The buoyancy diameter (Db) is the effective external diameter for buoyancy force calculations. If you are using the Default buoyancy option, the applied buoyancy force is based only on Db. If you are using the Distributed option, then the buoyancy force is calculated using Db and the outer diameter Do, as now described. Db is also used in some circumstances in the calculation of the added mass/inertia components of the Morison’s Equation hydrodynamic force – this is discussed in Element Diameter and Hydrodynamic Forces.
