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)

Background

An overview of the HawaII research project (2006 – 2012) is presented

sHAllow WAter InItIative

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Background

An overview of the HawaII research project (2006 – 2012) is presented

02 July 2015

Background – Design of nearshore terminals

02 July 2015

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

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Background

26 March 2015, Delft 6

2006 - 2008 2010 - 2012 2015 - ??

Design methodology of nearshore terminals

26 March 2015, Delft 7

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

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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

Example boussinesq-type model

Scale model tests of Molfetta Harbour compared to

B-type computations

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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

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

Test C3: Hs=6m, Tp=15s, Dir=30°

Total Hs

Low frequency Hs (T>33s)

Example SWASH (MSc. study João Hinke Dobrochinski (2014)

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

Results of Xbeach: large influence of 3D effects

14 14

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

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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)

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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)

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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

25 Oct 2011

Irregular long-crested wave forces

26 Oct. 2012

Relevance of LF wave direction

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)

Outcome of design methodology

Preliminary assessment of the expected downtime

26 March 2015, Delft 22

Outcome of design methodology

More accurate downtime estimates or downtime estimates with

confidence bands

26 March 2015, Delft 23

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

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02 July 2015