Predictive instantaneous optimal control of inelastic structures during earthquakes

A new inelastic structural control algorithm is proposed by incorporating the force analogy method (FAM) with the predictive instantaneous optimal control (PIOC) algorithm. While PIOC is very effective in compensating for the time delay for elastic structures, the FAM is highly efficient in performing the inelastic analysis. Unlike conventional inelastic analysis methods of changing stiffness, the FAM analyzes structures by varying the structural displacement field, and therefore the state transition matrix needs to be computed only once. This greatly simplifies the computation and makes inelastic analysis readily applicable to the PIOC algorithm. The proposed algorithm compensates for the time delay that happens in practical control systems by predicting the inelastic structural response over a period that equals the magnitude of the time delay. A one‐story frame with both strain‐hardening and strain‐softening inelastic characteristics is analyzed using this algorithm. Results show that the proposed control algorithm is feasibile for any inelastic structures. While the control efficiency deteriorates with the increase in magnitude of the time delay, the PIOC maintains acceptable performance within a wide range of time delay magnitudes. Finally, a computer model of a six‐story moment‐resisting steel frame is analyzed to show that PIOC has good control results for real inelastic structures. Copyright © 2003 John Wiley & Sons, Ltd.     

The Character of Shear-wave Splitting in Marble in the Critical State of Rupture

This paper mainly observed and analyzed the character of shear-wave splitting in rock specimens while they were in the critical state of rupture. The rock specimens for study are made of Laizhou marble from Shandong, China. A series of records were obtained from two rock specimens when they were in the critical state of rupture. The result shows that, in the critical state just before rock rupture, there may be the phenomenon of rise and fall in the time delay of shear-wave splitting, even though the load was kept constant. That is to say, the time delay of shear-wave splitting may have a falling process before rock rupture.     

亚暴期间等离子体对流速度及热层纬向风速度变化的统计学分析

本文利用2001年至2005年间CHAMP卫星及DMSP(F13,F15)卫星观测数据,对亚暴发生前后,亚暴初始位置所在磁地方时(Magnetic Local Time, MLT)东侧2 h(+2 h,MLT)至西侧4 h(-4 h,MLT)范围内等离子体对流速度(Vy)及热层纬向风速度(Uy)的变化进行了统计学分析.研究发现在亚暴发生后的1.5 h内,所有MLT区间的Vy均明显增大,且峰值位置的地磁纬度向赤道侧移动,1.5 h后,Vy减小,峰值的纬度向极区移动,表明亚暴的发生能显著增强等离子体对流速度;在亚暴发生位置的西侧0~2 h内,Vy增幅最大,这表明亚暴对热层的影响主要在西侧,影响最大的区域是西侧0~2 h MLT区间;Uy在亚暴发生后3 h持续增大,其对亚暴的响应相较于Vy有1.5 h的延迟.     

中纬热层大气质量密度经向结构差异研究

本文利用CHAMP卫星以及全球电离层-热层模型（GITM）来研究太阳活动低年（2007-2009年）中纬热层大气质量密度（ρ）的经度结构变化.结果如下：（1）ρ存在明显的经度单波结构（单峰和单谷）,且南北半球反相,波峰和波谷随着地方时增加而向东移动;（2）模拟表明离子拖曳效应在ρ结构差异的形成中起到了重要的作用,欧亚地区电子密度经度差异性较弱,不足以影响ρ经度分布,导致该地区ρ经度差异不明显;（3）在磁中纬地区,太阳天顶角的经度差异可达20°~30°,太阳光加热的经度不均匀性是导致ρ经度差异的另一个主要原因.     

基于改进的BP神经网络构建区域精密对流层延迟模型

利用神经网络算法挖掘海量数据的规律已成为科技发展的一种趋势,本文针对卫星信号的天顶对流层延迟进行建模.对流层延迟是影响卫星定位精度的重要因素之一,建立精密区域对流层模型对高精度定位有着重要的意义.对区域测站对流层延迟数据的分析,考虑到实时建模中传统BP（Back Propagation）神经网络计算量大,易出现"过拟合"现象、不稳定等因素,通过改进的BP神经网络建立了区域精密对流层模型.详细介绍了新模型的建立过程,并与常用的对流层区域实时模型进行了对比.还讨论了建模测站数目对预报精度的影响.相比现有的其他对流层延迟模型,基于改进的BP神经网络构建的区域精密对流层延迟模型无论在拟合和预报方面都有较好的精度,且随着测站数目的增加模型精度趋于平稳.改进的模型参数较少,可以进行实时的区域精密对流层延迟改正;需要播发的信息量小,适用于连续运行参考站系统（Continuously Operating Reference Stations,CORS）的应用.研究表明：改进的BP神经网络模型能够更好的充分利用大规模历史数据描述卫星信号对流层延迟的空间分布情况,适用于实时大区域精密对流层建模.基于日本地区2005年近1000多个测站的NCAR（National Center Atmospheric Research）对流层数据进行区域对流层延迟建模,结果表明改进的BP神经网络模型在拟合和预报精度上都有较大提升,RMSE（Root Mean Square Error）分别为：7.83 mm和8.52 mm,而四参数模型拟合、预报RMSE分别18.03 mm和16.60 mm.     

Predictive optimal control for seismic analysis of non-linear and hysteretic structures

In this paper, an effective active predictive control algorithm is developed for the vibration control of non-linear hysteretic structural systems subjected to earthquake excitation. The non-linear characteristics of the structural behaviour and the effects of time delay in both the measurements and control action are included throughout the entire analysis (design and validation). This is very important since, in current design practice, structures are assumed to behave non-linearly, and time delays induced by sensors and actuator devices are not avoidable. The proposed algorithm focuses on the instantaneous optimal control approach for the development of a control methodology where the non-linearities are brought into the analysis through a non-linear state vector and a non-linear open-loop term. An autoregressive (AR) model is used to predict the earthquake excitation to be considered in the prediction of the structural response. A performance index that is quadratic in the control force and in the predicted non-linear states, with two additional energy related terms, and that is subjected to a non-linear constraint equation, is minimized at every time step. The effectiveness of the proposed closed-open loop non-linear instantaneous optimal prediction control (CONIOPC) strategy is presented by the results of numerical simulations. Since non-linearity and time-delay effects are incorporated in the mathematical model throughout the derivation of the control methodology, good performance and stability of the controlled structural system are guaranteed. Copyright © 1999 John Wiley & Sons, Ltd.     

A stability analysis of a conduit flow model for lava dome eruptions

Periodic variations in magma discharge rate and ground deformation have been commonly observed during lava dome eruptions. We performed a stability analysis of a conduit flow model by Barmin et al. [Barmin, A., Melnik, O., Sparks, R.S.J., 2002. Periodic behavior in lava dome eruptions. Earth and Planetary Science Letters 199 (1-2), 173–184], in which the periodic variations in magma flow rate and chamber pressure are reproduced as a result of the temporal and spatial changes of the magma viscosity controlled by the kinetics of crystallization. The model is reduced to a dynamical system where the time derivatives of the magma flow rate (dQ/dt) and the chamber pressure (dP/dt) are functions of Q and P evaluated at a shifted time t − t_?. Here, the time delay t_? represents the time for the viscosity of fluid particle to increase in a conduit. The dynamical system with time delay is approximated by a simple two-dimensional dynamical system of Q and P where t_? is given as a parameter. The results of our linear stability analyses for these dynamical systems indicate that the transition from steady to periodic flow depends on nonlinearities in the steady state relation between Q and P. The steady state relation shows a sigmoidal curve in Q − P phase plane; its slope has negative values at intermediate flow rates. The steady state solutions become unstable, and hence P and Q oscillate periodically, when the negative slope of the steady state relation ([dP/dQ]_S) exceeds a critical value; that is [dP/dQ]_S < − t_?γ/(2V_ch), where V_ch is the chamber volume and γ is an elastic constant which is related to the rigidity of chamber wall. We also found that the period and the pattern of oscillation of the conduit flow primarily depend on a quantity defined by LV_ch/r⁴, where L is the conduit length and r is the conduit radius.     

基于HHT变换瞬时能量谱的长周期结构地震反应分析

基于HHT变换得到瞬时能量谱,并以简谐地震反应为理论基础进行多自由度体系在地震动作用下的瞬态反应计算。通过对一个长周期(十五层)结构工程实例的地震瞬态反应计算分析,揭示长周期结构有别于短周期结构动力响应的独特特性:长周期结构位移响应的瞬时能量峰值的时间滞后于地震动能量峰值的时间,且主要受到瞬态振动的控制,并以低阶振型的控制为主,第一阶振型峰值位移滞后的时间最长,滞后的时间主要取决于结构的第一阶自振周期。研究结果表明,长周期结构在强烈地震动作用下,地震动强度出现的最大时刻并不总是对应于结构破环与倒塌的时间。     

S波分裂在皖北地震中的研究应用

利用S波分裂方法的基本理论及计算方法,重点研究了皖北地区具有代表性的利辛张村附近周边地区25 km内,自1999年蒙城地震台数字化测震仪器正式记录以来至2010年9月,ML2.0及以上地方震的单台地震波形,利用有关S波分裂方法进行处理,得到该地区不同时段的S波的偏振方向及延迟时间,为皖北地区地震活动性研究及应力活动状态...