J. Gargouri, Ezzeddine Hadj-ta¨ıeb, C. Schmitt, G. Pluvinage
Un modele numerique, permettant d’obtenir de maniere automatique des informations sur la propagation des ondes de coup de belier dans les reseaux mailles de conduites, est presente. Le modele tient compte des bifurcations et des derivations dans les reseaux de conduites ainsi que des pertes de charges. Il est constitue d’un systeme de deux equations aux derivees partielles non-lineaires de type hyperbolique resolu par la methode des caracteristiques. L’algorithme numerique ainsi construit fournit une estimation des pressions maximales dans le fluide et des contraintes maximales dans les parois dues a la fermeture rapide de vannes. Dans certains cas, la contrainte maximale peut devenir superieure a la contrainte admissible et provoque la rupture des conduites. La dangerosite d’un defaut de type cratere de corrosion a ete analysee en determinant la distribution des contraintes en tete de ce defaut. Les resultats obtenus permettent de calculer le facteur d’intensite de contraintes d’entaille applique. Cette grandeur est inseree dans un diagramme Integrite-Rupture de type SINTAP et les nœuds en situation critique sont determines. Il y a risque de rupture si le facteur de securite est inferieur a 2. Les resultats de calcul montrent que presque tous les nœuds du reseau analyse sont situes en dehors du domaine d’integrite.
{"title":"Analyse des conditions de rupture des canalisations des réseaux maillés due au phénomène de coup de bélier","authors":"J. Gargouri, Ezzeddine Hadj-ta¨ıeb, C. Schmitt, G. Pluvinage","doi":"10.1051/MECA/2011015","DOIUrl":"https://doi.org/10.1051/MECA/2011015","url":null,"abstract":"Un modele numerique, permettant d’obtenir de maniere automatique des informations sur la propagation des ondes de coup de belier dans les reseaux mailles de conduites, est presente. Le modele tient compte des bifurcations et des derivations dans les reseaux de conduites ainsi que des pertes de charges. Il est constitue d’un systeme de deux equations aux derivees partielles non-lineaires de type hyperbolique resolu par la methode des caracteristiques. L’algorithme numerique ainsi construit fournit une estimation des pressions maximales dans le fluide et des contraintes maximales dans les parois dues a la fermeture rapide de vannes. Dans certains cas, la contrainte maximale peut devenir superieure a la contrainte admissible et provoque la rupture des conduites. La dangerosite d’un defaut de type cratere de corrosion a ete analysee en determinant la distribution des contraintes en tete de ce defaut. Les resultats obtenus permettent de calculer le facteur d’intensite de contraintes d’entaille applique. Cette grandeur est inseree dans un diagramme Integrite-Rupture de type SINTAP et les nœuds en situation critique sont determines. Il y a risque de rupture si le facteur de securite est inferieur a 2. Les resultats de calcul montrent que presque tous les nœuds du reseau analyse sont situes en dehors du domaine d’integrite.","PeriodicalId":49847,"journal":{"name":"Mecanique & Industries","volume":"12 1","pages":"131-137"},"PeriodicalIF":0.0,"publicationDate":"2011-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87451623","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Kwassi Anani, R. Prud’homme, S. d’Almeida, K. Assiamoua
We study the dynamic response to small acoustic oscillations of a vaporizing droplet in shape of a pastille (a small liquid cylinder, called “pastille” in the sequel, the height of which being smaller than the radius of the base). Contrary to some previously proposed models, where the thermal convection effect inside the droplet is often neglected, the continuously fed pastille-shaped model takes into account the effects of both thermal convection and conduction. Curves related to different heat exchange coefficients are presented for the frequency response of the vaporization rate. The case where the feeding process at the bottom of the pastille is assumed isothermal (isothermal bottom regime) is compared to the one where the feeding process at the bottom of the pastille is adiabatic (adiabatic bottom regime). The response factor curves for the pure conduction model of the spherical droplet and for the present model of the “equivalent pastille” are also compared. The temperature field perturbation is then examined. As well as for the evaporation mass flow rate perturbation, comparisons are made between the regime with an isothermal bottom and the one with an adiabatic bottom. We find that, in spite of some divergences observed between the various cases, the frequency response of a droplet submitted to acoustic oscillations presents also some common points. It is shown that the life time (or residence time), the thermal diffusion time, and the period of the harmonic perturbation do intervene strongly in the behaviour of the vaporizing pastille. The liquid propulsion is a possible application of this basic study conducted as part of a thesis.
{"title":"Effect of thermal convection on frequency response of a perturbed vaporizing pastille-shaped droplet","authors":"Kwassi Anani, R. Prud’homme, S. d’Almeida, K. Assiamoua","doi":"10.1051/MECA/2011102","DOIUrl":"https://doi.org/10.1051/MECA/2011102","url":null,"abstract":"We study the dynamic response to small acoustic oscillations of a vaporizing droplet in shape of a pastille (a small liquid cylinder, called “pastille” in the sequel, the height of which being smaller than the radius of the base). Contrary to some previously proposed models, where the thermal convection effect inside the droplet is often neglected, the continuously fed pastille-shaped model takes into account the effects of both thermal convection and conduction. Curves related to different heat exchange coefficients are presented for the frequency response of the vaporization rate. The case where the feeding process at the bottom of the pastille is assumed isothermal (isothermal bottom regime) is compared to the one where the feeding process at the bottom of the pastille is adiabatic (adiabatic bottom regime). The response factor curves for the pure conduction model of the spherical droplet and for the present model of the “equivalent pastille” are also compared. The temperature field perturbation is then examined. As well as for the evaporation mass flow rate perturbation, comparisons are made between the regime with an isothermal bottom and the one with an adiabatic bottom. We find that, in spite of some divergences observed between the various cases, the frequency response of a droplet submitted to acoustic oscillations presents also some common points. It is shown that the life time (or residence time), the thermal diffusion time, and the period of the harmonic perturbation do intervene strongly in the behaviour of the vaporizing pastille. The liquid propulsion is a possible application of this basic study conducted as part of a thesis.","PeriodicalId":49847,"journal":{"name":"Mecanique & Industries","volume":"39 1","pages":"301-313"},"PeriodicalIF":0.0,"publicationDate":"2011-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87533580","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
H. Phan, N. Caney, P. Marty, S. Colasson, J. Gavillet
This paper investigates the flow boiling heat transfer in microchannels with the aim of developing compact cooling systems which can be adapted to miniaturized power components. Nano- and micro-surface treatments were used as innovative techniques to improve the heat transfer performance as well as to delay the intermittent dryout. It was observed that the micro-structured surfaces show significant enhancements (up to 85%) in heat transfer compared to the smooth surfaces. Especially, using the highly-wetted structured surface, the intermittent dryout is improved.
{"title":"Enhancement of flow boiling heat transfer in microchannels by nano- and micro-surface treatments","authors":"H. Phan, N. Caney, P. Marty, S. Colasson, J. Gavillet","doi":"10.1051/MECA/2011111","DOIUrl":"https://doi.org/10.1051/MECA/2011111","url":null,"abstract":"This paper investigates the flow boiling heat transfer in microchannels with the aim of developing compact cooling systems which can be adapted to miniaturized power components. Nano- and micro-surface treatments were used as innovative techniques to improve the heat transfer performance as well as to delay the intermittent dryout. It was observed that the micro-structured surfaces show significant enhancements (up to 85%) in heat transfer compared to the smooth surfaces. Especially, using the highly-wetted structured surface, the intermittent dryout is improved.","PeriodicalId":49847,"journal":{"name":"Mecanique & Industries","volume":"10 1","pages":"151-155"},"PeriodicalIF":0.0,"publicationDate":"2011-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84376621","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper is intented to study both free and forced vibration of a nonlinear structure with cyclic symmetry, under geometric nonlinearity, through use of the harmonic balance method (HBM). In order to study the influence of nonlinearity due to the large deflection of blades, a simplified model has been developed. After adjusting the model parameters, this approach leads to a system of linearly-coupled, second-order nonlinear differential equations, in which nonlinearity appears via quadratic and cubic terms. Periodic solutions, are sought by applying HBM coupled with an arc length continuation method. In the free case, in addition to featuring similar and nonsimilar nonlinear modes, the unforced system is shown to contain localized nonlinear modes. In the forced case, several cases of excitation have been analyzed (low-engine-order excitation and detuned excitation) and we study the influence of the excitation level on the structure of dynamical response. For a sufficiently-detuned excitation, we show that several solutions can coexist, some of them being represented by closed curves in the frequency-amplitude domain.
{"title":"Simulation et analyse d’une structure non-linéaire à symétrie cyclique","authors":"Aurelien Grolet, F. Thouverez, Pierrick Jean","doi":"10.1051/MECA/2010047","DOIUrl":"https://doi.org/10.1051/MECA/2010047","url":null,"abstract":"This paper is intented to study both free and forced vibration of a nonlinear structure with cyclic symmetry, under geometric nonlinearity, through use of the harmonic balance method (HBM). In order to study the influence of nonlinearity due to the large deflection of blades, a simplified model has been developed. After adjusting the model parameters, this approach leads to a system of linearly-coupled, second-order nonlinear differential equations, in which nonlinearity appears via quadratic and cubic terms. Periodic solutions, are sought by applying HBM coupled with an arc length continuation method. In the free case, in addition to featuring similar and nonsimilar nonlinear modes, the unforced system is shown to contain localized nonlinear modes. In the forced case, several cases of excitation have been analyzed (low-engine-order excitation and detuned excitation) and we study the influence of the excitation level on the structure of dynamical response. For a sufficiently-detuned excitation, we show that several solutions can coexist, some of them being represented by closed curves in the frequency-amplitude domain.","PeriodicalId":49847,"journal":{"name":"Mecanique & Industries","volume":"83 1","pages":"453-463"},"PeriodicalIF":0.0,"publicationDate":"2010-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72642673","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
An emerging research topic in civil engineering is the dynamic interaction between crowds and structures. Structures such as footbridges, which oscillate due to the crossing of a group of pedestrians, or stands within stadia or concert halls, which vibrate due to the rythmic movement of the audience are of particular interest. The objective of this study is twofold: modelling the movement of pedestrians with consideration of pedestrian-pedestrian, and pedestrian-obstacle interactions, and the incorporation of a pedestrian-structure coupling in the previous model. Fremond’s model, which allows us to simulate the movement of an assembly of particles and accounts for collisions among considered rigid particles, is presented and adapted to the crowd by giving a willingness to the circular particles, which allows each pedestrian to move according to a given target. To handle the crowd-structure interaction in the case of lateral oscillations of footbridges, the Kuramoto differential equation governing the time evolution of the lateral motion of each pedestrian is implemented in the previous model. Preliminary results obtained from numerical simulations are presented and discussed.
{"title":"Modelling crowd-structure interaction","authors":"P. Pécol, S. Pont, S. Erlicher, P. Argoul","doi":"10.1051/MECA/2010057","DOIUrl":"https://doi.org/10.1051/MECA/2010057","url":null,"abstract":"An emerging research topic in civil engineering is the dynamic interaction between crowds and structures. Structures such as footbridges, which oscillate due to the crossing of a group of pedestrians, or stands within stadia or concert halls, which vibrate due to the rythmic movement of the audience are of particular interest. The objective of this study is twofold: modelling the movement of pedestrians with consideration of pedestrian-pedestrian, and pedestrian-obstacle interactions, and the incorporation of a pedestrian-structure coupling in the previous model. Fremond’s model, which allows us to simulate the movement of an assembly of particles and accounts for collisions among considered rigid particles, is presented and adapted to the crowd by giving a willingness to the circular particles, which allows each pedestrian to move according to a given target. To handle the crowd-structure interaction in the case of lateral oscillations of footbridges, the Kuramoto differential equation governing the time evolution of the lateral motion of each pedestrian is implemented in the previous model. Preliminary results obtained from numerical simulations are presented and discussed.","PeriodicalId":49847,"journal":{"name":"Mecanique & Industries","volume":"18 1","pages":"495-504"},"PeriodicalIF":0.0,"publicationDate":"2010-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82385158","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Bellino, S. Marchesiello, A. Fasana, L. Garibaldi
This paper approaches a novel technique to estimate cable tension simply based on its vibration response. The vibration response has been quite extensively adopted in the past due to its simplicity and, mainly, because the inverse approach allows the tension estimation with the cable in its original site. A first tentative approach consists in using a certain number of experimentally measured natural frequencies to be introduced in the theoretical vibration formula; this formula, however, involves also the cable length, the cable mass per unit length and its flexural rigidity. Unfortunately, some problems arise in its application to real structures, such as the case of suspended and cable-stayed bridges, because the exact cable length cannot be measured (it appears at the fourth exponent in the vibration formula); moreover section and weight can be estimated within a certain degree of accuracy, whilst the boundary conditions are often defined with difficulty. A novel extension of the method is here proposed, which takes advantage from a moving mass travelling on the cable. This is the case occurring when cables are verified with magnetic-based technology to detect rope faults and cross section reduction. In this way, the extracted natural frequencies are varying with time due to the moving load, and hence they have to be extracted adopting a time-varying approach. Although some approximation linked to the shape modification must be introduced, a simple iterative procedure can be settled, by considering the cable length as an unknown. An estimation of the equivalent length is given, and successively this value is used to obtain an estimation of the cable tension.
{"title":"Cable tension estimation by means of vibration response and moving mass technique","authors":"A. Bellino, S. Marchesiello, A. Fasana, L. Garibaldi","doi":"10.1051/MECA/2010058","DOIUrl":"https://doi.org/10.1051/MECA/2010058","url":null,"abstract":"This paper approaches a novel technique to estimate cable tension simply based on its vibration response. The vibration response has been quite extensively adopted in the past due to its simplicity and, mainly, because the inverse approach allows the tension estimation with the cable in its original site. A first tentative approach consists in using a certain number of experimentally measured natural frequencies to be introduced in the theoretical vibration formula; this formula, however, involves also the cable length, the cable mass per unit length and its flexural rigidity. Unfortunately, some problems arise in its application to real structures, such as the case of suspended and cable-stayed bridges, because the exact cable length cannot be measured (it appears at the fourth exponent in the vibration formula); moreover section and weight can be estimated within a certain degree of accuracy, whilst the boundary conditions are often defined with difficulty. A novel extension of the method is here proposed, which takes advantage from a moving mass travelling on the cable. This is the case occurring when cables are verified with magnetic-based technology to detect rope faults and cross section reduction. In this way, the extracted natural frequencies are varying with time due to the moving load, and hence they have to be extracted adopting a time-varying approach. Although some approximation linked to the shape modification must be introduced, a simple iterative procedure can be settled, by considering the cable length as an unknown. An estimation of the equivalent length is given, and successively this value is used to obtain an estimation of the cable tension.","PeriodicalId":49847,"journal":{"name":"Mecanique & Industries","volume":"24 1","pages":"505-512"},"PeriodicalIF":0.0,"publicationDate":"2010-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84670734","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Le Forage Grande Vitesse Vibratoire (FGVV) est un nouveau procede de percage qui permet de tripler la productivite des percages profonds en supprimant les cycles d’evacuation des copeaux ainsi que la lubrification. Pour cela un porte-outil specifique aete developpe, qui entre en vibrations axiales auto-entretenues lors de la coupe et permet le fractionnement du copeau, facilitant ainsi sonevacuation. Pour anticiper uneeventuelle diminution de la duree de vie des roulements a billes de l’electrobroche resultant de ces vibrations, un modele global du comportement dynamique du systeme tete vibratoire-electrobroche est presente. Ce modele est base sur la modelisation du comportement des entites structurales par deselements-finis de type « poutre-rotor» prenant en compte les effets dynamiques associes aux hautes frequences de rotations de l’electrobroche, couple a des modeles d’interfaces identifies par la methode de couplage de receptance. Le modele est valide a l’aide d’experimentations qui montrent une bonne correspondance entre les resultats experimentaux et numeriques. Le modele est ensuite utilise pour calculer la duree de vie des roulements a billes de l’electrobroche lors de differentes operations de percage. L’influence de la frequence de rotation et de l’avance sur la duree de vie des roulements estetudiee, permettant ainsi de faire ressortir des plages de fonctionnement optimal.
{"title":"Prédiction du comportement dynamique du système de forage grande vitesse vibratoire","authors":"F. Forestier, Vincent Gagnol, P. Ray, Henry Paris","doi":"10.1051/MECA/2010042","DOIUrl":"https://doi.org/10.1051/MECA/2010042","url":null,"abstract":"Le Forage Grande Vitesse Vibratoire (FGVV) est un nouveau procede de percage qui permet de tripler la productivite des percages profonds en supprimant les cycles d’evacuation des copeaux ainsi que la lubrification. Pour cela un porte-outil specifique aete developpe, qui entre en vibrations axiales auto-entretenues lors de la coupe et permet le fractionnement du copeau, facilitant ainsi sonevacuation. Pour anticiper uneeventuelle diminution de la duree de vie des roulements a billes de l’electrobroche resultant de ces vibrations, un modele global du comportement dynamique du systeme tete vibratoire-electrobroche est presente. Ce modele est base sur la modelisation du comportement des entites structurales par deselements-finis de type « poutre-rotor» prenant en compte les effets dynamiques associes aux hautes frequences de rotations de l’electrobroche, couple a des modeles d’interfaces identifies par la methode de couplage de receptance. Le modele est valide a l’aide d’experimentations qui montrent une bonne correspondance entre les resultats experimentaux et numeriques. Le modele est ensuite utilise pour calculer la duree de vie des roulements a billes de l’electrobroche lors de differentes operations de percage. L’influence de la frequence de rotation et de l’avance sur la duree de vie des roulements estetudiee, permettant ainsi de faire ressortir des plages de fonctionnement optimal.","PeriodicalId":49847,"journal":{"name":"Mecanique & Industries","volume":"26 1","pages":"465-475"},"PeriodicalIF":0.0,"publicationDate":"2010-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86188572","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The paper presents the experimental work developed by the authors for the identification of rotordynamic coefficients of air bearings. Air bearings work at very high rotation speeds and are known to have nonlinear dynamic characteristics depending at least on the excitation frequency. The paper presents two very similar test rigs, the testing procedure and the algorithm for identifying the rotordynamic coefficients. The test rigs consist of a rigid rotor guided by fixed bearings and driven by a spindle. The dynamic loads are applied by two orthogonally mounted shakers applying two linear independent excitations. Two air bearings are analysed in the present paper. The test procedure is first developed for a simple circular bearing with easily predictable dynamic characteristics. Its rotordynamic coefficients are identified by using a least square procedure based on rational functions. The coefficients are compared to theoretical results in order to underline the limits of the identification algorithm. The procedure is next applied to a first generation foil bearing. Rotordynamic coefficients are presented for different working conditions (static loads and rotation speeds) and are discussed comparing them to circular air bearings.
{"title":"Experimental investigation of air bearings dynamic coefficients","authors":"P. Matta, L. Rudloff, M. Arghir","doi":"10.1051/MECA/2010043","DOIUrl":"https://doi.org/10.1051/MECA/2010043","url":null,"abstract":"The paper presents the experimental work developed by the authors for the identification of rotordynamic coefficients of air bearings. Air bearings work at very high rotation speeds and are known to have nonlinear dynamic characteristics depending at least on the excitation frequency. The paper presents two very similar test rigs, the testing procedure and the algorithm for identifying the rotordynamic coefficients. The test rigs consist of a rigid rotor guided by fixed bearings and driven by a spindle. The dynamic loads are applied by two orthogonally mounted shakers applying two linear independent excitations. Two air bearings are analysed in the present paper. The test procedure is first developed for a simple circular bearing with easily predictable dynamic characteristics. Its rotordynamic coefficients are identified by using a least square procedure based on rational functions. The coefficients are compared to theoretical results in order to underline the limits of the identification algorithm. The procedure is next applied to a first generation foil bearing. Rotordynamic coefficients are presented for different working conditions (static loads and rotation speeds) and are discussed comparing them to circular air bearings.","PeriodicalId":49847,"journal":{"name":"Mecanique & Industries","volume":"18 1","pages":"477-488"},"PeriodicalIF":0.0,"publicationDate":"2010-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82696206","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In order to overcome the loss of performances issue when scaling resonant sensors down to NEMS, it proves extremely useful to study the behavior of resonators up to large displacements and hence high nonlinearities. A comprehensive nonlinear multiphysics model based on the Euler-Bernoulli equation which includes both mechanical and electrostatic nonlinearities in the case of a capacitive doubly clamped beam is presented. This purely analytical model captures all the nonlinear phenomena present in NEMS resonators electrostatically actuated including bistability, multistability which can lead to several physical limitations such as noise mixing, frequency stability deterioration as well as dynamic pull-in. Moreover, close-form expressions of the critical amplitudes and pull-in domain initiation amplitude are provided which can potentially serve for NEMS designers as quick design rules.
{"title":"Nonlinear phenomena in nanomechanical resonators: mechanical behaviors and physical limitations","authors":"N. Kacem, S. Baguet, S. Hentz, R. Dufour","doi":"10.1051/MECA/2010068","DOIUrl":"https://doi.org/10.1051/MECA/2010068","url":null,"abstract":"In order to overcome the loss of performances issue when scaling resonant sensors down to NEMS, it proves extremely useful to study the behavior of resonators up to large displacements and hence high nonlinearities. A comprehensive nonlinear multiphysics model based on the Euler-Bernoulli equation which includes both mechanical and electrostatic nonlinearities in the case of a capacitive doubly clamped beam is presented. This purely analytical model captures all the nonlinear phenomena present in NEMS resonators electrostatically actuated including bistability, multistability which can lead to several physical limitations such as noise mixing, frequency stability deterioration as well as dynamic pull-in. Moreover, close-form expressions of the critical amplitudes and pull-in domain initiation amplitude are provided which can potentially serve for NEMS designers as quick design rules.","PeriodicalId":49847,"journal":{"name":"Mecanique & Industries","volume":"206 1","pages":"521-529"},"PeriodicalIF":0.0,"publicationDate":"2010-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80425917","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A benchmark is organised to quantify the variability relative to structure dynamics computations. The chosen demonstrator is a pump in service in thermal central units, which is an engineered system with not well-known parameters, considered in its work environment. The blind modal characterisation of the separate pump components shows a 5%-12% variability on eigenfrequency values and a less than 15% frequency error in comparison with experimental values. The numerical-experimental MAC numbers reach 0.7 at the maximum, even after updating. An example of modal results on the pump assembly fixed is presented, which shows a larger discrepancy with measurement values, essentially due to the modelling of the interfaces and boundary condition, and to the possible simplification of the main components F.E. models to reduce their size. Though a significant frequency error, the first overall modes are correctly identified. If this tendency can be confirmed from all the participants' results, the conclusion to be drawn is that, if the predictive capability of F.E. models to represent the dynamical behaviour of sub-structures is satisfactory, the one relative to structures that are built-up of several components does not allow their confident use. Additional information issued from measurements is needed to improve their accuracy.
{"title":"SICODYN international benchmark on dynamic analysis of structure assemblies: variability and numerical-experimental correlation on an industrial pump","authors":"S. Audebert","doi":"10.1051/MECA/2010063","DOIUrl":"https://doi.org/10.1051/MECA/2010063","url":null,"abstract":"A benchmark is organised to quantify the variability relative to structure dynamics computations. The chosen demonstrator is a pump in service in thermal central units, which is an engineered system with not well-known parameters, considered in its work environment. The blind modal characterisation of the separate pump components shows a 5%-12% variability on eigenfrequency values and a less than 15% frequency error in comparison with experimental values. The numerical-experimental MAC numbers reach 0.7 at the maximum, even after updating. An example of modal results on the pump assembly fixed is presented, which shows a larger discrepancy with measurement values, essentially due to the modelling of the interfaces and boundary condition, and to the possible simplification of the main components F.E. models to reduce their size. Though a significant frequency error, the first overall modes are correctly identified. If this tendency can be confirmed from all the participants' results, the conclusion to be drawn is that, if the predictive capability of F.E. models to represent the dynamical behaviour of sub-structures is satisfactory, the one relative to structures that are built-up of several components does not allow their confident use. Additional information issued from measurements is needed to improve their accuracy.","PeriodicalId":49847,"journal":{"name":"Mecanique & Industries","volume":"44 1","pages":"439-451"},"PeriodicalIF":0.0,"publicationDate":"2010-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78557676","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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