A two-dimensional numerical wave tank is used to compute the nonlinear radiation step response of oscillating water column wave-power plants. The influence of several parameters of the device such as front wall thickness and slopes, submerged aperture width and initial water height on the first three spatial modes of the chamber free-surface is investigated. Some interesting qualitative relations between the column response and these parameters are shown; their interest, and more generally the interest of using such simulation tools at the design stage of owc wave-power devices, is highlighted.