Generalisation of the Total Linearisation Method to Three-dimensional Free-Surface Flows

TL;DR

This paper extends the Total Linearisation Method to three-dimensional free-surface flows, reducing system size and improving computational efficiency, validated through numerical examples involving capillary flows and contact angles.

Contribution

It introduces a generalized linearisation approach for 3D free-surface flows, including moving contact lines, with a novel preconditioner for large systems, improving efficiency over existing methods.

Findings

Effective in 3D capillary flow simulations

Reduces linear system size by nearly half

Validates extension to new contact angles

Abstract

An iterative Finite Element method predicated on a linearisation of the weak form around a reference configuration is derived for general, three-dimensional, free-surface flows, including systems with moving contact lines. The method is a rigorous generalisation of the Total Linearisation Method that was proposed by Kruyt et al. (1988) for two-dimensional flows with contact angles limited to $90^\circ$. In contrast to existing numerical methods for free-surface-flow problems, the present linearisation produces a weak form that is devoid of displacement degrees of freedom in the bulk, thus nearly halving the size of the linear system when compared to standard linearised methods. A novel preconditioner, whose implementation is made possible by the size reduction, is employed to solve the large resulting monolithic Jacobian systems with the Generalised Minimum Residual Method. The proposed method and the preconditioner are shown to be effective on two numerical examples of capillary flows, namely (i) the cylindrical die swell problem, solved both in 3D Cartesian coordinates and under the Ansatz of axisymmetry; and (ii) an enclosed 2D thermo-capillary problem. For the die swell, numerical results are validated by existing experimental results and prior simulations, and confirm both the extension to 3D and theoretical convergence rates. For the thermo-capillary problem, simulations verify earlier calculations. Additional simulations are also carried out for a new range of contact angles made possible by the extension.