Papers by Juraj Úradníček
Applied Sciences, 2021
The connection of two phenomena, nonconservative friction forces and dissipation-induced instabil... more The connection of two phenomena, nonconservative friction forces and dissipation-induced instability, can lead to many interesting engineering problems. We study the general material-dependent damping influence on the dynamic instability of disc brake systems leading to brake squeal. The effect of general damping is demonstrated on minimal and complex models of a disc brake. Experimental analyses through the frequency response function (FRF) show different damping of the brake system coalescent modes, indicating possible dissipation-induced instability. A complex system including material-dependent damping is defined in commercial finite element (FE) software. A FE model validated by experimental data on the brake-disc test bench is used to compute the influence of a pad and disc damping variations on the system stability using complexe igenvalue analysis (CEVA). Numerical analyses show a significant sensitivity of the experimentally verified unstable mode of the system to the ratio...
Acta Polytechnica, 2020
This paper deals with the evaluation of eigenvalues of a linear damped elastic two-degrees-of-fre... more This paper deals with the evaluation of eigenvalues of a linear damped elastic two-degrees-of-freedom system under a non- onservative loading. As a physical interpretation of a proposed mathematical model, a simplified disk brake model is considered. A spectral analysis is performed to predict an eigenvalues bifurcation, known as the Krein collision, leading to double eigenvalues, one of them having a positive real part causing a vibration instability of the mechanical systems. This defective behaviour of eigenvalues is studied with respect to a magnitude of non-conservative Coulomb friction force, through the variation of the friction coefficient. The influence of a proportional versus general damping on the system stability is further analysed. The generalized non-symmetric eigenvalue problem calculation is employed for spectral analyses, while a modal decomposition is performed to obtain a time-domain response of the system. The analyses are compared with an experiment.
The reduction of railway wagons´ vibration must be taken into account during a wagon design using... more The reduction of railway wagons´ vibration must be taken into account during a wagon design using appropriate vibro-isolation in order to reduce the transmission of structural noise from its main source. The paper analyses the vibration transmission, procedures and vibro-acoustic conditions with a view to reducing this vibration generated between the wagon wheel, as a main source of vibro-sound energy, and the tank body when applying a suitable vibro-isolation. The modal analysis of the tank wagon was complemented by the analysis of gravitational impact of the wheel on the rail generating its vibration. The transmission of the wheel components´ vibration from the wheel through the primary suspension, and the placement of the tank through the sliders and the ball joint into the tank body, is investigated. The solution is also based on the theoretical analysis and methodology of transmission of vibration energy, as well as on the measurement of vibration at the entry and exit measurement points of the main components of the wagon chassis. FFT and modal analysis were used to obtain the vibration parameters. Finally, this article aims at proposing some effective measures that may contribute to reducing the unwanted transmission of structural noise and thus decreasing both the noise emission and immission which have a negative impact on the environment and human health.
The paper deals with the study of a possible dissipation induced instability in a disc brake syst... more The paper deals with the study of a possible dissipation induced instability in a disc brake system, which leads to a self-excited vibration and thus to a brake squeal. The work describes an experimental estimation of the damping properties of a disc component of the simplified disc brake system. The stability of the system is analyzed numerically using the Finite Element approach and the Complex eigenvalue analysis. From the evolution of real parts of the eigenvalues with friction, the friction threshold value destabilizing the system is defined for the undamped and non-proportionally damped system. From the results, it can be seen how the damping non-proportionality can lead to the dissipation-induced instability of the disc brake system.
Traveling Waves in Non-conservative Mechanical Systems - Disk Brake Application
Brake squeal avoidance by adding a small mass on the right place
Assessment of Dissipation Induced Instability of Simplified Disc Brake System
Brake squeal - Traveling wave in simplified disc brake model calculated using Explicit Dynamics solver
Engineering Mechanics 2020
Undesirable levels of vibration are an especially common occurrence in modern engineering. Being ... more Undesirable levels of vibration are an especially common occurrence in modern engineering. Being able to effectively isolate and solve the problem areas of a structure would prove to be a valuable tool in correcting these levels of vibration. This work presents a method for modal synthesis that enables the structural properties to be purposefully changed and that can be applied to systems with nonproportional damping. In order to present the methodology in detail, the case where additional elements are made of aluminium foam are presented. These have very unique properties and broad applications. This methodology is demonstrated, for better understanding, on an example of a beam with added aluminium foam elements. A beam with aluminium foam was chosen since its connection with the base beam changes the inertial as well as stiffness and damping properties of the resulting system.
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Papers by Juraj Úradníček