Author(s): Aleksey Marchenko; Kenneth Eik
Linked Author(s):
Keywords: No Keywords
Abstract: Icebergs may cause a threat to offshore installations, vessels and operations in a number of Arctic regions. Based on experiences from the Canadian East Coast, it has been documented that the majority of icebergs can be deflected and thus avoiding iceberg structure collision. The preferred method for iceberg deflection is single vessel towing. While all successful iceberg towing operations so far have taken place in open water, future oil and gas developments are expected to take place in regions which occasionally are exposed to sea ice. This means that icebergs which are considered for towing may be affected by ocean currents, w inds, surface waves and sea ice. The poss ibility to manage icebergs both in open waters as well as ice covered waters will contribute to increased safety in future Arctic offshore operations. Experiments on iceberg towing in both open water and sea ice conditions in the HSVA ice tank have shown that the spectrum of tow rope tension includes several representative frequencies. One of these frequencies is associated with the first natural wave mode of the tank. Theoretical analysis shows the stability of steady towing of an iceberg floating in calm water. It was found that characteristic equation describing small perturbations of the system “vessel towing ropeiceberg” in the vicinity of steady towing has two complex and one rea l eigenvalues. The absolute value of the imaginary part of complex eigenvalues is much greater than their real parts. Therefore small perturbations of the system decay with oscillations on the frequency equaling to the imaginary part of the complex eigenvalues. In the present paper we analyze the eigenvalues for the conditions during the HSVA experiment in open water, compare them with the spectrum of tow rope tension and study the influence of a propagating surface wave on the iceberg tow. The main objective of the study is related to estimates of pick tension of the towing rope when affected by vessel propulsion and a surface wave.
Year: 2010