非旋转钝锥高超声速双平面拍摄风洞自由飞试验

在高超声速下(6 马赫) 开展了双平面拍摄风洞自由飞试验,对非旋转钝锥在小攻角下的运动特性和圆锥摆动问题进行了研究. 试验结果表明,虽然只预置了攻角而无侧滑角,模型仍然全部出现了圆锥摆动,且在观察窗范围内侧滑角幅值均大于攻角幅值. 模型角运动虽均处于小于10° 的小攻角和小侧滑角状态,但阻尼力矩项呈现较为明显的非线性,而静力矩项的非线性较弱,近似为线性. 5 组实验中,有1 组模型的角运动可能趋于极限平面运动或者是攻角幅值较小的极限圆锥运动,另外4 组试验模型角运动显示出了趋于极限圆锥运动的趋势. 尾端盖对模型的角运动影响不明显,而尾部对称布置的片条状凸起物对整个角运动幅值变化的稳定性存在明显影响,有凸起物的两组模型角运动幅值波动明显较小.      

细长锥边界层绊线转捩风洞自由飞试验

通过在半锥角θ_c=10°细长锥面上布置一定数量的人工绊线,促使细长锥表面边界层在相应轴向位置上发生层流向湍流转变的固定转捩,采用运动自由度不受约束的风洞自由飞试验技术研究边界层转捩对高超声速细长锥再入体无控自由飞行下的运动特性和气动特性影响规律,并与以往无人工绊线的细长锥风洞自由飞试验结果作对比.试验马赫数Ma=5.0,通过改变风洞前室总压P_0实现两个雷诺数的模拟,以模型长为特征尺寸自由流雷诺数分别为0.84×10~6和1.68×10~6.结果表明:当自由流雷诺数Re=0.84×10~6时,人工绊线尚不足以促使边界层发生转捩,有绊线的细长锥气动特性与无绊线基本一致,动稳定导数大于零;当自由流雷诺数Re=1.68×10~6时,人工绊线促使边界层发生固定转捩,细长锥的动稳定导数小于零,细长锥自由飞行动稳定.     

大型液体火箭姿控与跷振大回路耦合动力学建模与分析

大型液体火箭结构模态的空间化分布特征导致结构振动、姿态运动和推进系统液路脉动存在相互耦合,进而影响传统姿控回路的稳定性. 针对大型液体火箭, 充分考虑姿态控制系统对箭体姿态动力学和弹性振动的影响, 以及箭体结构弹性振动与推进系统的耦合作用(跷振(POGO)), 建立了姿控与跷振大回路耦合模型. 该模型包含了推进系统、结构系统与姿控系统之间的耦合因素, 可进行姿控-结构-推进大回路耦合机理研究. 该模型具有非奇异的优点, 可以直接用于频域分析和时域仿真. 基于该模型研究了我国某型号液体捆绑火箭推进系统参数——泵增益和蓄压器能量值对姿态运动与结构振动稳定性的影响. 研究得出, 泵增益和蓄压器能量值的变化不仅导致了结构振动的不稳定, 而且也导致了姿态运动的发散. 因此, 对于大型液体捆绑火箭, 推进系统与姿控系统之间存在不可忽略的耦合作用, 在设计姿控系统时, 有必要考虑推进系统对姿控系统稳定性的影响.      

Dynamic analysis of planar rigid-body mechanical systems with two-clearance revolute joints

In this paper, the behavior of planar rigid-body mechanical systems due to the dynamic interaction of multiple revolute clearance joints is numerically studied. One revolute clearance joint in a multibody mechanical system is characterized by three motions which are: the continuous contact, the free-flight, and the impact motion modes. Therefore, a mechanical system with n-number of revolute clearance joints will be characterized by 3 ⁿ motions. A slider-crank mechanism is used as a demonstrative example to study the nine simultaneous motion modes at two revolute clearance joints together with their effects on the dynamic performance of the system. The normal and the frictional forces in the revolute clearance joints are respectively modeled using the Lankarani–Nikravesh contact-force and LuGre friction models. The developed computational algorithm is implemented as a MATLAB code and is found to capture the dynamic behavior of the mechanism due to the motions in the revolute clearance joints. This study has shown that clearance joints in a multibody mechanical system have a strong dynamic interaction. The motion mode in one revolute clearance joint will determine the motion mode in the other clearance joints, and this will consequently affect the dynamic behavior of the system. Therefore, in order to capture accurately the dynamic behavior of a multi-body system, all the joints in it should be modeled as clearance joints.     

Nanofluidic energy absorption system: A review

基于纳米流控行为设计的新一代能量吸收耗散系统（nanofluidic en-ergy absorption system,NEAS）将会比传统吸能材料具有更高的能量吸收密度,而且还可以重复使用,特别是在小体积应用环境下具有显著的优势.本文从实验和计算模拟两方面综述了目前关于NEAS能量吸收耗散行为的最新研究进展,其中实验研究主要包括准静态压缩和动态压缩测试,计算模拟研究主要是采用基于经验势的分子动力学模拟方法.通过准静态压缩实验,可以测量NEAS模型的载荷–位移关系曲线,从而获得NEAS模型的临界渗透压强,了解卸载后系统是否能够恢复到加载前的状态（即是否可以重复使用）,并通过载荷–位移关系曲线下面积估算NEAS模型的吸能密度;通过动态压缩实验可以测量NEAS模型对脉冲载荷的缓冲保护作用,主要体现为降低脉冲载荷幅值和扩展脉冲宽度.计算模型研究可以明确给出NEAS对外载荷的微观响应,从而可以准确了解NEAS的能量吸收耗散机制以及吸能密度的主要影响因素.本研究可以帮助我们全面了解NEAS的研究进展,为NEAS的设计与优化提供重要指导.     

NUMERICAL SIMULATION STUDY ON DYNAMIC RESPONSE UNDER RUDDER CONTROL

针对超声速机动飞行器舵面操纵动态响应问题,开展了相应的算法研究,建立了适用于模拟舵面与弹体相对运动及弹体气动力动态响应的非定常计算方法和局部动态网格变形技术. 以方形弹超声速绕流为例,验证了所提出的定常和非定常计算方法. 对方形弹舵面操纵的3种基本过程(脉冲、阶跃和谐波) 进行了数值模拟,获得了舵面操纵下导弹的俯仰运动对操纵的响应过程. 研究结果表明,快速的舵面操纵过程,甚至会导致导弹的俯仰运动失稳.     

DYNAMIC MODELING OF MULTI-BODY SYSTEM BASED ON GAUSS'S PRINCIPLE

基于高斯最小拘束原理,以释放中的绳系卫星为背景,建立地球引力场内变长度大变形柔索联系的多体系统动力学模型. 利用基尔霍夫动力学比拟方法将柔索的变形转化为刚性截面沿中心线的转动,使包含刚性分体与变形体的刚柔耦合系统转化为由柔索的刚性截面与刚性分体组成的广义多刚体系统. 由于刚性截面的局部小变形沿弧坐标的积累不受限制,适合描述柔索的超大变形. 文中对此刚柔耦合多体系统导出其在地球引力场中的拘束函数,考虑各分体在空间中相对位置的几何约束条件,利用拉格朗日乘子构成以条件极值问题为特征的数学模型. 将高斯原理用于多体系统动力学的建模,其特点是以寻求函数极值的变分方法代替微分方程,通过数值计算直接得出运动规律. 其形式统一,不随系统拓扑结构的变化而改变,也无需区分树系统或非树系统.对于带控制的多体系统,动力学分析还可根据技术需要与系统的优化结合进行.     

末端带有刚体的旋转梁运动稳定性分析

在对含有柔性元件的复杂航天器进行稳定性等动力学行为的分析中, 通常采用的离散化方法, 可能会导致"动力刚化"等现 象.将梁作为带分布参数的子系统(无限自由度)分析, 基于Rumyancev定理, 通过计算系统相对势能泛函的一阶变分得到了系统的定常运动, 把系统定常运动稳定性的分析归结为系统变势能泛函存在孤立极小值的问题.在分析中不需要建立系统的运动微分方程, 简化了建模过程, 由系统相对势能泛函的二阶变分的正定性得到了使系统定常运动稳定的充分条件, 同时这个条件是使用基于李雅普诺夫直接法思想分析运动稳定性问题得到的最为广泛的充分条件.     

AN EFFICIENT DYNAMIC MODELING METHOD OF AN AXIALLY MOVING CANTILEVER BEAM AND FREQUENCY RESPONSE ANALYSIS

轴向移动梁动力学问题具有广泛的工程应用背景,如：机械手、机床主轴、武器身管等.计算轴向移动梁动力学响应是评估结构动力学性能以及最终指导结构设计的一个重要手段.采用Rayleigh-Ritz法、拉格朗日方程推导了轴向移动悬臂梁时变动力学方程.选取幂级数函数构造试函数对轴向移动系统动力问题进行求解.幂级数函数良好的积分与微分性能,使得推导容易以矩阵的形式快速进行,便于符号运算软件直接生成MATLAB程序.由于MATLAB基本数据单位为矩阵,符号软件生成的程序只需经过简单修改便可进行动力学计算.大大缩短了轴向移动梁从建模到动力学分析的时间,过程十分高效.通过四组算例,将本文方法计算得到的动力学响应与文献数据进行对比,对该方法准确性进行了验证,并给出了幂级数函数拟合阶数的选取原则.以此为基础,研究了轴向移动梁的频率响应特性.分为考虑重力与忽略重力两种情况,讨论了轴向振动幅度对其频率响应特性的影响.     

乘员股骨在轴向压力-弯矩下的损伤生物力学机理研究

汽车前碰撞事故中在冲击力作用下乘员股骨经常产生骨折创伤.为研究乘员股骨在不同的轴向压力-弯矩作用下的损伤机理及其耐受限度值,首先建立了一个较为精细的50百分位乘员的坐姿下肢有限元模型,并通过模拟股骨动态三点弯曲及下肢的轴向膝部冲击实验对模型的有效性进行了验证.在此基础上,针对股骨在轴向压力-弯矩载荷下的断裂失效分别进行了曲梁力学模型分析及有限元虚拟实验研究.结果表明:股骨骨折位置依赖于膝部轴向压力及弯矩的载荷大小的变化,在预加载弯矩从0增加到676Nm时,股骨失效部位由股骨颈部转移到股骨干末端区域;失效部位发生在颈部及股骨干时的最大力矩分别为285 296Nm和381443Nm.股骨损伤机理的分析结果阐释了在膝部轴向冲击实验中失效部位位于股骨颈部,而在汽车前碰撞事故中仍有大量的股骨干骨折出现的原因.      

Investigation of nonlinear characteristics of the motor-gear transmission system by trajectory-based stability preserving dimension reduction methodology

Gear-motor system is a typically nonlinear system because of many nonlinear factors, such as time-varying meshing stiffness, backlash, and the nonlinear relationship between the electric motor torque and speed. At present, the nonlinear analytical methods can only be used for simplified gear dynamic model. Though the numerical methods can be used for the complicated dynamic model, the quantitative analysis of stability is difficult and rarely conducted. Therefore, a kind of trajectory-based stability preserving dimension reduction (TSPDR) methodology is proposed to investigate nonlinear dynamic characteristics of the gear-motor system. In the TSPDR methodology herein, the complementary cluster center of inertia-relative motion (CCCOI-RM) transformation is chosen and the stability margins are specially defined for distinguishing the stable motion modes of the motor-gear system, to make the TSPDR methodology used in the nonlinear analysis of the gear-motor system. Furthermore, the critical values are obtained for alteration of different motion modes and the nonlinear characteristics of each motion modes are analyzed. At last, combined with modal analysis, the relationship between the stability and resonance of the gear-motor system is revealed.     

基于非局部效应和表面效应的输流碳纳米管稳定性分析简

应用非局部黏弹性夹层梁模型分析双参数弹性介质中输送脉动流碳纳米管的稳定性. 新模型中同时考虑了由管道内、外壁上的薄表面层引起的表面弹性效应和表面残余应力，经典的欧拉梁模型因此通过引入非局部参数和表面参数得到了改进. 用平均法对其控制方程进行求解，得到了管道稳定性区域. 数值算例揭示了纳米材料的非局部效应、表面效应及两个弹性介质参数对管道固有频率、临界流速和动态稳定性的复杂影响，结论可为纳米流体机械的结构设计和振动分析提供理论基础.     

AN ARBITRARILY MIXED EXPLICIT-IMPLICIT ASYNCHRONOUS INTEGRATION ALGORITHM BASED ON UNIFORM DISCRETIZATION FORMAT

动力学问题的有限元分析需要在每一时步求解系统信息,相对于静力学问题,其计算量要大得多.因而,提高计算效率,节省计算工作量是动力学求解方法研究的主要内容.该文针对大型复杂动力学系统的高效求解问题,提出了一种基于Newmark离散格式的显式、隐式任意混合异步算法,根据整体系统不同局部的物理力学特性和求解精度要求,在空间域及时间域内对动力学系统方程进行多尺度求解.该方法根据显式、隐式算法固有的信息传递机制,采取动态的可变边界处理方法,避免了异步边界上的误差积累;并通过对整体系统能量平衡的校验,动态地确定和修正仿真计算时步,可以有效地预防不稳定性的产生和发展.数值算例表明：该算法能在保持较高的计算精度的同时,极大地降低计算资源消耗,因而具有一定的实用价值.     

DEPLOYMENT DYNAMICS OF FLEXIBLE SOLAR ARRAYS CONSIDERING FRICTIONAL JOINT

研究了空间漂浮航天器太阳阵展开与锁定过程的刚柔耦合动力学问题. 基于Jourdain 速度变分原理和单项递推组集方法, 建立了太阳阵展开与锁定过程的刚柔耦合多体系统动力学模型,采用虚功率原理推导了铰摩擦对系统动力学方程的贡献. 在以上动力学模型中引入3-D 鬃毛摩擦模型来研究铰链的摩擦特性对太阳阵展开动力学的影响. 所建动力学模型的正确性通过与商业软件ADAMS 和NASTRAN 的联合仿真对比得到了验证,该模型能够有效地预测太阳阵的展开历程以及航天器姿态的动态行为.     

BACK CALCULATION METHODS FOR DEFORMATION MODULUS BASED ON SETTLEMENTS IN DYNAMIC COMPACTION

在运动方程法和能量法等强夯理论基础上,采用位移反分析方法建立二者反演格式,利用易于测量的夯沉量等数据反算地层变形模量,结合北京园博园强夯实验数据,计算并分析了变形模量随夯击次数的变化情况. 研究表明,地基变形模量随夯击次数逐渐增大,增幅逐渐减小,变形模量最终趋于稳定;反演得出该实验地基的初始变形模量在5～8MPa 之间,夯击7 次后在18～22MPa 之间,提高幅度约为3～4 倍;能量法反演过程相对简便,可在类似工程中推荐采用.     

Dynamics of windscreen wiper blades: Squeal noise,reversal noise and chattering

The motion of a windshield wiper blade is modelled by a mass-spring-damper system on a moving frictional surface. The system dynamics is time-varying, since three different regimes of motion, characterized by different degrees of freedom, are possible. Indeed the system, which schematizes a blade cross-section, can experience stick and slip motions when it is in contact with the glass surface, and free-flight motion when it is detached. The contact between the system and the surface is governed by Stribeck׳s friction law and Poisson׳s impact law, which make the dynamics non-smooth. The model is numerically implemented in an event-driven code, and simulations are performed which reproduce the three basic classes of undesired oscillations observed in the motion of real windscreen wipers, i.e., squeal, reversal and chattering noises. Attention is focused on the causes of these vibrations, and remedies for reducing or avoiding them are proposed.     

Estimating the dynamic coefficient of friction from experimental data: the motion of a rocket inside a smoothbore launcher

The motion of a spinning rocket inside a smoothbore launcher has drawn some attention in recent years. The inaccuracy of spin-stabilized rockets can be attributed, in part, to the initial motion of the rocket inside the smoothbore launcher. Recently, tests have indicated that a closer examination of the problem is required. The tests were performed to determine the time history of the spin and forward motion of the rocket by Fastax cameras. The evaluation of the data with respect to engineering-design parameters is difficult since the experimental results must be compared with an analytical model of the system. In this paper, the results of one test are reported and a nonlinear analytical model is used which includes both the rotary and forward motion of the rocket. The two motions are coupled through a dynamic friction coefficient. The intent of this paper is to show how an analytical model can be made to fit the experimental data, that is, the initial conditions and the coefficient of friction are found which define the solution giving the best least-square fit to the data.     

Stability of motion of two rigid bodies connected by a cable in the atmosphere

The spatial motion of two rigid bodies connected by a weightless inextensible cable in the atmosphere is considered. They are assumed to be bodies of revolution with static and dynamic symmetry. The condition of static stability of the system angular motion with respect to the direction of the incident airflow velocity vector is written out and analyzed. The influence of gyroscopic terms and damping moments on the stability condition is studied. An example of analysis of motion in the atmosphere of two connected bodies that are cones with a spherical tip is given. It is shown that the stable motion in the atmosphere can always be ensured by an appropriate matched choice of the parameters of the entire system on the basis of the obtained stability conditions. A numerical example of estimating the cable tension forces arising as the system descends on a ballistic trajectory in the atmosphere is presented.     

具有局部非线性动力系统周期解及稳定性方法

对于具有局部非线性的多自由度动力系统，提出一种分析周期解的稳定性及其分岔的方法该方法基于模态综合技术，将线性自由度转换到模态空间中，并对其进行缩减，而非线性自由度仍保留在物理空间中在分析缩减后系统的动力特性时，基于Ｎｅｗｍａｒｋ法的预估－校正－局部迭代的求解方法，与Ｐｏｉｎｃａｒé映射法相结合，推导出一种确定周期解，并使用Ｆｌｏｑｕｅｔ乘子判定其稳定性及分岔的方法     

空间可展机构非光滑力学模型和动力学研究

空间可展机构广泛应用于展开和支撑柔性太阳能帆板和航天工程领域中的有效载荷, 包括抛物面天线、平面相控阵雷达和合成孔径雷达等. 非光滑特性及其相应的动力学现象在空间可展机构的设计中有着非常重要的作用. 该文系统地综述了空间可展机构非光滑力学建模与非线性动力学的研究进展. 首先详细描述了含间隙铰链的接触碰撞力和摩擦力等非光滑特点;然后系统地介绍了含间隙机构的动力学建模方法、分析方法和参数设计;进一步简单介绍了含间隙铰链空间可展机构的非线性动力学特性, 如谐波共振、周期运动的稳定性和各类分岔等;最后提出了空间可展机构非光滑动力系统动力学、稳定性与控制中亟待解决的若干问题.