Active Vibration Damping and Model-Based Control for an Adaptronic Actuator

The static and dynamic flexibility of a machine tool is often the major limiting factor for the machining quality, especially if high processing speeds as well as high accuracies are desired. Particularly parallel kinematic machines, which have been developed for high processing speeds and accuracy and which often use lightweight structures, can suffer from severe problems with vibrations of system components and the loss of accuracy due to deformations of machine parts. Introducing so–called adaptronic or smart components into the machine tool structure opens up new and interesting possibilities to actively control the deformations and vibrations of flexible machine parts. They allow to specifically target such undesired properties and to significantly reduce or even eliminate their influence on the system performance. Concepts of active vibration damping and model–based control are presented here for such an adaptronic actuator implemented in a machine tool with parallel kinematics. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

主被动阻尼层合板结构的自由振动和阻尼特性分析

给出了含主被动阻尼非对称复合材料层合板结构的振动微分方程;得到了在压电材料和高粘弹材料作主被动阻尼层情况下,简支层合板结构自由振动的自然频率和损失因子的解析解;分析了正逆向压电效应对自然频率和损失因子的影响     

微重力环境下充液球腔非线性耦合动力学研究

采用球坐标系描述球腔中的液体动力学特性并建立一种轴对称贮腔类液刚耦合系统动力学模型．采用模态展开方法分析了微重环境下球形贮箱中的液体晃动问题,给出了球形贮箱内液体晃动速度势函数和波高函数的Gauss超几何级数解析表达式．采用变分原理推导了系统动力学系模型,利用Galerkin 方法对变分方程进行特征频率分析．运用Lagrange方法及非线性动力学方法导出了微重力环境下贮箱中液体与航天器结构耦合的动力学方程组,并对该方程组进行了数值计算,绘出了非线性耦合充液系统自由度随时间的变化历程．     

基于时域配点法的充液储箱系统多模态方程求解

采用时域配点法研究了充液储箱系统多模态方程的稳态周期解.在模型求解过程中,利用牛顿迭代法求解了配点法得到的非线性代数方程组,而牛顿迭代的初值来自谐波平衡法求解得到的低阶谐波近似.数值仿真结果验证了时域配点法的有效性,并验证以二倍激励频率为基频的第二模态的假设形式更为有效.最终通过对比谐波系数数量级提出一种更为简洁有效的模态表达形式.     

具有主动约束层阻尼板的振动杂交控制*

本文研究了局部附加主动约束阻尼层(LACL)板的主、被动杂交控制问题.基于弹性、粘弹性、压电材料的本构关系,建立了系统的控制方程.利用Galerkin方法和GHM方法将偏微分方程转换为维数不高的常微分方程组,应用LQR方法进行了数值模拟.计算结果表明,这种主动和被动结合的杂交控制方式具有良好的控制效果.     

主动约束阻尼开口柱壳的NLMS反馈减振控制

为缩减开口柱壳结构的振动,给出了一种局部主动约束阻尼(ALCD)敷设结构,并结合Lagrange方程和Sanders薄壳理论构建了压电耦合开口柱壳的动力学模型,根据推得的系统状态空间形式,应用归一化最小均方差自适应滤波算法(NLMS)和线性二次规划算法(LQR)设计了一种自适应反馈控制器,通过数值仿真研究了控制参数对开...     

小Bond数条件下圆柱贮箱中液体晃动的模部分析

运用模部分析方法考察了小Bond数条件下圆柱贮箱中弯曲静液面对液体晃动模态的重构作用.研究表明,圆柱贮箱中的液体作小幅晃动时,参与晃动的各阶基本模态的正交性若仅由Bessel模部来给出,则弯曲静液面将使各阶模态加权耦合,形成新的特征模态;参与晃动的各阶基本模态的正交性若由三角函数模部来给出,则弯曲静液面将独立改变各阶模态的固有频率,各阶模态之间不耦合.运用新的重构模态来研究圆柱贮箱中液体的横向受迫晃动,给出了其模态选择特征.     

Time-Accurate CFD Predictions and Data Validation for Side Load Generation by Flow-Structure Coupling in Over-Expanded Rocket Nozzles

The present paper validates results from numerical simulations for side load generation in rocket nozzles against related data from analytical models that are presently used for rocket engine nozzle design activities.Time-accurate two- and three-dimensional turbulent Navier–Stokes (N–S) computations are performed for separated flow in deflected and ovalized nozzles as well as for nozzles under forced harmonic oscillations. Based on this comparison conclusions are drawn concerning the validity of the physical model assumptions that the analytical design methods are based on.Mathematics Subject Classification (2000) 74F10.     

Modal criteria for robust optimization of vibroacoustic systems

This work is an extension of the work done in previous papers (Besset and Jézéquel in Intern J Numer Method Eng 70(5):523–542, 2007; J Vib Acoust 130(1):011008, 2008; Intern J Numer Method Eng 73:1347–1373, 2008; J Vib Acoust 130(3):031009, 2008). It deals with modal criteria allowing to process optimization of structures including robustness. The system considered in the paper is a fluid-structure system. The aim of the paper is to use component mode synthesis methods to optimize the geometry of the structure and the robustness with respect to the design parameter variations of its vibroacoustic behaviour. Two criteria will be proposed. The first one is directly linked to the pressure level in the acoustic cavity. The second one is linked to the robustness of the methods. It comes from the polynomial chaos study of the considered system. A classical multiobjective optimization is then processed and Pareto graphics are proposed to represent the optimal solutions of the optimization problem.     

自适应结构频率和阻尼比的计算

本文给出状态空间法的一种新技巧,用于求解自适应结构的振动频率和阻尼比。当采用集中质量法时,状态矩阵的Cholesky分解具有解析式。从而既可提高计算精度,又可节约计算时间。最后以算例加以说明。     

Modal Extensions of Sub-classical Logics for Recovering Classical Logic

In this paper we introduce non-normal modal extensions of the sub-classical logics CLoN, CluN and CLaN, in the same way that S0.5 ⁰ extends classical logic. The first modal system is both paraconsistent and paracomplete, while the second one is paraconsistent and the third is paracomplete. Despite being non-normal, these systems are sound and complete for a suitable Kripke semantics. We also show that these systems are appropriate for interpreting □ as “is provable in classical logic”. This allows us to recover the theorems of propositional classical logic within three sub-classical modal systems.     

带阻尼的非线性双曲型方程振动性的新结果

研究了一类带阻尼的非线性双曲型方程的振动性,利用新的处理阻尼项及非线性项的技巧,建立了该类方程在Dirichlet边值条件下所有解振动的若干新的充分判据.     

Numerical Methods for the Pricing of Swing Options: A Stochastic Control Approach

In the natural gas market, many derivative contracts have a large degree of flexibility. These are known as Swing or Take-Or-Pay options. They allow their owner to purchase gas daily, at a fixed price and according to a volume of their choice. Daily, monthly and/or annual constraints on the purchased volume are usually incorporated. Thus, the valuation of such contracts is related to a stochastic control problem, which we solve in this paper using new numerical methods. Firstly, we extend the Longstaff–Schwarz methodology (originally used for Bermuda options) to our case. Secondly, we propose two efficient parameterizations of the gas consumption, one is based on neural networks and the other on finite elements. It allows us to derive a local optimal consumption law using a stochastic gradient ascent. Numerical experiments illustrate the efficiency of these approaches. Furthermore, we show that the optimal purchase is of bang-bang type.      

A Method for Solving Container Packing for a Single Size of Box

There is an extensive literature on heuristic algorithms for two-dimensional cutting problems and three-dimensional packing, but there seems to be very little on the three-dimensional single-box type packing problem. This paper gives a structure for dealing with that problem as a heuristic. It also presents a set of upper bounds on the optimal fit. Finally, the paper compares a particular application of the algorithmic structure with the George and Robinson multiple-box type heuristic.     

Criteria for Modal Controllability of Completely Regular Differential-Algebraic Systems with Aftereffect

The problem of control of the coefficients of the characteristic quasipolynomial is studied for linear autonomous completely regular differential-algebraic systems with commensurate delays. Several criteria for modal controllability and weak modal controllability are obtained, schemes for synthesis of the corresponding controllers are proposed, and illustrative examples are given.     

量词模态逻辑的代数语义学（Ⅲ）──关于不含Barcan公式的正规模态系统的情形

本文首先讨论嵌套论域语义的相应代数语义并由Ｈｕｇｈｅｓ和Ｃｒｅｓｓｗｅｌｌ在［５］中建立的关于具有嵌套论域的正规量词模态系统的关系语义完全性定理推出其相应的代数语义完全性定理：然后对于具有任意可变论域语义的正规系统，我们用Ｈｅｎｋｉｎ方法给出其关于狭义Ｋｒｉｐｋｅ语义的关系语义完全性定理，由此通过将关系语义转化为代数语义从而亦推得其代数语义完全性定理。     

转动与摆动复合运动下脂润滑关节轴承的数值分析

建立了球面轴承的三维润滑模型,该模型将内圈的转动运动、轴颈倾斜引起的内圈倾斜和内圈的摆动运动等因素纳入考虑,推导出球坐标下适用于非Newton(牛顿)流体润滑的Reynolds(雷诺)方程.应用该模型,并考虑使用润滑脂的Ostwald流变模型,对向心关节轴承的润滑问题进行了数值计算,研究了在不同的幂律指数、内圈倾斜角度和摆动角速度下,脂润滑膜的压力分布、最大压力、承载力和流量.结果表明:在合适的操作条件下,脂润滑能产生明显的流体动压效应;在其它参数不变时,幂律指数对脂润滑膜的最大压力和承载能力影响显著,相对于Newton流体,剪切稠化流体可提高润滑膜的最大压力和承载能力,并增加周向流量,而剪切稀化流体的影响效果则相反;内圈倾斜角度对脂润滑膜最大压力和承载能力的影响较小,内圈摆动角速度的影响则较为明显.     

二阶非线性阻尼微分方程解的振动性质

研究了一类二阶非线性阻尼微分方程解的振动性,采用分类讨论和分析的方法,建立了两个新的振动性定理,推广和改进了已有的结果.