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Том 71, № 1 (2016)
- Год: 2016
- Статей: 5
- URL: https://journals.rcsi.science/0027-1330/issue/view/9998
Article
Numerical simulation of three-dimensional instability of flow past a short cylinder
Аннотация
The plane-parallel flow past an infinitely long circular cylinder becomes three-dimensional starting with Reynolds numbers Re ≈ 190. The corresponding instability mode is called mode A. When Re ≈ 260, vortex structures with a smaller cross scale are formed in the wake as a result of a secondary three-dimensional instability (mode B). The transition to three-dimensionality for a short cylinder bounded by planes is considered. The length of the cylinder is chosen to eliminate the unstable perturbations of mode A. Two instability modes similar to modes A and B modified under the effect of the bounding lateral planes are found. The problems of three-dimensional flow are numerically solved using the Navier-Stokes equations.
1-6
Natural frequencies of longitudinal oscillations for a nonuniform variable cross-section rod
Аннотация
The natural frequencies of longitudinal oscillations of a rod such that its Young’s modulus, the density, and the cross-sectional area are functions of the longitudinal coordinate are analyzed. For solving the corresponding problem, an integral formula is used to represent the general solution to the original Helmholtz equation with variable coefficients in terms of the general solution to the accompanying equation with constant coefficients. Frequency equations are derived in the form of rapidly converging Leibniz series for three types of boundary conditions. For these cases the frequency zerothapproximation equations are given to quickly find the lowest natural frequencies with an adequate accuracy.
7-15
Brief Communications
Shock wave acceleration in a gravitational field. A special case
Аннотация
A one-dimensional problem of shock wave acceleration in a uniform gravitational field is exactly solved. In front of the shock wave, the medium state is initially in equilibrium and its density decreases according to a power law. The shock wave is generated using a piston moving freely in the gravitational field. The adiabatic index is assumed to be equal to 3. The obtained solution is represented in terms of elementary functions.
16-18
Determination of trajectory parameters for a small satellite using raw satellite measurements
Аннотация
The problem of determining the trajectory parameters of a small satellite using a satellite navigation equipment is studied. A raw data processing algorithm is proposed when the measurements from a global navigation satellite system are not always regular.
19-22
A new approach to solve the problems of seismic vibrations for periodically nonuniform buried pipelines
Аннотация
The method proposed by E.A. Il’yushina is used to study the longitudinal vibrations of segmented buried pipelines. It is shown that the averaged wave velocity in a periodically nonuniform pipeline is specified by the effective static moduli of the periodicity cell and that, in the case of using a vibration damping material made of rubber or soft metal at joints between pipes, this velocity can be much less than the velocity of longitudinal waves in the main pipe. The last fact makes it reasonable to consider supersonic regimes in the problems of seismic vibrations when the wave velocity in a pipeline is less than the wave velocity in the soil.
23-26