惯性平台并联缓冲器复位精度的分析与综合

以一种用于惯性平台的并联缓冲器为研究对象,分析了其动平台位姿误差与各结构参数误差间的关系。首先,利用全微分理论建立了并联缓冲器的精度模型;然后,结合实际制造精度给定各结构参数误差的值,利用此模型估算出了缓冲器动平台的输出误差;最后,以尽量缩小各结构参数误差值的差异为附加约束条件,建立了精度综合的最优化模型,并根据惯性平台对精度的实际要求进行计算,结果表明：将动平台的复位精度控制在15?以内时,相应的结构参数制造公差应小于0.0134 mm。     

Hybrid approach for dynamic model identification of an electro-hydraulic parallel platform

In this paper, a hybrid optimization algorithm is proposed to identify the dynamic parameters of a 6-DOF electro-hydraulic parallel platform. The dynamic model of a parallel platform with arbitrary geometry, inertia distribution and frictions is obtained based on a structured Boltzmann–Hamel–d’Alembert formulation, and then the estimation equations are explicitly expressed in terms of a linear form with respect to the identified inertial and the friction coefficients in accordance with a linear friction model. However, when nonlinear friction models are considered, the parameter identification of the electro-hydraulic parallel platform is considered as an optimization process with an objective function minimizing the errors between the measurement and identification, and then an effective combination of the particle swarm optimization (PSO) method and the local quasi-Newton method is proposed to solve the identification problem. Experimental identification processes are carried out for the identified parameters, and the identified models are compared by the predicted forces between the LS method and the optimization technique as well as between the linear and nonlinear friction models.     

基于离散元法的干湿颗粒系统仿真

介绍了基于离散元法的干湿颗粒系统仿真软件DEMSIM。对于干颗粒系统,DEMSIM可以分析二维和三维颗粒系统的弹性和塑性接触碰撞过程;对于湿颗粒系统,DEMSIM采用传统的液桥模型;对于颗粒-流体系统,DEMSIM采用CFD-DEM细观耦合模型模拟。一系列典型算例的模拟分析,验证了干湿颗粒系统仿真软件DEMSIM的精度和有效性。     

The principle of virtual work and integral laws of motion

This paper furnishes a simple constructive proof of the equivalence of integral laws of motion for continua to the Principle of Virtual Work. The approach used is designed to avoid the artificiality of introducing the classical equations of motion in an intermediate step. The hypotheses employed are virtually the weakest possible that are consistent with the requirement that the integrals appearing in these formulations make sense as Lebesgue integrals. Particular attention is devoted to the treatment of boundary conditions, which may assume a very general form.     

A scalable parallel algorithm for the direct numerical simulation of three-dimensional incompressible particulate flow

Particulate flow is of great importance from both the scientific and engineering points of view. Owing to the complexity of particle-flow interactions, direct numerical simulations (DNS) of inertial particulate flow with finite-size particles have been limited to a very small number of particles, while the industrial applications involve larger numbers with many orders of magnitude. This article presents a parallel implementation of a fictitious domain method for the DNS of particulate flows. The method is thoroughly tested and its parallel performance on distributed memory clusters is evaluated on a large-scale problem. Finally, we present the results for the separation of 21,336 particles of two different densities in a viscous fluid. Although there is still a significant gap between DNS and the industrial applications, the present algorithm allows to simulate significantly large number of particles so that a meaningful statistical analysis can be performed. This will help in the development of new closure relations for the averaged models of multiphase flows.     

A numerical method for the simulation of an aggregation‐driven population balance system

A population balance system that models the synthesis of urea is studied in this paper. The equations for the flow field, the mass and the energy balances are given in a three‐dimensional domain, while the equation for the particle size distribution is given in a four‐dimensional domain. This problem is convection‐dominated and aggregation‐driven. Both features require the application of appropriate numerical methods. This paper presents a numerical approach for simulating the population balance system, which is based on finite element schemes, a finite difference method and a modern method to evaluate convolutIon integrals that appear in the aggregation term. Two experiments are considered and the numerical results are compared with experimental data. Unknown parameters in the aggregation kernel have to be calibrated. For appropriately chosen parameters, good agreements are achieved of the experimental data and the numerical results computed with the proposed method. A detailed study of the computational results reveals the influence of different parts of the aggregation kernel. Copyright © 2011 John Wiley & Sons, Ltd.     

Direct numerical simulation of driven cavity flows

Direct numerical simulations of 2D driven cavity flows have been performed. The simulations exhibit that the flow converges to a periodically oscillating state at Re=11,000, and reveal that the dynamics is chaotic at Re=22,000. The dimension of the attractor and the Kolmogorov entropy have been computed. Explicit time-integration techniques are discussed.     

An improved parallel compact scheme for domain-decoupled simulation of turbulence

An improved domain-decoupled compact scheme for first and second spatial derivatives is proposed for domain-decomposition-based parallel computational fluid dynamics. The method improves the accuracy of previously developed decoupled schemes and preserves the accuracy and bandwidth properties of fully coupled compact schemes, even for a very large degree of parallelism, and enables the Navier-Stokes equations to be solved independently on each processor. The scheme is analysed using Fourier analysis and error analysis, and tested on one-dimensional wave-packet propagation, a two-dimensional vortex convection problem, and in the direct numerical simulation of the three-dimensional Taylor-Green vortex problem and turbulent channel flow. Our results demonstrate the scheme's effectiveness in performing direct numerical simulation of turbulence in terms of accuracy and scalability.     

基于飞行仿真的捷联惯导算法测试平台

针对捷联惯导算法测试中真实飞行轨迹数据难以获得的问题,建立了一种基于飞行仿真的捷联惯导算法测试平台.首先构建了测试平台的系统结构,在建立六自由度非线性飞机数学模型基础上,采用Stateflow实现了预定航迹多模态的飞行仿真,并通过坐标变换将飞行参数转换为测试基准轨迹数据;然后根据捷联惯导系统原理,由测试基准轨迹参数推导出陀螺仪和加速度计的理想输出,并对其误差进行建模,由此获得惯性组件的模拟输出数据;最后通过两种不同的姿态更新算法进行惯导解算并比较.仿真实验结果表明:产生的测试基准数据符合飞行力学的特点,很好地反映了飞机的动态特性,可以有效地评估不同捷联惯导算法的性能.     

视轴稳定平台的装配误差机理分析与仿真

稳定机构的装配误差是造成视轴偏差的重要误差源。应用PIOGRAM图方法，以典型的直接式方位一俯仰式结构为例，分析了机械装配精度产生的运动学影响，并据此引入平台控制系统进行仿真研究，表明了各项误差与干扰运动的耦合关系。研究结果对平台总体设计阶段的精度分配具有借鉴作用。     

Design and analysis of a compliant parallel pan-tilt platform

In combination of the advantages of both parallel mechanisms and compliant mechanisms, a compliant parallel mechanism with two rotational degrees of freedom is designed to meet the requirement of a lightweight and compact pan-tilt platform. Firstly, two commonly-used design methods i.e. direct substitution and Freedom and Constraint Topology are applied to design the configuration of the pan-tilt system, and similarities and differences of the two design alternatives are compared. Then inverse kinematic analysis of the candidate mechanism is implemented by using the pseudo-rigid-body model, and the Jacobian related to its differential kinematics is further derived to help designer realize dynamic analysis of the 8R compliant mechanism. In addition, the mechanism’s maximum stress existing within its workspace is tested by finite element analysis. Finally, a method to determine joint damping of the flexure hinge is presented, which aims at exploring the effect of joint damping on actuator selection and real-time control. To the authors’ knowledge, almost no existing literature concerns with this issue.     

基于三环控制的惯性稳定平台不平衡扰动建模

不平衡扰动是惯性稳定平台的主要扰动因素之一,严重影响惯性稳定平台的稳定和跟踪性能,而且由于其形成原因的复杂性,对于惯性稳定平台的不平衡扰动,建立精确的模型比较困难。本文从不平衡扰动的来源出发,在惯性稳定平台三环控制系统模型的基础上,考虑到基座角运动和摩擦等扰动会使得平台偏转,而在偏转角的作用下会产生平台的不平衡扰动,进而完成不平衡扰动的建模。研究表明,不平衡扰动会对平台的性能造成较大影响,而且当干扰角运动幅值较大时,在不平衡扰动的作用下,系统角度输出稳态值会大大超过精度要求。研究成果为分析不平衡扰动对惯性稳定平台的影响提供了具体的模型依据,并为稳定平台不平衡扰动抑制方法的研究提供了对象条件。     

A novel 3D parallel mechanism for the passive motion simulation of the patella-femur-tibia complex

Parallel mechanisms have been exploited for the kinematic modelling of the passive motion, i.e. the motion under virtually unloaded conditions, of the patella-femur-tibia human joint. In particular, a new mechanism is devised in this paper: a 3D model of the patella-femur relative motion is presented which, combined with a previous simplified model of the femur-tibia relative motion, provides a suitable tool for the design of knee prostheses. Although less accurate than a previously presented model of the patella-femur-tibia joint, the new mechanism still replicates passive knee motion quite well and is simpler from a mechanical point of view. Experimental results validate the efficiency of the proposed model.     

An assessment of a parallel,finite element method for three‐dimensional,moving‐boundary flows driven by capillarity for simulation of viscous sintering

A parallel, finite element method is presented for the computation of three‐dimensional, free‐surface flows where surface tension effects are significant. The method employs an unstructured tetrahedral mesh, a front‐tracking arbitrary Lagrangian–Eulerian formulation, and fully implicit time integration. Interior mesh motion is accomplished via pseudo‐solid mesh deformation. Surface tension effects are incorporated directly into the momentum equation boundary conditions using surface identities that circumvent the need to compute second derivatives of the surface shape, resulting in a robust representation of capillary phenomena. Sample results are shown for the viscous sintering of glassy ceramic particles. The most serious performance issue is error arising from mesh distortion when boundary motion is significant. This effect can be severe enough to stop the calculations; some simple strategies for improving performance are tested. Copyright © 2001 John Wiley & Sons, Ltd.     

Three-dimensional parallel simulation of cornstarch-oxygen two-phase detonation

Numerical simulations were performed with a parallel computer to solve for the behavior of a three-dimensional gas-solid two-phase detonation. The numerical method is a second-order modified Harten-Yee TVD upwind scheme and time integration uses a first order Euler integration. A two-step chemical reaction model represents the reaction of cornstarch-particles and oxygen. The numerical results show that a periodic two-headed detonation appears with a three-dimensional propagation mechanism before and after a triple point collisions. A comparison between the numerical and experimental results reveals that the detonation velocity of numerical results agrees well with that of experimental results. Received 8 September 1999 / Accepted 7 May 2000     

绳牵引并联机器人弹性变形对动平台位姿精度的影响Influence of elastic deformation on pose precision of moving platform for wire-driven parallel robot

针对六自由度绳牵引并联机器人在风洞试验中的应用,分析了牵引绳弹性变形对动平台位姿精度的影响,其实质是运动学正解问题。鉴于牵引绳只能受拉力的特点,以及风洞试验的目的,须考虑系统的刚度和绳拉力的优化。基于系统运动学和动力学方程,推导了系统刚度矩阵;以提高系统主方向刚度为目标函数,对绳拉力进行了动态优化分布,以求解弹性变形;采用L‐M数值方法进行运动学正解,量化分析了两种不同弹性模量的牵引绳对系统刚度的影响,以及弹性变形引起的动平台位姿误差。研究结果表明,以刚度增强为优化目标,有利于提高系统稳定性;采用弹性模量较大的牵引绳,可以有效提高系统的刚度,减小绳长变形引起的飞行器模型位姿误差,满足风洞试验的精度要求。上述结果可为后续机构的改善和系统高精度的力位混合控制提供依据和指导。     

A parallel finite element sliding mesh technique for the simulation of viscous flows in agitated tanks

A parallel sliding mesh algorithm for the finite element simulation of viscous fluid flows in agitated tanks is presented. Lagrange multipliers are used at the sliding interfaces to enforce the continuity between the fixed and moving subdomains. The novelty of the method consists of the coupled solution of the resulting velocity–pressure‐Lagrange multipliers system of equations by an ILU(0)‐QMR solver. A penalty parameter is introduced for both the interface and the incompressibility constraints to avoid pivoting problems in the ILU(0) algorithm. To handle the convective term, both the Newton–Raphson scheme and the semi‐implicit linearization are tested. A penalty parameter is introduced for both the interface and the incompressibility constraints to avoid the failure of the ILU(0) algorithm due to the lack of pivoting. Furthermore, this approach is versatile enough so that it allows partitioning of sliding and fixed subdomains if parallelization is required. Although the sliding mesh technique is fairly common in CFD, the main advantage of the proposed approach is its low computational cost due to the inexpensive and parallelizable calculations that involve preconditioned sparse iterative solvers. The method is validated for Couette and coaxial stirred tanks. Copyright © 2011 John Wiley & Sons, Ltd.