基于Lagrange法的刚体与柔体动力学对比研究

对于机器人、航天器和车辆悬架部件等一些多体系统来说,其中一些部件的大尺寸、轻型化趋势使得传统的刚性体建模已经难以准确地模拟实际的工况,将部件所具有的柔性特性加入到多体系统模型中进行柔体动力学仿真,由于考虑了部件弹性变形与大范围刚性运动之间的耦合,故可以得到部件更为真实的动力学行为.文中通过与基于Lagrange法的刚体动力学基本方程进行对比研究,详细说明了柔体动力学方程中上述的耦合作用.以某大型雷达可展开天线为例,分别在刚体和柔体的假设下对其展开运动进行动力学仿真,结果表明采用柔性体仿真更能真实反映其动力学特性.     

Robust stabilization of non-linear systems by discontinuous dynamic state feedback

In this paper, a discontinuous dynamic state feedback that robustly stabilizes affine in control uncertain non-linear systems is proposed. The formulation is based on Hamilton-Jacobi-Isaacs partial differential equations with two boundary conditions. The resulting dynamic state feedback is then expressed in terms of the solution of the related PDEs. An interesting feature is that the internal state of the resulting dynamic state feedback may have discontinuous behaviour as a function of time. The proposed scheme is illustrated through the example of the stabilization of the angular velocities of a rigid body under two actuators.     

Trajectory tracking for a particle in elliptical billiards

An infinitely rigid unitary mass (particle) is considered, moving on a planar region delimited by a rigid elliptical barrier (elliptical billiards) under the action of proper control forces. A class of periodic trajectories, involving an infinite sequence of non-smooth impacts between the mass and the barrier at fixed times, is found by using an LMIs based procedure. The jumps in the velocities at the impact times render difficult (if not impossible) to obtain the classical stability and attractivity properties for the dynamic system describing the tracking error behaviour. Hence, the tracking control problem is properly stated using notions similar to the quasi stability concept in V. Lakshmikantham, D.D. Bainov and P.S. Simeonov, Theory of Impulsive Differential Equations, 6, World Scientific, 1989. A controller (whose state is subject to discontinuities) based on the internal model principle is shown to solve the proposed tracking problem, giving rise to control forces that are piecewise continuous function of time, with discontinuities at the desired impact times and at the impact times of the particle with the barrier.     

Dynamic analysis of a bulkhead flat car underframe structure

A dynamic analysis of the underframe (U/F) structure of a 100-ton bulkhead flat car was performed. Center plate accelerations and side bearing forces were obtained from the dynamic analysis of the car system using random track irregularity inputs. In this analysis the carbody was treated as two rigid elements connected by springs. The objective of this study was: (a) to investigate the effect of bulkheads on the natural frequencies and mode shapes of the U/F structure; (b) to evaluate the maximum dynamic stresses and stress ranges for a few selected critical members of the U/F structure; (c) to determine the influence of the bulkheads and structural damping, in both the original and new (statically optimized) U/F structure designs: (d) to compare the calculated dynamic stresses in a few selected members, with increased static stresses based on dynamic load factors for specified design loads; (e) to modify the design of the U/F structure according to the results of the dynamic analysis; and (f) to discuss the fatigue life of the U/F structure, based on the calculated stress ranges.     

Tactics‐Based Behavioural Planning for Goal‐Driven Rigid Body Control

Controlling rigid body dynamic simulations can pose a difficult challenge when constraints exist on the bodies' goal states and the sequence of intermediate states in the resulting animation. Manually adjusting individual rigid body control actions (forces and torques) can become a very labour‐intensive and non‐trivial task, especially if the domain includes a large number of bodies or if it requires complicated chains of inter‐body collisions to achieve the desired goal state. Furthermore, there are some interactive applications that rely on rigid body models where no control guidance by a human animator can be offered at runtime, such as video games. In this work, we present techniques to automatically generate intelligent control actions for rigid body simulations. We introduce sampling‐based motion planning methods that allow us to model goal‐driven behaviour through the use of non‐deterministic Tactics that consist of intelligent, sampling‐based control‐blocks, called Skills. We introduce and compare two variations of a Tactics‐driven planning algorithm, namely behavioural Kinodynamic Rapidly Exploring Random Trees (BK‐RRT) and Behavioural Kinodynamic Balanced Growth Trees (BK‐BGT). We show how our planner can be applied to automatically compute the control sequences for challenging physics‐based domains and that is scalable to solve control problems involving several hundred interacting bodies, each carrying unique goal constraints.     

Dynamics of serial chain systems using dual algebra

Multibody System Dynamics - Dynamic modelling of a multibody system is critical to analyse its behaviour under different circumstances. This paper proposes the dynamic modelling of a rigid...     

Substructure effective mass for mode identification

Mode identification of a complex structure is an essential task towards better understanding of its dynamic behaviour. Though graphical representation can give some idea of the behaviour, it is difficult to comprehend quantitative measures from such mode shape plots. Other existing methods of mode identification based on generalized mass principles give an indication only of the global modes. In this paper, the concept of substructure effective mass has been developed and its properties are discussed in detail. These are shown to form a valuable tool for understanding the dynamic behaviour of structures. The examples illustrated here show that this concept gives a clear indication of all the modes—global or local, coupling of various substructures and relative motion of the substructures in any given mode. The numerical results are shown to be very useful for the designer to understand and modify the dynamic characteristics of the particular subsystem to control the overall behaviour of the structure.     

Modelling the nonlinear dynamic behaviour of a boiler‐turbine system using a radial basis function neural network

Building an appropriate mathematical model that describes the system behaviour with a certain degree of satisfaction is quite challenging owing to the uncertain and volatile nature of thermodynamic constants and geometric parameters. In this paper, we present a technique to approximate and validate the dynamic behaviour of the Aström–Bell boiler‐turbine power plant based on an RBFNN over a large operating range. The proposed RBFNN is applied to solve the parametric identification problem for nonlinear and complex systems using an optimiser based on a hybrid genetic algorithm. This optimiser is composed of the gradient descent optimiser and a genetic algorithm for fast convergence. Two simulations were performed to show the effectiveness of the proposed technique under different situations with several boiler‐turbine input variables. The optimal structure and parameters of the obtained RBFNN‐based model emulates well the dynamic behaviour of the Aström–Bell boiler‐turbine system. Copyright © 2013 John Wiley & Sons, Ltd.     

基于相对形变模型及正则化技术的人体运动估计

为了使根据人体行走的单目动态图象序列，对人体手臂及腿部的运动及结构参数进行估计的结果更为可信、更具鲁棒性，提出了一种基于相对形变模型及正则化技术的人体运动估计方法，该方法首先在物体中心坐标的运动表示方式下，通过在刚体运动模型中加入形变系数的方法给出了基于相对形变概念的非刚体运动模型；然后，根据这一非刚体运动模型进行正则化运动及结构参数的估计，再以正则化的形式融入人体运动的先验知识，使运动估计的结果更具鲁棒性，实验结果证明，该方法有效地反映了人体的非刚体运动模式，运动模型中所加入的相对形变系数也一定程度反映了人体的运动规律。     

An instrumental variable approach for rigid industrial robots identification

This paper deals with the important topic of rigid industrial robots identification. The usual identification method is based on the use of the inverse dynamic model and the least-squares technique. In order to obtain good results, a well-tuned derivative bandpass filtering of joint positions is needed to calculate the joint velocities and accelerations. However, we can doubt whether the bandpass filter is well-tuned or not. Another approach is the instrumental variable (IV) method which is robust to data filtering and which is statistically optimal. In this paper, an IV approach relevant for identification of rigid industrial robots is introduced. The set of instruments is the inverse dynamic model built from simulated data which are calculated from the simulation of the direct dynamic model. The simulation assumes the same reference trajectories and the same control structure for both the actual and the simulated robot and is based on the previous IV estimates. Furthermore, to obtain a rapid convergence, the gains of the simulated controller are updated according to IV estimates. Thus, the proposed approach validates the inverse and direct dynamic models simultaneously and is not sensitive to initial conditions. The experimental results obtained with a 2 degrees of freedom (DOF) planar prototype and with a 6 DOF industrial robot show the effectiveness of our approach: it is possible to identify 60 parameters in 3 iterations and in 11 s.     

企业能耗过程性质判定及能量守恒性分析

为实现工业企业能源消耗过程行为和结构特性的分析,在企业能耗过程模型的基础上,研究了与模型相关的动态性质与结构性质,并有针对性地分析了网系统的能量守恒性。为实现生产中各物质流的动态逻辑关系以及工艺流程静态拓扑结构的描述,提出了动态与静态关联矩阵的概念并分别给出定义;分别研究了与动态行为有关的动态平衡量、稳态运行区间等性质;在模型加权守恒性研究的基础上,提出了一种基于S不变量的网系统能量守恒性计算方法并延伸出对设备与产品能效的分析计算。分析表明,方法有助于实际能源消耗过程中物料平衡性、产品或原料积压以及产品能效等特性的分析与检查。     

冷弯薄壁型钢蒙古包风雪作用下仿真研究

冷弯薄壁型钢蒙古包是一种新型房屋结构,结构质量轻、柔性大的特点决定了其控制荷载为风荷载与积雪荷载.通过计算流体动力学(CFD)方法,将蒙古包的风荷载体型系数与现行规范进行对比.模拟得到屋面的风荷载分布与不均匀雪荷载分布,定义2种风向角,将风荷载与风雪荷载分别作用于冷弯薄壁型钢蒙古包刚架,分析不均匀雪荷载与不同风向角对刚...     

基于改进弹簧质点模型的织物模拟算法

提出了一种基于改进弹簧质点模型的织物模拟算法。该算法首先引进刚性杆代替结构弹簧,对弹簧质点模型进行了改进。其次基于改进的弹簧质点模型,实现织物模型的建立。将织物看成是由分布均匀的质点组成,通过对模型中的质点进行受力分析,建立织物的力学方程。最后运用显式欧拉方程法对模型质点的空间位移进行数值求解,并在求解过程中运用动态约束算法改善超弹性问题。实验结果表明,提出的方法在确保织物模拟稳定和效率高的基础上,实现了对织物的高效模拟。     

空间杆系结构回传波射分析及程序实现

为有效地进行杆系结构应力波响应分析,基于传统的空间杆系结构回传波射矩阵法,考虑黏滞阻尼、复刚度阻尼及节点集中质量的影响,采用VC+ +编制通用回传波射矩阵法分析程序. 该程序可以计算空间杆系结构在任意动力集中载荷作用下任意位置的动力瞬态响应. 针对某刚架结构,比较运用该程序与运用有限元法得到的结果,验证该方法的精确度.     

Sea bed-structure interaction for submarine cables

In this study, the dynamic behaviour of a submarine cable constrained by a frictionless rigid sea profile is studied. After a suitable local and time discretization, the arising unilateral contact-impact problem is formulated as a sequence of variational inequality problems which lead equivalently to a sequence of quadratic programming problems. The solution method is based on some propositions which constitute the mechanical “interpretation” of some theorems of quadratic programming and combines the advantages of the optimization algorithms with the advantages of the “trial and error” methods. Finally the applicability of the proposed method is illustrated by means of a numerical example.     

Automated enforcement for relaxed information release with reference points

Language-based information ftow security is a promising approach for enforcement of strong security and protection of the data confidentiality for the end-to-end communications. Here, noninterference is the standard and most restricted security property that completely forbids confidential data from being released to public context. Although this baseline property has been extensively enforced in various cases, there are still many programs, which are considered secure enough, violating this property in some way. In order to control the information release in these programs, the predetermined ways should be specified by means of which confidential data can be released. These intentional releases, also called declassifications, are regulated by several more relaxed security properties than noninterference. The security properties for controlled declassification have been developed on different dimensions with declassification goals. However, the mechanisms used to enforce these properties are still unaccommodating, unspecific, and insufficiently studied. In this work, a new security property, the Relaxed Release with Reference Points （R3P）, is presented to limit the information that can be declassified in a program. Moreover, a new mechanism using reachability analysis has been proposed for the pushdown system to enforce R3P on programs. In order to show R3P is competent for use, it has been proved that it complies with the well-known prudent principles of declassification, and in addition finds some restrictions on our security policy. The widespread usage, precision, efficiency, and the influencing factors of our enforcement have been evaluated.     

Simulation of floating bodies with the lattice Boltzmann method

This paper is devoted to the simulation of floating rigid bodies in free surface flows. For that, a lattice Boltzmann based model for liquid–gas–solid flows is presented. The approach is built upon previous work for the simulation of liquid–solid particle suspensions on the one hand, and on an interface-capturing technique for liquid–gas free surface flows on the other. The incompressible liquid flow is approximated by a lattice Boltzmann scheme, while the dynamics of the compressible gas are neglected. We show how the particle model and the interface capturing technique can be combined by a novel set of dynamic cell conversion rules. We also evaluate the behaviour of the free surface–particle interaction in simulations. One test case is the rotational stability of non-spherical rigid bodies floating on a plane water surface–a classical hydrostatic problem known from naval architecture. We show the consistency of our method in this kind of flows and obtain convergence towards the ideal solution for the heeling stability of a floating box.     

Fast and compact dynamic data compression based on composite rigid body construction

3D dynamic datasets compression still poses two challenges. One is high time cost due to growing data and complex computation of compression algorithms. The other is low compression factor because of complex motions of dynamic scenes and unknown motion equations. In this paper, composite rigid body construction for fast and compact compression of 3D dynamic datasets is proposed to solve these two problems. It accelerates the compression with a fast rigid body decomposition based on disjoint union, and avoids serial searching, comparing and merging of the rigid body decomposition. To increase the compression factor, composite rigid body is introduced with consideration of motion consistency among rigid bodies at different time periods. The results of the experiments show that our algorithm compresses dynamic datasets quickly and achieves a high compression factor.     

A Specialised Element for Finite Element Model Updating of Moveable Joints

Multibody system dynamics is a vast area of study that mayoften involve the need to know the vibration behaviour of rigid/flexiblesystems with configurations that change with time due to the existenceof moveable joints. This paper introduces and discusses the motivationbehind the development of a technique, based on a modified springelement, to model the dynamic behaviour of such moveable joints. Thistype of joint generally connects the constituent components ofmechanical systems. The modified element is used to establish linksbetween nodes inside the joint volume, for an arbitrary jointconfiguration, without the need to introduce any distortions in thefinite element mesh pertaining to the connected components. Itintroduces two parameters ideally suited for model updating, a geometryindependent parameter that defines global link stiffness and a geometrydependent one that gives a measure of link effectiveness as a functionof joint configuration. The element usage and a comparison of resultsobtained with a model using standard elements for selectedconfigurations are illustrated by means of an example.     

细长柔性空间结构几种动力学模型的比较

对于自由-自由边界的大型柔性梁式空间结构在轨搬运过程中,其大范围刚体运动和柔性振动会相互耦合,是一类典型的刚柔耦合动力学问题.建立相对准确的动力学模型是设计良好控制系统的前提,但现有文献在研究该问题时却采用了忽略刚柔耦合作用的动力学模型并依此设计控制器,因此有必要建立耦合模型,并探讨其与非耦合模型之间的区别和适用性.首先针对结构自身运动特点选择以瞬时质心为原点的浮动坐标系作为辅助坐标系,将结构两类不同的运动形式进行分解,并利用其产生的附加约束条件简化虚功表达式;其次选择Euler-Bernoulli梁变形形式描述结构变形并采用假设模态法对变形进行变量分离;基于虚功原理推导得到结构大范围运动的刚柔耦合动力学模型;通过仿真算例1对非耦合模型、零次近似模型和一次近似模型进行了对比,验证了非耦合模型的不合理性及零次近似简化模型的准确性和有效性;通过仿真算例2对零次近似简化模型和一次近似模型的对比,说明了二者的使用范围;仿真对比为后续的运动控制系统设计和振动抑制研究提供了依据.