Vol 45, No 2 (2016)

As applied to the dynamics of machines with rheonomic constraints, the dynamic stability conditions are studied within the frequency range of parametric resonances, with due account taken of impulse and slow variations of parameters. A modification is suggested for the conditional oscillator method, and the level of dissipation is determined on its basis, which is necessary to suppress parametric resonances and eliminate the amplitude modulation of oscillations within the kinematic cycle. Given properly selected parameters, the stability conditions are demonstrated to be independent of dissipation.

Based on the mathematical model of a single-span turbine rotor featuring initial bending and residual imbalance, an estimate is made for the vibration amplitudes at the control points of the rotor span at speeds near the lowest critical values on the rundown. Two versions of rotor mounting on anisotropic foil bearings are considered, which simulate bench tests and interaction with the rest of the shafting during operation of the turbine, and two imbalance versions, one with the imbalance concentrated at one point and the other with the imbalance distributed along the rotor span. We present an example of calculations of vibration amplitudes at the lowest critical frequencies during rundown of the high-pressure rotor of a Model K-300-23.5 steam turbine. The rotor here is assumed to have the largest permissible initial deflection and residual imbalance values based on the limits imposed on these values in the operation of turbo units [1]. The results are analyzed.

In recent years the popularity of immersed boundary methods has been increasing in computational hydrodynamics. One of the most effective methods of this class is the LS-STAG method developed in 2010, which allows computations on sufficiently coarse grids. A software package was developed to solve a number of hydrodynamics and hydroelasticity problems by the LS-STAG method. We present the results of the testing the developed software package by simulating a flow around two fixed circular airfoils positioned in tandem at different distances between the airfoils. We simulate the flow modes for which two symmetric vortices, two asymmetrical vortices, and a vortex wake form behind the front airfoil. For each mode, the typical time dependences of the drag force and lift coefficients are presented. The results agree well with the experimental data in the literature and numerical results of other authors.

Data of an experimental–theoretical investigation of the deformation and strength characteristics of a carbon–carbide composite with a 2D reinforcement scheme are given. The nonlinear deformation of the material is described using the relationships of nonlinear elasticity of an orthotropic solid. The strength characteristics are calculated by the maximum stress criterion. Calculated deformation diagrams and ultimate strengths are compared with the experimental data of the authors.

The serviceability of polymer dry sliding bearings is governed by a number of parameters, such as the rotational velocity of the shaft, the friction coefficient, еру thermal and mechanical properties of bearing members, and hence, the resulting contact temperatures. This work was aimed at developing a calculation model of the operation of a two-layer polymer dry sliding bearing, determining the temperatures distributions and the equivalent and contact stresses in bearing members, and choosing the optimum parameters of the bearing system for which heat balance is achieved.

Existing models of damage accumulation under cyclic loading and software for the stress–strain state analysis makes it possible to calculate the damage distribution per structure volume. Knowledge of this distribution makes it possible to appropriately choose a repair technology or substantiate the need for complete replacement of a structure. Analysis of two different large-scale structures is used to illustrate this procedure.

Evaluation of the structural feasibility of folded fillers is a promising line of research aimed at their wider application in machine building design and construction. With all its evident advantages, such as high rigidity, good sound damping, and condensate removal, certain structures have drawbacks as well, such as the small area of filler surface adhesion to skin during panel gluing. This paper considers the simulation process for folded filler with flat contact faces used for gluing to skin, which makes it possible to improve the strength performance of sandwich panels.

A procedure is presented to improve the technology for producing turbocompressors that makes it possible to increase an aircraft engine’s quality indices by preassembling compressor blades based on the closeness of the geometric characteristics. Preassmbly uses an intelligence system, the essence of which is a model for analyzing and classifying the geometry of a blade’s complicated surface. The paper describes the mathematical model for analyzing and preassembling the blade geometry according to the closeness of the geometric characteristics using clusterization. The model and its software system are tested on a series of profiles of the concave parts of gas-turbine engine compressor blades as a result of measurement with a coordinate-measuring machine.