We report on the scaling between the lift force and the velocity lag experienced by a single particle of different size in a monodisperse dense granular chute flow. The similarity of this scaling to the Saffman lift force in (micro) fluids, suggests an inertial origin for the lift force responsible for segregation of (isolated, large) intruders in dense granular flows. We also observe an anisotropic pressure/stress field surrounding the particle, which potentially lies at the origin of the velocity lag. These findings are relevant for modelling and theoretical predictions of particle-size segregation. At the same time, the suggested interplay between polydispersity and inertial effects in dense granular flows with stress-and strain-gradients, implies striking new parallels between fluids, suspensions and granular flows with wide application perspectives. arXiv:1705.06803v4 [cond-mat.soft]

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We present an adjoint-based method for optimizing flapping motion kinematics in a viscous flow governed by the Navier-Stokes equations. We employ an arbitrary Lagrangian Eulerian formulation, discretized by a high-order discontinuous finite element method. Mesh motion is specified analytically, using parameters that we seek to optimize. Sensitivities are computed using a discrete unsteady adjoint approach, and these sensitivities drive a gradient-based optimization scheme. In this paper we show results for optimizations with a moderate number of parameters in a modal approximation to the kinematics.

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