超音速下热壁板的颤振分析

首先研究了热效应对壁板结构动力学特性的影响.将基于超音速活塞理论的非定常气动力模型与壁板的结构动力学方程相结合,得到了热壁板的颤振方程.利用p-k法进行了热壁板的颤振计算,讨论了气流偏角对颤振速度的影响.数值结果表明,热效应对壁板的固有特性有较大影响,进而影响壁板的颤振特性.     

超音速舵面热气动弹性仿真

为研究弹翼气动加热效应对结构气动弹性稳定性的影响,建立了热气动弹性仿真模型。根据分层求解的原理,首先采用平板参考温度法进行气动加热计算,进而分析热环境下结构的固有特性,并利用当地流活塞理论计算非定常气动力,在状态空间进行热颤振求解。对某弹性边界全动舵进行了超音速巡航段的热颤振特性分析;结果表明,随着时间的推移,热效应使舵面的固有频率逐渐降低,导致颤振边界下降;一段时间后,固有特性及热颤振特性趋于稳定。分析方法简捷有效,为飞行器结构设计提供了一种工程分析手段。     

航天器柔性附件对其驱动机构的干扰研究

带柔性附件的航天器在进行轨道机动或姿态调整等大范围运动时,柔性附件的弹性振动与航天器大范围运动的刚柔耦合作用将会对驱动机构产生一定的干扰.首先利用单向递推组集建模方法建立了带柔性附件的航天器的动力学模型,然后研究了航天器不同工况变轨时由于柔性附件的弹性振动与航天器大范围运动的刚柔耦合作用对驱动机构所产生的干扰,最后结合变轨条件和柔性附件的固有特性,具体地分析了干扰的作用机理.     

大展弦比机翼非线性颤振剪裁设计新方法

针对大展弦比机翼水平弯曲模态参与耦合颤振问题,首先用考虑几何非线性的颤振分析方法研究了某大展弦比机翼的颤振特性,结果表明水平一弯模态参与耦合降低了机翼传统模式的线性颤振速度;然后研究了复合材料的铺层主刚度方向角对机翼非线性振动特性和颤振特性的影响规律,提出了大展弦比机翼非线性颤振剪裁设计的新方法.结果表明主刚度方向角的变化主要引起了水平一弯模态振型的改变,一般表现为主刚度方向角从机翼后梁向后缘偏转,该阶模态的相对扭转振型节线位置向前缘移动;反之,该节线位置后移.进一步非线性颤振分析,发现水平一弯模态振型的变化引起了该阶模态参与耦合颤振速度的明显改变,主要表现为该颤振型的颤振速度随该阶模态的相对扭转振型节线位置前移量的增加而增大.通过两个算例验证了结论的正确性.     

考虑舵机动力学的舵回路系统颤振特性分析

针对液压舵机动刚度特性,研究了舵回路系统(舵机系统和舵面耦合系统)的颤振特性.利用分支模态法建立了基于舵机系统动力学方程的时域和频域颤振计算模型,提出了2种考虑舵机动态特性的颤振求解方法,第1种方法思想是对舵回路系统模型在各种来流速度下进行状态矩阵的稳定性判断;第2种方法是将舵机复刚度特性包含在频域颤振方程中,使用迭代法求解该方程得到舵系统颤振特性,并验证了两种方法的可行性.分析结果显示舵机动态特性对颤振特性有着很大的影响,说明舵机动态特性使得颤振边界提高,为飞机系统设计和结构振动分析提供有用的边界支持和设计依据.     

基于LQG自校正器的机翼颤振主动抑制

研究了一种基于LQG自校正器的机翼颤振主动抑制设计方法.以带有后缘控制面的柔性机翼为研究对象,采用在线辨识来获取系统的时变参数,利用Kalman滤波器重构状态,通过求解离散时间代数Riccati方程得出机翼颤振主动控制律.在Simulink仿真平台上实现了上述方法,仿真结果表明,该控制器能够有效抑制机翼颤振的发生并具有一定的鲁棒性.     

带柔性伸缩附件航天器几何非线性振动稳定性

研究由中心刚体和可伸缩柔性附件组成的非线性刚柔耦合系统，不同于大多数文献只研究柔性附件的横向弯曲变形对系统动态特性的影响，同时考虑了柔性附件的拉伸变形、截面转角变化同弯曲变形的相互耦合作用，并且以非线性几何关系作为基本出发点，建立了伸缩运动同柔性变形、姿态运动之间的非线性耦合动力学模型，然后基于能量积分和动量矩积分构造首次积分，分析了非线性耦合系统的运动稳定性。     

机翼有限元模型振动和颤振特性分析

采用MSC Patran,MSC Flds建立某型飞机机翼的动力学有限元模型. 应用MSC Nastran中求解序列SOL 103对其进行固有模态分析,利用求解序列SOL 145进行颤振分析. 通过分析得到该机翼的振动和颤振特性,为飞机研制提供依据.     

超光谱成像仪指向镜热光学特性描述方法研究

超光谱成像仪是"图谱合一"的光学遥感器,其指向反射镜位于超光谱成像仪最前端,尺寸大,热流复杂,容易受到热影响.指向反射镜的热光学特性反映指向反射镜的热适应性和热尺寸稳定性,是结构设计人员以及热设计人员关注的重要性能.分析了指向反射镜的工作环境,论述了指向反射镜热光学特性研究内容及技术路线.针对实例,利用有限元方法和理论公式进行了热光学分析,比较了两种描述指向反射镜热光学特性的方法.结果表明,对于指向反射镜,与基于温差的描述相比,基于热功率的描述更加真实的反映指向镜的热适应性和热尺寸稳定性.     

前缘变配重颤振分析

为了提高某型飞机机翼颤振速度,详细探讨利用副翼前缘配重提高颤振速度的方案. 用MSC Nastran对副翼前缘进行变配重重量和位置的振动、颤振计算分析. 得到的结果有助于改善机翼的颤振特性,为机翼改进设计及飞机振动、颤振试飞提供参考.     

Heteroclinic bifurcations in attitude maneuver of coupled slosh-spacecraft with flexible appendage

In this paper, the chaotic dynamics in an attitude transition maneuver of a slosh-spacecraft coupled with flexible appendage in going from minor axis to major axis spin under the influence of dissipative effects due to fuel slosh and a small flexible appendage constrained to only torsional vibration is investigated. The slosh-spacecraft coupled with flexible appendage in attitude maneuver carrying a sloshing liquid is considered as multi-body system with the sloshing motion modeled as a spherical pendulum. ...     

On Frequency Sensitivity and Mode Orthogonality of Flexible Robotic Manipulators

This paper presents sensitivity analysis of vibration frequencies of flexible manipulators with respect to variations of systems parameters such as rotational inertia of hub, and mass, moment, and side of tip load. Both Euler-Bernoulli and Timoshenko dynamical models of flexible manipulators are discussed. By using variational method, sensitivity indices are obtained with explicit expressions for measuring the sensitivity of frequencies. Based on variational formulations, a novel method for deriving the orthogonal relations among vibration modal shape functions of flexible manipulators is introduced. With this method, the orthogonal relations can be derived easily without invoking the tedious process of differentiation and integration by part, as commonly used in their derivation.      

Energy-based robust controller design for flexible spacecraft

This paper presents a class of non-model2based position controllers for a kind of flexible spacecraft. With the controllers, one can achieve not only the closed-loop stability of the original distributed parameter system, but also the asymptotic stability of the truncated system, which is obtained through representing the deflection of the appendage by an arbitrary finite number of flexible modes. The system dynamics are not explicitly involved in the controller design and stability proof. Instead, only a very basic system energy rehtionship of the flexible spacecraft is utilized. The controllers possess several remarkable advantages over the traditional model-based ones. Numerical simulations are carried out on a kind of spacecraft with one flexible appendage and satisfactory results are obtained.     

Control of flexible manipulators via singular perturbations and distributed vibration damping

A composite control strategy for a two-link flexible manipulator is analyzed which combines hub actuation with distributed vibration control. The hub actuation is based upon an integral manifold approach in which the system dynamics are approximately linearized to any order of a small parameter E representing stiffness of the robot arms. A polymer film is proposed as a distributed actuator to dampen vibrations due to elasticity in the links. Simulation results are provided which show that the addition of the distributed actuator significantly reduces the displacement and velocity of the first flexible mode in each link compared to hub actuation alone. Editor: T. Vincent     

On the coupled dynamics of small spacecraft and elastic deployable appendages

A thorough investigation of the dynamics of finite-mass satellites with a deployable elastic arm is presented. This work is focused on the interaction between spacecraft rigid body motion and its flexible arm dynamics during the deployment process. The classical Newton–Euler formulation and the Lagrangian approach are applied to the study of the dynamics of spacecraft and its deploying arm. Utilizing a non-Newtonian floating frame to define the arm elastic deformation field, the interactions between the spacecraft and its moving arm have been simulated. Complete equations of motion show that the spacecraft motion induces dynamical stiffness on the arm; in addition, axial and lateral motions of the deploying elastic arm change the spacecraft mass-characteristics and thus influence the spacecraft’s rigid body motions. The overall dynamic behavior is highly dependent on spacecraft mass characteristics in addition to the “arm deployment time (ADT)”. The results of case studies clearly indicate that some assumptions previously applied in appendage dynamic analysis are not conservative and produce erroneous results. This study realistically investigates the dynamics of elastic deploying appendages by considering finite-mass characteristics for small and massy spacecraft. The results reveal that for massive spacecraft the arm’s flexible dynamics is mainly excited through deployment, while for small spacecraft the energy transfers to the arm base and the spacecraft rigid body motion is considerably stimulated. Moreover, this work has further highlighted the effects of ADT in the overall system response. The findings of this work show that the energy distribution between arm’s elastic dynamics and spacecraft rigid body motions is an important factor in the design of any control system to limit unwanted arm-tip motions.     

充液柔性航天器非线性姿态动力学及再定向姿态机动

研究全充液柔性航天器大角度姿态机动中非线性姿态动力学及姿态再定向问题．采用Lagrange方法推导了液-柔耦合系统动力学方程并对系统进行了相空间动力学研究．由于能量耗散及柔性附件振动对系统产生扰动并由此引起混沌姿态运动，经历姿态转换后的航天器最终姿态定向不能预先确定．本文研究表明，通过一对互为反向的脉冲推进可以完成预期的姿态再定向机动．给出了实现姿态再定向机动的控制策略，并对控制前后的姿态本体轨迹及主角动量分量时间响应历程进行了数值仿真．     

Single-input/single-output transfer functions for a flexible slewing link

Truncated linear models based on constrained and unconstrained mode expansions for a flexible link with torque actuation at its hub led us to examine the behavior of the open-loop-zeros of five commonly used single-input single-output transfer functions. We arrive at new conclusions with regard to minimum- and non-minimum-phase zeros, and passivity of the transfer functions. The flexible-to-rigid inertia (FRI) ratio plays an important role in the determination of these characteristics. This article illustrates how the zero locations of some of the transfer functions are dramatically affected by the FRI ratio. We also investigate the performance of a hub angle, hub rate, and relative tip position static feedback controller based on a reduced-order constrained mode model when applied to both unconstrained and constrained mode models of the same dimension. Simulations indicate that the constrained model can be stable while the unconstrained model is not for high FRI ratios. Our findings can provide useful information to designers in cases where the controller is sensitive to the location of the plant's zeros.     

A criterion on inclusion of stress stiffening effects in flexible multibody dynamic system simulation

This paper presents a criterion on inclusion of stress stiffening effects in dynamic simulation of flexible multibody systems. The proposed criterion examines numerically the eigenvalue variation of the total modal stiffness matrix that is a combination of the modal stress stiffness matrix and the conventional linear modal stiffness matrix prior to actual dynamic simulation. If the variation is sufficiently large for any flexible body in the multibody system, then stress stiffening effects must be included in dynamic simulation of flexible multibody systems for accurate prediction of dynamic behavior. Since the criterion uses the most general stress stiffness matrix contributed from applied and constraint reaction loads as well as from a system of 12 inertial loads, this criterion is applicable to any general flexible multibody dynamic system. Several numerical results are presented to show the effectiveness of the proposed criterion.     

Reaching movements in dynamic environments: how do we move flexible objects?

The paper presents an analysis of human reaching movements in manipulation of flexible objects. To predict the trajectory of human hand, a minimum crackle criterion has been recently introduced in literature. A different approach is explored in this paper. To explain the trajectory formation, we resort to the minimum hand jerk criterion. First, we show that this criterion matches well experimental data available in literature. Next, we argue that, contrary to the minimum crackle criterion, the minimum hand jerk criterion produces bounded hand velocity profiles for multimass flexible objects. Finally, we present initial experimental results confirming the applicability of the minimum hand jerk criterion to the prediction of reaching movements with multimass objects.     

Controller design for flexible structure vibration suppression with robustness to contacts

Model-based feedback control of vibration in flexible structures can be complicated by the possibility that interaction with an external body occurs. If not accounted for, instability or poor performance may result. In this paper, a method is proposed for achieving robust vibration control of flexible structures under contact. The method uses robust linear state feedback, coupled with a state estimation scheme utilizing contact force measurement. Uncertain contact characteristics are modelled by a sector-bounded non-linear function, such that state feedback gains can be synthesized using a matrix inequality formulation of the Popov stability criterion. A separation theorem is used to establish a robust H₂ cost bound for the closed loop system. Experimental results from a multi-mode flexible structure testbed confirm that vibration attenuation and stability can be maintained over a broad range of contact characteristics, in terms of compliance and clearance.