Potential Flow with Quadratic Load Coefficients

1. Description

This functionality is still under development and not commercially supported.

This load model is intended for relatively slender structures such as spars and semi-submersibles.

Frequency-dependent added mass, radiation damping, and excitation forces based on the first order potential flow solution will be applied for this load type. The radiation and diffraction coefficients are to be given by in separate input file specified in the Potential flow library.

The hydrodynamic element forces based on potential theory (WAMIT) has been implemented in RIFLEX. The purpose of implementing hydrodynamic element forces based on potential theory (WAMIT) results, is to provide adequate hydrodynamic forces outside the area for which Morison’s equation is valid. It also accounts for interaction effects, e.g. with other structural member, sea floor etc.

Use of the implementation requires manual runs of:

  1. WAMIT

  2. User written scripts to integrate the WAMIT pressures

  3. SIMATOOL_retfun.exe that calculates retardation functions from frequency dependent added mass and damping and does a polynominal fitting to the retardation function.

Only translation components of pressure and forces are considered (3 degrees of freedom). Time series for the wave excitation forces are generated during pre-stochastic analysis and applied during dynamic analysis. If the time integration step is different to the pre-generated time step, the pre-generated time series will be interpolated.

The forces based on this method are calculated at the mid-point of the element and distributed to the element ends (nodes). The drag terms are calculated as described for the generalized Morison equation.

If the Froude-Krylov pressure is included in the longitudinal component of the calculated loads, the Froude-Krylov scaling factor in tangential direction must be deactivated, so that this term is not included twice.

2. Potential Flow Library

This is under development.

Frequency-dependent added mass, radiation damping, and excitation forces based on the first order potential flow solution will be applied for this load type.

The radiation and diffraction coefficients are to be given by in separate input file specified in the Potential flow library.