Element Diameter and Hydrodynamic Forces |
 
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Element Diameter and Hydrodynamic Forces |
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Traditionally, Flexcom has based the calculation of both the drag and the inertia/added mass components of the Morison’s Equation hydrodynamic force on the drag diameter Dd. This is accurate and reasonable for many riser systems and is retained as the default operation to maintain compatibility with older program versions. However, strictly speaking the added mass and inertia terms should be based on displaced volume (defined by the buoyancy diameter) as opposed to projected area (defined by the drag diameter). Flexcom provides an option for you to instruct the program to use Db rather than Dd for the added mass and inertia components of Morison’s Equation. This choice is actually made when defining hydrodynamic rather than geometric properties, since this relates to hydrodynamic force computations. Refer to Hydrodynamic Properties for more details.
•*HYDRODYNAMIC SETS is used to assign hydrodynamic coefficients to element sets. Specifically, the DIAMETER= input is used to specify whether element drag (used by default) or buoyancy diameters should be used during the computation of the added mass and inertia terms in Morison’s Equation.