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1.
陈琦  陈坚强  袁先旭  谢昱飞 《力学学报》2016,48(6):1281-1289
飞行器在大气环境中飞行时,经常受阵风等的干扰,引发非指令的自激振荡,威胁飞行安全.通过建立刚体六自由度运动方程和N-S方程的松耦合求解技术,研究强迫俯仰振荡过程对滚转特性的影响.针对背风区涡流形态及横侧向气动特性复杂的方形截面飞行器,数值模拟研究了其不同攻角下的静态滚转气动特性、自由滚转运动特性,以及俯仰振荡时不同振荡速率对滚转气动和运动特性的影响.结果表明,此飞行器在静态时临界攻角约为13°,当攻角小于临界攻角时,滚转方向是静不稳定的,诱发快速滚转运动;当攻角大于临界攻角时,滚转方向是静稳定,其滚转运动是收敛的.研究发现,俯仰振荡一般会降低飞行器滚转方向静稳定或静不稳定的量值,增强滚转方向的动态稳定性.在俯仰振荡的影响下,即使滚转方向是静不稳定的,如果俯仰振荡的频率足够大,飞行器的滚转运动也可能是收敛的.  相似文献   

2.
高剑军  卜忱  杜希奇 《实验力学》2010,25(2):207-211
在中航气动院FL-8低速风洞中,采用单自由度振荡机构进行了旋转流场下大幅俯仰运动的气动特性实验研究。模型在绕风速轴连续旋转的同时,进行给定频率和振幅绕体轴的俯仰振荡运动。测量了模型的动态气动特性,着重分析了不同运动参数对模型气动特性的影响。实验结果表明,旋转速度的存在使大振幅俯仰振荡实验中的滚转力矩和偏航力矩产生了明显的迟滞特性,但对俯仰力矩和法向力的迟滞特性影响不大。  相似文献   

3.
刘伟  张涵信 《力学学报》2005,37(4):385-392
耦合三维非定常Navier-Stokes方程与Euler刚体运动方程数值研究80°尖前缘后掠三角翼的机翼摇滚问题. 采用高精度的WNND(weighted non-oscillatory, containing no free parameters and dissipative)格式离散流动控制方程、采用时间二阶精度单边差分离散刚体运动方程数值模拟了马赫数为0.35, 攻角为10°, 22°, 30°下三角翼受扰后的自由滚转运 动. 结果表明:22°攻角附近为所给三角翼出现横向不稳定的摇滚运动的临界攻角;当攻角小于临界值时,受扰后的机翼滚转运动收敛,而当攻角大于临界值时,受扰后的机翼滚转运动发散并形成极限环形式的机翼摇滚.  相似文献   

4.
弹性振动对翼型气动特性影响的数值模拟   总被引:1,自引:0,他引:1  
通过求解雷诺平均非定常Navier-Stokes方程,采用数值模拟方法计算了俯仰和沉浮振动对NACA0012翼型平均气动特性的影响.结果表明:对于俯仰运动而言,在迎角13α≤时的升力°和力矩曲线的线性段部分,振幅角的变化对动态平均升力系数和动态平均力矩系数的影响不明显,与静态时的情况基本一致;当迎角14α≥时,翼型振动的平均升力系数和动态平均力矩系数小°于静态时的情况.同一迎角条件下的俯仰振动频率越高时,其动态的平均升力系数和动态平均力矩系数越大,频率较高时的失速迎角相对于频率较低时的情况有所推迟,但相对于静态的失速迎角而言,不同频率下的动态失速迎角均提前.对于沉浮运动而言,动态平均升力系数随振幅和频率的增加而减小,动态失速迎角随振幅和频率的增大而提前.  相似文献   

5.
快速俯仰三角翼的非定常空气动力实验研究   总被引:1,自引:1,他引:0  
李京伯  章子林 《实验力学》1994,9(3):253-261
展弦比为1.5和2.0的两个平板三角翼作快速俯仰振荡运动的非定常空气动力实验研究在南京航空航天大学3×2.5米低速风洞中进行。俯仰运动的振幅为60°和90°,无因次俯仰率参数范围为0.01 ̄0.03。以三角翼根弦为参考长度的雷诺数为0.72×10^6。用六分量应变天平测量模型的空气动力和力矩。实验结果表明:法向力和俯仰力矩系数相对于静态值的过冲量以及滞环大小与无因次俯仰率、振幅及展弦比密切相关,而  相似文献   

6.
应用有限体积方法求解三维可压缩雷诺平均N-S方程,计算了巡航导弹外形飞行器作小振幅俯仰运动时的动态绕流流场和空气动力特性,开展了导弹绕不同转轴、以不同频率和在不同迎角范围内进行俯仰运动的非定常气动力迟滞特性研究。计算结果表明,当导弹作快速俯仰运动时,在上仰和下俯过程中的同一迎角瞬间,绕导弹流场流动明显不同,表现出明显的非定常迟滞特性。导弹的非定常气动力迟滞特性随俯仰运动频率的增大明显增强,且气动力迟滞曲线随着俯仰轴位置的变化而变化。在同一减缩频率下,导弹在不同迎角范围内作周期俯仰运动时,相同的运动相位角所对应的升力系数对迎角的导数是一致的,而不同减缩频率下升力系数对迎角的导数随运动相位角变化曲线明显不同。  相似文献   

7.
陶洋  范召林  赵忠良 《实验力学》2009,24(2):171-175
介绍了在FL-23高速风洞中研究自由摇滚的装置、试验方法、数据采集等试验技术.在马赫数从0.3到0.6范围内,对应的雷诺数从0.56×107/m至1.126×107/m范围内,开展了双三角翼大迎角下的摇滚特性的研究,包括迎角、马赫数、初始释放等参数的影响,给出了典型的结果.结果表明,随着模型迎角的增加,双三角翼呈现不同的滚转运动形态,包括静态稳定、准极限环摇滚、双周期震荡等;试验中马赫数提高对翼摇滚起抑制作用;摇滚运动的最终平衡状态和摇滚幅值与初始状态无关.  相似文献   

8.
对磁场环境中轴向运动导电薄板的磁弹性强迫振动问题进行了研究。在给出薄板运动的动能、应变能、电磁力虚功的基础上,应用哈密顿变分原理推得了磁场中轴向运动矩形薄板的磁弹性振动方程;基于麦克斯威尔电磁场方程并考虑相应的电磁关系式,得到了薄板所受电磁力的表达式。针对横向磁场中矩形板的强迫振动问题,通过位移函数的设定并应用伽辽金积分法,分别得到了对边简支-对边自由、对边夹支-对边自由两种边界约束条件下轴向运动薄板的磁弹性强迫振动微分方程。通过数值算例,给出了横向磁场中均布动载作用下对边夹支对边自由边界约束条件下轴向运动矩形板的振幅放大因子随频率、轴向速度、磁感应强度的变化规律曲线图。结果表明:频率比和轴向运动速度的改变,均使振幅放大因子在共振区出现了峰值,外加磁场则起到了电磁阻尼的作用。  相似文献   

9.
介绍了在FL-23高速风洞中研究自由摇滚的装置、试验方法、数据采集等试验技术。在马赫数从0.3到0.6范围内,对应的雷诺数从0.56×10^7/m至1.126×10^7/m范围内,开展了双三角翼大迎角下的摇滚特性的研究,包括迎角、马赫数、初始释放等参数的影响,给出了典型的结果。结果表明,随着模型迎角的增加,双三角翼呈现不同的滚转运动形态,包括静态稳定、准极限环摇滚、双周期震荡等;试验中马赫数提高对翼摇滚起抑制作用;摇滚运动的最终平衡状态和摇滚幅值与初始状态无关。  相似文献   

10.
张颖  吴君正  张能辉 《力学季刊》2019,40(2):327-334
本文研究了连接部件的几何参数对变截面耦合微悬臂双梁振动特性的影响.首先,利用集总参数法建立了等效的两自由度系统耦合振动的解析模型;其次,利用分离变量法获得了耦合双梁自由振动的固有频率、振幅比和强迫振动的反共振频率;最后,通过比对解析解、有限元数值结果和实验数据,验证了解析预测的可靠性.研究结果表明,连接部件的宽度和初始偏转角的变化会对耦合双梁振动的特性产生较大的影响.  相似文献   

11.
Abohamer  M. K.  Awrejcewicz  J.  Amer  T. S. 《Nonlinear dynamics》2023,111(9):8217-8234

This paper focuses on the dynamical analysis of the motion of a new three-degree-of-freedom (DOF) system consisting of two segments that are attached together. External harmonic forces energize this system. The equations of motion (EOM) are derived utilizing Lagrangian equations, and the approximate solutions up to the third order are investigated using the methodology of multiple scales. A comparison between these solutions and numerical ones is constructed to confirm the validity of the analytic solutions. The modulation equations (ME) are acquired from the investigation of the resonance cases and the solvability conditions. The bifurcation diagrams and spectrums of Lyapunov exponent are presented to reveal the different types of the system’s motion and to represent Poincaré maps. The piezoelectric transducer is connected to the dynamical system to convert the vibrational motion into electricity; it is one of the energy harvesting devices which have various applications in our practical life like environmental and structural monitoring, medical remote sensing, military applications, and aerospace. The influences of excitation amplitude, natural frequency, coupling coefficient, damping coefficient, capacitance, and load resistance on the output voltage and power are performed graphically. The steady-state solutions and stability analysis are discussed through the resonance curves.

  相似文献   

12.
The effect of the control structure interaction on the feedforward control law as well as the dynamics of flexible mechanical systems is examined in this investigation. An inverse dynamics procedure is developed for the analysis of the dynamic motion of interconnected rigid and flexible bodies. This method is used to examine the effect of the elastic deformation on the driving forces in flexible mechanical systems. The driving forces are expressed in terms of the specified motion trajectories and the deformations of the elastic members. The system equations of motion are formulated using Lagrange's equation. A finite element discretization of the flexible bodies is used to define the deformation degrees of freedom. The algebraic constraint equations that describe the motion trajectories and joint constraints between adjacent bodies are adjoined to the system differential equations of motion using the vector of Lagrange multipliers. A unique displacement field is then identified by imposing an appropriate set of reference conditions. The effect of the nonlinear centrifugal and Coriolis forces that depend on the body displacements and velocities are taken into consideration. A direct numerical integration method coupled with a Newton-Raphson algorithm is used to solve the resulting nonlinear differential and algebraic equations of motion. The formulation obtained for the flexible mechanical system is compared with the rigid body dynamic formulation. The effect of the sampling time, number of vibration modes, the viscous damping, and the selection of the constrained modes are examined. The results presented in this numerical study demonstrate that the use of the driving forees obtained using the rigid body analysis can lead to a significant error when these forces are used as the feedforward control law for the flexible mechanical system. The analysis presented in this investigation differs significantly from previously published work in many ways. It includes the effect of the structural flexibility on the centrifugal and Coriolis forces, it accounts for all inertia nonlinearities resulting from the coupling between the rigid body and elastic displacements, it uses a precise definition of the equipollent systems of forces in flexible body dynamics, it demonstrates the use of general purpose multibody computer codes in the feedforward control of flexible mechanical systems, and it demonstrates numerically the effect of the selected set of constrained modes on the feedforward control law.  相似文献   

13.
14.
The present work investigates the performance of two systematic methodologies leading to hybrid modeling of complex mechanical systems. This is done by applying numerical methods in determining the equations of motion of some of the substructures of large order mechanical systems, while the dynamic characteristics of the remaining components are determined through the application of appropriate experimental procedures. In their simplest version, the models examined are assumed to possess linear characteristics. For such systems, it is possible to apply several hybrid methodologies. Here, the first of the methods selected is performed in the frequency domain, while the second method has its roots and foundation in time domain analysis. Originally, the accuracy and effectiveness of these methodologies is illustrated by numerical results obtained for two complex mechanical models, where the equations of motion of each substructure are first set up by applying the finite element method. Then, the equations of motion of the complete system are derived and their dimension is reduced substantially, so that the new model is sufficiently accurate up to a prespecified level of forcing frequencies. The formulation is developed in a general way, so that application of other methods, including experimental techniques, is equally valid. This is actually performed in the final part of this study, where experimental results are employed in conjunction with numerical results in order to predict the dynamic response of a mechanical structure possessing a linear substructure with high modal density, supported on four substructures with strongly nonlinear characteristics.  相似文献   

15.
基于VOF多相流模型和有限体积法求解水、汽、气多相流动的RANS方程,结合重叠网格技术和six DOF算法对某一型号舰载射弹倾斜入水过程进行数值模拟研究。首先基于该方法研究了射弹旋转效应对射弹运动特性及流体动力特性的影响,然后对不同入水角下倾斜入水过程进行分析,得到不同倾角下旋转射弹入水空泡形态发展规律、弹体运动特征及流体动力特性变化规律。研究结果表明:射弹的旋转有利于弹体在初始对称面内的弹道稳定性,但会降低弹体侧向稳定性,使射弹受到的阻力系数、俯仰力矩系数变小;入水角越小,形成的空泡越不对称,由射弹运动状态的改变引起的空泡形态变化越明显,在超空泡航行阶段,弹体运动较稳定,不同角度下流体动力系数差别很小,当弹体下表面刺破空泡壁沾湿时,弹体运动状态发生较大变化,流体动力系数迅速增大,此时入水角度过小,弹体容易失稳;弹体的沾湿对空泡形态、弹体运动稳定性和流体动力特性有着重要的影响。  相似文献   

16.
In this work, a thorough investigation is presented into the nonlinear resonant dynamics of geometrically imperfect shear deformable nanobeams subjected to harmonic external excitation force in the transverse direction. To this end, the Gurtin–Murdoch surface elasticity theory together with Reddy’s third-order shear deformation beam theory is utilized to take into account the size-dependent behavior of nanobeams and the effects of transverse shear deformation and rotary inertia, respectively. The kinematic nonlinearity is considered using the von Kármán kinematic hypothesis. The geometric imperfection as a slight curvature is assumed as the mode shape associated with the first vibration mode. The weak form of geometrically nonlinear governing equations of motion is derived using the variational differential quadrature (VDQ) technique and Lagrange equations. Then, a multistep numerical scheme is employed to solve the obtained governing equations in order to study the nonlinear frequency–response and force–response curves of nanobeams. Comprehensive studies into the effects of initial imperfection and boundary condition as well as geometric parameters on the nonlinear dynamic characteristics of imperfect shear deformable nanobeams are carried out through numerical results. Finally, the importance of incorporating the surface stress effects via the Gurtin–Murdoch elasticity theory, is emphasized by comparing the nonlinear dynamic responses of the nanobeams with different thicknesses.  相似文献   

17.
Dynamic motion of a conical frustum over a rough horizontal plane   总被引:1,自引:0,他引:1  
An analytical and numerical study of the dynamic motion of a conical frustum over a planar surface is presented resulting to a non-linear system of ordinary differential equations. Wobbling and rocking components of motion are discussed in detail concluding that, in general, the former component dominates the latter. For small inclination angles an asymptotic approximation of the angular velocities is possible, revealing the main characteristics of wobbling motion and its differences from rocking. Connection is made of the analysis with the behavior of the ancient classical columns, whose three dimensional dynamic response challenges the accuracy of the two dimensional models, usually applied in practice. The consideration of such discrete-blocky systems can benefit from the present study, through qualitative results and benchmarks for more complicated numerical methods, like the Distinct Element Method.  相似文献   

18.
Complete discretization scheme for milling stability prediction   总被引:1,自引:0,他引:1  
This study presents a Complete Discretization Scheme (CDS) for milling stability prediction. When compared with the Semi-Discretization Method (SDM) and Full-Discretization Method (FDM), the highlight of CDS is that it discretizes all parts of Delay Differential Equation (DDE), including delay term, time domain term, parameter matrices, and most of all the differential term, by using the numerical iteration method, such as Euler’s method, to replace the direct integration scheme used in SDM and FDM, which greatly simplifies the complexity of the discretization iteration formula. The present study mainly provides a numerical framework than a method that can be theoretically used by different numerical methods for solving Ordinary Differential Equation (ODE), such as Euler’s method, Runge–Kutta method, Adam’s multistep methods, etc., in this framework for derivation of iteration formula with corresponding construction of coefficient matrix of iteration formula. This study presented CDS with Euler’s method (CDSEM) for solving the one degree-of-freedom problem (one DOF) and two DOF motion equations, which are usually used as benchmark problems. When compared with SDM and FDM, the benchmark results of one DOF and two DOF milling stability prediction show that CDSEM can obtain acceptable precision in most ranges. The computational efficiency of SDM and FDM was also determined, and the results show that CDS with Euler’s method is faster than FDM. Furthermore, large approximation parameters (small time interval) were selected by SDM and CDSEM, and the results show that CDS has high effectiveness, accuracy, and reliability.  相似文献   

19.
This study intends to investigate the dynamic behavior of a nonlinear elastic beam of large deflection. Using the Galerkin principle, the dynamic nonlinear governing equations are derived based on the single and double mode methods. Two different kinds of nonlinear dynamic equations are obtained with the variation of the dimension and loading parameters. The chaotic critical conditions are given by Melnikov function method for the single mode model. The chaotic motion is investigated and the comparison between single and double mode models is carried out. The results show that the single mode method usually used may lead to incorrect conclusions in some conditions, and instead the double mode or higher order mode method should be used. Finally, the applicable condition of the single mode method is analyzed.  相似文献   

20.
针对雨刮器建立2自由度非线性摩擦振动动力学模型,基于复模态理论计算复特征值并进行稳定性及其对刮刷速度的依赖性分析;通过数值计算分析摩擦振动对刮刷速度的分岔特性,并利用相轨迹、庞加莱映射、频谱特性分析不同刮刷速度下的非线性振动现象.研究发现:摩擦-速度特性的负斜率是导致系统不稳定的根本原因,增大刮刷速度有利于提高系统的稳定性;在高、低刮速区,随着刮刷速度的下降,系统振动形态遵循周期→准周期→混沌的演化规律,并会伴随显著的粘滑振动;仅高速区的周期振动和非振动条件下,刮刷时无附加的粘滑振动.  相似文献   

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