| Rotor system is the core equipment that converts nuclear power into electrical energy in nuclear power steam turbine,in order to ensure its stable and safe operation,it is necessary to suppress the fatigue and fracture failure caused by the dangerous vibration of the blades.In the current project,the shroud structure is used to restrain the vibration by constraining the blade movement and consumpting energy through the shroud friction to increase the resistance.However,due to the fact that the shroud vibration displacement and contact-friction-separation time cannot be determined,the shroud friction damping cannot be calculated quantitatively and the shroud structure can only be designed based on experience,faced with the first design,manufacturing and then reexperimental simulation,analysis and optimization,which may cause technical problems such as "congenital deficiency" and waste of manufacturing resources to delay the production cycle.In this paper,the hysteresis differential equation of the rotor system considering the influence of the shroud parameters(contact angle,friction coefficient,contact stiffness,clearance)and rotation speed is established.Shroud friction internal damping quantitative calculation method(SDQM)is established and accurately design shroud dynamic characteristics for the design phase,the passive self-healing vibration suppressing technology that effectively uses the frictional energy of the blade shroud to consume vibration energy while improving the system stiffness solve the above problems.It provides theoretical basis and method for the design and manufacture of the turbine rotor system.It has important theoretical significance and engineering application value for ensuring the safe operation of the turbine.Taking a parallelogram shroud as an example,a three-dimensional macro-slip hysteresis friction model of the shroud considering the effects of friction coefficient,contact angle,contact stiffness,initial clearance and rotation speed is established.The shroud friction internal damping model was established based on the shroud friction model based on the harmonic balance method.Using CN group theory and finite element method to establish the hysteresis motion differential equations of the basic sector of the shroud-blade-rotor system considering the shroud friction internal friction and stiffness,and to solve the characteristic equation and the characteristic root of the corresponding homogeneous equation.According to the eigenvalues,a theoretical basis is provided for the subsequent establishment of the shroud friction internal damping quantitative calculation method.In the frequency domain,solve rotor system frequency response function considering shroud friction internal damping,and analyze the influence of the quality,damping and stiffness of the system on the dynamic characteristics of the system.According to the rotor system's motion differential equation,the quantitative calculation formula of shroud friction internal damping is solved,and shroud friction internal damping quantitative calculation method(SDQM)based on transient response amplitude envelope is established.Taking a low-pressure cylinder rotor system of a 1000MW nuclear power turbine as an example,the proposed SDQM is used to quantitatively calculate the internal friction of the shroud friction,and compare the system natural frequencies and vibration modes with or without shroud friction damping,and obtain shroud friction internal damping reduction the natural frequency.The spectrum of the system is analyzed by considering the shroud friction internal damping under the excitation of different rotational speed equivalent centrifugal loads.The vibration damping effect,hysteresis characteristics and frequency response characteristics of the internal damping are discussed.The test of the vibration response of the dry static rotor system is used to verify the friction internal damping model and quantitative calculation method in this paper.The multi-factor and multi-level orthogonal method and response surface method were used to identify the sensitive variables affecting the shroud friction internal damping(single variables and interactions among variables).The quadratic multivariate regression fitting method was used to obtain the frictional equivalent internal damping quantitative calculation formula for each parameter of the shroud,the influence of various factors on the shroud friction internal damping was calculated.Elucidating the damping mechanism of the limit of vibration caused by the restriction to change dynamic stiffness and the position and orientation reconstruction between neighboring shrouds inducing the damping energy dissipation.Based on the spectrum vibration diagram,the influence of various factors on the response characteristics of the system was analyzed.With the increase of the rotation speed,the increase of the friction coefficient and the contact stiffness increases,the magnitude of the amplitude decrease and the damping rate increases,and the contact angle and the initial gap increase,the magnitude of the amplitude decreased first and then decreased,and the damping rate first increased and then decreased.Rotor system stability criteria considering shroud friction internal damping were established,and analyzed the effect of shroud parameters(friction coefficient,contact stiffness,contact angle,initial clearance)on the stability of the system under different rotational speeds.The change range of the system stability zone was obtained as the rotation speed and the shroud parameter change.In order to improve the stability of the system,a method based on structural perturbation modification to dynamically optimize the shroud friction internal damping is established.It is determined that the shroud friction internal damping achieves the overall optimum under different operating conditions as the objective function,and the design variables are modified perturbation under perturbation conditions,and the modified shroud structure is re-analyzed until it meets the objective function and the optimized shroud parameters are obtained.The optimized shroud friction internal damping increases the amplitude reduction and the vibration reduction rate.In particular,under the normal operating speed,the shroud friction internal damping consumes vibration energy,suppresses the vibration response and the damping rate reaches 71%,and verify that the optimized shroud can effectively suppress vibration. |
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