Breakwater layout optimisation using a root-finding algorithm
Rustell, M. (2015). Breakwater layout optimisation using a root-finding algorithm, in: PIANC Yearbook 2014. pp. 110-120
In: (2015). PIANC Yearbook 2014. PIANC: Brussels. ISBN 978-2-87223-225-3. 64 pp., more
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| Keywords |
Berthing
Optimisation
Structures > Hydraulic structures > Coastal structures > Coast defences > Breakwaters
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| Author keywords |
Wave transformation; Concept design; Root-finding |
| Abstract |
Due to the remote and exposed coastal location of many proposed liquefied natural gas (LNG) exportation terminals, a breakwater is often required to reduce the wave energy at the vessel berth(s). Best practice and new research techniques for developing the cross section and sizing armour stone concepts are well established however, little research exists for developing topographical layouts. This paper describes a methodology which can be used to develop breakwater layouts, optimal for the vessels berthed in the shadow zone. This is achieved on the premise that for any given level of accept- able berth downtime, there exists a corresponding breakwater design. This premise allows the relation- ship to be expressed as downtime = f(length) which can be solved through an iterative approach. To achieve this, a random wave transformation model and a dynamic mooring analysis model have been embedded in an iterative root finding algorithm to transform the waves to, through and around the breakwater. The diffracted and transmitted wave energies are summed using the root mean square (RMS) approach before the ‘effective wave’ is used to determine whether the vessel mooring threshold is exceeded. Performing this for a time series gives an indication of the downtime that will be incurred with this breakwater layout, which is used to iteratively search for the breakwater length which offers the desired level of downtime. This methodology is applied to a rubble-mound breakwater, though could easily be transposed to a berm, caisson or any other kind. A case study is used to demonstrate the effectiveness of this methodology in developing accurate breakwater layouts in a very short time frame, allowing a greater variety of berth positions and arrangements to be trialled during the conceptual design stage. |
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