1. Overview of SHAllow WAter Initiative (HAWAI JIP)
Shallow Water Hydrodynamics Seminar, Trondheim, Dec 19, 2005 Radboud van Dijk and Bas Buchner, MARIN

2. History HAWAI JIP
April 21, 2004: Birth of initiative (SBM model tests)
Feb 1-2, 2005: Shallow Water MARIN
May 5, 2005: Informative mtg Houston
Oct 25, 2005: Kick-off mtg Cambridge (UK)

3. Background Model tests LNG Soft Yoke Mooring 2003 - 2004
Courtesy SBM
Model tests LNG Soft Yoke Mooring
Poor correlation between model tests and simulations
Similar phenomena observed in other basins

4. Comparison Model tests - Simulation
Amplitude is not correct
Phasing is not correct
LF modulation (beating pattern) is missing

5. Cause of Differences ?
Extensive study and model test program to determine cause of these differences
Causes:
Low damped surge of LNG carrier hull (<1%)
Low frequency waves in basin
Shallow water

6. Solution Determine wave content in basin
Take into account low frequency waves in basin
Split measured LF wave signal into:
LF bound wave (setdown)
LF free incident waves
LF free reflected waves

7. Developed Wave Splitting Technique
Incident WF waves
Incident bound waves (setdown)
Incident LF free waves
Reflected WF waves
Reflected LF free waves
Reflected bound waves (neglected)

8. Use of Wave Probe Array
WF array (5 probes)
LF array (6 probes)
Wave

9. Results Feed LF waves into simulations
Much better agreement between model tests and simulations:
Amplitude
Phase
LF modulation

10. Basin Effects versus Real Life
LF waves in real life are indeed measured
Shoaling
Reflection of LF waves on beach
Courtesy H. Bingham (DTU)
Courtesy K. Ewans (Shell)

11. Numerical Investigation on LF Waves
Shoaling
FE method (HUBRIS)
Wave generated by modeling of wave flap
Transient of wave spectrum from deep to shallow water
Shallow water effects and reflection
Boussinesq type wave model (TRITON)
Takes into account:
Bottom friction
Wave breaking
Reflection on beach

12. Pre-study: Work done so far
OMAE
Effect of shallow water wave on LNG carrier motions
Effect of shoaling calculated by FE numerical model (Hubris)

13. Pre-study: Work done so far
Effect of shoaling on waves:
1) 1st order wave and LF component
(movie PreStudy1.AVI)
2) Bound wave & free LF wave
(movie PreStudy2.AVI)

14. Pre-study: Effect of LF free waves due to shoaling
Result LF free waves: 27% increase in LF surge motions

15. Next: Effect of Reflected free Waves
Extent domain to include beach
Use of FE model (Hubris) and Boussinesq model (Triton )
Hubris: effect of shoaling (200 m WD  20 m WD)
Triton : effect of sea floor & beach
Output of Hubris = Input to Triton
Bathymetry:

16. Wave run up on beach (Boussinesq model)

17. Analysis of Nearshore Waves
Numerical wave split into following components:
Incident free (1st order & LF)
Incident bound (set down)
Reflected free (1st order & LF)

18. Reflected waves
Refl. coefficients for typical LNGC surge periods  5 - 6%
(reflected LF wave height = 20-25% of incident LF wave height)

19. Motion Response LNG Carrier in Nearshore Waves
Effect of incident LF free waves:
Stdev of LF LNGC surge:
Incident waves - WF only X = 3.0
Incident waves - WF + LF X = 4.3 m (+43%)

20. Motion Response LNG Carrier in Nearshore Waves
Effect of reflected LF free waves:
Stdev of LF LNGC surge:
WF+LF - incident waves only X = 4.3 m
WF+LF - inc. & refl. waves X = 4.1 m (-5%)

21. Results of Numerical Prestudy
Effect of LF free waves on LF vessel motions is significant
Pre-study shows small amount of reflected free waves in wave model (5% of incident free LF wave energy)
Effect of these LF reflected waves on LF vessel motions is small (decrease in motions observed)
What is actual LF free wave content (inc. & refl.) ?
Analysis of Duck data

22. Objective HAWAI JIP
To improve the reliability of offshore (LNG) terminals
in shallow water by
using the combined expertise of
offshore hydrodynamics and coastal engineering to
better address key issues regarding
motion and mooring prediction methods in shallow water

23. Scope of Work HAWAI JIP
Case study “LNG carrier in a nearshore wave field”
WP1: Nearshore Wave Modelling
WP2: Model Testing for Shallow Water
WP3: Hydrodynamic Wave Loading
WP4: Validation and Guidelines

24. Case study: “LNG carrier in a nearshore wave field”
Assess importance of nearshore wave data
Use of state-of-the-art mooring tools
Focus on the effect of
LF wave energy
Directional waves
Input: realistic wave data (including LF content)
Two different methods:
1) Classical approach: wave spectrum & diffraction calculations
2) Boussinesq-type wave model & diffraction analysis

25. WP1: Nearshore Wave Modelling
WP leader: Delft Hydraulics
Co-operation with Bingham
Deliverables:
a. State-of-the-art overview of nearshore wave modelling
b. Identify the relevant aspects of nearshore wave behaviour
c. Analysis of available nearshore wave data
d. Evaluation of short-crested/directional waves modelling by means of shallow water (Boussinesq-type) wave models

26. WP2: Model Testing WP leader: MARIN
Co-operation with Pinkster, MARINTEK & Oceanic
Deliverables:
a. Systematic database of current coefficients
b. Develop a wave splitting / separation technique & tool
c. Model tests for validation of hydrodynamic issues
d. Cross-bi-spectral method to determine the full QTF matrix from model tests
e. Recommendations for shallow water testing

27. WP3: Hydrodynamic Wave Loading
WP leader: Bureau Veritas
Deliverables:
a. Wave-current interaction in shallow water
b. Effects of sea bed bathymetry
c. Evaluation of QTFs in multi-directional waves
d. Inventory of various methods to compute QTF matrices
e. New formulations of second-order wave loads
f. Optimisation of wave drift force time-series reconstruction

28. WP4: Validation and Guidelines
WP leader: SBM
Deliverables:
a. Compare results of different diffraction codes
b. Investigate QTF approximations and limits
c. Methodology to include the free LF wave in time domain
d. Effect of wave directionality
e. Validation model tests and simulations
f. Summary report with detailed guidelines

29. Participants HAWAI JIP1
Bureau Veritas 14
FMC Sofec
Possible participants 2
Delft Hydraulics 15
Hyundai
Exxon 3
MARIN 16
Lloyds Register
Statoil 4
SBM 17
Marintek
Woodside 5
Chevron 18
Moffatt & Nichol 6
ConocoPhillips 19
Moss Maritime 7
Petrobras 20
Oceanic 8
Shell 21
Prosafe 9
Total 22
Sandwell 10
ABS 23
Technip 11
Bluewater 12
DnV
DTU (prof. Bingham) 13
DSME
TUD (prof. Pinkster)