Xiangjun Bi

A Spectral Model for Forces Due to Ice Crushing

This paper presents a model of dynamic ice forces on vertical offshore structures. The model concerns a loading scenario where a competent ice sheet is drifting and crushing against the structure. Full scale data obtained on two offshore structures were used in the derivation of a method that applies both to narrow and wide structures. A large amount of events with directly measured local forces was used to derive formulas for spectral density functions of the local ice forces. A nondimensional formula that was derived for the autospectral density is independent of ice thickness. Coherence functions were used to define cross-spectral density functions of the local ice forces. The two kind of spectral density functions were used to obtain the spectral density of the total ice force. The method takes into account both the spatial and time correlation between the local forces. Accordingly, the model provides a tool to consider the nonsimultaneous characteristics of the local ice pressures while assessing the total ice force.

Results of Field Monitoring on Ice Actions on Conical Structures

Ice-structure interaction plays a central part in determining ice loads and ice-induced vibrations. This is a controversial research issue, and many factors make the problem more complicated. The authors have been monitoring several ice resistant structures in the Bohai Sea for 20 years and have measured ice forces and simultaneously observed ice-structure interaction processes. This paper describes typical physical ice sheet–conical structure interaction processes, field data, and theoretical explanations for different ice conditions and structure dimensions. The conclusions are more widely applicable, and we relate them to field work on ice resistant conical structures in other ice-covered regions. Further work will quantify ice loads on conical structures once the interaction process is understood.

Model Test of Ice-Structure Interaction

Different scales of model tests for investigating ice-structure interaction due to ice crushing have been conducted, and successful experiences and conclusions obtained from previous tests are summarized. On the other hand, the uncertainties within current methodology of ice-structure interaction model tests are discussed. Considering the nature of dynamic ice loads, several main aspects which should be taken into account during design of model tests are analyzed, including layout of the test system, application of scaling laws, and techniques of making model ice sheet, etc. Decision can be made for each of these aspects according to objective of the test, and based on this viewpoint, a small scale model test system was designed and constructed, a series of model tests were conducted and the ice-structure interaction processes which are the same as prototype phenomenon were observed.Copyright

Main Factors of Ice Sheet-Conical Structure Interaction Process Based on Field Monitoring

Ice-structure interaction plays a central part in determining ice loads and ice-induced vibrations. This is a controversial research issue, and many factors make the problem more complicated. The authors have been monitoring several ice resistant structures in the Bohai Sea for twenty years, and have measured ice forces and simultaneously observed ice-structure interaction processes. This paper describes typical physical ice sheet-conical structure interaction processes, field data and theoretical explanations, for different ice conditions and structure dimensions. The conclusions are more widely applicable, and we relate them to field work on ice-resistant conical structures in other ice-covered regions. Further work will quantify ice loads on conical structures once the interaction process is understood.Copyright