Long waves in intermediate depths and their influence on the design of nearshore terminals

1. 02 July 2015
Long waves in intermediate depths
and their influence of the design of
nearshore terminals
A.J. van der Hout, M.P.C de Jong (Deltares)
F. Jaouen, O. Waals (Marin)

2. Background
An overview of the HawaII research project (2006 – 2012) is presented
sHAllow WAter InItIative
02 July 2015 2

3. Background
An overview of the HawaII research project (2006 – 2012) is presented
02 July 2015

4. Background – Design of nearshore terminals
02 July 2015

5. Mooring in intermediate water depths
Maritime Engineering Coastal Engineering
Deep water (> 100 m) Shallow water (<10 m)
No interaction with coast/bottom Interaction with coast/bottom
Limited LF waves present LF waves present
LF vessel motions Sand transport
Mooring in intermediate water depths
15 m – 40 m depth
Combination of Maritime and Coastal knowledge on infragravity (LF)
waves and vessel behavior required
Design aim: optimize terminal uptime
02 July 2015

6. Background
26 March 2015, Delft 6
2006 - 2008 2010 - 2012 2015 - ??

7. Design methodology of nearshore terminals
26 March 2015, Delft 7

8. Step 1 - 3
1. Define deep water sea states
2. Transform to shallow water
3. Define nearshore low frequency sea states
Aim: get a good prediction of the LF and primary
waves at the mooring location
02 July 2015

9. 9 juli 2015
Overview wave model classes
Several wave model classes have been considered in JIP HawaI:
• Spectral models
• Shallow water models forced on wave-group scale
• Mild-slope models
• Boussinesq-type models
• Multi-layer models
• Potential flow models
• Free-surface Navier-Stokes
Large model domain
Small model domain

10. Example boussinesq-type model
Scale model tests of Molfetta Harbour compared to
B-type computations
02 July 2015
Operational B-type models: consistent
underestimation of LF waves for kh> 1:
intermediate water depths (De Jong et al.,
2011)
Higher order B-type models: perform better,
but so far mainly restricted to academic
cases

11. 9 juli 2015
Overview wave model classes
Several wave model classes have been considered in JIP HawaI:
• Spectral models
• Shallow water models forced on wave-group scale
• Mild-slope models
• Boussinesq-type models
• Multi-layer models
• Potential flow models
• Free-surface Navier-Stokes
Large model domain
Small model domain
(not operational at start of project)

12. 12
Test C3: Hs=6m, Tp=15s, Dir=30°
Total Hs
Low frequency Hs (T>33s)
Example SWASH (MSc. study João Hinke Dobrochinski (2014)

13. 9 juli 2015
Overview wave model classes
Several wave model classes have been considered in JIP HawaI:
• Spectral models
• Shallow water models forced on wave-group scale
• Mild-slope models
• Boussinesq-type models
• Multi-layer models
• Potential flow models
• Free-surface Navier-Stokes
Large model domain
Small model domain

14. Results of Xbeach: large influence of 3D effects
1414

15. Choices made in Step 1 - 3
1. Define deep water sea states (Hindcast, primary waves only)
2. Transform to shallow water (SWAN, primary waves only)
3. Define nearshore LF sea states (IDSB/XBeach, LF waves only)
Typical 7 year wave climate: approx. 10.000 seastates
02 July 2015

16. Step 4
4. Select critical sea-states
Based on standard available “deep water” approach (10,000 cases):
• Wave forces based on diffraction method (DIFFRAC)
• Vessel motions and mooring line forces (ANYSIM)
• Estimate of free LF waves (IDSB)
02 July 2015

17. Step 5
• Perform detailed time-domain simulations
Aim: include a more realistic local LF wave field using XBEACH for a
small selection of cases (approx. 15)
02 July 2015

18. 25 Oct 2011
From LF waves to LF wave forces
To compute wave forces due to LF waves a coupling between
XBeach and the diffraction model Delmulti has been developed
Jonswap spectrum
Hs = 2 m
Tp = 13 s
γ = 3.3
Movie

19. 25 Oct 2011
Irregular long-crested wave forces

20. 26 Oct. 2012
Relevance of LF wave direction

21. 25 Oct 2011
Wave forces on the moored vessel
Combined Diffraction and XBeach-Delmulti Coupling
1st-order wave forces
• primary waves
• free (reflected) LF waves
2nd-order wave forces
• cross-products of 1st-order wave forces (I-IV)
• set-down / bound LF waves (V)

22. Outcome of design methodology
Preliminary assessment of the expected downtime
26 March 2015, Delft 22

23. Outcome of design methodology
More accurate downtime estimates or downtime estimates with
confidence bands
26 March 2015, Delft 23

24. Results
• An inventory of existing tools has been made
• New tools have been developed to improve downtime estimates
• A consistent design methodology has been developed
To be continued:
• Step 6: perform validation on numerical methods,
focused on intermediate water depths
02 July 2015

25. 02 July 2015