Variable gain feedback control technique of active mass damper and its application to hybrid structural control

A systematic design procedure and an algorithm are devised for variable gain feedback (VGF) control of buildings with active mass damper (AMD) systems. The limit of the stroke length of the auxiliary mass, which is considered to be one of the most important physical constraints for application of AMD systems to actual structures, is studied. A set of variable feedback gains is designed as a function of a single variable that indicates a trade-off between the reduction of the building response and the amplitude of the auxiliary mass stroke, and this variable is on-line controlled to keep the amplitude of the auxiliary mass stroke constant, and within its limits. A design method of static output feedback controller for modal control of buildings with non-classical damping is also presented. Next, an efficient control method for hybrid structural control is developed, with combined use of the VGF control and the static output feedback control. It is shown through numerical examples that the proposed control method effectively adapts the control performance according to the variation in the intensity level of the external excitations in such a manner that the amplitude of the auxiliary mass stroke is kept within its limits and the control power is restrained as well. The application range of the AMD systems is thereby improved significantly. © 1997 John Wiley & Sons, Ltd.     

地震偏移成像不确定性分析初探

勘探地球物理领域存在大量宏观动力学过程的物理数学表达及尚待深入探索的不确定性事实,其中一类是源自对偶量的不可交换性或不可对易性.本文从地震偏移成像中的不确定性分析入手,探讨偏移成像中受到波场延拓过程不确定性的影响.文中给出了若干深度偏移算法对Marmousi模型的偏移不确定度分布表达及图像显示;文中还对若干波场延拓方法,从不确定性估计的角度进行了比较.笔者认为对应用技术领域中的宏观不确定性分析,将有益于深化对宏观动力学过程的理性认识,也为偏移算法评价提供一种途径;重要的是,进行不确定性分析将有利于把握所用偏移算法的不确定度分布,继而有针对性地采取相应的改善措施,以期提高算法的整体确定性程度.     

岛屿环流理论发展回顾及展望

为了寻找岛屿环流理论进一步发展的突破口,使其在长期气候变化背景下海洋的响应以及深海环流等海洋领域前沿研究方向中继续起到指导作用,首先回顾了岛屿环流理论的发展过程,对其重要的发展里程碑和实际应用进行了系统梳理。同时,对岛屿环流理论未来进一步丰富发展的重点方向进行了展望。分析结果显示,该理论仍存在深入发掘的潜力,可在积分路径设计、时间变化项的影响和地形及斜压效应的影响等多方面进行细节修正和补充,拓展其应用的时间和空间尺度。     

钢悬链线立管强度可靠性计算研究

在钢悬链线立管分析中,材料性能、载荷参数、计算方法等都存在着大量不确定性。为考虑不确定性因素造成的影响,采用作用效应-抗力半随机过程构建可靠性模型,并采用极小化变换转化为静态可靠性问题。选用物理含义较为明确的屈服判定准则建立功能函数,通过单样本K-S检验对载荷随机过程的概率特性进行极值统计,提出载荷转化的方法以实现与目标可靠性指标的比对,并引入模型和主观不确定性随机变量。在此基础上采用改进的一次二阶矩法,对立管的强度可靠性进行了计算。结果表明此方法与利用系数方法能够相互印证,可以为立管的可靠性计算提供参考。     

基于滞后变量模型的城市群建设用地增长对经济增长的滞后期和效应分析——以京津冀城市群为例

城市群建设用地增长对经济增长存在客观的时间滞后效应,即“用地投入—建设开发—效益产生—效益爬坡—效益稳定”的全周期过程。计算其滞后期长短和总效应大小,并挖掘导致差异的内在机制,对区域建设用地的供给与管理及经济社会的可持续发展具有重要意义。论文以1995—2017年京津冀城市群13个主要城市的统计数据为支撑,提出了建设用地增长对经济增长的滞后变量模型,定量确定了京津冀城市群各城市的滞后期长短、各滞后期的效应以及总效应,并发现了以下规律：① 城市群建设用地增长对经济增长存在普遍的滞后效应,滞后期在0~4 a;② 城市群建设用地增长对经济增长存在显著的正面效应,总效应介于1.66~49.5亿元/km2;③ 城市群建设用地增长对经济增长的滞后期和总效应均呈现出“中心—边缘”的空间分异特征;④ 滞后期主要与城市的等级和功能定位有关,高等级的中心型城市、中等级的副中心型城市和低等级的节点型城市对应的滞后期分别为4 a、2 a和0~2 a;⑤ 总效应主要与产业构成有关,城市产业高、中、低端对应的效应分别为30亿~50亿、10亿~20亿、1亿~10亿元/km2。     

Simulating monthly streamflow using a hybrid feature selection approach integrated with an intelligence model

ABSTRACT

Streamflow prediction is useful for robust water resources engineering and management. This paper introduces a new methodology to generate more effective features for streamflow prediction based on the concept of “interaction effect”. The new features (input variables) are derived from the original features in a process called feature generation. It is necessary to select the most efficient input variables for the modelling process. Two feature selection methods, least absolute shrinkage and selection operator (LASSO) and particle swarm optimization-artificial neural networks (PSO-ANN), are used to select the effective features. Principal components analysis (PCA) is used to reduce the dimensions of selected features. Then, optimized support vector regression (SVR) is used for monthly streamflow prediction at the Karaj River in Iran. The proposed method provided accurate prediction results with a root mean square error (RMSE) of 2.79 m³/s and determination coefficient (R² ) of 0.92.     

变厚度钢板内芯防屈曲支撑试验研究

提出了一种变厚度钢板内芯防屈曲支撑（VTBRB）。设计了2个足尺变厚度钢板内芯防屈曲支撑试件,其中:1个试件在变厚度内芯端部设置加劲肋;另1个试件采用无肋式变厚度内芯。通过拟静力试验分析了2种内芯构造形式对变厚度钢板内芯防屈曲支撑的滞回性能、失效模式、受压承载力调整系数和累计塑性变形等的影响。研究表明:2个变厚度钢板内芯防屈曲支撑均表现较好的抗震耗能特性,其受压承载力调整系数均满足相关规范的限值要求。设置加劲肋可以减少变厚度内芯端部无粘结材料的磨损,并可以有效提高变厚度内芯防屈曲支撑的低周疲劳性能。     

Brightness variability investigation of BD+61°154

Photoelectric ubvyHαHβ observations of the Herbig Ae/Be star BD+61°154 are presented. The observational data are analyzed proceeding from the simple hypothesis that the light variation is mainly due to temperature changes of gaseous envelope.