I have fitted my hull RANS (full hydrodynamics with hydrostatics) data in Gomboc and I am now using the fit in my model. However, I can observe important instabilities when running the model in dynamic mode. How can I solve that issue?
It’s fairly typical to observe instabilities when using fitted hydrostatics. To use fitted hull data we would recommend to fit with hydrostatics removed, and keep the Gomboc hull model just for hydrostatics and damping. Note that it is not impossible have usable dynamics with fully fitted hull forces, but it requires a big matrix and probably also a substitute for the damping model.If the hydrostatics are not initially removed from the RANS data, Gomboc can be used to compute the hydrostatics which can then be removed from the RANS data before doing the fit. Here is an outline of the procedure:
- Build a script that loops through all the rows of the RANS source data:
- Set the boat attitude (sink, heel, trim) to match the RANS point
- Read the hydrostatics force in the same reference frame than the RANS data
- In excel, remove the hydrostatics computed by Gomboc and create a new *.pz.csv” file
- Re-fit the new file
- Disable wave and friction drag in the Gomboc model (set “SkinFriction” and “kWaveDrag” parameters to 0.
- Add the post-processed RANS drag