Freak waves, alternatively called rogue waves or giant waves, are exceptionally
large, steep, and asymmetric waves whose heights usually
exceed by 2 times the significant wave height. They have
also been described as ‘‘holes in the sea’’ or ‘‘walls
of waters’’. These waves have been long known to be notorious hazards to
navigation vessels and marine structures. Our research
aims to explore the occurrence of freak waves and
investigate the mechanisms to generate freak waves.
Specifically, we are interested in further understanding
the formation mechanisms, limiting characteristics, and
temporal-spatial-spectral evolution of freak waves on
currents. Experimental results confirm that a random wave
field does not prevent freak wave formation due to
dispersive focusing. Strong opposing currents inducing
partial wave-blocking significantly elevate the limiting
steepness and asymmetry of freak waves. At the location
where a freak wave occurs, the Fourier spectrum exhibits
local energy transfer to high-frequency waves. The
Hilbert-Huang spectrum, a time-frequency-amplitude
spectrum, depicts both the temporal and spectral evolution
of freak waves. A strong correlation between the magnitude
of inter-wave instantaneous frequency modulation and the
freak wave non-linearity (steepness) is observed. The
experimental results provide an explanation to address the
occurrence and characteristic of freak waves in
consideration of the onset of wave breaking.
freak wave on a 10 cm/s following current freak wave on a 10 cm/s opposing current
To capture freak waves, we have been developing a novel Automated Trinocular Stereo Imaging System (ATSIS), a non-intrusive remote sensing technique, to measure temporal evolution of three-dimensional wave characteristics. The system consists of three progressive digital cameras to accurately estimate depth of a scene. In addition the advantage of using extra camera resolves the correspondence problems due to specular reflection on the water surface and provides additional constraints on image matching, dramatically reducing the chance of a mismatch. An oblique configuration for the trinocular system effectively increases spatial coverage, allowing observations of wave phenomena over a broad range of spatial scales. A new exterior calibration procedure is also developed to determine the orientation of cameras in the field. The height resolution is increased with the optical axes of the cameras pointed at an oblique angle with respect to vertical surface wave displacements.
Stereo-imaging of a 3D breaking wave 3D view of the processed image Virtual wave gauge array
Furthermore. we also developing the-state-of-the art models for depict freak wave motions. For several decades, a great deal of efforts has been paid to develop unified models that can effectively predict water wave propagation with varying degree of dispersive and nonlinear effects. Our research group is focusing on develop an efficient and accurate non-hydrostatic modeling frame to predict large scale surface wave dynamics. Overall the goal is to develop full non-hydrostatic model using a small number of vertical layers (two ~ five layers) to simulate nearshore wave transformation including shoaling, dispersion, refraction, and diffraction phenomena. Furthermore we are also working on developing a non-hydrostatic model that can examine deep-water wave-wave interactions including slowly modulated and rapidly evolving wave processes leading to the formation of freak waves.
Shoaling and diffraction Refraction and diffraction Frequency dispersion focusing