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... section contains plotted time series of the total tandem mooring forces as well as the mooring forces in each individual mooring line. In Figures 6 and 7, the number indicates when the bow of the tanker entered level ice and the moment when the bow of the tanker started to penetrate the ridge is marked with the number . Note that both vessels are embedded in ice at the end of the time series. ...
Context 2
... tandem mooring forces from test run 3100 are shown in Figure 6. The maximal total mooring force was 3.7 MN and 5.9 MN in level ice and the ridge, respectively. ...
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Citations
... Comfort et al. (1999) assembled an extensive set of ice model test data for floating and moored structures and presented the data in a common format to identify overall trends, and the Kulluk is also included as a typical structure. Aksnes et al. (2008) and Bonnemaire et al. (2008) carried out ice model tests of an arctic tandem offloading terminal with a focus on mooring forces in level and ridged ice. Later, Aksnes et al. (2010) and Bonnemaire et al. (2010) conducted ice basin tests on a moored offloading icebreaker in variable ice drifting directions. ...
... Comfort et al. (1999) assembled an extensive set of ice model test data for floating and moored structures and presented the data in a common format to identify overall trends, and the Kulluk is also included as a typical structure. Recently, Aksnes et al. (2008) and Bonnemaire et al. (2008) carried out ice model tests of an arctic tandem offloading terminal with a focus on mooring forces in level and ridged ice. Later, Aksnes et al. (2010a) and Bonnemaire et al. (2010) conducted ice basin tests on a moored offloading icebreaker in variable ice drifting directions. ...
The dynamic ice forces on a moored icebreaking tanker induced by drifting level ice were simulated with a two dimensional numerical model. Based on a heading controller which aimed to keep the hull head towards the drifting ice, ice resistance on ship was mainly estimated when taking the relative motion between the hull and ice into account. The mooring force and responses of the moored vessel were also looked into through parameter sensitivity studies with different ice thicknesses and ice drift speeds.
... Results from model tests of moored ships have also been published recently. A submerged turret loading concept was studied by Jensen et al. (2000), while a tandem mooring concept was discussed by ; ; Aksnes et al. (2008); Aksnes and Bonnemaire (2009a). The two latter papers can be found in Chapters 3 and 4 of this thesis, respectively. ...
... The analysis is based on observations and measurements from model tests of the Arctic Tandem Offloading Terminal (ATOT) at Hamburg Ship Model Basin (HSVA) in Germany in 2007. Details about the concept and the tests are given by , Bonnemaire et al. (2008a,b) and Aksnes et al. (2008). ...
... Comfort et al. (1999) assembled an extensive set of ice model test data for floating and moored structures and presented the data in a common format to identify overall trends, and the Kulluk is also included as a typical structure. Recently, Aksnes et al. (2008) and Bonnemaire et al. (2008) carried out ice model tests of an arctic tandem offloading terminal with a focus on mooring forces in level and ridged ice. Later, Aksnes et al. (2010a) and Bonnemaire et al. (2010) conducted ice basin tests on a moored offloading icebreaker in variable ice drifting directions. ...
This paper describes a 2D numerical model for the interaction between drifting level ice and a moored structure. The floating structure is treated as a rigid body kept on station by a mooring system, and it can only move in the horizontal plane. The ice-breaking process is modelled using a geometrical method that characterises the contact zones between the hull of moored structure and the ice sheet. Ice rotating and sliding processes are modelled semi-empirically using ship ice resistance formulations. The numerical model predicts the time history of both the ice forces and the global mooring forces as well as the dynamics of the floating structure. The proposed model is validated by comparison with field data. The simulation results obtained with this model are compared with full scale measurements and experimental data from model tests on the Kulluk platform conducted in the Beaufort Sea during the 1980s. The results show good agreement between the field measurements and the model tests. This model is also used to study the influence of turret position on the stability of a moored icebreaking tanker (MT Uikku) under typical varying ice drift speeds and directions. Based on the heading controller, which keeps the hull aligned with the drift ice direction, the effects of ice thickness, ice drift speed and global mooring stiffness on mooring forces and responses of the moored vessel are studied.
... Further details on the test setup can be found in Bonnemaire et al. (2008a), and Aksnes et al. (2008). ...
... If the tandem mooring loads exceed the winched braking load, these start to pay out. Details of the analysis can be found in Aksnes et al. (2008), but some main points are summarized herein: ...
A new concept for offshore offloading in ice-infested waters is tested in the Large Ice Tank at the Hamburg Ship Model Basin. The model includes an offloading icebreaking moored on a turret, and a tanker moored in tandem. Thanks to a dry mooring arrangement, simulations of interactions with variable ice drift and ice ridges were performed. The extensive monitoring of the tests led to new results in various fields: Response of tandem moored vessels to ice ridge interactions, Response of tandem moored vessels to ice drift changes in level ice, Response of a single moored vessel to ice drift changes in level ice, Observation of sub-surface ice transport and measurement of sub-surface ice actions under a moored vessel.
... The analysis is based on observations and measurements from model tests of the Arctic Tandem Offloading Terminal (ATOT) at Hamburg Ship Model Basin (HSVA) in Germany in 2007. Details about the concept and the tests are given by Jensen et al. (2008), Bonnemaire et al. (2008a,b) and Aksnes et al. (2008). ...
A challenge withmoored ships in ice is their response and themooring forces caused by changes in ice drift direction. Variability in ice drift direction is mostly driven by variations in speed and direction of current and wind. In this paper, the behaviour of a moored ship in level ice is studied in several ice drift scenarios, based on model tests performed at the Hamburg Ship Model Basin (HSVA). Three types of ice drift scenarios are studied; straight drift, drift along circular arcs and sudden changes in drift direction. Ice behaviour, vessel response and mooring forces are reported and discussed for the different ice drift scenarios. It was found that ice failed along large parts of the ship's waterline, due to changes in ice drift direction. The waterline geometry of the ship varied a lot around its perimeter and thus ice failed in various failure modes at different parts of the hull. The failure modes changed with the relative angle between the vessel heading and the ice drift direction, and influenced the response of the ship and the mooring forces. The magnitude of the peak mooring force caused by drifting level ice was comparable to the peak mooring force caused by a relatively large first-year ice ridge. Actions by drifting level ice should be considered as a possible design mooring load for moored ships in certain areas.
... In two test series (3000 and 4000 series), a tanker model is moored in close tow at the stern of the OIB. The tanker is then connected to the OIB via two lines and a weight system limiting the tension in the lines to simulate the towing winches at the OIB stern, Reference is made to Aksnes et al. (2008) for more details on the mooring of the tanker. ...
... The load capacity is based on an operating philosophy that the tanker should have a rapid loading cycle, i.e. stay in the wake as short as possible and avoid any load scenarios that involve changing drift directions of the ice. Figure 5b) gives an overview of the tanker mooring system, and details of the model set-up is found in Aksnes et al., (2008). ...
... • In level ice, the helmsman has little control over the OIB steering as the tanker with its long parallel vertical sides is embedded in the level ice. In case of ice drift changes, the OIB can be pushed to "over-steer" and will drift sideways causing increased mooring forces (see Aksnes et al., 2008). The OIB is equipped with reamers on the bow sides. ...
... Results on measured loads and observed sub surface ice interactions are presented by Bonnemaire (2008a,b) and Aksnes (2008). Prior to the testing campaign a feasibility study of the ATOT was performed. ...
... The ATOT concept was tested at the HSVA ice tank (Hamburg, Germany) during summer 2007 (see companion papers Jensen et al., 2008, Aksnes et al., 2008 and Bonnemaire et al., 2008). The present paper discusses observations on the subsurface ice transport and the measured ice impact forces on the loading turret. ...
