SUMMARYNonequilibrium radiation diffusion problems are described by the coupled radiation diffusion and material conduction equations. Because of the highly nonlinear, strong discontinuous, and tightly coupled phenomena, solving this kind of problems is a challenge. We construct two finite volume element schemes for the equations. One of them is monotone on many kinds of meshes, which is proved theoretically and verified by numerical tests. The other one is hard to satisfy the monotonicity, but this defect can be corrected by different repair techniques. Numerical results show that these new methods are practical and efficient on distorted meshes.Copyright © 2013 John Wiley & Sons, Ltd.

Two-dimensional three-temperature (2-D 3-T) radiation diffusion equations are widely used to approximately describe the evolution of radiation energy within a multi-material system and explain the exchange of energy among electrons, ions and photons. Their highly nonlinear, strong discontinuous and tightly coupled phenomena always make the numerical solution of such equations extremely challenging. In this paper, we construct two finite volume element schemes both satisfying the discrete conservation property. One of them can well preserve the positivity of analytical solutions, while the other one does not satisfy this property. To fix this defect, two as repair techniques are designed. In addition, as the numerical simulation of 2-D 3-T equations is very time consuming, we also devise a mesh adaptation algorithm to reduce the cost. Numerical results show that these new methods are practical and efficient in solving this kind of problems.

a b s t r a c tA covolume method is proposed for the mixed formulation of second-order elliptic problems. The solution domain is divided by a quadrilateral grid, corresponding to which a nonoverlapping dual grid is constructed. The velocity and pressure are approximated by the lowest-order Raviart-Thomas space on quadrilaterals. We prove its first order optimal rate of convergence for the approximate velocities in the H(div)-norm as well as for the approximate pressures in the L 2 -norm. A second order error estimate between a suitable projection of the exact velocity (or pressure) and the approximate velocity (or approximate pressure) is also presented. Numerical experiments are provided to illustrate the error behavior of the scheme.