Asymptotic stability in probability and stabilization for a class of discrete‐time stochastic systems

This paper investigates asymptotic stability in probability and stabilization designs of discrete‐time stochastic systems with state‐dependent noise perturbations. Our work begins with a lemma on a special discrete‐time stochastic system for which almost all of its sample paths starting from a nonzero initial value will never reach the origin subsequently. This motivates us to deal with the asymptotic stability in probability of discrete‐time stochastic systems. A stochastic Lyapunov theorem on asymptotic stability in probability is proved by means of the convergence theorem of supermartingale. An example is given to show the difference between asymptotic stability in probability and almost surely asymptotic stability. Based on the stochastic Lyapunov theorem, the problem of asymptotic stabilization for discrete‐time stochastic control systems is considered. Some sufficient conditions are proposed and applied for constructing asymptotically stable feedback controllers. Copyright © 2014 John Wiley & Sons, Ltd.     

Continuum electrostatic approach for evaluating positions and interactions of proteins in a bilayer membrane

Orientations of proteins in the membranes are crucial to their function and stability. Unfortunately the exact positions of these proteins in the lipid bilayer are mostly undetermined. Here, the spatial orientation of membrane proteins within the lipid membrane was evaluated using a Poisson–Boltzmann solvent continuum approach to calculate the electrostatic free energy of the protein solvation at various orientations in an implicit bilayer. The solvation energy was obtained by computing the difference in electrostatic energies of the protein in water and in lipid/water environments, treating each as an implicit solvent model. The optimal position of transmembrane proteins (TMP) in a lipid bilayer is identified by the minimum in the “downhill” pathway of the solvation energy landscape. The energy landscape pattern was considerably conserved in various TMP classes. Evaluation of the position of 1060 membrane proteins from the orientations of proteins in membranes (OPM) database revealed that most of the polytopic and β-barrel proteins were in good agreement with those of the OPM database. The study provides a useful scheme for estimating the membrane solvation energy made by lipid-exposed amino acids in membrane proteins. In addition, our results tested with the bacterial potassium channel model demonstrated the potential usefulness of the approach in assessing the quality of membrane protein models. The present approach should be applicable for constructing transmembrane proteins–lipid configuration suitable for membrane protein simulations and will have utility for the structural modeling of membrane proteins.     

空间太阳能电站的轨道、姿态和结构振动的耦合动力学建模及辛求解

作为一种从太空获得清洁能源的系统,空间太阳能电站(SPS)吸引着许多国家和科研机构的关注.由于其超大、超轻的柔性结构特点,研究其在轨动力学行为时需要考虑轨道、姿态和结构振动的耦合作用.本文在考虑地球的非球形摄动影响下,建立了集成对称聚光系统(ISC)的动力学模型.通过Legendre变换引入广义动量,在Hamilton体系下建立了其轨道、姿态、轴向振动耦合的动力学方程.采用辛Runge-Kutta方法对耦合动力学方程进行数值求解.根据数值结果,分别研究了其在地球同步轨道下二阶摄动项对轨道、姿态和结构振动的影响,并分析了总能量的变化情况.     

非线性减震器的多脉冲轨道和同宿树研究

针对一类非线性减震器,应用能量相位法研究了减震器系统在1∶0内共振,第一阶主共振情形下系统的多脉冲轨道和同宿树.首先,将系统的无量纲动力学控制方程转化为近可积哈密顿系统的标准形式.其次,研究了该系统的未扰动力学行为和扰动动力学行为,分析了耗散因子及相位漂移角对多脉冲轨道脉冲数和层半径的影响,揭示了这类非线性减震器能量从高频模态向低频模态转移的动力学机理.     

铰支柔性梁主参数共振的时滞反馈控制

研究了时滞反馈控制作用下铰支柔性梁主参数共振问题.采用多尺度法,从理论上推导了时滞位移反馈控制作用下铰支柔性梁非线性主参数共振,分析了时滞、反馈控制增益,非线性系数等系统参数对系统非线性主参数振动的影响,分析了主参数动力响应随参数变化的规律.结果表明:随着反馈增益的增大,系统响应幅值得到明显抑制,合理地控制系统参数选取可提高振动控制的效率.     

尾段主梁刚度变化对T型尾翼颤振特性的影响

由于T型尾翼结构和气动布局的特殊性,其颤振特性的分析比较复杂.T型尾翼安装在机身尾部,这体现在有限元结构模型中即为T型尾翼与尾段主梁相连接.为了研究尾段主梁的刚度变化对T型尾翼颤振特性的影响,以某T型尾翼飞机的尾段为研究对象,根据其原始刚度,分别改变其垂直弯曲刚度和扭转刚度,并计算分析相应刚度下的固有振动特性与颤振特性.最后分别以这两个刚度为变量,另一个刚度的原始值为常量进行分析.结果表明尾段主梁的刚度变化对垂尾弯扭耦合颤振的影响较为显著.     

南水北调中线工程几个技术问题的解决与思考

根据南水北调中线一期工程建设过程中的科技攻关,本文重点介绍了长距离自流输水线路输水型式选择、施工测量控制、混凝土重力坝再加高和软基中承受内水压力的水工隧洞设计施工中的几个关键技术问题,系统阐述了上述关键技术问题的解决思路和作者的再思考。     

寒冷地区电站长距离输水明渠冬季运行方式探讨

通过大量工程资料收集和类似工程经验分析,对寒冷地区引水式水电站长距离输水明渠在冬季各种输、排冰运行方式的适用性进行了对比分析,着重对结冰盖运行方式的建筑物布置、流量控制和水位控制等进行深入分析和研究,提出了完整的分段壅水结冰盖输水方式的输水渠道建筑物布置、水位运行控制的设计和运行控制方法,消除了寒冷地区电站输水长明渠冬季运行中的冰冻危害问题,并成功运用于实际工程设计和运行。     

爆破振动对邻近水工建筑物影响的监测与分析

在邻近水工建筑物环境下进行爆破开挖,爆破振动会产生一些负面效应,因此爆破振动监测十分必要。以大渡河深溪沟水电站安装间排水灌浆廊道开挖工程为例,对厂房机组及其他关键部位进行了爆破振动监测,并对数据进行回归分析,通过调整和优化爆破参数,既确保了原有机组的正常运行和其他水工建筑物的安全,同时又加快了工程施工进度,可为类似工程提供借鉴和参考。      

垂向振荡对螺旋桨敞水性能的影响研究

船舶在波浪中航行时,船身垂荡运动的同时也带动着螺旋桨相对于周围流体振荡。为了研究振荡对螺旋桨推进性能的影响,该文采用相对运动的数值模拟方法,实现了螺旋桨自身旋转运动和垂向振荡运动的同步进行。对比了不同振荡频率、振幅对螺旋桨敞水性能的影响,结果表明,垂荡会提高螺旋桨的敞水性能,且随着振荡频率、幅值的增大,螺旋桨的推力系数、扭矩系数和敞水效率也略有增大。