Imperial College London

DrLoicSalles

Faculty of EngineeringDepartment of Mechanical Engineering

Research Fellow
 
 
 
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Contact

 

+44 (0)20 7594 2243l.salles Website

 
 
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Assistant

 

Mr Peter Higgs +44 (0)20 7594 7078

 
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Location

 

556City and Guilds BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

61 results found

Vizzaccaro A, Givois A, Longobardi P, Shen Y, Deü J-F, Salles L, Touzé C, Thomas Oet al., 2020, Non-intrusive reduced order modelling for the dynamics of geometrically nonlinear flat structures using three-dimensional finite elements, Computational Mechanics, ISSN: 0178-7675

Non-intrusive methods have been used since two decades to derive reduced-order models for geometrically nonlinear structures, with a particular emphasis on the so-called STiffness Evaluation Procedure (STEP), relying on the static application of prescribed displacements in a finite-element context. We show that a particularly slow convergence of the modal expansion is observed when applying the method with 3D elements, because of nonlinear couplings occurring with very high frequency modes involving 3D thickness deformations. Focusing on the case of flat structures, we first show by computing all the modes of the structure that a converged solution can be exhibited by using either static condensation or normal form theory. We then show that static modal derivatives provide the same solution with fewer calculations. Finally, we propose a modified STEP, where the prescribed displacements are imposed solely on specific degrees of freedom of the structure, and show that this adjustment also provides efficiently a converged solution.

Journal article

Vizzaccaro A, Salles L, Touzé C, 2020, Comparison of nonlinear mappings for reduced-order modellingof vibrating structures: normal form theory and quadraticmanifold method with modal derivatives, Nonlinear Dynamics, ISSN: 0924-090X

The objective of this contribution is to compare two methods proposed recently in order to build efficient reduced-order models for geometrically nonlinear structures. The first method relies on the normal form theory that allows one to obtain a nonlinear change of coordinates for expressing the reduced-order dynamics in an invariant-based span of the phase space. The second method is the modal derivative (MD) approach, and more specifically the quadratic manifold defined in order to derive a second-order nonlinear change of coordinates. Both methods share a common point of view, willing to introduce a nonlinear mapping to better define a reduced-order model that could take more properly into account the nonlinear restoring forces. However the calculation methods are different and the quadratic manifold approach has not the in variance property embedded in its definition. Modal derivatives and static modal derivatives are investigated, and their distinctive features in the treatment of the quadratic nonlinearity is underlined.Assuming a slow/fast decomposition allows understanding how the three methods tend to share equivalent properties. While they give proper estimations for flat symmetric structures having a specific shape of nonlinearities and a clear slow/fast decomposition between flexural and in-plane modes, the treatment of the quadratic nonlinearity makes the predictions different in the case of curved structures such as arches and shells. In the more general case, normal form approach appears preferable since it allows correct predictions of a number of important nonlinear features,including for example the hardening/softening behaviour, whatever the relationships between slave and master coordinates are.

Journal article

Yuan J, Schwingshackl C, wong C, Salles Let al., 2020, On an improved adaptive reduced order model for the computation of steady state vibrations in large-scale non-conservative system with friction joints, Nonlinear Dynamics, ISSN: 0924-090X

Joints are commonly used in many large-scale engineering systems to ease assembly, and ensure structural integrity and effective load transmission. Most joints are designed around friction interfaces, which can transmit large static forces, but tend to introduce stick-slip transition during vibrations, leading to a nonlinear dynamic system. Tools for the complex numerical prediction of such nonlinear systems are available today, but their use for large-scale applications is regularly prevented by high computational cost. To address this issue, a novel adaptive reduced-order model (ROM) has recently been developed, significantly decreasing the computational time for such high fidelity simulations. Although highly effective, significant improvements to the proposed approach is presented and demonstrated in this paper, further increasing the efficiency of the ROM. An energy-based error estimator was developed and integrated into the nonlinear spectral analysis, leading to a significantly higher computational speed by removing insignificant static modes from the stuck contact nodes in the original reduced basis, and improving the computational accuracy by eliminating numerical noise. The effectiveness of the new approach was shown on an industrial-scale fan blades system with a dovetail joints, showing that the improved adaptive method can be 2–3 times more computationally efficient than the original adaptive method especially at high excitation levels but also effectively improve the accuracy of the original method.

Journal article

Sun Y, Vizzaccaro A, Yuan J, Salles Let al., 2020, An extended energy balance method for resonance prediction in forced response of systems with non-conservative nonlinearities using damped nonlinear normal mode, Nonlinear Dynamics, Pages: 1-19, ISSN: 0924-090X

The dynamic analysis of systems with nonlinearities has become an important topic in many engineering fields. Apart from the forced response analyses, nonlinear modal analysis has been successfully extended to such non-conservative systems thanks to the definition of damped nonlinear normal modes. The energy balance method is a tool that permits to directly predict resonances for a conservative system with nonlinearities from its nonlinear modes. In this work, the energy balance method is extended to systems with non-conservative nonlinearities using the concept of the damped nonlinear normal mode and its application in a full-scale engineering structure. This extended method consists of a balance between the energy loss from the internal damping, the energy transferred from the external excitation and the energy exchanged with the non-conservative nonlinear force. The method assumes that the solution of the forced response at resonance bears resemblance to that of the damped nonlinear normal mode. A simplistic model and full-scale structure with dissipative nonlinearities and a simplistic model showing self-excited vibration are tested using the method. In each test case, resonances are predicted efficiently and the computed force–amplitude curves show a great agreement with the forced responses. In addition, the self-excited solutions and isolas in forced responses can be effectively detected and identified. The accuracy and limitations of the method have been critically discussed in this work.

Journal article

Sun Y, Yuan J, Pesaresi L, Denimal E, Salles Let al., 2020, Parametric study and uncertainty quantification of the nonlinear modal properties of frictional dampers, Journal of Vibration and Acoustics, ISSN: 0739-3717

A numerical methodology is described to study the influ-ence of the contact location and contact condition of fric-tion damper in aircraft engines. A simplified beam model isused to represent the blade for the preliminary design stage.The frictional damper is numerically analysed based on twoparameters, contact angle and vertical position of the plat-form. The nonlinear modal analysis is used to investigatethe nonlinear dynamic behaviour and damping performancesof the system. Harmonic balanced method with continua-tion technique is used to compute the nonlinear modes for alarge range of energy levels. Using such a modelling strat-egy, modal damping ratio, resonant amplitude and resonantfrequency are directly and efficiently computed for a rangeof design parameters. Monte Carlo simulations togetherwith Latin hypercube sampling is then used to assess the ro-bustness of the frictional damper, whose contact parametersinvolve much uncertainties due to manufacturing toleranceand also wear effects. The influences of those two parame-ter are obtained and the best performances of the frictionaldamper can be achieved when the contact angle is around25◦-30◦. The vertical position of the platform is highlymode-dependent and other design considerations needs to beaccounted. The results have been proved that the uncertain-ties involved contact surfaces do not have significant effects∗Address all correspondence for other issues to this author.on the performance of frictional damper.

Journal article

Yuan J, Salles L, El Haddad F, Wong Cet al., 2020, An adaptive component mode synthesis method for dynamic analysis of jointed structure with contact friction interfaces, Computers and Structures, Vol: 229, ISSN: 0045-7949

Component model synthesis (CMS) has been widely used for model order reduction in dynamic analysis of jointed structures with localized non-linearities. The main drawback of these CMS methods is that their computational efficiency largely depends on the size of contact friction interfaces. This work proposes an adaptive reduction approach to improve these CMS based reduction methods in the application to the assembled structure with frictional interfaces. The main idea of this method is that, instead of retaining the whole frictional interface DOFs in the reduced model, only those DOFs in a slipping or separating condition are retained. This would significantly reduce the size of classical CMS based reduced models for dynamical analysis of jointed structure with micro-slip motion, leading to an impressive computational saving. This novel approach is based on a reformulated dynamic system that consists of a underlying linearised system and an adaptive internal variable to account the effects of non-linear contact friction force on the interface. The paper also describes the detailed implementation of the proposed approach with harmonic balance method for non-linear spectral analysis, where a new updating algorithm is put forward to enable the size of the reduced model can be automatically updated according to the contact condition of interface nodes. Two distinct FE joint models are used to validate the proposed method. It is demonstrated that the new approach can achieve a considerable computing speed-up comparing to the classic CMS approach while maintain the same accuracy.

Journal article

Wollmann T, Dannemann M, Langkamp A, Modler N, Gude M, Salles L, Hoffmann N, Filippatos Aet al., 2020, Combined experimental-numerical approach for the 3D vibration analysis of rotating composite compressor blades: An introduction

© CCM 2020 - 18th European Conference on Composite Materials. All rights reserved. As compressor blades are subjected to highly dynamic loads, there is a particular interest in determining their modal properties under operating condition. Furthermore, intensive research is conducted for the development of fibre-reinforced epoxy blades due to the high specific stiffness and strength as well as the high damping of composite materials. Traditional modal analysis techniques are state of the art to determine the vibration behaviour of non-rotating/stationary blades, where some new approaches show the vibration analysis of rotating blades. These approaches for rotating structures have the disadvantage, that either the excitation or the measurement method are influencing the dynamic behaviour of the investigated structure or the method itself cannot be applied for composite materials. Other techniques do not allow a continuous or full-field measurement of the rotating structure. To determine the vibration behaviour of rotating composite compressor blades, a combined experimental-numerical approach is introduced. Therefore, an experimental system for the vibration excitation and a 3-dimensional determination of the vibration behaviour of rotating components are presented. An overview of the main addressed research topics is given.

Conference paper

Saeed Z, Jenovencio G, Arul S, Blahoš J, Sudhakar A, Pesaresi L, Yuan J, El Haddad F, Hetzler H, Salles Let al., 2020, A Test-Case on Continuation Methods for Bladed-Disk Vibration with Contact and Friction, Pages: 209-212, ISSN: 2191-5644

© 2020, Society for Experimental Mechanics, Inc. Bladed-disks in turbo-machines experience harsh operating conditions and undergo high vibration amplitudes if not properly damped. Friction at the blade-to-blade or blade-to-disk interfaces plays a key role in dampening the high amplitudes. Due to the inherent complexity of these structures and non-linearities introduced by the friction joints, accurate response prediction becomes very difficult. There are variety of methods in the literature to predict non-linear vibration due to contact friction. However, their application to the bladed-disks remains limited. Furthermore, there are not many 3D realistic test-cases in the open literature for testing those methods and serve as a benchmark. A bladed-disk representative of a real turbine is presented as an open numerical test-case for the research community. It is characterized by a blade root joint and a shroud joint. The bladed-disk sector is meshed in different ways along with component mode synthesis (CMS) model order reduction for onward non-linear computations. The steady-state solution is obtained by multi-Harmonic Balance method and then continuation method is employed to predict the non-linear frequency response. Thus, it can serve as a case for testing previous and new methods as well as a benchmark for comparative studies.

Conference paper

Wollmann T, Dannemann M, Langkamp A, Modler N, Gude M, Salles L, Hoffmann N, Filippatos Aet al., 2020, Combined experimental-numerical approach for the 3D vibration analysis of rotating composite compressor blades: An introduction

© CCM 2020 - 18th European Conference on Composite Materials. All rights reserved. As compressor blades are subjected to highly dynamic loads, there is a particular interest in determining their modal properties under operating condition. Furthermore, intensive research is conducted for the development of fibre-reinforced epoxy blades due to the high specific stiffness and strength as well as the high damping of composite materials. Traditional modal analysis techniques are state of the art to determine the vibration behaviour of non-rotating/stationary blades, where some new approaches show the vibration analysis of rotating blades. These approaches for rotating structures have the disadvantage, that either the excitation or the measurement method are influencing the dynamic behaviour of the investigated structure or the method itself cannot be applied for composite materials. Other techniques do not allow a continuous or full-field measurement of the rotating structure. To determine the vibration behaviour of rotating composite compressor blades, a combined experimental-numerical approach is introduced. Therefore, an experimental system for the vibration excitation and a 3-dimensional determination of the vibration behaviour of rotating components are presented. An overview of the main addressed research topics is given.

Conference paper

Wollmann T, Dannemann M, Langkamp A, Modler N, Gude M, Salles L, Hoffmann N, Filippatos Aet al., 2020, Combined experimental-numerical approach for the 3D vibration analysis of rotating composite compressor blades: An introduction

© CCM 2020 - 18th European Conference on Composite Materials. All rights reserved. As compressor blades are subjected to highly dynamic loads, there is a particular interest in determining their modal properties under operating condition. Furthermore, intensive research is conducted for the development of fibre-reinforced epoxy blades due to the high specific stiffness and strength as well as the high damping of composite materials. Traditional modal analysis techniques are state of the art to determine the vibration behaviour of non-rotating/stationary blades, where some new approaches show the vibration analysis of rotating blades. These approaches for rotating structures have the disadvantage, that either the excitation or the measurement method are influencing the dynamic behaviour of the investigated structure or the method itself cannot be applied for composite materials. Other techniques do not allow a continuous or full-field measurement of the rotating structure. To determine the vibration behaviour of rotating composite compressor blades, a combined experimental-numerical approach is introduced. Therefore, an experimental system for the vibration excitation and a 3-dimensional determination of the vibration behaviour of rotating components are presented. An overview of the main addressed research topics is given.

Conference paper

Pesaresi L, Fantetti A, Cegla F, Salles L, Schwingshackl CWet al., 2020, On the use of ultrasound waves to monitor the local dynamics of friction joints, Experimental Mechanics, Vol: 60, Pages: 129-141, ISSN: 0014-4851

Friction joints are one of the fundamental means used for the assembly of structural components in engineering applications. The structural dynamics of these components becomes nonlinear, due to the nonlinear nature of the forces arising at the contact interface characterised by stick-slip phenomena and separation. Advanced numerical models have been proposed in the last decades which have shown some promising capabilities in capturing these local nonlinearities. However, despite the research efforts in producing more advanced models over the years, a lack of validation experiments made it difficult to have fully validated models. For this reason, experimental techniques which can provide insights into the local dynamics of joints can be of great interest for the refinement of such models and for the optimisation of the joint design and local wear predictions. In this paper, a preliminary study is presented where ultrasound waves are used to characterise the local dynamics of friction contacts by observing changes of the ultrasound reflection/transmission at the friction interface. The experimental technique is applied to a dynamic friction rig, where two steel specimens are rubbed against each other under a harmonic tangential excitation. Initial results show that, with a controlled experimental test procedure, this technique can identify microslip effects at the contact interface.

Journal article

Fantetti A, Tamatam, Volvert, Laval, Liu, Salles L, Brake M, Schwingshackl C, Nowell Det 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.

Journal article

Rendu Q, Vahdati M, Salles L, 2019, Radial Decomposition of Blade Vibration to Identify a Stall Flutter Source in a Transonic Fan, 15th International Symposium on Unsteady Aerodynamics, Aeroacoustics and Aeroelasticity of Turbomachinery (ISUAAAT), Publisher: ASME, ISSN: 0889-504X

Conference paper

Yuan J, Salles L, Wong C, Patsias Set al., 2019, A novel penalty-based reduced order modelling method for dynamic analysis of joint structures, IUTAM Symposium on Model Order Reduction of Coupled Systems, Publisher: Springer, Pages: 165-176

This work proposes a new reduced order modelling method to improve the computational efficiency for the dynamic simulation of a jointed structures with localized contact friction non-linearities. We reformulate the traditional equation of motion for a joint structure by linearising the non-linear system on the contact interface and augmenting the linearised system by introducing an internal non-linear penalty variable. The internal variable is used to compensate the possible non-linear effects from the contact interface. Three types of reduced basis are selected for the Galerkin projection, namely, the vibration modes (VMs) of the linearised system, static modes (SMs) and also the trial vector derivatives (TVDs) vectors. Using these reduced basis, it would allow the size of the internal variable to change correspondingly with the number of active non-linear DOFs. The size of the new reduced order model therefore can be automatically updated depending on the contact condition during the simulations. This would reduce significantly the model size when most of the contact nodes are in a stuck condition, which is actually often the case when a jointed structure vibrates. A case study using a 2D joint beam model is carried out to demonstrate the concept of the proposed method. The initial results from this case study is then compared to the state of the art reduced order modeling.

Conference paper

Armand J, Pesaresi L, Salles L, Wong C, Schwingshackl CWet 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.

Journal article

Yuan J, El-Haddad F, Salles L, Wong Cet al., 2019, Numerical Assessment of Reduced Order Modeling Techniques for Dynamic Analysis of Jointed Structures With Contact Nonlinearities, JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER-TRANSACTIONS OF THE ASME, Vol: 141, ISSN: 0742-4795

Journal article

Fontanela F, Grolet A, Salles L, Chabchoub A, Champneys AR, Patsias S, Hoffmann Net al., 2019, Dissipative solitons in forced cyclic and symmetric structures, MECHANICAL SYSTEMS AND SIGNAL PROCESSING, Vol: 117, Pages: 280-292, ISSN: 0888-3270

Journal article

Fontanela F, Grolet A, Salles L, Hoffmann Net 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

Journal article

Filippatos A, Wollmann T, Minh N, Kostka P, Dannemann M, Langkamp A, Salles L, Gude Met al., 2019, Design and Testing of a Co-Rotating Vibration Excitation System, SENSORS, Vol: 19, ISSN: 1424-8220

Journal article

Tatar A, Salles L, Haslam AH, Schwingshackl CWet al., 2019, Comparison of Computational Generalized and Standard Eigenvalue Solutions of Rotating Systems, 36th International Modal Analysis Conference and Exposition (IMAC) on Structural Dynamics, Publisher: SPRINGER INTERNATIONAL PUBLISHING AG, Pages: 187-194, ISSN: 2191-5644

Conference paper

Lacayo R, Pesaresi L, Gross J, Fochler D, Armand J, Salles L, Schwingshackl C, Allen M, Brake Met 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.

Journal article

Venkatesh S, Rendu Q, Vahdati M, Salles Let al., 2019, Effect of manufacturing tolerance in flow past a compressor blade

Copyright © by the Authors. This paper presents the effect of manufacturing tolerance on performance and stability boundaries of a transonic fan using a RANS simulation. The effect of tip gap and stagger angle was analysed through a series of single passage and double passage simulation; based on which an optimal arrangement was proposed for random tip gap and random stagger angle in case of a whole annulus rotor. All simulations were carried out using NASA rotor 67 as a test case and AU3D an in-house CFD solver. Results illustrate that the stagger angle mainly affects efficiency and hence its circumferential variation must be as smooth as possible. Furthermore, the tip gap affects the stability boundaries, pressure ratio and efficiency. Hence its optimal configuration mandates that the blades be configured in a zigzag arrangement around the annulus i.e. larger tip gap between two smaller ones.

Conference paper

Fontanela F, Grolet A, Salles L, Hoffmann Net 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

Conference paper

Pesaresi L, Armand J, Schwingshackl C, Salles L, Wong Cet 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.

Journal article

Sun Y, Yuan J, Pesaresi L, Salles Let al., 2018, Nonlinear Vibrational Analysis for Integrally Bladed Disk Using Frictional Ring Damper, Modern Practice in Stress and Vibration Analysis (MPSVA) 2018, ISSN: 1742-6588

© Published under licence by IOP Publishing Ltd. The use of integrally bladed-disk is now very popular in turbomachinery industry since they feature significant aerodynamic and structural improvements along with a significant mass reduction. However, these integrated single structures can arise a major high cycle fatigue issue due to the lack of sufficient damping for dissipating the vibrational energy. This work describes a numerical investigation of the nonlinear dynamic behaviour and nonlinear normal mode for such a bladed-disk with frictional ring damper using the Harmonic Balanced Method (HBM) with alternating Fourier transformation. Jenkins element is used to model the nonlinear contact friction between the disc and ring damper. Using such a modeling strategy, the modal damping and resonance amplitude are directly and efficiently computed through nonlinear normal mode analysis. The initial results show the vibrational level on the blades can be effectively controlled by the parameters of the ring damper model. The effectiveness of ring damper and damping performance is evaluated. This study also indicates the nonlinear normal mode analysis based HBM may be an effective method to analyse the dynamic behaviour of the integrated bladed-disk with frictional ring damper.

Conference paper

Armand J, Salles L, Schwingshackl CW, Süß D, Willner Ket 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.

Journal article

Fontanela F, Grolet A, Salles L, Chabchoub A, Hoffmann Net 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

Journal article

Yuan J, El -Haddad F, Salles L, Wong Cet al., 2018, NUMERICAL ASSESSMENT OF REDUCED ORDER MODELING TECHNIQUES FOR DYNAMIC ANALYSIS OF JOINTED STRUCTURES WITH CONTACT NONLINEARITIES, ASME Turbo Expo: Turbomachinery Technical Conference and Exposition, Publisher: AMER SOC MECHANICAL ENGINEERS

Conference paper

Pesaresi L, Armand J, Schwingshackl CW, Salles L, Wong Cet 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.

Conference paper

Franz D, Salles L, Stapelfeldt S, 2017, Analysis of a Turbine Bladed Disk With Structural and Aerodynamic Mistuning, ASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition

Conference paper

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