The steel jackets of offshore structures can usually be regards as hydro dynamically transparent. So in order to figure out the waves forces on the submerged member can therefore be calculated by Morrison's equation which express the wave force as the sum of an inertia force proportional to the particle acceleration and a non linear drag force proportional to the square of particle velocities.
F = CM * (r * 3.142 * D^2)/4*v + CD * (rD/2)*v*/v/
F = wave force per unit length on a circular cylinder (N)
r = water density (kg/m3)
D = member diameter including marine growth (m)
CD = drag coefficient
CM = inertia coefficient
v = water particle velocity normal to cylinder
/v/ = water particle acceleration normal to cylinder
According to API-RP2A:
CD> 0.6 - 1.2
CM > 1.3 - 2.0
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