| Wind energy has been widely used as a kind of clean energy.The foreign wind power industry started earlier and developed more maturely.The domestic wind power industry has also risen rapidly.The installed capacity and total power generation have reached forefront level of the world and can maintain growth every year.For such a huge wind power industry,there are still many imperfect areas in its construction,operation,and management systems.The industry norms and standards have not yet been unified.Many safety standards need to learn from other similar building codes or rely on engineering experience,which leads to frequent wind turbine safety accidents and causes loss of life and property.Bolts are an important component of a wind turbine and are responsible for the interconnection of the main components.However,the wind turbine is exposed to alternating wind loads for a long time,and the bolts are easily loosened,which will affect the fatigue life of the structure.Once the cracks are formed,the wind turbine tower may become unstable and collapse.Scholars at home and abroad have done a lot of research on the safety design of wind turbine towers,but rarely study the impact of bolt fracture on the structure.This paper takes the FD77C wind turbine tower of a wind farm in Haixing as the research object,establishes a wind turbine model with flange bolts,uses numerical simulation to study the impact of flange bolt fracture,and at the same time uses theoretical calculations and experimental test results.Verification and analysis of the influence of bolt fracture on structural static force,modal and fatigue,has a great reference value for the evaluation of the research on fan flange bolt fracture.The main research contents and results are as follows:(1)The basic theory of wind turbine tower calculation is reviewed,and the overall model of wind turbine with flange-bolt is established.The results show that the strength of the wind turbine and the tower displacement meet the design requirements of the wind turbine,and the calculation and test results are in good agreement,thus verifying the reasonable reliability of the model.(2)Using ABAQUS software,a finite element calculation model is established,and the stress and strain analysis of the flange,sugar ratio and bolt structure under 11 working conditions are carried out.The research shows that after the bolts are broken,stress concentration is prone to occur at the bolt hole of the flange where the front bolt was not broken,the junction of the flange-tube wall and the flange chamfer.As the number of bolt fractures increases,the flange yields first,followed by the bolts,and the tower wall yields last,and the plastic deformation range expands.(3)With the increase in the proportion of bolt fracture,the displacement of the tower top increases,and the increase in displacement increases,and the bolt fracture at FL1 has a greater impact on the tower displacement than the bolt fracture at FL2.Therefore,the rapid change of the displacement of the tower top can be used as an observation index to determine the fracture situation and position of the bolt.(4)The wind turbine tower is analyzed by numerical modal analysis method,and the first 6-order frequency and mode shape of each working condition are obtained.The results show that when the bolt at FL1 breaks,the first order frequency of the tower is the most sensitive,the second order frequency is the second,the third and fourth orders frequency are the least sensitive,and the higher order is basically unchanged;when the bolt at FL2 breaks,the third order of the tower frequency is the most sensitive,the first order frequency is the second,the second and the fourth order frequency are the least sensitive;therefore,it can be judged whether the bolt is broken according to the low-order frequency of the tower.Flange vibration mode is very sensitive to bolt fracture,so the flange 3rd and 4th vibration mode can be used to monitor whether the bolt is broken..(5)According to the fatigue analysis theory,a numerical model of pulsating wind was established,and the fatigue life of the wind turbine tower when the bolts are broken is calculated and analyzed.The study shows that when the wind turbine tower has been running at the rated wind speed,if the bolts are not broken,the stress amplitude of each key point of the fan is small,and the fatigue damage can be ignored;if the fatigue damage of each key point increases sharply after the bolt is broken,the damage at the flange hole is the largest,and the life is only 97 hours,the flange chamfer is second,and the cylinder wall is the smallest.Therefore,during the operation of the wind turbine,whether the bolts are broken should be monitored at all times.After the bolts are broken,the machine should be shut down and repaired in time to avoid cracks in the tower and affect the safe operation of the wind turbine. |
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