Experimental Study On Three New Types Of TMD Based On Electromagnetic Damping And Its Control Of Footbridge Vibration

With the rapid development of the construction indu stry,there are many typical large-span,lightweight and flexible structures.This kind of s tructure has small damping and low natural frequency,so it is easy to resonate and even cause structural damage.Therefore,the application of structural vibration control in this kind of structure is more worthy of study,and the most commonly used is to install dampers for vibration control.The existing research on damper has been quite extensive,among which eddy current damper is favored because of its simple f abrication.The main highlight of this paper is to consider the influence of the magnetic fo rce generated by the traditional eddy current damper and the moving magnet after installing the magnetic iron plate on its damping performance,and apply the magnetic force to improve the damping performance of the damper,design and manufacture the eddy current magnetic hybrid damper,and then make the magnetic damper to study the magnetic force as the damping eleme nt alone.Finally,considering the influence of temperature on the conductivity of copper plate,an intelligent temperature control eddy curren t electromagnetic force hybrid damper is designed.This paper studies the subject from the following aspects(1)Taking the traditional eddy current damper as the r esearch object,firstly,through theoretical analysis,the different properties of copper an d iron are introduced to show that the direction of the magnetic force between the magnetic iron plate and the moving magnet is not perpendicular to the direction o f motion.Then,the design and manufacture process of the eddy current damper are introduced,and the performance of the eddy current damper is tested and analyzed.Finally,the vibration reduction of the footbridge in the laboratory is controlled by the e ddy current damper.The vibration reduction rate of the eddy current damper before and after the installation of the magnetite plate is mainly discussed,and the vibration reduction rate under different excitation amplitude and frequency is compared.The results show that the magnetic force between the magnetite plate and the moving magnet of the traditional eddy current damper will reduce the vi bration reduction performance of the eddy current damper in the low damping state.The acceleration damping rate can be reduced by 8%.(2)Based on the research of magnetic force,a new magnet is introduce d to change the properties of magnetic force(sucti on or repulsion),and then an eddy current magnetic hybrid damper is designed to improve the damping performance of the damper.Firstly,the principle of vibration reduction and structural vibration control model are introduced.Then,three different magnetic circuits of eddy current magnetic hybrid damping element are designed and the manufacturing process is introduced in detail.Finally,it is applied to the pedestrian bridge for vibration reduction test.The influence of magnet size and magnet polarity on its vibration reduction performance is discussed.The results show that the proposed eddy current magnetic hybrid damper can further reduce the vibration response of the structure on the basis of the eddy current damper vibration control.Under the optimal magnetic circuit design,the maximum vibration reduction rate of eddy current magnetic hybrid damper can reach 95.9%,which is 6.8% higher than that of eddy current TMD under the same working condition.(3)Then,considering the magnetic force as a dam ping element,a magnetic damper is designed and manufactured.Its working principle,hysteresis loss,calculation method of hysteresis loss and its damping control model are introduced.Then,the manufacturing process is described in detail,and its own parameter test is carried out,and the influence of different magnet spacing and different magnetism on its damping ratio is obtained.Finally,it is used to control the vibration of footbridge,and the vibration reduction rate under different magnet spacing,different magnetism and different excitation is discussed.The results show that there is the best spacing and the best magnetic circuit,which makes the magnetic TMD have good vibration reduction performance.When superharmonic resonance occurs in the s tructure caused by pedestrian load,the vibration reduction rate is 59.2% after installing magnetic TMD,which has good vibration reduction performance.(4)Finally,in order to solve the influence of temp erature on the performance of eddy current damping,an intelligent temperature control eddy current electromagnetic force hybrid damper is designed and manufactured.Firstly,the mechanism of temperature on copper conductivity is analyzed,and then the manufacturing process of intelligent temperature control system is introduced.Finally,it is used to reduce the vibration of footbridge.The test results show that th e vibration reduction performance of the eddy current damper will decrease when the copper plate temperature rises after long-time working.At this time,the intelligent temperature controller will electrify the electromagnet and conduct the eddy current electromagnetic force hybrid vibration reduction,which will effectively improve its vibration reduction performance and solve the influence of temperature on it.