Slender-body Approximations of Hydrodynamic Forces for Spar Platforms

摘要

The 2nd order difference frequency forces on Spar platforms are evaluated analytically and numerically using various nonlinear hydrodynamic force models. The models studied are the full time domain Morison equation (ME), a 2nd order Morison equation (ME2), the 2nd order diffraction-radiation theory (Φ2 theory) and the Φ2 theory assuming very slender structural dimensions (slender Φ2 theory). The purpose is to show the effect of different nonlinear forces on the dynamic response of Spars, and to illustrate their basic differences. The use of Morison's equation as the slender-body approximation of Φ2 theory is also shown to be inappropriate in this context.