Seakeeping, fw-factor and combined CFD/EFD methods hot topics at the ITTC Full Conference in Wuxi

The International Towing Tank Conference (ITTC) has an important role as a cooperation platform for all towing tank organizations. It gives SSPA, as an active member, an opportunity to influence the worldwide shipping community. At the ITTC’s 28th Full Conference, the Seakeeping Committee presented a recommended procedure for determining “f_w”. The procedure is largely based on work by SSPA’s experts. After a suggestion from SSPA, the conference took the decision to start up a new Specialist Committee on Combined CFD/EFD Methods that will run at least during the next three years. The Chairman is one of SSPA’s experts.

ITTC’s 28th Full Conference was held in Wuxi, China on September 18-22. Our colleagues at China Ship Science Research Centre (CSSRC) hosted this very well organized conference. ITTC’s primary aim, since its beginnings in 1933, has been to “solve technical problems of importance to towing tank organizations”. The Advisory Council is the guardian of this aim and ensures that the work of the committees is in the long term beneficial for our clients and society. Susanne Abrahamsson, CEO, represented SSPA on the Advisory Council during the last ITTC period (2014-2017), and she will continue for the next 3-year term (2017-2020).

- “With our knowledge and expertise we can contribute to some of the most important issues facing the maritime sector today” says Susanne Abrahamsson, CEO at SSPA.

ITTC’s Seakeeping Committee presented their work to the conference. One very important topic was the determination of the speed loss factor f_w in the Energy Efficiency Design Index (EEDI) formula. This factor reflects the percentage of a ship’s calm water speed that can be maintained in Beaufort 6 and corresponding waves. As such, the speed loss factor f_w will have a large impact on ship design because it allows for the reduction of a vessel’s EEDI by optimizing for performance in waves.

According to the International Maritime Organization (IMO) resolution MEPC.212(63) this factor is currently still f_w=1 when calculating the attained EEDI. This is because IMO was not able to prescribe in detail how f_w should be determined. Instead, IMO have requested ITTC to give a clear recommendation. At the full conference, the Seakeeping Committee presented a recommended procedure for determining f_w. The procedure is largely based on work by SSPA’s specialist Dr Frederik Gerhardt, who was a member of the Seakeeping Committee during the period 2014-2017. The work is also reported in Determining the EEDI “weather factor” f_w [1]. Dr Gerhardt will continue to work actively in the Seakeeping Committee for the next 3 years. One of the first tasks will be to present the new f_w guideline to IMO. This illustrates the important role of the ITTC as a common voice for all towing tank organizations towards legislation organs like IMO. It also shows how the skill and hard work by a specialist from an individual towing tank organization like SSPA can influence the worldwide shipping community via ITTC.

After a suggestion from SSPA, the full conference took the decision to start up a new Specialist Committee on Combined CFD/EFD Methods. (CFD stands for Computations Fluid Dynamics and EFD stands for Experimental Fluid Dynamics, i.e. model testing). The purpose of the committee is to initiate and support the process of introducing combined EFD/CFD methods into ITTC’s procedures. We all appreciate the new possibilities that CFD offers in terms of improving the EFD based predictions, for example with new treatment of scale effects. On the other hand, we can still not in general rely purely on CFD for ship hydrodynamic predictions for commercial or legal purposes. By using the best combination of CFD and EFD, rather than viewing them as competing methods, we can deliver even better predictions. However, demonstrating the credibility of CFD predictions is still an open question. New methods based on EFD/CFD combinations should have the same confidence level as the existing Recommended Procedures give to the end client today.

The Specialist Committee on Combined CFD/EFD Methods will run from September 2017 to at least September 2020. The Chairman is Dr Sofia Werner from SSPA, who will work on the extensive task list together with nine experts from China, South Korea, Japan, Canada, USA, United Kingdom and Germany.

[1] Gerhardt, F.C., Kjellberg, M.: DETERMINING THE EEDI ‘WEATHER FACTOR’ f_w, RINA conference on Influence of EEDI on Ship Design & Operation, p. 61-68 London 2017.

The International Towing Tank Conference

The International Towing Tank Conference (ITTC) is a voluntary association of worldwide organizations that has responsibility for the prediction of hydrodynamic performance of ships and marine installations and has the status as observer at the International Maritime Organisation (IMO - the United Nations agency with responsibility for the safety and security of shipping and the prevention of marine pollution by ships). Read more at www.ittc.info

Photos and illustrations

The International Towing Tank Conference (ITTC) has an important role as a cooperation platform for all towing tank organizations. It gives SSPA, as an active member, an opportunity to influence the worldwide shipping community.

The delegation from SSPA. From left to right: Dr Sofia Werner, Chairman of the Specialist Committee on Combined CFD/EFD Methods. Dr Frederik Gerhardt, member of the Seakeeping Committee. Susanne Abrahamsson, CEO at SSPA, member of the Advisory Council.

One very important topic was the determination of the speed loss factor f_w in the Energy Efficiency Design Index (EEDI) formula.