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Section: Application Domains

Ecology and sustainable energies

Sustainable development and environment preservation have a growing importance and scientists have to address difficult issues such as: management of water resources, renewable energy production, biogeochemistry of oceans, resilience of society w.r.t. hazardous flows,...

Hydrodynamics-biology coupling

Nowadays, simulations of the hydrodynamic regime of a river, a lake or an estuary, are not restricted to the determination of the water depth and the fluid velocity. They have to predict the distribution and evolution of external quantities such as pollutants, biological species or sediment concentration.

Hydrodynamics-biology coupling for algae culture and biofuel production

The potential of micro-algae as a source of biofuel and as a technological solution for CO2 fixation is the subject of intense academic and industrial research. Large-scale production of micro-algae has potential for biofuel applications owing to the high productivity that can be attained in high-rate raceway ponds.

One of the key challenges in the production of micro-algae is to maximize algae growth with respect to the exogenous energy that must be used (paddlewheel, pumps,...). There is a large number of parameters that need to be optimized (characteristics of the biological species, raceway shape, stirring provided by the paddlewheel); consequently our strategy is to develop efficient models and numerical tools to reproduce the flow induced by the paddlewheel and the evolution of the biological species within this flow. Here, mathematical models can greatly help us reduce experimental costs.

Owing to the high heterogeneity of raceways due to gradients of temperature, light intensity and nutrient availability through water height, we cannot use depth-averaged models. We adopt instead more accurate multilayer models that have recently been proposed.

It is clear however that many complex physical phenomena have to be added to our model, such as the effect of sunlight on water temperature/ density, evaporation and external forcing (wind).

Lacustrian ecosystems

Many problems previously mentioned also arise in larger scale systems like lakes. Hydrodynamics of lakes is mainly governed by atmospheric forcing terms: wind, temperature variations,...

If the interactions between hydrodynamics and biology are known via laboratory experiments, it is more difficult to predict the evolution – especially for the biological quantities – in a real and heterogeneous system. The objective is to model and reproduce the hydrodynamics modifications due to forcing term variations (in time and space). We are typically interested in phenomena such as eutrophication, development of harmful bacteria (cyanobacteria) and upwelling phenomena.

Marine energies

One of the booming lines of business is the field of renewable and decarbonated energies. In particular in the marine realm, several processes have been proposed in order to produce electricity thanks to the recovering of wave, tidal and current energies. We may mention water-turbines, buoys turning variations of the water height into electricity or turbines motioned by currents. Although these processes produce an amount of energy which is less substantial than in thermal or nuclear power plants, they have smaller dimensions and can be set up more easily.

The fluid energy has a kinetic and potential part. The buoys use the potential energy whereas the turbines are activated by currents. To become economically relevant, these systems need to be optimized (shape, position, durability, ...) in order to improve their productivity. This is a complex and original issue which requires efficient numerical tools.

Some processes are currently running. However, they have not been studied from an optimization point of view. While for the construction of a harbour, the goal is to minimize swell, in our framework we intend to maximize the wave energy. A key-point is the optimization of the bathymetry in a given geometrical domain which influences the swell and thus the effectiveness of processes. Optimization involving fluid mechanics is quite complex. Although such an approach seems innovative, it clearly requires the development of methodological tools. In a second step, experiments will be necessary for the validation.