典型流线桥梁断面缩阶微分方程抖振气动力模型

目前的桥梁断面气动力理论框架中,气动力通常采用Scanlan线性准定常公式和Davenport气动导纳概念对准定常抖振力进行修正。已有的研究表明,导纳函数随来流特性变化较为明显,对同一桥梁断面也没有统一适用的导纳函数表达。除此之外,抖振力非线性特性方面的理论研究亦为国际风工程前沿热点问题。结合上述两方面,以桥梁抖振分析的关键问题抖振气动力合理建模为出发点,建立了基于状态空间方程的非定常、非线性时域抖振力模型。提出了能同时准确模拟非定常、非线性效应的纯时域气动力模型——缩阶微分方程抖振气动力模型。利用主动控制风洞试验技术进行桥梁节段模型抖振力荷载测量试验,对比研究了窄带和宽带谐波来流条件下的桥梁断面气动力荷载的非定常、非线性特性。

不同阶混沌系统缩阶混合函数投影同步

以3阶单模激光洛伦兹(Lorenz)系统与2阶达芬(Duffing)系统为例,研究两混沌系统之间的缩阶混合函数投影同步.选用不同的时变函数作为尺度因子,通过构造非线性控制器使得2阶达芬系统的状态变量按照时变尺度因子跟踪由3阶单模激光洛伦兹系统前两个状态方程所构成的投影子系统状态变量的变化.证明了非线性控制器增益强度大于0时,同步误差系统在原点处是指数稳定的.仿真实验表明,文中提出的缩阶混合函数投影同步方案是可行的、有效的,且在高斯白噪声干扰下具有一定的鲁棒性.

单模激光Lorenz系统与Duffing系统缩阶反同步

对于2阶Duffing系统与3阶单模激光Lorenz系统,用主动控制方法设计了一种同步控制器,实现二者之间的缩阶反同步。依据罗斯-霍维兹判据,给出误差系统在原点处渐进稳定的条件。数值试验证实:在控制器作用下,2阶Duffing系统的状态变量与3阶单模激光Lorenz投影子系统的状态变量振动的幅值相同但方向相反,且在随机噪声干扰下反同步仍能很好地实现。这表明所设计的控制器对于不同阶的Duffing系统与Lorenz系统的缩阶反同步的实现是可行的、有效的,而且具有很好的鲁棒性。

量子细胞神经网络缩阶混沌函数投影同步

量子细胞神经网络是一种纳米级细胞神经网络,具有丰富的混沌动力学行为。针对该超混沌系统,提出了一种通用的缩阶混沌函数投影同步方案和控制器设计规则。以Lorenz混沌系统为比例函数,分别设计了二维和三维控制器,实现了该超混沌系统的缩阶自同步以及与R9ssler系统的异结构同步。分别用Lyapunov稳定性理论和MATLAB数值仿真方法验证了缩阶混沌函数投影同步方案的有效性。相对于一般的函数投影同步方案,提出方案的比例函数是混沌信号,且不要求驱动系统和响应系统具有相同的阶数,使得该方案具有更强的保密性和更好的灵活性。

刺槐与环境因子相关性的缩元递阶矢量分析

为了研究环境因子对刺槐综合影响,揭示其重要影响因子,研究设置了水分适宜、干旱、严重干旱3种不同生境,从环境因子——刺槐生理变化——刺槐生长状况3个层次采用多个指标进行了实验观测。根据实验结果,利用缩元递阶矢量分析法对层与层间的关系进行分析。分析结果表明:土壤有效供水量和温度是两个重要的因子。在水分适宜的条件下,环境因子对叶水势和WUE有一定的影响,对其它生理指标没有明显影响,刺槐基本上不受环境因子的制约,能够按自身生理发展。但随着干旱加重,环境因子对刺槐的影响加重,刺槐的生理变化受环境因子的制约。在干旱、严重干旱的条件下,光合速率,蒸腾速率,WUE是3个重要指标,生理变化对枝条生长有制约性。刺槐在生长季内的生物总量明显下降,土壤水分对刺槐的生长、成活有重要影响。由此得出:刺槐的生长与土壤水分、土壤有效供水量、温度等环境因子关系密切,种植刺槐时要注意它的生存环境,特别是土壤的水分含量。缩元递阶矢量分析法是一种值得应用的好方法。

基于一阶速度-胀缩-旋转方程的多分量联合逆时偏移

弹性波逆时偏移是多分量地震勘探领域的重要研究内容,逆时偏移过程中纵、横波传播方向的准确求取是实现纵、横波偏移噪声压制和横波极性校正的前提,坡印廷矢量是指示纵横波传播方向的重要依据。常规一阶速度-应力方程只能求取纵、横波混合波场的坡印廷矢量,其指示的波场传播方向也只是混合波场的传播方向而非单纯纵波或横波的传播方向,故无法准确解决偏移噪声压制和横波极性校正等问题。理论上,一阶速度-胀缩-旋转方程能够求取纯纵波或纯横波的坡印廷矢量,获得单一类型波的传播方向信息,从而克服常规方法的局限。基于一阶速度-胀缩-旋转方程的弹性波逆时偏移技术,首先给出了该方程逆时延拓的交错网格时间2阶、空间2N阶差分格式和稳定性条件,其次在波场延拓过程中通过求取纵、横波的坡印廷矢量获得了单一类型波的传播方向,并利用基于行波分离的互相关成像条件实现了该方程的多分量联合逆时偏移。模型试算表明:基于一阶速度-胀缩-旋转方程的弹性波逆时偏移能够准确解决横波的极性校正问题,并取得优于常规算法的偏移噪声压制效果。

一阶速度—胀缩—旋转弹性波方程交错网格数值模拟

弹性波正演在地震波传播机理研究以及多波地震资料采集、处理、解释和反演中发挥着重要作用。现有的弹性波方程正演模拟常常数值求解一阶速度—应力方程或二阶位移弹性波方程,只能直接得到同时包含纵波和横波的三个质点振动速度分量或位移分量,要想得到更直观的纯纵波和纯横波分量记录,还需要在模拟过程中采用波场解耦算子进行纵、横波分离,因此纵、横波模拟精度同时受制于模拟算法和波场解耦算法的精度。为此,推导了一阶速度—胀缩—旋转弹性波方程在三维交错网格空间中的高阶有限差分格式,并给出了相应的稳定性条件;推导了适应该方程的PML吸收边界条件,实现了一阶速度—胀缩—旋转弹性波方程的正演模拟;分析了模拟结果中各分量的物理意义。由于一阶速度—胀缩—旋转弹性波方程不仅包含了质点的振动速度矢量,而且显式地包含了横波振动速度矢量和纵波振动速度矢量,还包含了一个体应变和一个旋转矢量,因此应用该方程模拟除了能得到三个质点振动速度分量外,还可以直接得到解耦后的纵、横波分量,避免了解耦算法对模拟精度的影响。模型试算证明了该模拟方法的正确性和优越性。

Pipe reduction of miniature inner grooved copper tubes through rotary swaging process

A rotary swaging machine was applied to fabricating pipe reduction for miniature inner grooved copper tube （MIGCT） heat pipes. Compared with conventional swaging method, the axial feed of the designed rotary swaging machine was reached by a constant pushing force. The deformation of grooves in pipe reduced section during rotary swaging was analyzed. The shrinkage and extensibility of pipe reduction were measured and calculated. Furthermore, four aspects, including outer diameter, surface roughness, extensibility and processing time of pipe reduction, which were influenced by the pushing force, were considered. The results show that the tube wall thickness increases gradually along the z-axis at sinking section. However, the outer diameters, surface roughness and micro-cracks at reduced section tend to decrease along the z-axis. Besides, the effect of variation in the pushing force on the extensibility is limited while an increase in the pushing force results in a decrease of surface roughness. Therefore, a large pushing force within the limit is beneficial to pipe reduction manufacturing during rotary swaging process.

Regularity and mechanism of coal resistivity response with different conductive characteristics in complete stress-strain process

The stress,strain as well as resistivity of coal during uniaxial compression process were tested based on self-built real-time testing system of loaded coal resistivity.Furthermore,the coal resistivity regularity and mechanism were analyzed at different stages of complete stress-strain process,which includes the two kinds of coal body with typical conductive characteristics.The results indicate that coal resistivity with different conductive characteristics has different change rules in complete stress-strain process.It is mainly represented at the densification and flexibility phases before dilatation occurs.The variation of resistivity can be divided into two kinds,named down and up.Dilatation of coal samples occurred between 66%σ_(max) and 87%σ_(max).Because of dilatation,coal resistivity involves sudden change.The overall representation is shifting from reducing into improving or from slow improving into accelerated improving.Thus,coal resistivity always shows an increasing tendency at the plastic stage.After peak stress,coal body enters into failure stage.The expanding and communicating of macro fracture causes further improvement of coal resistivity.The maximum value of resistivity rangeability named λ reached 3.49.Through making real-time monitoring on coal resistivity,variation rules of resistivity can be deemed as precursory information so as to reflect the dilatation and sudden change before coal body reaches buckling failure,which can provide a new technological means for forecasting the dynamic disaster of coal petrography.

Extraction of P-and S-wave angle-domain common-image gathers based on first-order velocity-dilatation-rotation equations

Accuracy of angle-domain common-image gathers(ADCIGs)is the key to multiwave AVA inversion and migration velocity analysis,and of which Poynting vectors of pure P-and S-wave are the decisive factors in obtaining multi-component seismic data ADCIGs.A Poynting vector can be obtained from conventional velocity-stress elastic wave equations,but it focused on the propagation direction of mixed P-and S-wave fields,and neither on the propagation direction of the P-wave nor the direction of the S-wave.The Poynting vectors of pure P-or pure S-wave can be calculated from first-order velocity-dilatation-rotation equations.This study presents a method of extracting ADCIGs based on first order velocitydilatation-rotation elastic wave equations reverse-time migration algorithm.The method is as follows:calculating the pure P-wave Poynting vector of source and receiver wavefields by multiplication of P-wave particle-velocity vector and dilatation scalar,calculating the pure S-wave Poynting vector by vector multiplying S-wave particle-velocity vector and rotation vector,selecting the Poynting vector at the time of maximum P-wave energy of source wavefield as the propagation direction of incident P-wave,and obtaining the reflected P-wave(or converted S-wave)propagation direction of the receiver wavefield by the Poynting vector at the time of maximum P-(S-)wave energy in each grid point.Then,the P-wave incident angle is computed by the two propagation directions.Thus,the P-and S-wave ADGICs can obtained Numerical tests show that the proposed method can accurately compute the propagation direction and incident angle of the source and receiver wavefields,thereby achieving high-precision extraction of P-and S-wave ADGICs.

一种模态振型的直接扩阶方法

传统的模型缩阶及模态扩阶方法是以计算传递矩阵为手段。该文提出一种实测模态振型空间不完备问题的直接处理方法,即未测试自由度振型值的直接估计方法。通过引入一复合向量,该向量由对应于主自由度的实测振型值与对应于从自由度的待估算值组成。依靠实测模态及有限元模型信息对复合向量中未测试自由度的振型值进行重新估算,进而获得空间完备的模态振型。该文采用5自由度的弹簧-质量体系验证方法的正确性;借助平面框架结构探讨新方法较传统方法在低阶模态振型估算精度上的优势。数值结果表明:所提出方法不需质量归一化条件以及实测模态与有限元振型的比例条件;同时,该方法较传统方法在低阶模态振型扩阶上具有更好的精度,并允许有限元模型具有一定的模型误差。

Time Evolution,Dynamical Quantum Fluctuation and High-Order Squeezing Feature in Polariton System——Ⅰ

We have set up a new reduced model Hamiltonian for the polariton system, in which the nonlinear interaction contains the rotating term k l （ a ＋ b ＋ ab＋） and the attractive two-mode squeezed coupling - k2 （ a ＋ b＋ ＋ ab ） . The dynamical evolution of this system has been solved and the nonclassical features relevant to the second-order and high-order squeezing have been obtained in an analytical form. For the first time, in contrast to the existing result, we have confirmed for the phonon field that the attractive two-mode squeezed interaction will not only result in the second-order and high-order squeezing in X-component with the time evolution, but also in time average. Furthermore, the phenomena of collapse and revival of inversion will occur as well in the time evolution of the average number of photon and phonon, as also in the second-order and high-order squeezing of photon field, particularly, in the high-order squeezing of phonon field.

One-Stage Technology for Production of Concentrated Ethylene Glycol-Water Solutions （Automotive Antifreeze）

The reactor unit for one-stage technology for production of concentrated ethylene glycol-water solutions is described.Such solutions could be useful for production of automotive antifreezes. The technology is based on the highly selective hydration ofethylene oxide in the presence of heterogeneous catalyst-anion-exchange resin in HCO3-/CO/3/2-_form. The mathematical model of reactor allowed evaluating of economical benefit in comparison with conventional method.

一种基于不完备模态信息的有限元模型修正方法

提出了一种基于交叉模型交叉模态(CMCM)方法和Guyan模型缩阶的迭代模型修正方法,该方法扩展了CMCM方法,可利用空间不完备模态信息进行模型修正。在方程求解时采用约束最小二乘法,避免了修正后模型出现负刚度或负质量。通过一个五层三维框架结构和一个导管架平台结构的研究,验证了该方法可以有效地利用空间不完备模态信息进行有限元模型修正,修正后的模型具有良好的精度,且保持了良好的物理意义。

Realized niche shift associated with Galinsoga quadriradiata(Asteraceae)invasion in China

Shifts in the realized niches of exotic species may play an important role in their invasion.Galinsoga quadriradiata has invaded China widely and occupied many climate zones that are different from its native range.We addressed the climatic niche shift of G.quadriradiata and evaluated how this could contribute to its invasion in China.We used the Maxent model to predict the potential distribution of G.quadriradiata using its native and invaded range occurrences and climatic variables.Principal component analysis was conducted to measure climatic niche shifts of G.quadriradiata during its invasion in China.The models revealed only 32.7%niche overlap between the native and invasive populations.The niche similarity of the two populations was significantly low(Schoener’s D=0.093,P<0.005),suggesting the occurrence of a niche shift.The envelop and center of the realized climatic niche in China has shifted to lower temperature and less precipitation compared to that in its native range.The majority of invaded areas in southern China are in the stabilizing zone,whereas the colonization and adaptation zones are predicted to be at the leading edge of G.quadriradiata invasion in northern China.This suggests that the regional distribution of G.quadriradiata may be in a quasi-equilibrium state,and that the species continues to invade environmentally suitable areas.Alterations in G.quadriradiata’s niche would help to explain why this species is so invasive in China.

The relative energies of polypeptide conformers predicted by linear scaling second-order M?ller-Plesset perturbation theory

We describe an implementation of the cluster-in-molecule （CIM） resolution of the identity （RI） approximation second-order Moller-Plesset perturbation theory （CIM-RI-MP2）, with the purpose of extending RI-MP2 calculations to very large systems. For typical conformers of several large polypeptides, we calculated their conformational energy differences with the CIM-RI-MP2 and the generalized energy-based fragmentation MP2 （GEBF-MP2） methods, and compared these results with the density functional theory （DFT） results obtained with several popular functionals. Our calculations show that the conformational energy differences obtained with CIM-RI-MP2 and GEBF-MP2 are very close to each other. In comparison with the GEBF-MP2 and CIM-RI-MP2 relative energies, we found that the DFT functionals （CAM-B3LYP-D3, LC-ωPBE-D3, M05-2X, M06-2X and coB97XD） can give quite accurate conformational energy differences for structurally similar conformers, but provide less-accurate results for structurally very different conformers.

Investigation of modification design of the fan stage in axial compressor

The S2 flow path design method of the transonic compressor is used to design the one stage fan in order to replace the original designed blade cascade which has two-stage transonic fan rotors.In the modification design,the camber line is parameterized by a quartic polynomial curve and the thickness distribution of the blade profile is controlled by the double-thrice polynomial.Therefore,the inlet flow has been pre-compressed and the location and intensity of the shock wave at supersonic area have been controlled in order to let the new blade profiles have better aerodynamic performance.The computational results show that the new single stage fan rotor increases the efficiency by two percent at the design condition and the total pressure ratio is slightly higher than that of the original design.At the same time,it also meets the mass flow rate and the geometrical size requirements for the modification design.

Nonlinear Schrdinger equations on compact Zoll manifolds with odd growth

We study nonlinear Schr¨odinger equations on Zoll manifolds with nonlinear growth of the odd order.It is proved that local uniform well-posedness are valid in the Hs-subcritical setting according to the scaling invariance, apart from the cubic growth in dimension two. This extends the results by Burq et al.(2005) to higher dimensions with general nonlinearities.