FREELY FLOATING STRUCTURES TRAPPING TIME-HARMONIC WATER WAVES

We study the coupled small-amplitude motion of the mechanical system consisting of infinitely deep water and a structure immersed in it. The former is bounded above by a free surface, whereas the latter is formed by an arbitrary finite number of surface-piercing bodies floating freely. The mathematical model of time-harmonic motion is a spectral problem in which the frequency of oscillations serves as the spectral parameter. It is proved that there exist axisymmetric structures consisting of N >= 2 bodies; every structure has the following properties: (i) a time-harmonic wave mode is trapped by it; (ii) some of its bodies (maybe none) are motionless, whereas the rest of the bodies (maybe none) are heaving at the same frequency as water. The construction of these structures is based on a generalisation of the semi-inverse procedure applied earlier for obtaining trapping bodies that are motionless although float freely.