Response Calculation Of Multi-Module VLFS And Analysis Of Dynamic Characteristics And Structure Optimization Of Connector

Very Large Floating Structure is a new type of offshore floating platform which is connected by a number of modules with length of 250?350 meters through specific connectors.Because of its long-term layout on the sea,it is easily affected by bad sea conditions,which inevitably leads to a series of strength problems.This paper investigates on a primarily designed VLFS,including the following three parts of the core content:predicting the fatigue life of single-module of VLFS through the S-N curve fatigue analysis approach based on design wave;Based on the three-dimensional potential wave theory,the connector dynamic characteristics and hydrodynamic response of floating body are analyzed in-depth;Making numerical simulation analysis for the connector model designed and used in simulation experiments and then the structure of the connector is optimized for the satisfaction of the stiffness requirement.Through a gradual approach,some work has been done for the study of VLFS.The main work of this article is detailed as follows:1)The research significance and the research status at home and abroad of VLFS are introduced.At the same time,the fatigue research methods based on S-N curve are reviewed.2)Hydrodynamic response and overall strength of VLFS single-module are analyzed by ANSYS software,and then three hot spot locations are identified for subsequent fatigue strength checks.Characteristic hydrodynamic responses are used as the control load parameters to determine the six group of design waves,and then the fatigue damage and life of the dangerous spots are calculated by using the S-N curve method.Compared with the results of spectral analysis,the rationality of the design wave method applied to VLFS is analyzed.3)The software Sesam which based on the three-dimensional potential wave theory is applied to calculate the hydrodynamic coefficients and wave loads of 5-modules MOB.Motion equation of the floating multi-body system into which connector forces introduced is established and solved to obtain the connector dynamic characteristics and hydrodynamic response of floating body.Firstly,the short term predictions of connector forces and motion responses are calculated in consideration of 60 connector stiffness cases and then the rational connector stiffness option is determined.After that,the impacts of connector transverse positions and adjacent modules space on the module motions and connector forces are analyzed.Finally,the key factors that impact on the connector longitudinal force are discussed.The result shows that the optimal connector transverse position is ±45 meters,the optimal adjacent modules space is 20 or 25 meters and the relative yawing motion and wave angles have a great impact on the connector longitudinal force.4)Using ANSYS software,the finite element modeling analysis of the connector model designed and used in simulation experiments is carried out.The effects of unidirectional load and combined load on the stiffness of the connector are investigated.Then the connector is simulated in the form of actual load and the lack of the structure is analyzed.The optimization design of the connector structure size is carried out to make the connector meet the requirements of the design stiffness.