Viscous-Inviscid Interactions in a Boundary-Layer Flow Induced by a Vortex Array

In this paper we investigate the asymptotic validity of boundary layer theory. For a flow induced by a periodic row of point-vortices, we compare Prandtl's solution to Navier-Stokes solutions at different $Re$ numbers. We show how Prandtl's solution develops a finite time separation singularity. On the other hand Navier-Stokes solution is characterized by the presence of two kinds of viscous-inviscid interactions between the boundary layer and the outer flow. These interactions can be detected by the analysis of the enstrophy and of the pressure gradient on the wall. Moreover we apply the complex singularity tracking method to Prandtl and Navier-Stokes solutions and analyze the previous interactions from a different perspective

Ekman layers near wavy boundaries

International audienceWe investigate the effect of boundary roughness on the dynamical properties of the flow in laminar Ekman boundary layers. The study considers wavy boundaries having both horizontal wavelength and vertical extent comparable in size with the boundary layer width. In the case of flat boundaries, Ekman layers are known to be active, i.e. to affect significantly the dynamics of the mainstream flow. We show how the layer modelling needs to be modified to account for such wavy boundaries. In particular, nonlinear terms enter the laminar description. This model can be linearized in the limit of small Reynolds numbers. The resulting equations are studied using both asymptotic expansions and full numerical simulations. We find that small-scale roughness significantly alters energy dissipation in the boundary layer. This can result in either a reduction or an increase of dissipation, depending on, in particular, the orientation of the mainstream flow with respect to boundary modulation. Agreement is obtained between theoretical and computational results

Moral Hazard in Teams with Uncertainty, and Transfers or Repetition as Enforcement Mechanisms

Properties of stochastic outcome functions are exploited to solve the moral hazard problem in teams under unobservable individual actions and different individual objectives. Two kinds of enforcement mechanisms are considered: Enforcement through utility transfers and enforcement through repetition. For both more general results are obtained by adapting conditions previously derived to ensure truthful revelation of private information for collective deciSion-making. These conditions are shown to be generic. Also, one of these being weaker than the condition of pairwise identifiability used by Fudenberg, Levine and Maskin, a new Folk theorem is obtained.Mechanism design, team moral hazard, folk theorem

Moral Hazard in Teams and Repeated Partnership : The Role of Information Quality

We analyse the sharing of an uncertain joint output among risk-neutral members of a team whose actions are not observable. Adapting techniques used to treat the pure adverse selection problem to this team moral hazard problem, we define a first condition that is sufficient to implement a first best joint action and a second condition that is sufficient to implement. any joint action . These conditions hold generically. Finally we show ttw usefulness of such eonditions in repeated partnership with imperfect monitoring and prove a folk-theorem.

Endogenous Business Cycles And Business Formation With Strategic Investment

We study an endogenous business cycle model with Cournotian monopolistic competition and an endogenous number of firms in each sector

On the Dixit-Stiglitz Model of Monopolistic Competition as Enforcement Mechanisms

We examine two variants of the monopolistic competition model of Dixit and Stiglitz (1993). One is a simple general equilibrium model with n produced monopolistic goods and a numeraire good, the other in an "enlarged model", that includes labor time an an addiitonal good. In the case of alarge n, it is reasonable to consider in both variants only the direct effects of individual pricing decisions on demand, neglecting all indirect effects, either through the price index or through income. However, for other cases, we show that all these indirect effects can be taken into account and explicit solutions obtained. The derivations are even simpler for the enlarged model.