Minimum-resistance shapes in linear continuum mechanics

Abstract

A necessary optimality condition for the problem of the minimum-resistance shape for a rigid threedimensional inclusion displaced in an unbounded isotropic elastic medium subject to a constraint on the volume of the inclusion is obtained through Betti's reciprocal work theorem. It generalizes Pironneau's optimality condition for the minimum-drag shape for a rigid body immersed into a uniform Stokes flow and is specialized for axisymmetric inclusions in axisymmetric and transversal translations. In both cases of translation, the three-dimensional displacement field is represented in terms of generalized analytic functions, and the three-dimensional elastostatics problem is reduced to boundary-integral equations (BIEs) via the generalized Cauchy integral formula. Minimum-resistance shapes are found in the semi-analytical form of functional series from an iterative procedure coupling the optimality condition and the BIEs. They are compared with the minimumresistance spheroids and with the minimum-resistance spindle-shaped and lens-shaped bodies. Remarkably, in the axisymmetric translation, the minimumresistance shapes transition from spindle-like shapes to almost prolate spheroidal shapes as the Poisson ratio changes from 1/2 to 0, whereas in the transversal translation, they are close to oblate spheroidal shapes for any Poisson ratio.

The other optimal Stokes drag profile

“…By computing the drag, we can create a series of profiles with decreasing drag relative to the equivalent sphere. For this, we adopt the approach of Bourot (1974) whereby the drag is minimised within a family of parametrized shapes, a method also used by Zabarankin (2013) to determine optimal profiles in elastic media. By symmetry of the underlying equations, we restrict our attention to axisymmetric shapes with front-back symmetry (Pironneau 1973).…”