Space-time discontinuous Galerkin discretization of rotating shallow water equations on moving grids

A space-time discontinuous Galerkin (DG) discretization is presented for the (rotating) shallow water equations over varying topography. We formulate the space-time DG finite element discretization in an efficient and conservative discretization. The HLLC flux is used as numerical flux through the finite element boundaries. When discontinuities are present, we locally apply dissipation around these discontinuities with the help of Krivodonova's discontinuity indicator such that spurious oscillations are suppressed. The non-linear algebraic system resulting from the discretization is solved using a pseudo-time integration with a second-order five-stage Runge-Kutta method. A thorough verification of the space-time DG finite element method is undertaken by comparing numerical and exact solutions. We also carry out a discrete Fourier analysis of the one dimensional linear rotating shallow water equations to show that the method is unconditionally stable with minimal dispersion and dissipation error. The numerical scheme is validated in a novel way by considering various simulations of bore-vortex interactions in combination with a qualitative analysis of PV generation by non-uniform bores. Finally, the space-time DG method is particularly suited for problems where dynamic grid motion is required. To demonstrate this we simulate waves generated by a wave maker and verify these for low amplitude waves where linear theory is approximately valid

Space-time discontinuous Galerkin finite element method for shallow water flows

A space-time discontinuous Galerkin (DG) finite element method is presented for the shallow water equations over varying bottom topography. The method results in non-linear equations per element, which are solved locally by establishing the element communication with a numerical HLLC flux. To deal with spurious oscillations around discontinuities, we employ a dissipation operator only around discontinuities using Krivodonova's discontinuity detector. The numerical scheme is verified by comparing numerical and exact solutions, and validated against a laboratory experiment involving flow through a contraction. We conclude that the method is second order accurate in both space and time for linear polynomials.\u

Port-Hamiltonian formulation of shallow water equations with Coriolis force and topography

We look into the problem of approximating the shallow water equations with Coriolis forces and topography. We model the system as an infinite-dimensional port-Hamiltonian system which is represented by a non-constant Stokes-Dirac structure. We here employ the idea of using different finite elements for the approximation of geometric variables (forms) describing a distributed parameter system, to spatially discretize the system and obtain a lumped parameter port-Hamiltonian system. The discretized model then captures the physical laws of its infinite-dimensional couterpart such as conservation of energy. We present some preliminary numerical results to justify our claims

Port-Hamiltonian discretization for open channel flows

A finite-dimensional Port-Hamiltonian formulation for the dynamics of smooth open channel flows is presented. A numerical scheme based on this formulation is developed for both the linear and nonlinear shallow water equations. The scheme is verified against exact solutions and has the advantage of conservation of mass and energy to the discrete level

Variational space-time (dis)continuous Galerkin method for nonlinear free surface waves

A new variational finite element method is developed for nonlinear free surface gravity water waves. This method also handles waves generated by a wave maker. Its formulation stems from Miles' variational principle for water waves together with a space-time finite element discretization that is continuous in space and discontinuous in time. The key features of this formulation are: (i) a discrete variational approach that gives rise to conservation of discrete energy and phase space and preservation of variational structure; and (ii) a space-time approach that guarantees satisfaction of the geometric conservation law which is crucial in handling the deforming flow domain due to the wave maker and free surface motion. The numerical discretization is a combination of a second order finite element discretization in space and a second order symplectic Stormer-Verlet discretization in time. The resulting numerical scheme is verified against nonlinear analytical solutions and discrete energy conservation is demonstrated for long time simulations. We also validated the scheme with experimental data of waves generated in a wave basin of the Maritime Research Institute Netherlands

On the rate of convergence of the Hamiltonian particle-mesh method

The Hamiltonian Particle-Mesh (HPM) method is a particle-in-cell method for compressible fluid flow with Hamiltonian structure. We present a numer- ical short-time study of the rate of convergence of HPM in terms of its three main governing parameters. We find that the rate of convergence is much better than the best available theoretical estimates. Our results indicate that HPM performs best when the number of particles is on the order of the number of grid cells, the HPM global smoothing kernel has fast decay in Fourier space, and the HPM local interpolation kernel is a cubic spline

Some studies on the deformation of the membrane in an RF MEMS switch

Radio Frequency (RF) switches of Micro Electro Mechanical Systems (MEMS) are appealing to the mobile industry because of their energy efficiency and ability to accommodate more frequency bands. However, the electromechanical coupling of the electrical circuit to the mechanical components in RF MEMS switches is not fully understood. In this paper, we consider the problem of mechanical deformation of electrodes in RF MEMS switch due to the electrostatic forces caused by the difference in voltage between the electrodes. It is known from previous studies of this problem, that the solution exhibits multiple deformation states for a given electrostatic force. Subsequently, the capacity of the switch that depends on the deformation of electrodes displays a hysteresis behaviour against the voltage in the switch. We investigate the present problem along two lines of attack. First, we solve for the deformation states of electrodes using numerical methods such as finite difference and shooting methods. Subsequently, a relationship between capacity and voltage of the RF MEMS switch is constructed. The solutions obtained are exemplified using the continuation and bifurcation package AUTO. Second, we focus on the analytical methods for a simplified version of the problem and on the stability analysis for the solutions of deformation states. The stability analysis shows that there exists a continuous path of equilibrium deformation states between the open and closed state

Flooding and drying in discontinuous Galerkin discretizations of shallow water equations

Flooding and drying in space or space-time discontinuous Galerkin (DG) discretizations provides an accurate and efficient numerical scheme. Moreover, the space-time DG method is particularly suitable for moving or deforming meshes. The shallow water equations, which can exhibit flooding and drying due to the movement of water front, are considered and discretized with linear polynomial approximations. In the finite elements connected to the water front, the means (zeroth order term) are used to conserve the mass and momentum, and the slopes (first order term) are used to follow the front movement accurately, which contrasts finite volume schemes where the slopes have to be reconstructed. The front movement can be governed by a front equation in a restricted situation in which the front is single valued in either one of the horizontal coordinate directions. In general, however, the water line can be complicated and the topology of the domain can change as islands become flooded or fall dry. We are developing the following two approaches for this general case. In an Eulerian-Lagrangian space DG method, the free boundary nodes at the water line are allowed to move, while the time step is restricted and the mesh is locally updated to keep the dry and wet mesh around the water line well-behaved. In the space-time DG method a level set is introduced to demarcate the water line while the water depth and level set are matched properly. As a preliminary step, we have obtained numerical results for two exact solutions by prescribing the exact front movement. These are second order accurate in space and time

Variational space-time (dis)continuous Galerkin method for linear free surface waves

A new variational (dis)continuous Galerkin finite element method is presented for the linear free surface gravity water wave equations. We formulate the space-time finite element discretization based on a variational formulation analogous to Luke's variational principle. The linear algebraic system of equations resulting from the finite element discretization is symmetric with a very compact stencil. To build and solve these equations, we have employed PETSc package in which a block sparse matrix storage routine is used to build the matrix and an efficient conjugate gradient solver is used to solve the equations. The numerical scheme is verified for linear harmonic free surface waves in a periodic domain and linear free surface generated by a harmonic wave maker in a rectangular wave basin. We conclude that the scheme is second order accurate and, shows no dissipation and minimal dispersion errors in the wave propagation