Dynamic Analysis Of Fluid-induced Vibration Of Heat Exchange Tubes

Fluid induced vibration is a phenomenon that induces vibration when a fluid traverses a heat transfer element.Its causes are diverse,but most of them do not give a specific scope of application.Based on experience,the speed mechanism and displacement mechanism of the induced vibration instability criterion are summarized,but these two lack a good unity.In addition,vibration is very easy to cause various forms of damage to the equipment.GB /T 151-2014 only gives the general formula of the critical flow rate,and it is impossible to judge the specific type of vibration damage.Therefore,clarifying the formation and action mechanism of induced vibration and analyzing the corresponding stress and dynamic characteristics of the heat transfer element can provide an important theoretical basis for the prevention and treatment of induced vibration.In this paper,the theoretical analysis method is firstly used to explain the causes of fluid-induced vibration in heat exchanger,and summarize the limitations and scope of application of different causes.In view of the problems in the induced vibration instability speed mechanism and displacement mechanism,the damping-based instability criterion for the induced vibration process was established,and the physical significance under the "negative damping" condition and the effect on system stability were innovatively proposed.Combined with the Routh criterion,give a method for judging the instability of higher-order vibration systems.Taking the second-order vibration system as an example,the method is proved to be reasonable.According to the support conditions of the tube bundle in heat exchanger,it is divided into different regions.The stress analysis of the tube bundle is carried out,and solve the maximum bending stress point,maximum static deflection and shear stress of the tube bundle in different regions respectively.According to the possible damage of the heat exchange element,establish the calculation methods of three critical flow velocities: fatigue critical flow velocity,collision critical flow velocity,and shear critical flow velocity,and analyse the frequency ratio and dynamic amplificationfactor in the expression of critical flow velocity.And then,obtained the safety criterion of anti-vibration of the heat exchanger.In addition,estimate the fatigue life of heat exchange tubes while using linear damage theory.Starting from the single-degree-of-freedom vibration equation of the heat exchange tube,calculated the response of each dynamic parameter by combining with Simulink simulation.The equation is compared with the RLC circuit equation to establish the correspondence between mechanical parameters and electrical parameters.Using Simulink,establish a simulation model suitable for both vibration system and RLC system,and give the corresponding relationship of each module parameter,which further proves that the two can be converted into each other.The comparison with the exact value verifies the rationality of the model.This method provides a new idea for the study of the dynamic response of the vibration system,that is,the vibration system can be equivalent to the RLC system with the same module parameters.The dynamic model of the single-span heat exchange tube of the distributed parameter system is established,the natural frequency and mode of different support conditions are solved,and analyse the dynamic response of some parameters.The single-span tube dynamic model is extended multi-span tubes,and the natural frequencies of the multi-span tubes with different spans and different support conditions are solved by using the generalized coordinate method and the Rayleigh method,which provides a reference and method for changing the natural frequency in vibration design.Finally,using the series-parallel relationship between the admittance and impedance of each mechanical element in the mechanical system,establish the equivalent mechanical circuit of the multi-span heat exchange tube dynamic model.Substituting the corresponding relationship between the force and electrical parameters,the multi-span vibration model of the heat exchange tube is equivalent to the RLC system.