Combined Wind-Wave Loading on Coastal Structures
Motivation & Objective
During extreme weather events such as hurricanes, coastal structures are subjected to complex, multiphysics hazards such as simultaneous high winds, storm surge flooding, and wave action. Hurricanes cause damages on the order of tens of billions of dollars in the US alone each year[1], yet the coupled interactions of these multi-physics loads are not fully understood.
Similitude incompatibilities of the different flow physics mean that geometrically scaled-down experiments cannot fully represent the various interactions present. Load analyses recommended in buildings codes such as ASCE-7 take a fundamentally decoupled approach (analyzing wind loads separately from surge and waves). However, from our current understanding of wind-wave interaction in literature, we expect that the wind influences waves (causing white-capping, steepening, and earlier onset of breaking) and that the waves influence the wind (injecting coherent motions at length scales near the wavelength, generating turbulence due to separation at the wave crest and during wave breaking).
The objective of this research is to improve our understanding of these multiphysics interactions and their effects on combined wind-wave loading on coastal structures through the use of computational models. As full-scale, fully-coupled experimental and field datasets are limited, we evaluate and build confidence in these computational models by first validating wind- and wave-only loading, then validating wind-wave interaction without structures, and finally looking at combined wind-wave loading on structures.
Methods
The first stage of this project used wave-only loading data collected at Oregon State University's Large Wave Flume (LWF) to validate 3D, Large Eddy Simulation (LES) modeling in the open-source CFD solver OpenFOAM. We identified that the choice of interface capturing scheme (i.e., the way that the interface between air and water is described numerically) can have a large effect on resulting loads, especially at small scales.
Visualizations of a simulated wave breaking just before a cylinder. (Top) Simulated using the isoAdvector geometric VOF approach developed by Roenby et al. [2] in OpenFOAM. (Bottom) Simulated using the algebraic Volume-of-Fluid (VOF) with MULES limiter approach in OpenFOAM, as described in [3].
The next stage of this project will evaluate the suitability of interface modeling approaches for young (hurricane-like) and old (swell-like) wind-wave conditions, using the CFD solver CharLES by Cascade Technologies.
Acknowledgement and Resources
[1] Lomonaco, P., Maddux, T., Bosma, B., Myers, A. T., Arwade, S. A., Hallowell, S., & Johlas, H. M. (n.d.). Physical Model Testing of Wave Impact Forces on Fixed Foundations of Offshore Wind Turbines.
[2] Roenby, J., Bredmose, H., & Jasak, H. (2016). A computational method for sharp interface advection. Royal Society Open Science, 3(11), 160405. https://doi.org/10.1098/rsos.160405
[3] Deshpande, S. S., Anumolu, L., & Trujillo, M. F. (2012). Evaluating the performance of the two-phase flow solver interFoam. Computational Science & Discovery, 5(1), 014016. https://doi.org/10.1088/1749-4699/5/1/014016