Minimum-drag shapes in magnetohydrodynamics

Theory of optimum shapes in free-surface flows. Part 2. Minimum drag profiles in infinite cavity flow

The problem considered here is to determine the shape of a symmetric twodimensional plate so that the drag of this plate in infinite cavity flow is a minimum. With the flow assumed steady and irrotational, and the effects due to gravity ignored, the drag of the plate is minimized under the constraints that the frontal width and wetted arc-length of the plate are fixed. The extremization process...

Explosively launched spores of ascomycete fungi have drag-minimizing shapes.

The forcibly launched spores of ascomycete fungi must eject through several millimeters of nearly still air surrounding fruiting bodies to reach dispersive air flows. Because of their microscopic size, spores experience great fluid drag, and although this drag can aid transport by slowing sedimentation out of dispersive air flows, it also causes spores to decelerate rapidly after launch. We hyp...

Minimum energy states of the cylindrical plasma pinch in single-fluid and Hall magnetohydrodynamics

Stability of critical shapes for the drag minimization problem in Stokes flow

We study the stability of some critical (or equilibrium) shapes in the minimization problem of the energy dissipated by a fluid (i.e. the drag minimization problem) governed by the Stokes equations. We first compute the shape derivative up to the second order, then provide a sufficient condition for the shape Hessian of the energy functional to be coercive at a critical shape. Under this condit...

Efficient Approximation Algorithms for Minimum Enclosing Convex Shapes

We address the problem of Minimum Enclosing Ball (MEB) and its generalization to Minimum Enclosing Convex Polytope (MECP). Given n points in a d dimensional Euclidean space, we give a O(nd/ √ ) algorithm for producing an enclosing ball whose radius is at most away from the optimum. In the case of MECP our algorithm takes O(1/ ) iterations to converge. In both cases we improve the existing resul...