Publications
131 results found
Armand J, Salles L, Schwingshackl CW, et al., 2018, On the effects of roughness on the nonlinear dynamics of a bolted joint: a multiscale analysis, European Journal of Mechanics - A/Solids, Vol: 70, Pages: 44-57, ISSN: 0997-7538
Accurate prediction of the vibration response of friction joints is of great importance when estimating both the performance and the life of build-up structures. The contact conditions at the joint interface, including local normal load distribution and contact stiffness, play a critical role in the nonlinear dynamic response. These parameters strongly depend on the mating surfaces, where the surface roughness is well known to have a significant impact on the contact conditions in the static case. In contrast, its effects on the global and local nonlinear dynamic response of a build-up structure is not as well understood due to the complexity of the involved mechanisms. To obtain a better understanding of the dependence of the nonlinear dynamic response on surface roughness, a newly proposed multiscale approach has been developed. It links the surface roughness to the contact pressure and contact stiffness, and in combination with a multiharmonic balance solver, allows to compute the nonlinear dynamic response for different interface roughness. An application of the technique to a single bolted lap joint highlighted a strong impact of larger roughness values on the pressure distribution and local contact stiffness and in turn on the nonlinear dynamic response.
Kreider M, Schwingshackl CW, 2018, Experimental evaluation of pressure dependent tangential contact stiffness, Pages: 1385-1393
The modelling of nonlinear dynamic behaviour of interfaces is of great interest, with one of the main challenges being the provision of reliable friction interface parameters. One of these parameters is the tangential contact stiffness which represents the in-plane compliance at the interface. It is traditionally assumed to be constant, but recent findings in the literature indicate a dependence of the tangential contact stiffness on the normal load. To investigate this behaviour in detail, the 1D friction rig at Imperial College London was fitted with a High-Speed Camera and Digital Image Correlation system to initially validate its accuracy and then investigate the relationship between tangential contact stiffness and contact pressure. A strong increase of contact stiffness at low contact pressure was observed, followed by a saturation of the contact stiffness at higher values. An increase in contact stiffness due to wear was also present, indicating that current modelling approaches may need to be refined.
Tatar A, Schwingshackl CW, 2018, EFFECT OF A PLANETARY GEARBOX ON THE DYNAMICS OF A ROTOR SYSTEM, ASME Turbo Expo: Turbomachinery Technical Conference and Exposition, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 573-583
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- Citations: 4
Heller D, Sever I, Schwingshackl CW, 2018, VIBRATION ANALYSIS FROM SIMULATED TIP TIMING SENSOR SIGNAL SHAPE MODULATION, ASME Turbo Expo: Turbomachinery Technical Conference and Exposition, Publisher: AMER SOC MECHANICAL ENGINEERS
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- Citations: 5
Pesaresi L, Armand J, Schwingshackl CW, et al., 2017, An advanced underplatform damper modelling approach based on a microslip contact model, 17th International Symposium on Transport Phenomena and Dynamics of Rotating Machinery
High-cycle fatigue caused by large resonance stresses remains one of the most common causes of turbine blades failures. Friction dampers are one of the most effective and practical solutions to limit the vibration amplitude, and shift the resonance frequencies of the turbine assemblies far from operating speeds. However, predicting with good accuracy the effects of underplatform dampers on the blades dynamics, still represents a major challenge today, due to the complex nature of the nonlinear forces at the interface, characterised by transitions between stick, slip, and separation conditions. The most common modelling approaches developed recently are based on the explicit FE model for the damper, and on a dense grid of 3D contact elements comprised of Jenkins elements, or on a single 2D microslip element on each surface. In this paper, a combination of the two approaches is proposed. A 3D microslip element, based on a modified Valanis model is proposed and a series of these elements are used to describe the contact interface. The proposed model and its predicting capabilities are then evaluated against a simplified blade-damper model, based on an underplatform damper test rig recently developed by the authors. A comparison with a more simplistic modelling approach based on macroslip contact elements, highlights the improved accuracy of the new model to predict the experimental nonlinear response.
Brake MRW, Groß J, Lacayo RM, et al., 2017, Reduced order modeling of nonlinear structures with frictional interfaces, The Mechanics of Jointed Structures: Recent Research and Open Challenges for Developing Predictive Models for Structural Dynamics, Pages: 427-450, ISBN: 9783319568164
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- Citations: 11
Smith SA, Catalfamo S, Bilbao-Ludena JC, et al., 2017, Considerations for measurements of jointed structures, The Mechanics of Jointed Structures: Recent Research and Open Challenges for Developing Predictive Models for Structural Dynamics, Pages: 109-133, ISBN: 9783319568164
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- Citations: 1
Pesaresi L, Stender M, Ruffini V, et al., 2017, DIC measurement of the kinematics of a friction damper for turbine applications, 35th IMAC Conference and Exposition on Structural Dynamics, Publisher: Springer, Pages: 93-101, ISSN: 2191-5644
High cycle fatigue (HCF) caused by large resonant stresses is a common cause for turbine blades failure. Passive damping systems, such as friction dampers are often used by aero-engine manufacturers to reduce the resonant stresses and mitigate the risk of HCF. The presence of friction dampers makes the dynamics of the system highly nonlinear, due to the complex stick-slip and separation phenomena taking place at the contact interface. Due to this nonlinear behaviour, an accurate understanding of the operating deflection shapes is needed for an accurate stress prediction.In this study, digital image correlation (DIC) in combination with a high speed camera is used to provide insights into the kinematics of the damper in a recently developed test rig. The in-phase and out-of-phase first bending modes of the blades were investigated leading to a full field measurement of the global ODS of the blades, and the local motion of the damper against its platforms. A significant change in the blades operational deflection shape could be observed due to the damper, and the sliding and rolling motion of the damper during a vibration cycle was accurately visualised.
Panunzio AM, Salles L, Schwingshackl CW, 2017, Uncertainty propagation for nonlinear vibrations: a non-intrusive approach, Journal of Sound and Vibration, Vol: 389, Pages: 309-325, ISSN: 0022-460X
The propagation of uncertain input parameters in a linear dynamic analysis is reasonably well established today, but with the focus of the dynamic analysis shifting towards nonlinear systems, new approaches is required to compute the uncertain nonlinear responses.A combination of stochastic methods (Polynomial Chaos Expansion, PCE) with an Asymptotic Numerical Method (ANM) for the solution of the nonlinear dynamic systems is presented to predict the propagation of random input uncertainties and assess their influence on the nonlinear vibrational behaviour of a system. The proposed method allows the computation of stochastic resonance frequencies and peak amplitudes based on multiple input uncertainties, leading to a series of uncertain nonlinear dynamic responses. One of the main challenges when using the PCE is thereby the Gibbs phenomenon, which can heavily impact the resulting stochastic nonlinear response by introducing spurious oscillations. A novel technique to avoid the Gibbs phenomenon is be presented in this paper, leading to high quality frequency response predictions.A comparison of the proposed stochastic nonlinear analysis technique to traditional Monte Carlo simulations, demonstrates comparable accuracy at a significantly reduced computational cost, thereby validating the proposed approach.
Pesaresi L, Salles L, Jones A, et al., 2017, Modelling the nonlinear behaviour of an underplatform damper test rig for turbine applications, Mechanical Systems and Signal Processing, Vol: 85, Pages: 662-679, ISSN: 1096-1216
Underplatform dampers (UPD) are commonly used in aircraft engines to mitigate the risk of high-cycle fatiguefailure of turbine blades. The energy dissipated at the friction contact interface of the damper reduces the vibrationamplitude significantly, and the couplings of the blades can also lead to significant shifts of the resonance frequenciesof the bladed disk. The highly nonlinear behaviour of bladed disks constrained by UPDs requires an advancedmodelling approach to ensure that the correct damper geometry is selected during the design of the turbine, and thatno unexpected resonance frequencies and amplitudes will occur in operation. Approaches based on an explicit modelof the damper in combination with multi-harmonic balance solvers have emerged as a promising way to predict thenonlinear behaviour of UPDs correctly, however rigorous experimental validations are required before approaches ofthis type can be used with confidence.In this study, a nonlinear analysis based on an updated explicit damper model having different levels of detail isperformed, and the results are evaluated against a newly-developed UPD test rig. Detailed linear finite element modelsare used as input for the nonlinear analysis, allowing the inclusion of damper flexibility and inertia effects. The nonlinearfriction interface between the blades and the damper is described with a dense grid of 3D friction contact elementswhich allow accurate capturing of the underlying nonlinear mechanism that drives the global nonlinear behaviour. Theintroduced explicit damper model showed a great dependence on the correct contact pressure distribution. The use ofan accurate, measurement based, distribution, better matched the nonlinear dynamic behaviour of the test rig. Goodagreement with the measured frequency response data could only be reached when the zero harmonic term (constantterm) was included in the multi-harmonic expansion of the nonlinear problem, highlighting its importance when thecontact inter
Ondra V, Sever IA, Schwingshackl CW, 2017, A method for detection and characterisation of structural non-linearities using the Hilbert transform and neural networks, Mechanical Systems and Signal Processing, Vol: 83, Pages: 210-227, ISSN: 0888-3270
This paper presents a method for detection and characterization of structural non-linearities from a single frequency response function using the Hilbert transform in the frequency domain and arti cial neural networks. A frequency response function is described based on its Hilbert transform using several common and newly introduced scalar parameters, termed non-linearity indexes, to create training data of the artificial neural network. This network is subsequently used to detect the existence of non-linearity and classify its type. The theoretical background of the method is given and its usage is demonstrated on di erent numerical test cases created by single degree of freedom non-linear systems and a lumped parameter multi degreeof freedom system with a geometric non-linearity. The method is also applied to several experimentally measured frequency response functions obtained from a cantilever beam with a clearance non-linearity and an under-platform damper experimental rig with a complex friction contact interface. It is shown that the method is a fast and noise-robust means of detecting and characterizing non-linear behaviour from a single frequency response function.
Pesaresi L, Armand J, Schwingshackl CW, et al., 2017, An advanced underplatform damper modelling approach based on a microslip contact model
High-cycle fatigue caused by large resonance stresses remains one of the most common causes of turbine blades failures. Friction dampers are one of the most effective and practical solutions to limit the vibration amplitude, and shift the resonance frequencies of the turbine assemblies far from operating speeds. However, predicting with good accuracy the effects of underplatform dampers on the blades dynamics, still represents a major challenge today, due to the complex nature of the nonlinear forces at the interface, characterised by transitions between stick, slip, and separation conditions. The most common modelling approaches developed recently are based on the explicit FE model for the damper, and on a dense grid of 3D contact elements comprised of Jenkins elements, or on a single 2D microslip element on each surface. In this paper, a combination of the two approaches is proposed. A 3D microslip element, based on a modified Valanis model is proposed and a series of these elements are used to describe the contact interface. The proposed model and its predicting capabilities are then evaluated against a simplified blade-damper model, based on an underplatform damper test rig recently developed by the authors. A comparison with a more simplistic modelling approach based on macroslip contact elements, highlights the improved accuracy of the new model to predict the experimental nonlinear response.
Ondra V, Sever IA, Schwingshackl CW, 2017, NON-PARAMETRIC IDENTIFICATION OF ASYMMETRIC SIGNALS AND CHARACTERIZATION OF A CLASS OF NON-LINEAR SYSTEMS BASED ON FREQUENCY MODULATION, ASME International Mechanical Engineering Congress and Exposition (IMECE2016), Publisher: AMER SOC MECHANICAL ENGINEERS
Ondra V, Riethmueller R, Brake MRW, et al., 2017, Comparison of Nonlinear System Identification Methods for Free Decay Measurements with Application to MEMS Devices, 35th IMAC Conference and Exposition on Structural Dynamics, Publisher: SPRINGER, Pages: 29-46, ISSN: 2191-5644
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- Citations: 4
Schwingshackl CW, 2017, Identification Reassembly Uncertainties for a Basic Lap Joint, 35th IMAC Conference and Exposition on Structural Dynamics, Publisher: SPRINGER INTERNATIONAL PUBLISHING AG, Pages: 53-61, ISSN: 2191-5644
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- Citations: 3
Smith S, Bilbao-Ludena JC, Catalfamo S, et al., 2017, The Effects of Boundary Conditions, Measurement Techniques, and Excitation Type on Measurements of the Properties of Mechanical Joints, 33rd IMAC Conference and Exposition on Structural Dynamics, Publisher: SPRINGER INTERNATIONAL PUBLISHING AG, Pages: 415-431, ISSN: 2191-5644
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- Citations: 13
Dossogne T, Jerome TW, Lancereau DPT, et al., 2017, Experimental Assessment of the Influence of Interface Geometries on Structural Dynamic Response, 35th IMAC Conference and Exposition on Structural Dynamics, Publisher: SPRINGER INTERNATIONAL PUBLISHING AG, Pages: 255-261, ISSN: 2191-5644
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- Citations: 17
Ruffini V, Nauman T, Schwingshackl CW, 2017, Impulse Excitation of Piezoelectric Patch Actuators for Modal Analysis, 35th IMAC Conference and Exposition on Structural Dynamics, Publisher: SPRINGER, Pages: 97-106, ISSN: 2191-5644
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- Citations: 3
Ondra V, Sever IA, Schwingshackl CW, 2017, Non-linear System Identification Using the Hilbert-Huang Transform and Complex Non-linear Modal Analysis, 35th IMAC Conference and Exposition on Structural Dynamics, Publisher: SPRINGER INTERNATIONAL PUBLISHING AG, Pages: 77-86, ISSN: 2191-5644
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- Citations: 3
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.
Armand J, Pesaresi L, Salles L, et al., 2016, A Multiscale Approach for Nonlinear Dynamic Response Predictions With Fretting Wear, JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER-TRANSACTIONS OF THE ASME, Vol: 139, ISSN: 0742-4795
Armand J, Pesaresi L, Salles L, et al., 2016, A multi-scale approach for nonlinear dynamic response predictions with fretting wear, Journal of Engineering for Gas Turbines and Power, Vol: 139, ISSN: 0742-4795
Accurate prediction of the vibration response of aircraft engine assemblies is of great importance when estimating both the performance and the lifetime of their individual components. In the case of underplatform dampers, for example, the motion at the frictional interfaces can lead to a highly nonlinear dynamic response and cause fretting wear at the contact. The latter will change the contact conditions of the interface and consequently impact the nonlinear dynamic response of the entire assembly. Accurate prediction of the nonlinear dynamic response over the lifetime of the assembly must include the impact of fretting wear. A multi-scale approach that incorporates wear into the nonlinear dynamic analysis is proposed, and its viability is demonstrated for an underplatform damper system. The nonlinear dynamic response is calculated with a multiharmonic balance approach, and a newly developed semi-analytical contact solver is used to obtain the contact conditions at the blade-damper interface with high accuracy and low computational cost. The calculated contact conditions are used in combination with the energy wear approach to compute the fretting wear at the contact interface. The nonlinear dynamic model of the blade-damper system is then updated with the worn profile and its dynamic response is recomputed. A significant impact of fretting wear on the nonlinear dynamic behaviour of the blade-damper system was observed, highlighting the sensitivity of the nonlinear dynamic response to changes at the contact interface. The computational speed and robustness of the adopted multi-scale approach are demonstrated.
Catalfamo S, Smith SA, Morlock F, et al., 2016, Effects of Experimental Methods on the Measurements of a Nonlinear Structure, 34th IMAC Conference and Exposition on Structural Dynamics, Publisher: SPRINGER, Pages: 491-500, ISSN: 2191-5644
This paper continues the investigation from a paper presented at IMAC XXXIII that looked into the influence of various experimental setups on the nonlinear measurements of structures with mechanical joints. The previous study reported how the system stiffness and damping was affected by the force input method, boundary conditions and measurement techniques. However, during the stepped sine excitation experiments the parameters for the control schemes were neglected. In this paper, different control strategies, namely force and acceleration control, are used to observe how the parameters affect the measurements at different levels of excitation. The experiments are conducted on bolted beams containing a lap joint with different boundary conditions. The beams are excited by a shaker using a stepped sine signal using narrow bandwidths around three of the natural frequencies. The results show that acceleration amplitude control can produce cleaner transfer functions compared to the force amplitude control method.
Schwingshackl CW, Natoli A, 2016, Explicit Modelling of Microslip Behaviour in Dry Friction Contact, 34th IMAC Conference and Exposition on Structural Dynamics, Publisher: SPRINGER, Pages: 265-272, ISSN: 2191-5644
In many engineering applications the influence of a slipping contact interface has a major impact on the experienced damping in the structure. Predicting the generated damping is of uttermost importance to ensure an accurate analysis of the dynamic response of the system. Microslip, during which part of the contact is still stuck, and part is already slipping, plays a significant role in this damping, since many applications experience only this from of energy dissipation during operation. This paper investigates the possibility to capture microslip accurately with an explicit, quasi static modelling approach, where a large amount of traditional friction elements are distributed over a small contact area and a realistic pressure field is applied to reproduce the contact conditions. The resulting predicted hysteresis loops show microslip like behaviour, and the detailed contact mesh allows identifying the underlying nonlinear mechanism.
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.
Di Maio D, Schwingshackl C, Sever IA, 2016, Development of a test planning methodology for performing experimental model validation of bolted flanges, Nonlinear Dynamics, Vol: 83, Pages: 983-1002, ISSN: 0924-090X
This work presents a strategy for testing and validating structures connected together with bolted joints, which are the most common components in mechanical structures. Considering the great number of coupled mechanical structures and research studies on this subject, the authors focused this research work on bolted flanges of aircraft engine casings. In fact, the coupling of engine casings is generally obtained by a large number of joints which assure the correct sealing at the flanges’ interfaces. From a finite element (FE) modelling perspective, joints are often modelled by either rigid connections or springs, otherwise incurring a very expensive computational time. This modelling approach is not a problem when dealing with low amplitude levels of vibrations. For higher levels of vibrations, joints and flanges cannot be considered rigidly connected and that exerted flexibility at the joints’ area can determine nonlinear dynamic behaviour. This work aims to study the dynamic behaviour of bolted flanges by using modal testing performed under controlled response amplitude. Two test structures, (1) a simple bolted flange test case and (2) a sector of a Rolls-Royce aero-engine casing, are tested under high level of vibrations. Both test structures are modelled by FE method, and nonlinear elements are used for modelling the flanges’ interfaces so as to perform prediction of nonlinear responses. These predictions are eventually correlated with the measured data.
Armand J, Pesaresi L, Salles L, et al., 2016, A multi-scale approach for nonlinear dynamic response predictions with fretting wear
Accurate prediction of the vibration response of aircraft engine assemblies is of great importance when estimating both the performance and the lifetime of its individual components. In the case of underplatform dampers, for example, the motion at the frictional interfaces can lead to a highly nonlinear dynamic response and cause fretting wear at the contact. The latter will change the contact conditions of the interface and consequently impact the nonlinear dynamic response of the entire assembly. Accurate prediction of the nonlinear dynamic response over the lifetime of the assembly must include the impact of fretting wear. A multi-scale approach that incorporates wear into the nonlinear dynamic analysis is proposed, and its viability is demonstrated for an underplatform damper system. The nonlinear dynamic response is calculated with a multiharmonic balance approach, and a newly developed semi-Analytical contact solver is used to obtain the contact conditions at the blade-damper interface with high accuracy and low computational cost. The calculated contact conditions are used in combination with the energy wear approach to compute the fretting wear at the contact interface. The nonlinear dynamic model of the blade-damper system is then updated with the worn profile and its dynamic response is recomputed. A significant impact of fretting wear on the nonlinear dynamic behaviour of the blade-damper system was observed, highlighting the sensitivity of the nonlinear dynamic response to changes at the contact interface. The computational speed and robustness of the adopted multi-scale approach are demonstrated.
Salles L, Swacek C, Lacayo RM, et al., 2016, Numerical round robin for prediction of dissipation in lap joints, 33rd IMAC, A Conference and Exposition on Structural Dynamics, 2015, Publisher: Springer, Pages: 53-64, ISSN: 2191-5644
Joints, interfaces, and frictional contact between two substructures can be modelled as discrete nonlinearities that connect the substructures. Over the past decade, a number of phenomenologically different approaches to modelling and simulating the dynamics of a jointed structure have been proposed. This research focuses on assessing multiple modelling techniques to predict the nonlinear dynamic behaviour of a bolted lab joint, including frequency based sub-structuring methods, harmonic balance methods, discontinuous basis function methods, and high fidelity FEA approaches. The regimes in which each method is best suited are identified, and recommendations are made for how to select a modelling method and for advancing numerical modelling of discrete nonlinearities.
Stender M, Papangelo A, Allen M, et al., 2016, Structural Design with Joints for Maximum Dissipation, 34th IMAC Conference and Exposition on Structural Dynamics, Publisher: SPRINGER, Pages: 179-187, ISSN: 2191-5644
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- Citations: 6
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