https://hal.archives-ouvertes.fr/hal-00822044/document

A Lattice Boltzmann-Immersed Boundary method to simulate the fluid interaction with moving and slender flexible objects

https://hal.archives-ouvertes.fr/hal-01225681/document

An immersed boundary-lattice Boltzmann method for single- and multi-component fluid flows

http://www.off-ladhyx.polytechnique.fr/people/delangre/gosselin-2011.pdf

Drag reduction by reconfiguration of a poroelastic system

Natural and engineered surfaces are never smooth, but irregular, rough at different scales, compliant, possibly porous, liquid impregnated or superhydrophobic. The correct numerical modelling of fluid flowing through and around them is important but poses problems. For media characterized by a periodic or quasi-periodic microstructure of characteristic dimensions smaller than the relevant scales of the flow, multiscale homogenization can be used to study the effect of the surface, avoiding the numerical resolution of small details. Here, we revisit the homogenization strategy using adjoint variables to model the interaction between a fluid in motion and regularly micro-textured, permeable or impermeable walls. The approach described allows for the easy derivation of auxiliary/adjoint systems of equations which, after averaging, yield macroscopic tensorial properties, such as permeability, elasticity, slip, transpiration, etc. When the fluid in the neighbourhood of the microstructure is in the Stokes regime, classical results are recovered. Adjoint homogenization, however, permits simple extension of the analysis to the case in which the flow displays nonlinear effects. Then, the properties extracted from the auxiliary systems take the name of effective properties and do not depend only on the geometrical details of the medium, but also on the microscopic characteristics of the fluid motion. Examples are shown to demonstrate the usefulness of adjoint homogenization to extract effective tensor properties without the need for ad hoc parameters. In particular, notable results reported herein include:(i) an original formulation to describe filtration in porous media in the presence of inertial effects;(ii) the microscopic and macroscopic equations needed to characterize flows through poroelastic media;(iii) an extended Navier’s condition to be employed at the boundary between a fluid and an impermeable rough wall, with roughness elements which can be either rigid or linearly elastic;(iv) the microscopic problems needed to define the relevant parameters for a Saffman-like condition at the interface between a fluid and a porous substrate; and(v) the macroscopic equations which hold at the dividing surface between a free-fluid region and a fluid-saturated poroelastic domain.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/2335407C172B7C0FF276EBA19B7B0DF5/S0022112019006074a.pdf/div-class-title-flow-over-natural-or-engineered-surfaces-an-adjoint-homogenization-perspective-div.pdf

Flow over natural or engineered surfaces: an adjoint homogenization perspective

The flow control of a circular cylinder by using a flexible filament has been numerically investigated in this work. The cylinder is either fixed or elastically mounted, and the filament is attached to the base of the cylinder. Its leading end is fixed and its trailing end is free to flap. To execute the numerical simulation and deal with the fluid-structure interaction (FSI) of the filament as well, an improved immersed boundary-lattice Boltzmann method (IB-LBM) is presented. As compared to the conventional IB-LBM for handling the FSI of a filament, the current method can incorporate the mass effect of the filament and no user-defined spring parameter is needed to calculate the interaction force on the filament. After validating the employed method, the effects of the filament on the flow control of the cylinder are systematically examined by varying the bending coefficient (Kb) and length (L) of the filament. The laminar flow with a Reynolds number of 150 is considered in this study. Based on the numeri...

Flow control of a circular cylinder by using an attached flexible filament

A model of hairy medium is developed using a homogenized approach, and the fluid flow around a circular cylinder partially coated with hair is analyzed by means of nu- merical simulations. The capability of this coating to adapt to the surrounding flow is investigated, and its benefits are discussed in the context of separation control. This fluid-structure interaction problem is solved with a partitioned approach, based on the direct resolution of the Navier-Stokes equations together with a non-linear set of equa- tions describing the dynamics of the coating. A volume force, arising from the presence of a cluster of hair, provides the link between the fluid and the structure problems. For the structure part, a subset of reference elements approximates the whole layer. The dy- namics of these elements is governed by a set of equations based on the inertia, elasticity, interaction and losses effects of articulated rods. The configuration chosen is that of the two-dimensional flow past a circular cylinder at Re = 200, a simple and well documented test case. Aerodynamics performances quantified by the Strouhal number, the drag and the maximum lift in the laminar unsteady regime are modified by the presence of the coating. A set of parameters corresponding to a realistic coating (length of elements, porosity, rigidity) is found, yielding an average drag reduction of 15% and a decrease of lift fluctuations by about 40%, associated to a stabilization of the wake.

/pdf/passive-separation-control-using-a-self-adaptive-hairy-1p4u9y5ce3.pdf

Passive separation control using a self-adaptive hairy coating

This paper presents an extension of impedance control of robots based on fractional calculus. In classical impedance control, the end-effector reactions are proportional to the end-effector position errors through the stiffness matrix K, while damping is proportional to the first-order time-derivative of the end-effector coordinate errors through the damping matrix D. In the proposed approach, a half-derivative damping is added, proportional to the half-order time-derivative of the end-effector coordinate errors through the half-derivative damping matrix HD. The discrete-time digital implementation of the half-order derivative alters the steady-state behavior, in which only the stiffness term should be present. Consequently, a compensation method is proposed, and its effectiveness is validated by multibody simulation on a 3-PUU parallel robot. The proposed approach can be considered the extension to MIMO robotic systems of the PDD1/2 control scheme for SISO mechatronic systems, with potential benefits in the transient response performance.

/pdf/application-of-the-half-order-derivative-to-impedance-3mox7xja.pdf

Davide Basso

Papers

Passive separation control using a self-adaptive hairy coating

Application of the Half-Order Derivative to Impedance Control of the 3-PUU Parallel Robot