Gravitational motion of a two-particle cluster between two parallel plane solid wallsSédimentation de deux particules solides entre deux plans parallèles

The slow viscous settling migration of a 2-particule cluster between two solid and parallel plane walls is investigated by resorting to a Boundary Element Method. The procedure, valid for arbitrarily-shaped bodies, is presented and preliminary numerical results for both identical spheres and a spheroid-sphere cluster are discussed. To cite this article: L. Pasol, A. Sellier, C. R. Mecanique 334 (2006).     

Study of a new semi-continuous model of the Boltzmann equation

For a semi-continuous model of the Boltzmann equation (1) peculiar solutions are obtained and generally the global existence of solutions of the initial value problem is discussed. The global existence is possible even in some cases for partially negative initial number densities, which are not physical problems, but mathematical ones. It can be shown that in some cases the entropy begins to increase, reaches a maximum and decreases again.     

Spectral norms on valued fields

Let be a perfect valued field, be an algebraic closure of be an extension of to and be the G-spectral norm on Let be an algebraic extension of K and be the completion of L relative to We associate to any element a real number and prove that if for all x in , then and is a zero-dimensional regular ring. We show that and prove that is algebraic over (with some additional conditions on K and L). We give a Galois type correspondence between the set of all closed K-subalgebras of and the subfields of L. We prove that is an algebraic closed and zero-dimensional regular ring. Received: 3 March 1999; in final form: 21 February 2000 / Published online: 4 May 2001     

Migration of a solid particle in the vicinity of a plane fluid–fluid interface

The slow migration of a small and solid particle in the vicinity of a gas–liquid, fluid–fluid or solid–fluid plane boundary when subject to a gravity or an external flow field is addressed. By contrast with previous works, the advocated approach holds for arbitrarily shaped particles and arbitrary external Stokes flow fields complying with the conditions on the boundary. It appeals to a few theoretically established and numerically solved boundary-integral equations on the particle’s surface. This integral formulation of the problem allows us to provide asymptotic approximations for a distant boundary and also, implementing a boundary element technique, accurate numerical results for arbitrary locations of the boundary. The results obtained for spheroids, both settling or immersed in external pure shear and straining flows, reveal that the rigid-body motion experienced by a particle deeply depends upon its shape and also upon the boundary location and properties.     

A sphere in a second degree polynomial creeping flow parallel to a wall

Comprehensive results are provided for the creeping flow arounda spherical particle in a viscous fluid close to a plane wall,when the external velocity is parallel to the wall and variesas a second degree polynomial in the coordinates. By linearityof Stokes equations, the solution is a sum of flows for typicalunperturbed flows: a pure shear flow, a ‘modulated shearflow’, for which the rate of shear varies linearly inthe direction normal to the wall, and a quadratic flow. Solutionsconsidered here use the bipolar coordinates technique. Theycomplement the accurate results of Chaoui and Feuillebois (2003)for the pure shear flow. The solution of Goren and O'Neill (1971)for the quadratic flow is reconsidered and a new analyticalsolution is derived for the ambient modulated shear flow. Theperturbed flow fields for these two cases are presented in detailand discussed. Results for the force and torque friction factorsare provided with a 5 x 10^–17 accuracy as a reference.For the quadratic flow, there is a force and a torque on a fixedsphere. A minimum value of the torque is found for a gap ofabout 0·18a, where a is the sphere radius. This minimumis interpreted in term of the corresponding flow structure.For the modulated shear flow, there is only a torque. The freemotion of a sphere in an ambient quadratic flow is also determined.