Model Tests for the Effect of Random Waves on the Hydrodynamic Forces on Rigid Vertical Cylinders

Abstract— Evaluation of accurate hydrodynamic forces on
slender pipes has great significance in designing offshore
structures. For the analysis and design of jacket platforms made
up of small diameter tubular members, consultants use
Morison’s equation, where the wave forces are calculated using
drag (CD) and inertia (CM) coefficients. The hydrodynamic
coefficients used by consultants are constant values, although CD
and CM are dynamic coefficients that depend on Keulegan
Carpenter number (KC) and Reynolds’s number (Re). This
paper provides the preliminary results of model tests on rigid
vertical cylinders with different pipe diameters subjected to
random waves. The experimental data are derived from 1:70
scale model tests in which the hydrodynamic forces acting on
individual tubular pipes were investigated in the wave tank. The
hydrodynamic forces on the model were measured using
aluminium block load sensors. The model pipe diameters used
for the preliminary tests were 22 mm, 34 mm and 42 mm, and the
effects of random waves on the magnitude of prototype
hydrodynamic forces were analyzed in terms of power spectral
density.
Keywords — Dynamic responses, Inertia coefficient, Drag
coefficient, Malaysian locations, Morison equation.