The futures of Arctic offshore exploration meet the problems of ice dangers accounting for more severe conditions in comparison e.g. Northern Sea. The experience of operation of platforms in north-eastern Sakhalin offshore allowed to improve the ice test procedures. The main aim for practice for designing offshore structures is estimation of extreme ice forces on structure. The calculation procedures are based on ice strength values which is proved to be the main parameter but it determination meet many obstacles. The paper presents the correlation between ice strength and dynamic hardness considering the Drop Ball Test procedures.
Reliability and durability of offshore ice-resistant structures largely depend on the values of the ice force. Concrete gravity bases of oil and gas platforms (IRP) on the Sakhalin offshore withstand to highly dynamic drifting ice formations associated with a number of problems. The non-stationary process of ice breaking at the contact of the edge of drifting ice field and IRP leads to dangerous vibrations and dynamic forces. Extreme resonant oscillations can cause not only violations of the regular functioning of IRP, but also significantly reduce the reliability of the structure, causing fatigue fracture. Dynamic ice fracture is a complex process and depends on the choices of combinations of many factors: dimensions and flexibility of IRP; ice velocity and temperature, ice properties etc.
The object of this research is the process of energy transfer of the drifting ice fields, elastic energy causing failure with a certain frequency. The aim of the study is to identify and describe the regularities of formation of cyclic ice forces on the IRP, describing the process taking into account the phenomenological features of sea ice fracture - is as a mechanism for converting the kinetic energy of the ice field into elastic energy of IRP deflections.
The experimental observations (Croasdale et al. 1977; Hyrayama et al., 1975; Jordaan et al., 1980; Tuhkuri, 1995) have become the base for the development of analytical description the oscillations of structure during it interaction with drifting ice features.
