Current Load Model Orient To Failure Modes Of Underwater Structures

Current load is one of the most important environmental loads for underwater structures in marine engineering.In deeper water,the spatial non-linearity along the depth,the strong random and non-stationarity in the time domain make current load have much uncertainty.The structural design and mechanical analysis of underwater engineering thus faces great challenges.It is of great significance to establish accurate current load models for security service,reducing the cost of development and guiding production operations.From the viewpoint of mechanical analysis,the current load is closely related to the mechanical failure behavior of the floating structures and the underwater structures.Current load usually acts on the structures in a variety of forms,including the drag force,joint forces with wave and causing the vortex-induced vibration of flexible structures.The above problems can be summarized as strength failure and dynamic failure problems of underwater structures.Therefore,it's very necessary to carry out the research on current load from the mechanical background and consider the failure modes of underwater structures.Besides,it also needs to combine new theories and methods with regard to complex spatio-temporal distribution characteristics of current load.This paper carried out the research on measured current load in the South China Sea based on the field monitoring data.From the structural failure modes,two types of current load problems in marine engineering were solved specially and more general analysis methods of current load have been discussed.With the basic statistical characteristics,such as the distribution of speed and direction,typical periods,probability distribution,etc.of surface current firstly analyzed,the design verifications for platform position and main moorings were carried out.Secondly,ACER method was adopted to carry out the large profile current extreme value prediction and design verification.The FPS design index needs to be modified in the deep water area according to the actual engineering practice,while the TLP design index is closer to the predicted value.Furthermore,the adopted correlation analysis shows that the measured current has strong correlations in adjacent space,and current load models considering correlations were established.In order to solve the problem of underwater structural strength failure,current load models based on inverse reliability method were proposed.Aiming at the of underwater structure dynamic failure,a method of identifying characteristic profiles based on CLARA clustering was proposed,and 28 kinds of measured current load models were presented through this cluster analysis from the tens of thousands of original measured current profiles.Finally,the direction was introduced to the existing model of strength design.With the correlations between high-dimensional variables analyzed,three-dimensional current load model was established.The results of contrast analysis with measured profiles verified the accuracy and completeness of the three-dimensional model.