21 results on '"Laurent Borsoi"'
Search Results
2. On using the Hilbert transform for blind identification of complex modes: A practical approach
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Pilippe Piteau, Laurent Borsoi, Xavier Delaune, Vincent Debut, Jose Antunes, Laboratoire d'études de DYNamique (DYN), Service d'Etudes Mécaniques et Thermiques (SEMT), Département de Modélisation des Systèmes et Structures (DM2S), CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire) (CEA-DES (ex-DEN)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire) (CEA-DES (ex-DEN)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Département de Modélisation des Systèmes et Structures (DM2S), and Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay more...
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Acoustics and Ultrasonics ,Dynamical systems theory ,02 engineering and technology ,Hilbert transform ,[SPI]Engineering Sciences [physics] ,symbols.namesake ,0203 mechanical engineering ,SOBI ,Normal mode ,0202 electrical engineering, electronic engineering, information engineering ,Modal matrix ,Modal identification ,Mathematics ,Covariance matrix ,Mechanical Engineering ,020206 networking & telecommunications ,Ranging ,Control engineering ,Blind identification ,Condensed Matter Physics ,System dynamics ,020303 mechanical engineering & transports ,Modal ,Mechanics of Materials ,Complex modes ,symbols ,Algorithm - Abstract
The modal identification of dynamical systems under operational conditions, when subjected to wide-band unmeasured excitations, is today a viable alternative to more traditional modal identification approaches based on processing sets of measured FRFs or impulse responses. Among current techniques for performing operational modal identification, the so-called blind identification methods are the subject of considerable investigation. In particular, the SOBI (Second-Order Blind Identification) method was found to be quite efficient. SOBI was originally developed for systems with normal modes. To address systems with complex modes, various extension approaches have been proposed, in particular: (a) Using a first-order state-space formulation for the system dynamics; (b) Building complex analytic signals from the measured responses using the Hilbert transform. In this paper we further explore the latter option, which is conceptually interesting while preserving the model order and size. Focus is on applicability of the SOBI technique for extracting the modal responses from analytic signals built from a set of vibratory responses. The novelty of this work is to propose a straightforward computational procedure for obtaining the complex cross-correlation response matrix to be used for the modal identification procedure. After clarifying subtle aspects of the general theoretical framework, we demonstrate that the correlation matrix of the analytic responses can be computed through a Hilbert transform of the real correlation matrix, so that the actual time-domain responses are no longer required for modal identification purposes. The numerical validation of the proposed technique is presented based on time-domain simulations of a conceptual physical multi-modal system, designed to display modes ranging from normal to highly complex, while keeping modal damping low and nearly independent of the modal complexity, and which can prove very interesting in test bench applications. Numerical results for complex modal identifications are presented, and the quality of the identified modal matrix and modal responses, extracted using the complex SOBI technique and implementing the proposed formulation, is assessed. more...
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- 2018
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Catalog
3. A modal Udwadia-Kalaba formulation for vibro-impact modelling of continuous flexible systems with intermittent contacts
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Laurent Borsoi, Jose Antunes, Philippe Piteau, Xavier Delaune, and Vincent Debut
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Coupling ,Mathematical optimization ,Engineering ,business.industry ,Computation ,Context (language use) ,General Medicine ,01 natural sciences ,Displacement (vector) ,010305 fluids & plasmas ,Constraint (information theory) ,Nonlinear system ,Acceleration ,Modal ,0103 physical sciences ,business ,010301 acoustics - Abstract
Most systems consist on dynamical substructures connected at a number of constraining points. Moreover, constraints often display intermittent contact phenomena, such as arising from clearance supports. A significant difficulty when computing time-domain responses is the manner to enforce such coupling constraints. Here, we explore the Udwadia-Kalaba (U-K) formulation, which has been very seldom used in this context. By extending the basic U-K analytical framework, we address continuous flexible subsystems modelled by their unconstrained modes and coupled through the highly nonlinear intermittent point-constraints. For continuous flexible systems, a modal U-K formulation is implemented such that the constraint is applied when contact is detected at the clearance location. A crucial aspect is that constraint violations must be prevented, not only at the acceleration level, but also at the velocity and displacement levels, in order to avoid computational drift. This is achieved through a constraint violation correction method. For single gap-constraints, a convenient formulation is obtained, in which the constraint matrix is pre-computed prior to the simulation time-loop and applied whenever an intermittent contact is detected, leading to an efficient computation of vibro-impact responses. For systems with several intermittent constraints, an essential difficulty within the context of the proposed formulation is that every possible combination of contact/non-contact conditions is expressed by a different constraint matrix. A pragmatic solution is to keep track of the current system contact configuration and rebuild the constraint matrix whenever a change in the constraint state is detected. We formulate and illustrate such computational strategy, as applied to random-excited multi-supported beams with a significant number of clearance supports. Results are compared with dynamical computations performed using a classic penalty technique for enforcing the nonlinear support constraints, emphasizing the viability of the proposed technique for performing predictive analysis of flexible structures with multiple clearance supports. more...
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- 2017
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4. Competition between Turbulence and Fluid-Elastic Forces in the Response of a Loosely Supported Tube under Cross-Flow
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Laurent Borsoi, Xavier Delaune, Philippe Piteau, and Jose Antunes
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Engineering ,business.industry ,Turbulence ,K-epsilon turbulence model ,020209 energy ,Perturbation (astronomy) ,02 engineering and technology ,General Medicine ,01 natural sciences ,Instability ,010305 fluids & plasmas ,Physics::Fluid Dynamics ,Classical mechanics ,Bundle ,0103 physical sciences ,0202 electrical engineering, electronic engineering, information engineering ,Dissipative system ,business ,Mirror symmetry ,Excitation - Abstract
In some degraded situations of heat-exchangers, tubes may be loosely supported while subjected to intense cross-flow generating both turbulence and fluid-elastic forces, and so have vibro-impacting responses. This paper aims at providing a better understanding of the dynamics of such systems in which the conjunction of stops with gaps, broadband random excitation, and fluid-elastic coupling forces, either stabilizing or destabilizing, produces some rather amazing effects linked to a general capacity for the system to be auto-adjusted by the impacts. It is especially shown, (i) how a non-linear gap-system “escapes from instability” by reinforcing the sequence of impacts, (ii) the almost perfect time-history mirror symmetry between the works of turbulence and fluid-elastic forces in the energy balance; (iii) the dissipative aspect of turbulence in some cases. Moreover the paper deals with the relative weight of turbulence and fluid-elastic forces in the tube response that notably depends on the gap size. For this, turbulence is considered as a perturbation of limit cycles obtained when the fluid-elastic forces are the only acting fluid-forces. The study is based on configurations mainly 1-DOF, like the one that has been experimentally tested, but extrapolations for real tube bundle are evoked in conclusion. more...
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- 2017
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5. Experimental identification of the fluid-elastic coupling forces on a flexible tube within a rigid square bundle subjected to single-phase cross-flow
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Philippe Piteau, Laurent Borsoi, Jose Antunes, Xavier Delaune, Laboratoire d'études de DYNamique (DYN), Service d'Etudes Mécaniques et Thermiques (SEMT), Département de Modélisation des Systèmes et Structures (DM2S), CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire) (CEA-DES (ex-DEN)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire) (CEA-DES (ex-DEN)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Département de Modélisation des Systèmes et Structures (DM2S), and Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay more...
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Physics ,Mechanical Engineering ,Reynolds number ,02 engineering and technology ,Mechanics ,01 natural sciences ,FIV ,010305 fluids & plasmas ,Vibration ,Lift (force) ,symbols.namesake ,[SPI]Engineering Sciences [physics] ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Flow velocity ,Tube bundle ,Bundle ,0103 physical sciences ,symbols ,Coupling (piping) ,Tube (fluid conveyance) ,Transverse flow ,Fluid-elastic instability ,Experimental identification ,Added mass - Abstract
The importance of fluid-elastic coupling forces in tube bundle vibrations is well documented and can hardly be over-emphasized, in view of their damaging potential. Even when adequate tube supports are provided to suppress fluid-elastic instabilities, the flow-coupling forces still affect the dynamical tube responses and remain a significant issue, in particular concerning the vibro-impact motions of tubes assembled using clearance supports. Therefore, the need remains for more advanced models of fluid-elastic coupling, as well as for experimental flow-coupling coefficients to feed and validate such models. In this work, we report an extensive series of experiments performed at CEA-Saclay leading to the identification of stiffness and damping fluid-elastic coefficients, for a 3×5 square tube bundle (D = 30 mm, P/D = 1.5) subjected to single-phase transverse flow, in a water test-loop. The bundle is rigid, except for the central tube which is mounted on a flexible suspension (two parallel steel blades) allowing for translation motions of the tube in the lift direction. The system is thus single-degree of freedom, allowing fluid-elastic instability to arise through a negative damping mechanism. The flow-coupling stiffness and damping coefficients, Kf(Vr) and Cf(Vr), are experimentally identified as functions of the reduced velocity Vr. The maximum value of the Reynolds number ranged from 105 to 2.16 105 (based on the maximum pitch velocity), according to the tested configuration. Identification is achieved on the basis of changes in tube vibration frequency and reduced damping as a function of flow velocity, assuming a constant fluid added mass. In the present experiments, coefficient identification is performed well beyond the instability boundary, by using active control, thereafter allowing exploration of a significant range of flow velocity. The modal frequency and the modal mass of the system are respectively modified by changing the tube suspension stiffness, and/or by adding a mass to the system. We can thus assert how the fluid-elastic coefficients change, for this configuration, with these two system parameters, all other parameters being kept constant. The results obtained from the configurations tested suggest that formulations for coefficient reduction may be improved, in order to better collapse the identified data. more...
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- 2019
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6. Time-domain numerical simulations of a loosely supported tube subjected to frequency-dependent fluid–elastic forces
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Laurent Borsoi, Jose Antunes, Xavier Delaune, Philippe Piteau, Laboratoire d'études de DYNamique (DYN), Service d'Etudes Mécaniques et Thermiques (SEMT), Département de Modélisation des Systèmes et Structures (DM2S), CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire) (CEA-DES (ex-DEN)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire) (CEA-DES (ex-DEN)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Département de Modélisation des Systèmes et Structures (DM2S), and Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay more...
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Coupling ,Computer science ,Turbulence ,Mechanical Engineering ,Computation ,Vibro-impact dynamics ,Mechanics ,01 natural sciences ,FIV ,010305 fluids & plasmas ,Convolution ,Vibration ,Nonlinear system ,[SPI]Engineering Sciences [physics] ,Tube bundle ,Fluid–elastic instability ,0103 physical sciences ,Time domain ,Transverse flow ,010301 acoustics ,Impulse response - Abstract
Flow-induced vibrations of heat-exchanger tubes are extensively studied in the nuclear industry for safety reasons. Adequate designs, such as anti-vibration bars in PWR steam generators, prevent excessive vibrations provided the tubes are well supported. Nevertheless, degraded situations where the tube/support gaps would widen, must also be considered. In such a case, the tubes become loosely supported and may exhibit vibro-impacting responses due to both turbulence and fluid–elastic coupling forces induced by the cross-flow. This paper deals with the predictive analysis of such a nonlinear situation, given the necessity of taking into account both the strong impact nonlinearity due to the gap and the linearized fluid–elastic forces. In time-domain numerical simulations, computation of flow-coupling forces defined in the frequency-domain is a delicate problem. We recently developed an approach based on a hybrid time–frequency method. In the present paper a more straightforward and effective technique, based on the convolution of a flow impulse response pre-computed from the frequency-domain coefficients, is developed. Illustrative results are presented and discussed, in connection with the previous hybrid method and with experiments. All results agree in a satisfactory manner, validating both computational methods, however the convolutional technique is faster than the hybrid method by two orders of magnitude. Finally, to highlight the subtle self-regulating frequency effect on the stabilization of such system, additional demonstrative computations are presented. more...
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- 2018
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7. A new method for the generation of representative time-domain turbulence excitations
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Xavier Delaune, Jose Antunes, Philippe Piteau, Laurent Borsoi, Laboratoire d'études de DYNamique (DYN), Service d'Etudes Mécaniques et Thermiques (SEMT), Département de Modélisation des Systèmes et Structures (DM2S), CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire) (CEA-DES (ex-DEN)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire) (CEA-DES (ex-DEN)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Département de Modélisation des Systèmes et Structures (DM2S), and Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay more...
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Random field ,K-epsilon turbulence model ,Turbulence ,Mechanical Engineering ,Computation ,Flow-induced vibrations ,Projection (linear algebra) ,Physics::Fluid Dynamics ,[SPI]Engineering Sciences [physics] ,Nonlinear system ,Modal ,Classical mechanics ,Time-domain simulations ,Time domain ,Statistical physics ,Mathematics - Abstract
In this paper we address the issue of generating, from the spectral and spatial parameters of turbulent flow excitations, time-domain random excitations suitable for performing representative nonlinear numerical simulations of the dynamical responses of flow-excited tubes with multiple clearance supports. The new method proposed in this work, which is anchored in a sound physical basis, can effectively deal with non-uniform turbulent flows, which display significant changes in their spatial excitation properties. Contrary to the classic technique developed by Shinozuka and coworkers, which generates a large set of correlated physical forces, the proposed method directly generates a set of correlated modal forces. Our approach is particularly effective leading to a much smaller number of generated time-histories than would be needed using physical forces to simulate the turbulence random field. In the case of strongly non-uniform flows, our approach allows for a suitable decomposition of the flow velocity profile, so that the spectral properties of the turbulence excitation are modeled in a consistent manner. The proposed method for simulating turbulence excitations is faster than Shinozuka׳s technique by two orders of magnitude. Also, in the framework of our modal computational approach, nonlinear computations are faster, because no modal projection of physical turbulent forces is needed. After presenting the theoretical background and the details of the proposed simulation method, we illustrate it with representative linear and nonlinear computations performed on a multi-supported tube. more...
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- 2015
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8. Gap Effect on the Random and Fluid-Elastic Forces Acting in the Vibration of a Loosely Supported Tube Under Cross-Flow
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Jose Antunes, Philippe Piteau, Xavier Delaune, and Laurent Borsoi
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Physics::Fluid Dynamics ,Vibration ,Gap effect ,Materials science ,Flow (mathematics) ,business.industry ,Turbulence ,Phase space ,Tube (fluid conveyance) ,Structural engineering ,business - Abstract
In degraded situations of heat-exchangers, tubes may become loosely supported while subjected to intense crossflow which generates both turbulent and fluid-elastic forces. The vibro-impacting regimes that result have been studied by the authors during these last few years, based on analytical experiments and numerical simulations. Taking advantage of this material, the paper aims at showing some dynamic effects that have been observed and drawing lessons concerning the vibration of tubes under cross-flow when they are linearly unstable. If the fluid-elastic damping drops until the total damping becomes negative when the flow reduced velocity increases, a non-linear gap-system escapes from instability by reinforcing the sequence of impacts and its apparent frequency. On the other hand, the turbulent excitation is characterized by broadband PSDs that decrease with frequency. Thus the vibro-impacting response of the tubes results from a competition between the turbulent and fluid-elastic forces, according to a process that depends on the gap size. The fluid-elastic coupling forces may be either stabilizing (positive damping) or destabilizing (negative one), and, in a more amazing way, the random forces may be dissipative. The paper illustrates the previous points from the tested experimental configuration which was mainly 1-DOF. Dimensionless results are given for this configuration. Extensions to more realistic tubes are discussed from numerical simulations of a straight beam with three loosely supports. The starting point of simulations is though experiments where the fluid-elastic forces would act, but not the turbulent ones, which would produce limit cycles in the phase space. Turbulence is then considered as perturbation of limit cycles, and as shown below by notably introducing a dimensionless “gap-turbulence” parameter, smaller the gap sizes are, larger the relative weight of turbulence is. The Rice frequency and the mean impact force are indicators of this relative weight and the competition between the fluid-forces. From this general understanding, and using preliminary results with the beam model, a few guidelines are finally evoked for determining allowable gaps sizes in degraded situations. But a lot of work has to be done with more sophisticated models to concretize these ideas. more...
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- 2017
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9. On using the Hilbert transform for blind identification of systems with complex modes
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José Antunes, Philippe Piteau, Xavier Delaune, Laurent Borsoi, Vincent Debut, and Instituto de Etnomusicologia - Centro de Estudos em Música e Dança (INET-MD - NOVA FCSH)
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SOBI ,Complex modes ,System identification ,Hilbert transform - Abstract
UID/EAT/00472/2013 The modal identification of dynamical systems under operational conditions, when subjected to wide-band unmeasured excitations, is today a viable alternative to more traditional modal identification approaches based on processing sets of measured FRFs or impulse responses. Among current techniques for performing operational modal identification, the so-called blind identification methods are the subject of considerable investigation. In particular, the SOBI (Second-Order Blind Identification) method was found to be quite efficient. SOBI was originally developed for systems with normal modes. To address systems with complex modes, various extension approaches have been proposed, in particular: (a) Using a first-order state-space formulation for the system dynamics; (b) Building complex analytic signals from the measured responses using the Hilbert transform. In this paper we further explore the latter option, which is conceptually interesting while preserving the model order and size. Focus is on applicability of the SOBI technique for extracting the modal responses from analytic signals built from a set of vibratory responses. Aspects of the theoretical formulation for complex SOBI using the Hilbert transform are clarified and a convenient computational procedure for obtaining the complex cross-correlation response matrix is developed. We show that the correlation matrix of the analytic responses can be computed through a straightforward Hilbert transform of the standard real correlation matrix typically obtained from measurements. Then, based on numerical simulations of a physical multi-modal system subjected to distribute random excitation, we assert the quality of the identified modal matrix and modal responses extracted using both the standard and the complex SOBI techniques. To perform such analysis, a simple and feasible physical device is proposed, which enables controlled levels of the modeshapes complexity, without introducing significant modal damping even for strongly complex modes. publishersversion published more...
- Published
- 2016
10. Experimental Identification of Fluid-Elastic Coupling Forces on a Square Tube Bundle Subjected to Single-Phase Cross-Flow
- Author
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Jose Antunes, Philippe Piteau, Laurent Borsoi, and Xavier Delaune
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Vibration ,Physics ,Flow (mathematics) ,Bundle ,Coupling (piping) ,Tube (fluid conveyance) ,Single phase ,Composite material ,Square (algebra) - Abstract
The importance of fluid-elastic coupling forces in tube bundle vibrations is well documented and can hardly be over-emphasized, in view of their damaging potential. Even when adequate tube supports are provided to suppress fluid-elastic instabilities, the flow-coupling forces still affect the dynamical tube responses and remain a significant issue, in particular concerning the vibro-impact motions of tubes assembled using clearance supports. Therefore, the need remains for more advanced models of fluid-elastic coupling, as well as for experimental flow-coupling coefficients to feed and validate such models. In this work, we report an extensive series of experiments performed at CEA-Saclay leading to the identification of stiffness and damping fluid-elastic coefficients, for a 3×5 square tube bundle (D = 30 mm, P/D = 1.5) subjected to single-phase transverse flow. The bundle is rigid, except for the central tube which is mounted on a flexible suspension (two parallel steel blades) allowing for translation motions of the tube in the lift direction. The system is thus single-degree of freedom, allowing fluid-elastic instability to arise through a negative damping mechanism. The flow-coupling stiffness and damping coefficients, Kf(Vr) and Cf(Vr), are experimentally identified as functions of the reduced velocity Vr. Identification is achieved on the basis of changes in tube vibration frequency and reduced damping as a function of flow velocity, assuming a constant fluid added mass. In the present experiments, coefficient identification is performed well beyond the instability boundary, by using active control, thereafter allowing exploration of a significant range of flow velocity. The modal frequency and the modal mass of the system are respectively modified by changing the tube suspension stiffness, and/or by adding a mass to the system. We can thus assert how the fluid-elastic coefficients change, for this configuration, with these two system parameters, all other parameters being kept constant. The results obtained from the configurations tested suggest that formulations for coefficient reduction may be improved, in order to better collapse the identified data. more...
- Published
- 2016
- Full Text
- View/download PDF
11. Primitive Model for the Random Excitation of a Tube Under Two-Phase Cross Flow
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Philippe Piteau, Laurent Borsoi, Jose Antunes, and Xavier Delaune
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Momentum ,Vibration ,Physics ,Flow (mathematics) ,Stochastic process ,Phase (waves) ,Tube (fluid conveyance) ,Two-phase flow ,Mechanics ,Excitation - Abstract
Flow-induced vibration of heat-exchangers tubes is particularly studied in the nuclear industry for safety and cost reasons. It implies to have, among others, relevant characterizations of the random buffeting forces the cross-flow applies to the tube bundle. Work is still needed in this domain, particularly for two-phase flow, to improve the available data as the ones for PWR steam generator, currently very envelope. In parallel to get new experimental data, using “real” or substitutional mixtures (e.g. air-water instead of steam-water for PWR), it is essential to understand the basic excitation mechanisms which induce the vibrations under two-phase flow, as e.g. the influence of flow regimes. In this general framework, what can be learnt from deliberately simple models may be a contributive help. As a first attempt on this issue, the paper deals with the elementary case of a single rigid tube under air-water cross flow. This case is part of experiments carried out at CEA-Saclay with bundles where both tube support reactions and flow characteristics are measured, with respectively piezo-electrical sensors and bi-optical probes (BOP). The information provided by the BOP (mean interface velocity, statistical distribution, etc.) feeds a primitive model of water “droplet” impulses on the tube, based on a lot of crude assumptions about impact velocity, momentum conservation, impulse shape, statistical independence, etc., and which uses analytical results of random processes constructed from the superposition of random pulses. The “equivalent” excitation force, obtained in terms of dimensional PSD, is compared to the one measured in the drag and lift direction with an acceptable agreement, at least in order of magnitude. Comments and lessons are drawn from this first attempt, and some paths are advanced to improve this kind of primitive models, especially for treating rigid square bundles under air-water cross flow. more...
- Published
- 2016
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12. Experiments and computations of a loosely supported tube in a rigid bundle subjected to single-phase flow
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Jose Antunes, Laurent Borsoi, Xavier Delaune, and Philippe Piteau
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Coupling ,Engineering ,Cantilever ,business.industry ,Turbulence ,Mechanical Engineering ,Flow (psychology) ,Mechanics ,Structural engineering ,Nonlinear system ,Vortex-induced vibration ,Bundle ,Time domain ,business - Abstract
In this paper the problem of computing the nonlinear vibro-impact responses of loosely supported heat-exchanger tubes subjected to fluidelastic coupling forces, as well as to the turbulence excitation from transverse flows, is addressed. Emphasis is on the fluidelastic modeling within a time domain nonlinear framework, as well as on the stabilizing effect of impacts on the fluidelastic coupling forces. Theoretical computations of the linear and vibro-impacting regimes of a flow-excited flexible cantilever test tube, within a rigid 3×5 square bundle, are based on the experimentally identified fluidelastic coupling force coefficients and turbulence spectrum. Computations are then compared with the experimental vibratory responses, enabling a full validation of the modeling approach. Furthermore, interesting conclusions are drawn, concerning (a) the energy balance between sources and sinks, for a vibro-impacting tube subjected to fluidelastic forces and (b) the dependence of the vibration response frequency on impacts at the loose supports, and their effect on the nonlinear restabilization of fluidelastically unstable tubes. Details on the following aspects are reported in the paper: (1) numerical modeling of the fluidelastic coupling forces for the time domain computations; (2) experimental identification of the fluidelastic coupling coefficients; (3) computations and experiments of both linear and vibro-impacting responses under the combined action of turbulence and fluidelastic coupling and (4) energy aspects of the vibro-impacting fluidelastically coupled tube responses. more...
- Published
- 2012
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13. Computation of a Loosely Supported Tube Under Cross-Flow by a Hybrid Time-Frequency Method
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Laurent Borsoi, Philippe Piteau, Xavier Delaune, Ioannis Politopoulos, and Jose Antunes
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Vibration ,Engineering ,business.industry ,Turbulence ,Computation ,Bundle ,Frequency domain ,Dissipative system ,Extrapolation ,Structural engineering ,Mechanics ,Time domain ,business - Abstract
Flow-induced vibrations of heat-exchanger tubes are particularly analyzed in the nuclear industry for safety reasons. Adequate designs, such as anti-vibration bars in PWR steam generators, prevent any excessive vibrations provided the tubes are well supported. Nevertheless degraded situations, where the tube/support gaps would widen, must also be considered. In such a case, the tubes become loosely supported and may exhibit vibro-impacting responses due to both turbulence and fluid-elastic coupling forces induced by the cross-flow. This paper deals with the predictive analysis of such a situation, based on a time-frequency hybrid method, given the necessity of taking into account both the strong impact nonlinearity due to the gap and the linearized fluid-elastic forces defined in the frequency domain. It comprises four parts. 1) The experimental campaign carried out at CEA Saclay on this issue, with a rigid square bundle surrounding a flexible cantilever tube under water cross-flow, is briefly recalled. 2) The hybrid time-frequency method is presented. The technique consists in an iterative solving, going back and forth from the frequency domain to the time domain, until convergence. Focus is made on the key points that are the algorithm convergence, and the non-causality of fluid-elastic forces stemming from the extrapolation of the frequency-limited experimental data. 3) The experimental and computational results are compared for a large range of flow velocities and three values of gaps, with a satisfying overall agreement. The comparison includes also previous results obtained from a simplified method based on the concept of “instantaneous” frequency. 4) Finally two a priori surprising behaviors are noted in the energy balances that have been computed: the sometimes dissipative aspect of turbulence forces, and the “mirror effect” between the work of turbulence and fluid-elastic forces. more...
- Published
- 2015
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14. Identification of Random Excitation Fields From Vibratory Responses With Application to Multisupported Tubes Excited by Flow Turbulence
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Philippe Piteau, Jose Antunes, Xavier Delaune, Laurent Borsoi, Laboratoire d'études de DYNamique (DYN), Service d'Etudes Mécaniques et Thermiques (SEMT), Département de Modélisation des Systèmes et Structures (DM2S), CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire) (CEA-DES (ex-DEN)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire) (CEA-DES (ex-DEN)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Département de Modélisation des Systèmes et Structures (DM2S), and Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay more...
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Physics ,Turbulence ,Mechanical Engineering ,Modal analysis ,Acoustics ,Spectral line ,[SPI]Engineering Sciences [physics] ,Modal ,Amplitude ,Flow velocity ,Mechanics of Materials ,Excited state ,Safety, Risk, Reliability and Quality ,Excitation - Abstract
In this paper, we address the identification of the spectral and spatial features of random flow excitations for multisupported tubular components such as steam generator tubes and nuclear fuel rods. In the proposed work, source identification is performed from a set of measured vibratory responses, in the following manner: (1) The modal response spectra and modeshape amplitudes at the measurement locations are first extracted through a blind decomposition of the physical response matrix, using the second order blind identification (SOBI) method; (2) the continuous modeshapes are interpolated from the identified values at the measurement locations; (3) the system modal parameters are identified from the modal responses using a simple single degree of freedom (SDOF) fitting technique; (4) inversion from the modal response spectra is performed for the identification of the modal excitation spectra; (5) finally, an equivalent physical excitation spectrum as well as the flow velocity profiles are estimated. The proposed approach is illustrated with identification results based on realistic numerical simulations of a multisupported tube under linear support conditions. more...
- Published
- 2014
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15. Applications of hybrid time–frequency methods in nonlinear structural dynamics
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Jose Antunes, Laurent Borsoi, Ioannis Politopoulos, Ph. Piteau, Laboratoire d'Etudes de Mécanique Sismique (EMSI), Service d'Etudes Mécaniques et Thermiques (SEMT), Département de Modélisation des Systèmes et Structures (DM2S), CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire) (CEA-DES (ex-DEN)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire) (CEA-DES (ex-DEN)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Département de Modélisation des Systèmes et Structures (DM2S), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay, and Laboratoire d'études de DYNamique (DYN) more...
- Subjects
Hybrid time–frequency ,Laplace transform ,Mathematical analysis ,Inverse Laplace transform ,Bilinear time–frequency distribution ,Transfer function ,symbols.namesake ,[SPI]Engineering Sciences [physics] ,Fourier transform ,Laplace transform applied to differential equations ,Nonlinear dynamics ,symbols ,Two-sided Laplace transform ,Time-Laplace ,Impulse response ,Civil and Structural Engineering ,Mathematics - Abstract
This paper presents a study on methods which may be used to compute the nonlinear response of systems whose linear properties are determined in the frequency or Laplace domain. Typically, this kind of situation may arise in soil–structure and fluid–structure interaction problems. In particular three methods are investigated: (a) the hybrid time–frequency method, (b) the computation of the convolution integral which requires an inverse Fourier or Laplace transform of the system’s transfer function, and (c) the identification of an equivalent system defined in the time domain which may be solved with classical time integration methods. These methods are illustrated by their application to some simple, one degree of freedom, non-linear systems and their advantages and drawbacks are highlighted. more...
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- 2014
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16. Quelques exemples d'interaction fluide-structure dans les réacteurs nucléaires
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Laurent Borsoi
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Physics ,Bearing (mechanical) ,law ,Fluid–structure interaction ,Mechanics ,Cartography ,Elaboration ,Water Science and Technology ,law.invention - Abstract
Having gone through the specificity of nuclear energy beforehand, this article deals with the issue of Fluid Structure Interaction (FSI) in nuclear reactors. In this respect, it makes use of some cases taken out of the French electro-nuclear project. Bearing these examples in mind, it ends with a prospective elaboration of the needs of FSI in 10 years time. more...
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- 2000
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17. Simple Relations for Estimating the Unknown Functions of Incomplete Experimental Spectral and Correlation Response Matrices
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Laurent Borsoi, Jose Antunes, Philippe Piteau, and Xavier Delaune
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Vibration ,Correlation ,Transducer ,Cover (topology) ,Computer science ,Consistency (statistics) ,Simple (abstract algebra) ,Mathematical analysis ,System identification ,Algorithm ,Spectral line - Abstract
In this paper we suggest two simple approximate methods to estimate the unknown terms of incomplete spectral or correlation matrices, when the cross-spectra or cross-correlations available from multiple measurements do not cover all pairs of transducer locations. The proposed techniques may be applied whenever the available data includes the auto-spectra at all measurement locations, as well as selected cross-spectra which implicates all measurement locations. The suggested formulae can also be used for checking the consistency between the spectral or correlation functions pertaining to measurement matrices, in cases of suspicious data. After presenting the proposed formulations, we discuss their merits and limitations. Then we illustrate their use on a realistic simulation of a multi-supported tube subjected to turbulence excitation from cross-flow. more...
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- 2013
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18. Identification of the Turbulence Force Field Excitation From a Set of Vibratory Responses of a Multi-Supported Tube
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Philippe Piteau, Laurent Borsoi, Jose Antunes, and Xavier Delaune
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Engineering ,Amplitude ,Modal ,Flow velocity ,business.industry ,Turbulence ,Modal analysis ,Acoustics ,business ,Spectral line ,Excitation ,Rod - Abstract
In this paper we address the identification of the spectral and spatial features of random flow excitations, for multi-supported tubular components such as steam generator tubes and nuclear fuel rods. In the proposed work, source identification is performed from a set of measured vibratory responses, in the following manner: (1) The modal response spectra and modeshape amplitudes at the measurement locations are first extracted through a blind decomposition of the physical response matrix, using the SOBI method; (2) The continuous modeshapes are interpolated from the identified values at the measurement locations; (3) The system modal parameters are identified from the modal responses using a simple SDOF fitting technique; (4) Inversion from the modal response spectra is performed for the identification of the modal excitation spectra; (5) Finally, an equivalent physical excitation spectra as well as the flow velocity profiles are estimated. The proposed approach is illustrated with identification results based on realistic numerical simulations of a multi-supported tube under linear support conditions.Copyright © 2013 by ASME more...
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- 2013
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19. Vibro-Impact Experiments and Computations of a Gap-Supported Tube Subjected to Single-Phase Fluid-Elastic Coupling Forces
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Jose Antunes, Philippe Piteau, Laurent Borsoi, and Xavier Delaune
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Coupling ,Engineering ,Cantilever ,Turbulence ,business.industry ,Computation ,Mechanics ,Physics::Fluid Dynamics ,Vibration ,Nonlinear system ,Transverse plane ,Classical mechanics ,Bundle ,business - Abstract
In this paper we address the problem of computing the nonlinear vibro-impact responses of gap-supported heat-exchanger tubes subjected to fluid-elastic coupling forces, as well as to the turbulence excitation from transverse flows. Emphasis is on the fluid-elastic modeling within a time-domain nonlinear framework, as well as on the stabilizing effect of impacts on the fluid-elastic coupling forces. Theoretical computations of the linear and vibro-impacting regimes of a flow-excited cantilever test tube, within a rigid 3×5 square bundle, are based on the experimentally identified fluid-elastic coupling force coefficients and turbulence spectrum. Computations are then compared with the experimental vibratory responses, enabling a full validation of the modeling approach. Furthermore, interesting conclusions are drawn, concerning: (a) the energy balance between sources and sinks, for a vibro-impacting tube subjected to fluid-elastic forces; (b) the dependence of the vibration response frequency on impacts at the loose supports, and their effect on the nonlinear re-stabilization of fluid-elastically unstable tubes. Details on the following aspects are reported in the paper: (1) Numerical modeling of the fluid-elastic coupling forces for time-domain computations; (2) Experimental identification of the fluid-elastic coupling coefficients; (3) Computations and experiments of both linear and vibro-impacting responses under the combined action of turbulence and fluid-elastic coupling; and (4) Energy aspects of the vibro-impacting fluid-elastically coupled tube responses.Copyright © 2010 by ASME more...
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- 2010
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20. Modal Techniques for Remote Identification of Nonlinear Reactions at Gap-Supported Tubes Under Turbulent Excitation
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Laurent Borsoi, Jose Antunes, Vincent Debut, Xavier Delaune, and Philippe Piteau
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Engineering ,business.industry ,Mechanical Engineering ,Modal analysis ,Computation ,Acoustics ,Inverse problem ,Contact force ,Vibration ,Nonlinear system ,Contact mechanics ,Modal ,Mechanics of Materials ,Safety, Risk, Reliability and Quality ,business ,Simulation - Abstract
Predictive computation of the nonlinear dynamical responses of gap-supported tubes subjected to flow excitation has been the subject of very active research. Nevertheless, experimental results are still very important, for validation of the theoretical predictions as well as for asserting the integrity of field components. Because carefully instrumented test tubes and tube-supports are seldom possible, due to space limitations and to the severe environment conditions, there is a need for robust techniques capable of extracting, from the actual vibratory response data, information that is relevant for asserting the components integrity. The dynamical contact/impact (vibro-impact) forces are of paramount significance, as are the tube/support gaps. Following our previous studies in this area using wave-propagation techniques (De Araújo, Antunes, and Piteau, 1998, “Remote Identification of Impact Forces on Loosely Supported Tubes: Part 1—Basic Theory and Experiments,” J. Sound Vib., 215, pp. 1015–1041; Antunes, Paulino, and Piteau, 1998, “Remote Identification of Impact Forces on Loosely Supported Tubes: Part 2—Complex Vibro-Impact Motions,” J. Sound Vib., 215, pp. 1043–1064; Paulino, Antunes, and Izquierdo, 1999, “Remote Identification of Impact Forces on Loosely Supported Tubes: Analysis of Multi-Supported Systems,” ASME J. Pressure Vessel Technol., 121, pp. 61–70), we apply modal methods in the present paper for extracting such information. The dynamical support forces, as well as the vibratory responses at the support locations, are identified from one or several vibratory response measurements at remote transducers, from which the support gaps can be inferred. As for most inverse problems, the identification results may prove quite sensitive to noise and modeling errors. Therefore, topics discussed in the paper include regularization techniques to mitigate the effects of nonmeasured noise perturbations. In particular, a method is proposed to improve the identification of contact forces at the supports when the system is excited by an unknown distributed turbulence force field. The extensive identification results presented are based on realistic numerical simulations of gap-supported tubes subjected to flow turbulence excitation. We can thus confront the identified dynamical support contact forces and vibratory motions at the gap-support with the actual values stemming from the original nonlinear computations. The important topic of dealing with the imperfect knowledge of the modal parameters used to build the inverted transfer functions is thoroughly addressed elsewhere (Debut, Delaune, and Antunes, 2009, “Identification of Nonlinear Interaction Forces Acting on Continuous Systems Using Remote Measurements of the Vibratory Responses,” Proceedings of the Seventh EUROMECH Solids Mechanics Conference (ESMC2009), Lisbon, Portugal, Sept. 7–11). Nevertheless, identifications are performed in this paper based on both the exact modes and also on randomly perturbed modal parameters. Our results show that, for the system addressed here, deterioration of the identifications is moderate when realistic errors are introduced in the modal parameters. In all cases, the identified results compare reasonably well with the real contact forces and motions at the gap-supports. more...
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- 2009
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21. Experimental and Computational Investigation Into Vibration Wear of Control Rods in French PWRs
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Laurent Borsoi, Christian Canteneur, and Gérard Barbe
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The under-card wear of control rods due to flow-induced vibration was discovered in 1986. To cope with this phenomenon, Framatome at once erected the full-scale Magaly test facility, in operation since 1988. Then in 1991 Framatome initiated exploratory numerical simulations using the Nat03 structural code specifically developed for this purpose. After introducing Magaly and Nat03, this paper illustrates how the following ill-posed inverse-problem has been attacked: from rod vibration measured with Magaly, how to calibrate via Nat03 computation a rustic model of the rod excitation created by the main flow coming from the fuel assembly. A single force applied on the control rod just beyond the continuous guidance section is sufficient to “support” after adjustment all the available experiment-computation comparisons: rod displacement (trajectory, standard deviation, PSD), contact force (average value, contact duration), and wear work rate, for three control rods differently located in the cards and nine card elevations with different flow rates. more...
- Published
- 1997
- Full Text
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