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Added mass

Hello, Dr. David, I cannot understand why the added mass coefficient (Caz) for base columns in z-direction is not set to 1 to properly model the column base added mass when the drag coefficient (Cdz) for base columns in z-direction is set to 4.8 in the OC4 platform file .

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Hi Sun,

there are many ways in which a floater can be modeled in QBlade. The main differences are:

Structural Model:

  • Rigid Elements
  • Flexible Elements

Hydrodynamic Model:

  • Potential Flow (WAMIT, NEMOH, etc…)
  • Morison Equation

In the case of the OC4 model that you mention the model is composed of rigid elements. Hydrodynamics are evaluated from potential flow theory, with the exception of the viscous drag which is model via the Morison approach (viscous drag cannot be evaluated from potential flow theory). That is why only the drag coefficient is used for this model and all other coefficients are zero. The complete lumped added mass is taken into account via the SUB_HYDROADDEDMASS 6×6 table.



Thank you, Professor David.