PhD Position DCNS Research / INSA Lyon – 2017
Modelling of the vibro-acoustic behavior of hulls of submarine vehicles partially coated with anechoic or masking materials

Hosting institution:
Laboratoire Vibrations-Acoustique EA677, INSA Lyon, Univ Lyon 25 bis av. Jean Capelle, 69621
Villeurbanne cedex, France
Short stays at the ndustrial site of DCNS in Toulon are considered.

Supervision and contacts:
L. Maxit, associate professor, Laboratoire Vibrations-Acoustique, INSA Lyon, France
+33 4 72 43 62 15, laurent.maxit (at) insa-lyon.fr
V. Meyer, research engineer, DCNS Research, Ollioules, France
+33 4 94 11 66 27, valentin.meyer (at) dcnsgroup.com

Background:
The vibro-acoustic response of hulls plays an important role on the operational capabilities of submarine vehicles:
• In the case of an internal excitation, the far-field acoustic radiation increases the risk of being detected by a passive detection system (acoustic stealth), and the near-field radiation influences the performances of the integrated SONAR system.
•    In the case of an external acoustical excitation, the submarine vehicle can be detected by a system measuring the scattering from the hull (target strength).
In order to be able to design the system prior to its industrialization, it is necessary to have efficient tools for numerical simulation. ORCAA is a tool recently developed at DCNS in collaboration with the LVA at INSA Lyon. This tool predicts numerically the vibro-acoustic behavior of submerged cylindrical shells. It is based on a sub-structuring approach called CAA (Circumferential Admittance Approach) [1,2]. This approach enables coupling an analytical model of a submerged cylindrical shell with axisymmetric internal structures such as stiffeners and bulkheads modelled by the Finite Elements Method. The three main operational capabilities can be tackled (acoustic stealth, sonar performances and target strength) by considering mechanical,
acoustical and hydrodynamic  excitations (turbulent boundary layer). During V. Meyer’s PhD thesis (2013-2016), the sub-structuring approach has been extended for the general case of the coupling between thin mechanical subsystems, yielding the CTF (Condensed Transfer Function) method [3].
Non-axisymmetric internal frame such as engine foundations or floors can be included in the stiffened submerged cylindrical shell [4,5]. However, these methods cannot take into account acoustic cloaking used to improve the acoustical performances. The PhD offer aims at filling this gap.

PhD topic:
The PhD work consists in developing an approach to take into account partial cloaking in vibro-acoustic models of submerged cylindrical shells. Two types of acoustic cloaking are considered: the anechoic materials and the masking materials [6,7]. They are characterized by completely different mechanical properties. The cloaking can be made of visco-elastic, micro- or macro-voided materials [8]. Meta-materials can also be considered [9]. The materials models (finite elements, analytical, periodical cells, etc…) will be considered as input data. No work will be done regarding new models for these materials. The work aims at linking the existing materials models to the cylindrical shells models. The main challenge lies in the partial cloaking (i.e. on a longitudinal or angular section of the hull), which can couple the circumferential orders of the submerged cylindrical shell [10]. An original approach based on the Condensed Transfer Functions is going to be developed in order !
to tackle this issue.  In the end, the method is going to be used to estimate the benefits of the acoustic cloaking on the operational capacities.

Who can apply?
The candidate holds a MsC (or equivalent) and is keen on modeling physical phenomena. He/she has skills in the fields of acoustics and/or mechanics (solid mechanics, dynamics, vibrations).

To apply, send your resume, cover letter and the grades from the last three university years to laurent.maxit (at) insa-lyon.fr and valentin.meyer (at) dcnsgroup.com.

References:
[1] L. Maxit, J.M. Ginoux – Prediction of the vibro-acoustic behavior of a submerged shell non periodically stiffened by internal frames. JASA, 2010, Vol. 128 (1), p. 137-151.
[2] L. Maxit, Scattering model of a cylindrical shell with internal axisymmetric frames by using the circumferential admittance approach, Applied Acoustics, 80 (2014) 10-22.
[3] V. Meyer, L. Maxit, J.-L. Guyader, T. Leissing, C. Audoly, A condensed transfer function method as a tool for solving vibroacoustic problems. Proc. IMechE Part C: Journal of Mechanical
Engineering Science, 230 (2016) 928-938.
[4] V. Meyer, L. Maxit J.-L. Guyader,, T. Leissing, Prediction of the vibroacoustic behaviour of a submerged shell with non-axisymmetric internal substructures by a condensed transfer function method, Journal of Sound and Vibration, 360 (2016) 260-276.
[5] V. Meyer, L. Maxit, C. Audoly, A substructuring approach for modelling the acoustic scattering from stiffened submerged shells coupled to non-axisymmetric internal structures. Journal of the Acoustical Society of America, 140 (2016) 1609-1617.
[6] E.A. Skelton, ‘Theoretical Acoustics of Underwater Structures’, Imperial College Press, 1997.
[7] C. Dutrion, Etude de la faisabilité d’un revêtement élastique pour la furtivité acoustique, Thèse de l’Université de Toulouse, 2014.
[8] C. Audoly, Acoustic analysis of panels made with viscoelastic materials containing resonant cavities , Acta Acust., vol. 2 (5), pp. 393-402, 1994.
[9] A. N. Norris, Acoustic cloaking theory. Proceedings of the Royal Society A, 464:2411–2434, avril 2008.
[10] J. M. Cuschieria, D.Feit, Influence of circumferential partial coating on the acoustic radiation from a fluid-loaded shell. The Journal of the Acoustical Society of America, 107(6):3196–3207, 2000.

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