| Regulating valve-pipeline system plays a very important role in modem industfial automation process control,and its overall dynamic characteristics affect the performance of the whole industrial control process.The vibration of the regulating valve and the transmission pipeline caused many safety accidents,which seriously affect the economic efficiency of enterprises.In this paper,taking the regulating valve-pipe conveying fuid as the research object,considering the nonlinear factors in the system,by establishing and solving the nonlinear system transfer matrix model,the dynamic characteristics and response of the system are analyzed.First of all,according to the working principle of tje valve positioner,calculation formula of control force is deduced:According to the relatiohship between the fluid flow rate and the pressure flow rate of the valve throttle,the formula for calculating the unbalance force is derived;According to the relationship between the fluid flow rate and the pressure floxv rate,the calculation formula of the unbalanced force is derived;By analyzing the way of the friction of the valve stem,the friction force is calculated;According to the structure and working principle of the single seat regulating valve,the consideration of the nonlinear dynamic model of a nonlinear fluid force and Coujomb friction core stem system is established and the corresponding equivalent linear dynamic model is deduced;Using MATLAB softwarP and combining with the Runge Kutta algoritbm,we analyzed the nonlinear dynamic response of the regujation valve core stem system in difFerent working condirions(pressure,open degree and direction).Simulation results show that,when the opening degree is smaller,the pressure difference is bigger,the steady-state displacement relarive to the target opening is larger;When the steady state displacement of the valve core is higher than that of the target,the steady-state displacement of the flow closed state is lower than that of the target;In the small opening,the steady-state displacement in the condition of close flow state less than open flow state and in the large opening,the result is opposite;Under the large pressure difference,the steady-state displacement of the open flow state is almost equal to the closed state.Comparing the simulation results with equivalent linear model and nonlinear model,the nonlinear model can fairly reflect the vibration of the valve core.Therefore,in the terms of the design of the control valve,the use of a linear model is more conservative.Secondly,we set up the valve core stem system dynamics model and equivalent linear regulator-coupled linear model constitute pipeline eight equation of fluid conveying pipe system model,use the linear transfer matrix method to analyze the dynamic characteristics of the linear regulator valve-pipeline system and obtain the natural frequencies and modes of the system under the condition of water.Comparing to the finite element method,the error is less than 7%.In addition,the valve response frequency and system simulation of pipeline fluid system harmonic are analyzed.Results show that in the fixed open degree,the pressure difference is the greater and the amplitude of vibration is the greater;At the same pressure difference,basically accord with the vibration amplitude is greater in the smaller opening and the vibration amplitude becomes smaller in the greater opening;The small opening(1～5)mm,the amplitude of vibration with larger opening change;Under large opening(10～20)mm and small pressure difference(0.1～0.5)MPa,vibration amplitude change is small;But under large pressure difference(1～2)MPa,vibration amplitude varies greatly with the pressure difference.Finally,we use the combination method of multi-body system transfer matrix method and dynamic method to analyze the time domain of nonlinear regulator,linear flow pipeline valve-flow pipeline system and qualitatively analyze the frequency domain of nonlinear regulating valve,regulating valve of fluid solid coupling transmission pipeline,and compare the nonlinear and linear valves regulating valve-flow pipeline system vibration amplitude.Comparison results show that:Differential pressure has much effect on the valve body and valve core.The pressure difference is greater and the vibration amplitude change of the valve body is larger,but the offset deviated from the target opening of the balance position of the value core becomes very large;Under the big pressure difference(1～2)MPa,when the valve core vibration amplitude moments over the valve opening,the valve will be close to the moment phenomenon in an instant;Regulator-flow pipeline model of nonlinear valve vibration amplitude is larger than that of linear valve;The pipe with valve has a larger vibration amplitude than that without value;The nonlinear fluid structure interaction can lead to the instability of the transverse vibration of the pipeline and fluid pressure pulsation is also affected by the transverse vibration;The greater the excitation coefficient of flow rate,the higher the amplitude of vibration;The greater the excitation frequency,the amplitude of vibration has been attenuated;Due to valve is affected by the pipeline,valve core vibration is not stable,may have serious consequences for the valve core. |
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