Research On Digital Technology For Safety Assessment On Offshore Jacket Platforms

Digitalization of Offshore platform safety technology is not just a new concept. Although theoretical basis, technical data and engineering applications involved in it are built on the existing knowledge, digital safety simulation develops and integrates existing knowledge from a higher level and point of view of system theory and integration, thus it's beneficial for mining and using various data of existing platforms more comprehensively, more deeply, and more effectively, performing simulation based structure safety analysis,which ensures the safe operation of platforms. It plays an active role in improving the safety and life-cycle management of our country's offshore platform.Relied on a special issue of National High Technology Research and Development Program of China--"Offshore Aged Platform Life Extension Research", National Natural Science Foundation of China--"the Research on Life Prediction, Management Theories and Methods for the Aging Platform Life Extension Project", and Natural Science Foundation of Shandong Province--"Study on Offshore Structures Virtual Safety Theory and Its Application", in this paper the offshore fixed jacket platform is its study object, new idea about building digital safety technology systems of a marine engineering structure is proposed, and the research on jacket platform digital safety simulation and its application is carried out systematically. The studies in several aspects including offshore platform environment digital loads modeling, offshore platform digital structure modeling, offshore platform ice-induced fatigue load modeling, complex tubular joints modeling method, platform collision risk assessment, dynamic nonlinear analysis of platform progressive collapse, aged platform life extension decision-making model, platform digital safety simulation environment, technical systems of offshore platform safety assessment, marine structures digital safety simulation software development and so on, have made great progress, which can provide effectively technical support for the drilling and producing equipment safety of China's offshore oil and gas resources. Main researches are summarized as follows:1. Study on offshore jacket platform digital load modelModeling steps of the marine platform digital load model is studied; system framework of marine platform digital load model is designed and the corresponding 6 digital load calculation modules are developed, i.e. sea wind load module, wave load module, ocean currents load module, sea ice load module, seismic load module and pile-soil digital module. Offshore platforms digital load module program development is achieved. Ice-induced fatigue load division method in the traditional approach misses mutual relations'impact among the ice speed, ice breaking cycle, platform natural frequency; thus it is difficult to meet the need of platform fatigue life fine assessment in ice zone. Based on two basic forms of structural resonance and non-resonant vibration existing in ice-induced platform, a new environmental load model of assessing platform ice-induced fatigue life is proposed. This model divides ice load ice-breaking cycle by considering the structure natural cycle; therefore it can effectively ensure that most of the structure ice-induced resonance working conditions will not be missed when they are divided.2. Study on offshore jacket platform digital structure modelThe equation mapped from intersecting line in structure space of tubular joints with complex space to circular planar ring is proposed, and on this basis, the uniform and fine modeling method for complex tubular joints is presented. The key technology for complex tubular joints to achieve digitalization and digital tubular joints unified modeling process are studied and a theoretical model is provided for complex tubular joints'modularized design. Offshore platforms coupling system analysis program is developed; and the difficult problem that offshore platform pipe-solid element coupling fine local analysis is not able to be achieved by ANSYS software sub-model method, is solved. The creative proposal that Stress concentration factor be calculated separately by dividing complex tubular joints into eight blocks along the tube wall is put forward, on which complex tubular joints stress concentration factor calculation module is developed. The modeling principles of offshore jacket platform digital structure simulation is studied, and a system framework of ocean platform loading digital mode is established; through setting up structures key nodes in the digital model, digital modeling modules for jacket platform integral structure and local fine structure are developed.3. Offshore Platform Collision Risk and collapse analysisBased on the ship-platform collision system model, ship types, average speed, shock loads involved in offshore jacket platform collision are analyzed; the study on risk of collision between ship and platform is conducted including the ship's collision probability, loss of energy, collision consequence analysis, and social risk assessment and individual mortality assessment analysis is conducted by taking Shengli Oilfield sea area platform collision as an example. Considering the dynamic non-linear response processes of structural failure, taking cylinders in platform splash zone as key initial failure components, equivalent static model of platform structure happening initial destruction is established. Based on the instantaneous load method, dynamic response process of vibration caused by platform structure local mutation is analyzed and dynamic response detailed analysis process of marine platform continuous collapse is suggested.4 The platform life extension decision-making under uncertain environmentPlatform whole life cycle cost is analyzed and major risks of platform running are studied. Analysis and adjustment is conducted from four dimensions----engineering factors, structural factors, load factors and risk factors which affect platform service state, and hiberarchy structures are built; adopting fuzzy theory, positive inverted value matrix is established, and weight of each factor is calculated by integrating experts'advice. Introducing depression factor, crack factor, corrosion factor, as well as the ice load factor quantifies factors reasonably and establish marine oil aged platform life extension decision-making score criteria. Using logical computation calculates a comprehensive score, and establishes aged platform life extension decision-making reference tables, thereby based on the table to determine platform life extension reference period. Utilizing decision-making model, life extension decision-making for two marine platforms is proceeded and comparative analysis between the results and the traditional evaluation results is conducted. The study results indicate that using this model, the platform dynamic economic life is able to be described more accurately, and a new computing idea can be provided for aged platform life extension decision-making under complex and uncertain environment.5. Offshore Platform Digital Safety Simulation System DevelopmentOffshore platform digital safety simulation system framework is set up; digital platform data are divided into seven categories and SASOS software system database development is completed; offshore platform digital safety virtual simulation environment module development is achieved which is composed by three dynamic link libraries including the geometry dynamic library, graphics dynamic library and geometric kernel library;platform safety assessment module is developed which can achieve platform structural integrity assessment, maintenance decision evaluation, strengthening effect assessment and the remaining life assessment; and jacket platform digital safety simulation system software SASOS is developed; by visiting database module, this software can automatically generate offshore platform digital loads model, the overall structure digital model, the local structure fine model, the structure service damage model and maintenance and reinforcement model; SASOS software is divided into 12 functional modules: project management, platform database, virtual display module, digital load module, digital structure module, design level assessment module, ultimate loading evaluation module, the structure damage assessment module, residual life assessment module, the collision risk assessment module, progressive collapse simulation module, and life extension decision-making module. Finally, engineering demonstration application assessment is carried out for two platforms in Shengli Oilfield by this software.