Experimental investigation of Morison Equation in calculating the drag and inertia forces on single pile under current and wave simultaneously

The accurate estimation of the forces acting on marine piles is very important from the point of view of evaluating the bending and axial strength, the base shear values and also the drifts of pile caps connected to the deck of offshore structures. Morison's equation is considered as the most widely used relation to evaluate these forces induced by linear sinusoidal waves and deep water conditions. Several experimental tests on an scaled model of an offshore monopile under the effect of current, wave and the simultaneous effect of wave and current in laboratory conditions along with the comparison of the obtained results with the forces derived from Morison's theoretical equation have been done in this article. It seems that in the presence of individual waves or currents, by correctly applying the drag and inertia coefficients, a very good estimate of the forces can be achieved. However, in case of simultaneous application of wave and current loads, even though Morison's equation correctly predicts the average values of induced forces, the fluctuations around the average value are more than the reality, and the differences will even reach 25 percent.