Presented work concerns with a sensitivity analysis of a harmonically excited bending vibration of a rotating couple of blades with a friction element with regard to the parameters of the friction characteristic. Either of the blades is discretized by FEM using beam elements and continuously distributed weight is concentrated in nodal points. The friction in central contact points between blade shrouds and the friction element is approximated by a continuous function depending on slip velocities of the shrouds relative to the friction element. Considered friction characteristic respects the micro-slip phase at the very low slip velocities and the macro-slip (full-slip) phase at the higher slip velocities. The values of the friction characteristic parameters are identified by comparison of the numerical simulations of a transient vibration with experiments used in IT AS CR. and Obsahuje seznam literatury
The paper deals with the modelling of balancing machine vibration and the identifícation of the stiffness and damping coefficients of oil-film bearings. The real balancing machine consists of a flexible rotor, oil-film bearings and bearing heads on spring elements. The mathematical model enables to calculate eigenvalues, critical revolutions and unbalance vibrations in dependence on the rotational speed. The identification method of the oil-film bearing stiffness and damping matrices is based on the minimization of differences between measured and calculated rotor critical speeds and bearing head displacements in balancing machines. The rotor is excited by attached known trial masses fixed in chosen balancing planes. and Obsahuje seznam literatury
This presented work is concerned with a friction element impact and detuning mass impact of the bending oscillation of a couple of blades with a friction element embodied between the blade shrouds. Either of the blades is discretized by FEM using beam elements and continuously distributed weight is concentraed in nodal points. One of the blades is excited by harmonic varying force. The friction element, which is considered as a rigid body, is pulled using constant tension force into a wedge gap between the blade shrouds. The detuning of this system is caused by an additional mass mounting on one of the blade shrouds. Numerical simulation results are compared with results of the equivalent linearization method. The effects of the friction and detuning on the blades vibration suppression are analyzed. and Obsahuje seznam literatury
This paper deals with the basic dynamical model of electromotor whose creation motivated by problems of electromotor vibrations and its subsequent fatigue. The model is chaacrterized by a flexible shaft with mounted padket of sheet metals that are equipped with parallel copper bars connected by end shortcircuit rings. Finite element analysis is used for the disretization of the shaft, while the sheet metal packet of cylindrical shape is modelled as a set of rigid bodies joined using chosen viscoelastic forces and torques. The shortcircuit rings are supposed to be rigid in this basic dynamical model and the pieces of copper bars are substituted by massless springs of calculated properties. Problematic model parameters are identified by means of performed experimental modal analysis. and Obsahuje seznam literatury
The paper deals with mathematical modelling of dynamic response of the electric locomotive wheelset drive caused by short-circuit traction motor torque. The individual wheelset drive is composed of five subsystems - rotor of the traction motor with driving gear, driven gear, stator of the traction motor with gear housing, hollow graduated shaft with clutches and wheelset. The couplings between subsystems are linearized in dependence on longitudinal creepage and locomotive forward velocity before sudden short-circuit in the asynchronous traction motor. In comparison with previous models of the wheelset drives, the rotor of the electromotor is characterized by flexible shaft suppported on flexible rolling-element bearings. The sheet metal packjet of cylindrical shape is connected by parallel cooper bars with two short circuit rings. In conseqquence of strong excitation an interruption of gear mesh can be observed. This nonlinear effect and dynamic load of individual wheelset drive with large number of DOF is investigated using the condensed mathematical model created by model synthesis method. and Obsahuje seznam literatury
The paper deals with the mathematical modelling and the computer simulation of forced vibrations of the reactor core barrel excited by pressure pulsations generated by main circulation pumps. The modelling is focused on a possible core barrel flange slip along a pressure vessel flange. The slip in this internal reactor linkage is analysed providing the solid friction and the backlash between slip tongues of the pressure vessel flange and grooves in the core barrel flange. The impact motion can produce an excessive abrasive wear of the tongues and grooves. A guarantee of the fail-safe operation is achieved by calculated pre- stressing of toroidal tubes inserted between the upper flange of the core barrel and the pressure vessel cover. and Obsahuje seznam literatury
The paper deals with the modelling of forced vibrations of reactor components excited by pressure pulsations generated by main circulation pumps. For the vibration analysis a new generalised model of the reactor with spatial localization of the nuclear fuel assemblies and protection tubes, continuously mass distribution of beam type components and more accurate model of the linear stepper drives for actuation of control cassettes was applied. Slightly different pump revolutions are sources of the heating which causes an amplification of vibration and possibility of the contact loss in internal linkages of the core barrel. and Obsahuje seznam literatury
The paper deals with derivation of the dynamical model of the turbochargers with rotor supported on the two floating ring bearings. The model respects the bearing forces acting upon the journals and floating bearing rings by means of inner and outer oil-films. The gyroscopic effects, external and internal damping of the flexible rotor shaft and the rigid turbine and compressor wheels are respected. The modal analysis and the Campbell diagram is used in the turbocharger linearized model to find the critical speeds. and Obsahuje seznam literatury
This paper focuses on the modelling of harmonic vibration of two rotating blades affected by friction in contact of a rigid body placed in between the blade shroud. Harmonic blade excitation uniformly distributed in blade nodes in circumferential and axial direction is supposed. Flexible blades are discretized by FEM using 1D Rayleigh beam elements. The nonlinear friction forces in contact surfaces between the blade shroud and the friction element are taken into account using the harmonic balance method. Orbits of central contact points and dissipation energy are investigated in dependence on the excitation frequency. Dissipation energy amount in contact surfaces is confronted with blade tips vibration. and Obsahuje seznam literatury