Research On Loose Identification Technology Of Wind Turbine Tower Flange Connection Bolts Based On Influence Line

China’s energy industry is undergoing major changes in sustainable development.In order to achieve the strategic goal of peaking carbon dioxide emissions by 2030 and carbon neutrality by 2060.The development of clean energy ushered in unprecedented opportunities.Wind energy is one of the most important sustainable clean energy sources.It puts forward higher standards for the stability and safety of normal operation of wind turbines,and improves the strength and fatigue resistance of connecting parts.Real-time monitoring is required.In this paper,through the on-site collection and analysis,the strain influence line of the wind turbine tower flange connection based on the change of the nose azimuth angle is established,and the theoretical model for the evaluation and positioning of the loosening degree of the tower flange bolts is proposed,and the finite element analysis software ABAQUS is used.Verification of multiple working conditions,the main contents are as follows:(1)Based on the basic principles such as the assumption of plane section,the force model of flange bolt group based on local bolt loosening is established;the concept of influence line is introduced,and the looseness detection method of wind turbine tower connection flange based on the influence line of compliance coefficient is proposed;By drawing the nose azimuth angle-compliance coefficient curve,the identification and degree evaluation of local bolt loosening in the main wind direction can be realized.(2)A finite element analysis model of the bolt group of the wind turbine tower connection flange is established,and the dynamic behavior of local bolt loosening in the main wind direction is simulated.The calculation results show that the finite element calculation value of the nose azimuth angle-compliance coefficient is basically consistent with the theoretical results,and the bolt loosening position and degree can effectively reflect the actual stress situation,which verifies the effectiveness of the bolt loosening online monitoring method proposed in this paper.It can be applied to practical projects.(3)According to the fact that more than two main wind directions are prone to occur in the actual engineering environment of wind turbines,and the bolts at the corresponding positions are prone to loosening due to wind fatigue,a theoretical analysis model and finite element calculation example of the bolt loosening sector in double main wind directions are established.The calculation results It shows that when the measuring point is close to the bolt loosening sector,the strain value response is more sensitive.In actual engineering,multiple measuring points must be arranged to verify together.Multiple main wind directions and different loosening sectors can effectively realize the identification of local bolt loosening position and degree.(4)The wheel hub speed is approximately regarded as the equivalent load of the wind turbine tower,and an online monitoring and evaluation method for the loose identification of wind turbine tower flange connection bolts based on the influence line is proposed.Strain gauges are arranged in orthogonal orientations,and connected to the wind turbine SCADA system at the same time,and the upper unit parameters such as wind direction angle and hub speed of the wind turbine are collected synchronously.Online monitoring and evaluation of the looseness of the connection bolts of the tower connection flange.