Chapter 9 - Hydroelasticity theory of ship–water interactions

Abstract

Historically, the earliest concern on fluid–solid interaction (FSI) problems is with airplane design, and the related well-developed FSI theory is termed aeroelasticity, in which the air is considered a compressible fluid, and the main aim of analysis is to determine the critical speed of airplane flutter. For ship design, the water is traditionally treated as an incompressible fluid with its flows irrotational, and the term hydroelasticity in naval engineering first appeared in the literature in 1959. In offshore and maritime engineering, highly complex fluid–structure interaction mechanisms are encountered between the seaway and structure, as described in the theories relating to waves, resistance, and propulsion, sea keeping, maneuvering, wave loads, and structural responses. Ships generally move with a mean forward velocity, and their oscillatory motions in waves are superposed upon a steady flow field. Traditionally, a ship is regarded as an unrestrained rigid body with 6 degrees of freedom, and the unsteady motions of the ship and the waves are assumed to be of small amplitude. One of the principal problems encountered is the solution of the steady-state case, particularly with regard to the calculation of wave resistance in calm water. The ship–wave interaction case is considered separately as the superposition of two problems. Namely, a radiation problem, where the ship undergoes prescribed oscillatory motion in otherwise calm water, and a diffraction problem, where incident waves act upon the ship in its equilibrium position. Interaction between these two first-order radiation and diffraction problems is of second order in the oscillatory amplitudes and is therefore neglected. This topic was reviewed in 1971 and early numerical solutions were described in 1978. The linear problem of ship motions in waves is solved by a superposition of the steady- and unsteady-state cases. Interaction between the steady and oscillatory flow fields complicates the more general problems, which were discussed and presented in detail the theory of ship motion and formulated hydrodynamic forces of oceangoing rigid ships. In 1979, it was developed a two-dimensional (2D) linear hydroelasticity theory, based on superposition methods for the incident, diffraction, and radiation potentials, including the vibration modes of the structure, in order to deal with beam-like flexible ships interacting with the water. From their contribution, the term hydroelasticity for incompressible water–ship interactions has been widely used as same as the term aeroelasticity for compressible air–plane interactions. This linear hydroelasticity theory has been further developed into a more general three-dimensional (3D) case for ship–water interaction dynamical analysis, for which the related investigations have been completed successfully and used in the engineering design of ships. Recently, in a special issue of Journal of Engineering for the Maritime Environment two review papers on hydroelasticity were given in which more historical publications, developments, and future trends were described. Interested readers may refer to these sources for more information.