On the stability of resonant rotation of a symmetric satellite in an elliptical orbit

We deal with the stability problem of resonant rotation of a symmetric rigid body about its center of mass in an elliptical orbit. The resonant rotation is a planar motion such that the body completes one rotation in absolute space during two orbital revolutions of its center of mass. In [1–3] the stability analysis of the above resonant rotation with respect to planar perturbations has been performed in detail.In this paper we study the stability of the resonant rotation in an extended formulation taking into account both planar and spatial perturbations. By analyzing linearized equations of perturbed motion, we found eccentricity intervals, where the resonant rotation is unstable. Outside of these intervals a nonlinear stability study has been performed and subintervals of formal stability and stability for most initial data have been found. In addition, the instability of the resonant rotation was established at several eccentricity values corresponding to the third and fourth order resonances.Our study has also shown that in linear approximation the spatial perturbations have no effect on the stability of the resonant rotation, whereas in a nonlinear system they can lead to its instability at some resonant values of the eccentricity.     

On stability in Fuzzy Linear Programming problems

This study focuses on the problem of stability (with respect to changes of centres of fuzzy parameters) of the solution in Fuzzy Linear Programming (FLP) problems with symmetrical triangular fuzzy numbers and extended operations and inequalities.     

On the centre of mass of a random walk

For a random walk $S_n$ on ${\mathbb{R}}^d$ we study the asymptotic behaviour of the associated centre of mass process $G_n=n^{?1}{\sum }_{i=1}^n{S}_i$. For lattice distributions we give conditions for a local limit theorem to hold. We prove that if the increments of the walk have zero mean and finite second moment, $G_n$ is recurrent if $d=1$ and transient if $d\ge 2$. In the transient case we show that $G_n$ has a diffusive rate of escape. These results extend work of Grill, who considered simple symmetric random walk. We also give a class of random walks with symmetric heavy-tailed increments for which $G_n$ is transient in $d=1$.     

Slow rotation of a sphere with source at its centre in a viscous fluid

In this note, the problem of a sphere carrying a fluid source at its centre and rotating with slow uniform angular velocity about a diameter is studied. The analysis reveals that only the azimuthal component of velocity exists and is seen that the effect of the source is to decrease it. Also, the couple on the sphere is found to decrease on account of the source.     

Free rotation of a circular ring about a diameter

A circular ring rotates about a diameter in space. Deformations of the ring depend on a non-dimensional parameterJ which represents the relative importance of centrifugal forces to flexural rigidity. The solutions are found by three methods: series expansion for smallJ, matched asymptotic expansions for largeJ and exact numerical solution using both quasi-Newton and homotopy methods.

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Zusammenfassung Ein Kreisring rotiert um einen Durchmesser im Raum. Verformungen des Ringes hängen vom dimensionslosen ParameterJ ab, der die relative Bedeutung der zentrifugalen Kräfte im Verhältnis zur Biegesteifigkeit angibt. Die Lösungen wurden durch drei Methoden gefunden: Reihenentwicklung für kleinesJ, asymptotische Expansion für großesJ, und exakte numerische Integration sowohl mit einer quasi-Newtonschen als auch mit einer homotopischen Methode.

     

The stability of the rotation of a heavy body with a viscous filling

The stability of the permanent rotation of a symmetrical heavy body with a viscous filling is investigated. A finite-dimensional phenomenological model of the “internal friction” with which the filling acts on the wall of the cavity is constructed based on the Helmholtz equations for a vortex. The boundaries of the stability limit are constructed and the interaction between the internal friction and the external damping is tracked. It is shown that the cases of a cavity that is oblate and prolate along the axis of rotation lead to the existence of different forms of stability regions.     

On the stability of the vertical rotation of a solid suspended on a rod

The problem of the motion of a dynamically symmetric solid suspended from a fixed point by a weightless rod and two ball and socket joints one of which is fixed at the fixed point O', and the other is on the body axis of symmetry at the point O is considered. The question of the stability of the uniform body rotation when points O' and O, and the body centre of inertia C lie on the same vertical, and at the same time point O may be either above or below point O', and point C either above or below point O, is discussed. An analysis of the necessary and sufficient conditions for stability is given. The set of all the system's parameters is reduced to three independent dimensionless parameters L, Ω and β, and in the plane (L, Ω), for fixed values of β, the regions for which the unperturbed rotation is steady, or steady to a first approximation, or non-steady are indicated. The regions for which the body rotation is steady to a first approximation when the point O is situated higher than the point O', and the point C lies higher or lower than the point O are determined.

The sufficient conditions for the vertical rotation of a dynamically symmetric body suspended on a filament were obtained in /1/ and investigated for the cases where in non-perturbed motion the point C is below point O, when points C and O coincide, and when the length of the filament is zero (Lagrange gyroscope). In /2/ an analysis is given of the sufficient conditions for stability obtained in /1/, and also the necessary conditions for the cases where in a non-perturbed motion point C is located above point O.     

Proof of a conjecture about rotation symmetric functions

Rotation symmetric Boolean functions have important applications in the design of cryptographic algorithms. We prove the conjecture about rotation symmetric Boolean functions (RSBFs) of degree 3 proposed in Cusick and St?nic? (2002) [2] and its generalization, thus the nonlinearity of such functions is determined.     

The stability boundaries of the steady motion of a satellite with a gyroscope

Parts of the asymptotic stability boundaries of the uniform motion of the centre of mass of a system of bodies consisting of an asymmetrical satellite with a three-axis gyroscope in a circular orbit are investigated by the second Lyapunov method. Terms of the Lyapunov function that are higher than the second order are enlisted for the investigation. The sign-definiteness criterion of inhomogeneous forms is employed for the corresponding function. Parts of the stability boundaries in which the steady motion investigated is asymptotically stable are established using the Lyapunov asymptotic stability theorem. Application of the Barbashin and Krasovskii theorems reveals parts of the stability boundaries in which the steady motion is unstable. It is established that the asymptotic stability of the steady motion investigated is solved by expanding the Lyapunov function to sixth-order terms.     

Linear stability of a system of Gauss vortices

The stability problems are studied of the rigid body rotation of a regular polygonal system of pointwise and Gauss vortices. A stability criterion is obtained for a system of Gauss vortices which generalizes an available criterion for stability of the rigid body rotation of a system of pointwise vortices. The influence of dispersion of the vorticity distribution on stability of rigid body rotation is studied. It is shown, that there is some finite value of dispersion whose achievement yields the stabilization of known unstable perturbations.     

The mass centre,the gravity centre and their duals on the elliptic plane

In this article the mass centres belonging to the force-free motions of a rigid particle system of the elliptic plane are defined. We examine the elementary geometrical connection between the mass centres and the gravity centre of any triangle on the elliptic plane. We search for those lines of an elliptic triangle that can be considered as the dual notions of the gravity centre, the centre of the incircle and the mass centre.     

Existence of positive solutions to Kirchhoff type problems with zero mass

The existence of positive solutions depending on a nonnegative parameter λ to Kirchhoff type problems with zero mass is proved by using variational method, and the new result does not require usual compactness conditions. A priori estimate and a Pohozaev type identity are used to obtain the bounded Palais–Smale sequences for constant coefficient nonlinearity, while a cut-off functional and Pohozaev type identity are utilized to obtain the bounded Palais–Smale sequences for the variable-coefficient case.     

不可压缩流动问题混合Galerkin型方法稳定性的数值研究

研究了求解不可压缩流动问题的混合Galerkin型方法的稳定性问题,提出了一种在混合Galerkin型方法中满足离散LBB条件的一般性方法,即速度逼近空间维数大于压力逼近空间维数,并且两个逼近空间同时连续时,离散LBB条件可以得到满足.文中以混合有限元方法和混合无单元Galerkin方法为例,通过数值实验,验证了结论的正确性.     

On the fast rotation of a heavy rigid body about a fixed point

Fast rotation of a symmetric heavy rigid body about a fixed point (the kinetic energy is large in comparison with the potential) is considered in cases when the resonance equations of Euler's motion /1, 2/ are approximately satisfied at the initial instant (the body is assumed to effect turns, ε is small, during time . It is shown that during that time ( ) a finite deviation from inertial motion takes place. Such mechanical effect is similar to the precession of a fast top, except that it is more “early” (in the considered time scale the top precession is slow). Approximate equations that define the motion in the principal order and are integrable in quadratures. The formal process of derivation of higher approximations is indicated, and a geometric interpretation of motions is given.     

Existence and Ulam's type stability results for a class of fractional boundary value problems on a star graph

This paper is concerned with a nonlinear fractional boundary value problem on a star graph. By using a transformation, the suggested problem is converted into an equivalent system of fractional boundary value problem. Schaefer's fixed point theorem and Banach's contraction principle is used to establish its existence and uniqueness results. Further, different kinds of Ulam's type stability results for the proposed problem have been discussed. Finally, two examples are presented to illustrate the application of the obtained results.     

The stability of the steady rotation of a system of three equidistant vortices outside a circle

A complete non-linear analysis of the stability of the steady rotation of three point vortices, placed in a plane at the vertices of a regular triangle outside a circular domain is carried out using the results of the Kolmogorov–Arnold–Moser theory. All the resonances of up to fourth order inclusive encountered here are listed and studied. The investigations of Havelock who solved this problem in a linear formulation are thereby completed.     

Linear problems of the dynamics of a floating fluid. Existence theorems

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