Publications
192 results found
Fontanela F, Grolet A, Salles L, et al., 2019, Computation of quasi-periodic localised vibrations in nonlinear cyclic and symmetric structures using harmonic balance methods, Journal of Sound and Vibration, Vol: 438, Pages: 54-65, ISSN: 0022-460X
In this paper we develop a fully numerical approach to compute quasi-periodic vibrations bifurcating from nonlinear periodic states in cyclic and symmetric structures. The focus is on localised oscillations arising from modulationally unstable travelling waves induced by strong external excitations. The computational strategy is based on the periodic and quasi-periodic harmonic balance methods together with an arc-length continuation scheme. Due to the presence of multiple localised states, a new method to switch from periodic to quasi-periodic states is proposed. The algorithm is applied to two different minimal models for bladed disks vibrating in large amplitudes regimes. In the first case, each sector of the bladed disk is modelled by a single degree of freedom, while in the second application a second degree of freedom is included to account for the disk inertia. In both cases the algorithm has identified and tracked multiple quasi-periodic localised states travelling around the structure in the form of dissipative solitons.
Hartmann M, von Bock RUF, Polach, et al., 2019, NUMERICAL STUDY ON NONLINEAR WAVE-ICE-INTERACTION, 38th ASME International Conference on Ocean, Offshore and Arctic Engineering (OMAE 2019), Publisher: AMER SOC MECHANICAL ENGINEERS, ISSN: 2153-4772
Klein M, Dudek M, Clauss GF, et al., 2019, SYSTEMATIC EXPERIMENTAL VALIDATION OF HIGH-ORDER SPECTRAL METHOD FOR DETERMINISTIC WAVE PREDICTION, 38th ASME International Conference on Ocean, Offshore and Arctic Engineering (OMAE 2019), Publisher: AMER SOC MECHANICAL ENGINEERS, ISSN: 2153-4772
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- Citations: 2
Fontanela F, Grolet A, Salles L, et al., 2019, Solitons in Cyclic and Symmetric Structures, 36th International Modal Analysis Conference and Exposition (IMAC) on Structural Dynamics, Publisher: SPRINGER INTERNATIONAL PUBLISHING AG, Pages: 175-178, ISSN: 2191-5644
Oberst S, Niven RK, Lester DR, et al., 2018, Detection of unstable periodic orbits in mineralising geological systems, CHAOS, Vol: 28, ISSN: 1054-1500
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- Citations: 13
Oberst S, Baetz J, Campbell G, et al., 2018, Vibro-acoustic and nonlinear analysis of cadavric femoral bone impaction in cavity preparations, INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES, Vol: 144, Pages: 739-745, ISSN: 0020-7403
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- Citations: 9
Stender M, Tiedemann M, Hoffmann N, et al., 2018, Impact of an irregular friction formulation on dynamics of a minimal model for brake squeal, MECHANICAL SYSTEMS AND SIGNAL PROCESSING, Vol: 107, Pages: 439-451, ISSN: 0888-3270
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- Citations: 26
Koellisch N, Behrendt J, Klein M, et al., 2018, Nonlinear real time prediction of ocean surface waves, OCEAN ENGINEERING, Vol: 157, Pages: 387-400, ISSN: 0029-8018
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- Citations: 24
Tsitoura F, Gietz U, Chabchoub A, et al., 2018, Phase domain walls in weakly nonlinear deep water surface gravity waves, Physical Review Letters, Vol: 120, ISSN: 0031-9007
We report a theoretical derivation, an experimental observation and a numerical validation of nonlinear phase domain walls in weakly nonlinear deep water surface gravity waves. The domain walls presented are connecting homogeneous zones of weakly nonlinear plane Stokes waves of identical amplitude and wave vector but differences in phase. By exploiting symmetry transformations within the framework of the nonlinear Schrödinger equation we demonstrate the existence of exact analytical solutions representing such domain walls in the weakly nonlinear limit. The walls are in general oblique to the direction of the wave vector and stationary in moving reference frames. Experimental and numerical studies confirm and visualize the findings. Our present results demonstrate that nonlinear domain walls do exist in the weakly nonlinear regime of general systems exhibiting dispersive waves.
Hadjihoseini A, Lind PG, Mori N, et al., 2018, Rogue waves and entropy consumption, EPL, Vol: 120, ISSN: 1286-4854
Based on data from the Sea of Japan and the North Sea the occurrence of rogue waves is analyzed by a scale-dependent stochastic approach, which interlinks fluctuations of waves for different spacings. With this approach we are able to determine a stochastic cascade process, which provides information of the general multipoint statistics. Furthermore the evolution of single trajectories in scale, which characterize wave height fluctuations in the surroundings of a chosen location, can be determined. The explicit knowledge of the stochastic process enables to assign entropy values to all wave events. We show that for these entropies the integral fluctuation theorem, a basic law of non-equilibrium thermodynamics, is valid. This implies that positive and negative entropy events must occur. Extreme events like rogue waves are characterized as negative entropy events. The statistics of these entropy fluctuations changes with the wave state, thus for the Sea of Japan the statistics of the entropies has a more pronounced tail for negative entropy values, indicating a higher probability of rogue waves.
Fontanela F, Grolet A, Salles L, et al., 2018, Dark solitons, modulation instability and breathers in a chain of weakly nonlinear oscillators with cyclic symmetry, JOURNAL OF SOUND AND VIBRATION, Vol: 413, Pages: 467-481, ISSN: 0022-460X
Chabchoub A, Hoffmann N, Akhmediev N, et al., 2018, DRIFTING ROGUE PACKETS, 37th ASME International Conference on Ocean, Offshore and Arctic Engineering, Publisher: AMER SOC MECHANICAL ENGINEERS, ISSN: 2153-4772
Brunetti J, D'Ambrogio W, Hoffmann N, et al., 2018, Investigating the bi-stable behavior of a lumped system with frictional contact, International Conference on Noise and Vibration Engineering (ISMA) / International Conference on Uncertainty in Structural Dynamics (USD), Publisher: KATHOLIEKE UNIV LEUVEN, DEPT WERKTUIGKUNDE, Pages: 2727-2738
Oberst S, Baetz J, Campbell G, et al., 2018, Vibro-acoustic and nonlinear analysis of cadavric femoral bone impaction in cavity preparations, International Conference on Engineering Vibration (ICoEV), Publisher: E D P SCIENCES, ISSN: 2261-236X
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- Citations: 4
Papangelo A, Hoffmann N, Grolet A, et al., 2017, Multiple spatially localized dynamical states in friction-excited oscillator chains, Journal of Sound and Vibration, Vol: 417, Pages: 56-64, ISSN: 0022-460X
Friction-induced vibrations are known to affect many engineering applications. Here, we study a chain of friction-excited oscillators with nearest neighbor elastic coupling. The excitation is provided by a moving belt which moves at a certain velocity v d while friction is modelled with an exponentially decaying friction law. It is shown that in a certain range of driving velocities, multiple stable spatially localized solutions exist whose dynamical behavior ( i.e. regular or irregular) depends on the number of oscillators involved in the vibration. The classical non-repeatability of friction-induced vibration problems can be interpreted in light of those multiple stable dynamical states. These states are found within a “snaking-like” bifurcation pattern. Contrary to the classical Anderson localization phenomenon, here the underlying linear system is perfectly homogeneous and localization is solely triggered by the friction nonlinearity.
Papangelo A, Ciavarella M, Hoffmann N, 2017, Subcritical bifurcation in a self-excited single-degree-of-freedom system with velocity weakening-strengthening friction law: analytical results and comparison with experiments, Nonlinear Dynamics, Vol: 90, Pages: 2037-2046, ISSN: 0924-090X
The dynamical behavior of a single-degree-of-freedom system that experiences friction-induced vibrations is studied with particular interest on the possibility of the so-called hard effect of a subcritical Hopf bifurcation, using a velocity weakening–strengthening friction law. The bifurcation diagram of the system is numerically evaluated using as bifurcation parameter the velocity of the belt. Analytical results are provided using standard linear stability analysis and nonlinear stability analysis to large perturbations. The former permits to identify the lowest belt velocity (vlw) at which the full sliding solution is stable, the latter allows to estimate a priori the highest belt velocity at which large amplitude stick–slip vibrations exist. Together the two boundaries [vlw,vup] define the range where two equilibrium solutions coexist, i.e., a stable full sliding solution and a stable stick–slip limit cycle. The model is used to fit recent experimental observations.
Oberst S, Marburg S, Hoffmann N, 2017, Determining periodic orbits via nonlinear filtering and recurrence spectra in the presence of noise, X International Conference on Structural Dynamics, EURODYN 2017, Publisher: Elsevier, Pages: 772-777, ISSN: 1877-7058
Published by Elsevier Ltd. In nonlinear dynamical systems the determination of stable and unstable periodic orbits as part of phase space prediction is problematic in particular if perturbed by noise. Fourier spectra of the time series or its autocorrelation function have shown to be of little use if the dynamic process is not strictly wide-sense stationary or if it is nonlinear. To locate unstable periodic orbits of a chaotic attractor in phase space the least stable eigenvalue can be determined by approximating locally the trajectory via linearisation. This approximation can be achieved by employing a Gaussian kernel estimator and minimising the summed up distances of the measured time series i.e. its estimated trajectory (e.g. via Levenberg-Marquardt). Noise poses a significant problem here. The application of the Wiener-Khinchin theorem to the time series in combination with recurrence plots, i.e. the Fourier transform of the recurrence times or rates, has been shown capable of detecting higher order dynamics (period-2 or period-3 orbits), which can fail using classical FouRiER-based methods. However little is known about its parameter sensitivity, e.g. with respect to the time delay, the embedding dimension or perturbations. Here we provide preliminary results on the application of the recurrence time spectrum by analysing the Hénon and the Rössler attractor. Results indicate that the combination of recurrence time spectra with a nonlinearly filtered plot of return times is able to estimate the unstable periodic orbits. Owing to the use of recurrence plot based measures the analysis is more robust against noise than the conventional Fourier transform.
Papangelo A, Hoffmann N, Ciavarella M, 2017, Load-separation curves for the contact of self-affine rough surfaces., Scientific Reports, Vol: 7, ISSN: 2045-2322
There are two main approximate theories in the contact of rough solids: Greenwood-Williamson asperity theories (GW) and Persson theories. Neither of them has been fully assessed so far with respect to load-separation curves. Focusing on the most important case of low fractal dimension (D f = 2.2) with extensive numerical studies we find that: (i) Persson's theory describes well the regime of intermediate pressures/contact area, but requires significant corrective factors: the latter depend also on upper wavevector cutoff of the roughness; hence, (ii) Persson's theory does not predict the correct functional dependence on magnification; (iii) asperity theories in the discrete version even neglecting interaction effects are more appropriate in the range of relatively large separations, also to take into consideration of the large scatter in actual realization of the surface.
Salles L, Staples B, Hoffmann N, et al., 2016, Continuation techniques for analysis of whole aeroengine dynamics with imperfect bifurcations and isolated solutions, Nonlinear Dynamics, Vol: 86, Pages: 1897-1911, ISSN: 0924-090X
The analysis of whole engine rotordynamic models is an important element in the design of aerojet engines. The models include gyroscopic effects and allow for rubbing contact between rotor and stator components such as bladed discs and casing. Due to the nonlinearities inherent to the system, bifurcations in the frequency response may arise. Reliable and efficient methods to determine the bifurcation points and solution branches are required. For this purpose, a multi-harmonic balance approach is presented that allows a numerically efficient detection of bifurcation points and the calculation of both continuous and isolated branches of the frequency response functions. The method is applied to a test case derived from a commercial aeroengine. A bifurcation structure with continuous and isolated solution branches is observed and studied in this paper. The comparison with time marching based on simulations shows both accuracy and numerical efficiency of the newly developed approach.
Oberst S, Zhang Z, Campbell G, et al., 2016, Towards the understanding of hip squeak in total hip arthroplasty using analytical contact models with uncertainty, INTER-NOISE 2016, Pages: 5539-5549
© 2016, German Acoustical Society (DEGA). All rights reserved. Osteoarthritis in hip joints affects patients' quality of life such that often only costly orthopaedic surgeries i.e. total hip arthroplasty (THA) provide relief. Common implant materials are metal alloys, steel or titanium-based, plastics such as ultra-high molecular weight polyethylene, or biocompatible alumina and composite ceramics. Hard-on-hard (HoH) bearing articulations, i.e. ceramic-on-ceramic, or hard-on-soft combinations are used. HoH implants have been known to suffer from squeaking, a phenomenon commonly encountered in friction-induced self-excited vibrations. However, the frictional contact mechanics, its dynamics related to impingement, the effect of socket position, stem configuration, bearing size and patient characteristics are poorly understood. This study gives an overview of the state of the art biomechanical research related to squeaking in THA, with a focus on the effects of friction, stability, related wear and lubrication. An analytical model is proposed to study the onset of friction-induced vibrations in a simplified hemispherical hip stem rubbing in its bearing by varying the contact area. Preliminary results of the complex eigenvalue analysis and stick-slip motion analysis indicate that an increased contact fosters the development of instabilities, even at very small values of the friction coefficient owing to large local contact pressures.
Papangelo A, Grolet A, Salles L, et al., 2016, Snaking bifurcations in a self-excited oscillator chain with cyclic symmetry, Communications in Nonlinear Science and Numerical Simulation, Vol: 44, Pages: 108-119, ISSN: 1007-5704
Snaking bifurcations in a chain of mechanical oscillators are studied. The individual oscillators are weakly nonlinear and subject to self-excitation and subcritical Hopf-bifurcations with some parameter ranges yielding bistability. When the oscillators are coupled to their neighbours, snaking bifurcations result, corresponding to localised vibration states. The snaking patterns do seem to be more complex than in previously studied continuous systems, comprising a plethora of isolated branches and also a large number of similar but not identical states, originating from the weak coupling of the phases of the individual oscillators.
Salles L, Staples B, Hoffmann NP, et al., 2016, Nonlinear dynamic analysis of whole aeroengine models with harmonic balance method and continuation techniques for imperfect bifurcations and isolated solutions., Nonlinear Dynamics, ISSN: 1573-269X
The analysis of whole engine rotor-dynamic models is an important element in the design of aerojetengines. The models include gyroscopic effects and allow for rubbing contact between rotor and statorcomponents such as bladed discs and casing. Due to the non-linearities inherent to the system, bifurcationsin the frequency response may arise. Reliable and efficient methods to determine the bifurcation pointsand solution branches are required. For this purpose a multi-harmonic balance approach is presented thatallows a numerically efficient detection of bifurcation points and the calculation of both continuous andisolated branches of the frequency response functions. The method is applied to a test-case derived from acommercial aero-engine. A bifurcation structure with continuous and isolated solution branches is observedand studied in this paper. The comparison with time-marching based on simulations shows both accuracyand numerical efficiency of the newly developed approach
Grolet A, Hoffmann N, Thouverez F, et al., 2016, Travelling and standing envelope solitons in discrete non-linear cyclic structures, Mechanical Systems and Signal Processing, Vol: 81, Pages: 75-87, ISSN: 0888-3270
Envelope solitons are demonstrated to exist in non-linear discrete structures with cyclic symmetry. The analysis is based on the Non-Linear Schrodinger Equation for the weakly non-linear limit, and on numerical simulation of the fully non-linear equations for larger amplitudes. Envelope solitons exist for parameters in which the wave equation is focussing and they have the form of shape-conserving wave packages propagating roughly with group velocity. For the limit of maximum wave number, where the group velocity vanishes, standing wave packages result and can be linked via a bifurcation to the non-localised non-linear normal modes. Numerical applications are carried out on a simple discrete system with cyclic symmetry which can be seen as a reduced model of a bladed disk as found in turbo-machinery.
Hadjihosseini A, Wächter M, Hoffmann NP, et al., 2016, Capturing rogue waves by multi-point statistics, New Journal of Physics, Vol: 18, ISSN: 1367-2630
As an example of a complex system with extreme events, we investigate ocean wave states exhibiting rogue waves. We present a statistical method of data analysis based on multi-point statistics which for the first time allows the grasping of extreme rogue wave events in a highly satisfactory statistical manner. The key to the success of the approach is mapping the complexity of multi-point data onto the statistics of hierarchically ordered height increments for different time scales, for which we can show that a stochastic cascade process with Markov properties is governed by a Fokker–Planck equation. Conditional probabilities as well as the Fokker–Planck equation itself can be estimated directly from the available observational data. With this stochastic description surrogate data sets can in turn be generated, which makes it possible to work out arbitrary statistical features of the complex sea state in general, and extreme rogue wave events in particular. The results also open up new perspectives for forecasting the occurrence probability of extreme rogue wave events, and even for forecasting the occurrence of individual rogue waves based on precursory dynamics.
Kruse S, Tiedemann M, Zeumer B, et al., 2015, The influence of joints on friction induced vibration in brake squeal (vol 340, pg 239, 2014), JOURNAL OF SOUND AND VIBRATION, Vol: 351, Pages: 311-312, ISSN: 0022-460X
Grolet A, Hoffmann NP, Schwingshackl C, 2015, Solitons in Non-Linear Cyclic Systems, Euromech Colloquium 573: Coupling and Nonlinear Interactions in Rotating Machinery
Tiedemann M, Kruse S, Hoffmann N, 2015, Dominant damping effects in friction brake noise, vibration and harshness: the relevance of joints, PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART D-JOURNAL OF AUTOMOBILE ENGINEERING, Vol: 229, Pages: 728-734, ISSN: 0954-4070
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- Citations: 11
Kruse S, Tiedemann M, Zeumer B, et al., 2015, The influence of joints on friction induced vibration in brake squeal, JOURNAL OF SOUND AND VIBRATION, Vol: 340, Pages: 239-252, ISSN: 0022-460X
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- Citations: 48
Akhmediev N, Soto-Crespo JM, Devine N, et al., 2015, Rogue wave spectra of the Sasa-Satsuma equation, PHYSICA D-NONLINEAR PHENOMENA, Vol: 294, Pages: 37-42, ISSN: 0167-2789
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- Citations: 38
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