Optimize your hull forms with minimum wave added resistance
The new framework of the global economy has stimulated and expanded the shipbuilding- and shipping-industries. At the same time, environmental concerns and green shipping concepts have put more pressure and demands on designers to minimize the energy consumption, maximize the protection of the marine environment and maximize the efficiency and economy of maritime operations. This is increasing the interest of wave added resistance study for ocean-going vessels.
Wave added resistance is a second order force which is known as an increased allowance due to waves comparing to calm water condition. Accurate prediction of added resistance enables optimization of ship designs for a given route or trade. So it is important to have efficient and reliable methods to predict it.
Sesam Wasim extends the time domain Rankine source method to enable the functionality of added resistance calculation. This approach applies the momentum conservation principle on the near field fluid volume enclosed by the wet surface of a floating body, the free surface and a control surface. The wave added resistance is then calculated by the integration over the control surface of the fluid velocities and free surface elevations.
Four steps are needed to realize this function in HydroD and Wasim:
- Input in Wasim_Setup. The ‘Calculate added resistance’ function is selected, setting up the dimension of control surface. The figure below shows a container ship model S175 and its control surface.
- Refine free surface mesh. Panels between hull and control surface needs to be refined. Triangular elements should be avoided in the refined zone. If there are more than one patch, try to merge them and use patch continuity.
- Methodology setup in Wasim_Solve. Frequency domain analysis is needed and use single wave component in each run. Double body linearization is recommended.
- Execute analysis and View the results. Added resistance results can be easily plotted in Wasim and can be exported to a file. The figure below shows the plot of added resistance in Wasim. Non-zero average value of the curve gives the mean value (added resistance).
Outputs from Wasim have been carefully verified against model test for different hull shapes under a wide range of sea states. Good agreements have been found which documents the calculations well. The figure below shows added resistance comparison between Wasim and model test for ship model S175 with certain forward speed. Good agreement can be clearly seen.
A conference paper, ‘Computation of wave added resistance by control surface integration’, will be published in OMAE, 2016. This paper is developed by the Floater analysis tem in DNVGL – Software. A full discussion about the methodology adopted by Wasim and also a thorough validation and verification of the results can be accessed there.