Analysis Of Dynamics Of Pipeline Based On Model Reduction

As an important part of nuclear power plant,pipeline system’s dynamic characteristics are directly related to the safety of the whole system.Under the action of high intensity ground motion,the instability of nuclear engineering pipeline system is easy to occur,so the safety of pipeline system has always been the focus of research in the industry.Especially after the Fukushima nuclear accident,it is proved that the vibration response of nuclear engineering pipeline system under the action of ground motion is an urgent problem to be solved.In addition,the pipeline due to environmental factors,fatigue damage,damage of uncertain factors,material aging and other phenomena are likely to lead to pipeline rupture,earthquake accident.Therefore,it is necessary to analyze the natural frequency and dynamic characteristics of pipelines.Dynamic analysis of pipeline structure by finite element software has become a widely used method.However,the finite element model is not accurate because of the uncertainty of many parameters in the pipeline.It is a basic means to improve the accuracy of numerical model to modify the model with experimental data.But in fact,the test data,measurement points are limited,the test data matching is not complete.Yi Tinghua et al.used model condensation method to optimize the sensor layout of Guangzhou new TV tower.Therefore,in pipeline analysis,the number of degrees of freedom of the pipeline should be consistent with the measured degrees of freedom,which can be achieved by model condensation.Guyan method and IRS method were used to reduce the structure and find the most suitable condensation method for model modification.The mode expansion method can also solve the degrees of freedom matching problem,but it needs several iterations in the correction process.Time history analysis is one of the common methods to solve structures under excitation.Compared with the superposition principle,the time-history analysis method is not limited to linear elastic structures.The time-history analysis method directly solves the differential equation of motion and calculates the displacement,velocity and acceleration of each instant,so as to observe the change of internal force of the structure.Through the time history analysis of the pipeline structure,the displacement response of the pipeline before and after the correction is observed to test the correction effect.The results show that the model condensation not only solves the problem of degree of freedom matching,but also improves the computational speed,and the modified model results are more consistent with the real situation.Modal expansion can also solve the problem of degree of freedom matching,but the quality of correction has a great relationship with the number of experimental data,and the frequency correction effect of high-order terms is very small.Therefore,model condensation is more suitable for dealing with degrees of freedom matching in model modification.