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European industrial doctorate for advanced, lightweight and silent, multifunctional composite structures

Periodic Reporting for period 2 - N2N (European industrial doctorate for advanced, lightweight and silent, multifunctional composite structures)

Reporting period: 2020-03-01 to 2022-02-28

Modern aeronautical structures are increasingly made of composite materials due to their lightweight benefits. However, composite structures exhibit poor dynamic and acoustic isolation levels compared to conventional metallic ones. Consequently, optimally designed composite with acoustic and vibrational isolation properties should be developed.
The N2N Training Network developed a high-fidelity and efficient Multidisciplinary Design Optimization (MDO) toolbox for multifunctional composites having poroelastic inclusions and combining minimum mass with maximum damping and comfort levels.
On the research side, N2N focused on developing multiscale models for obtaining a comprehensive description of random poroelastic materials coupled to a composite structural segment and understanding the interaction of acoustic waves with such complex.
Technical achievements include:
Virtual Element method (VEM) to treat coupled poromechanical problems, and the Multiscale Virtual Element Method (MsVEM) applied to elastostatic and poromechanical problems.
Analytical condensation model for three-layer structures which is easy to use and applicable to multilayer panels including poroelastic materials.
A new condensation model applicable to thicker structures, which drastically reduces the meshing effort and computational load.
A new finite element scheme which has shown to be at least 15 times faster than existing full finite element modelling (FEM).
An MDO environment for layering optimisation of industrial sound packages.
N2N provided a fully supportive training environment with an industrial and academic focus.
1. Multiscale aeroelastic modelling in porous composite structures
ESR1-A detailed review on multi-scale methods on poromechanics applicable for foam materials and a functional finite element code was developed in MATLAB. WP1 submissions were:
Review of micro-mechanical frameworks currently employed for porous media.
Coupled-field Multiscale FEM framework.
Dynamic flow multiscale methodology, theoretical framework and source code implementation.
A set of multiscale models to be implemented in WP2 and WP3.
Delivery of optimal designs of the poroelastic acoustic package for targeted industrial applications.
2. Vibroacoustic performance modelling
ESR2- An analytical expression of the frequency limit of a thin plate model has been derived. A simple analytical model based on thin plate theory as well as a fully comprehensive condensation model valid for thicker multi-layer structures were developed. Both enable significant reduction of the computational load compared to conventional multi-layer modelling strategies. WP2 submissions were:
Report on the vibroacoustic methodologies currently employed to model sound transmission through complex structural ensembles.
Set of extended Biot-Allard models accounting for the coupling of porous and structural layers.
TMM methodology for computing the vibroacoustic performance of multilayer industrial composites.
Delivery of advanced vibroacoustic models for implementation within the MDO platform developed by ESR3.
Manufactured structural specimens and experimental test results on the investigated case studies and validation of numerical models.
3. Design optimisation and experimental validation
ESR3- Different metaheuristics have been used for the optimisation of porous sound-absorbing packages with the objective of maximizing the sound absorption coefficient. Furthermore, comparisons of the performance of different solution representations to obtain improved algorithms for acoustic package optimisation were considered. The task was done in two steps, namely, material optimisation and shape optimisation. WP3 submissions were:
Set of three industrial and academic case studies for which the multifunctional structures were optimised.
A set of material properties for composites and poroelastics through experimental characterisation.
Assessment of alternative efficient optimisation techniques in structural engineering problems.
Experimental test results on the investigated case studies.
Delivery of N2N’s technological demonstrator as a fully functional MDO platform along with the manufactured multifunctional structures. This deliverable was an overall project contribution, lead by ESR3.

The Network has produced 7 journal papers and 12 conference presentations.
All the Network deliverables have been submitted.
All the Network milestones have been attained.
The advances of N2N have significant impact in increasing social awareness on modern aircraft safety as well as inspire the new generation of structural designers and vibroacoustics engineers. The following actions were taken in order to ensure that the developments will be successfully communicated to the public.
UNOTT participated in the two biggest European Airshows. All ESR fellows exhibited their work at the Farnborough International Airshow and the Paris Airshow, having a stand dedicated to illustrating the N2N technologies.
Engagement with schools in UK and France: all ESRs visited local schools to deliver a presentation on modern industrial structural design challenges and promote science and engineering education through their talks and posters.
Moreover, the ESRs presented their work at the annual UNOTT Faculty of Engineering Annual Christmas Lecture. The lecture was attended by 200 school children. Each fellow showcased their research and communicated with the children about the merits of engineering education and aircraft safety awareness.
Demonstrators along with accompanying informative posters and presentations have proved particularly efficient for inspiring and excite the curiosity of visitors in the developed technologies.
All ESRs prepared a technological demonstrator ( which presents the project main objectives and the individual work of each ESR. This includes interactive web-based tools where the visitor can adjust the configuration parameters (material properties, excitation...) and see live the effect of these modifications.
In addition, two dedicated webpages related to the work of ERS2 including interactive webtools have been published on the APMR website (Acoustical Porous Material Recipes) ( This website designed and hosted by Matelys-RL is widely known within the vibro-acoustic community in general and within the porous media community.
A project homepage was created and has been updated monthly with N2N news and research outputs.
A LinkedIn account ( was set and managed by the ESRs. Regular posts accelerated research impact and aid the profile of all ESRs for being ‘spotted’ by potential future employers.
A N2N YouTube channel ( was also set which gathers the series of lectures given at the different Network Short Courses held during the course of the project. This channel also proposes individual videos aimed for a broader dissemination to a wide audience: PhD viva resume, 3-minutes thesis contest.
Final project meeting online March 2022
Mid-Term Review in Lyon April 2019