重离子碰撞中同位旋分馏对碰撞系统同位旋的依赖性

利用同位旋相关的量子分子动力学模型，研究了中能重离子碰撞过程中同位旋分馏现象及其对于碰撞系统同位旋的依赖性.计算结果表明:在碰撞系统膨胀的低密度区, 气相(发射核子)与液相(碎片)的中子-质子比出现不均等分配现象,即同位旋分馏. 同位旋分馏的强弱明显地依赖于碰撞系统的中子-质子比,其强度随着系统中子-质子比的增大而增大. 丰中子碰撞系统产生丰中子的气相和缺中子的液相,而缺中子碰撞系统产生缺中子的气相和丰中子的液相.在丰中子的碰撞系统中同位旋分馏强度敏感地依赖于对称势,而对于两体碰撞的同位旋效应并不敏感，但对于缺中子的碰撞系统,同位旋分馏强度对于对称势不敏感， 同时发现动量相关作用对于同位旋分馏过程的作用不明显. 关键词： 中能重离子碰撞 同位旋分馏 同位旋效应 对称势     

相干光伏空间孤子非对称碰撞研究

采用数值方法研究了三个呈非对称分布的相干光伏空间孤子碰撞相互作用.结果表明,随着信号光的入射角度在一定范围内逐渐改变,三个孤子在晶体中碰撞后会产生孤子的分裂或湮没现象.当孤子碰撞后出现分裂或湮没时,若保持孤子的碰撞角度不变,改变其中任意一个孤子的初始相对相位,孤子的碰撞行为也将随之迅速改变,产生新的孤子分裂、湮没或其他碰撞现象.另外,研究结果还表明,作为具有不可积哈密顿系统特性的光伏孤子,其小角度碰撞过程中动量和能量仍然是守恒的. 关键词： 光伏孤子 非对称碰撞 分裂 湮没     

彗星研究和彗星空间探测进展

 彗星是一种冰冻的小天体, 是由冰(主要是水冰)和尘埃组成的“脏雪球”, 俗称扫帚星。彗星是太阳系早期形成时期遗留下的残骸, 被认为是太阳系中最原始的天体, 研究彗星的起源、演化和成分有助于研究太阳系的起源和行星系统形成和演化。此外, 彗星富含水冰和有机分子, 这些都是生命形成的必要元素, 因此研究彗星也有助于研究生命起源。发育完整的彗星由彗核、彗发、氢云、离子彗尾(又称等离子体或Ⅰ型彗尾)和尘埃彗尾(又称Ⅱ型彗尾)构成(图1), 彗核集中了彗星的绝大部分质量, 是彗星的本体。     

费米能区重离子碰撞动力学(Ⅱ)动力学与碰撞参数的关系

借助于Boltzmann-Uehling-uhlenbeck理论,对 ²⁰Ne+²⁰Ne碰撞系统,在不同碰撞参数下,系统地研究了费米能区的碰撞机制.结果表明:深部非弹性碰撞已由非完全深部非弹性碰撞所取代;随着轰击能量升高,非完全深部非弹性碰撞分量变小,50MeV/u时已有碎裂发生,150MeV/u时已是典型的碎裂过程.同时对中间质量碎片发射的起因做了讨论.     

基于平板叶栅的颤振关键参数研究

颤振是航空发动机和燃气轮机运行安全的重要威胁,判断颤振发生的传统经验法已经不再完全适用于新一代高负荷定制叶片,而大规模的三维非定常颤振计算在设计阶段难以实现。因此,为了给设计阶段提供参考,与叶片颤振特性相关的关键参数研究必不可少。本文基于二维平板叶栅,对折合频率、安装角、攻角、振动模态(平动和扭转)等影响颤振的关键参数开展了研究,旨在总结颤振稳定性随关键参数的变化趋势,为可能出现颤振风险部件的设计提供参考。     

超高速碰撞闪光强度与碰撞角度关系

为了测量超高速碰撞过程中产生的闪光现象,进而研究相近碰撞速度、不同入射角度(弹道与靶板平面的夹角)条件下超高速碰撞产生闪光在整个物理过程的闪光强度随时间的变化规律,设计了适用于瞬态闪光测量的光学高温计测量系统。通过二级轻气炮加载LY12球形铝弹丸,运用设计的瞬态高温计测量系统分别进行了入射角度为30°,45°,60°和90°相近碰撞速度条件下碰撞LY12铝靶产生闪光现象的测量。获得了平均碰撞闪光强度峰值与碰撞角度的关系,平均碰撞闪光强度峰值随碰撞角度的减小而增大,碰撞角度为30°时表现更为明显。     

碰撞等离子体中电中性条件对单探针测量的约束

在碰撞等离子体中使用单探针测量系统测得的伏安特性曲线会发生畸变. 实验中分别测量了非碰撞条件下(20 Pa)和碰撞条件下(400 Pa)氩气(Ar)电感耦合等离子体的单探针伏安特性曲线, 并进一步通过在400 Pa下测量不同位置处的单探针伏安特性曲线和引入干扰电极调节整体电中性约束的程度的方法来分析研究曲线的畸变现象. 结果表明碰撞等离子体中整体电中性约束条件会对非碰撞探针测量系统进行约束, 并通过理论分析和实验证明:在单探针测量过程中, 以真空室壁为电位参考点, 等离子体将通过改变自身等离子体电位来满足整体电中性的要求, 此时, 单探针测得的伏安特性曲线就不是理论上的单探针的鞘层伏安特性.     

永磁同步风力发电机随机分岔现象的全局分析

永磁同步风力发电机在运行过程中不可避免地会受到风能的随机干扰,本文建立了在输入机械转矩存在随机干扰情况下永磁同步风力发电机的数学模型,采用胞映射方法分析了随机干扰强度变化时系统全局结构的演化行为,并通过数值模拟对理论分析进行验证.研究结果表明,随着随机干扰强度的增大,系统中会出现随机内部激变和随机边界激变,即由于随机吸引子与其吸引域内的随机鞍发生碰撞而产生的随机分岔现象和由于随机吸引子与其吸引域边界发生碰撞而产生的随机分岔现象.研究结果揭示了随机干扰对永磁同步风力发电机运行性能影响的机理,为永磁同步风力发电系统的运行和设计提供了理论依据.     

一类含非黏滞阻尼的Duffing单边碰撞系统的激变研究

以一类含非黏滞阻尼的Duffing单边碰撞系统为研究对象, 运用复合胞坐标系方法, 分析了该系统的全局分岔特性. 对于非黏滞阻尼模型而言, 它与物体运动速度的时间历程相关, 能更真实地反映出结构材料的能量耗散现象. 研究发现, 随着阻尼系数、松弛参数及恢复系数的变化, 系统发生两类激变现象: 一种是混沌吸引子与其吸引域内的混沌鞍发生碰撞而产生的内部激变, 另一种是混沌吸引子与吸引域边界上的周期鞍(混沌鞍)发生碰撞而产生的常规边界激变(混沌边界激变), 这两类激变都使得混沌吸引子的形状发生突然改变. 关键词： 非黏滞阻尼 Duffing碰撞振动系统 激变 复合胞坐标系方法     

基于能量对称分布相位相关配准的资源三号02星颤振探测

颤振是卫星平台在轨运行的固有现象之一,也是高分辨率对地观测卫星研究的难点和热点。针对资源三号02星在轨运行过程中的平台颤振情况,提出了一种基于能量对称分布的相位相关配准算法。结合多光谱相机各谱段相机之间的安装关系,考虑到平台的线性平滑运动特性,采用二次函数消除系统变化量,得到线性拟合的平台颤振曲线,最后利用星敏陀螺数据联合滤波得到卫星姿态复合验证曲线。实验结果表明:在模拟数据情况下,所提配准算法的配准精度能够达到0.05 pixel,可有效辅助探测卫星平台的颤振,并首次探测到资源三号02星平台存在0.63～0.65 Hz的颤振,振幅为0.41″～1.12″。     

Tracking Desired Trajectory in a Vibro-Impact System Using Backstepping Design

Based on the backstepping design of smooth systems, we developed a new control law to achieve chaos control for a vibro-impact system. In our control strategy, a novel and effective controller is designed such that the output of the vibro-impact system can track any desired trajectory in its domain. The single-degree-of-freedom vibro-impact system is taken as an example to show this control procedure. Numerical simulations are provided to verify the effectiveness of the proposed method.     

Analytic treatment of a system with a vibro-impact nonlinear energy sink

This Communication reports on an approximate analytic procedure for analysis of transient damped response in a system comprising a primary linear oscillator and vibro-impact nonlinear energy sink (NES). Multiple-scale expansion reduces the problem in the first approximation to low-dimensional vibro-impact system with forcing and damping; the latter problem yields to direct analytic approach. The results computed by this way fairly correlate with direct numeric simulations. The analysis takes advantage of small ratio of the NES and the primary masses, but does not require the restitution coefficient to be close to unity. The proposed approach paves the way for efficient design of systems with vibro-impact NESs.     

Stochastic responses of Duffing–Van der Pol vibro-impact system under additive colored noise excitation

A response analysis procedure is developed for a vibro-impact system excited by colored noise. The non-smooth transformation is used to convert the vibro-impact system into a new system without impact term. With the help of the modified quasi-conservative averaging, the total energy of the new system can be approximated as a Markov process, and the stationary probability density function （PDF） of the total energy is derived. The response PDFs of the original system are obtained using the analytical solution of the stationary PDF of the total energy. The validity of the theoretical results is tested through comparison with the corresponding simulation results. Moreover, stochastic bifurcations are also explored.     

Duffing单边碰撞系统的混沌鞍合并激变

以典型的Duffing单边碰撞系统为研究对象,对系统中的混沌鞍进行了细致的分析.研究表明,系统的混沌鞍同样存在合并激变,合并激变是由连接两个混沌鞍的周期鞍的稳定流形与不稳定流形相切所诱发,相切使得边界上的混沌鞍与内部的混沌鞍发生碰撞而突然合并为一个较大的边界混沌鞍.混沌鞍的合并激变行为最终会诱导混沌吸引子的合并激变发生. 关键词： Duffing碰撞系统 混沌鞍 周期鞍 稳定与不稳定流形     

Lyapunov exponent calculation of a two-degree-of-freedom vibro-impact system with symmetrical rigid stops

A two-degree-of-freedom vibro-impact system having symmetrical rigid stops and subjected to periodic excitation is investigated in this paper. By introducing local maps between different stages of motion in the whole impact process,the Poincar′e map of the system is constructed. Using the Poincar′e map and the Gram-Schmidt orthonormalization,a method of calculating the spectrum of Lyapunov exposents of the above vibro-impact system is presented. Then the phase portraits of periodic and chaotic attractors for the system and the corresponding convergence diagrams of the spectrum of Lyapunov exponents are given out through the numerical simulations. To further identify the validity of the aforementioned computation method,the bifurcation diagram of the system with respect to the bifurcation parameter and the corresponding largest Lyapunov exponents are shown.     

Stochastic response of vibro-impact Duffing oscillators under external and parametric Gaussian white noises

This study presents a solution procedure for the stationary probability density function (PDF) of the response of vibro-impact Duffing oscillators under external and parametric Gaussian white noises. First the Zhuravlev non-smooth coordinate transformation is adopted to convert a vibro-impact oscillator into an oscillator without barriers. The stationary PDF of the converted oscillator is governed by the Fokker–Planck (FP) equation. The FP equation is solved by the exponential-polynomial closure (EPC) method. Illustrative examples are presented with vibro-impact Duffing oscillators under external and parametric Gaussian white noises to show the effectiveness of the solution procedure. The parametric excitation is acting in displacement and the constraint is a unilateral zero-offset barrier. The restitution coefficient of impacts is taken as 0.90. Comparison with the simulated results shows that the proposed solution procedure can provide good approximate PDFs for displacement and velocity although a little difference exists in the tail of these PDFs. This difference may be due to the weak approximation on the response of the vibro-impact oscillators using a continuous Markov process when the restitution coefficient is not very close to unity.     

A comparative study of the harmonic balance method and the orthogonal collocation method on stiff nonlinear systems

The high-order purely frequency-based harmonic balance method (HBM) presented by Cochelin and Vergez (2009) [1] and extended by Karkar et al. (2013) [2] now allows to follow the periodic solutions of regularized non-smooth systems (stiff systems). This paper compares its convergence property to a reference method in applied mathematics: orthogonal collocation with piecewise polynomials. A first test is conducted on a nonlinear smooth 2 degree-of-freedom spring mass system, showing better convergence of the HBM. The second test is conducted on a one degree-of-freedom vibro-impact system with a very stiff regularization of the impact law. The HBM continuation of the nonlinear mode was found to be very robust, even with a very large number of harmonics. Surprisingly, the HBM was found to have a better convergence than the collocation method for this vibro-impact system.     

三自由度含间隙碰撞振动系统Neimark-Sacker分岔的反控制

分岔反控制作为传统分岔控制的逆问题, 其目的是在预先指定的系统参数点通过控制主动设计出具有所期望特性的分岔解. 以一类三自由度含间隙双面碰撞振动系统为研究对象, 在不改变原系统平衡解结构的前提下, 考虑到在碰撞振动系统反控制过程中由Poincaré映射的隐式特点和传统的映射Neimark-Sacker分岔临界准则带来的困难, 通过对原系统施加线性反馈控制器并利用不直接依赖于特征值计算的Neimark-Sacker分岔显式临界准则研究了此系统的分岔反控制问题. 首先对原系统施加线性反馈控制, 建立闭环控制系统的六维Poincaré映射. 由于六维映射的雅克比矩阵的特征值没有解析的表达式, 利用高维映射Neimark-Sacker分岔的显式临界准则, 获得了系统出现拟周期碰撞振动运动的控制参数区域. 然后采用中心流形-正则形方法分析了拟周期分岔解的稳定性. 数值仿真结果表明本文方法可以在指定的系统参数点通过控制设计出稳定的拟周期碰撞运动.     

Interchannel pulse collision in a wavelength-division-multiplexed system with strong dispersion management

We develop a perturbation theory to analytically calculate the effects of complete and incomplete interchannel collisions of Gaussian pulses in a wavelength-division-multiplexed system with strong dispersion management. We show that, for complete collisions, the collision-induced frequency shift of a Gaussian pulse is negligible, whereas its position shift is significant and can be found in a simple analytical form. For strong dispersion management we find that incomplete collisions can be neglected, whereas for dispersion management of moderate strength the contribution of the incomplete collisions can be significant. The analytical predictions are in satisfactory agreement with numerical results. We also give an estimate of the limit imposed on the transmission distance by such collisions.