Modeling and boundary control of a flexible marine riser coupled with internal fluid dynamics

In this paper, vibration reduction of a flexible marine riser with time-varying internal fluid is studied by using boundary control method and Lyapunov's direct method. To achieve more accurate and practical riser's dynamic behavior, the model of marine riser with time-varying internal fluid is modeled by a distributed parameter system (DPS) with partial differential equations (PDEs) and ordinary differential equations (ODEs) involving functions of space and time. The dynamic responses of riser are completely different if the time-varying internal fluid is considered. Boundary control is designed at the top boundary of the riser based on original infinite dimensionality PDEs model and Lyapunov's direct method to reduce the riser's vibrations. The uniform boundedness and closed-loop stability are proved based on the proposed boundary control. Simulation results verify the effectiveness of the proposed boundary control.

Passive seismic velocity tomography on longwall mining panel based on simultaneous iterative reconstructive technique (SIRT)

Mining operation, especially underground coal mining, always has the remarkable risks of ground control. Passive seismic velocity tomography based on simultaneous iterative reconstructive technique (SIRT) inversion is used to deduce the stress redistribution around the longwall mining panel. The mining-induced microseismic events were recorded by mounting an array of receivers on the surface, above the active panel. After processing and filtering the seismic data, the three-dimensional tomography images of the p-wave velocity variations by SIRT passive seismic velocity tomography were provided. To display the velocity changes on coal seam level and subsequently to infer the stress redistribution, these three-dimensional tomograms into the coal seam level were sliced. In addition, the boundary element method (BEM) was used to simulate the stress redistribution. The results show that the inferred stresses from the passive seismic tomograms are conformed to numerical models and theoretical concept of the stress redistribution around the longwall panel. In velocity tomograms, the main zones of the stress redistribution around the panel, including front and side abutment pressures, and gob stress are obvious and also the movement of stress zones along the face advancement is evident. Moreover, the effect of the advance rate of the face on the stress redistribution is demonstrated in tomography images. The research result proves that the SIRT passive seismic velocity tomography has an ultimate potential for monitoring the changes of stress redistribution around the longwall mining panel continuously and subsequently to improve safety of mining operations.

具有闸、堰的一维河网非恒定流数学模型及其在多闸联合调度中的应用

对含有多个闸、堰等水利工程的河网,从闸门运用和河道行洪两方面考虑,采用三级联解法建立一维河网非恒定流数学模型,提出双向迭代内边界控制法对具有闸、堰的特殊河段求解。将这种模型应用于天津市永定新河洪水演进计算,考虑了该河网复杂的水闸控制条件,模型验证的结果和实测资料基本一致,将其应用于多闸联合调度方案的数值模拟,对永定新河下闸位建闸方案的确定和建闸工程的实施具有积极的指导作用。

海洋输油立管的建模及边界控制

为了更准确地描述海洋输油立管结构的动力学特性,文中基于Hamilton原理建立了耦合时变内流和海流的动力学的立管模型,该模型由一组偏微分方程(PDEs)和一组常微分方程构成,具有无限维特点.随后基于该原始无穷维PDEs模型,结合边界控制技术和Lyapunov方法,分别设计了纵向和横向二维边界控制器用以抑制立管振动.之后利用Lyapunov方法对立管系统的稳定性和一致有界性进行了证明,并通过仿真实验验证了文中控制算法的有效性.

水下结构声固耦合振动的特征值计算

针对水下结构声固耦合振动计算中出现的非对称矩阵(与频率相关)的特征值问题,本文基于共轭子空间迭代法,提出了计算水下结构振动固有频率和振型的双重迭代算法。数值算例表明:该算法收敛性好,用于水下结构声固耦合振动的特征值计算是有效的。文中分别将流体视为不可压缩和可压缩两种情况建立了流固耦合方程,计算了板、加筋板和方箱振动的固有频率和振型,将干模态和湿模态、不可压缩流体和可压缩流体的计算结果进行了比较,并分析了结构刚度和流体边界条件对附加水质量影响系数的影响。

非线性相似组合大系统最优控制的逐次逼近过程

研究一类仿射非线性相似组合大系统关于二次型性能指标的最优控制问题.首先通过模型简化,将非线性相似组合大系统化为若干个准解耦的子系统;然后利用非线性系统最优控制的逐次逼近设计方法,将求解高阶强耦合的非线性两点边值问题简化为求解一族解耦的线性两点边值问题序列.该线性两点边值问题序列的解一致收敛于非线性相似组合大系统的最优控制,得到的最优控制律由线性最优控制的解析项与非线性补偿序列的极限项组成.通过截取最优控制非线性补偿序列的有限次逼近值,得到了非线性组合大系统的次优控制律.

大尺度弱边界单层平面索网玻璃幕墙关键技术研究

新疆中石油生产指挥中心单层平面索网幕墙结构尺度大且为复杂弱边界,并长年处于强风环境下。该文对单层索网的结构模型、找形、索力设计、动力响应分析、玻璃翘曲、预应力张拉控制等设计中的关键技术进行详细研究。研究表明,结构整体模型应考虑索网和复杂弱边界(支承刚架)共同工作和竖索与横索在不同阶段的工作特性。确定单层平面索网幕墙零状态的非线性有限元逆迭代找形方法明显提高迭代收敛的速度,有效地解决横索悬垂问题。通过找形分析和预张力设计,可得到合理的索网初始形态和最经济的索截面。选用平均风压作用位置作为初始位置,对索网进行脉动风作用下的非线性时程分析,风振分析结果表明单层索网幕墙为风敏感结构。大变形下单层索网幕墙边界处玻璃翘曲问题不容忽视,需设计专门方案来控制。根据预应力张拉各阶段的有限元模拟和优化分析得出的预应力张拉控制要求,可有效指导单索幕墙的施工。

基于逆系统迭代学习观测器的故障调节方法

针对一类满足Lipschitz条件的多输入多输出非线性可逆系统执行器故障问题,提出了一种基于迭代学习观测器的逆系统内模故障调节方法。引入PD型迭代学习策略,设计了迭代学习故障诊断观测器,用于对执行器未知时变故障进行快速、准确估计。根据故障估计值,结合逆系统方法对逆模型进行补偿,使得补偿后的逆模型与非线性被控对象串联仍为伪线性系统;再结合内模控制实现了伪线性系统的容错控制。最后,通过仿真算例验证了该方案的有效性。

宽顶堰紊流场的数值模拟

本文采用k-τ紊流模式求解完整的Reynolds方程,模拟了有坎宽顶堰自由堰流.在求解中,发展了一套用边界拟合坐标、控制体积法求解二维恒定有自由表面紊流的数值方法,提出了分区光滑变换、反馈迭代等新概念.结果表明,本文提出的计算堰流的数值方法,计算量较小,具有良好的稳定性和收敛性,能够满足工程实际需要.

椭圆方程约束的最优边界控制问题的非重叠型区域分解迭代方法

研究了一类椭圆方程约束的最优边界控制问题的数值求解方法。为了避免运用传统数值方法所产生庞大的计算量,我们采用非重叠型区域分解迭代方法。即:将求解区域Ω分解成若干个非重叠子区域,把上述的最优边界控制问题分解成这些子区域上的局部问题,这些局部问题间的内边界条件采用Robin条件。建立了求解这些局部问题的迭代格式,推导证明了迭代格式的收敛性。最后,给出一个数值算例,验证了迭代格式的有效性。