  We derive the macroscopic stress tensor for plug-free dense granular flow,
using a first-principles coarse-graining of the inter-granular forces. The
derivation is based on the assumption, which defines the da Vinci Fluid model,
that the inter-granular interactions are dominated by normal contact forces and
solid friction. An explicit form for the stress -- strain rate relation is
obtained, providing closure for the flow equations of dense granular fluids and
improves on existing models, which are also based on solid friction as the
dominant drag mechanism.
