柱顶受轴力的柱列支撑受力分析

采用蒙特卡罗方法,考虑柱子初始缺陷和撑杆初始缺陷的随机遇合问题,应用有限元程序ANSYS对柱顶受轴力的柱列支撑体系进行了大量的仿真分析,得到了柱列纵向支撑体系的两种失稳模式;通过概率统计得到柱中水平撑杆所受内力的双正态概率密度函数,据此确定了可用于实际工程设计的支撑力的大小。结果表明:当柱顶轴力相等时,采用《钢结构设计规范》(GB 50017—2003)中柱列支撑设计公式计算支撑力偏大;当柱顶轴力不等时,采用规范公式计算支撑力将更保守;柱子初始缺陷和撑杆初始缺陷的随机遇合作用导致柱中水平撑杆受压力或拉力的随机性,降低了支撑力。     

Pipe failure rate prediction in water distribution networks using multivariate adaptive regression splines and random forest techniques

ABSTRACT

This paper presents the results of a comparison between multivariate adaptive regression splines (MARS) and random forest (RF) techniques in pipe failure prediction in two water distribution networks. In this regard, pipe diameter, pipe length, pipe installation depth, pipe age and average hydraulic pressure are considered as input variables. Results show that the RF outperforms the MARS which is found as an accurate pipe failure rate predictor. The proposed models are further evaluated through dividing the data into three parts of lower, medium and higher pipe failure rate values. According to the equations produced by MARS technique, three variables of pipe diameter, pipe age and average hydraulic pressure are distinguished as the most effective variables in predicting pipe failure rate in the first case study. Four variables of pipe diameter, pipe length, pipe age and average hydraulic pressure are determined as the most effective variables in the second case study.     

基于整体承载极限状态的钢结构可靠度设计方法及其在门式钢刚架设计中的应用

本文提出了基于整体承载极限状态的钢结构可靠度设计思路。这种思路建立在钢结构整体非线性分析和验算的基础上,并确保结构整体而非构件的可靠度水平,使结构整体的实际可靠度水平尽可能地接近于设计的目标值。本文针对门式钢刚架结构建立了一套实现这种设计的方法,包括结构整体非线性分析、结构体系可靠度计算以及实用的设计表达式。通过三个门式钢刚架结构设计实例比较了传统的构件设计方法,不考虑体系可靠度的整体承载极限状态设计方法和本文考虑体系可靠度的整体承载极限状态设计方法的设计结果,说明本文所提出设计思想的先进性。     

自适应有限元不同网格间力学结果传递方法及程序实现

对于依赖于加载历史的自适应有限元分析问题,不同网格间力学结果的传递过程起着重要作用。基于按距离加权平均的改进插值方法,研究分步加载时自适应有限元不同网格间力学结果的继承问题。为使传递结果合理并减小计算工作量,插值方法采取选择邻近数据点、考虑方向影响、适当提高结果场的光滑性并使其通过全部已知数据点等措施;针对开挖过程中结构介质不断改变、开挖工作面不断移动及不同开挖步引入的介质之间场变量不连续等特点,采取分区划分网格并插值方式,构造不同网格间应力及位移结果的传递过程。所述传递过程,能为自适应有限元模拟多步骤开挖及弹塑性增量荷载分析等各种分步加载计算问题的解决提供有利条件。最后,给出2个算例以验证传递过程的可靠性。按增量荷载初应力方法对厚壁筒弹塑性分析表明,其结果与理论解吻合;模拟多步开挖的工程实例计算结果亦展示出所述传递方法的有效性。     

Random vibration of a train traversing a bridge subjected to traveling seismic waves

Non-stationary random vibration of 3D time-dependent train-bridge systems subjected to multi-point earthquake excitations, including wave passage effect, is investigated using the pseudo-excitation method (PEM). The motion equation of such a system is established by coupling the train and bridge through wheel-rail contact relationships and accounting for the phase-lags between pier excitations. The horizontal and vertical earthquake excitations are both assumed to be uniformly modulated, fully coherent random excitations with different phases, while the excitation due to track irregularities is assumed to be a 3D, fully coherent random excitation with velocity-dependent time lags. PEM is first proven to be applicable to such time-dependent systems, and is then used to transform the random excitations into a series of deterministic pseudo excitations. By solving for the corresponding deterministic pseudo responses, various non-stationary random responses, including the time-dependent power spectral density functions (PSD) and standard deviations (SD), can be obtained easily. A case study is then presented in which the China-Star high-speed train traverses a seven-span continuous bridge that is being excited by an earthquake. The results show the effectiveness and accuracy of the proposed method by comparison with a Monte Carlo simulation. Additionally, the influences of seismic apparent wave velocity and train speed on the system random responses are discussed.     

Optimization of indoor climate conditioning with passive and active methods using GA and CFD

This study aims at the development of an optimal design tool using a genetic algorithm (GA) and computational fluid dynamics (CFD). Random variables (fluctuating outdoor conditions), passive design elements (model variables) and active design elements (HVAC system) were set up to represent a realistic building environment. A combination of designs is determined based on the relationship between fluctuating outdoor conditions and the HVAC system in the optimal design search. Building environment designs should consider both active and passive design elements because the HVAC system keeps adjusting the supply air flow rate until the indoor climate reaches target conditions when outdoor conditions are changing.     

岩石的细胞元特性及其非均质分布对岩石全曲线性态的影响

采用非均质数值试验方法,研究了在无限大刚度的试验机条件下,岩石的细胞元特性及其非均质分布对岩石单轴压缩全程曲线性态的影响。结果表明,当岩石的非均质参数m≥6时,细胞元的非均质参数m是决定岩石单轴压缩全程曲线性态的主要因素;当m<6时,岩石的细胞元特性是决定岩石单轴压缩全程曲线性态的主要因素。     

一种基于业务区分的随机接入方案

通过对移动通信系统关键技术的发展趋势和网络实时业务服务质量（QoS）需求的分析,提出了一种适用于时分－正交频分多址接入系统（TD-OFDMA）的简单高效的随机接入方案。在该方案中,网络终端利用特有的优先随机接入信道（FRRACH）对不同时延特性的业务采用不同的随机接入机制,从而有效地避免分组碰撞,保障实时业务的QoS需求。理论分析和仿真结果表明,该方案在成功接入概率、接入时延以及资源利用率等方面的性能较目前常用的随机接入方案有着较大的改善。     

精细搜索策略应用于质量交换网络综合

质量交换网络是化工过程系统的重要组成部分,其优化设计对降低污染排放具有重要意义。采用启发式算法优化质量交换网络时,存在难以兼顾全局搜索和局部搜索的问题。通过分析不同精度优化参数下的优化结果,揭示了该问题的成因,并提出一种精细搜索策略用于基础算法所得结构的深度优化。该策略包含两种方法,方法1采用具有个体回代与分化的高精度强制进化随机游走算法,可保留个体结构变异能力;方法2采用确定性方法依次对多维目标函数中的每个变量进行一维搜索,具有精度高收敛快的优点。将该策略应用于焦炉气脱硫和空气除氨算例,得到的结果分别为407308 USD·a^-1和127807 USD·a^-1,经济性优于现有文献中的结果,验证了本策略的有效性。     

基于过程模拟和随机森林模型的生物质制氢过程因素分析与预测

生物质可以替代化石燃料,减少温室气体排放,是一种有前途的可再生能源。生物质通过化学链气化制备氢气,碳化活化制备活性炭,两条工艺路线耦合可以联产绿色能源氢气和具有高附加值的活性炭,但是原材料选择和工艺参数优化成为规模化生产的主要障碍。在生物质联产氢气和活性炭工艺模型的基础上,建立高性能的随机森林预测模型,并探究生物质组分、工艺参数和过程产物对联产工艺的相对重要性。结果表明：生物质组分中的灰分、碳元素、氢元素的含量以及气体重整温度和水蒸气用量是准确预测氢气浓度和产量的重要影响因素。其中,重整温度、合成气中氢气浓度、水蒸气用量三个影响因素对氢气浓度的影响高达61%,活化剂用量、水蒸气用量两个因素对氢气产量的影响高达63%。此外,基于随机森林模型对生物质制氢过程中的因素进行分析和优化,可以实现氢气浓度达到96.8%(体积)。