1. Benchmark study on uncertainty
assessment in numerical predictions of global
wave loads in damaged ships
J. Parunov, C. Guedes Soares, S. Hirdaris, Y. Lee, S. Liu, A. Papanikolau, J. Prpić-Oršić , M. Rodrigues, P. Ruponen
ISSC-ITTC Workshop on load uncertainties - Wuxi, China
16/09/2017

2. Background & Aims
Initiated within MARSTRUCT Virtual Institute in December 2016
Challenges:
How to incorporate damage effects in seakeeping analysis ?
Quantification and modelling of wave load uncertainties (ISSC-ITTC Special Task Committee) .
Goals:
To conduct the first uncertainty study on numerical prediction of loads on damaged ships;
Aquiring valuable information regarding damage modelling in seakeeping analysis of damaged ship;
Providing a rational basis for definition of the uncertainty model to be used in structural reliability studies of damaged ships.

3. Benchmark ship
Lee, Y., Chan, H.-S., Pu, Y., Incecik, A. and Dow, R. S., 2012., Global wave loads on a damaged ship, Ships and Offshore Structures, 7(3). pp
SSC-459, Reliability-Based Performance Assessment of Damaged Ships, Ship Structure Committee,
E. Begovic,A.H. Day, A. Incecik: An experimental study of hull girder loads on an intact and damaged naval ship, Ocean Engineering 133 (2017) 47–65

4. Benchmark ship

5. Benchmark ship

6. Benchmark participants
NTUA - Newdrift (3D panel code ) (S. Liu, A. Papanikolau)
University of Rijeka -WASIM(3D panel code) (J.Prpić-Oršić, N. Vitali )
NAPA - Strip method (P. Ruponen, S. Kalske and T. Manderbacka)
University of Zagreb - BV HydroSTAR (J. Parunov, M.Ćorak)
Lloyd’s register– WAVELOAD-FD software (3D panel frequency domain ship motion analysis) ( Y. Lee)
University of Lisbon - Weakly nonlinear (nonlinear Froude-Krylov ) time-domain method with GAMPIT (Generalized Adaptive Mesh Pressure Integration Technique) (M. Rodrigues, C. Guedes Soares)

7. Model visualisation (panelization of wetted surface)

8. Test matrix and model verification
Hydrostatic particulars :
V (m3)
LCB (m)
UNIRI
8690
72.4
IST
----
-----
NAPA
8774
70.1 LR
8749
69.8
NTUA
8379
70.2
UNIZG
8351
70.6

9. Quantification of uncertainties
Also known as ”Frequency-Independent Modal Error” (FIME)

10. Results for intact ship
X-axis : ω sqrt (L/g) Y-axis: non-dimensional transfer function

11. FIME for intact ship

12. Results for damaged ship - symetrical damage DS3

13. FIME for damaged ship - symetrical damage DS3

14. Results for damaged ship - unsymetrical damage DS2

15. FIME for damaged ship - unsymetrical damage DS2

16. Comparison of FIME

17. Comparison of FIME

18. Conclusions
Provisional results of uncertainty assessment using Frequency Independent Model Error (FIME) indicate:
Motion components are in good agreement with experiments for intact and damaged ship, for both head waves (HW) & quartering waves (QW). FIME is always within +/-10% error band.
VWBM in HW for intact ship shows good agreement with experiments. FIME of VWBM in HW for damaged ship is note worse compared to the intact ship (surprising!)
Even more surprising, FIME of VWBM for QW is improved compared to the intact ship.
Strip theory overestimates VWBM amidships for HS for intact and damaged ship. For QS, however, such conclusion is not valid as FIME is not always larger then 1.
TM shows large discrepancy compared to the experiments. (It could be meaningful to investigate the effects due to linearised viscous roll damping values.) 
Experimental uncertainties: carried out the model tests in 2004 and 2005, and that time error bars have not been used (used averaged values). 
These conclusions may be useful for classification societies, SOLAS and navies as they show that the added mass method for modelling effects of damage leads to the results of the same level of accuracy for damaged as for the intact ship.

19. Aknowledgement
Croatian Science Foundation - projects 8722 & 8658
SHOPERA - Energy Efficient Safe SHip OPERAtion, which was partially funded by the EU under contract and the University of Rijeka (contract no )
European Commission research project HOLISHIP under the European Union Horizon 2020 research and innovation program with grant agreement no
University of Zagreb – International Mobility Grant and Research Support Grant