A Well-Balanced Runge-Kutta Discontinuous Galerkin Method for Multilayer Shallow Water Equations with Non-Flat Bottom Topography
2021
A well-balanced Runge-Kutta discontinuous Galerkin method is presented for the numerical solution of multilayer shallow water equations with mass exchange and non-flat bottom topography. The
governing equations are reformulated as a nonlinear system of conservation laws with differential source
forces and reaction terms. Coupling between the flow layers is accounted for in the system using a
set of exchange relations. The considered well-balanced Runge-Kutta discontinuous Galerkin method
is a locally conservative finite element method whose approximate solutions are discontinuous across
the inter-element boundaries. The well-balanced property is achieved using a special discretization
of source terms that depends on the nature of hydrostatic solutions along with the Gauss-LobattoLegendre nodes for the quadrature used in the approximation of source terms. The method can also
be viewed as a high-order version of upwind finite volume solvers and it offers attractive features for
the numerical solution of conservation laws for which standard finite element methods fail. To deal
with the source terms we also implement a high-order splitting operator for the time integration. The
accuracy of the proposed Runge-Kutta discontinuous Galerkin method is examined for several examples of multilayer free-surface flows over both flat and non-flat beds. The performance of the method
is also demonstrated by comparing the results obtained using the proposed method to those obtained
using the incompressible hydrostatic Navier-Stokes equations and a well-established kinetic method.
The proposed method is also applied to solve a recirculation flow problem in the Strait of Gibraltar.
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