Abstract
A long-standing problem in maritime operations and ocean development projects has been the prediction of instantaneous wave energy. Wave measurements collected using an array of freely drifting arrays of Surface Wave Instrument Float with Tracking (SWIFT) buoys are used to test methods for phase-resolved wave prediction in a wide range of observed sea states. Using a linear inverse model in directionally-rich, broadbanded wave fields can improve instantaneous heave predictions by an average of 63% relative to statistical forecasts based on wave spectra. Numerical simulations of a Gaussian sea, seeded with synthetic buoys, were used to supplement observations and characterize the spatiotemporal extent of reconstruction accuracy. Observations and numerical results agree well with theoretical deterministic prediction zones proposed in previous studies and suggest that the phase-resolved forecast horizon is between 1–3 average wave periods for a maximum measurement interval of 10 wave periods for ocean wave fields observed during the experiment. Prediction accuracy is dependent on the geometry and duration of the measurements and is discussed in the context of the nonlinearity and bandwidth of incident wave fields.
Highlights
Real-time, phase-resolved reconstruction of irregular ocean waves is critical for optimizing many offshore operations ranging from developing early warning systems for surface vessels to reducing fatigue loads on offshore structures
Following a similar procedure used in Thomson et al, estimates of wave steepness (4) and Benjamin–Feir Index (BFI) (3) are compared to the kurtosis (12) and skewness (13) of observed wave records to further assess the role of nonlinearities in generating high runs of waves:
While κ is related to BFI and includes measures of nonlinearities that arise from four-wave interactions, γ is useful in diagnosing triad interactions that are theoretically limited to wave group formation in shallow water (Peregrine, 1967; Madsen and Sørensen, 1993)
Summary
Real-time, phase-resolved reconstruction of irregular ocean waves is critical for optimizing many offshore operations ranging from developing early warning systems for surface vessels to reducing fatigue loads on offshore structures. Morris et al (1998) first suggested that for some measurement interval there exists a finite zone in space–time where the sea surface can be accurately reconstructed from observations. Within this theoretical prediction zone, it is feasible to accurately predict instantaneous wave elevation and related fields over short periods (Wu, 2004; Naaijen et al, 2014; Qi et al, 2018a)
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