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Dead water effect on drift of icebergs

Presented by: 
John Grue University of Oslo
Date: 
Monday 2nd October 2017 - 14:15 to 15:00
Venue: 
INI Seminar Room 1
Abstract: 
Observations/measurements of the drift of an iceberg in Antarctica are motivation of the lecture. Particularly two measurements of the internal waves generated by the iceberg are discussed. These measurements are connected to Fridtjof Nansen's historical observations of the dead water on FRAM, published in Nansen (1897). The dead water resistance on FRAM is first obtained empirically from Nansen's observations. A strongly nonlinear interfacial model of the dead water resistance is then outlined with calculations relevant to the FRAM ship. The intersection of the resistance curves obtained empirically and theoretically determines accurately the speed of FRAM. This intersection becomes a function of the level of the pycnocline. The nonlinear and linear dead water wakes are then obtained at the low subcritical speeds. The connection between the dead water effect on FRAM and the ice berg case are discussed. The considerable increase in the dead water resistance at small subcritical speed, which FRAM did not overcome, is discussed. The same resistance slope seems to limit the speed of the iceberg drift where the observed internal wave Froude number is subcritical at a value of 0.6. References: J. Grue (2015). Nonlinear dead water resistance at subcritical speed. Phys. Fluids 27, 08213. J. Grue (2017). Calculating FRAM's dead water. In: The Ocean in Motion - Circulation, waves polar oceanography. Springer-Verlag, Oceanography Series. Eds. M.G. Velarde, R. Yu. Tarakanov, A.V. Marchenko. 70th Anniversary of Eugene G. Morozov. J. Morison and D. Goldberg (2012). A brief study of the force balance between a small iceberg, the ocean, sea ice, and atmosphere in the Weddell Sea. Cold regions science and technology, 76-77, 69-76.
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University of Cambridge Research Councils UK
    Clay Mathematics Institute London Mathematical Society NM Rothschild and Sons