A numerical procedure is described for predicting steady drift forces on multiple 3-D bodies of arbitrary shape freely floating in waves. The developed numerical approach is based on a combination of a 3-D source distribution method, wave interaction theory and the far-field method of using momentum theory. This its application should make it unnecessary to perform full diffraction or radiation computation for multiple 3-D floating bodies of arbitrary shape in waves. Also the hydrodynamic interactions among the floating bodies are taken into account in their exact form within the context of linear potential theory. The proposed method is applicable to an arbitrary number of 3-D bodies having any individual body geometries and geometrical arrangement with the restriction that the circumscribed, bottom-mounted, imaginary vertical cylinder for each body does not certain any part of the other body. Numerical results are compared with the experimental or numerical ones, which are obtained in the literature, of steady drift forces on 33 (3 by 11) floating composite vertical cylinders in waves. The results of comparison confirmed the validity of the proposed approach. Finally, the interaction effects are examined in the case of an array of 40 (4 by 10) freely floating rectangular bodies in shallow water.
Two principally different approaches have been presented in the literature for the determination of steady drift forces on an isolated floating body. The first one so called far-field method is based on the application of the momentum conservation principle to a control volume surrounding the body. It was introduced by Maruo(1960) for the calculation of the mean horizontal drift forces on a simple shaped body floating in infinite water depth and it was extended by Newman (1967) to include yaw drift moments as well. Faltinsen et al.(1974) derived the expressions for the steady drift forces and moments by extending Maruo's theory to a finite water depth and calculated the steady drift forces on an arbitrary shaped floating body.