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The bottom topography of ridged sea ice differs greatly from that of other sea-ice types. The form drag of ridge keels has an important influence on sea-ice drift and deformation. In this study, both laboratory experiment (LabE) and fluid dynamics numerical simulation (FDS) have been carried out for a physical ridge model in a tank to better understand the quantitative characteristics of the form drag. The LabEs covered both laminar and turbulent conditions. The local form drag coefficient of a keel, C-dw, varied with the keel depth h(w) and the slope angle alpha(w) in the turbulent regime. After validated by the LabE measurements, the FDSs were employed to extend the parameterization from the finite water depth to deep water. The results gave C-dw = 0.68 center dot ln (alpha(w)/7.8 degrees), R-2 = 0.998, 10 degrees = 0.01), the variation of the local form drag coefficient and its contribution to total drag coefficient were sensitive to the keel slope angle. Assuming the log-normal distribution for this angle, the average value of the local form drag coefficient was 0.75, recommended for sea-ice dynamic models.

An experimental campaign to investigate sea ice ridge interaction with bottom-fixed structures was carried out in the Aalto ice tank in Espoo Finland in August, 2019. The aim was to investigate a) the scaled ridge properties, b) the ice processes during testing and c) the scaling of ridge forces with respect to a cylindrical and conical structures at the water line. This presentation focuses to analyses of ridge keel punch tests. In a punch test, a circular platen of consolidated layer is first cut free from the surrounding ice field. Thereafter, the ice is pushed vertically downwards with a cylindrical indentor to break the underlying keel. The measured load-displacement relationship can be used for the evaluation of the mechanical properties of rubble. Three ice sheets were created and used to build ridges, in which the ridge consolidation temperature and time were varied. All together 24 punch tests were carried out, whereas 14 of them were done for consolidated ridge, six for unconsolidated ridge, three for surrounding level ice and one in the open water to determine the buoyancy load in the indentor. Both the structural tests and punch tests showed clearly, that the ridge strength and load depends strongly on the consolidation.

An experimental campaign to investigate sea ice ridge interaction with bottom-fixed structures was carried out in the Aalto ice tank in Espoo Finland in August, 2019. The aim was to investigate a) the scaled ridge properties, b) the ice processes during testing and c) the scaling of ridge forces with respect to a cylindrical and a conical structure at the water line. This presentation focuses on analyzing ridge keel punch tests. In a punch test, a circular platen of consolidated layer is first cut free from the surrounding ice field. Thereafter, the ice is pushed vertically downwards with a cylindrical indentor to break the underlying keel. The measured load-displacement relationship can be used for the evaluation of the mechanical properties of rubble. Three ice sheets were created and used to build ridges, in which the ridge consolidation temperature and time were varied. All together 24 punch tests were carried out, whereas 14 of them were done for consolidated ridge, six for unconsolidated ridge, three for surrounding level ice and one in the open water to determine the buoyancy load on the indentor. Both the structural tests and punch tests showed clearly that the ridge strength and load depend strongly on the consolidation.

Sets of measurements of underwater ridge parts usually contain a limited amount of data. Outcomes need to be made while relying on small sample sizes. In this event, the chance of making inaccurate estimations increases. This paper proposes to use stochastic confidence regions in the estimation of the unknown parameters of keel depths. A model for a random variable with a lognormal distribution for keel depths is assumed. Regions for the mean and standard deviation of keel depths are obtained from Mood’s and minimum-area confidence regions for parameters of the normally distributed random variable. Conservative safety probability of non-exceeding the critical keel depth in one random interaction of the ridge with structure is estimated. An algorithm for statistically assessment of ice ridge keel data by means of confidence region building is here offered. The assessment of a set of ridge keel depths for the Gulf of Bothnia (Baltic Sea) is performed.

Ice ridges are the most difficult ice features that ships encounter in first-year ice conditions. Our understanding on ridge resistance on ships is currently limited, but we can assume that the keel of a ridge can have a significant impact to the resistance due to its large volume. In order to study the ridge resistance, we measured ridge profiles and recorded ship machinery and operational data during RV Aranda sea ice cruise in the Baltic Sea on spring 2016. This paper presents results from our ridge profile measurements made by drilling and with a sonar. We found a fairly good correspondence between these two methods. The maximum depth of the profiled ridges varied between 3 and 5 meters and the width of the cross sections from 10 to 25 meters.

Drifting sea ice ridge introduces often a major load scenario for the design of offshore structure. Major load contribution is presented by the consolidated layer and the underlying keel. Mechanical properties of the ridge keel are essential input to predict ridge loads.In a punch shear test, a circular platen of consolidated layer is first cut free from the surrounding ice field. Thereafter, the platen is pushed down to break the underlying keel. The measured load-displacement relationship can be used for the evaluation of rubble properties and also for the model validation. Ridge keel punch tests were carried out in the Bothnian Bay 1998-2003 with various platen diameters and keel thicknesses. This data has been earlier studied by the finite element simulations in Lagrangian framework. Presently, Coupled Eulerian-Lagrangian (CEL) framework was applied. The main benefit of CEL is that it enables robust modelling of large deformations due to material failure during the punch load. The ice rubble was modelled as a continuum with a shear-cap failure criterion, which describes both the shear failure and compaction. Parametric studies were carried out for two punch shear tests to determine the rubble properties. Main objective was to evaluate a suitable combination of the cohesion and friction angle which can be further utilized in ridge load analyses.

Drifting sea ice ridge introduces often a major load scenario for the design of offshore structure. Major load contribution is presented by the consolidated layer and the underlying keel. Mechanical properties of the ridge keel are essential input to predict ridge loads.In a punch shear test, a circular platen of consolidated layer is first cut free from the surrounding ice field. Thereafter, the platen is pushed down to break the underlying keel. The measured load-displacement relationship can be used for the evaluation of rubble properties and also for the model validation. Ridge keel punch tests were carried out in the Bothnian Bay 1998-2003 with various platen diameters and keel thicknesses. This data has been earlier studied by the finite element simulations in Lagrangian framework. Presently, Coupled Eulerian-Lagrangian (CEL) framework was applied. The main benefit of CEL is that it enables robust modelling of large deformations due to material failure during the punch load. The ice rubble was modelled as a continuum with a shear-cap failure criterion, which describes both the shear failure and compaction. Parametric studies were carried out for two punch shear tests to determine the rubble properties. Main objective was to evaluate a suitable combination of the cohesion and friction angle which can be further utilized in ridge load analyses.