The dynamic response of a structure or a mechanical system has a great influence upon comfort (vibration, noise), lifespan (durability) and safety (damaging). A protection against dynamic excitation and an isolation of systems like bridges, slim buildings, vehicles and their passengers, rotating machines, ships, domestic or industrial appliances, etc. are generally required to preserve their integrity. To this aim, designers often make use of specific devices named 'dynamic absorbers' to attenuate the system vibration. This project aims to develop new kinds of dynamic absorbers that are essentially non linear. They differ very much from (i) standard linear absorbers which are mainly efficient within close margins of a target frequency to be attenuated (ii) active absorbers which require a feedback control and some extra energy to feed the control loop and which remain costly. The concept of energy pumping was settled in 2001. The underlying principle consists in connecting a relatively small oscillator to the system to be protected, and characterized by an essentially nonlinear attachment. After a judicious tuning of coupling nonlinearity, a nonlinear mode of vibration is possibly created and therefore permits a one-way irreversible energy transfer from the leading structure to the absorber, phenomenon commonly referred as 'energy pumping'. This phenomenon is followed by a sudden decay and a fast cancellation of vibration settling in the structure, most vibration being localized in the absorber. Contrary to its linear counterpart, nonlinear absorbers may be depicted by very interesting features (i) they can automatically get tuned to the frequency of the system to be attenuated and (ii) they work both under periodic or transient excitation beyond an energy threshold. Having an improved knowledge of their behaviour also appears to be crucial in order to reach an optimal compromise depending on real applications. The domain of application of these new generation of non linear absorbers is indeed very broad and related stakes are huge. The two research teams involved in this project will first begin to explore a panel of applications in their respective traditional background. It concerns the building protection for the DGCB, which has a well recognized activity in Civil engineering and building acoustics. As for the LMA, the challenge is to develop new systems of noise reduction that could be efficient at low frequency, when usual technology of porous material is poorly efficient. The project is divided in three parts (i) a theoretical part devoted to a better understanding of energy pumping phenomenon and an improvement of its efficiency (parameter sensibility, robustness, influence of coupling, design of non linearity), (ii) an experimental part that aims to complete the feasibility of irreversible energy transfer on elementary systems, for instance in acoustic, and to apply energy pumping principle with more realistic devices in the two traditional domains of activity of the laboratories. Design and optimization of the absorber is the key point here. (iii) a prospective part to explore new application fields and to establish connections with others scientific topics like molecular chains, micro and nano-systems, piezoelectric systems. The capacity to recover and to store energy will also be investigated. The two research teams involved in this project have already been working together for years on the more general topic of 'nonlinear modes of vibrations'. They have organized a Euromech colloquium named « non linear modes of vibrating systems » in 2004, were asked to organize a course on that theme at the CISM (Udine, Italy). These two teams are internationally reputed and the leading motivation is that the project will help them to preserve their advance and skills in the domain. Not only, these teams are complementary with regards to new absorber design but they also have complementary skills in applied mathematics, computational mechanics, and in experimental dynamics. With regards to the numerous potential innovations, this ANR project will help to broadcast information and to promote nonlinear dynamic absorber technology in the industrial world.
Bruno COCHELIN (CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE PROVENCE CORSE)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE PROVENCE CORSE
CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE RHONE-AUVERGNE
Help of the ANR 310,000 euros
Beginning and duration of the scientific project: - 36 Months