Research On Fault Tree Analysis Software For Ocean Engineering

Offshore structures are large-scale and multifunctional products, the application of complex systems and harsh marine environment will lead to many failures of them.Furthermore, possible accidents such as collision, fire, explosion and corrosion may cause environmental pollution and casualties. The reliability of offshore structure is always a focus of attention.Fault tree analysis (FTA) is one of the major methods in safety system engineering and widely used to evaluate reliability of complex systems. Based on FTA and the characteristics of ocean engineering, the FTA software for ocean engineering is developed in this thesis, the main research contents are listed below:(1) Considering the systems of offshore structures are complex, the FTA algorithm for large fault trees is researched, which adopts numerical array to encode fault trees. Through the numerical operations between arrays, the non-deterministic polynomial problem is solved and the qualitative and quantitative analysis is completed to calculate the parameters (minimum cut sets,non-cross minimum cut sets,minimum path sets,occurrence probability of top event and importance of basic event) of a fault tree.(2) Considering offshore structures contain many units with a variety of life distributions,it is difficult to calculate reliability parameters using an analytical method. The method of reliability numerical simulation is studied,which adopts Weibull distribution to fit failure distribution functions of basic events. The Monte Carlo method is used to sample the lifetime of basic events, the occurrence probability of top event is calculated through the structure function of the fault tree. Moreover, the time-varying curve of system unreliability is obtained.(3) Considering offshore structures are repairable, the method of reliability numerical simulation for repairable system is studied. Through sampling failure and maintenance time of the units, the time arrays of state changing are created. The system failure time of each simulation is calculated based on minimal cut sets of the fault tree.(4) The FTA algorithm is implemented by MATLAB. The GUI development environment is applied to make the interface of FTA software, subsequently the instruction of which is introduced. Finally, the reliability model of offshore floating wind turbine is built and the reliability evaluation used the FTA software is conducted for it.