杜芬方程的1／3纯亚谐解及其过渡过程

通过谐波平衡法和数值积分法研究了杜芬方程的1／3纯亚谐解,对参数变化的过渡过程的敏感性和扰动初始值的过滤进行了研究,同时,还对谐波平衡法和数值积分法的精度进行了比较,也考虑了亚谐波成分的渐近稳定性。     

弱阻尼广义KdV方程的整体吸引子

证明了具有弱阻尼项的广义KdV方程约周期初边值问题解的存在唯—性及整体吸引子存在性,最后获得了吸引子的Hausdorff维数和分形维数的上界估计．     

带有阻尼项的广义对称正则长波方程的指数吸引子

考虑了带有阻尼项的广义对称正则长波方程的整体快变动力学．证明了与该方程有关的非线性半群的挤压性质和指数吸引子的存在性．对指数吸引子的分形维数的上界也进行了估计．     

PSE在超音速边界层二次失稳问题中的应用

用抛物化稳定性方程（PSE）研究超音速边界层中的二次失稳问题．结果显示无论二维基本扰动是第一模态还是第二模态的T-S波,二次失稳机制都起作用．三维亚谐波的放大率随其展向波数和二维基本波幅值的变化关系与不可压缩边界层中所得类似．但是,即使二维波的幅值大到2％的量级,三维亚谐波的最大放大率仍远小于最不稳定的第二模态二维T-S波的放大率．因此,二次失稳应该不是导致超音速边界层转捩的主要因素．     

某些周期微分方程的亚纯解

本文讨论了两类具周期亚纯系数的微分方程(1．2)，(1．3)亚纯解的表示，得到两个Malmqusit 型定理(定理1，定理3)，即方程(1．2)，(1．3)的亚纯解分别是其系数类的子类。     

调制白噪声激励下的单自由度强非线性系统的近似瞬态响应概率密度

研究调制白噪声激励下,包含弱非线性阻尼及强非线性刚度的单自由度系统的近似瞬态响应概率密度．应用基于广义谐和函数的随机平均法,导出关于幅值瞬态概率密度的平均Fokker－Planck－Kolmogorov 方程．该方程的解可近似表示为适当的正交基函数的级数和,其中系数是随时间变化的．应用Galerkin方法,这些系数可由一阶线性微分方程组解得,从而可得幅值响应的瞬态概率密度的半解析表达式及系统状态响应的瞬态概率密度和幅值的统计矩．以受调制白噪声激励的van der Pol-Duffing振子为例验证其求解过程,并讨论了线性阻尼系数及非线性刚度系数等系统参数对系统响应的影响．     

具阻尼的非线性波动方程整体吸引子的Hausdorff维数、分形维数估计

本文得到了一类具有线性阻尼且非线性项满足临界增长条件的非线性波动方程整体吸引子的Hausdorff维数、分形维数估计．     

亚纯系数的高阶线性微分方程的解的增长性

本文研究亚纯系数的高阶线性微分方程,当方程系数满足一定条件时,得到方程的每一非零亚纯解具有无穷级且超级为n.此外,还研究了非齐次线性微分方程的亚纯解.     

一类复系数微分方程解的增长性

研究了一类系数是亚纯函数的高阶微分方程解的性质,假设其中某一个系数具有有限亏值,然后对其它的系数添加相应的限制条件,使得方程的每一个非零亚纯解都具有无穷级.     

关于高阶线性微分方程亚纯解的增长率

本文研究了二种类型的高阶线性齐次亚纯函数系数微分方程的亚纯解的增长性,当存在某个系数对方程的解的性质起主要支配作用时,我们对方程的亚纯解的增长率得到了精确的估计。     

Subharmonic Resonances and Chaotic Motions of a Bilinear Oscillator

A bilinear oscillator with different stiffnesses for positiveand negative deflections arises frequently in off-shore marinetechnology due to the slackening of mooring lines. A limitingcase, in which one of the stiffnesses becomes infinite, is theimpact oscillator which has applications to vessels moored ina harbour. The subharmonic resonances, bifurcations and chaotic motionsof these oscillators are studied using the concepts of topologicaldynamics. Problems of the existence, uniqueness and stabilityof the steady state motions are investigated, and particularuse is made of the Poincaré map. The bilinear oscillatoris shown to have co-existing small amplitude solutions undermost of its subharmonic resonances, showing that one-off andautomated computer integrations could easily miss an importantresonant peak. The domains of attraction of the competing stablesolutions are explored. Cascades of period-doubling bifurcationsand the exponential divergence of adjacent starts indicate thatthe impact oscillator has a régime of chaotic motionsgoverned by a strange attractor.     

变速度轴向运动粘弹性梁的动态稳定性

研究速度变化的轴向运动粘弹性梁在亚谐波共振及组合共振范围内的参数振动．通过平均法,在运动参数激励频率为2倍固有频率或为两阶固有频率之和附近时得到了自治的常微分方程组．在参数激励频率和激励振幅平面上,可以找到由于共振而产生的失稳区域,并应用数值方法验证了理论推导结果的正确性．分析了粘弹性阻尼,速度和预紧张力对失稳区域的影响．粘弹性阻尼使得共振失稳区域减小,而速度和预紧张力使共振失稳区域在频率-振幅平面上发生漂移．     

Zur Theorie der erzwungenen Schwingungen des symmetrischen Kreisels

Summary The object of this paper is to give a theory of the experiments described in the foregoing paper. The applied system of non-linear differential equations byA. Föppl is first solved approximately for small angles, that means small deviations of the axis of the gyroscope from the verticaldirection, the cases without and with consideration of damping force being discussed separately. All characteristic features of the motion observed in the experiments are explained.—After that, an exact particular solution is given for the case of a circular periodic force. An approximate calculation is carried out for the case of a periodic elliptical force acting on afast rotating gyroscope. The solution contains an infinite number of resonance frequencies (subharmonic resonances and resonances with sums and differences of the forced and natural frequencies).     

Resonance,stability and chaotic vibration of a quarter-car vehicle model with time-delay feedback

This paper examines dynamical behavior of a nonlinear oscillator with a symmetric potential that models a quarter-car forced by the road profile. The primary, superharmonic and subharmonic resonances of a harmonically excited nonlinear quarter-car model with linear time delayed active control are investigated. The method of multiple scales is utilized to obtain first order approximation of response. We focus on the influence of delay in the system. This naturally gives rise to a delay deferential equation (DDE) model of the system. The effect of time delay and feedback gains of the steady state responses of primary, superharmonic and subharmonic resonances are investigated. By means of Melnikov technique, necessary condition for onset of chaos resulting from homoclinic bifurcation is derived analytically. We describe a method to identify the critical forcing function and time delay above which the system becomes unstable. It is found that proper selection of time-delay shows optimum dynamical behavior. The accuracy of the method is obtained from the fractal basin boundaries.     

计算倍分叉的一种方法

本文从Melnikov函数的物理意义出发,建立了一种计算倍分叉方法.利用这种方法,具体地讨论了软弹簧Duffing系统的倍分叉现象,发现了与次谐分叉相类似结论——即在阻尼小、外激励幅度大时,会出现倍分叉.这样的结果与物理事实是相吻合的.     

Chaotic responses on gear pair system equipped with journal bearings under turbulent flow

This study performs a systematic analysis of the dynamic behavior of a gear-bearing system with the turbulent flow effect, nonlinear suspension, nonlinear oil-film force and nonlinear gear mesh force. The dynamic orbits of the system are observed using bifurcation diagrams plotted using the dimensionless damping coefficient, unbalance coefficient and the dimensionless rotational speed ratio as control parameters. The onset of chaotic motion is identified from the phase diagrams, power spectra, Poincaré maps, Lyapunov exponents and fractal dimension of the gear system. The numerical results reveal that the system exhibits a diverse range of periodic, sub-harmonic and chaotic behaviors. The results presented in this study provide a detailed understanding of the operating conditions under which undesirable dynamic motion takes place in gear-bearing system and therefore offer a useful source of reference for engineers in designing and controlling such systems.     

Active control of secondary resonances piezoelectric sandwich beams

Secondary resonances of piezoelectric/elastic/piezoelectric sandwich beams submitted to active control are studied in this paper. The proportional and derivative nonlinear potential feedback controls via piezoelectric sensor and actuator layers are used. The dynamics of the beam is modelled by a highly nonlinear ordinary-differential equation. The method of multiple scales is applied and approximate solutions are obtained for hard excitations. Analytical frequency and phase-amplitude relationships as well as the time response are explicitly given for various super- and subharmonic resonances. Static and dynamic stability criteria are elaborated and critical displacement and excitation amplitudes associated to the resulting unstable zones are analytically given. The feedback parameters effects on the subharmonic and superharmonic resonances and on their stability are investigated.     

On parametric instability of viscous two-layer fluid in a vessel with a permeable bottom

A linear problem of parametric oscillations of a low-viscous two-layer fluid in a closed vessel partially filled with a porous medium is studied. An asymptotic solution is constructed on the basis of combined application of boundary functions and averaging methods. Approximate formulas for boundaries of instability domains in the case of subharmonic and harmonic resonances are derived.