The paper preseiits an investigation on vibrations of mechanical systems arising from unbalanced masses. At the experimental stage, a power transmission shaft is driven at different operating speeds, therefore, the paranieters, such as displacement, velocity and acceleration in vertical direction due to body vibrations are measured at various points on the frame before and after balancing. Balancing has provided a definite decrease in the amplitudes of vibration parameters.
In addition to these studies mentioned above, the use of Neural Network (NN) for vibration analysis of a frame due to unbalanced transmission shaft is also achieved. The results show that the NN approach exactly follows the foregoing results. This implies the necessity of the non-linear modelling capabilities of the NN for vibration problems of mechanical systems.
Vibration of engineering structures results in time variable displacements functions. For realistic structures modes of vibration are determined by exciting frequency and the natural frequencies of the structure. Hence, the components of stress tensor are time function too. In the presented paper the general idea of method of cycle-counting based on the FFT analysis for engineering structures is discussed and analytically verified for the case vibrating beam excited by series pulse-type force with no damping. and V názvu článku je jazyková chyba/překlep - analitical - správně = analytical
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
The vibrodiagnostic system VDS-UT2 was developed for the investigation of a tram wheel operational vibration and deformation. The system consists of measuring, acquisition and processing tools for monitoring of tram wheels and their operational parameters, e.g. static and dynamic deformation, displacement, velocity, acceleration and temperature. The measuring on a rotating wheel is realized both by telemetric and by top-timing system. Measured data can be remote-observed via Internet connection with the control PC. The acquisition system by Starmans Electronics s.r.o. provides continuous analog and digital data logging. The control PC processes digital logical signals and evaluates time intervals representing circumferential turning angles between disk and rim.. In the contribution, the diagnostic system is described and the measured data including damage analysis are presented. and Obsahuje seznam literatury
Fibres, cables, wires and fibres can play an important role in design of many machines. One of the most interesting applications is replacement of chosen rigid elements of a manipulator or a mechanism by cables. The main advantage of this design is the achievement of a lower moving inertia, which leads to a higher mechanism speed, and lower production costs. An inverted pendulum attached and driven by two fibres serves as a typical testing system for the investigation of the fibres properties influence of the system dynamic response. Motion of the pendulum of this nonlinear system is investigated using the alaska simulation tool and an in-house program created in the MATLAB system. Since mass of fibres can influence employed types of fibre models, chosen dynamic quantities (e.g. pendulum angle, vibration amplitude etc.), are investigated in dependence on the excitation frequency for various fibres weights. and Obsahuje seznam literatury
This paper presents the procedure for designing electromagnetic bladed wheel excitation. This procedure comes from phase-synchronization of multiple electromagnets distributed around the wheel with a movement of the blade to obtain its resonant vibration. This procedure can be used with merit for dynamic tests of inter-blade couplings. The verification was performed on the tested wheel using two-point electromagnetic excitation of blades under rotation. and Obsahuje seznam literatury
Eggs of the migratory locust, Locusta migratoria (Orthoptera: Acrididae), hatch synchronously when in a pod, but only sporadically when kept separately. Here, we aimed to detect the vibrational stimuli emitted by eggs that initiate synchronous hatching. First, we recorded the vibrations emitted by an egg pod and single eggs. One bout of vibrations consisted of 2 to 46 vibrations. The total number and amplitude of vibrations in single eggs increased as the time to hatch decreased. Eggs kept separately were continuously subjected during the last 2 days before hatching to recordings of vibrations from a single egg. Recordings made during the last 2.5 h before hatching caused these eggs to hatch significantly earlier than those not subjected to this treatment, the control. In contrast, eggs subjected to recordings made 8 to 10 h before hatching significantly delayed their hatching relative to the controls, which indicates that synchronous hatching of eggs is induced by age-dependent changes in vibrations from neighbouring eggs. Exposure to one large bout of vibrations (consisting of 40 vibrations in 101 s) was sufficient to induce synchronous hatching in eggs kept separately when applied 5 h before hatching, but not 36 or 11.5 h before hatching. Visual inspection of the spectra indicated that the vibrations had two peaks at about 100 Hz and 1.5 kHz. Only exposure to the latter altered the hatching time of eggs. The embryo moved the posterior part of its abdomen when emitting the vibrations. These results indicate that the synchronous hatching of locust eggs is induced when the embryos emit particular vibrations.
This article describes a technique for noise reduction of the differential bearings. Noise is excited by the mechanical looseness of the system and by the vibrations of the engine. The mathematical model enables the optimization of the radial stiffness of the differential bearings. A test rig has been designed for the simulation of the phenomenon outside the vehicle. Analytical software has been created that is capable of classifying the types of noise from the measured data. The optimal solution is tested on the rig at the end, thus proving that the technique works. and Obsahuje seznam literatury
Positive Position Feedback (PPF) is one of the most attractive vibration control method due to its stability and ease of implementation. On the other hand, low robustness makes the PPF design more complicated in multimodal control case. It is known that a little change in optimal parameters setup, especially the change in controller frequency, can strongly degrade the control effort. Thus knowing a good approximation of optimal PPF parameters can be very helpful in practical implementations and simplified analytical relations between optimal parameters and modal properties of the structure are inevitable for efficient control design. In this paper derivation of such relations is introduced, based on simplified transfer function of controlled structure. Furthermore influence of the parallel PPF controllers in multimodal vibration suppression is analyzed and formulae for optimal parameters updating are suggested. Optimal multimodal PPF control design is demonstrated on experimental example of vibration suppression of beam structure. and Obsahuje seznam literatury
Whole-body vibration (WBV) is a new exercise method, with good acceptance among sedentary subjects. The metabolic response to WBV has not been well documented. Three groups of male subjects, inactive (SED), endurance (END) and strength trained (SPRINT) underwent a session of side-alternating WBV composed of three 3-min exercises (isometric half-squat, dynamic squat, dynamic squat with added load), and repeated at three frequencies (20, 26 and 32 Hz). VO2, heart rate and Borg scale were monitored. Twenty-seven healthy young subjects (10 SED, 8 SPRINT and 9 END) were included. When expressed in % of their maximal value recorded in a treadmill test, both the peak oxygen consumption (VO2) and heart rate (HR) attained during WBV were greatest in the SED, compared to the other two groups (VO2: 59.3 % in SED vs 50.8 % in SPRINT and 48.0 % in END, p<0.01; HR 82.7 % in SED vs 80.4 % in SPRINT and 72.4 % in END, p<0.05). In conclusions, the heart rate and metabolic response to WBV differs according to fitness level and type, exercise type and vibration frequency. In SED, WBV can elicit sufficient cardiovascular response to benefit overall fitness and thus be a potentially useful modality for the reduction of cardiovascular risk., B. Gojanovic, F. Feihl, G. Gremion, B. Waeber., and Obsahuje bibliografii