Exploitable results
International trade and the transportation of oil are making Europe's northern waterways - many of them narrow and iced over in winter - increasingly hectic hives of activity. At the same time, the Arctic represents an extremely fragile environment, making the prospect of maritime accidents potentially devastating to local ecosystems and hugely expensive to clean up.
The Safeice project aim was to create a scientific basis for ice class rules (ship hull strength) and for placing requirements on ice classes. The main purpose of the Safeice project was to develop semi-empirical methods based on measurements to determine the ice loads on ship hull, to find relationship between operational conditions and ice load, to develop ship-ice interaction models to assess the design ice loads on ship hull, to develop methods to estimate ultimate strength of shell plating and frames and to develop methods for the analysis of ice damages.
The target was to decrease the risk involved in winter navigation. Baltic Sea, Okhostk Sea and Canadian waters are used as validation areas for ice load predictions. The aims were achieved by compiling a database of earlier information on ice loads and ice pressures. This is a collection of full scale ice load data measured on board ships of various types sailing in different sea areas. Ice load data sets were used in validation of deterministic ice load models.
The main achievements of the project can be summarised as:
- The inventory of sources of ice loads and ice damage data have been compiled, the database design was conducted and the ice loading database was compiled. The database now contains 47 datasets with over 10 000 events for the five ice-going ships.
- A series of model tests were conducted in Japan to measure the ice load acting on the models. Two different types of model ships were tested - an icebreaker and a cargo vessel. The detailed ice load data have been compared with ice load computations.
- Identification of the major lacks in existing field data on ice load on ship hulls has been initiated. The results of the task will be taken into account in the design the full-scale or model-scale tests planned later in the project so that the lacking data can be obtained.
- The current ice service and icebreaking practices have been summarised. The report contains a brief description of the main icebound sea areas of the northern hemisphere where shipping is active, an in-depth analysis of different practices used in observing and describing ice conditions, together with an analysis of the Baltic and Canadian icebreaking systems.
- The identification of ice loading scenarios relevant for ship hull loading and an inventory of calculation methods applicable for ice load estimate has been defined. Numerical simulations of the ice load level in specific ice conditions for few ship types have been conducted and these have been compared with the ice load database and the model scale test results.
- A sea ice dynamics model development was initiated to calculate the plane stresses in the sea area in question. The main purpose of the model is to hind- and forecast ice drift, ridging, leveling and it gives also ice concentrations in real wind forcing conditions. This model can be used to compute the pressure in the ice field and it can also be used to give boundary conditions for a local finite element (FE)-model predicting ice forces on the hull of a ship in a compressive ice field.
- The literature study of the structural response calculation methods have been conducted for the strength of shell plating under ice loading. Various methods to evaluate permanent deflection on the shell plating under ice loading has been critically reviewed and compared with nonlinear FE-analysis.
- Applying non-linear finite elements the ship-ice interaction has been simulated including also the failure mechanism of ice in addition to the response of the shell structures. Few reported damage cases have been calculated to determine the load configurations i.e. contact area and pressure which has caused the damages.
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