An unfitted boundary algebraic equation method with static-dynamic reduction for evolving implicit geometries

Repeated elliptic solves on domains with evolving boundaries arise in moving-interface simulation, design, and reactive navigation.

Even when a fixed Cartesian grid avoids remeshing, rebuilding all boundary interactions for every configuration can limit the efficiency of repeated solves.

We develop a static--dynamic boundary reduction for an unfitted lattice Green's function method on prescribed moving planar domains.

Like boundary integral and boundary element methods, the formulation reduces the problem to boundary-supported unknowns through a Green representation.

Its construction, however, reverses the usual order: the Cartesian operator is discretized before the Green representation is formed, rather than representing the continuous problem first and then discretizing the boundary.

This discretize-then-represent viewpoint avoids boundary meshes and singular quadrature.

The method also separates interactions associated with stationary geometry from those affected by motion, reuses the invariant part throughout a simulation, and updates only couplings involving the changing boundary.

Boundary conditions are imposed at true interface intersections, lattice-kernel data are reused, and the interior field is reconstructed by a fast sine-transform solver.

The principal contribution is an implemented and validated update strategy for translating, deforming, appearing, and topology-changing obstacles.