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Second-order forces and moments acting on ships in waves

By Soizic Annick Gabrielle Joncquez, Ph.D., Project Manager, FORCE Technology

 

 

The goal of this project is to build an accurate model for a ship in waves with emphasis on the drift forces and hence added resistance in waves. The model is characterized by:

  • Fully three-dimensional flow field
  • All three forces and three moments can be calculated
  • Time domain
  • Rudder and propeller included (if time permits)

A potential flow description of the water flow over the ship is used. This allows a very accurate description of the free-surface (non-linear) and the position of the ship which will both be updated during the calculations that will be carried out in the time domain. This will make it possible to simulate special occurrences of wave sequences, turning manoeuvres in waves etc…The model can be extended to include the rudder and propeller, to model the whole propulsive performance in waves, although still within the limits of the potential theory.
The program used is based on the code AEGIR. This program is a panel method that employs a NURBS based high-order boundary element method. The boundary conditions in AEGIR can be imposed in either linear or nonlinear form.

 

Historically, ships have been optimised for still water performance. However, considering that ships operate in a seaway, added resistance should also be taken into account. A new method and computational tool has proven to be very effective.

Soizic Annick Gabrielle Joncquez has made an impressive Ph.D. study about added resistance in waves. In the study, Soizic proves that with a particular timedomain 3D-panel method, it is possible to calculate response functions of added resistance with a reasonably high accuracy.

Based on the hull lines of the Diamond 53 bulk carrier designed by Grontmij | Carl-Bro, Soizic calculated the response functions of added resistance in a seaway and compared it to model tests. The results are very encouraging and indicate that it may be possible to use the method actively in the design process.

Soizic has used different types of linearization and conservation methods, and her results show that the momentum conservation method is preferred, as this method provides good and robust results.

The calculations have been made with the AEGIR code which is a time-domain 3D-panel method.

The code effectively calculates the response function of added resistance in waves for different encounter frequencies which may then be used for calculation of the added resistance in a particular sea state.

The results have been so promising and encouraging that Soizic will now continue her work with AEGIR targeting the practical application of the code. Based on her findings and knowledge, she will apply the method to typical designs of bulk carriers and containerships in order to optimise for operation in a seaway rather than in still water.

With the promising results of Soizic’s Ph.D. study, there is now a large potential for propulsive performance evaluation of ships in a seaway using first principle calculations of the added resistance. The improved method for calculation of added resistance in a seaway may also be used for improvements of performance monitoring and route planning programmes.

In addition, the new methods may be used for evaluation and optimisation of bow shapes and for input to route simulation programmes.

Michael Højsholm Schmidt, at Schmidt Maritime is encouraged by the findings in Soizic’s study:

’Based on my long experience with design of ships, the propulsive performance in a seaway is highly relevant - but often very little attention is paid to this issue. Therefore, the development of advanced tools for fast and efficient calculation of added resistance in a seaway is highly interesting. I am really looking forward to seeing the final conclusions on this project, and I trust that the knowledge developed will be very important for the industry.’

 

Papers on the topic:


Second-Order Forces and Moments Acting on Ships in Waves

 

 


 

   
Produced by Adapt A/S