The Criterion Of The Pre-warning Of The Off-shore Platform In Ice Induced Vibration

Offshore structures located in ice-infested areas need to resist static and dynamic ice forces. It is well-known that most jacket platforms designed in Bohai Bay are subject to ice-induced vibrations. The vibrations may cause the fatigue of the structure,the crew , and the flanges of the platform. In 2000, one of the flanges leaked in the JZ202 MSW platform due to ice induced vibrations causing the leakage of natural gas. In the early stages of the JZ202 MSW and MUQ jacket platform production, it is proposed that pre-warning of the platform of ice-induced vibration should be done so that workers can do something to protect the platform before ice damage occurs. However, the criterion of pre-waming was previously unavailable. It is now necessary to give the platform pre-warning of an ice load in the environment.Previous research of the full-scale tests conducted on the offshore jacket platforms is first summarized. Based on the ISO criterion of human fatigue due to vibration, the evaluation of human fatigue on the JZ202 MSW and MUQ jacket platform in an ice-induced vibration environment is given. Then, we give a forecast of human fatigue on the JZ202 MUQ jacket platform and the countermeasures that should be taken by the workers before ice-induced vibration damage occurs. In the fourth part of article, the mechanism of flanges and the cause of the flange leakage in the winter of 2000 are given. The whole work is generalized below:1. Based on the data monitored on the platforms of JZ202 MUQ and MSW in Bohai Sea in several winters, human fatigue is evaluated on the platforms referring to the ISO standard concerning the human body in vibration environments. The natural frequency, amplitude of equivalent acceleration and equivalent exposure time of two platforms are determined according to the ISO standard. After comparing with the ISO standard, the conclusion reveals that on one of the platforms, the ice-induced vibrations may decrease the working efficiency in normal conditions, and in heavy situations, crew workers may have problems of body fatigue. On another platform, the crew may feel uneasy in normal situations and their work efficiency may decrease in heavy states.2. By analyzing the data of the velocity, thickness of the ice, and the deformation response of the JZ202 MUQ jacket platform monitored in several winters, we foundthat there was a close relationship between the velocity, thickness of the ice, and the deformation response of the jacket platform. By analyzing the data, we give the formula of velocity, thickness of ice and the deformation of the jacket platform. Based on this formula, the pre-warning of the equivalent acceleration and equivalent exposure time at the MUQ jacket platform is given. Considering the frequency of the JZ202 MUQ jacket platform based on the ISO criterion of human fatigue in vibration condition, the pre-warning system of human fatigue at the JZ202 jacket platform is given. At the end of this part, the countermeasure for reducing human fatigue due to ice-induced vibration before the ice induced vibration damage occurs is given. 3. After researching the previous work done in the leakage of flange, we analyzed the mechanism of the flange. It is also indicated that the ice-induced vibration is the main cause of the leakage of the flange on the JZ202 MSW platform in 2000. Research on the pre-warning system to protect against ice-induced vibrations like those that took place on the JZ202 MUQ and MSW jacket platform is a very complex and systemic procedure. There is still a great deal of work that needs to be done. Research on the pre-warning of tubular joints fatigue of the jacket platform and other work concerning flanges is still necessary. Some of these works have been completed, while some still require more work.