The Damping Characteristics Of Clearance-type Low Index Viscous Damper

Viscous damper is a new type of energy dissipation and damping device,which absorbs and dissipates energy from external input to achieve the purpose of energy dissipation and is widely used in the engineering field.Viscous damper is a type of velocity dependent damper.Generally,the velocity index of the damper ranges fro m0.3 to 1.0,and the magnitude of the velocity index affects the energy dissipation capacity of the damper.In the clearance viscous damper,the flow of fluid medium in the damping clearance can be considered as the flow of parallel plate gap.In this pap er,considering the physical properties of the medium,the calculation model of the output damping force of the clearance viscous damper is derived from the basic fluid mechanics.On the basis of the calculation model of output damping force,the double-out rod clearance viscous damper with four specifications satisfying the relation of F=Cv~a was designed,with the velocity index of 0.3 and the maximum damping force of 300kN,350 kN,500 kN and 1500 kN respectively.A simulation model was built in matlab-simulink for four designed clearance viscous dampers.The motion of the clearance viscous dampers under differ ent working conditions was simulated and their damping characteristics were analyzed.The simulation results show that the force-displacement simulation curve of the damper is a full ellipse with good energy dissipation performance.In the velocity-load curve,with the increase of piston speed,the output damping force is nonlinear,and the output damping force of the viscous damper is in good agreement with the design requirements.In addition,as a non-newtonian fluid,the shear thinning property of dimethyl silicone oil makes the viscosity decrease with th e increase of the shear rate.When the piston speed increases,the greater the shear rate of dimethyl silicone oil in the damping gap,the more obvious the change of dimethyl silicone oil viscosity,and the change of its viscosity value affects the output damping force of the viscous damper.The mechanical properties of four designed clearance vi scous dampers are tested,and the output performance of viscous dampers under different operating condition s is analyzed.The experimental results show that the force-displacement curve of the damper is a full ellipse,which is similar to the word"hui".The comparison theory is consistent with the experimental speed-load curve and the curve growth trend,which is basically consistent.The relative error of the output damping force does not exceed15%,which conforms to the national standard(JG/T 209-2012).At the same time,the experiment proves the correctness of the calculation model of the output damping fo rce of the clearance viscous dampers,and this design method is feasible for the design of the conventional clearance viscous dampers,which has impo rtant guiding significance in the practical engineering application.There is a certain lag Angle between the output damping force and velocity(F-V)of viscous dampers.Based on the simplified model of viscous dampers,the calculation expression of dynamic stiffness is derived,and the dynamic stiffness of viscous dampers of four specifications is calculated.With the gradual increase of piston motion frequency and amplitude,the piston motion speed increases,the dynamic stiffness value increases,and the greater the lag Angle,the more obvious the influence on the viscous damper output performance.It is proved that the dynamic stiffness caused by the compressibility of the medium leads to the generation of the hysteresis Angle.