Interaction Forces on Oscillating and Translating Two Cylinders Submerged under a Free Surface

抄録

With attention focused on the effects of forward speed on hydrodynamic interactions, radiation and diffraction problems are studied for submerged two circular cylinders moving with forward velocity in head and following waves. Under a linear assumption, the velocity potential is exactly obtained from the boundary-integral-equation on the body surface, using a numerical technique. The added-mass and damping coefficients, exciting forces, resultant cylinder motions, and added resistance are computed and then the hydrodynamic interaction effects on these quantities are discussed.
In the frequencies lower than τ= Uω/g=11 4 (whereU is forward speed, ω oscillation frequency, andg gravity acceleration), the effects of hydrodynamic interaction on radiation forces are great, particularly for the upstream cylinder. However for τ>1/4 the effects on the upstream cylinder are markedly reduced, but those on the downstream cylinder still exist. The interaction effects on exciting forces are small compared with radiation forces. The added resistance is approximately zero in head waves, whereas in following waves it is drastically changed by the interaction effects, while keeping the positive value for U/C<1/2 and the negative value for 1/2<U/C<1 (where C is phase velocity of incident wave). These numerical results are explained qualitatively by the information of the diffraction characteristics of a single circular cylinder.