain the distributed collaborative response surface model based on structure failure criterion.Finally,the given turbine disc structure was employed to illustrate the feasibility and validity of the presented method.Through the comparison of DCRSM,Monte Carlo method(MCM) and the traditional response surface method(RSM),the results show that the computational precision for DCRSM is more consistent with MCM than RSM,while DCRSM needs far less computing time than MCM and RSM under the same simulation conditions.Thus,DCRSM is demonstrated to be a feasible and valid approach for improving the computational efficiency of reliability analysis for aeroengine turbine disc fatigue life with multiple random variables,and has great potential value for the complicated mechanical structure with multi-component and multi-failure mode.

RELIABILITY ANALYSIS METHODFOR STRUCTURAL STIFFNESS

The reliability analysis for stiffness of large and complex structure systemsis present. and relative significance is introduced as a criterion to enumerate significantrandom variables. Simplications of limit state functions and selections of interpolatio

Stochastic analysis of excavation-induced wall deflection and box culvert settlement considering spatial variability of soil stiffness

In this study, a three-dimensional (3D) finite element modelling (FEM) analysis is carried out to investigate the effects of soil spatial variability on the response of retaining walls and an adjacent box culvert due to a braced excavation. The spatial variability of soil stiffness is modelled using a variogram and calibrated by high-quality experimental data. Multiple random field samples (RFSs) of soil stiffness are generated using geostatistical analysis and mapped onto a finite element mesh for stochastic analysis of excavation-induced structural responses by Monte Carlo simulation. It is found that the spatial variability of soil stiffness can be described by an exponential variogram, and the associated vertical correlation length is varied from 1.3 m to 1.6 m. It also reveals that the spatial variability of soil stiffness has a significant effect on the variations of retaining wall deflections and box culvert settlements. The ignorance of spatial variability in 3D FEM can result in an underestimation of lateral wall deflections and culvert settlements. Thus, the stochastic structural responses obtained from the 3D analysis could serve as an effective aid for probabilistic design and analysis of excavations.

Seismic performance analysis of underground structures based on random field model of soil mechanical parameters

Soils with spatial variability are the product of natural history.The mechanical properties tested by soil samples from boreholes in the same soil layer may be different.Underground structure service in surrounding soils,their seismic response is controlled by the deformation of the surrounding soils.The variability of soil mechanical parameters was not considered in the current research on the seismic response of underground structures.Therefore,a random field model was established to describe the spatial variability of surrounding soils based on the random field theory.Then the seismic response of underground structures in the random field was simulated based on the time-domain explicit global FEM analysis,and the soil mechanical parameters and earthquake intensity influencing the seismic response of surrounding soils and underground structures were studied.Numerical results presented that,the randomness of soil parameters does not change the plastic deformation mode of surrounding soils significantly.The variation coefficients of inter-story deformation of structures and lateral deformation of columns are much smaller than that of mechanical parameters,and the randomness of soil parameters has no obvious effect on the structural deformation response.

Advanced reliability analysis of slopes in spatially variable soils using multivariate adaptive regression splines

This study aims to extend the multivariate adaptive regression splines(MARS)-Monte Carlo simulation(MCS) method for reliability analysis of slopes in spatially variable soils. This approach is used to explore the influences of the multiscale spatial variability of soil properties on the probability of failure(P_f) of the slopes. In the proposed approach, the relationship between the factor of safety and the soil strength parameters characterized with spatial variability is approximated by the MARS, with the aid of Karhunen-Loeve expansion. MCS is subsequently performed on the established MARS model to evaluate Pf.Finally, a nominally homogeneous cohesive-frictional slope and a heterogeneous cohesive slope, which are both characterized with different spatial variabilities, are utilized to illustrate the proposed approach.Results showed that the proposed approach can estimate the P_f of the slopes efficiently in spatially variable soils with sufficient accuracy. Moreover, the approach is relatively robust to the influence of different statistics of soil properties, thereby making it an effective and practical tool for addressing slope reliability problems concerning time-consuming deterministic stability models with low levels of P_f.Furthermore, disregarding the multiscale spatial variability of soil properties can overestimate or underestimate the P_f. Although the difference is small in general, the multiscale spatial variability of the soil properties must still be considered in the reliability analysis of heterogeneous slopes, especially for those highly related to cost effective and accurate designs.

Reliability analysis of slopes considering spatial variability of soil properties based on efficiently identified representative slip surfaces

Slope reliability analysis considering inherent spatial variability(ISV)of soil properties is timeconsuming when response surface method(RSM)is used,because of the"curse of dimensionality".This paper proposes an effective method for identification of representative slip surfaces(RSSs)of slopes with spatially varied soils within the framework of limit equilibrium method(LEM),which utilizes an adaptive K-means clustering approach.Then,an improved slope reliability analysis based on the RSSs and RSM considering soil spatial variability,in perspective of computation efficiency,is established.The detailed implementation procedure of the proposed method is well documented,and the ability of the method in identifying RSSs and estimating reliability is investigated via three slope examples.Results show that the proposed method can automatically identify the RSSs of slope with only one evaluation of the conventional deterministic slope stability model.The RSSs are invariant with the statistics of soil properties,which allows parametric studies that are often required in slope reliability analysis to be efficiently achieved with ease.It is also found that the proposed method provides comparable values of factor of safety(FS)and probability of failure(Pf)of slopes with those obtained from direct analysis and lite rature.

Structural Reliability Analysis and Design Optimization of Hot-Rolled H-beam Steel Universal Mill

The structure of a hot-rolled H-beam steel universal mill was optimized,including bearing chocks( upper and lower) and mill frame. To verify the reliability of the optimized structure, the parameters of rolling mill and parts were analyzed by finite element,including the maximum stress,strain and maximum displacement.The results showed that the maximum displacement of the mill frame and the bearing chock was 0. 049 mm,and the maximum stress was2. 659 MPa. The maximum stress of the mill was 3. 181 MPa. There were no obviously elastic deformation and plastic deformation,which satisfied the structural requirements. The reliability of the optimized mill structure was verified.

Extremum selection method of random variable for nonlinear dynamic reliability analysis of turbine blade deformation

To effectively select random variable in nonlinear dynamic reliability analysis,the extremum selection method(ESM)is proposed.Firstly,the basic idea was introduced and the mathematical model was established for the ESM.The nonlinear dynamic reliability analysis of turbine blade radial deformation was taken as an example to verify the ESM.The results show that the analysis precision of the ESM is 99.972%,which is almost kept consistent with that of the Monte Carlo method;moreover,the computing time of the ESM is shorter than that of the traditional method.Hence,it is demonstrated that the ESM is able to save calculation time and improve the computational efficiency while keeping the calculation precision for nonlinear dynamic reliability analysis.The present study provides a method to enhance the nonlinear dynamic reliability analysis in selecting the random variables and offers a way to design structure and machine in future work.

Hybrid Structure Reliability Analysis Based on the Damped Newton Method

This paper presents a hybrid model reliability analysis method based on the damped Newton method with both random and interval variables to solve the hybrid structure reliability problem.The method combines an outer iterative solution and inner layer numerical calculation.In the outer iteration,the method seeks an optimized solution to the interval variable iterative by adding the boundary constraint condition based on the damped Newton optimization theory.In the inner layer solution,the method first reduces the dimension of the random variable through the dimension reduction method,then obtains the first four-order central moment of the function through the application of the Taylor expansion method,and finally calculates the reliability index of the structure according to the fourth-order moment calculation structure of the function.The results of a numerical example and an engineering ten-rod truss structure show that the proposed method can effectively solve the random-interval hybrid reliability problem and has better calculation accuracy than that of the two-layer iterative method.

Asymptotic Analysis Methods for Structural Reliability

Applying Laplace asymptotic approximation of integral, asymptotic analysis methods of structural reliability are proposed in generalized and orthogonal random space. Analytic results show that the proposed methods are simple in calculation and accurate enough for problems of continuous random variables.

考虑套筒灌浆随机缺陷的装配式剪力墙结构可靠度评估

在装配整体式剪力墙结构中,由于套筒灌浆连接的质量具有一定的随机性,势必影响结构的竖向连接性能和结构抗震性能。根据不同缺陷程度的套筒灌浆拉拔试验,建立了一套等效套筒灌浆缺陷连接承载力模型,并基于某实际工程结构,建立了装配整体式剪力墙结构有限元模型。通过考虑灌浆缺陷的随机性,赋予连接接头相应缺陷程度的力学连接性能,来反映套筒灌浆中可能存在的缺陷。通过非线性有限元分析并结合概率密度演化方法(probability density evolution method,PDEM)进行了结构随机非线性反应分析和可靠度评估。结果表明:在动力作用下,结构非线性与随机性具有明显的耦合效应;缺陷的随机性会随着时间的推移,逐渐放大对结构响应的影响;在不同的安全域内,结构的整体可靠度将存在较大的差异。

基于混合元的变刚度层合板静力学分析

针对变刚度层合结构,大多采用板壳理论或常规的位移有限元法分析其力学行为。相较位移元,非协调广义部分混合元同时引入位移和应力边界条件,提高了应力结果精度,且边界应力更符合真实情况。扩展了纯弹性体的非协调广义部分混合元理论,提出适用于变刚度层合结构修正的非协调广义部分混合元模型。与ABAQUS计算结果对比证明,即使在网格较稀疏的情况下,该文方法也具有较好的适用性,且数值结果精确度高。通过算例分析了纤维铺设角度的变化对变刚度层合板平面内位移场的影响,可为变刚度结构的设计提供一定的思路。

基于抓持力补偿策略的变刚度软性手指结构优化与实验研究

针对以往研究主要关注对已有手指结构的参数进行优化,而缺乏根据所需抓持性能进行结构设计的问题,提出了一种基于抓持力补偿策略的变刚度软性手指结构的优化设计方法。首先,为了更加全面地评估软性手指的抓持性能,提出了三种评价指标;为使所提出的基本结构手指具有更早且线性变化的抓持力及更好的抓持稳定性,提出了一种利用变刚度机构特性补偿手指抓持力的设计策略,并基于该策略设计出了一种悬臂梁结构变刚度手指;然后,利用ANSYS有限元分析软件,使用多目标优化方法对悬臂梁结构变刚度手指进行了结构优化,分析了悬臂梁变刚度特性,并将优化后的手指与基本结构手指的抓持性能进行了对比;最后,利用测试平台进行了抓持性能试验,对仿真结果进行了验证。研究结果表明:与基本结构手指相比,基于抓持力补偿策略所得手指的抓持力响应点提前了33.3%,抓持后期的抓持力变化线性拟合相关系数R 2高达0.9997,抓持力方向角减小了约71.4%;抓持力实验结果与仿真结果相比,抓持力的误差最大值小于0.5 N,抓持力方向角误差最大值小于4°,说明基于抓持力的补偿策略能够指导软性手指的设计,并有效提高手指的抓持性能。

APPLICATION OF STOCHASTIC FINITE ELEMENT METHOD TO STRENGTH AND STABILITY ANALYSIS OF EARTH DAMS

This paper applies the stochastic finite element method to analyse the statistics of stresses in earth dams and assess the safety and reliability of the dams. Formulations of the stochastic finite element method are briefly reviewed and the procedure for assessing dam's strength and stability is described. As an example, a detailed analysis for an actual dam Nululin dam is performed. A practical method for studying built-dams based on the prototype observation data is described.

考虑渗透系数空间变异性的超高心墙堆石坝渗流分析

为探究超高心墙堆石坝多组防渗材料空间变异性对渗流安全的影响,根据建立的随机渗流分析模型,对某超高心墙堆石坝内多组防渗材料的渗透系数进行空间离散,系统研究坝体和坝基内渗流控制指标的演变规律。结果表明:心墙渗透系数的变异系数每增加0.1,其最大水力坡降的均值增大约9.8%,远高于帷幕灌浆和天然坝基。同时考虑基岩与帷幕灌浆的随机渗流特性后,帷幕前压力水头的最大值与仅考虑帷幕灌浆时增大了5%,坝基材料的空间变异性对帷幕灌浆渗流安全有一定影响。忽视防渗体的空间变异性,会高估防渗结构的渗流安全状态。

基于埃尔曼神经网络的高压涡轮叶片低周疲劳可靠性分析

涡轮叶片是航空发动机的关键部件,其主要失效模式为低周疲劳。为了提高涡轮叶片低周疲劳寿命的计算精度和效率,考虑材料参数和载荷的分散性,探索埃尔曼神经网络与蒙特卡罗抽样相结合的方法对涡轮叶片低周疲劳可靠性进行分析。首先利用有限元分析软件对涡轮叶片进行热-结构耦合分析,得到最大等效应力和应变数据;然后将数据代入到低周疲劳寿命理论模型中得到涡轮叶片的低周疲劳寿命;再将涡轮叶片有关随机参数作为输入变量,低周疲劳寿命作为输出变量,训练具有高精度的埃尔曼神经网络模型,实现对高压涡轮叶片的低周疲劳寿命预测和可靠性评估。与传统响应面法和蒙特卡罗方法进行对比,结果表明埃尔曼神经网络不但可以满足精度要求,而且计算效率得到显著提高。

随机参数桁架结构的有限元与可靠性分析

对随机参数桁架结构在随机荷载作用下的有限元分析方法进行了研究.分别或同时考虑了结构的物理参数、构件的几何尺寸和作用荷载幅值等的随机性;应用代数综合法,对结构位移和应力响应随机变量的数字特征计算表达式进行了推导,进而得到结构各响应量的可靠度指标.通过算例表明文中提出的基于概率的随机桁架结构分析与可靠性分析方法的合理性与可行性.

平稳随机激励下随机机架结构动力可靠性分析

研究了随机桁架结构在平稳随机激励下的动力可靠度求解方法。同时考虑结构物理参数、几何尺寸的随机性,利用求解随机变量数字特征的代数综合法和矩法,从结构随机响应的频域表达式出发,导出了随机桁架结构在平稳随机激励下的位移、应力及其导数响应均方值的数字特征,再由动力可靠性的Poisson公式导出了结构动力可靠度的计算公式。通过算例分析了各参数的随机性对结构动力可靠度的影响,验证了该方法的可行性和有效性。

公路路堤结构可靠性设计方法研究

在综合分析路堤结构边坡稳定和沉降设计方法的基础上，引入可靠性理论，提出了适合可靠性设计的极限状态方程和路堤结构设计参数的变异水平，并在对可靠度方法及目标可靠度研究的基础上，建立了路堤结构可靠性设计框图。其成果可供路基结构设计方法由确定型向概率型转变参考使用。

工程结构可靠度分析方法综述

对现有的工程结构可靠度分析方法进行了分类概括、评述,介绍了各种分析方法的特点和进展.