双频激励下超晶格系统的混沌行为

假设超晶格“折沟道”对粒子的作用等效为形状相似的周期调制; 引入正弦平方势, 在小振幅近似下, 把粒子运动方程化为具有双频激励的Duffing方程。 用Melnikov方法分析了系统的混沌行为。 结果表明, 当外场为双频激励时, 系统将存在不同的次谐和超次谐分叉序列。 由于系统的混沌行为与系统参数有关, 于是, 只需控制材料组分、 或掺杂浓度, 就可望达到避免或控制混沌的目的, 为半导体超晶格的制备及其光磁电效应提供了理论分析。     

Chaotic motions of the L-mode to H-mode transition model in tokamak

The chaotic dynamics of the transport equation for the L-mode to H-mode near the plasma in a tokamak is studied in detail with the Melnikov method. The transport equations represent a system with external and parametric excitation. The critical curves separating the chaotic regions and nonchaotic regions are presented for the system with periodically external excitation and linear parametric excitation, or cubic parametric excitation, respectively. The results obtained here show that there exist uncontrollable regions in which chaos always take place via heteroclinic bifurcation for the system with linear or cubic parametric excitation. Especially, there exists a controllable frequency, excited at which chaos does not occur via homoclinic bifurcation no matter how large the excitation amplitude is for the system with cubic parametric excitation. Some complicated dynamical behaviors are obtained for this class of systems.     

Bifurcation of Limit Cycles of a Perturbed Pendulum Equation

This paper investigates the limit cycle bifurcation problem of the pendulum equation on the cylinder of the form $\dot{x}=y, \dot{y}=-\sin x$ under perturbations of polynomials of $\sin x$, $\cos x$ and $y$ of degree $n$ with a switching line $y=0$. We first prove that the corresponding first order Melnikov functions can be expressed as combinations of anti-trigonometric functions and the complete elliptic functions of first and second kind with polynomial coefficients in both the oscillatory and rotary regions for arbitrary $n$. We also verify the independence of coefficients of these polynomials. Then, the lower bounds for the number of limit cycles are obtained using their asymptotic expansions with $n=1,2,3$.     

Melnikov方法和圆型平面限制性三体问题的横截同宿研究*

本文对由两自由度近可积哈密顿系统经非正则变换而得到的,具有高阶不动点的非哈密顿系统给出了判别横截同宿轨和横截异宿轨存在性的两条判据。对原二体质量比很小时近可积圆型平面限制性三体问题,采用本文判据证明存在横截同宿轨,从而存在横截同宿穿插现象;还在一定假设下证明了存在横截异宿轨;并给出了全局定性相图。     

一个非线性振子的浑沌现象*

本文利用Mel'nikov方法和数值模拟对含二次非线性项的受迫振动系统=fcosωτ的分叉与浑沌进行了研究。     

An analysis on the flow resistance in the entrance region of diffuse laminar flow between two parallel spherical surfaces

In this paper, V.V. Golubef method is first extended to the diffuse laminar flow between two parallel spherical surfaces. With the boundary layer motion equation in spherical coordinates, we derive the momentum integral equation together with the energy integral equation for the laminar boundary layer of the entrance region between two parallel spherical surfaces. And then by applying Picards gradually approaching method for the momentum integral equation, we get the approximate expression which the entrance region length varies with the thickness of boundary layer. In the end every coefficient of entrace region effect is analyzed and calculated. Projects Suported by the Science Fund of the Chinese Academy of Sciences.     

非线性弹性杆的异常动态响应

讨论了拉伸速度呈周期变化的受拉非线性弹性直杆的动力行为。采用Melnikov方法研究时发现,材料的非线性使得动力响应发生异常,对确定的直杆而言,当拉伸速度超过某个临界值时,动力系统将出现次谐分岔和混沌。     

Anomalous dynamics response of nonlinear elastic bar

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有界噪声与谐和激励联合作用下Duffing-Rayleigh振子的Melnikov混沌

研究了有界噪声与谐和激励作用下的Duffing-Rayleigh振子的动力学行为.首先运用随机Melnikov过程方法得到系统出现混沌的条件,结果表明随着非线性阻尼参数的增加系统会从混沌运动到周期运动,随着Wiener过程强度参数的增加,系统由混沌进入周期的临界幅值会先递增后不变.最后,用两类数值方法即最大Lyapunov指数与Poincare截面验证了上述结果. 关键词： 有界噪声 随机Melnikov过程 混沌运动 周期运动     

ANALYSIS OF BREATHER STATE IN THIN BAR BY USING COLLECTIVE COORDINATE

Considering Peierls-Nabarro (P-N) force and viscous effect of material, the dynamic behavior of one-dimensional infinite metallic thin bar subjected to axially periodic load is investigated. Governing equation, which is sine-Gordon type equation, is derived. By means of collective-coordinates, the partial equation can be reduced to ordinary differential dynamical system to describe motion of breather. Nonlinear dynamic analysis shows that the amplitude and frequency of P-N force would influence positions of hyperbolic saddle points and change subharmonic bifurcation point, while the path to chaos through odd subharmonic bifurcations remains. Several examples are taken to indicate the effects of amplitude and period of P-N force on the dynamical response of the bar. The simulation states that the area of chaos is half-infinite. This area increases along with enhancement of the amplitude of P-N force. And the frequency of P-N force has similar influence on the system.