Solid State Phenomena Vols. 147-149

Abstract: An identification procedure of the active vibration damping system with the piezo-elements glued to the structure is presented in the paper. Such identification can be carried out in analytical way (Guyan reduction) by using of low-band pass amplifiers. First, we have identified the open loop system in the frequency domain by using experimental setup with real amplifier and beam equipped in piezo-strips working as actuators and sensor, respectively. For the frequency range 1 Hz to 400 Hz we have obtained Bode plots with helped of Dynamic Signal Analyzer which were base to further calculations. Second, mathematical model have been adjusted to the experimental results by the least square sum approach and also by the consideration of a system which was modeled by finite elements. A three first resonance frequencies and three first anti-resonance frequencies have obtained.

Abstract: Application of the transformation of experimentally-obtained compliance into dynamic stiffness for the identification of discrete rotor model parameters is described. Simple examples are examined to illustrate the fact that a fully satisfactory discrete model can or cannot be achieved.

Abstract: The problem of mathematical simulation of the origin and evolution of low-cycle fatigue cracks is quite actually for many high-loaded machines and units of power industry, aerospace engines, oil and gas pipelines and other structures operating under repeated loading. Successful prediction of low-cycle resource depends on solution of several interrelated problems: creation and development of structure model (loads, boundary conditions, materials model) that will adequately describe all aspects stress-strain history in the structures paths; creation plasticity and creep models adequate to the processes taking place during sing-alternating elastic-plastic deformation; the creation of lifetime fatigue failure rate criteria; and development of effective numerical simulation technique.

Abstract: The paper focuses on dynamics of an electromechanical system composed of a DC motor and a planar four-bar mechanism. Minimization of mechanism/frame interactions is considered. Simultaneous elimination of frame shaking forces and torques is requested. The employed balancing method is counterweights allocation. Their parameters are found with a numerical modelling and a numerical optimization. They depend on shape of the mechanism’s velocity. Three alternative drives are tested in the paper: constant velocity drive; constant torque drive; and DC motor. The optimal counterweight’s parameters are derived for all these drives. Obtained results approved necessity of precise electromechanical modelling.

Abstract: In the article, the equation of the equivalent movement of the oscillator with viscous friction is provided. The statistical specifications and the spectral approach for the density of intensity of the established vibrations are provided. Non-stationary vibrations in the closed form are investigated. The statistical characteristic for intensity of vibrations is obtained. The work presents a method of investigation of vibration processes of random mechanical vibrations in the equipment and apparatus. The vibratory system of a sufficiently small (as compared to vibrations of a long wave) size is described; the models with the limited number of degrees of freedom are applied. The statistical theory for discussing of vibrations at constructional damping is applied.

Abstract: The paper describes the semi-active suspension laboratory system (SAS), built to demonstrate and test a number of control algorithms. The heart of the system is the automotive engineering damper with the restoring force controlled by magnetic field. We use in our apparatus the Lord 1097 magnetorheological (MR) damper manufactured by the American company. MR devices benefit from the ability of MR fluids to rapidly change rheological properties upon exposure to a magnetic field. The main advantage of the SAS is its portability as a demonstrative experimental rig to test control damping algorithms. The damped less oscillations are compared to the On-off damped oscillations of the apparatus. The MR damper provides an effective solution to SAS control in a variety of applications.

Abstract: The paper describes the mathematical model for C axis of the multifunction turning center with worm gear. Talks about the mathematical model with multi-body mass dynamic system. The drive works in the positional feedback and his mathematical model is specified for detection of the dynamical behaviors of the C axis. The turning center is designed for a heavy roughing forged piece from high carbon steels by the power of main motor 71kW. The C axis must be designed as accurate angle position axis and with big dynamic stability of regulation by step or pulse loading. The C axis drive is constructed with help of a hydraulic connected up the worm gearing on a spindle. The driven side of the worm gear is created two dual worms with own servomotors. Worm wheel is solved as one part with two gears. Servomotors are controlled with the mode speed/torque coupling (MASTER-SLAVE), which guarantees the constant torque prestressing between the servomotors. The difference of a torques guarantees leaning of both worm teeth on opposite tooth faces of both gears of the worm wheel. In the dynamic model are involved the friction on the worm gears, torsion stiffness located with help of the FEM and moment of inertia for all parts. 3D models of the C axis is designed in the program ProEngineer. From complete 3D model of the C axis are transfered individual parts to the FEM in surroundings Ansys as volume parts. In this paper is main output influence of the diference between the 3D and 2D for calculation of the stiffness in the contact of the worm gear on the whole dynamic system of the C axis. The value of the torsion stiffness by more situation of the load on the worm gear is used subsequently to the multi-body mass system of the C axis drive and to the eigen frequencies analyses. Results of this paper will be sensitivity check of the changing torsion stiffness on the worm gear by the loading changing on the resulted position accuracy on the C axis. Next review is, if the control modul MASTER-SLAVE is partially this problem of the difference between values of stiffness from 2D or 3D model or also stiffness non-linearity eliminated.

Abstract: Diagnostic FDM-A method [2] based on a measurement of frequency modulation of a pulsation component as well as FAM-C method based on a measurement of a alternating current’s frequency have been developed in Air Force Institute of Technology. These methods provide to define a level of a sub-assembly’s abrasive wear and its localization during normal work of a power unit. It is possible to define numerous parameters of bearings and their kinematics pairs as well as a rotor assembly. They are: a level of a bearing rolling friction, smoothness of a bearing cage’s motion, a quantity of a radial clearance. It also provides to detect resonances in elements as well as observe a shape and a relative height of characteristic patterns, from which it is possible to calculate, among others, a quantity of a mechanical quality factor of a kinematics pair – it is possible to define an operating time reserve of the kinematics pair to resonance.

Abstract: The aim of this paper is to develop a simplified method for analysis of free vibration of floor system consisting of continuous steel plate and steel frame in plane to reinforce it. The study of such orthotropic system is of practical interest and aimed at small businesses, which are not able to obtain expensive programs for performing such calculations.

Abstract: This article deals with automatic balancing (self-equalizing) of rotors with vertical axis of rotation by means of liquid. There used to be a statement claiming that automatic balancing was possible only after first critical (above resonance) rotation zone of rotors. However in 1995 the phenomenon of automatic balancing with liquid in both below resonance zone of rotor rotation and in the resonance itself was registered using the method of high speed video shooting. The paper suggests theoretical explanation of the phenomenon stated by means of carried out experiments.