On a submerged wave energy converter with snap-through power take-off

•An internal snap through PTO is applied to a submerged cylinder WEC.•The equation of motion of the surging WEC is derived in the time domain by using the Euler–Lagrange equations.•Three response regimes, i.e. local oscillation, aperiodic snap through and periodic snap through, of the PTO are observed when varying the wave heights.•Compared with the linear PTO, higher efficiency is noticed with the use of the present nonlinear PTO.