Reliability And Risk Assessment Of VIV Power Generator

In recent years,governments have to think about energy conservation and emission reduction because of the warning of climatic damage.In order to decrease dependence on fossil fuels,energy companies and researchers turned their eyes on the research of clean renewable energy,and a series of achievements have been made.Although the renewable energy is one of the main sources of energy since the beginning of human development,the concepts have changed in today's research.A major trend of nowadays renewable energy research is how to extract energy from fluid(wind,rivers and oceans)steadily and rapidly.As the exploitation of different kinds of renewable energy,the installed capacity is improved constantly,which leads to the growing of security requirements.Risk and reliability analysis is reasonable and imminent in such case.Ship Vortex Induced Vibrations for Aquatic Clean Energy(VIVACE)is a Converter of horizontal Marine Hydro-Kinetic(MHK)energy invented by the Marine Renewable Energy Lab(MRELab)and the University of Michigan.The device harnesses hydrokinetic energy of ocean/tidal/river currents.Using Passive Turbulence Control(PTC),VIVACE maximizes and utilizes Flow Induced Motion(FIM)in the form of Vortex Induced Vibration(VIV).The VIVACE Converter can harness hydrokinetic energy from currents as slow as 0.65 knots,while the lowest operational flow rate of water-mills/turbines is usually 4 knots.The failure probabilities of VIVAC are derived from experiments and practical texts in river.More than 2,000 hours of testing data is available from MRElab actual installation during 2009 to 2013.The importance degrees of failed components are also determined from the experiment based upon experts' advice.In this paper,taking VIVACE as a subject,a series of studies are conducted from the perspectives of risk assessment and reliability analysis according to experimental data.First of all,feasibility analysis for VIVACE has been conducted.In the first place,the mathematical model of power generation system is provided.According to the experimental results and single freedom theory,the model of vibration,frequency and energy formulas of each vibration system are put forward.The model can be used to calculate the conversion between mechanical and electrical energy of each vibration system.And according to several key parameters involved in the mathematical model,the experiment is designed to obtain the optimal energy curve,and then the power generation efficiency under different flow rates and the feasibility analysis of the system are verified.Secondly,considering less study on VIV power generation system,an overall reliability analysis and risk assessment for VIVACE is carried on based on its functions,subsystems and mission profiles.The reliability prediction block diagram is built to ascertain the relationship between the various systems.Accordingly the system diagram is established,based on which the RBD block diagram is accomplished with calculations of time curve of system availability.A preliminary understanding of elements and subsystems in risk analysis is performed during construction and service.Methodologies of ocean engineering risk identification during service are investigated,as well as the necessity of fault tree analysis.Studies on FTA of three subsystems of power generation system including PTO power generation system,Vck and mechanical conversion system are conducted and the devived results are given.References are provided for failure analysis and design of component parts and maintenance procedures of tidal current energy VIV generating devices.Timely maintenance to eliminate risk plays an important role in improving reliability of the devices.Thirdly,the related application of FMEA in ocean engineering reliability and risk analysis,particularly in the field of renewable energy has been carried out.Considering complexity of the generation system's mission profiles and existence of repeated elements between subsystems and components,by adding correlation analysis into FMEA,the failure mode correlation analysis is introduced and applied to the object under study in the paper,the vortex-induced vibration energy power generation device.FMEA of components of the system and the larger RPN failure mode analysis are obtained in this paper.Correlation analysis of main failure modes according to the theory of correlation is finally addressed and the whole analysis process is well done.The weakest failure mode groups are attained through PNET method,as well as the key elements,which are most likely to lead to the system failure.This work provides design and operational references for risk assessment of tidal energy VIV generating devices,and establishes the design criteria of risk analysis on complex offshore engineering.Finally,based on the risk and prognosis analysis of the system,the main failure modes of system are refined.On this basis,with the combination of the reliability and the weakest failure mode,investment-benefit risk analysis is proceeded.Starting from the whole mission profiles of the device,further evaluation of risk's influence on investment benefit is accomplished.Combined with the optimization algorithm,relative results is analyzed,which can be used for reference of investment...