BEGIN:VCALENDAR VERSION:2.0 PRODID:-//CERN//INDICO//EN BEGIN:VEVENT SUMMARY:PACO#6 - Control based continuation of autonomous system — Stabi lization mechanisms DTSTART;VALUE=DATE-TIME:20230712T134000Z DTEND;VALUE=DATE-TIME:20230712T140000Z DTSTAMP;VALUE=DATE-TIME:20260308T101441Z UID:indico-contribution-193-788@events.isae-supaero.fr DESCRIPTION:Speakers: Etienne Gourc ()\nExperimental analysis of nonlinear dynamical system is always a complicated task because these system can ex hibit bifurcations\, multi-stability or unstable behavior. When a mathemat ical system is available\, numerical continuation algorithm constitute a p owerful tool to investigate the so-called bifurcation diagram. Sieber and Krauskopf introduced the idea of control based continuation\, obviating th e need of a mathematical model so that it can be used to obtain the bifurc ation diagram from a physical experiment [1]. Control based continuation m ethods rely on a feedback controller to stabilize the possibly unstable re sponse of the system under test. This feedback controller must be non-inva sive to ensure that the solution of the controlled system is also a soluti on of the uncontrolled system.\nSince then\, control based continuation re ceived a growing interest and has been mostly used to track branches of pe riodic solutions of non-autonomous (i.e. forced) systems [4\, 3\, 2]. Alth ough it has already been applied on various experiments\, only few papers deal with the detailed analysis of the underlying stabi- lization mechanis m [5]. Applying these methods to autonomous systems presents an additional difficulty since the frequency of the limit cycle is also an unknown. Num erical continuation algorithms solve this problem by appending the system with a phase condition.\nThe objectives of this study are twofold. (i) des ign a controller able to stabilize limit cycle oscillations\, (ii) investi gate the underlying stabilization mechanism of the designed controller.\n\ nhttps://events.isae.fr/event/22/contributions/788/ LOCATION: URL:https://events.isae.fr/event/22/contributions/788/ END:VEVENT BEGIN:VEVENT SUMMARY:"PACO#5 - A passive nonlinear absorber for controlling pathologica l tremors of human arm" DTSTART;VALUE=DATE-TIME:20230712T132000Z DTEND;VALUE=DATE-TIME:20230712T134000Z DTSTAMP;VALUE=DATE-TIME:20260308T101441Z UID:indico-contribution-193-701@events.isae-supaero.fr DESCRIPTION:Speakers: Gebai Sarah ()\nMechanical vibration absorbers are a pplied in different domains to protect structures and machines from undesi red vibrations. One of the precise applications of such control systems is reducing tremors of the human arm caused by some neurological disorders s uch as essential tremors. In recent studies\, active and linear passive co ntrollers are designed\, in the form of a wearable bracelets\, to reduce t he shaking in the upper limbs of patients. Active controllers require a po wer source to operate\, and their components are a matter of concern regar ding safety. Passive linear absorbers need accurate calibration of their o perating frequency to be efficient and require the usage of multi-absorber s to solve this problem. Passive nonlinear absorbers are proposed to overc ome the shortcomings of linear absorbers because they can be designed to h ave a broadened frequency bandwidth. In the current work\, the arms of the upper limbs are modeled as links connected by joints\, and the passive ti ssues of the muscles as springs and dampers. A voluntary moment is conside red to represent the torque exerted by the human to place his arms at a de sired position. The involuntary moment is used to excite the system and to reflect the activity of the muscles generating the tremor. Tremor signals at the upper limbs\, of a patient with essential tremor\, are measured to obtain the translational and angular responses. These measurements are us ed to calibrate the modeled dynamical system of the upper limbs and to del iver a reliable numerical response very close to the measured one. The sys tem is coupled to a passive nonlinear absorber and the multiscale method i s used to study the behavior of the system at the fast and slow timescales . It allows us to obtain the invariant manifold of the system and to detec t the equilibrium and singular points needed for the design of a nonlinear energy sink (NES). A non-smooth\, piece-wise linear NES is used for its d esign. The response of the system obtained analytically is validated by th ose obtained from numerical simulations. The designed NES is fabricated an d the preliminary prototype is obtained.\n\nhttps://events.isae.fr/event/2 2/contributions/701/ LOCATION:Toulouse URL:https://events.isae.fr/event/22/contributions/701/ END:VEVENT BEGIN:VEVENT SUMMARY:"PACO#4 - Understanding vibroimpact damping through a numerical en ergy based approach" DTSTART;VALUE=DATE-TIME:20230712T130000Z DTEND;VALUE=DATE-TIME:20230712T132000Z DTSTAMP;VALUE=DATE-TIME:20260308T101441Z UID:indico-contribution-193-700@events.isae-supaero.fr DESCRIPTION:Speakers: Sadoulet-Reboul Emeline ()\nVibroimpact damping clas sically consists in the integration in a main vibrating structure of oscil lating masses. The energy is dissipated thanks to the impact interactions with the main vibrating structure. An assumption is that an energy transfe r towards high frequencies occurs thanks to nonlinear effects\, leading to a faster and more efficient energy dissipation compared to lower frequenc ies. This hypothesis is investigated within the framework of the work pres ented\, in the case of a beam equipped with a vibroimpact absorber\, assum ing conservative impacts. A numerical study is developed to solve the equa tions of motion and derive energy balance with negligible error. Then\, th e energy transfers in the case of a harmonic excitation centered on not on ly the first\, but also the second\, and third mode are considered demonst rating the effectiveness of the vibro-impact absorber in each case. Additi onally\, the way the energy is dissipated is explained and quantitatively assessed. At least\, the results obtained for the three first modes are co mpared.\n\nhttps://events.isae.fr/event/22/contributions/700/ LOCATION:Toulouse URL:https://events.isae.fr/event/22/contributions/700/ END:VEVENT BEGIN:VEVENT SUMMARY:"PACO#3 - Nonlinear passive control of galloping of overhead trans mission lines: design and numerical verifications" DTSTART;VALUE=DATE-TIME:20230712T124000Z DTEND;VALUE=DATE-TIME:20230712T130000Z DTSTAMP;VALUE=DATE-TIME:20260308T101441Z UID:indico-contribution-193-699@events.isae-supaero.fr DESCRIPTION:Speakers: Leroux Matthieu ()\nIn the field of power delivery\, the vibration of overhead conductors affects the sustainability of transm ission lines. The passive control of galloping of conductors is the subjec t of this study. Galloping oscillations are caused by ice accretion on a c able that creates an aerodynamic instability. The consequences of gallopin g on transmission lines are electrical outages\, fatigue failure of cables \, and the impacts between cables. The study focuses on the nonlinear pass ive control of a single conductor. The use of a nonlinear absorber called as nonlinear energy sink (NES) with a piecewise linear restoring forcing f unction for galloping mitigation on a single span of a suspended cable is proposed. An analytical model of a single conductor span coupled to a NES is developed. The fluid-structure interaction\, i.e. the interactions of t he wind and the ice-accreted cable\, is modeled by a parametric excitation supposing the quasi-steady theory. A complexification technique accompani ed by the time multiple scale method is used to determine the slow and fas t dynamics of the system. The bifurcation diagrams are analytically determ ined and compared with results obtained from the numerical integration of the governing equations of the system. The system with harmonic excitation is modeled using the finite element (FE) method with the software Code_As ter. An equivalence between harmonic and parametric excitation is addresse d to compare the results from the FE model and the analytical developments . The influence of the parameters of the nonlinear absorber: clearance\, s tiffness\, and damping coefficient on galloping mitigation is studied.\n\n https://events.isae.fr/event/22/contributions/699/ LOCATION:Toulouse URL:https://events.isae.fr/event/22/contributions/699/ END:VEVENT BEGIN:VEVENT SUMMARY:"PACO#2 - Nonlinear damper approaches to flutter mitigation in hig hly-flexible wings" DTSTART;VALUE=DATE-TIME:20230712T122000Z DTEND;VALUE=DATE-TIME:20230712T124000Z DTSTAMP;VALUE=DATE-TIME:20260308T101441Z UID:indico-contribution-193-698@events.isae-supaero.fr DESCRIPTION:Speakers: Alcorta Roberto ()\nThe High-Altitude\, Long Enduran ce (HALE) aircraft is an innovative concept with great potential in teleco mmunications and surveillance applications due to its ability to function as a "pseudo-satellite" within the stratosphere. Its unique features are a ccomplished in practice through numerous design requirements that ensure m aximal efficiency. Regarding the airframe in particular\, these lead to li ght wings with extremely high aspect ratios. The resulting -very flexible- structure is consequently sensitive to dynamic instabilities emerging fro m aeroelastic effects (i.e.\, flutter)\, which produce large-amplitude osc illations and drastically diminish the aircraft's flight envelope. Hence\, accurate prediction of flutter and the ability to mitigate it are crucial to enable reliable HALE aircraft design and operation. In the present wor k\, we explore passive control strategies for flexible wing flutter throug h the nonlinear effects introduced by an added damper system. To this end\ , an original aeroelastic model of the wing is introduced\, whose structur al component provides a degree of accuracy and complexity that lies at a m idpoint between linear and geometrically-exact nonlinear beam models. The damper is modelled as a single-degree-of-freedom secondary subsystem attac hed to the wing through a linear spring\, and the equations of motion of t he full system are implemented numerically. Mitigation performance is asse ssed with regard to flutter speed\, instability range and vibration amplit ude. Parametric studies are conducted for varying stiffness\, span-wise lo cation and dissipation mechanism of the damper. The latter of these aspect s is given special attention\, and the respective performances of viscous and nonlinear damping are compared. Overall\, our results show that dynami c stability of the wing can definitely be improved through the use of a we ll-tuned damper. However\, the choice of design parameters leading to opti mal performance is far from obvious. Furthermore\, the simplistic mechanis m proposed herein is subjected to evident practical limitations\, and thus this work concludes with a discussion on potential extentions and conside rations for implementation.\n\nhttps://events.isae.fr/event/22/contributio ns/698/ LOCATION:Toulouse URL:https://events.isae.fr/event/22/contributions/698/ END:VEVENT BEGIN:VEVENT SUMMARY:"PACO#1 - Vibration response of a machine structure filled with hi gh-damping material" DTSTART;VALUE=DATE-TIME:20230712T120000Z DTEND;VALUE=DATE-TIME:20230712T122000Z DTSTAMP;VALUE=DATE-TIME:20260308T101441Z UID:indico-contribution-193-697@events.isae-supaero.fr DESCRIPTION:Speakers: Martini Alberto ()\nThis work focuses on the use of a polymer concrete as a filling material of structural parts to damp vibra tions in machine tools. The goal of the overall project is to improve the dynamic behavior of CNC lathe systems by limiting at most the vibrations t riggered in operative conditions\, in order to guarantee a high productivi ty of the machine tool while keeping the machining quality of the final pr oducts. The task is very challenging since the vibrations transmitted to t he tool-workpiece area through the structures of both the lathe and its jo ined bar-feeder are mainly associated with the bars' critical velocities\, which are extremely variable in a wide range. Indeed\, the latter depend on operative factors that are not constant for all the working conditions of the system\, e.g. material and geometry of the bar to be machined\, wor king angular speed\, instantaneous free-length of the bar supported by the bar-feeder... As a consequence\, designing the machine structures in orde r to avoid resonances in the large broadband of the excitations is basical ly impossible. Hence\, a successful strategy could be levering the structu ral components' damping in order to limit the vibration levels in a wide f requency band. To this purpose\, polymer concretes\, mineral casts\, and m etal foams can be used as filler of machine tools and automatic machines b eds. The prototype of a new base €“ filled with a commercial polymer c oncrete €“ of an automatic bar-feeder was developed and many laborator y tests were performed. Vibration signals were acquired for different work ing conditions (varying both the bars and the spindle velocity of the conn ected lathe). The comparison of the dynamic responses of the original mach ine (no filler) and the new variant highlights an overall favorable effect of the high-damping material properties\, though a slight worsening appea red in a few circumstances (likely due to the additional mass of the fille r that lowers natural frequencies thus making the vibration amplitudes inc rease). This work illustrates the design of the new prototype\, the perfor med experiments\, the results of the signal analyses\, and some concluding remarks on possible future developments for the presented application.\n \nhttps://events.isae.fr/event/22/contributions/697/ LOCATION:Toulouse URL:https://events.isae.fr/event/22/contributions/697/ END:VEVENT END:VCALENDAR