2 research outputs found
A convergent SAV scheme for Cahn--Hilliard equations with dynamic boundary conditions
The Cahn-Hilliard equation is one of the most common models to describe phase
separation processes in mixtures of two materials. For a better description of
short-range interactions between the material and the boundary, various dynamic
boundary conditions for this equation have been proposed. Recently, a family of
models using Cahn-Hilliard-type equations on the boundary of the domain to
describe adsorption processes was analysed (cf. Knopf, Lam, Liu, Metzger,
ESAIM: Math. Model. Numer. Anal., 2021). This family of models includes the
case of instantaneous adsorption processes studied by Goldstein, Miranville,
and Schimperna (Physica D, 2011) as well as the case of vanishing adsorption
rates which was investigated by Liu and Wu (Arch. Ration. Mech. Anal., 2019).
In this paper, we are interested in the numerical treatment of these models and
propose an unconditionally stable, linear, fully discrete finite element scheme
based on the scalar auxiliary variable approach. Furthermore, we establish the
convergence of discrete solutions towards suitable weak solutions of the
original model. Thereby, when passing to the limit, we are able to remove the
auxiliary variables introduced in the discrete setting completely. Finally, we
present simulations based on the proposed linear scheme and compare them to
results obtained using a stable, non-linear scheme to underline the
practicality of our scheme
A convergent stochastic scalar auxiliary variable method
We discuss an extension of the scalar auxiliary variable approach which was
originally introduced by Shen et al.~([Shen, Xu, Yang, J.~Comput.~Phys., 2018])
for the discretization of deterministic gradient flows. By introducing an
additional scalar auxiliary variable, this approach allows to derive a linear
scheme, while still maintaining unconditional stability. Our extension augments
the approximation of the evolution of this scalar auxiliary variable with
higher order terms, which enables its application to stochastic partial
differential equations. Using the stochastic Allen--Cahn equation as a
prototype for nonlinear stochastic partial differential equations with
multiplicative noise, we propose an unconditionally energy stable, linear,
fully discrete finite element scheme based on our stochastic scalar auxiliary
variable method. Recovering a discrete version of the energy estimate and
establishing Nikolskii estimates with respect to time, we are able to prove
convergence of appropriate subsequences of discrete solutions towards pathwise
unique martingale solutions by applying Jakubowski's generalization of
Skorokhod's theorem. A generalization of the Gy\"ongy--Krylov characterization
of convergence in probability to quasi-Polish spaces finally provides
convergence of fully discrete solutions towards strong solutions of the
stochastic Allen--Cahn equation