Reliability of Daniels systems subject to Gaussian load processes

A general method is developed for estimating reliability of Daniels systems subject to quasistatic and dynamic Gaussian load processes. The method is based on a generalization of the Slepian model, an identity involving first passage time probabilities and conditional mean crossing rates of response processes, and first/second order reliability methods. The use of the method is illustrated by an example.     

A hierarchical system to predict behavior of soil and cantilever sheet wall by data-driven models

The study proposes a framework combining machine learning (ML) models into a logical hierarchical system which evaluates the stability of the sheet wall before other predictions. The study uses the hardening soil (HS) model to develop a 200-sample finite element analysis (FEA) database, to develop the ML models. Consequently, a system containing three trained ML models is proposed to first predict the stability status (random forest classification, RFC) followed by 1) the cantilever top horizontal displacement of sheet wall (artificial neural network regression models, RANN1) and 2) vertical settlement of soil (RANN2). The uncertainty of this data-driven system is partially investigated by developing 1000 RFC models, based on the application of random sampling technique in the data splitting process. Investigation on the distribution of the evaluation metrics reveals negative skewed data toward the 1.0000 value. This implies a high performance of RFC on the database with medians of accuracy, precision, and recall, on test set are 1.0000, 1.0000, and 0.92857, respectively. The regression ANN models have coefficient of determinations on test set, as high as 0.9521 for RANN1, and 0.9988 for RANN2, respectively. The parametric study for these regressions is also provided to evaluate the relative insight influence of inputs to output.     

瞬态瑞雷面波技术在人工填土勘察中的应用

查明场地内人工填土的分布范围与厚度是岩土工程勘察工作的一项基本内容。尤其是市政工程,如顶管工程、道路工程等,填土勘察的准确性直接影响到设计方案的选取。本文以滨海新区南港工业区某管道穿越工程为例,开展了多道瞬态面波测试技术在人工填土勘察中的应用,根据瞬态面波测试结果结合少量钻孔资料,较为准确地查明了场地范围内填土的分布及厚度,为施工方案设计以及管道穿越深度的确定提供了重要参考资料,取得了较好的工程效果。     

应力波通过非线性平行节理的能量分析

 应力波在节理岩体中传播规律的研究是开展地下工程安全性分析的基础。着重研究纵波(P波)以任一角度入射一组非线性平行节理的能量传递规律,其中节理的法向模型采用双曲线型的BB模型,而节理的切向模型为线性模型。首先,基于应力波在时域内的递归分析方法,建立P波通过某一岩体的应力波传播方程,其中该岩体中存在一组非线性平行节理;其次,通过计算应力波通过该岩体前后的透反射能量,分析应力波能量大小的改变;最后,引入透射能量系数与反射能量系数,对影响能量传递的因素开展参数分析,即研究节理的初始刚度、间距、数量以及应力波幅值、频率和入射角度等因素对P波能量传递规律的影响。研究表明,应力波在节理处的能量传递规律不仅与节理的力学特性有关,而且也和节理的空间分布相关,且当应力波的物理特性如频率和波幅发生改变时,能量传递规律会出现不同的变化。     

Modeling the spread of COVID-19 in New York City

This paper proposes an ensemble predictor for the weekly increase in the number of confirmed COVID-19 cases in the city of New York at zip code level. Within a Bayesian model averaging framework, the baseline is a Poisson regression for count data. The set of covariates includes autoregressive terms, spatial effects, and demographic and socioeconomic variables. Our results for the second wave of the coronavirus pandemic show that these regressors are more significant to predict the number of new confirmed cases as the pandemic unfolds. Both pointwise and interval forecasts exhibit strong predictive ability in-sample and out-of-sample.     

A comprehensive bulk chlorine decay model for simulating residuals in water distribution systems

Chlorine decay models provide efficient ways to develop disinfection strategies for water distribution systems, provided they account separately for bulk and wall decay, and accurately describe decay with a single set of coefficients. The augmented two-reactant (2RA) model is shown to be the simplest model to accurately describe effects of rechlorination dose/timing on bulk chlorine decay, in combination with effects of initial concentration and temperature over long periods. The two-reactant (2R) and variable reaction-coefficient (VRC) models provided predictions of comparable accuracy under higher and successive rechlorination doses at constant temperature. However, the 2RA model provides a more general basis for strategy development, as the VRC model cannot describe the effect of temperature variation. The minimal data-set required for 2RA calibration was similar for all cases considered. The 2RA model is readily applied by incorporation into system modelling software such as the multi-species extension (MSX) to EPANET software.     

基于反分析方法的沉桩过程分析

可靠的土性资料是准确预测沉桩可打入性的前提条件。崖城气田RDPP1平台建设中的土性资料离散性较大,给进行准确的打桩分析带来了困难。根据现有的地质勘察资料和试桩的打桩记录,采用反分析方法借助波动方程和相关的计算程序,经过对比分析最终确定了适宜的土性参数并用于该工程的打桩分析中,沉桩过程的分析结果与工程实测资料吻合较好。说明该方法具有较好的可行性和实用性,可为工程设计人员参考使用。     

基于低空倾斜摄影与三维激光扫描技术的城市三维建模研究

城市三维模型是基础地理信息的重要组成部分之一,是建设三维地理信息系统、实现三维城市规划和城市信息化建设的基础.本研究综合利用倾斜摄影测量技术和三维激光扫描技术,探索三维精细化模型生成的新工艺.采用低空飞行平台同时搭载航摄仪和三维激光扫描仪获取多源数据,利用ContextCapture等软件实现点云数据的拼接、生产和编辑...     

基于TSP地震波法的长大隧道不良地质探测

应用TSP203地震波法对某长大隧道不良地质区段进行了超前探测,对TSP系统所采集到的数据进行分析,判定了断层破碎带和隐伏含水构造发育的规模与位置,并在TSP报告指导下进行超前钻探,进一步精确确定不良地质区段位置,为超前预注浆加固提供了参数。对开挖后的地质情况进行了跟进观测,验证了TSP地震波法对不良地质探测的准确性与有效性,对类似工程有一定的指导意义。     

GPS水准高程异常模型及模型诊断

讨论了 GPS水准测量高程异常模型的建立。根据数据诊断理论 ,对高程异常拟合模型进行分析。研究了对建模作用显著的控制点检验方法 ,使模型达到优化并提高精度。最后 ,结合实例分析表明 ,利用合适的差值模型或二次模型 ,在一定范围内实施 GPS水准跨江高程传递 ,达到 等水准精度是可行的。     

软土应力各向异性及其对深基坑工程的影响

天然软粘土一般都具有应力各向异性.在有些大型深基坑工程中,忽略了土体应力各向异性的影响将可能无法保证分析结果的准确性.作者首先回顾了有关土体应力各向异性对基坑抗隆起稳定性影响的研究现状,包括极限平衡法、常规弹塑性位移有限单元法以及极限分析有限单元法等.对于理论分析方法,尤其是有限单元法,均需要合理描述应力各向异性对土体应力-应变-强度特性的影响.为此通过对Wheeler各向异性模型进行改进以得到一个更为合理的模型,并与Boston Blue粘土的有关三轴试验结果进行了比较,验证了模型的合理性.     

A method to consider replaced pipes in modeling of sewer pipe deterioration

Statistical models that predict the deterioration of sewer pipes are useful for planning financial resources required for sewer renewal. Usually, data that are available to calibrate these models solely concern pipes that are still in place, leading to underestimated deterioration rates. A new method is proposed to consider possible past replacement of pipes in the statistical modeling of their deterioration. The proposed method considers the aging of pipes, simulated with a Cox model, and their probability to be replaced separately. Application to a synthetic sewer network, for which it was assumed that information regarding all pipe replacements over the lifetime of the network was available, showed that the proposed method allows for improved predictions of the sewer deterioration model, when compared to predictions of a model calibrated without considering the information about replaced pipes.     

波形钢板混凝土黏结滑移性能试验研究与数值模拟分析

通过波形钢板混凝土推出试验,对波形钢板混凝土黏结滑移受力机理、黏结强度和黏结滑移本构关系等关键问题进行研究。设计8个推出试件,主要研究波角和波谷长度因素对黏结滑移性能的影响,考察波形钢板波角、波脊和波谷处混凝土黏结性能。结果表明,对于波谷和波脊尺寸相同的波形,当波角为钝角时,黏结强度随着波角的增大而增大;当波角为锐角时,黏结强度随着波角的增大而减小。同时,对于相同波角的波形,黏结强度随着波谷的增大而减小。在微滑移阶段和滑移阶段,波形钢板应变沿埋置长度方向呈指数分布;波脊和波角处的应变要大于波谷轴心处的应变;在破坏阶段、荷载下降阶段和残余阶段,波形钢板应变分布复杂,并且在埋置长度上有过零点现象。根据所有试件加载端和自由端的荷载 滑移曲线试验结果,利用统计回归的方法得到波形钢板混凝土特征黏结强度的计算公式。通过建立力学平衡方程,得知波形钢板黏结应力沿着锚固深度呈指数分布,进一步建立考虑位置函数的黏结滑移本构模型。基于ANSYS有限元软件分别从基准黏结滑移本构关系、考虑位置函数的黏结滑移本构关系对试件进行数值模拟,结果表明考虑位置函数的黏结滑移本构关系更具有准确度。     

Extreme values — an improved method of fitting

The Fisher—Tippet Type 1 (FT1) probability distribution has been widely used for plotting extreme values and making long-term predictions from individual sets of data. Commonly some 20–40 annual maximum values may be available whereas an estimate of the 50- or 100-year return period value is actually required.This paper examines the implications of current procedures for fitting wind data to the FT1 distribution. Using a Monte Carlo simulation technique it is shown that, for a set of data generated from the FT1 distribution, a “better” regression model (in the sense that all values, including outliers, are better accounted for) is obtained by selectively ignoring upper percentiles of the data than by including all of the data. The optimum regression model ignores ~10% of the highest values. For the purposes of this paper a new method of determining the “betterness” of a regression model is developed.The variation in the results obtained by using different regression models suggests that the accuracy to which estimates are currently quoted, namely at least two significant figures, should be revised. It is concluded that the true significance of the results would be better expressed by classifying the data recording stations into groups,characterised by a group mean. It remains then to determine the range for each group.     

基于外海环境预报的近岸岛礁桥址区波高ANN推算模型

中国跨海桥梁多建于近岸岛礁海域,桥址区的波浪要素随时空演变复杂。桥址区波高的准确推算对于桥梁结构设计和施工组织具有十分重要的意义。提出一种基于外海环境预报数据的近岸岛礁桥址区波高人工神经网络（ANN）推算模型,并以平潭海峡公铁两用大桥桥址海域为研究对象,运用ANN算法中常用的BP神经网络对外海海洋预报台提供的波高、风速数据以及在桥址区实测波高数据进行训练,建立二者之间的映射关系及ANN推算模型。为验证推算模型的可行性和有效性,运用上述模型对桥址区连续80 d的海浪波高进行推算,通过对比前人模型和实测数据发现,推算波高和实测波高的变化趋势基本吻合,均方根误差满足预测要求,获得了理想的预测效果。研究表明,提出的波高ANN推算模型可以利用外海预报信息进行近岸岛礁桥址区的波高推算,且建模过程较为简单。     

两种跨河水准测量方法的实测分析

某隧道工程采用了光学测微法和三角高程两种方法实施跨河水准测量,分析了两种测量方法的施测过程和测量结果。跨河水准测量采用水准仪不过河的双线过河测量方法在短距离、成像清晰的条件下是可行的,可以消除水准仪i角对线路闭合差的影响,但成果计算时应考虑i角对高差的影响,不量取仪器高和棱镜高进行三角高程测量可以较方便地完成跨河测量,并能够满足国家规范的二等水准测量要求;照准误差是三角高程测量高差中误差的主要来源,因此应尽可能地采用高精度的测量仪器。     

The application of a genetic algorithm to estimate material properties for fire modeling from bench-scale fire test data

A methodology based on an automated optimization technique that uses a genetic algorithm (GA) is developed to estimate the material properties needed for CFD-based fire growth modeling from bench-scale fire test data. The proposed methodology involves simulating a bench-scale fire test with a theoretical model, and using a GA to locate a set of model parameters (material properties) that provide optimal agreement between the model predictions and the experimental data. Specifically, a GA based on the processes of natural selection and mutation is developed and integrated with the NIST FDS v4.0 pyrolysis model for thick solid fuels. The combined GA/pyrolysis model is used with cone calorimeter data for surface temperature and mass loss rate histories to estimate the material properties of two charring materials (redwood and red oak) and one thermoplastic material (polypropylene). This is done by finding the parameter sets that provide near-optimal agreement between the model predictions and experimental data, given the constraints imposed by the underlying physical model and the accuracy with which the boundary and initial conditions can be specified. The methodology is demonstrated here with the FDS pyrolysis model and cone calorimeter data, but it is general and can be used with several existing fire tests and almost any pyrolysis model. Although the proposed methodology is intended for use in CFD-based prediction of large-scale fire development, such calculations are not performed here and are recommended for future work.     

爆炸冲击波传播的数值模拟与试验数据对比

针对爆炸冲击波在坑道自由场传播的试验，建立了相应的有限元模型，运用大型有限元软件争DYNA进行了数值模拟。并与试验数据进行了对比，得出了数值模拟方法可行的结论，为今后研究坑道自由场爆炸冲击波的传播规律提供了理论依据和计算方法，同时也为坑道防护设计提供了参考依据。     

Three-dimensional finite difference analysis of shallow sprayed concrete tunnels crossing a reverse fault or a normal fault: A parametric study

Urban tunnels crossing faults are always at the risk of severe damages. In this paper, the effects of a reverse and a normal fault movement on a transversely crossing shallow shotcreted tunnel are investigated by 3D finite difference analysis. After verifying the accuracy of the numerical simulation predictions with the centrifuge physical model results, a parametric study is then conducted. That is, the effects of various parameters such as the sprayed concrete thickness, the geo-mechanical properties of soil, the tunnel depth, and the fault plane dip angle are studied on the displacements of the ground surface and the tunnel structure, and on the plastic strains of the soil mass around tunnel. The results of each case of reverse and normal faulting are independently discussed and then compared with each other. It is obtained that deeper tunnels show greater displacements for both types of faulting.