“…This paper develops, implements, and tests a numerical scheme for (1.1). In our proposed approach, the resulting system is discretized in time by a semi-implicit backward Euler method and in space by a suitable finite volume element (FVE) method whose main novelty lies in the formulation of a unified scheme for a coupled problem, while several FVE methods have been proposed for Stokes and quasi-linear scalar elliptic problems only; see, e.g., [7,15,48]. Besides the finite element (FE) primal mesh, we introduce two additional meshes on which we discretize velocity and solids fraction by continuous and discontinuous piecewise linear elements, respectively.…”