Overview
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.
- Decrease the environmental and material risks to shipping in ice covered waters by creating a unified basis for winter navigation system for first year ice conditions including the methods to get the required ice class;
- Develop semi-empirical methods based on measurements and advanced theoretical models to determine the ice loads on ship hull and relate these to the operational scenarios and the ice conditions;
- Develop ship-ice interaction models and stochastic models to assess the design loads on ship hull. The outcome is a description of the ice load versus ice and operational parameters;
- Create a framework to develop design codes and regulations for plastic design basis for icebound ships.
The SAFEICE project's aim was to create a scientific basis for ice class rules (ship hull strength) and for placing requirements on ice classes. The main purposes in the SAFEICE project were 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 to analyse ice damages.
The target was to decrease the risk involved in winter navigation. Baltic Sea, Okhostk Sea and Canadian waters were 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 was a collection of full scale ice load data measured on board ships of various types sailing in different sea areas. Ice load data sets are used in validation of deterministic ice load models. The ice loading process has a stochastic nature. The stochasticity of ice loads influences the design ice load value.
In the SAFEICE project probability based methods in ice load evaluation were developed and validated with measured data. First yield load of ships operating in the Baltic Sea were often exceeded. However, serious ice damages were rare. Ultimate load carrying capacity of hull structure was therefore utilised. Instead of elastic design, ice rules could be based on plastic design. Probability of loads exceeding ultimate strength of various structural elements could then be estimated and the design load level will be explicitly determined.
The project was carried out with the participation of universities, maritime authorities and European, Canadian and Japanese marine research institutes. The partners represented the vertical chain from basic research into implementing the ice rules and enforcing safety at sea.
Funding
Results
The main achievements of the project so far 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 5 ice-going ships.
- A series of model tests were conducted inJapanto 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, levelling 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 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 non-linear FE-analysis.
- Applying non-linear finite elements the ship-ice interaction has been simulated including also the failure mechanism of ice in