81 results found
Mace T, Taylor J, Schwingshackl CW, 2020, A novel technique to extract the modal damping properties of a thin blade, Pages: 247-250, ISSN: 2191-5644
© Society for Experimental Mechanics, Inc. 2020. Extracting accurate material modal damping from a specimen can be very challenging due to the potential influence of the excitation and measurement system, and the required support of the specimen. This becomes particularly challenging if large amplitudes are required to determine nonlinear behavior, or large damping is present due to the material under investigation. An improved approach is proposed here to enable large amplitude, single harmonic, free decay damping extraction of a flat test specimen. It is based on a setup that uses the inertia of two large, free hanging end masses to enforce a pinned-pinned boundary condition with predetermined nodal locations, ensuring minimum effect of the support structure on the damping behavior. Excitation is achieved with the help of a removable electromagnetic shaker system that enables large amplitude single harmonic excitation, and smooth transition to a free, single harmonic decay. A Laser Doppler Vibrometer is used to measure the free decay, from which amplitude dependent damping can be obtained for individual modes via logarithmic decrement. Initial results of the approach show its great potential to provide reliable, amplitude dependent parameters with minimum impact of the test setup.
Fantetti A, Tamatam, Volvert, et al., 2019, The impact of fretting wear on structural dynamics: experiment and simulation, Tribology International, Vol: 138, Pages: 111-124, ISSN: 0301-679X
This paper investigates the effects of fretting wear on frictional contacts. A high frequency friction rig is used to measure the evolution of hysteresis loops, friction coefficient and tangential contact stiffness over time. This evolution of the contact parameters is linked to significant changes in natural frequencies and damping of the rig. Hysteresis loops are replicated by using a Bouc-Wen modified formulation, which includes wear to simulate the evolution of contact parameters and to model the evolving dynamic behaviour of the rig. A comparison of the measured and predicted dynamic behaviour demonstrates the feasibility of the proposed approach and highlights the need to consider wear to accurately capture the dynamic response of a system with frictional joints over its lifetime.
Tatar A, Schwingshackl CW, Friswell MI, 2019, Dynamic behaviour of three-dimensional planetary geared rotor systems, Mechanism and Machine Theory, Vol: 134, Pages: 39-56, ISSN: 0094-114X
© 2018 Elsevier Ltd A six degrees of freedom dynamic model of a planetary geared rotor system with equally spaced planets is developed by considering gyroscopic effects. The dynamic model is created using a lumped parameter model of the planetary gearbox and a finite element model of the rotating shafts using Timoshenko beams. The gears and carrier in the planetary gearbox are assumed to be rigid, and the gear teeth contacts and bearing elements are assumed to be flexible. The modal analysis results show that torsional and axial vibrations on the shafts are coupled in the helical gearing configuration due to the gear helix angle whereas these vibrations become uncoupled for spur gearing. Mainly, the vibration modes are classified as coupled torsional-axial, lateral and gearbox for the helical gear configuration, and torsional, axial, lateral and gearbox for the spur gear configuration. Modal energy analysis is used to quantify the coupling level between the shafts and the planetary gearbox, highlighting the impact of the gearbox on certain mode families. Gyroscopic effects of the planetary gearbox are found to be of great importance in the gearbox dominated modes.
Armand J, Pesaresi L, Salles L, et al., 2019, A modelling approach for the nonlinear dynamics of assembled structures undergoing fretting wear, Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, Vol: 475, ISSN: 1364-5021
© 2019 The Author(s) Published by the Royal Society. All rights reserved. Assembled structures tend to exhibit nonlinear dynamic behaviour at high excitation levels due to the presence of contact interfaces. The possibility of building predictive models relies on the ability of the modelling strategy to capture the complex nonlinear phenomena occurring at the interface. One of these phenomena, normally neglected, is the fretting wear occurring at the frictional interface. In this paper, a computationally efficient modelling approach which enables considerations of the effect of fretting wear on the nonlinear dynamics is presented. A multiscale strategy is proposed, in which two different time scales and space scales are used for the contact analysis and dynamic analysis. Thanks to the decoupling of the contact and dynamic analysis, a more realistic representation of the contact interface, which includes surface roughness, is possible. The proposed approach is applied to a single bolted joint resonator with a simulated rough contact interface. A tendency towards an increase of real contact area and contact stiffness at the interface is clearly observed. The dynamic response of the system is shown to evolve over time, with a slight decrease of damping and an increase of resonance frequency, highlighting the impact of fretting wear on the system dynamics.
Ondra V, Sever IA, Schwingshackl CW, 2019, A method for non-parametric identification of non-linear vibration systems with asymmetric restoring forces from a resonant decay response, Mechanical Systems and Signal Processing, Vol: 114, Pages: 239-258, ISSN: 0888-3270
© 2018 Elsevier Ltd A method for non-parametric identification of systems with asymmetric non-linear restoring forces is proposed in this paper. The method, named the zero-crossing method for systems with asymmetric restoring forces (ZCA), is an extension of zero-crossing methods and allows identification of backbones, damping curves and restoring elastic and dissipative forces from a resonant decay response. The validity of the proposed method is firstly demonstrated on three simulated resonant decay responses of the systems with off-centre clearance, bilinear and quadratic stiffness. Then, the method is applied to experimental data from a micro-electro-mechanical resonator in order to quantify its non-linear damping and stiffness effects. Throughout the paper the proposed method is also compared with the Hilbert vibration decomposition to demonstrate that the ZCA yields more accurate results with much less effort.
Haslam AH, Schwingshackl CW, Rix AIJ, 2019, Analysis of the Dynamic Response of Coupled Coaxial Rotors, Pages: 53-65, ISSN: 2191-5644
© 2019, The Society for Experimental Mechanics, Inc. The fundamental dynamics of a single rotor are very well understood, and extensively covered in the literature. However, many rotating machines such as aircraft engines consist of multiple shafts, which are often directly coupled by inter-shaft bearings. This paper aims to provide better insight into the underlying dynamics of such systems by analysing a simple but representative model of a rigid dual-rotor system. The modes and natural frequencies were computed numerically and it was found that the different modes could be classified by the following criteria: (i) relative phase of the motion of each rotor, (ii) whirl direction of the rotors, and (iii) presence of rotational or translational motion. The high-speed mode shapes could also be classified into (i) “static” modes with very low frequencies, (ii) “flat” modes which tend towards constant frequencies, and (iii) “precessional” modes which have a frequency which linearly increases with speed. A parameter study was performed in order to obtain a better understanding of the sensitivity of the modal properties. It was found that increasing the inter-shaft bearing stiffness can raise the natural frequencies of the modes at low speeds as well as the critical speeds, but has less influence at high speeds. The speed ratio influences the whirl direction of the modes and hence plays a crucial role in determining how each mode varies with speed. Since the speed ratio also controls the frequency of excitation from unbalances, it has a particularly profound effect on the critical speeds, and extra ones can arise. The importance of considering the dynamics of the complete system in the design of turbomachinery with multiple-shafts was highlighted.
Seeger B, Butaud P, Baloglu MV, et al., 2019, In situ measurements of interfacial contact pressure during impact hammer tests, Pages: 225-236, ISSN: 2191-5644
© The Society for Experimental Mechanics, Inc. 2019. Understanding the nonlinear dynamical contact interactions within joints is crucial for understanding and predicting the dynamics of assembled structures. In spite of this, most experimental investigations focused on the global vibration behavior, since the local interactions at the interface cannot be observed with standard techniques. In the present work, an advance contact pressure measurement system is used in a unique way to analyze, in situ, the interfacial contact pressures and the contact area inside a bolted lap joint connecting two beams (Brake-Reuß beam). An important feature of the measurement system is that it is designed for frequency ranges including the typical vibration frequency of the Brake-Reuß beam’s first eigenmode, and thus permits measurement under dynamic excitation. The dynamics of the contact pressures were investigated with different bolt torque levels and with different excitation levels. The experiments found that significant variations of the contact state occurred and that the contact pressure measurement system could adequately resolve this effect. The influence of the measurement system itself on the global vibration response of the Brake-Reuß beam was shown to be tolerable.
Sanchez A, Schwingshackl CW, 2019, Low order nonlinear dynamic modelling of fuel supply pipes, Pages: 113-120, ISSN: 2191-5644
© The Society for Experimental Mechanics, Inc. 2019. In industrial applications the vibration analysis mostly focuses on the main components, while accessories, such as pumps, electronics or pipe work are often neglected. This can lead to failures in these support systems, which can lead to performance reduction, shut down, or in the worst case catastrophe failure of the application due to secondary effects. One such accessory system is the fuel manifold of an aero engine, which delivers the kerosene to the fuel injectors. Previous experimental work has highlighted a strong nonlinear dynamic response of this setup, making an accurate prediction during the design process very challenging. In this study, a low order nonlinear modelling approach for fuel supply pipes, based on linear finite element and implicit nonlinear element analysis, is presented and its advantages and limitations are discussed.
Lawal I, Shah S, Gonzalez-Madrid M, et al., 2019, The effect of non-flat interfaces on system dynamics, Pages: 187-197, ISSN: 2191-5644
© The Society for Experimental Mechanics, Inc. 2019. Manufactured surfaces are never completely flat due to a variety of reasons including: variability in manufacturing operations, material behavior and achievable geometric tolerances. The curvature of surfaces is a local geometric effect that affects part-to-part variability of jointed surfaces. Joints with different interface geometries behave in unpredictable ways (Brake (2018) The Mechanics of Jointed Structure: Recent Research and Open Challenges for Developing Predictive Models for Structural Dynamics. Sandia National Laboratories, William Marsh Rice University. Springer, Cham). Among the factors that drive the uncertainty in joint performance are frictional micro and macro sliding events, surface tribology effects, residual stress from manufacturing and assembly, loss of bolt pre-load, changes in contact area and the resulting pressure field variation around the joint. The goal of this research is to identify key variables that account for the measured uncertainty in the dynamics of jointed structures, which may have local regions of conformal and non-conformal contact due to variability inherent in the manufacturing process. Using the standard benchmark system of the Brake-Reuβ beam (BRB), recommendations are made for which design parameters require higher tolerances than others to minimize variability in a cost-effective manner. Conformal beams with strong and weak curvature are studied as well as non-conformal (flat vs. curved) beams. Experimental and numerical approaches model and validate the physical behavior of beams to understand primary causes of non-linearity in joints with different interface geometries.
Tatar A, Salles L, Haslam AH, et al., 2019, Comparison of computational generalized and standard eigenvalue solutions of rotating systems, Pages: 187-194, ISSN: 2191-5644
© The Society for Experimental Mechanics, Inc. 2019. Modal analysis is regularly used to compute natural frequencies and mode shapes of structures via eigenvalue solutions in vibration engineering. In this paper, the eigenvalue problem of a 6 degrees of freedom rotating system with gyroscopic effects, including axial, torsional and lateral motion, is investigated using Timoshenko beam theory. The main focus thereby is the investigation of the computational time and the numerical errors in generalized and standard eigenvalue solutions of rotating systems. The finite element method is employed to compute the global stiffness, mass and gyroscopic matrices of the rotating system. The equations of motion is expressed in the state space form to convert the quadratic eigenvalue problem into the generalized and standard forms. The number of elements in the finite element model was varied to investigate the convergence of the natural frequencies and the computational performance of the two eigenvalue solutions. The numerical analyses show that the standard eigenvalue solution is significantly faster than the generalized one with increasing number of elements and the generalized eigenvalue solution can yield wrong solutions when using higher numbers of elements due to the ill-conditioning phenomenon. In this regard, the standard eigenvalue solution gives more reliable results and uses less computational time than the generalized one.
Lacayo R, Pesaresi L, Gross J, et al., 2019, Nonlinear modeling of structures with bolted joints: a comparison of two approaches based on a time-domain and frequency-domain solver, Mechanical Systems and Signal Processing, Vol: 114, Pages: 413-438, ISSN: 0888-3270
Motivated by the current demands in high-performance structural analysis, and by a need to better model systems with localized nonlinearities, analysts have developed a number of different approaches for modeling and simulating the dynamics of a bolted-joint structure. However, it is still unclear which approach might be most effective for a given system or set of conditions. To better grasp their similarities and differences, this paper presents a numerical benchmark that assesses how well two diametrically differing joint modeling approaches – a time-domain whole-joint approach and a frequency-domain node-to-node approach – predict and simulate a mechanical joint. These approaches were applied to model the Brake-Reuß beam, a prismatic structure comprised of two beams with a bolted joint interface. The two approaches were validated first by updating the models to reproduce the nonlinear response for the first bending mode of an experimental Brake-Reuß beam. Afterwards, the tuned models were evaluated on their ability to predict the nonlinearity in the dynamic response for the second and third bending modes. The results show that the two joint modeling approaches perform about equally as well in simulating the Brake-Reuß beam. In addition, the exposition highlights improvements that were made in each method during the course of this work and reveal further challenges in advancing the state-of-the-art.
Pesaresi L, Armand J, Schwingshackl C, et al., 2018, An advanced underplatform damper modelling approach based on a microslip contact model, Journal of Sound and Vibration, Vol: 436, Pages: 327-340, ISSN: 0022-460X
High-cycle fatigue caused by large resonance stresses remains one of the most common causes of turbine blade failures. Friction dampers are one of the most effective and practical solutions to limit the vibration amplitudes, and shift the resonance frequencies of the turbine assemblies far from operating speeds. However, predicting the effects of underplatform dampers on the dynamics of the blades with good accuracy 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. This new approach allows to implicitly account for the microscale energy dissipation as well as the pressure-dependent contact stiffness caused by the roughness of the contact surface. 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 semi-analytical contact solver is used to tune the parameters of the contact element starting from the profilometer measurements of the real damper surface. 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, when information about the surface roughness is available.
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
© Proceedings of ISMA 2018 - International Conference on Noise and Vibration Engineering and USD 2018 - International Conference on Uncertainty in Structural Dynamics. All rights reserved. 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.
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
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
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
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
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.
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
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
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
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
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
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
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
Panunzio AM, Salles L, Schwingshackl CW, 2016, Uncertainty propagation for nonlinear vibrations: A non-intrusive approach, JOURNAL OF SOUND AND VIBRATION, Vol: 389, Pages: 309-325, ISSN: 0022-460X
Pesaresi L, Salles L, Jones A, et al., 2016, 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
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
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.
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