Energy dissipation rates Ė_ave/10³⁵ ⟨ ρ ⟩  as a function of β₀ = ω/Ω₀ for four different eccentricities, e = 0.1 (top left), 0.3 (top right), 0.5 (bottom left) and 0.8 (bottom right). The first three cases are for an orbital period P = 6 d and the last is for 20 d. The ordinate is in units of 10³⁵ ⟨ ρ ⟩  erg s^-1, where  ⟨ ρ ⟩  is the average density. The dotted line indicates the level of minimum Ė_ave which, for e = 0.1 and 0.3 coincides with the analytical results of Hut (1981).