Research On The Structure Crack Monitoring Of Offshore Platform Based On Distributed Optical Fiber

As an important equipment for the development and utilization of resources on marine,the offshore platform structure has to work in the ocean environment with high temperature,high salinity,and high humidity for a long time,and it's continuously affected by loads such as wind,waves and currents.The structure of the platform at different positions causes various forms of damage.As the main facility of the main deck of the offshore platform,the living building does not directly serve as the load-bearing structure of the overall platform,but it is still necessary to pay attention to damages such as cracks.This paper takes a certain offshore platform living building as the analysis object.Due to the large span of the living building,the both sides of structural participate in the overall platform strength,and cracks of different degrees are generated at the four corners of the living building.Therefore,several reinforcement schemes for cracks in the living building were designed.Extract the motion parameters under the survival conditions,and consider the wind load at the same time to check the reinforcement plan.The finite element results show that the reinforcement scheme can effectively reduce the stress concentration at the four corners.Then the Extend Finite Element Method(XFEM)is used to simulate the crack propagation process when the initial crack is existence,and install the toggle plate at the corresponding position can effectively suppress the expansion of the initial crack.However,the size of the toggle plate will be restricted by many factors.According to the characteristics of the gradient distribution of the strain during the crack propagation process,a multi-scale strain monitoring scheme using distributed optical fiber sensors is proposed.To verify the performance of one-dimensional strain monitoring of the distributed optical fiber,the continuous displacement result of the beam is obtained by designing the beam deformation test.And according to the strain distribution in the finite element crack growth results,the multi-scale strain extraction scheme based on distributed optical fiber is determined.The 20-dimensional multi-scale strain in the simulation results is used as the sample feature,and the corresponding crack length is used as the sample label.Taking multi-scale strain and crack length as the characteristic input and output respectively,the Support Vector Regression(SVR)crack length prediction model is established.The SVR model parameters C and g are obtained through three-fold cross-validation combined with particle swarm algorithm,and the model prediction error is about 2%.The model is randomly divided into training set and test set,to train and verify the model respectively.When the test set and training set each account for 50%,the model has better prediction results.The noise level about1?10% is adding to the sample,to test the system Resistance ability.The result of analysis shows that the model has a good ability to suppress noise level within 5%.