Cyrille Bonamy

The interaction between selection, demography and selfing and how it affects population viability.

Population extinction due to the accumulation of deleterious mutations has only been considered to occur at small population sizes, large sexual populations being expected to efficiently purge these mutations. However, little is known about how the mutation load generated by segregating mutations affects population size and, eventually, population extinction. We propose a simple analytical model that takes into account both the demographic and genetic evolution of populations, linking population size, density dependence, the mutation load, and self-fertilisation. Analytical predictions were found to be relatively good predictors of population size and probability of population viability when verified using an explicit individual based stochastic model. We show that initially large populations do not always reach mutation-selection balance and can go extinct due to the accumulation of segregating deleterious mutations. Population survival depends not only on the relative fitness and demographic stochasticity, but also on the interaction between the two. When deleterious mutations are recessive, self-fertilisation affects viability non-monotonically and genomic cold-spots could favour the viability of outcrossing populations.

Split Bregman iteration and infinity Laplacian for image decomposition

In this paper, we address the issue of decomposing a given real-textured image into a cartoon/geometric part and an oscillatory/texture part. The cartoon component is modeled by a function of bounded variation, while, motivated by the works of Meyer [Y. Meyer, Oscillating Patterns in Image Processing and Nonlinear Evolution Equations, vol. 22 of University Lecture Series, AMS, 2001], we propose to model the oscillating component v by a function of the space G of oscillating functions, which is, in some sense, the dual space of BV(@W). To overcome the issue related to the definition of the G-norm, we introduce auxiliary variables that naturally emerge from the Helmholtz-Hodge decomposition for smooth fields, which yields to the minimization of the L^~-norm of the gradients of the new unknowns. This constrained minimization problem is transformed into a series of unconstrained problems by means of Bregman Iteration. We prove the existence of minimizers for the involved subproblems. Then a gradient descent method is selected to solve each subproblem, becoming related, in the case of the auxiliary functions, to the infinity Laplacian. Existence/Uniqueness as well as regularity results of the viscosity solutions of the PDE introduced are proved.

Tailored nearfield Green's functions for arbitrary geometries.

An iterative technique, taken from the field of optics, is used to obtain tailored Greens functions suitable for the evaluation, in the nearfield, of pressure fluctuations generated by turbulent flow in the vicinity of solid boundaries. Comparisons are made with the analytical solution for the solid sphere, and with results obtained using conventional boundary element method (BEM) for the case of a thick semi-infinite plate. A divergence issue in the case of the solid sphere is resolved by the introduction of a relaxation factor. The performance of the iterative approach is found to be comparable to that of conventional BEM, except at irregular frequencies, where the bandwidth of the error is slightly larger than that of the conventional BEM. The main advantage of the iterative approach is a significantly reduced computational cost, which allows for higher surface mesh densities and a broader useful frequency range.

Two-phase flow simulation of scour around a cylindrical pile

In this contribution we present the validation of different OpenFoam solvers and turbulence models for application to scour under steady current. The final goal is to demonstrate the applicability of the two-phase flow Eulerian approach for scour simulations. The hydrodynamic model has been validated using ROULUND et al. (2005) experimental and numerical data for flow around a vertical cylinder over a smooth bed. The preliminary result of the two-phase flow simulation of scour is also presented but more work has to be done.

Time-Domain Tailored Green's Functions for Arbitrary Geometries

Understanding the relationship between pressure and velocity fields in flows containing solid obstacles is a challenge in both incompressible and compressible contexts. In this paper we consider low Mach number flows around obstacle and focus our interest on the tailored Green’s function in the time domain. As many aeroacoustic problems involve intermittent and/or transient mechanisms, time-domain analysis is often essential for a clear analysis of data. We present the iterative procedure by which the time-domain tailored Green’s functions are calculated, which is similar to a procedure already validated in the frequency domain. The main advantage of the iterative timeand frequency-domain approaches is that these avoid the necessity for inversion of large matrices as in conventional BEM.

Experimental analysis of the wall aerodynamics and acoustic radiation of the trailing edge of an airfoil in subsonic flow

This experimental study treats of the trailing edge noise mechanisms, especially broadband noise, resulting from the hydrodynamic wave diffraction on the sharp edge of a foil in flow, with the aim of improving its modeling. A detailed review of the dynamic behaviour of the phenomenon characteristic aerodynamic quantities (wall pressure and velocity fluctuations) has been made on a Naca 0012 airfoil and particular statistical data analysis have been performed (POD, temporal and spectral visualizations, spatial filtering by transducer array). Some models from the literature related to the wall pressure statistics (Corcos, Chase) have been adjusted and validated, and finally used for the modeling of the noise from the trailing edge of the airfoil. To conclude, measurements of the radiated acoustic pressure have been made in an anechoic wind tunnel, showing as a result the validity and limits of the implemented aeroacoustic model. The approach proposed by Chase in terms of wall pressure statistic modeling app...