A pioneer in ocean science, IFREMER’s cutting-edge research is grounded in sustainable development and open science. Our vision is to advance science, expertise and innovation to:

  • Protect and restore the ocean
  • Sustainably use marine resources to benefit society
  • Create and share ocean data, information & knowledge.

With more than 1,500 personnel spread along the French coastline in more than 20 sites, the Institute explores the 3 great oceans: the Indian, Atlantic and Pacific oceans. A leader in ocean science, IFREMER is managing the French Oceanographic Fleet and its dedicated scientists create ground-breaking technology to push the boundaries of ocean exploration and knowledge, from the abyss to the atmosphere-ocean interface.

Well-established in the international scientific community, our scientists, engineers and technicians are committed to advance knowledge about our planet’s last unexplored frontiers. They provide the science we need for informed decision-making and public policy and they transfer this knowledge and technology to businesses to fulfill public and private needs. Core to our mission is also to strengthen public awareness about the importance of understanding the ocean and its resources, and empowering future generations of leaders through education and outreach national campaigns.

Founded in 1984, IFREMER is a French public organization and its budget approximates 240 million euros. It is operating under the joint authority of the French Ministry for Higher Education, Research and Innovation, the french Ministry of the Sea, the French Ministry for the Ecological and Solidary Transition, and the French Ministry of Agriculture and Food.

 

General areas of responsibility

The DYNECO (Dynamics of Coastal Ecosystems) research unit is one component of the “Oceanography and Ecosystems Dynamics” department. Its main objective is to study how coastal ecosystems respond to anthropogenic or natural pressures. DYNECO conducts scientific and expert assessment activities in this field. The global approach is supported by the understanding and analysis of physical and biogeochemical processes and is based on experimentations, in-situ observations and modelling.

Within DYNECO unit, the Hydro-Sedimentary Dynamics laboratory (DHYSED) studies the hydrodynamic processes and sediment dynamics at different spatial scales (French coasts, bays and estuaries) and time scales (from tidal up to multi-decadal scales). The DHYSED laboratory investigates sediment processes, sediment fluxes and morphodynamics changes within coastal systems through i) experimental studies on sediment behaviour / sediment processes, in relation with the ecosystem; ii) in-situ observations (conducting process-oriented field campaigns and managing long-term and high-frequency measurement stations within the COAST-HF network); iii) the development of complementary modelling strategies, from grain scale to sediment material scale, and coupling full deterministic and machine learning approaches. In particular, DHYSED develops the MUSTANG sediment transport numerical model, coupled to various hydrodynamics cores (MARS3D, SYMPHONIE, ROMS/CROCO).

Summary

Coastal systems shelter mixed sand/mud habitats, supporting marine biodiversity. These sediment habitats are strongly driven by sediment availability, physical tidal forcing and extreme hydrological and meteorological events. These forcing erode and transport sediments and hence contribute to dynamically change coastal landscape. Understanding and simulating these processes is crucial to anticipating future trajectories of coastal systems in response to global change. The processes controlling the formation or erosion of a heterometric sand/mud bottom are intrinsically linked to the physical and geometrical properties of their constitutive sediment particles but also to their transport modes dictated by the types of forcing applied on the carrier fluid. The heterogeneity of the constitutive sediment particles properties in concentration, density, size or modes of interaction (frictional, cohesive…) in addition to the properties of the carrier fluid leads to non-trivial behaviors. These heterogeneities generate sediment bed patterns of well identifiable size classes segregation, e.g., alternance of sand/mud layers.

Current approaches to model sediment transport at the systemic scale (estuary, coastal sea or facades) are based on empirical or semi-empirical approaches (a sediment-based approach) of exchange processes between water column and sediment, at best inherited from experimental works, otherwise based on idealized concepts. The mechanics of erosion/deposition processes of fine sediments, sand/mud, at the water-sediment interface is identified as a major lock of hydro-morpho-sedimentary modeling, both in the experimental description of the processes and in their formalization within numerical models. To overcome this lack of knowledge, an innovative grain-based approach to simulate erosion/deposition processes at the water-sediment interface can be used. At the small-scale, physics of granular media allows to propose a solution to break with (semi-)empirical concepts of erosion/deposition processes. The grain-based approach includes a realistic physical basis at the scale of the particles constituting the material and whose specific/intrinsic properties govern the processes at the water-sediment interface. This is typically a change of scale in the sediment dynamic approach that focuses on the particle scale rather than on the material scale, a transdisciplinary methodology, (i.e., sediment-based and grain-based approach). Since the 2000s, new numerical approaches called Direct Numerical Simulation (DNS) coupling discrete element methods such as the Non-Smooth Contact Dynamics (NSCD), for the modelling of particle dynamics and fluid dynamics methods such as the Lattice Boltzmann Method (LBM) have been developed. This approach allows access to the grain-scales with a very realistic description of the physics of the problem (interaction between particles and with the carrier fluid, size distribution of particles, fluid and particles properties as well as the fluid hydrodynamics variables at the pore-scale). Nevertheless, despite this scientific and technological progress, the taking into account these disparities in a unified model remains unexplored.

At DHYSED laboratory, we continuously have been investigating and innovating in the hydro-morpho-sedimentary modeling through sediment-based approach over the last 20 years with the development of the sediment community model MUSTANG coupled with multiple hydrodynamic models (e.g., MARS3D, CROCO, SYMPHONIE). While internationally considered as one of the most complex process-based sediment transport models, the MUSTANG strategy for simulating erosion/deposition processes is currently based on empirical and/or phenomenological approaches of sediment behavior that rely on few experimental investigations and strong hypothesis on bed formation/erosion. These approaches need to be explicated, confronted and challenged with physical based model at small-scale solving physics of the particle-particle and particle-fluid interactions where this should end-up by adapting and revisiting the conceptualization of the erosion/deposition processes models (e.g., MUSTANG or similar tools) used at the system scale.

This doctoral project aims to revisit and upscale mixed sediment behavior (i.e., erosion/deposition processes) in large scale sediment transport numerical models (through MUSTANG-CROCO coupled code) by numerically investigating small (grain) scale physical processes at the water-sediment interface (by means of an in-house NSCD-LBM coupled code). This work will focus in particular on the variations and evolution of the sediment microstructure (porosity, particles re-arrangement, particles contact force distribution…) at the scales of the particles and of the interactions between the particles and with the fluid, and how these small-scale results can upgrade rheological laws and/or phenomenological concepts in MUSTANG or similar models. The doctoral project will in particular allow to: i) provide a physical understanding of the near-bed sedimentation processes from the settling phase of variable suspended sediment particles, characterized by different physical properties down to bed layer formation within the (pre-)consolidation phase; ii) understand the influence of the variability and heterogeneity in the physical properties of the fluid-particle mixture on the erodibility of a weakly to strongly consolidated sedimentary bed and; iii) revisit and challenge MUSTANG (semi-)empirical / phenomenological concepts on erosion/deposition processes using grain-scale physical knowledge and common material-integrated parameters such as particle size distribution or porosity.

This thesis will allow the candidate to develop skills in the field of numerical modeling of the behavior of dense and diluted granular materials, fluid mechanics and fluid-structure interaction on an innovative subject with direct applications to sediment hydrodynamics. In addition to the publication of the results of this work in international journals and their presentation at international conferences, the collaboration with INRAE/UMR 1208 IATE (Montpellier) will be an interesting opening for the candidate.

Key words

Numerical modelling, sediment hydrodynamics, erosion, suspension physics, granular materials, micromechanics of discrete materials, computational fluid dynamics.

Required Knowledge, skills, and characteristics

  • Master 2 or Engineering school in computational engineering, fluid mechanics, physics, or similar. Good knowledge of numerical modeling (C, C++, Fortran, Python…).
  • Skills or/and knowledge of a high-performance computing environments will be appreciated.
  • Fluent in English.

How to apply for this position?

Your application file must include:

  • a curriculum vitae
  • a covering letter
  • a reference letter
  • an academic transcript (Bachelor + Master 1 and first semester Master 2)

Your application must be compiled into 2 PDF files, up to 1.5 MB for each file on Ifremer careers website.

In case of any problem in attaching your documents, please upload your CV on Ifremer careers website (this step is mandatory for your application to be considered) and send all the documents to the thesis supervisors: romaric.verney@ifremer.fr, jean-yves.delenne@umontpellier.fr and , patrick.mutabaruka@ifremer.fr

The deadline for applications is October 31st, 2022. Nevertheless, we strongly urge you to let us know as soon as possible of your intention to apply, by contacting the subject supervisor.

In parallel, please submit your application to the doctoral school: EDSML, IUEM

Doctoral students’ contracts will start as of January 2nd, 2023, subject to the submission of administrative documents authorizing Ifremer to recruit the doctoral student (certificate of completion of the Master 2 or engineering degree + visa for foreign doctoral students outside the EU).

Specific working conditions

  • The Ph.D. project will be conducted at IFREMER/DYNECO/DHYSED (Centre Bretagne) and the candidate should, for a short period, visit INRAE/UMR 1208 IATE (Montpellier) for his work.
  • The selected candidate should participate in national/international conferences.

Ph.D. is a real opportunity to work on Ifremer’s scientific and technological priority themes. It entitles the holder to a gross monthly salary of 2300 euros for a period of 3 years, which cannot be combined with other scholarships.

How to apply for this position

Deadline for applications: 31/10/2022

All applications are processed exclusively via our website. Interested candidates can apply by clicking the “Apply” button. 

Further information can be found in this link.