Air-Sea Interactions and Surface Wave Dynamics
     We are developing a fundamental understanding of surface wave and current interactions in the estuarine and coastal/marine environments. In the past we have developed methods to generate and detect three-dimensional breaking waves and wave-current interaction in the laboratory. The overall goal is to understand the role of shear currents on wave evolution and breaking and develop a temporal form of physics-based parametrization of momentum, heat, and humidity fluxes across wave boundary layer processes for the coupled atmosphere-ocean models. In the last two decades, tremendous progress has been made to use imaging techniques like an in-situ ethernet-based (CBLAST-LIVE) and a real time self-contained video system (CBLAST-EYE) for observing air-sea surface wave characteristics at the Air-Sea Interaction Tower (ASIT) off the south shore of Martha’s Vineyard. In addition, observations of subsurface wave and current have been measured. The project is one component of the Coupled Boundary Layers, Air-Sea Interaction Experiment in Low to Moderate Winds (CBLAST-LOW).
      s
       3D and Wave-current induced breaking waves                            Processes of air-sea interactions                                      Observatory for air-sea interactions

     An image taken from the ASIT during the experiments is shown here. Using a digital photogrammetry processing technique, the whitecapping area can be estimated from the rectified ortho-image and correlated with the recorded wind speed. In addition, the following ortho-image shows a developing Langmuir streak under a wind speed of approximately 5 m/s. Time series of whitecapping areas other concurrent measurements are correlated to obtain breaking-wave induced parametrization of momentum, heat, and humidity fluxes momentum, heat, and humidity fluxes.
 
                 Breaking waves at the ASIT                                          Orthophoto of the marked red area                                          Langmuir Circulation

    To characterize complicated surface wave processes, 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. 

VWG
        Stereo-imaging of a 3D breaking wave                              3D view of the processed image                                               Virtual wave gauge array

     Efficient and accurate modeling of surface wave motions plays an important role in many coastal and ocean. 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.  

f_w       near         freak                  

     Meteotsunamis can pose a serious threat to the Lake Michigan coast, owing to the lake’s characteristics that facilitate the formation of destructive meteotsunamis including frequent fast-moving storm fronts, resonance-promoting bathymetry, and harbors to finally amplify the wave. The most vivid historical meteotsunami on record in the Great Lakes occurred in 1954,  when a squall line-induced longwave wave struck Chicago in Lake Michigan. The coast was inundated up to 50 meters inland and unexpectedly swept many fishermen off of the Montrose Harbor piers, killing seven. While the threat of meteotsunamis in Lake Michigan has been recognized, to date no infrastructure for detecting and warning of a pending meteotsunami disaster is available. Furthermore the potential hot spots in Lake Michigan that can be threatened by meteotsunamis has yet been identified and characterized. In collaboration researchers in Great Lakes Environmental Research Laboratory, we are currently implementing an observation network system to better understand the occurrence of meterotsunamis. An operational meteotsunami forecasting and warning system is also being developed to keep residents safe and avoid dangerous events.


Sponsor : Office of Naval Research 
                 NSF-Ocean Science
                 NOAA, University of Wisconsin Sea Grant Institute
                 UW-Madison/UW-Milwaukee Intercampus Research Incentive Grants Program
                Wisconsin Alumni Research Foundation
                Wisconsin Coastal Management Program - Freak waves in Apostle Islands
                Wisconsin Hilldale Faculty/Undergraduate Research Fellowships
                 
Status :   Active
Student Investigators:
Adam Bechle (PhD), Josh Anderson (PhD),  Liu Liu (PhD), Alex Campbell (MS)
Ian Dupont (undergraduate)

Graduated: Jay Young (PhD), Doo-Yong Choi (PhD), Henry Yuan (PhD), Aifeng Yao (Ph.D.),
                   Adam Bechle (MS), Justin Wanek (MS), Chris Petykowski (MS)

Collaborators:
Dr. Paul Liu, NOAA, Great Lakes Environmental Research Laboratory
Dr. Eric Anderson, Cooperative Institute for Limnology and Ecosystems Research (CILER)
Dr. Y. Joseph Zhang, Center for Coastal Margin Observation & Prediction (CMOP)

Openings         
        
Publications
  • Bechle, A.J. and Wu, C.H., Virtual wave gauges based upon stereo imaging for measuring surface wave characteristics, Coastal Engineering, Coastal Engineering, 58(4), 305-316, 2011.
  • Choi, D.Y., Wu, C.H., Young, C.C., An efficient curvilinear non-hydrostatic model for simulating surface water waves, International J. for Numerical Methods in Fluids, International J. for Numerical Methods in Fluids, 66(9), 1093-1115, 2011.
  • Liu, P.C., Wu, C.H., Bechle, A.J., MacHutchon, K.R., and Chen, H.S., What do we know about freaque waves in the ocean and lakes and how do we know it, Natural Hazards and Earth System Sciences, 10, 2191-2196, 2010.
  • Young C.C. and Wu, C.H., A σ - coordinate non-hydrostatic model with embedded Boussinesq-type like equations for modeling deep-water waves. International J. for Numerical Methods in Fluids,63(12),1448-1470, 2010.
  • Wu, C.H., Young, C.C., Chen, Q.J., and Lynett, P.J., Efficient non-hydrostatic modeling of nonlinear waves from shallow to deep waters, J. of Waterway, Port, Coastal, and Ocean Engineering, 136(2), 104-118, 2010.
  • Young, C.C. and Wu, C.H., Non-hydrostatic modeling of nonlinear deep-water wave groups, J. of Engineering Mechanics-ASCE, 136(2), 155-167, 2010.
  • Young, C.C., Wu, C.H., Liu, W.C., and Kuo, J.T.,A higher-order non-hydrostatic sigma model for simulating non-linear refraction-diffraction of water waves. Coastal Engineering, 56(9), 919-930, 2009.
  • Young, C.C. and Wu, C.H., An efficient and accurate non-hydrostatic model with embedded Boussinesq-type like equations for surface wave modeling, International J. for Numerical Methods in Fluids, 60(1), 27-53, 2009.
  • Wu, C.H. and Yuan, H.L., Efficient non-hydrostatic modelling of surface waves interacting with structures, Applied Mathematical Modelling, 31(4), 687-699, 2007.
  • Young, C.C., Wu, C.H., Kuo, J.T., and Liu, W.C., A higher-order sigma-coordinate non-hydrostatic model for nonlinear surface waves, Ocean Engineering, 34(10), 1357-1370, 2007.
  • Yao, A. and Wu, C.H., Spatial and temporal characteristics of transient extreme waves on depth-varying currents, J. of Engineering Mechanics-ASCE, 132 (9), 1015-1025, 2006.
  • Choi, D.Y. and Wu, C.H., A new efficient 3D non-hydrostatic free-surface flow model for simulating water wave motions, Ocean Engineering, 33(5-6), 587-609, 2006.
  • Yuan, H.L. and Wu, C.H., Fully non-hydrostatic modeling of surface waves,  J. of Engineering Mechanics-ASCE, 132 (4), 447-456, 2006.
  • Wanek, J. and Wu, C.H., Automated trinocular stereo imaging system for three-dimensional surface wave measurements, Ocean Engineering, 33(5-6), 723-747, 2006.  (see breaking wave evolution here)
  • Yao, A. and Wu, C.H., Incipient breaking of unsteady waves on sheared currents, Physics of Fluids, 17, 082104, 2005.
  • Yao, A. and Wu, C.H., An automated image-based technique for tracking surface wave profiles, Ocean Engineering, 32(2) 157-173, 2005.
  • Wu, C.H. and Yao, A., Laboratory measurements of limiting freak waves on currents, J. Geophysical Research-Oceans, 109, C12, C12002, 1-18, 10.1029/2004JC002612, 2004.
  • Yao, A. and Wu, C.H., Energy dissipation of unsteady wave breaking on currents, J. Physical Oceanography, 34, N10, 2288-2304, 2004.
  • Wu, C.H., Yao, A., and Chang, K.A., DPIV measurements of unsteady deep-water wave breaking on following currents, "PIV and Modeling Water Wave Phenomena, World Scientific Publication Co., Advances in Coastal and Ocean Engineering - Vol. 9, 2004.
  • Wu, C.H., Nepf, H.M., Cowen, E.A., Surface current and vorticity generated by three-dimensional breaking waves, accepted under revision J. Fluid Mech., 2004.
  • Wu, C.H. and Nepf, H. M, Breaking wave criteria and energy losses for three-dimensional breaking waves, C10, 3177, 10.1029 2001JC001077, 41-1-18, J. Geophysical Research-Oceans, 2002.
  • Nepf, H.M., Wu, C.H., Chan, E.S., A comparison of two- and three-dimensional wave breaking, J. Physical Oceanography, 28, N7, 1496-1510, 1998.
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