| Wind energy is a kind of sustainable and clean energy.It has been widely used and occupies an important place in new energy system of China.Wind turbine plants are one of the most critical equipment in wind power generation.For offshore wind turbine plants,they are excited by wind and wave loads for long time.These loads not only influence the operation of wind turbine plants,but also can bring wind turbines with fatigue.They are key factors of the damage of the wind turbine plants.Many accidents of the wind turbine plants caused by structural damage occur every year,which affects the stability of wind power production and leads to serious economic losses.Therefore,it is of great significance to investigation the dynamic stress and fatigue life of wind turbine plants with multi-state states.Moreover,the load of wind turbine plants depends on climate and regional characteristics.The loads of wind turbine plants are obviously uncertainty.Therefore,the reliability design of wind turbine plants should take uncertainties into account to accurately analyze the reliability of wind turbine plants.The object of study in this thesis is a 5MW wind turbine plant.The wind and wave load of it is numerically investigated.Based on the dynamic stress results,the fatigue life and reliability are analyzed.The main work of this thesis is as follows:1)The finite element model of the wind turbine plant is established.By comparing the frequency results of the beam element model and the multi-scale finite element model with the frequency results of the references,the accuracy of the finite element model established in this paper is proved.Based on the stochastic wind and wave theory,the wind and wave loads simulation methods based on the harmonic superposition method are established.Based on the above method,the wind and wave loads under five situations within the range of 5 m/s-25 m/s are obtained;2)The ANSYS software was used to complete the transient analysis under the situations of only wind load occuring,only wave load occuring and wind and wave load boht occuring.After the transient analysis,the time-history of displacement,acceleration and stress of the wind turbine were obtained.The static analysis of the wind turbine under eight working conditions within the range of 0°-180° are carried out.And the thehot spot stress coefficient of different situations are obtained and the stress mapping relationship between the beam element model and the multi-scale finite element model are established.Based on the rain flow counting method and linear damage theory and S-N curve,the fatigue life assessment methods of wind turbine based on nominal stress and hot spot stress are established respectively.After the life assessment of the wind turbine plant,the fatigue life of the hole and flange is20.13 years and 21.76 years when the wind and wave load occurs simultaneously,which indicates that the design of the wind turbine plant meets the requirements of safety and long-term service;3)Based on the polynomial chaos expansion method,a reliability assessment method for wind turbine plants is established.To overcome the problem that the Monte Carlo method requires a large number of sample points and is likely to cause “dimensional disaster”,sparse sample generation technique is established based the Smolyak algorithm.Compared with the Monte Carlo method,the method established in this thesis can greatly reduce the number sample points required for random process evaluation and shorten the calculation time.By comparing the reliability evaluation results under different working conditions,it can be found that the wind turbine can operate safely and stably when excited by wind and wave loads. |
PDF Full Text Request