Section: New Results

Assessments of models by means of experimental data and assimilation

Evaluation and calibration of mobile phones for noise monitoring application

Participants : Vivien Mallet, Raphaël Ventura.

In collaboration with V. Issarny, P-G. Raverdy, F. Rebhi.

The Ambiciti application was developed so as to acquire a larger control over the acquisition process by mobile phone sensors. Pink and narrowband noises were used to evaluate the phones' accuracy at levels ranging from background noise to 90 dB(A) inside the lab. Conclusions of this evaluation lead to the proposition of a calibration strategy that has been embedded in Ambiciti and applied to more than 50 devices during public events. In the perspective of citizens-driven noise sensing, in situ experiments were carried out, while additional tests helped to produce recommendations regarding the sensing context (grip, orientation, moving speed, mitigation, frictions, wind).

Assimilation of noise pollution data

Participants : Vivien Mallet, Raphaël Ventura.

In collaboration with P. Aumond, A. Can, V. Issarny.

We studied the generation of hourly noise maps in urban area at street resolution, based on temporally averaged simulation maps and mobile phone audio recordings. A data assimilation method produces an analysis noise map which is the so-called best linear unbiased estimator. We illustrated the method with a neighborhood-wide experiment.

Another work, lead by IFSTTAR, was dedicated to the spatial interpolation of point measurements collected at high density in Paris with a sound level meter. Compelling results were obtained with universal Kriging and a linear trend based on the distance to certain types of roads.

Granular and particle-laden flows: from laboratory experiments to field observations

Participant : Anne Mangeney.

In collaboration with R. Delannay, A. Valance, O. Roche and P. Richard.

A review article was written to provide an overview of dry granular flows and particle fluid mixtures, including experimental and numerical modelling at the laboratory scale, large scale hydrodynamics approaches and field observations. We also emphasize that the up-scaling from laboratory experiments to large scale geophysical flows still raises some theoretical physical challenges.

Continuum viscoplastic simulation of a granular column collapse on large slopes: $\mu \left(I\right)$ rheology and lateral wall effects

Participant : Anne Mangeney.

In collaboration with N. Martin, I. Ionescu, F. Bouchut and M. Farin.

We simulate here dry granular flows resulting from the collapse of granular columns on an inclined channel and compare precisely the results with laboratory experiments. The 2-D model is based on the so-called $\mu \left(I\right)$ rheology that induces a Drucker-Prager yield stress and a variable viscosity. We show that the use of a variable or a constant viscosity does not change significantly the results provided that these viscosities are of the same order. Finally, we observed that small-scale instabilities develop when refining the mesh.