Two different methods for calculations of the multibody interactions in seakeeping are considered. The problem is formulated under the classical assumptions of the potential flow theory and Boundary Integral Equation methods. More classical approach based on the straightforward application of the basic mechanical principles is compared to the so called generalized modal approach. The advantages of the generalized modal approach lies in its generality and an easy implementation in the existing "single body" seakeeping codes. The second important point of the paper is the treatment of the resonance phenomena in between the bodies when they are placed very close to each other. Indeed the straightforward application of the linear potential theory leads to the unrealistic results for these conditions. An simple and original method based on the direct modifications of the existing Boundary Integral Equation method is proposed and validated. Finally a new method for evaluation of the second order drift forces is also presented.
There are many situations in pactice, where the several closely spaced bodies are exposed to the wave action. Probably the most significant ones are related to the offloading operations either for tankers or LNG carriers. Few typical situations are presented in Figure 1. The first one is the so called "tandem" configuration and the second one the"side-by-side" configuration. In order to correctly asses the seakeeping behaviour of two vessels, a correct mathematical model is needed. Indeed, the relative position of the bodies will strongly influence their behavior, and fully coupled model is required. The purpose of this paper is to discuss two different methods able to take into account these interactions properly.
Even if it is rather well known and for the sake of clarity, first we briefly present the general methodology for linear seakeeping of the single body.
