Initial Transients in Long Wave Computations

Initial transients in long wave computations are identified as free mode responses, forced by the incompatibility between the initial conditions and the forced response. Their character is described in the context of two typical one‐dimensional channel problems and an analytical solution to the linearized equations. Strategies to avoid initial transients are investigated in detail, in particular, initially‐enhanced friction, the gradual introduction of forcing and various radiation boundary conditions. A modified Reid radiation boundary condition is recommended for general application, supplemented where necessary by gradual introduction of the forcing to minimize initial spike responses.