Evaluation of a source-function wavemaker for generating random directionally spread waves in the sea-swell band

A source-function wavemaker for wave-resolving models is evaluated for its capability to reproduce random directionally spread wave fields in the sea-swell band (0.04-0.3 Hz) relevant for realistic nearshore applications. The wavemaker is tested with a range of input wave characteristics defined by the non-dimensional amplitude (a/h), wavenumber (kh), wavemaker width, mean wave angle and directional spread. The (a/h) and kh dependency of modeled results are collapsed with the Ursell number (Ur = (a/h)/(kh)2). For monochromatic waves, the wavemaker accurately reproduced the input wave height for Ur < 1, with no dependence on non-dimensional wavemaker width. For random uni-directional waves, the wavemaker simulated well a Pierson-Moskowitz input spectrum. Frequency-integrated statistics are also reproduced with less than 2% difference between modeled to input significant wave height and < 10% difference between modeled to input mean frequency for Ur < 0.2. For random directionally spread waves, the wavemaker reproduced input frequency-dependent and bulk mean wave angle and directional spread to within 4° at Ur < 0.12. Lastly, the wavemaker simulated well the spectra, mean wave angle, and directional spread of a bimodal wave field with opposing sea and swell. Based on the Ur < 0.12 constraint, a range of dimensional wave height, period, and depth constraints are explored for realistic sea-swell band field application. The wavemaker's ability to generate waves that match the input statistical properties commonly derived from field measurements demonstrates that it can be used effectively in a range of nearshore science and engineering applications.