A hydroelastic method of analysis is developed which combines a three-dimensional structural model with fluid forces from strip theory. The method allows direct computation of member forces and stresses, while the large computational effort of three-dimensional hydroelasticity, as a result of three-dimensional potential theory, is avoided. The method is used to analyze the prying response of a simple, twin-hull structure. Results show satisfactory agreement with three-dimensional hydroelasticity, indicating that the method may be useful in preliminary design of large, slender, multi-hull structures.


The analysis of wave-induced motion, internal forces, and stresses of floating structures is typically a two-step process. First, the motions are determined by a hydrodynamic analysis in which the structure is assumed rigid. Then, the internal forces and stresses are determined by applying to the structure the fluid pressures and inertia forces calculated in the hydrodynamic analysis (Ogilvie, 1971). Linear theory is usually used, and the calculations are typically carried out in the frequency domain. The decoupling of the two analyses is somewhat inconvenient, and it also assumes that:

  1. the flexibility of the structure does not affect the fluid pressure, and hence, the motions, and

  2. the internal forces are not affected by the inertia associated with deformational motion.

Both assumptions are acceptable for many conventional structures, which behave essentially as a rigid body. However, for very large structures, these assumptions tend to breakdown. Hydroelasticity theory, in which the coupled hydrodynamic and structural dynamic problems are solved simultaneously, has been introduced to overcome the limitations of the decoupled procedure. Hence, this approach is numerically efficient. Its primary application is to ship structures, although it also has been used for large, multi-hull structures (Riggs, et al., 1991; Che, et al., 1992; Riggs and Ertekin, 1992).

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