Abstract

We present a nonlinear multigrid implementation for the two-dimensional Cahn–Hilliard (CH) equation and conduct detailed numerical tests to explore the performance of the multigrid method for the CH equation. The CH equation was originally developed by Cahn and Hilliard to model phase separation phenomena. The CH equation has been used to model many interface-related problems, such as the spinodal decomposition of a binary alloy mixture, inpainting of binary images, microphase separation of diblock copolymers, microstructures with elastic inhomogeneity, two-phase binary fluids, in silico tumor growth simulation and structural topology optimization. The CH equation is discretized by using Eyre’s unconditionally gradient stable scheme. The system of discrete equations is solved using an iterative method such as a nonlinear multigrid approach, which is one of the most efficient iterative methods for solving partial differential equations. Characteristic numerical experiments are conducted to demonstrate the efficiency and accuracy of the multigrid method for the CH equation. In the Appendix, we provide C code for implementing the nonlinear multigrid method for the two-dimensional CH equation.

Highlights

  • We summarize here the nonlinear multigrid method for solving the discrete CH system as follows: First, let us rewrite Equations (5) and (6) as NSO(φn+1, μn+1 ) = (ξ n, ψn ), where the linear operator NSO is defined as NSO(φn+1, μn+1 ) = φn+1 /∆t − ∆h μn+1, μn+1 −3 + e2 ∆h φn+1, and the source term is denoted by (ξ n, ψn ) =

  • We presented a nonlinear multigrid implementation for the CH equation in a two-dimensional space

  • We described the implementation of our numerical scheme in detail

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Summary

Introduction

We consider a detailed multigrid [1] implementation of the following two-dimensional Cahn–Hilliard (CH) equation [2] and provide its C source code:. The second boundary condition (2) implies that the total mass is conserved. Conservation of mass implies the following CH equation φt = −∇ · F , where the flux is given by F = − M ∇μ. Details regarding the implementation, multigrid performance, and source codes have not been provided. The main purpose of this paper is to describe a detailed multigrid implementation of the two-dimensional CH equation, evaluate its performance and provide its C programming language source code. In the Appendix A, we provide the C code for implementing the nonlinear multigrid technique for the two-dimensional CH equation

Numerical Solution
Discretization
Multigrid V-Cycle Algorithm
Numerical Experiments
Phase Separation
Non-Increase in Discrete Energy and Mass Conservation
Convergence Test
Effect of Tolerance
Effects of the Smooth Relaxation Numbers ν1 and ν2
Effect Of V-Cycle
Comparison between Gauss–Seidel and Multigrid Algorithms
3.10. Effect of e
Conclusions

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