TY - JOUR AU - Beregi, Sándor AU - Barton, David A. W. AU - Rezgui, Djamel AU - Neild, Simon TI - Using scientific machine learning for experimental bifurcation analysis of dynamic systems JF - MECHANICAL SYSTEMS AND SIGNAL PROCESSING J2 - MECH SYST SIGNAL PR VL - 184 PY - 2023 PG - 16 SN - 0888-3270 DO - 10.1016/j.ymssp.2022.109649 UR - https://m2.mtmt.hu/api/publication/33432672 ID - 33432672 AB - Augmenting mechanistic ordinary differential equation (ODE) models with machine-learnable structures is a novel approach to create highly accurate, low-dimensional models of engineering systems incorporating both expert knowledge and reality through measurement data. Our exploratory study focuses on training universal differential equation (UDE) models for physical nonlinear dynamical systems with limit cycles: an aerofoil undergoing flutter oscillations and an electrodynamic nonlinear oscillator. We consider examples where training data is generated by numerical simulations, whereas we also employ the proposed modelling concept to physical experiments allowing us to investigate problems with a wide range of complexity. To collect the training data, the method of control-based continuation is used as it captures not just the stable but also the unstable limit cycles of the observed system. This feature makes it possible to extract more information about the observed system than the open-loop approach (surveying the steady state response by parameter sweeps without using control) would allow. We use both neural networks and Gaussian processes as universal approximators alongside the mechanistic models to give a critical assessment of the accuracy and robustness of the UDE modelling approach. We also highlight the potential issues one may run into during the training procedure indicating the limits of the current modelling framework. LA - English DB - MTMT ER - TY - JOUR AU - Horváth, Hanna Zsófia AU - Takács, Dénes TI - Stability and local bifurcation analyses of two-wheeled trailers considering the nonlinear coupling between lateral and vertical motions JF - NONLINEAR DYNAMICS J2 - NONLINEAR DYNAM VL - 107 PY - 2022 SP - 2115 EP - 2132 PG - 18 SN - 0924-090X DO - 10.1007/s11071-021-07120-9 UR - https://m2.mtmt.hu/api/publication/32572363 ID - 32572363 N1 - Export Date: 29 April 2022 CODEN: NODYE Correspondence Address: Horvath, H.Z.; Department of Applied Mechanics, Hungary; email: hanna.horvath@mm.bme.hu AB - The nonlinear dynamics of two-wheeled trailers is investigated using a spatial 4-DoF mechanical model. The non-smooth characteristics of the tire forces caused by the detachment of the tires from the ground and other geometrical nonlinearities are taken into account. Beyond the linear stability analysis, the nonlinear vibrations are analyzed with special attention to the nonlinear coupling between the vertical and lateral motions of the trailer. The center manifold reduction is performed leading to a normal form up to third degree terms. The nature of the emerging periodic solutions, and, thus, the sense of the Hopf bifurcations are verified semi-analytically and numerically. Simplified models of the trailer are also used in order to point out the practical relevance of the study. It is shown that the linearly independent pitch motion affects the sense of the Hopf bifurcations at the linear stability boundary. Namely, the constructed spatial trailer model provides subcritical bifurcations for higher center of gravity positions, while the commonly used simplified mechanical models explore the less dangerous supercritical bifurcations only. Domains of loss of contact of tires are also detected and shown in the stability charts highlighting the presence of unsafe zones. Experiments are carried out on a small-scale trailer to validate the theoretical results. A good agreement can be observed between the measured and numerically determined critical speeds and vibration amplitudes. LA - English DB - MTMT ER - TY - JOUR AU - Beregi, Sándor AU - Takács, Dénes AU - Stépán, Gábor TI - Bifurcation analysis of wheel shimmy with non-smooth effects and time delay in the tyre–ground contact JF - NONLINEAR DYNAMICS J2 - NONLINEAR DYNAM VL - 98 PY - 2019 IS - 1 SP - 841 EP - 858 PG - 18 SN - 0924-090X DO - 10.1007/s11071-019-05123-1 UR - https://m2.mtmt.hu/api/publication/30840377 ID - 30840377 N1 - Funding Agency and Grant Number: National Research, Development and Innovation Office [NKFI-128422] Funding text: This research was funded by the National Research, Development and Innovation Office under Grant No. NKFI-128422. Export Date: 28 November 2019 CODEN: NODYE LA - English DB - MTMT ER - TY - JOUR AU - Beregi, Sándor AU - Takács, Dénes AU - Gyebrószki, Gergely AU - Stépán, Gábor TI - Theoretical and experimental study on the nonlinear dynamics of wheel-shimmy JF - NONLINEAR DYNAMICS J2 - NONLINEAR DYNAM VL - 4 PY - 2019 SP - 2581 EP - 2593 PG - 13 SN - 0924-090X DO - 10.1007/s11071-019-05225-w UR - https://m2.mtmt.hu/api/publication/30893747 ID - 30893747 LA - English DB - MTMT ER - TY - JOUR AU - Beregi, Sándor AU - Takács, Dénes AU - Stépán, Gábor TI - Tyre induced vibrations of the car-trailer system JF - JOURNAL OF SOUND AND VIBRATION J2 - J SOUND VIB VL - 362 PY - 2016 SP - 214 EP - 227 PG - 14 SN - 0022-460X DO - 10.1016/j.jsv.2015.09.015 UR - https://m2.mtmt.hu/api/publication/2991438 ID - 2991438 LA - English DB - MTMT ER - TY - JOUR AU - Takács, Dénes AU - Stépán, Gábor TI - Micro-shimmy of towed structures in experimentally uncharted unstable parameter domain JF - VEHICLE SYSTEM DYNAMICS J2 - VEHICLE SYST DYN VL - 50 PY - 2012 IS - 11 SP - 1613 EP - 1630 PG - 18 SN - 0042-3114 DO - 10.1080/00423114.2012.691522 UR - https://m2.mtmt.hu/api/publication/2187047 ID - 2187047 AB - In this paper, the lateral instability of towed structures (trailers, caravans and articulated buses) is investigated with special attention to the small amplitude lateral vibration that leads to a higher energy consumption in certain parameter domains. A low degree-of-freedom mechanical model of a shimmying towed tyre is used that describes the dynamics of the tyre-ground contact patch by the time delayed differential equation. Stability charts are calculated and the theoretically predicted linear unstable islands of small amplitude shimmy motions are validated by laboratory experiments. A tyre is towed by a relatively long caster, and its temperature and the input current of the conveyor belt are measured in order to show the increased value of the rolling resistance. LA - English DB - MTMT ER - TY - JOUR AU - Takács, Dénes AU - Orosz, Gábor AU - Stépán, Gábor TI - Delay effects in shimmy dynamics of wheels with stretched string-like tyres JF - EUROPEAN JOURNAL OF MECHANICS A-SOLIDS J2 - EUR J MECH A-SOLID VL - 28 PY - 2009 SP - 516 EP - 525 PG - 10 SN - 0997-7538 DO - 10.1016/j.euromechsol.2008.11.007 UR - https://m2.mtmt.hu/api/publication/1234370 ID - 1234370 LA - English DB - MTMT ER - TY - JOUR AU - Stépán, Gábor TI - Chaotic motion of wheels JF - VEHICLE SYSTEM DYNAMICS J2 - VEHICLE SYST DYN VL - 20 PY - 1991 IS - 6 SP - 341 EP - 351 PG - 11 SN - 0042-3114 DO - 10.1080/00423119108968994 UR - https://m2.mtmt.hu/api/publication/106066 ID - 106066 AB - Trolleys have wheels which can choose the direction of their rolling. Studying the motion of a wheel like this, we can often find periodic motions ('shimmy') or even chaotic ones. It has also been experienced that the chaotic motions sometimes disappear quite unexpectedly. A strongly simplified model of these systems is analysed in the paper by means of the methods of bifurcation theory. Analytical and numerical results are shown to characterize the system, including simulation results. Similar behaviour can be found in more complicated systems as well, like the trailers or the nosegears of aeroplanes. The development of the so-called transient chaotic motion is explained in these systems. LA - English DB - MTMT ER -