We consider the time-dependent magnetic induction model where the sought magnetic field interacts with a prescribed velocity field. This coupling results in an additional force term and time dependence in Maxwell's equation. We propose two different magnetic diffusivity stabilized continuous nodal-based finite element methods for this problem. The first formulation simply adds artificial magnetic diffusivity to the partial differential equation, whereas the second one uses a local projected magnetic diffusivity as stabilization. We describe those methods and analyze them semi-discretized in space to get bounds on stabilization parameters where we distinguish equal-order elements and Taylor-Hood elements. Different numerical experiments are performed to illustrate our theoretical findings. KEYWORDS layer phenomena, local projection stabilization, magnetic diffusivity, magnetic induction equation, stabilized finite element methods, stability and convergence analysis 4554 4555
State-of-the-art methodsBefore stating our contributions, we discuss methods mainly used in computational electrodynamics. Curl-conforming finite element methods are the standard approach for approximating (3) and (4). 9,13-16 Although these elements work well with the problem's structure, they have some drawbacks in implementation. One important disadvantage is the occurrence of ill-posed matrices. In problems with many degrees of freedom, the corresponding problem's matrix can even be singular. The introduction of Lagrangian multipliers improves this situation. However, this increases the number of unknowns and can cause trouble in calculations. 17 Because of their efficiency and their ease in implementation, nodal-based finite element methods seem to be an attractive alternative.Costabel and Dauge proposed a weighted regularization for Maxwell's equation in polyhedral domains with reentrant corners in 2002. 18 This article caused a rehabilitation of nodal-based finite element methods in computational electromagnetism. Follow-up works suggested different regularizations for Maxwell's problem. [19][20][21] These ideas led to different stabilization techniques in case of magnetohydrodynamics. 7,8,11
ContributionsOur starting point is the stabilization method in Kaya et al. 12 It stabilizes the divergence constraint and the gradient of the magnetic pseudo-pressure. Although this algorithm works well for moderately small magnetic diffusivity , our work will demonstrate that it is not well suited for nearly vanishing . This observation motivates our following contributions: 1) We first expand the aforementioned method by a local projection stabilization of the induction term ∇ × (u × b) as solely done in numerical simulations in Bonito et al. 22 Further and in contrast with Kaya et al 12 and Bonito et al, 22 we stabilize the magnetic diffusion term in two possible ways. We either simply add artificial magnetic diffusivity or local projected magnetic diffusivity. These ideas are inspired by stabilization techniques from turbulence modeling. 5,23...