Simulation Research On Fatigue Life And Crack Growth Of Ocean Jacket Platform Structure

Jacket platform is a common marine structure form which has been widely appliedfor a long time. It can inevitably get aged with damage due to long time working incomplex ocean environment. Considering the cost,a large number of old jacketplatforms have been imported and rebuilt by our country so that they could continue tobe used. So it is necessary to assess the safety of these old platforms with damages,which requires not only the consideration of overall life but also the remaining life ofthe old platforms which bear damages.This article takes a jacket platform as an example, using the finite elementsoftwares to calculate its response in the wave flow coupling case,then it discusses thesafety performance during its service time,and figures out its fatigue life when thestructure suffers random waves.Firstly, the author looks up the fundamental data about jacket platform structure,thesteel product materials,fatigue SN curve and so on, which provide the necessary basicdata for the following tasks of simulation analysis.Secondly, this article states the load condition of the jacket platform in thecomplicate ocean environment. The author utilizes the ANSYS software to build up theoverall model of the platform, according to the theory of wave design method, and thenthe author gives load to the finite model and calculates the response according to thestatistic data of the sea current water and the sea wave nearby the platform,to judge thesafety and the strain-stress range of the platform.Thirdly,the author obtains the first six steps of the modal and calculates thedamping coefficient of the structure by means of the software of ANSYS.Then buildspartial modal-tube joints of the jacket structure,and calculates the factor of the stressconcentration SCF. The author sets up the partial modal-tube joint of the jacket structure,uploads it and goes for the strain-stress result of the platform structure.On the basis ofstating the method of SN,using the theory of Airy wave, selects reasonable data of seawaves to loads the finite model,calculating the time-stress response of the structure,andthen calculates the fatigue life with the SN curve and rain flow counting method.Finally, in accordance with the crack growth theory and the Paris formula,thearticle imports finite model of the tube joint via simulation analysis. Then it examinesthe cycle life time from crack emerging to fatigue fracture happening,suffered different stress range or with different initial crack length. It tests the coverage and the degree ofthe impact which crack has on the carrying capacity of the structure. It can put forwardreasonable suggestions on the examination and repairing of the jacket platform.