Prototype Measurements And Analysis Of Ice-resist Offshore Structures

The offshore platform is a very important facility in the offshore oil exploitation. There are still many uncertainties in the design of offshore platform, which had induced many security risks in the service period of it, although the design of it has been developing for more than half a century. The offshore platform is a very complex engineering structure which usually suffered from various complex loads. The conventional methods, such as theoretical analysis, numerical simulation and model test, can not solve satisfactorily the existing problems of the offshore platform in service. Thus, the prototype measurement is needed for the real offshore platform in field, through which we not only can get the real load and response information to verify the problems in the design and service process, but also can provide early warning information on the risk of the structures. Therefore, the prototype measurement methods of offshore platform structures have attracted increasing attention widely in recent years.However, there are still many theoretical and technical problems in the prototype measurement on a real complex offshore platform, such as how to design the prototype measurement system, how to obtain the desired and complete data in field, how to deal with and use the real measured data and so on. Therefore, the prototype measurement is designed specifically for each project using the theoretical analysis and numerical simulation methods and some experiences. Secondly, we need to solve the measurement technical problems in the prototype measurement according to the realistic conditions. Sometimes, we need to monitor the prototype structure continuously so as to capture the desired information. Finally, analysis and evaluation of the measured data provide a guide of the design and operation of the structures. The modern monitoring technologies and the numerical analysis methods are very helpful to the researches on the prototype measurement method. Actually, researches on the prototype measurement method and related technologies are very hot not only in ocean engineering but also in other engineering.This dissertation deals with the prototype measurement method of the service platform for solving some uncertain problems in the design and operation process of the platforms in Bohai. The prototype measurement method has been used for various problems including the ice force problem, ice-induce vibration risks analysis and warning, the evaluation of the ice-resist design. The studies in this dissertation are also useful for other engineering prototype measurement research, although the work is based on the offshore jacket platforms. The main works of this dissertation are as follows:1. The research on prototype measurement technologiesMore than a dozen ice-resist offhore jacket platforms were established in Bohai Sea of China since the early 1990s. Much prototype measurement research work had been taken on these platforms by Dalian University of technology. I have joined the prototype monitoring work for five winters and improved the on-site monitoing system. A shared prototype monitoring system was designed for the problems induced by ice, such as ice force problem, ice-induce vibration risks analysis and warning, the evaluation of the ice-resist design and so on. Furthermore, more analysis and research work had been taken on the core technologies of prototype measurement on ice-resist strcutures. These work built a nut foundation for further prototype measurement research on ice-resist strucutres in Bohai Sea.2. The research on prototype measurement of ice forceThe ice force is the dominant force for offshore platform in cold regions, and also is the main uncertainties in the ice-resist structure design. The ice force is produced by the ice-structure interaction process. There is not a very well-developed method for numerical simulation and model test of ice force. Therefore, the research of ice force through prototype measurement method is the main primary means in ice force research and widely adopted in many countries. In this chapter, complete measured data for the establishment of dynamic ice force and extremum ice force, were obtained through direct ice force measurement, indirect ice force measurement and ice parameters measurement on the prototype structures in Bohai.3. The research on ice-induce vibration risks through prototype measurement methodDue to the behindhand research on the ice force, especially the dynamic ice force, the offshore platform is very dangerous in cold regions. As there are many uncertainties in the design of the ice-resist platforms including the uncertainty of the failure mode of ice-induced vibration. In this chapter, the failure mode and failure criterion of the platforms in Bohai, are analysed through prototype measurement method. A prototype monitoring system was built in field to evaluate the ice-induce vibration risks; A prediction model was established for ice-induced acceleration forecast, based on the monitoring information; Finally the warning criterion and processes were proposed.4. The research on evaluating ice-resist design through prototype measurement methodThe researches on ice-resist design in Bohai are very hot recently. Many methodologies were proposed including the ice-break cone, the isolation technologies and so on. It is a key problem that how to test and evaluate these new methodologies used in ice-resist structures design. This dissertation proposes a method for the first time to evaluate the design through prototype measurement method. It has a very high value for the ice-resist structure design, as it can well compensate the shortcomings of the numerical analysis and the model tests in the laboratory. The main works includes the prototype monitoring on the platforms before and after the adding cone changing; the prototype monitoring on a new design ice-resist platform and the evaluation of the ice-resist design based on measured data.