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Takuji Waseda / Associate Professor / Division of Environmental Sciences
Department of Ocean Technology Policy and Environment / / Oceanography and Ocean Engineering
http://waseda2.t.u-tokyo.ac.jp/~waseda/

Career Summary
1990: B.Eng., The University of Tokyo
1997: Ph.D., University of California, Santa Barbara
1997-2004: Researcher, Frontier Research System for Global Change, JAMSTEC, Japan and International Pacific Research Center, SOEST, University of Hawaii
2004-2008: Associate Professor, Graduate School of Engineering, The University of Tokyo
2008-present: Associate Professor, Graduate School of Frontier Sciences, The University of Tokyo
Educational Activities
Graduate school: Dynamics of Ocean Surface Processes, Environmental Fluid Modeling, Exercises on Ocean Information
Research Activities
Observational study to determine causes of freak wave generation in open ocean (2008-):
We are developing a GPS wave buoy to monitor freak waves in the deep ocean. Freak waves are abnormal waves that appear in the middle of the ocean. Their generation mechanism includes non-linear self focusing, wave-current interaction, and dispersive focusing due to changing wind fields. We have hypothesized that a freakish sea state with a narrow directional spectrum develops as a result of the external forces of wind and current. As the directional spectrum narrows, the waves become unstable and large amplitude waves develop.

Experimental and numerical study of freak waves (2004-):
The fundamental process of the freak wave generation mechanism is being studied at the Ocean Engineering Tank of the University of Tokyo. Evolution of a directional wave was studied systematically, revealing that the narrowing of the directional spectrum enhances the occurrence of freak waves due to quasi-resonance. The influence of the current is also being investigated. Various marine accident cases are being analyzed using wave forecast models.

Ocean Renewable Energy (2008-):
Site selection is a crucial step in utilizing ocean renewable energy. We are using state-of-the-art wave, ocean current, and wind models to identify potential sites. Acoustic Doppler current profiler current measurements and GPS wave buoy measurements are being conducted to verify these numerical models. High-resolution models are under development to fine tune energy converters in the Izu Islands.

Safety and efficiency of navigation (2004-):
Wave forecast models will be used to predict dangerous seas (freakish seas). Wind forecasts will be used to route the sailing cargo ship which is in the planning stage. To improve the predictability, an ensemble forecast will be used.

Kuroshio modeling and observation (2000-):
Short-term variation of the Kuroshio Current south of Japan is caused by the interaction of the jet and the mesoscale eddies. In addition, due to complicated topography south of Japan, flow fields are rather complicated. Of particular interest is the identification and understanding of sub-mesoscale current field around islands and peninsulas. High-resolution numerical modeling as well as in-situ observations are conducted.

Data Server (2004-):
Ocean information is efficiently disseminated by using user-friendly web interfaces and back-end data servers. http://157.82.253.137/

Literature
1) Waseda, T., M. Hallerstig, K. Ozaki and H. Tomita, 2011, Enhanced freak wave occurrence with narrow directional spectrum in the North Sea, Geophys. Res. Lett., doi:10.1029/2011GL047779

2) Babanin, A. V., T. Waseda, T. Kinoshita, A. Toffoli, 2011, Wave breaking in directional fields, Journal of Physical Oceanography, 41, 145-156

3) Lamont-Smith T., M. Mitomi, T. Kawamura, T. Waseda, 2010, Electromagnetic scattering from wind blown waves and ripples modulated by longer waves under laboratory conditions, IET Radar, Sonar and Navigation, 4, 265-279

4) Toffoli, A., A. Babanin, M. Onorato, T. Waseda, 2010, Maximum steepness of oceanic waves: Field and laboratory, Geophysical Research Letters, 37, doi:10.1029/2009GL041771

5) Tamura, H., T. Waseda, Y. Miyazawa, 2010, Impact of nonlinear energy transfer on the wave field in Pacific hindcast experiments, Journal of Geophysical Research, 115, doi:10.1029/2009JC006014

6) Waseda, T., T. Kinoshita, H. Tamura, 2009, Evolution of a random directional wave and freak wave occurrence, J. Phys. Oceanogr., 38(3), 621-639

7) Waseda, T., T. Kinoshita, H. Tamura, 2009, Interplay of resonant and quasi-resonant interaction of the directional ocean wave, J. Phys. Oceanogr., 39, 2351-2362

8) Onorato, M., T. Waseda, A. Toffoli, L. Cavaleri, O. Gramstad, P. A. E. M. Janssen, T. Kionoshita, J. Monbaliu, N. Mori, A. Osborne, M. Serio, C. T. Stansberg, H. Tamura, K. Trulsen, 2009, Statistical properties of directional ocean waves: the role of the modulational instability in the formation of extreme events, Phys. Rev. Lett., 36, doi:10.1103/PhyRevLett.102.114502

10) Tamura, H., T. Waseda, Y. Miyazawa, 2009, Freakish sea state and swell-windsea coupling-numerical study of Suwa-Maru incident, Geophys. Res. Letters, 36, L01607, doi:10.1029/2008GL036280

11) Tamura, H., T. Waseda, Y. Miyazawa, K. Komatsu, 2008, Current-induced modulation of the ocean wave spectrum and the role of nonlinear energy transfer, J. Phys. Oceanogr., 38, 2662-2684

12) Lamont-Smith, T., T. Waseda, 2008, Wind wave growth at short fetch, J. Phys. Oceanogr., 38(7), 1597-1606

13) In, K., T. Waseda, K. Kiyomatsu, H. Tamura, Y. Miyazawa, K. Iyama, 2009, Analysis of a marine accident and freak wave prediction with an operational wave model, 19th International Offshore (Ocean) and Polar Engineering Conference, 2009/6/23 Kobe

14) Waseda, T., S. Masato, T. Nishida, H. Tamura, Y. Miyazawa, Y. Kawai, H. Ichikawa, H. Tomita, A. Nagano, K. Taniguchi, 2011, GPS-based wave observation using a moored oceanographic buoy in the deep ocean, 21th International Offshore (Ocean) and Polar Engineering Conference, 2011/6/22 Maui, U.S.A.

Other Activities
Oceanographic Society of Japan
Japan Society for Naval Architecture and Ocean Engineering
American Geophysical Union

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Future Plan
Development of high-resolution wind-wave-current coupled model for predicting freak waves, estimating ocean energy resources and safety of ship navigation and sea operations. Observations of current, waves, and wind near the Izu-Islands.

Messages to Students
Dream about what you can accomplish and stay focused on your own research. Try hard to establish a solid foundation on which your future will be based after graduation. Enjoy the freedom you have at university.

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