{"id":6396,"date":"2025-08-08T13:26:33","date_gmt":"2025-08-08T02:26:33","guid":{"rendered":"https:\/\/www.leapaust.com.au\/blog\/?p=6396"},"modified":"2025-08-12T14:30:20","modified_gmt":"2025-08-12T03:30:20","slug":"fsi-simulation-for-coastal-hazard-mitigation","status":"publish","type":"post","link":"https:\/\/www.leapaust.com.au\/blog\/dem\/fsi-simulation-for-coastal-hazard-mitigation\/","title":{"rendered":"Fluid-structure interaction simulation of wave overtopping flow and vegetation for coastal hazard mitigation"},"content":{"rendered":"
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Guest Blog by Joshua Bagg, University of Auckland and research colleagues<\/a><\/span><\/strong>.<\/p>

Climate change is increasing the exposure of communities to coastal hazards [1 \u2013 4]. Traditional solutions, such as seawalls or revetments, can have a high financial, social, and environmental cost [3, 5, 6]. As a result, nature-based solutions are encouraged in coastal policy [6 \u2013 8]. A novel hybrid solution is salt marsh grass placed on the crest of a revetment (Figure 1), which has the potential to reduce the momentum of waves washing over the structure, mitigating wave overtopping hazards [9, 10]. However, the implementation of this novel hybrid solution, and nature-based solutions in general, is hampered by the lack of quantitative data, validated models, and technical design guidance [1, 3, 11, 12]. This is due to the challenges of representing live, flexible vegetation in numerical models and in scaled laboratory experiments. This research aimed to investigate the interaction between salt marsh grass and wave overtopping flow to inform the design of nature-based solutions.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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Figure 1 \u2013 Diagram of salt marsh grass on the crest of a sloped revetment. The dashed region identifies the experimental and numerical modelling domain.<\/em><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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With human safety and high-value coastal assets at risk, coastal engineers need methods, results and design tools they can trust. Appropriately scaled laboratory wave-flume experiments are relied upon to assess coastal protection performance, as complex fluid dynamics can be accurately replicated. Therefore, live salt marsh grass was placed in a flume without geometric scaling and impacted by flow that represents non-impulsive overtopping waves (more details about the experiments are available in [10, 13]).<\/p>

It is inevitable that coastal engineers will need to design for different overtopping flows or vegetation types than were tested in the experiments by Bagg et al. [10]. Additionally, there are many variables such as flow velocity, turbulence and aeration which are challenging to measure in the laboratory.<\/p>

Numerical models can overcome these challenges but must first be compared with reality, to understand the model accuracy and limitations.<\/p>

The two-way coupled CFD-DEM model methodology, using ANSYS Fluent and ANSYS Rocky, was identified to include the dominant physics required to simulate the fluid-structure interaction. Inspiration was taken from a Rocky simulation of a combine harvester [14], which shows Rocky\u2019s ability to simulate many individually moving flexible fibers, large deflection, fiber-fiber contact and fiber breakage. Furthermore, Rocky allows two-way coupling with Fluent and GPU acceleration.<\/p>

Thanks to the technical support from Angelo Christakakis at LEAP Australia, a stable Fluent-Rocky simulation was setup. An animation of the model results compared with the experimental results is shown in Figure 2.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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