Question:

My RAOs look weird, what do I do?

Answer:

Before you do anything else: check the geometry file. The majority of issues are usually related to bad geometry. Look for things like out-of-order stations, incorrect deductions, erroneous geometric features such as poorly fitted components, odd intersections, etc. Also look for hydrodynamically insignificant features that may cause meshing issues. A good first step is to run MC FIXUP. This command will likely fix most (if not all) of these issues if they are found by the program.

If a thorough inspection of the geometry yields no solution, check the following:

Which RAO looks unusual?
If the problem appears localized to just one mode, heave for example, then consider focusing on factors that may affect heave response.
Check the loading condition.
Be sure the condition is realistic. Check to be sure realistic gyradii are being used.
Write all of the data to text files.
Consider using /DATA:HY,FO to write the hydrodynamic coefficients and forcing data to text files for review. Plot the coefficients that are related to the RAO in question and look for unexpected results. Plot the forcing amplitudes. This data can give a very detailed description of the underlying solution.
Resample the wave spectrum.
Increase the number of samples,or use a different sampling method, and look for changes in the results. Changes observed due to sampling adjustments may indicate a poorly sampled spectrum or highly irregular RAO.
Increase the length factor and/or beam factor.
Increasing the density of the mesh should provide some insight into the convergence (or lack thereof) of the results. Significant changes due to modification of these parameters may indicate a meshing issue or a geometry issue.

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