Print Email Facebook Twitter The impact of modulational instability on coastal wave forecasting using quadratic models Title The impact of modulational instability on coastal wave forecasting using quadratic models Author Akrish, G. (TU Delft Environmental Fluid Mechanics) Reniers, A.J.H.M. (TU Delft Environmental Fluid Mechanics) Zijlema, Marcel (TU Delft Environmental Fluid Mechanics) Smit, P.B. (Sofar Ocean Technologies) Date 2024 Abstract Coastal wave forecasting over large spatial scales is essential for many applications (e.g., coastal safety assessments, coastal management and developments, etc.). This demand explains the necessity for accurate yet effective models. A well-known efficient modelling approach is the quadratic approach (often referred to as frequency-domain models, nonlinear mild-slope models, amplitude models, etc.). The efficiency of this approach stems from a significant modelling reduction of the original governing equations (e.g., Euler equations). Most significantly, the description of wave nonlinearity essentially collapses into a single mode coupling term determined by the quadratic interaction coefficients. As a result, it is expected that the efficiency achieved by the quadratic approach is accompanied by a decrease in prediction accuracy. In order to gain further insight into the predictive capabilities of this modelling approach, this study examines six different quadratic formulations, three of which are of the Boussinesq type and the other three are referred to as fully dispersive. It is found that while the Boussinesq formulations reliably predict the evolution of coastal waves, the predictions by the fully dispersive formulations tend to be affected by false developments of modulational instability. Consequently, the predicted wave fields by the fully dispersive formulations are characterized by unexpectedly strong modulations of the sea-swell part and associated unexpected infragravity response. The impact of the modulational instability on wave prediction based on the quadratic approach is further demonstrated using existing laboratory results of bichromatic and irregular wave conditions. Subject Modulation instabilitySpectral modellingQuadratic modellingCoastal wavesWave nonlinearityInfragravity waves To reference this document use: http://resolver.tudelft.nl/uuid:08100443-b972-48cc-9582-ec2478cc247f DOI https://doi.org/10.1016/j.coastaleng.2024.104502 ISSN 0378-3839 Source Coastal Engineering, 190 Part of collection Institutional Repository Document type journal article Rights © 2024 G. Akrish, A.J.H.M. Reniers, Marcel Zijlema, P.B. Smit Files PDF 1-s2.0-S0378383924000504-main.pdf 1.58 MB Close viewer /islandora/object/uuid:08100443-b972-48cc-9582-ec2478cc247f/datastream/OBJ/view