Slow-drift motions of a moored two-dimensional body in irregular waves

Weak points in the traditional way of analyzing slow-drift motion are discussed. A theory consistent to second order in wave amplitude and first order in slow-drift velocity for the slow-drift motion of a structure is presented. The interaction between the waves and the local quasi-steady flow due to the slow-drift velocity is incorporated. A new numerical procedure to solve the first- and second-order problem is presented. Generalized Haskind relations for the first-order excitation force and the force due to the second- order potential are derived.