城市化效应对上海短历时设计暴雨强度的影响

了解城市化对短历时设计暴雨强度的影响，对改善市政基础设施的设计、管理有重要意义。利用上海徐汇区40年完整的降雨资料和市郊站点25年的短历时降雨年最大值资料，分别推求了上海市中心城区和市郊区县的暴雨强度公式。通过同一时期中心城区和区县设计雨量的对比，结合气候和地理因素的影响分析，揭示了上海中心城区与市郊短历时设计暴雨强度的差异及其与重现期的关系。在国内目前的设计重现期下，城市化效应对上海城区排水系统的设计标准并无实质性影响；重现期〉1a，则中心城区的设计雨量反而小于郊县，其暴雨强度公式应用于多数区县排水系统的设计不甚安全；南汇区的短历时设计暴雨强度明显大于中心城区，其排水系统设计宜考虑采用当地的暴雨强度公式。     

Selecting a series of storm events for a model-based assessment of combined sewer overflows

The hydraulic verification of combined sewer systems as well as the assessment of combined sewer overflows (CSOs) can be conducted using a hydrodynamic model. Unfortunately, long-term simulations with hydrodynamic models for the assessment of CSOs can cause unacceptably long computation times. Using only a series of storm events instead of a precipitation continuum can reduce this time and enables parallel simulation of single storm events. We introduce a method to select this series of storm events. The method’s parameters have been optimized to replicate the overflow volume of the continuous simulation and to minimize the overall computation time. This optimization revealed a generally applicable parameter set that results in series of storm events that are shorter than the precipitation continuum by 86.2–95.2% for the investigated cases. Additionally, the deviation of overflow volume between continuous simulation and series simulation ranges between only 0.1% and 4.1%.     

Quantitative fault tree analysis for urban water infrastructure flooding

Flooding in urban areas can be caused by heavy rainfall, improper planning or component failures. Few studies have addressed quantitative contributions of different causes to urban flood probability. In this article, we apply probabilistic fault tree analysis for the first time to assess the probability of urban flooding as a result of a range of causes. We rank the causes according to their relative contributions. To quantify the occurrence of flood incidents for individual causes we use data from municipal call centres complemented with rainfall data and hydrodynamic model simulations. Results show that component failures and human errors contribute more to flood probability than sewer overloading by heavy rainfall. This applies not only to flooding in public areas but also to flooding in buildings. Fault tree analysis has proved useful in identifying relative contributions of failure mechanisms and providing quantitative data for risk management.     

计算机模拟技术在镇江市城区排水管理中的应用

根据镇江市的地面积水点、排水管道水位、雨量自动监测和天气预报数据,应用SWMM5.0软件建立了城区排水管网的计算机模拟模型,它可对不同强度的降雨是否产生城市内涝灾害进行模拟,预测特定地点在降雨之后的积水状况,预警暴雨灾害,发布沥涝预警信息,及时为城市暴雨事故抢险和雨季交通管理等提供科学决策依据.     

Multinormal integrals by importance sampling for series system reliability

A structural system with multi-failure modes can be modeled as a series system if it fails whenever any of the failure mode occurs. Applying FORM, failure probability of a series system can be expressed using a complementary standard multinormal integral. However, the integral is increasingly more difficult as the dimension increases. Importance sampling method can be used to deal with such multi-fold integration. Considering the fact that the optimal importance sampling function can be determined for a linear limit state function in a uncorrelated standard normal space, this paper proposes an importance sampling function for multinormal integral as a linear combination of such optimal sampling functions. The accuracy and applicability of the method are investigated using numerical examples.     

Sensitivity estimation within first and second order reliability methods

An efficient method to compute the sensitivity of failure probability estimates to changes in distribution parameters is proposed. The method is applicable to failure probability estimates obtained by first and second order reliability methods (FORM and SORM). It is based on the fact that current FORM and SORM approaches require transforming the problem into standard normal space and then numerically fitting first/second order approximations. To compute the change in failure probability due to a change in parameter, one can transform the points that were used to numerically fit the approximation into a new standard normal space corresponding to the changed parameter, fit a new approximation and use the new approximation to compute the changed failure probability.The proposed method is computationally efficient because it does not require any new structural response evaluations. In contrast to conventional methods that are accurate for FORM estimates of component problems, the proposed method is accurate for FORM and SORM estimates of both component and system problems.     

Continuous simulation of CSO emissions

Modelling is an essential method to predict the behaviour of various water systems in urban areas. A common problem of modelling these systems is that it is hardly possible to model them fully in a detailed way. The applications of existing hydrodynamic models are very data-intensive and time-consuming, particularly for continuous simulation using a long rainfall record. It is thus necessary to develop a new modelling approach which is correct in representing and efficient in dealing with the processes involved in urban water systems. SewSim is such a conceptual combined sewer overflow (CSO) emission model. SewSim has been developed using a dynamic programming package MATLAB and its toolbox SIMULINK. This paper presents some case studies using this model for continuous simulation.     

基于城市内涝数值模拟的设计暴雨雨型研究

以南昌市青山湖排涝片区为研究对象,从典型暴雨的选择入手,结合现行规范要求,分析了不同典型暴雨的放大方法以及水利部门"综合雨型"的优缺点,应用MIKE软件模拟不同设计暴雨雨型对城市排涝过程的影响。通过对泵站开机负荷、主要控制断面的水位和流量等情况的对比分析,提出城市内涝防治体系设计暴雨雨型计算方法的选择建议。研究结果表明,同倍比放大法虽然便于应用,但其主要统计时段降雨量的重现期差异很大,难以客观评价市政排水与流域排涝系统的能力;同频率放大法能够控制主要时段的"同频",但其时间刻度需要细化,调算过程较为复杂,而且不同典型暴雨同频放大条件下的排涝过程差异较大;"复合雨型"可以兼顾城市排水与流域排涝系统的能力复核,雨型生成过程相对简单,便于应用。     

Reliability analysis of rock slopes involving correlated nonnormals

A two-dimensional rock slope in Hong Kong and a three-dimensional hypothetical tetrahedral wedge are analyzed probabilistically using an intuitive and transparent constrained optimization approach for the first-order reliability method (FORM). The results are compared with Monte Carlo simulations. Simple procedures for incorporating truncated non-normal distributions in reliability analysis are described. The effects of statistical correlations on the computed reliability index are studied. The difference between probabilities of failure inferred from reliability index and from Monte Carlo simulations are investigated via the response surface method. It is shown that the efficiency of reliability-based approach can be combined with the robustness of Monte Carlo simulation. The meanings of reliability index and probability of failure are also discussed.     

基于Beta分布的改进的一次可靠度法研究

为了提高一次可靠度方法的计算精度和计算效率,文章利用Beta分布拟合了功能函数中的随机变量的概率分布,利用VBA语言给出了将Beta分布和对数正态分布转化为标准正态分布的方法,采用蒙特卡洛模拟法比较了采用不同概率分布的一次可靠度计算精度。算例分析表明:当功能函数中随机变量服从对数正态分布时,失效概率被高估;当随机变量服从正态分布时失效概率被低估。利用本文提出的Beta分布拟合随机变量的概率不仅大大提高了计算精度,而且在保证迭代收敛的前提下提高了计算效率。     

Multiple design points in first and second-order reliability

A method is developed to successively find the multiple design points of a component reliability problem, when they exist on the limit-state surface. FORM or SORM approximations at each design point followed by a series system reliability analysis is shown to lead to improved estimates of the failure probability. Three example applications show the generality and robustness of the method.     

Kriging response surface reliability analysis of a ship-stiffened plate with initial imperfections

The use of structural reliability methods with implicit limit state functions (LSFs) shows the increasing demand for efficient stochastic analysis tools, because the structural behaviour predictions are often obtained by finite element analysis. All stochastic mechanics problems can be solved by Monte Carlo simulation method, nevertheless, in most cases, at a prohibitively high computational cost. Several approximations can be achieved using first-order reliability method (FORM) and second-order reliability method and response surface methods. In this paper, a method that combines the FORM and Kriging interpolation models, as response surface, is proposed. The prediction accuracy of the Kriging response surface obtained from different sampling techniques is assessed, and the failure probability estimates calculated by the FORM using the classical second-order polynomial regression models and the Kriging interpolation models as surrogates of nonlinear LSFs are compared. The usefulness and efficiency of the reliability analysis using the Kriging response surface are demonstrated on the basis of existing results available in the literature and with an application problem of a stiffened plate structure with initial imperfections.     

EVALUATION OF THE PROBABILITY OF FAILURE WITH UNCERTAIN DISTRIBUTION PARAMETERS

Formulations are presented for estimating probability of failure considering uncertainty of distribution parameters in time invariant and time variant reliability analyses. Based on the formulations the probability of failure can be calculated by recursively using the first order reliability method. Also, a more efficient approximate analysis procedure by using the point estimate method to estimate the probability of failure is given. In this analysis procedure, the point estimate method is used to discretize the uncertain distribution parameters in the time invariant reliability analysis, and to discretize the time-independent random variables and uncertain distribution parameters in the time variant reliability analysis. The probability of failure is then obtained by weighting the probability of failure conditioned at each of discrete points. The conditional probability of failure can be calculated by using first order reliability method, second order reliability method or any other convenient methods. The use of point estimate method to treat uncertain distribution parameters in calculating probability of failure is less computer time consuming than the one of recursively using FORM. Illustrative numerical examples of calculating probability of failure are presented.     

基于单变量降维模型和坐标旋转的可靠度混合分析方法

经典的一次可靠度方法对于隐式功能函数和强非线性功能函数的可靠度问题存在适用性问题,尽管二次可靠度方法可以一定程度上处理强非线性功能函数的问题,但理论基础和计算过程均颇为复杂,不利于实用。为克服上述问题,将一次可靠度确定验算点的过程与响应面法的思路相结合是一种行之有效的思路。为此,文中首先引入具有普适性的一次可靠度法,其中考虑了相关非正态随机变量的Nataf变换,并引入单边差分法针对性地解决了隐式功能函数求偏导数的问题|其次,根据梯度值引入坐标旋转向量,并对旋转后的功能函数引入单变量函数降维近似模型|再次,结合验算点的函数值、梯度值以及附加点的函数值,确定各分量函数的二次多项式近似,从而获得近似的整体功能函数|然后,采用重要性抽样法计算近似功能函数的失效概率|最后,分别通过数值算例和工程算例对建立方法的精度和效率进行了验证。结果表明建议方法具有高精度、高效率的特点,且无论对于显式和隐式功能函数均具有广泛适用性。     

Time-dependent system reliability analysis by adaptive importance sampling

A method for evaluating time-dependent reliability of a structural system subjected to stochastic loads is presented. Structural deterioration due to environmental stressors is also taken into account. An adaptive Monte Carlo simulation procedure combined with conditional expectation is proposed. The optimum common ratio of the standard deviation of an importance sampling variables to that of the corresponding original valuables is estimated iteratively as well as their mean values. Unlike systems evaluated by simple Monte Carlo simulations, the accuracy of the failure probability evaluated by adaptive importance sampling is relatively insensitive to the magnitude of the probability.     

基于扩散波方法的管网排水过程数值模拟

基于扩散波方法,构建了一套排水管网水动力模型,并与已开发的高分辨率城市地表水文水动力模型进行了耦合。以理想排水管网和陕西省西咸新区沣西新城某小区实际排水管网的排涝过程验证模型,并模拟城市暴雨致涝过程。结果表明:理想算例中,该模型与SWMM模拟排水口流量过程高度吻合;实际算例中,与实测排水口流量过程对比,该模型的Nash-Sutcliffe效率系数分别为0.74、0.72、0.93和0.71,大于SWMM模型的0.62、0.66、0.73与0.65。在模拟研究区内涝积水过程时,计算数据与实测数据吻合度高,内涝积水点均实现精确模拟。     

Structural reliability under monotony: Properties of FORM, simulation or response surface methods and a new class of Monotonous Reliability Methods (MRM)

In many mechanical or physical systems, the failure function, albeit complex and computationally intensive, happens to be monotonous with respect to its uncertain model inputs. In that case, some properties can be derived on the partial robustness of classical methods such as FORM, Monte–Carlo or response surfaces to estimate rare failure probabilities under the constraint of the number of expensive model runs, such as robust probability bounds, saved number of model runs or guaranteed variance reduction. A new formulation taking full advantage of monotony is introduced along with a family of associated Monotonous Reliability Methods (MRM). They consist in narrowing progressively some robust upper and lower bounds on the failure probability through an adaptive design of experiment. A number of variants can be considered: they comprise adaptive Monte–Carlo, dedicated response surfaces and deterministic design of experiments or hybrid variants with classical FORM or simulation methods. Their common advantages are that the prediction accuracy of the failure probability is guaranteed with certainty; additional model runs always ameliorate the accuracy; a change of the uncertainty model is possible without additional runs. Performance is compared on benchmarks including a nuclear finite-element mechanical study and a simple flooding model. Simple MRM variants appear quite promising in low input dimensions with highly efficient computation of a bounding established with certainty. Research perspectives are given to extend the efficiency of the methods in higher dimensions and address the relaxing of full monotony hypotheses.     

基于SWMM模型与低影响开发模式的 滨水地区内涝防控方案——以厦门市杏林湾 选区为例

在快速城镇化进程中,由于硬质下垫面面积比例增加,导致城市内涝问题日益突出。选取厦门市杏林湾地区作为研究对象,以绿色经济与低影响开发为目标,运用SWMM技术构建降雨-径流模型,分别对低影响开发前后的地块进行暴雨重现期2年一遇和5年一遇情景的模拟,确定地块内涝易发区域积水节点,根据节点位置布设低影响开发(LID)措施,以此提高研究区对内涝灾害的承受能力。情景模拟结果为:杏林湾选区在重现期2年一遇时,地块东部海湾口处容易出现内涝现象;重现期5年一遇降雨导致杏林湾选区排水系统出现大范围节点溢流,主要集中在湾区滨水空间及海湾口处。通过对易涝区增设LID措施降低径流总量、削减洪峰小时流量,从而使年径流控制率提升至77.5%,降低城市内涝灾害风险。     

基于SWMM耦合模型的道路行泄通道设计方法与应用

针对现有道路行泄通道的设计方法仅适用于道路单独排水、忽略道路明渠流与管道压力流之间水动力相互作用的问题,提出了一种基于SWMM构建道路明渠流与管道压力流耦合的水力排涝模型,来进行道路行泄通道设计以应对极端降雨事件的方法。并以某山地城市为例,构建SWMM雨水管道水力模型,进行50年一遇降雨情景下的内涝模拟,获得易涝点分布。在此基础上,根据内涝区域的竖向分析和水文分析,结合管道排水能力,设置道路行泄通道系统,构建水力耦合排涝模型。并利用耦合排涝模型优化行泄通道设计参数,对比不同方案下情景模拟结果,获得符合实际情况的行泄通道,最终确定行泄通道设计方案。案例分析表明,基于水力耦合排涝模型的道路行泄通道设计方法,考虑了道路明渠流与管道压力流之间水动力相互作用以及流量交换,反映了极端暴雨条件下道路与管道联合排涝系统的实际运行状态,使得行泄通道的设计更为系统、合理。     

基于暴雨雨型的设计径流量研究及应用

为简化排水模型在城市排水防涝规划中的应用,利用武汉短历时暴雨雨型,采用三角概化法推导出雨型径流量计算公式。通过武汉雨型径流量设计程序在9个排水区的应用,在相同重现期标准下与武汉暴雨强度公式进行对比,同频率雨型设计径流量的平均绝对值相对误差为1. 29%,最大误差<5%。采用相关因子拟合公式计算排水区节点雨水汇流时间,可建立雨型径流量节点管控简化模型,无需排水管网建模,可实现城市排水防涝规划水位管控,也可进行雨水溢流污染控制调节池容量的计算。