A novel hybrid IGA-EIEQ numerical method for the Allen-Cahn/Cahn-Hilliard equations on complex curved surfaces

We present an efficient fully discrete algorithm for solving the Allen-Cahn and Cahn-Hilliard equations on complex curved surfaces. The spatial discretization employs the recently developed IGA (isogeometric analysis) framework, where we adopt the strategy of Loop subdivision with the superior adaptability of any topological structure, and the basis functions are quartic box-splines used to define the subdivided surface. The time discretization is based on the so-called EIEQ (explicit-Invariant Energy Quadratization) approach, which applies multiple newly defined variables to linearize the nonlinear potential and realize the efficient decoupled type computation. The combination of these two methods can help us to gain a linear, second-order time accurate scheme with the property of unconditional energy stability, whose rigorous proof is given. We also develop a nonlocal splitting technique such that we only need to solve decoupled, constant-coefficient elliptic equations at each time step. Finally, the effectiveness of the developed numerical algorithm is verified by various numerical experiments on the complex benchmark curved surfaces such as bunny, splayed, and head surfaces.(c) 2022 Elsevier B.V. All rights reserved.