A Dynamic Ice-structure Interaction Model for Prediction of Ice-induced Vibration

Sea ice crashing against offshore structures can cause strong ice-induced vibration and have a major impact on offshore structural safety and serviceability. This paper describes a numerical method for the prediction of ice-induced vibration when a vertical offshore structure is subjected to the impact of sea ice. In this approach, negative damping theory and fracture length theory are combined and, along with ice strength-stress rate curve and ice failure length, are coupled to model the internal fluctuating nature of ice load. Considering the elastic deformation of ice and the effect of non-simultaneous crushing failure of local contact between ice and structures, the present ice-induced vibration model is established, and the general features of the interaction process are captured. To verify its efficacy, the presented simulation methodology is subjected to a model test and two full-scale measurements based on referenced studies. Example calculations show good agreement with the results of the model test and full-scale measurements, which directly indicates the validity of the proposed simulation method. In addition, the numerical simulation method can be used in connection with FE programs to perform ice-induced vibration analysis of offshore structures.

Structural Optimization for the Ice-Resistance Platform in Bohai Bay

Bohai Bay is a major offshore oil and gas production area in China, a number of oil and gas fields are located there. The offshore facilities in this area are subject to ice loads in the winter, and the ice loads on the platform are one of the major concerns in the structural design in this area. The loads include ice impact, ice-induced-vibration and floating ice influence to the offshore operations. Compared to the loads combination of wind, wave and current, the ice load may be the governing loading condition in the structural design. The ice induced vibration to the production facilities and the living quarters may also seriously affect safety and the health of the operating personnel. This paper briefly introduces the development history of the ice-resistance platform design in Bohai Bay, and based on previous experience, the ice loads calculation method, the structure configuration of primary steel, the appurtenance arrangement and the conical structure at ice abrasive zones are discussed to optimize the ice-resistance capability. The material selection and different vibration mitigation methods are also discussed in this paper. Although significant progress has been made on the ice-resistance platform design, the problems still remain such as the floating ice accumulation around well slots. Further study on ice-induced vibration is necessary. This paper summarizes the main issues and challenges in the ice-resistance platforms and proposes the key points for future development. This paper also provides helpful references to the design and optimization of the offshore platform in an ice active environment.