用记忆材料模拟流变大变形问题

本文采用具有记忆特性的有机玻璃材料结合网格法测量技术，以软岩巷道围岩流变形为例展开了有限变形模拟试验的研究工作，并以有限变形理论为基础结合现代计算机技术进行了实验数据处理。实例分析表明，所用方法和技术具有广泛的灵活性、可靠性的实用性。     

重载滑动轴承非牛顿流体的三维弹性液体动力润滑分析的加权平均法

本文采用加权平均法成功地求解了由广义Ｒｅｙｎｏｌｄｓ方程（幂次型）和三维弹性方程组成的非牛顿体弹流模型，该方法较好的解决了大偏心率的弹流迭代收敛困难的问题。该方法具有收敛快，对初值要求松且计算精度高等优点，是一种解决弹流问题较好的迭代模式。     

环空泥浆流场的超声波测试及应用

本文介绍了超声波流速仪测试非牛顿流（如泥浆，水泥浆）流场的方法和特点，对牛顿流和非牛顿流在管内的速度分布剖面作了对比，用该仪器对石油钻井工程环空套管旋流器产生的螺旋衰减流场进行了测试分析。     

磁绝缘理论综述

本文是对磁绝缘认识的综述。提出了对常值阻抗区稳态流的单粒子描述，层流理论，准层流及任意动量流理论；讨论了非稳态流及相关的层流近似，最小能量运动点及有关稳定性的一些问题；介绍了等效电路模拟，粒子模拟及任意动量流的二维时变计算方法；介绍了过渡的概念，进行层流分析，得到一些准则。     

重载滑动轴承非牛顿流体的三维弹性流体动力润滑分析的加权平均法

本文采用加权平均法成功地求解了由广义Ｒｅｙｎｏｌｄｓ方程（幂次型）和三维弹性方程组成的非牛顿体弹流模型，该方法较好的解决了大偏心率下的弹流迭代收敛困难的问题。该方法具有收敛快，对初值要求松且计算精度高等优点，是一种解决弹流问题较好的迭代模式。     

绕流直接数值模拟误差分析

对于无边界绕流问题的计算流体力学模拟通常是将物体置于“足够大”的槽道中，而通过不断改变槽道尺寸以及离散网格密度，后验对比方式来检查模拟误差。本文结合多种经典流场理论，提出一种简单的先验误差估计方法来确定槽道尺寸以及相应的网格分布。在此方法中，对于槽道尺寸的确定基于线性叠加原理（即在极小雷诺数下采用Stokes理论解叠加，而在其他雷诺数条件下采用势流理论解叠加），来估计槽道尺寸对绕流结果的影响。而对网格尺寸与分布，则是使用多项式逼近中的基本误差分析工具，应用到速度边界层，远场势流，以及Rankine涡等简单流动，从而确定整个绕流问题中的离散误差。为了验证前面的理论分析结果，本文模拟了相当大雷诺数范围内的二维翼型以及三维圆球绕流，所得数值结果非常好地验证了理论分析。结果表明，对于Stokes流动问题，槽道尺寸需要大约100倍于物体特征尺寸来保证其结果与无边界绕流相差不超过1%；而在雷诺数超过大约100时，槽道尺寸只需10倍（二维绕流）或者5倍（三维绕流）于物体特征尺寸来达到同等精度。在此先验误差估计方法可应用于一般化的绕流问题。     

用管轴流速确定动脉中血液振荡流的速度剖面

本文通过求解圆管内血液振荡流的基本方程，求得圆管内血液流的速度与压力梯度之间的关系式，文章提出一种利用管轴外流速计算管内压力梯度，进而确定血液振荡流动速度分布的方法，该方法用于检测活体血管内血液振荡流的速度剖面，具有操作简单，精度较高的优点，最后，以人体颈动脉为例，讨论血液周期振荡流的速度分布特征，发现在任意时刻，除了邻近管壁速度迅速降为零之外，沿管截面速度分布相当均匀，呈现出与定常流不同的速度分布特征。     

面向对象的土石坝参数随机反演程序设计

将储液容器流固耦合系统中的液体和容器分别视为理想可压缩流体和线弹 性固体，采用流体压力单元和固体壳单元对流固耦合系统进行有限元离散，得到一个非对称 的大型流固耦合有限元方程. 采用Arnoldi方法求解上面这个大型有限元方程的非对称特征 值问题，以得到储液容器的动力特性. 通过移频技术避免了处理零频问题，并构造了迭代格 式计算Arnoldi向量. 数值算例表明所用解法对于流固耦合系统都是非常有效的.     

研究多相介质运动的意义、内容和方法

本文从连续介质假设、守恒方程、本构关系和固壁上的边界条件等方面的分析出发，指出二相流体动力学虽是流体力学的一个分支，但在研究内容上与流体力学有较大差异，从分析二相流特点与稀薄气体、稠密气体、非平衡流动和可压缩流动特点之间的相似性出发，指出二相流研究可借鉴相关学科的研究成果和研究方法。本文用弛豫时间概念解释了二相混合物与均相混合物在运动特征上的差异，以及在描写运动的方法上（双流体模型和单流体模型等）的相应差异。最后以风沙运动、泥沙运动和泥石流运动为例，说明在二相流研究中突出主要因素进行合理简化的重要性，并指出：对于不同类型的二相流、对于具有不同流动参数的同类二相流、对于同一二相流的不同区域或不同的研究目的，简化的方法都会有所不同。     

求附连水质量的一种直接方法

本文基于势流理论，提出了计算附连水质量的一种直接方法     

外伸梁离散系统模态的若干定性性质

在已证明外伸梁的差分离散模型频率和位移振型基本振荡性质的基础上,首先揭示了两跨外伸梁的共轭系统是一端铰支一端固定并有一个中间铰的两跨连续梁,证明了两跨外伸梁的共轭梁的刚度矩阵是符号振荡矩阵,进而确定了外伸梁的弯矩振型的符号改变数;由此进一步讨论了它的转角振型和剪力振型的符号改变数规律以及位移振型的其他一些定性性质.      

Principal Trajectories of Forced Vibrations for Discrete and Continuous Systems

Principal trajectories of forced vibration of linear and nonlinear continuous systems are introduced as such motions in which the system is equivalent to a Newtonian particle in the function space of the system configurations. The corresponding 'effective mass' of the particle gives physical characteristics of the system response, so that zero effective mass is associated with resonance. The methodology can be viewed as a complementary tool to the method of normal modes, when considering the class of forced vibrating systems, since the related basis accounts for the system physical properties as well as the external forcing factor. In particular, it is shown that a two degrees of freedom system can possess an infinite discrete set of in-phase and out-of-phase forced vibrations of the normal modes type. The corresponding forcing vector-functions obey the second Newton law due to the definition of principal trajectories.     

Trapped modes in coastal waveguides

Postnova and Craster (Wave Motion, 45, 2008, pp. 565-579) describe a method for determining the frequency of trapped modes in slowly-varying elastic plates, and ocean and quantum waveguides. The purpose of the present note is to show that the accuracy of the frequency estimates for ocean waveguides can be significantly increased by taking into account the fact that, as posed, the ocean waveguide problem is not self-adjoint. For an example where the asymptotic problem has an exact solution, comparison with a numerical solution of the full problem shows that the correction to the asymptotically determined frequency is of order the fourth power of the ratio of the shelf width to the scale for longshore variations in the shelf. An explicit simple formula is also given for the trapped mode frequency of an arbitrarily, but extremely weakly and positively, curving coast.     

On the sensitivity of non-generic bifurcation of non-linear normal modes

It is shown that a non-generic bifurcation of non-linear normal modes may occur if the ratio of linear natural frequencies is near r-to-one, r=1,3,5,… . Non-generic bifurcations are explicitly obtained in the systems having certain symmetry, as observed frequently in literatures. It is found that there are two kinds of non-generic bifurcations, super-critical and sub-critical. The normal mode generated by the former kind is extended to large amplitude, but that by the latter kind is limited to small amplitude which depends on the difference between two linear natural frequencies and disappears when two frequencies are equal. Since a non-generic bifurcation is not generic, it is expected generically that if a system having a non-generic bifurcation is perturbed then the non-generic bifurcation disappears, and generic bifurcation appears in the perturbed system. Examples are given to verify the change in bifurcations and to obtain the stability behavior of normal modes. It is found that if a system having a super-critical non-generic bifurcation is perturbed, then two new normal modes are generated, one is stable, but the other unstable, implying a saddle-node bifurcation. If the system having a sub-critical non-generic bifurcation is perturbed, then no new normal mode is generated, but there is an interval of instability on a normal mode, implying two saddle-node bifurcations on the mode. Application of this study is discussed.     

Thermal convection in a cylindrical annulus under a combined effect of the radial and vertical gravity

The stability of the flow of a dielectric fluid confined in a cylindrical annulus submitted to a radial temperature gradient and a radial electric field is investigated theoretically and experimentally. The radial temperature gradient induces a vertical Archimedean buoyancy and a radial dielectrophoretic buoyancy. These two forces intervene simultaneously in the destabilization of the flow, leading to the occurrence of four types of modes depending on the relative intensity of these two buoyancies and on the fluid's properties: hydrodynamic and thermal modes that are axisymmetric and oscillatory, stationary columnar modes and electric modes which are stationary and non-axisymmetric modes. Experiments performed in a parabolic flight show the existence of non-axisymmetric modes that should be either columnar or helicoidal vortices.     

On the completeness of Lamb modes

A completeness result for Lamb modes in homogeneous waveguides is proved. The problem is formulated as a linear eigenvalue problem in an appropriate Hilbert space of functions. Orthogonality and biorthogonality relations are given. A detailed spectral analysis which is necessary for the application of a general completeness theorem is presented.     

Transient mode localization in coupled strongly nonlinear exactly solvable oscillators

Coupled strongly nonlinear oscillators, whose characteristic is close to linear for low amplitudes but becomes infinitely growing as the amplitude approaches certain limit, are considered in this paper. Such a model may serve for understanding the dynamics of elastic structures within the restricted space bounded by stiff constraints. In particular, this study focuses on the evolution of vibration modes as the energy is gradually pumped into or dissipates out of the system. For instance, based on the two degrees of freedom system, it is shown that the in-phase and out-of-phase motions may follow qualitatively different scenarios as the system’ energy increases. So the in-phase mode appears to absorb the energy with equipartition between the masses. In contrast, the out-of-phase mode provides equal energy distribution only until certain critical energy level. Then, as a result of bifurcation of the 1:1 resonance path, one of the masses becomes a dominant energy receiver in such a way that it takes the energy not only from the main source but also from another mass.     

Transverse-roll global modes in a Rayleigh–Bénard–Poiseuille system with streamwise variable heating

The effect of a spatially inhomogeneous heating of the bottom wall in Rayleigh–Bénard–Poiseuille convection is studied for slow streamwise variations of the temperature profile. The problem is defined by the constant Reynolds number of the Poiseuille through flow, assumed to be low (typically 10), the constant Prandtl number, and the spatial evolution of the Rayleigh number , assumed to be subcritical everywhere except in a limited region around its single maximum . In this initial study, all spanwise inhomogeneities such as side walls or spanwise variable heating are neglected to obtain two-dimensional (transverse roll) global mode solutions by means of WKBJ asymptotics. The resulting frequency selection yields, at leading order, a global mode frequency equal to the local absolute frequency ω^t at the streamwise location where the Rayleigh number is maximum, with higher-order corrections for non-parallelism. These allow the determination of critical values of for global instability as a function of the profile of the local Rayleigh number and of Prandtl and Reynolds numbers.     

Performance of Nonlinear Vibration Absorbers for Multi-Degrees-of-Freedom Systems Using Nonlinear Normal Modes

Linear vibration absorbers are a valuable tool used to suppressvibrations due to harmonic excitation in structural systems. Whilelimited evaluation of the performance of nonlinear vibrationabsorbers for nonlinear structures exists in the literature forsingle mode structures, none exists for multi-mode structures.Consequently, nonlinear multiple-degrees-of-freedom structures areevaluated. The theory of nonlinear normal modes is extended toinclude consideration of modal damping, excitation and smalllinear coupling, allowing estimation of vibration absorberperformance. The dynamics of the N +1-degrees-of-freedom system areshown to reduce to those of a two-degrees-of-freedom system on afour-dimensional nonlinear modal manifold, thereby simplifying theanalysis. Quantitative agreement is shown to require a higher-order model which is recommended for future investigation.