  A method is proposed for the characterisation of the entropy of cellular
structures, based on the compactivity concept for granular packings.
Hamiltonian-like volume functions are constructed both in two and in three
dimensions, enabling the identification of a phase space and making it possible
to take account of geometrical correlations systematically. Case studies are
presented for which explicit calculations of the mean vertex density and
porosity fluctuations are given as functions of compactivity. The formalism
applies equally well to two- and three-dimensional granular assemblies.
