The thermal protection systems used in the missile launch areas can limit their heating and protect their structural integrity.

The REACH directives nevertheless induce a risk of obsolescence, thereby making it obligatory to plan for solutions to replace these composite materials. Their thermal degradation mechanisms under severe aerothermal loading therefore have to be identified and understood. which is the purpose of this thesis.

The following questions are envisaged: What is the impact of the material composition on its thermal and ablative performances? How does the material composition influence the degradation mechanisms brought into play? What levers can be used to reduce degradation speeds?

The Steam Generator (SG) is a key component in electricity generation and propulsion of Naval Group ships. The physical phenomena brought into play in these heat exchangers are especially complex to simulate, mainly because the wealth of the underlying physics results in huge diversity of flow topologies and thermal transfer regimes.

The main goal of this thesis is to develop a programme suitable for modelling the different Naval Group SG. The installed methodology proposes coupling an 1D code and a CFD calculation based on the equivalent environment approach.

Tracking can use sensor measurements to estimate the trajectory of targets moving in the field of vision of the sensors.

A radar measures angle, distance and possibly radial speed which are extracted from the raw radar signal after processing which constitutes the detection stage. Traditional tracking methods are then applied to these measurements, which can correspond to targets but also to false alarms. There are all the more false alarms when the targets sought have a low signal-to-noise ratio.

An approach using the raw signal seems to improve the rate of false alarms in targets with low signal-to-noise ration. But new tracking methods need to be developed for this "track before detect" strategy.

The purpose of this thesis is to develop a tracking algorithm on a raw 2D radar signal. The framework of the recursive Bayesian estimation underpinning the tracking methods used in this study will be presented. Special attention will be paid to the raw radar signal measuring model. The presentation will conclude with the results of tracking on simulated data.

Advances in underwater detection suggest a need to improve the very low frequency acoustic performances of hull coatings. This is a difficult task given the constraints facing these coatings, including thickness, that have to remain low for reasons of buoyancy.

Metamaterials are promising in responding to this challenge. Local resonances of their internal structure can be exploited to create effective absorption or acoustic attenuation of the metamaterial once low frequencies are reached.

This thesis work focuses on the study of periodic metamaterials formed by resonant inclusions in a matrix. The main goal is to understand and exploit the physical phenomena brought into play to improve the anechoic and/or masking performances. Homogenisation methods are developed for the 1D and 2D periodic structures for this purpose. Optimisation algorithms are then implemented to optimise the internal structure from the homogenised environment (also called effective).

A selection of materials is tested in the ISEN acoustic dock to check certain metamaterial characteristics experimentally.

This management science thesis covers the role of trade skills in the performance and safety of complex industrial projects. It consists mainly of a field study conducted over two years at the Duguay-Trouin nuclear submarine construction shipyard, targeting the specific trade of pipe fitters in charge of fitting pipework in the vessel.

The study hopes to understand to what extent this partly-outsourced trade carried out by several companies with different perceptions of work nevertheless constitutes a unifying force for the project.

We also show that pipe fitters form cohesive communities of practice that cross traditional organisational boundaries and help make it more resilient. Two characteristics of the pipe fitter activity are highlighted and discussed: the materiality of their work and their affinity with a strong professional culture.

Reduction gearing can transmit the mechanical energy from power sources to the propeller.

This actual ship's gearbox is subject to many constraints (size, mass, power, robustness and acoustic discretion, etc.), and its optimisation requires tools that reproduce as accurately as possible the complex phenomena that occur.

The main challenge of this thesis is to produce a computer code that can simulate the vibration behaviour of this system to optimise its operation.

The innovation sought is the consideration of several scales, one "local" at the contacts (gears, bearings) and the other "global" at the impeller shafts and structures.

A specific feature of the thesis will be to take into account the filling of cavities with damping material in these simulations where appropriate.

The model developed following the thesis work will be presented and the influence of the filling material will be compared with the more usual power transmission optimisation methods such as profile corrections.

A submarine is only effective in operation if it can position itself precisely and absolutely. But the error in its means of inertial navigation increases inexorably over time, necessitating regular resetting of its position, for example using a GPS.

The GPS however has two major disadvantages: it is easy to jam and the submarine has to surface on a regular basis, thereby revealing itself. An alternative solution is correlation with a marine environment profile: this is an absolute, independent reset procedure that is difficult to jam.

The principle is a comparison of the profile(s) measured by the submarine in its environment and those read on a chart instead of the position calculated by the navigation algorithm. This approach can feed back the absolute error of the calculated position. Two types of profile correlation are envisaged, bathymetric and gravimetric. The first measures the relief of the ground under the device and compares it with a bathymetric chart.

The second measures the local gravity and compares it with a gravity anomaly chart. This method is highly effective but very much non-linear and multi-modal, which means using advanced filtering algorithms.

Under the JLMT joint laboratory and the European RAMSSES project, Centrale Nantes and Naval Group have joined forces for the Additive Manufacturing of two hollow blade demonstrators - a world first - using WAAM capabilities.

Hollow blades lighten the propeller compared with solid blades whilst improving hydrodynamic performances and reducing noise and vibrations. The presentation will cover the large part manufacturing methodology which has been developed and applied for this purpose.

A second 1.5 m hollow blade demonstrator weighing 780 kg has in particular been produced successfully using multi-axial manufacture that can reduce the weight by 50%.