有多余坐标完整系统的自由运动

对于完整力学系统,若选取的参数不是完全独立的,则称为有多余坐标的完整系统. 由于完整力学系统的第二类Lagrange 方程中没有约束力,故为研究完整力学系统的约束力,需采用有多余坐标的带乘子的Lagrange方程或第一类Lagrange 方程. 一些动力学问题要求约束力不能为零,而另一些问题要求约束力很小. 如果约束力为零,则称为系统的自由运动问题. 本文提出并研究了有多余坐标完整系统的自由运动问题. 为研究系统的自由运动,首先,由d'Alembert-Lagrange 原理, 利用Lagrange 乘子法建立有多余坐标完整系统的运动微分方程;其次,由多余坐标完整系统的运动方程和约束方程建立乘子满足的代数方程并得到约束力的表达式;最后,由约束系统自由运动的定义,令所有乘子为零,得到系统实现自由运动的条件. 这些条件的个数等于约束方程的个数,它们依赖于系统的动能、广义力和约束方程,给出其中任意两个条件,均可以得到实现自由运动时对另一个条件的限制. 即当给定动能和约束方程,这些条件会给出实现自由运动时广义力之间的关系. 当给定动能和广义力,这些条件会给出实现自由运动时对约束方程的限制. 当给定广义力和约束方程,这些条件会给出实现自由运动时对动能的限制. 文末,举例并说明方法和结果的应用.      

具有可积微分约束的力学系统的Lie对称性

研究具有可积微分约束的力学系统的Ｌｉｅ对称性与守恒量。采用两种方法：一是用不可积微分约束系统的方法;另一是用积分后降阶系统的方法,研究两种方法之间的关系。     

New integrable problems in the dynamics of rigid bodies with the kovalevskaya configuration. I - The case of axisymmetric forces

Despite the rarity of integrable problems in rigid body dynamics, amazing relative abundance of these problems is observed when the body has the famous Kovalevskaya configuration A=B=2C. In the present work, the general problem of motion of such a rigid body about a fixed point under the action of axially symmetric conservative forces is considered. The classical problem of motion of a heavy rigid body or a gyrostat and the problem of motion of a body in an ideal fluid are special cases.Three new integrable cases valid for Kovalevskaya's configuration are introduced of which one is general and the other two are restricted to the zero level of the cyclic integral. It is also shown that all the previously known results concerning the preesent problem are special versions of four different cases.     

On Uniqueness in the Elastoplastic Analysis of Frames

ABSTRACT

A very simple example of elastoplastic analysis is adduced to illustrate how more than one deformed configuration can be associated with a single prescribed load state. The encoding of holonomic elastoplastic analysis in quadratic programming form leads to an uniqueness theorem for the bending moments (static solution), and yet, even for holonomic elastoplasticity, the uniqueness of the deformed configuration (kinematic solution) cannot be guaranteed. Different kinematic solutions, when they exist, are seen from the simple example to be physically induced by different load paths terminating at the same prescribed load state, and thus it is proved that holonomic elastoplasticity is not strictly path independent. Any two valid kinematic solutions can only differ by the motion of a special mechanism, called a pseudo-mechanism. This device is used to establish a uniqueness theorem for the kinematic solution obtained by quadratic programming or any other form of holonomic elastoplastic analysis. Finally, it is shown that load states exhibiting non-unique kinematic solutions always He on pseudomechanism lines in load space, and that a load path which lies along some part of such a line produces a completely indeterminate deformed configuration.     

Non-integrability and chaos of a conservative compound pendulum

By using a series of canonical transformations (Birkhoffs series), an approximate integral of a conservative compound pendulum is evaluated. Level lines of this approximate integral are compared with the numerical simulation results. It is seen clearly that with a raised energy level, the nearly integrable system becomes non-integrable, i.e. the regular motion pattern changes to the chaotic one. Experiments with such a pendulum device display the behavior mentioned above.     

基于对偶变量变分原理的完整约束系统保辛算法

基于对偶变量变分原理,选择积分区间两端位移为独立变量,构造了求解完整约束哈密顿动力系统的高阶保辛算法。首先,利用拉格朗日多项式对作用量中的位移、动量及拉格朗日乘子进行近似;然后,对作用量中不包含约束的积分项采用Gauss积分近似,对作用量中包含约束的积分项采用Lobatto积分近似,从而得到近似作用量;最后,在此近似作用量的基础上,利用对偶变量变分原理,将求解完整约束哈密顿动力系统问题转化为一组非线性方程组的求解。算法具有保辛性和高阶收敛性,能够在位移的插值点处高精度地满足完整约束。算法的收敛阶数及数值性质通过数值算例验证。     

关于完整非保守系统的基本积分变量关系

本文证明,完整非保守系统不存在 Poincare-Cartan 积分不变量和 Poincare 通用积分不变量。取而代之,给出非保守系统的 Poincare-Cartan 型和 Poincare 型积分变量关系,并将这种积分变量关系用于求解非线性振动问题。我们还证明了文[1]、[2]所谓的积分不变量只是我们所引入的基本积分变量关系。     

First integral and stability of motion in the critical cases

In this paper, we indicate that after the Liapunov function by using linear combination of mechanical first integral was suggested by Chetayev in 1946. He and his students solved stability of conservative system by means of this method. But he had trouble to solve the problems by means of cut and try. Moreover, the condition of stability is imperfect. Solution by this method is limited for problems of purely imaginary roots. The cases of zero roots have not been considered. Condition of stability secured is more strict.This paper suggests that the differential equation can be transformed into standard form by method of cancellation of cyclic coordinates (method of lowering degree of order). and condition of stability can be determined by energy integral. By this method not only the computation is clear and concise. But also zero roots can be considered. Therefore the problems of two cyclic coordinates can be transformed into second-order system, and we get new conclusion of the condition of stability simply. As for problems of single cyclic coordinate, infact, Chetayev and his students did not solve the stability of the gyroscope of auter-gimbal with horizontal axis or arbitrary angle. In this paper, it shows that the method suggested here is useful for stability of these problems. The condition of conditional stability and instability were derived.     

Extension of Noether's theorem to constrained non-conservative dynamical systems

A method based on a differential variational principle is developed in order to extend Noether's theorem to constrained non-conservative dynamical systems. The result is applied to generate constants of the motion for a generic example of a non-linear, dissipative dynamical system with time-varying coefficients represented by the Emden equation. The converse of Noether's theorem, whereby the symmetries of the system are determined from the knowledge of the Lagrangian and a first integral is also considered for both the Emden equation, and that of the damped harmonic oscillator. It is further shown that the presence of ideal constraints (whether holonomic or non-holonomic) does not affect the statement of Noether's theorem. The constraints affect the Jacobi energy integral, however, because they enter into consideration through real work instead of virtual work. It is shown that the Jacobi integral is conserved provided that: (a) the Lagrangian is explicitly independent of time, (b) the real power of the generalized forces not derivable from a potential vanish, (c) the holonomic constraints are explicitly independent of time, (d) the non-holonomic constraints are linear and homogeneous in the generalized velocities.     

About the basic integral variants of holonomic nonconservative dynamical systems

In this paper, we prove that for holonomic nonconservative dynamical system the Poincaré and Poincaré-Cartan integral invariants do not exist. Instead of them, we introduce the integral variants of Poincaré-Cartan's type and of Poincare's type for holonomic nonconservative dynamical systems, and use these variants to solve the problem of nonlinear vibration. We also prove that the integral invariants introduced in references [1] and [2] are merely the basic integral variants given by this paper. Project supported by National Natural Science Foundation of China     

Cyclic-stress studies by time-averaged photoelasticity

This paper describes an experimental method whereby the amplitude of cyclic stresses may be readily determined by time-averaged photoelasticity. Using an ordinary polariscope with a monochromatic-light source, ‘time-averaged isochromatics fringes’ are formed if the photographic film in the camera is exposed with an exposure time equal to one or several periods while the photoelastic model is undergoing steady-state cyclic loading. The fringe pattern depicts amplitudes of the oscillating stresses according to the zeroth-order Bessel function. These properties permit the determination of a time-averaged cyclic stress-optic law. It is also possible to use the method to determine time-averaged isoclinics. The method has great potentiality in the study of in-plane vibrations.     

移动的线源平稳随机荷载激励下梁的随机响应

利用广义Ｄｕｈａｍｅｌ积分和积分变换，研究了粘弹性Ｋｅｌｖｉｎ地基上无限长梁在运动的线源平稳随机荷载作用下的随机响应．发现此时梁的挠度响应为非平稳随机过程．通过引入随动坐标系，建立了有明确物理意义的随动谱分析方法，使随机位移响应在随动坐标系下成为平稳随机过程     

Whittaker's reduction method for poincaré's dynamical equations

Whittaker's reduction method invokes the energy integral to reduce the order of Lagrange's equations of motion of a holonomic dynamical system. This paper treats the corresponding results for a nonholonomic conservative system described by Poincare's equations which are constructed from the standpoint of the theory of Lie groups.     

D'alembert principle in the velocity space

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Extension of Whittaker equations to non-holonomic mechanical systems

In 1904, using the energy integral Whittaker studied the reduction of a dynamical problem to a problem with fewer degrees of freedom for the holonomic conservative systems and obtained the Whittaker equation^[1].In this article, Whittaker equations are extended to non-holonomic systems and the generalized Whittaker equations are obtained. And then these equations are transformed into Kiel-sen’s form.Finally an example is given.     

AN EXTENDED BOUNDARY INTEGRAL EQUATION METHOD FOR THE REMOVAL OF IRREGULAR FREQUENCY EFFECTS

Numerical techniques for the analysis of wave–body interactions are developed by the combined use of two boundary integral equation formulations. The velocity potential, which is expressed in a perturbation expansion, is obtained directly from the application of Green's theorem (the ‘potential formulation’), while the fluid velocity is obtained from the gradient of the alternative form where the potential is represented by a source distribution (the ‘source formulation’). In both formulations, the integral equations are modified to remove the effect of the irregular frequencies. It is well known from earlier works that if the normal velocity is prescribed on the interior free surface, inside the body, an extended boundary integral equation can be derived which is free of the irregular frequency effects. It is shown here that the value of the normal velocity on the interior free surface must be continuous with that outside the body, to avoid a logarithmic singularity in the source strength at the waterline. Thus the analysis must be carried out sequentially in order to evaluate the fluid velocity correctly: first for the velocity potential and then for the source strength. Computations are made to demonstrate the effectiveness of the extended boundary integral euations in the potential and source formulations. Results are shown which include the added-mass and damping coefficients and the first-order wave-exciting forces for simple three-dimensional bodies and the second-order forces on a tension-leg-platform. The latter example illustrates the importance of removing irregular frequency effects in the context of second-order wave loads.     

Chaotic motion in a class of asymmetrical Kelvin type gyrostat satellite

This work is an investigation on the roots of chaotic attitudinal motion in a class of asymmetrical gyrostat satellites. The result shows that for a class of Kelvin type gyrostat satellite, there is an equivalent rigid spinning satellite with the same attitude dynamics. Finding some constants of motion and eliminating the cyclic coordinates, the rotational kinetic energy is changed to a quadratic form and using Jordan canonical form of the associated inertia tensor and transforming the coordinate system, the Hamiltonian has been changed to those of a rigid satellite. The Hamiltonian has been split into integrable and non-integrable parts. Using Deprit canonical transformation and Andoyer variables the integrable part has been reduced to a one-dimensional form. The reduced Hamiltonian shows that the regular dynamics of the satellite can be chaotic, under the influence of gravitational effects. To demonstrate various attitudinal dynamics of the satellite, a second-order Poincaré map is employed. This research shows firstly, that the attitudinal dynamics of Kelvin type gyrostat satellites and rigid satellites follow the same dynamical patterns, secondly, for non-linear analysis of dynamics of gyrostat satellite based on the perturbation methods, there is a preferable form for Hamiltonian of the system in the near-integrable fashion and thirdly the chaotic motion is originated from the gravitational field effects that can be suppressed by increasing the attitudinal energy of the satellite in comparison with the translational energy.     

Circuit simulation for synchronization of a fractional-order and integer-order chaotic system

We design a new three-dimensional double-wing fractional-order chaotic system with three quadratic terms, confirmed by numerical simulation and circuit implementation. We then study the synchronization between the new double-wing fractional-order chaotic system and different Lorenz systems with different structures. In the process of the synchronization, the definition of ‘the simplest response system’ and the practical method of designing the circuit have been originally proposed. The circuit of ‘the simplest response system’ (even the simplest incommensurate-order response system), holding different structures with the drive system, of any one integral or fractional drive system now can be designed effectively and sufficiently. Our results are supported by numerical simulation and circuit implementation.