Strong imposition of Dirichlet boundary velocities in structure-preserving discretizations of elastodynamics
This work addresses the challenge of enforcing Dirichlet boundary velocities in structure-preserving discretizations, which traditionally either introduce Lagrange multipliers—yielding differential-algebraic equations—or weakly impose boundary conditions at the expense of accuracy. The authors propose a continuous-level additive kinematic decomposition that splits the displacement and velocity fields into a dynamic component satisfying homogeneous boundary conditions and a prescribed lifting function. Building on the principle of virtual power, they formulate a lifted port-Hamiltonian system. Upon finite element discretization, the resulting system is an ordinary differential equation that strongly enforces Dirichlet velocity boundary conditions—a first within the port-Hamiltonian framework—while preserving energy conservation and the ODE structure. The approach also unifies classical finite element matrix partitioning techniques. Numerical experiments confirm its energy balance, computational efficiency, and equivalence to standard formulations.