Research On Vibration Reduction Characteristic Of Particle Damping System

Particle damping is a kind of passive vibration control technology.Micro particles are packed into an enclosed container which is attached to the vibrating structure,the vibration energy of the system is dissipated by the impact and frictional movement of the particle-to-particle and particle-to-container.The particle damping technology has the advantages of the frequency band of vibration reduction is wide,its structure is simple,it has good structural durability,and can be used in high temperature and other harsh environment.It has been successfully applied to mechanical engineering vibration reduction and other fields.However,the damping characteristics of particle dampers are difficult to predict due to complex collision of particles in the container.Therefore,the research on the damping characteristics of particle damping system has become an important part of domestic and foreign scholars.The damping characteristics of particle dampers are studied by both experimental and numerical simulations in the thesis.It simulates the whole structure and the damper system based on the discrete element,which has not been used by domestic and foreign scholarsFirst,the particle damping experiment based on single-degree-of-freedom cantilever beam was carried out,the effects of filling rate,particle size,particle material with different density,initial displacement and the position of the damper on the damping ratio of the system were studied.Then the particle damping experiment based on the single layer steel frame was carried out,the influence of filling rate,the installation position of the damper and the shape of the metal box on the damping effect was analyzed.The PFC3D program based on discrete element method was used to simulate the whole system.The main structure(cantilever beam,steel frame,metal box and fixed particles)was separated into the dense combination of many small particle units,and could achieve the continuous characteristics of solid materials through the parallel-bond model.The interaction among free particles is described by the slip model,and the contact force is calculated by the Hertz-Mindlin contact model.The damping characteristics of the particle damper was studied by the simulation of the free vibration of the single-degree-of-freedom cantilever beam and the forced vibration of the single layer steel frame under the sinusoidal excitation.Combined with experimental and numerical studies,the following conclusions were obtained:The filling rate of 75%or so more is reasonable,the internal space of the damper is fully utilized,so that the particle-to-particle and particle-to-container are fully collided and rubbed with each other.Damping particles should be selected with a larger density of materials,such as carbon steel,and even greater density of metal.The damping ratio of the system increases with the increase of the density of material.The choice of damping particle size is related to the external excitation(the initial displacement).When the external excitation(the initial displacement)is large,it is recommended to use particles with small size,so that the friction energy dissipation will increase effectively and the collision energy dissipation is utilized at the same time.The particles with larger size should be chosen when the external excitation is small,so that the collision among particles and container can be brought into full paly.The position of the damper should be installed in a position with a large amplitude in the direction of vibration of the system.The greater the initial displacement and the amplitude,the collision and friction among particle-to-particle and particle-to-container is more fully,the vibration effect is more obvious.Sinusoidal excitation vibration experiments were carried out with the same total mass,the same particle size,the same material,and the same number of particles by comparing the different cross-section(circular and square).The amplitude of the power spectral density of the steel frame at its first order natural frequency was collected.The length of motion path of the particles has a great influence on the damping effect when the number of particles is less than 100.At this moment,the motion path of the particles in the cylindrical metal box is shorter,the number of collision and friction times occurred in the unit time is more,and the vibration reduction effect is better.However,the height of particle layer has a greater influence on the damping effect when the number of particles is more than 100.At this moment,the height of particle layer in the square metal box is shorter and the pressure of the bottom particles is smaller,particles are easier to start vibration.The collision and friction within a unit time can be brought into full pay,the vibration reduction effect is better.